Attic vents in a camper, what are they and what do they do?

[JohnGB]

A camper attic vent is a roof vent installed on the top of the roof, which vents the air space above the ceiling and below the roof membrane. They look like this installed on the camper.

The inside looks like this with the top cover off.

I have been researching attic vents for a while to find out the pros and cons of what is available. In years past, attic vents only seemed to show up on high end 4 season campers and some 5th wheels. I have not yet found Sunline travel trailers with them installed by the factory. These attic vents were not that popular across the RV industry years ago. And still today, many new campers do not have them. Attic vents are now starting to show up on some Keystone product line models, and as reported by a fellow Sunline club member, their new Grand Design travel trailer. Not sure which models/series of those brands have them.

What problems are there with the camper attics?

1. High summer heat buildup in the attic is trapped inside.
2. During the right conditions in cool weather, mold can form in the attic from trapped moisture.

Both problems can create problems within the camper, depending on the camping or storage conditions of the camper.

High heat buildup: An example most can relate to is when your car is parked and closed up “tight” all day in the hot summer sun. High heat builds up inside the vehicle beyond the heat absorbed from coming in the window glass. You can feel the heat blast hit you in the face when you open the door as the vehicle does not breathe. The camper has the same heat buildup in the attic as there is no venting of the attic airspace. The attic's high heat eventually migrates to the living space combined with heat coming in the windows. This heat buildup happens when the camper is parked in the sun or long-distance towing down the road on hot summer days. The high heat exposes stored food to elevated temperatures when stored in the camper, and the high heat makes the AC unit work harder, trying to cool the trailer once you are at camp.

Trapped moisture: Small spaces with people living in them during cool months of the year can create high moisture if the living space or attic is not humidity-controlled. High humidity naturally migrates itself to areas of lower humidity. When the living space is stationary (like a parked camper), higher humidity/moisture tends to migrate upwards and into the attic if the moisture cannot get out an easier lower path.

When the outdoor conditions are right, higher moisture collects inside the camper from people living inside, cooking, washing, and sleeping. When you see single pane windows inside the camper sweat, conditions of higher moisture exist. These higher moisture conditions happen during the spring, fall, and winter camping when the windows and roof vents are usually closed, trying to keep the heat inside.

Camper attic findings. Now, close to about two years ago, I restored two campers for friends by replacing the roof on both as part of the project. With the roof off, you could see inside the attic space what excess moisture conditions can create. The larger camper in the project, a 2007 T286SR Sunline, was not used much in the early spring or later fall and had a lower level of moisture signs in the attic. The smaller camper, a 2005 T2363 Sunline, was often used for spring to fall camping, which exhibited signs of a much higher moisture level in the attic. Both campers were bought new by the original owners, so they had the full history. Neither friend knew about the venting needs of a camper for excess moisture and never thought to vent the trailer or control the humidity inside. Their main goal was, try and keep all the heat in you can. Many of the older camper manuals do not mention this higher moisture topic and what to do about it.

After seeing the corrosion of the heads of steel screws and how mold can form in the camper attic, I now have firsthand information on what can happen if the camper's overall moisture is left uncontrolled during these high humidity conditions. This moisture issue is an RV industry problem, not just unique to Sunline. The RV industry knows about attic vents, and the cost is minimal, so why not install them in every camper at the factory? Granted, what you will see is not mega damage, but it is not wanted and can be minimized or eliminated without too much effort.

See these pics from the 2005 T2363 camper, built in August of 2004. I do not have a timeline of when this attic molding issue started. Fifteen years later, after being built, the roof is opened up, and we see this. This mold growth did not all happen at once and may not have occurred during some years.

This camper did have a rear roof corner and front roof seam leak, but there was a strange wet spot in front of the AC unit. The moisture meter showed high 90 percentage readings that “something” was going on in the roof in front of the AC unit. There was no apparent leak path from a roof penetration to this area using the meter scanning from the ceiling inside pointing up and outside on the roof scanning down. The roof was dry near any roof penetrations in that location.

This red circle shows the area in question. High 90 percent on the moisture meter, yet outside that area is 0%.

Here is a picture of the roof before taking up the membrane. You can see there are no holes in the roof in the circle area.

When we rolled up the membrane, I found the wet spot. Water droplets were lying on top of the pink insulation. I felt the insulation with my bare hand, and it was like a fine mist of water was sprayed over all of it. When I lifted the insulation, the water droplets ran off the top. I did not get a picture of that water, but I described what I saw. This wetness was an eye-opener having that much moisture still present when we opened the roof up. It was late October 2018, and the couple camped in a camper only one night before. You can see the blackened stain on the 1/8” luan sheet, which helps hold up the membrane by the AC hole opening.

Here is a picture looking towards the rear of the camper. The insulation is over the top of the rafters. The rubber membrane and the thick corrugate liner nicknamed “bud board,” which I think is a product called Unicore, is directly against the insulation.

Here are some pics with no insulation installed showing molding on every rafter center location and corroding screw heads and speakers in the bedroom.

An overall view looking from the back of the camper to the front

A close up looking forward

An overall view from the roof AC area looking towards the back, see the fuzzing corroding screw heads.

Over the bedroom area

The 2007 T286SR did not have the molding issue, but all the screw heads in the attic over the bedroom area had the same screw head corrosion starting, and you could see moisture stains on the budboard when we rolled up the roof.

This water stain was on the budboard of the rubber membrane where ever there was an opening in the insulation. This water stain is just one example, and there were many others just like it.

And the corroding screw heads over the bedroom area.

The excess moisture vapor in the camper migrates/seeks an area of lower moisture naturally. It rises upward while doing this. The humidity gets up into the attic through any tiny openings in the ceiling of the camper. And there are many of them, such as;
1. Trailers with both ducted and non-ducted AC units have small spaces in the attic's airbox system in the attic.
2. Ducted AC units have small openings in the ceiling air registers in the attic.
3. The shower steam dome area has small openings to the attic.
4. Ceiling radio speakers, the 14 x 14 crank up air vents all have small openings to the attic.
5. The ceiling lights have small wire hole openings to the attic.

There are many openings, and trying to seal them up solid may not be practical. The water vapor keeps rising until it hits the rubber membrane impervious to water and stops there. The vapor cannot get out of the attic. With enough time and quantity of moisture, mold can start to grow on the wettest surfaces. It appears the center of the camper in the rafter area is the place it can begin.

More in the next reply.

For more pics on this topic, see my Flickr photo site here https://www.flickr.com/photos/camper-johnb/albums/72157717497136833

 

[JohnGB]

So how do you control the high attic heat and moisture problems?

For the moisture issues, here are some methods I use to help keep it under control. I learned about venting from winter camping with the Scouts in a tent. We knew you have to vent the tent, or else, come morning, the top of your sleeping bag and the whole inside of the tent will have excess moisture buildup inside it. And when it gets down to 10F or below, it may even snow inside the tent from your breathing overnight. Yes, we had a few 16-year-old Scouts prove that concept of snowing inside the tent. By opening a tent door flap a few inches at the top, the problem comes under control. The higher moisture inside the tent is trying to get out to the lower moisture area outside, so with the door flap open a little at the top, you let the excess moisture go where it wants to go, out.

I re-learned the same venting lesson long ago one night when we winter camp in the Sunline. This one night, I forgot to vent the living space, and come morning, the walls were soaking wet, 70% - 75% relative humidity inside the camper. This high humidity can develop in the trailer with two adults sleeping overnight with no venting.

To control camper humidity, I start with a humidity meter with a high/low feature to tell the last 24 hours extremes reached. Knowing the humidity level helps know you have the problem or not. I have used both of these meters, and they work well.

AcuRite 00325 Indoor Thermometer & Hygrometer. See here https://www.amazon.com/AcuRite-0032...qid=1609022017&sprefix=acurtie,aps,258&sr=8-3

Or here, an AcuRite 00613 https://www.amazon.com/AcuRite-Humi...qid=1609022017&sprefix=acurtie,aps,258&sr=8-4

To vent the camper, I started out learning how far open to open a roof vent at the opposite end of the trailer from where we slept. I started at about 1/4", and a small amount kept growing to the right size of 1” up to help keep the moisture in check ( 40 – 50% relative humidity). We also use shrink-wrap on the windows to keep the heat in and reduce the sweating windows. When showering, cooking, and washing dishes that create excess moisture, we take extra action steps to lower the humidity in those areas. We open the bathroom ceiling vent about 3” while showering, then close it when done. When cooking or washing dishes, we crack open the window next to the stove and close it when done. We found that venting alone did not keep the moisture down far enough in all condtions, but it immensely helped the problem. Next came running a small dehumidifier, which worked the best. We could keep the camper at 35 – 45% humidity and have the ceiling vents closed. These measures kept the moisture in check, and we camped about eight years of winter camping with the small dehumidifier and the venting practices. Early spring and late fall, we practiced the same methods.

Next came installing attic vents, which started about 1 3/4 years ago. I wanted to get firsthand data on the high heat in the summer, to cool weather camping in the spring/fall to see if I can find the difference made by the attic vents before posting about it.

During the high heat of summer in 2019, we started towing cross-state from OH to PA, up into NY, then VT, and back to Ohio as the first long trip with the attic vents installed. Here are the findings after installing them in our T310SR. Note: The mini blinds are down and fastened when towing to help keep some heat out. The ceiling vents are also closed, with foam cushions installed to keep the sun heat out, which is standard practice for us.

1. For an 8-hour tow, starting early morning, ending mid-afternoon, the camper temperature inside was the same as the ambient outdoor temperature. 85F outdoors, 85 F inside. Before installing the attic vents, outdoor temperatures of 85F would create 95 to 100F inside by the end of an 8-hour tow.

2. For a 4 hour tow, starting mid to late morning, ending mid-afternoon, the camper temperature inside was 5 to 10 F degrees lower than the ambient outdoor temp. 85F outdoors, 75 - 80 F inside. Before installing the attic vents, it was always hotter inside by approximately 5 to 10 F degrees.

3. For a 2 - 3 hour tow, starting late morning to noontime, ending mid-afternoon, the camper temperature inside was 10F lower than the ambient outdoor temperature. 80F outdoors, 70F inside. Before installing the attic vents, it was always the same or approximately 5 F hotter inside.

This pattern above continues to hold for any summer towing. There was a very notable drop in the inside temperature after adding the attic vents. By adding the attic vents, we allowed the trapped high heat in the attic space to vent to the outside either when towing or the camper stored outdoors in the sun.

Cool-weather and humidity. We camped mid-November this year for three nights here in OH. We had the shrink-wrap on the windows and the dehumidifier with us in case we needed it.

Nighttime temps dropped to 35 F the first night and just below freezing, 28F, the other two nights. The days were mid 40’s to 50F. The weather conditions were right to create high moisture in the camper.

The first night, I had the roof vent in the living area my traditional 1” open all night and day and practiced our standard venting for cooking, cleaning, and showering. Just no dehumidifier was running. During the first daytime hours, the humidity in the camper was 35 to 45%. Come the next morning, and still with no dehumidifier running overnight, the inside was at 45% humidity. I was amazed at this and thought it was a fluke or warmer that made a difference during the day.

The second night, I closed the roof vent. Daytime humidity in the camper was 40 to 45%. Come the next morning, and still, with no dehumidifier running overnight, the inside was at 45% - 50% humidity. Wow, OK, this is different.

The third night, the roof vent closed. Daytime humidity in the camper was 35 to 40%; the sun was shining that day. Come the next morning; still, with no dehumidifier running overnight, the inside was at 40% - 45% humidity. OK, the attic vents are doing something positive the pattern is repeating.

I only have three nights to report on the cool weather camping so far. We had many days of summer towing to prove out the lower inside temps than we used to have. At this point, we will still keep the dehumidifier in the camper when we winter camp until I get more data if and when I would need it. I will update this post as future cool weather camping comes.

The attic vents do help. They are not the total cure; you still have to practice good venting habits during high moisture times in the camper.

This post is not intended to have everyone run out and put attic vents in, but to be aware of the need to vent the camper during times of cool weather camping. If you are doing a roof replacement, that is an excellent time to consider adding attic vents. If your camping conditions find that you want to slow down the summer high heat from towing or when the camper is stored, adding attic vents can help.

I will show the install methods for both walk on and non-walk on roofs in the next reply.

Hope this helps

John

 

[JaycoJake06]

Hi John,


You and I talked a couple weeks ago about my roof replacement project on the Jayco. I was mystified by the amount of moisture damage because there were no tears or penetrations in the roofing membrane. I thought about attic venting because we do that in houses. A couple of question tho:
1) If I just add a vent to the roof, am I expecting "makeup air" to simply seep through openings around ceiling fittings and what-not? Houses have soffit vents for makeup air.
2) If my "attic" is fully insulated, how could there be adequate air exchange?


I'll be installing a new roof, I'm thinking one (or two?) of these attic vents may be worth doing.


Thanks!
Chuck

 

[JohnGB]

Here is how I go about mounting the attic vents in a Sunline budboard rubber roof and a decked roof.

Here is the vent brand I use. A couple of different brands offered; I found this style/brand to be the best. JR Products 02-29125

https://jrproducts.net/product/02-29125/

I bought many of these off of eBay from two different sellers. The pricing varies. JR Products is an RV aftermarket seller of RV parts packaged for them. A molder makes them, and JR sells them. You can find this style on eBay, but you have to look closely that the screen and the segmented parts are the same as the JR brand. Amazon has them too. Since I bought six campers worth of them, I shopped around for the right quality and the better pricing.

Pending the size of the camper, 3 to 4 vents are installed. More on this and why later in the post.

There are two issues I found with all of the brands I tested and corrected before installing. The first correction is the stainless center bolt. The bolt is not captive to the vent. That means the bolt can fall out in the attic if you take the vent apart once it is sealed to the roof. I hot melt glued the head of the bolt to the vent's base to overcome the problem.

Holt melt glued the hex head to the hex molded head socket.

Next, dealing with the Sunline budboard roof, which also applies to a Sunline metal roof. The roof structure does not have any backing to accept screws to hold the vent to the roof. To overcome this, I added 1/2" thick plywood backer boards to install under the roof membrane to accept the screws.

I first tested the 4” hole saw on a scrape leftover piece of Sunline roof to make sure the roof would cut out a clean hole as needed. There can also be 1/8” luan board in the Sunline roof system, so I tested that too. A sharp hole saw will cut clean. Just hang onto the drill motor and go slow. That large bit can grab and twist your wrist if you are not prepared/holding on for it.

Making backer boards, start with laying out an 8” x 8” square (or larger) with a center mark to drill a 4” hole saw a hole in the center. Mark the hole centerlines X and Y across the entire board.

I drill the 4” hole saw before cutting the squares apart, easier to hold the board while drilling.

Cut out the squares, then turn the squares into circles and spit down the center. You are making two halves of a complete circle. Mark which cut-outs go with each. Sand off rough cut edges.

Then sort out where to install them on the roof. Here are the needs, every floor plan and roof rafter layout will alter where they go. The main needs are:

1. One vent to be installed over the bedroom/sleeping attic area. This area is a high moisture area from people breathing overnight.
2. One vent to be installed over the bathroom attic area. This area is to vent the moisture leaks from the shower dome into the attic.
3. One vent to be installed over the kitchen/living room area. This area is to vent the moisture migrating to the attic from cooking/ dishwashing. It also covers the small spaces of the roof AC unit, leaking room moisture into the attic.
4. The vents are ideally mounted “behind” any Maxx air covers, crank up roof vents, AC units. This method creates a wind block when towing in the rain to not force water up into the vent.
5. The vents are to be installed in the open space between the rafters.

Here are a few floor plans showing the above needs.

2007 T286SR. 1 vent over rear bedroom, 1 over the bathroom area, 1 vent over the kitchen/living room area

2005 T2363. 1 vent over the rear bedroom, 1 vent near bathroom/AC unit, 1 vent in the kitchen/living area

2004 T310SR. 1 vent over the front bedroom, 1 vent over the bathroom area, 2 vents over the kitchen living area. This more extended floor plan needed an extra vent, and the rafter spacing behind the AC unit forced one vent back a little.

I install these on the centerline of the camper. And they get installed centered front to back between two rafters. Feel the roof for the rafters on the nominal 16” centers, and back into the middle of the two rafters. Draw center lines on the roof and test-fit the vent before drilling the 4” hole. NOTE: there is “front” to the vent. Note the vent screw locations with the front pointing forwards.

Most rubber roofs have small 1/8” luan sheets at the roof vents to add water drainage support. You will be drilling the rubber/budboard and the luan. Take care not to drop into the attic with the hole saw to grab the insulation.

Test fit the half-circle backer board to get it in the hole and not hit anything, wires, rafters etc. NOTE. The split line of the half-circle backer board to be rotated to not fall into the screw holes of the attic vent.,

Apply construction adhesive to the backer board to bond to the underside of the budboard.

Stick the backer board half in place.

Use a clamp (I used a toggle clamp) and clamp the half you just glued in. Note the backer board split line orientation. Use fender washers and flat head screws to screw in the backer board. Put screws to the backer board inside the vent outline circle when one half is screwed in place, glue-in, and screw in the second half.

Clean the roof surface with a high flash cleaner to get any dirt off. This rubber must be clean and dry. I use Naphtha as a cleaner. You can use denatured alcohol, isopropanol rubbing alcohol, or lacquer thinner. Wipe cleaner with a rag, do not soak rubber with cleaner.

Apply butyl sealing tape to the bottom of the vent mounting flange. Leave the release paper still on. Remove the top cover by unscrewing it from the vent. Take the nut off the center bolt and remove the top deflector shield. This will allow more room to get to the screws. Note: This is why I hot-melt glued the hex bolt to stay captive, or it would fall out into the attic.

Remove the butyl release paper, heat gun warm the butyl.

Align the screw holes to the center lines and press vent to roof. You can use a drill driver to get screws started, do not use the drill to tighten, hand tightened. I use no. 8 stainless screws and fender washers to help spread the compression load out on the plastic flange. Trim excess butyl.

Place top shield on and tighten the center nut. Orient the front of the shield to the front of the camper. Next, we will measure the dome cover for a lock screw. 2 3/8” is where we will drill a hole in the cover “once” the cover is tight.

Screw the cover onto the vent. Hand tighten the cover on the center bolt, do not over tighten. Find the center of the cover and draw a line up the centerline of the camper. Measure 2 3/8” from the center and put a cross mark to drill a hole. This will be for a screw cover lock screw.

Using an1/8” drill bit, hold the bottom of the vent shield, spread your fingers so you do not drill them, and drill the top cover and the shield straight down through both. Go slow to not over poke through the vent shield.

Using a no. 8 x 1 1/2" long stainless screw, hold the vent shield and by hand, screw the screw through the cover and the shield. You will cut threads in the plastic of both parts as you screw it on.

You can now remove the screw, the nut, and the top shield. Clean the vent flash and apply Dicor self leveling lap sealant over the flange screws and outer flange.

Assemble the vent shield, the cover, and the lock screw. Apply a dab of Dicor over the top of the screw head. A soapy water finger will allow you to flatten the wet Dicor and not have it stick to you.

If you use Eternabond, wait 3 weeks to 1 month to allow Dicor to gas off and cure. Then apply Etnernabond.

The reason I added the lock screw, online reports are folks reporting the domes unscrew themselves over time, and they have to buy the entire vent to get the cover to replace it. In my mind, the cover vibrating off is problem one. I came up with the lock screw to prevent the cover from loosening, but yet you can get it off if needed.

If you have a thick enough deck board, you do not need to make the half-circle backer boards. Or if doing a new roof that is thin, add backer boards as needed before screwing the deck down.

Hope this helps,

John

For more pics on this attic vent topic, see my Flickr page https://www.flickr.com/photos/camper-johnb/albums/72157717497136833

 

[JohnGB]

Hi Chuck,

Some answers to your questions.

snip..

I was mystified by the amount of moisture damage because there were no tears or penetrations in the roofing membrane.

I thought about attic venting because we do that in houses. A couple of question tho:

1) If I just add a vent to the roof, am I expecting "makeup air" to simply seep through openings around ceiling fittings and what-not? Houses have soffit vents for makeup air.

2) If my "attic" is fully insulated, how could there be adequate air exchange?


I'll be installing a new roof, I'm thinking one (or two?) of these attic vents may be worth doing.

1. The attic vents allow moisture and excess heat pressure/build to get out of the camper attic. It is a "step" in solving the attic issues. The camper is not built to allow soffit venting like a house, but at least creating a path for the heat & moisture to escape is a really good start. For the moisture, the only fresh air intake is all the tiny holes and crevice's moisture leaks its way up there. I know that amount of air intake is a fraction of the fresh air a house gets, but from my testing, these attic vents do help. The rubber membrane seals the attic up so tight, nothing can get out. The wet just sits and rots the camper.

We see this a lot in restoring camper. If you ever get a roof leak, and you actually caulk the leak shut, the trapped wet insulation will never dry out in a reasonable time as the attic has no escape for the moisture to get out.

My Sons camper had a front leak in the roof. The prior owner caulked it, it looks like a year earlier before trading it to a dealer. His did dry out in the front, as they stopped the leak, but have no idea how long that took. I'm guessing a year of more after the leak stopped. Dry rot then took out a rafter where the water puddled. If that could of dried out in a few weeks, a lot less damage would of happened.

2. The insulation, yes the wet sock up there... the water vapor that leaks up the cracks in the ceiling and any permeation through the ceiling board (very little) does find it's way up through the insulation. Any hole in the insulation left by the assembly crew is an easy path, in the tight areas, it takes longer, but it does work it's way to the top. If I did not feel the dripping wet insulation on the 2005 camper I mentioned above, I would not have believed that, but it did.

I fully agree, add 3 of these attic vents to your camper when you put the new roof on. The last post on how I do it, shows the placement needs.

I feel after learning all this, every camper should have these installed from the factory. It is not much effort at the factory level to do this.

Hope this helps and ask away any questions.

John

 

[315RLTS in PA]

John, I know every model from Grand Design have the vents.

 

[JohnGB]

John, I know every model from Grand Design have the vents.

Thanks Mike, good to know. How many does your camper have and where are they located?

 

[apackof2]

Awesome detail post as usual. I want them!!

 

[Stubborn1]

Great post with stats to encourage this adaption to our T1950. The tent stories brought back some memories, which have encouraged us to use venting techniques so very well described.

We are the second owners of our 21 year old unit, it's been ours 3 years and was pristine! We use a very small electric dehumidifier when we have shore power and I have been amazed this winter at the small amounts collected when unoccupied. Bought that after finding windows wet inside during cold weather. Have since bubble wrapped a few of the windows, easy off/on.

We do keep a oil heater on 600wt during our E. TN winters, it's worth it to us. Sunline is right out our side door and a retreat. There are few months of the year we don't get to camp. Looks like a worthy project even before any new membrane! I wonder that 2 would be sufficient, we don't shower inside. Thank you John!!

 

[JohnGB]

Looks like a worthy project even before any new membrane! I wonder that 2 would be sufficient, we don't shower inside.

Hi Stubborn,

The oil filled heaters, yes we have one too for the camper. No noise, safe and you still get the heat from it. Ours looks like an old fashion cast iron stand up radiator.

Yes, adding the attic vents before a re-roof can be worthwhile gaining the benefits in summer and cool weather times makes it worth the effort. When a new roof times comes, there are coating systems that can be done to extend the original roof. I am testing one of those newer high solids silicone treatments now. If you do a coating, then the vents can stay. And if you go the re-roof route, the cost of the attic vents that would be tore off is not that large compared to the gain of the features.

On how many vents in a T1950, I just added the attic vent bases to my 2004 T1950 project camper. I picked 3 of them for that floor plan. See the pics here on the placement.

The 4" holes in the decking before the new rubber went on,

The attic vents bases installed over the new membrane.

The reasoning behind why I placed them in those areas.

1. The front living room area. This vent allows the entire front of the camper attic to be vented. Excess heat leaves in the summer for this whole area. The moisture generation is lower in this section, but the roof AC unit hole allows kitchen moisture into the attic and this front vent allow it to escape from the front section.

2. Behind the roof AC unit. This location is based on the kitchen area moisture generated from cooking, washing dishes. If lets the summer heat out of the middle of the attic and is close to high area in the camper of moisture generation. The AC unit is in this section and the hole in the ceiling for the AC allows moisture into the attic.

3. Over the rear bedroom. Two adults sleeping at night creates a lot of moisture. The bedroom area is a high moisture generator. It also lets the heat out of the attic in the back of the camper in the summer. With the T1950 floor plan, there is no attic vent in the bathroom, it is so small. There is a crank open ceiling vent that can be opened to let shower steam get out of this space. With the bathroom so small, it is really is not practical to add an attic vent in bathroom with this floorplan.

By going with three attic vents, it makes it easier for the moisture to escape. With only two vents, it would be one in the back and one in the front. That distance even though it is a short camper, is pretty long for moisture collected in the center to get out.

That was my reasoning. Two attic vents is hands down better then none and it would for sure help. I just have no data to show that it would be good enough. Adding the third vent made my whole thought process all fit better.

Hope this helps and let us know how this comes out for you if you add them. You might even hold the title of being the 6th Sunline to have attic vents! . There are 5 others as of right now that I know of.

John

 

[Stubborn1]

Thank you for the response, much appreciated. The pictures of your T1950 roof vent spacing do show how much more beneficial 3 would be. It was those bedroom windows that sweat in winter. Well done! Interested to see how the silicone material works out!

 

[Twitch-SUN]

So this is an old thread but I've got a couple of questions and you sound like the person to talk to.

I'm gutting and rebuilding the Living Quarters in a horse trailer due to some major water damage. I'm located in Saskatchewan Canada so temps range from +40*C to -40*C. The trailer is sheet metal on steel ribs and the damage I'm finding is... pervasive. Here's my challenge, once the roof is sealed any moisture that gets through the walls and insulation is going to run into the solid metal which transfers heat well but does not allow any moisture through. Which for most of the year means condensation will be a major problem. I want to do a pseudo attic. I don't have the room for a real one, the ceiling is only 2 meters tall (bare metal to the floor so it'll be less once closed in). However, since the roof curves down into the walls of the trailer I will have some "dead" space there.

I'd like to put a vapor barrier in between the interior of the space and the insulation. However, I know inevitably some moisture is going to get through cause I'm not an expert and I'm learning as I go. Since I have this "dead air" space runs the entire length of the living quarters on both sides and wraps the front as well, would I be able to install some sort of vent there? Saskatchewan is typically really dry so I feel like even if it's not the highest point the moisture should still wick out fairly well. Also given the way the roof curves, any condensation that can't escape at the peak will end up sliding down to the sides anyways.

Am I on the right path with this idea? Since the trailer will often be boondocking I don't have much choice but to use the propane furnace for heat and so I can't escape the potential of moisture creation there. However the trailer does currently have a hand crank vent at the peak that will allow moisture inside the main area out, I just want to ensure moisture buildup along the walls doesn't become a problem again.

Thanks for your time I really appreciate it, and this thread has been extremely helpful so far.

 

[JohnGB]

snip...

Here's my challenge, once the roof is sealed any moisture that gets through the walls and insulation is going to run into the solid metal which transfers heat well but does not allow any moisture through. Which for most of the year means condensation will be a major problem. I want to do a pseudo attic. I don't have the room for a real one, the ceiling is only 2 meters tall (bare metal to the floor so it'll be less once closed in). However, since the roof curves down into the walls of the trailer I will have some "dead" space there.

I'd like to put a vapor barrier in between the interior of the space and the insulation. However, I know inevitably some moisture is going to get through cause I'm not an expert and I'm learning as I go. Since I have this "dead air" space runs the entire length of the living quarters on both sides and wraps the front as well, would I be able to install some sort of vent there? Saskatchewan is typically really dry so I feel like even if it's not the highest point the moisture should still wick out fairly well. Also given the way the roof curves, any condensation that can't escape at the peak will end up sliding down to the sides anyways.

Am I on the right path with this idea? Since the trailer will often be boondocking I don't have much choice but to use the propane furnace for heat and so I can't escape the potential of moisture creation there. However the trailer does currently have a hand crank vent at the peak that will allow moisture inside the main area out, I just want to ensure moisture buildup along the walls doesn't become a problem again.

Thanks for your time I really appreciate it, and this thread has been extremely helpful so far.

Hi,

I'm not 100% following how your camper is built, pics showing it apart would help, You can post them here. If you need help on how to post pics, ask away.

I'll pass along some of what I have learned along the way our Sunline campers are built, and you may be able to apply this to your situation.

First, you are absolutely correct, the way campers are built, Sunline's, yours and many other brands, moisture that goes up into the attic is trapped and cannot get out. Over time and pending how bad the moisture is, mold will grow in the attic. The attic vents I show above in the post help greatly to lower the moisture and excess heat in the summer. It it not as good a system as a house with soffit vents to allow fresh air in, and a ridge vent to let hot air and excess moisture out, but it is a lot better then having nothing.

To your comment on using a vapor barrier on the walls. Sunline and many other camper manufactures use vinyl covered wall paper and vinyl covered ceiling board on the newer campers. I'm not sure what model year that vinyl paper came but I suspect some time in the 90's. The 80's campers may not have had it.

The vinyl papered wall board and ceiling boards acts like a vapor barrier. It does a good job of keeping water damaged wall and ceiling cavities from leaking into the living space until the luan backing is all but rotted totally. The ceiling has many air space holes in it to allow moisture up in the attic, and the walls have slight holes too from light switches, wall outlets, light fixtures etc. I have seen mold in the attic, but from all the campers I have had apart, I have not found mold in the wall cavities of areas that have pristine new wood. Yes, in the water damaged areas, the rot is everywhere, but many of the campers I have had apart where no water/rot made it to, the wood and insulation in the walls are pristine like new. Even the camper I posted above with mold in the attic, did not have mold in the good parts of the walls.

This could be, the camper breathes through the aluminum siding joints. While the siding does a good job preventing rain water from getting in, it is not water/air tight and the water vapor may just evaporate out. From my food science background, it takes 14 days for mold to grow given the right wet conditions. It may be the walls dry out in time and no mold grows. But the attic is very different, the moisture goes up and it cannot get out, thus mold can and will grow even if no leaks are in the roof.

Your walls, I'm not sure if they are seamed solid like in some cargo trailers. If they are, then there could be no way for wall moisture to get out of the walls in your trailer just like the attic would be. You would have to create some kind of pathway to the outside for the wall, ideally at the top of the wall, or a path from the wall up into the attic and then out an attic vent.

From winter camping in our Sunline, I'll say this, you have to deal with the internal moisture in the living space when ever the heat runs and it is cold outside. The walls will be dripping wet inside in the winter if you do not control it. We use a combo of things to keep moisture down into at least the 50% relative humidity range. We first practice letting high moisture out from cooking and washing. We have created a semi insulated window with shrink wrap to stop the window condensation on single pane glass. We have a dehumidifier, and now we have attic vents. The combo of all of them work for 2 people staying in the camper for days in a row.

You mentioned LP gas heat, we need to know what furnace you are using, as many RV furnaces use a heater exchanger type of furnace on LP gas and all the LP fumes and moisture vent outside. The inside has a fan that blows inside living space air over the heat exchanger inside the camper, thus there is no moisture inside coming from a LP furnace that uses a heater exchanger. If your LP heater vents inside the camper, that is a source of water.

Hope this helps, post some pics and we might be able to help suggest a few things to help spark and idea for you to pick up on and implement. I'm curious on how you make out. Please post back.

John

 

[Jfred78]

Wow great post! Appreciate all of the information, real world testing, and in depth explanation. I am building a camper and have been struggling to figure out the best solution for insulation while managing condensation and humidity. I was thinking about attic vents because that's how houses are done and actually found those same JR vents you used and have them sitting in my cart. I was just unsure of my thoughts. After reading your post it's clear this is the way to go. Thank you so much for your help and all of the time you spent creating this post!

 

[JohnGB]

Hi Jfred78

You are very welcome. Glad you found the attic vents post helpful. They do work, just make sure you add the lock screw as I have shown to not have the vent cap unscrew while towing down the road.

Good luck on your camper build

John

 

[Kingerna1]

Hi Jfred78

You are very welcome. Glad you found the attic vents post helpful. They do work, just make sure you add the lock screw as I have shown to not have the vent cap unscrew while towing down the road.

Good luck on your camper build

John

Hello Sir, I got to this forum researching attic vents as I just tore my whole ceiling out after it warmed up here as it was dripping with moisture. I noticed it had no vapor barrier on the warm side but one at the roof. Anyway im trying to research a good way to do this and I am not willing to do spray foam with the chemicals so I came across your amazing detailed post and I am ordering some vents now. My question is do you think its required to have an airspace to vent properly?

The closest thing I can find is on 8:51 mark of this

where he talks about using a smart vapor barrier that if installed properly can prevent moisture up but allow moisture back to the room. But then in the comments he replied that it would be better to have a type of vent.

So my plant is to installed 6 vents across 42 feet of ceiling, use a smart vapor barrier, and either blow in cellulose and fill the entire space or use roxul batting and have maybe a 1 inch gap down the middle. I wont be able to have a space the whole 8' across becasue I only have 1.5" on the very ends for insulation but should be able to have a small airspace about 4' wide maybe 1"thick down the center for sure

I wonder if that small air space would be better or fill it full of cellulose and wonder if it will still breath and vent?

Also I should mention now that I am aware of this issue I realize that the front and back are also batting with no barrier as well and now I am happily looking at planning to remove the front and back end caps (easier than demo the interior)so then I will join the vapor barrier the whole length and properly insulate as well

I understand these units were never designed with cold use in mind but I believe these things can be solved its just this one is so contridicting when you google for help.

Appreciate all the help in advance!

 

[JohnGB]

Hi Kingerna1.

First off, welcome to the forum.

Thank you for that YouTube video on building a flat roof design. It was very interesting and provided good information, as the speaker described the problems very well and how to address them in a building. Now, how to translate that into an RV, and one that is already built. There are some things to overcome for sure, both structurally and practically, given the issues of how a camper is built.

I need to think about this some more to ensure that my first response addresses most of the issues.

We also have some members who are building contractors who may chime in too as they deal with this in home and building construction.

I will respond later with thoughts on your approach and some things to consider.

Thanks

John

 

[JohnGB]

Hi Kingerna1,

Getting back to you. Here are some comments and questions. Your topic is for sure interesting and we can all learn about what happens with moisture in a camper when the heat runs and we have people inside.

I will start with the comments.

Hello Sir, I got to this forum researching attic vents as I just tore my whole ceiling out after it warmed up here as it was dripping with moisture. I noticed it had no vapor barrier on the warm side but one at the roof.

Your picture of the open attic for sure helps. The silver material on top of the rafters; you call it a vapor barrier. Well, yes and no on the vapor barrier. I'm not totally sure about your brand camper, but what that looks like is a product similar to a product called Reflectix. https://www.reflectixinc.com/products/double-reflective-insulation/

Some RV manufacturers add the Reflectix or another similar brand of the same thing, as added insulation, and sell it as a feature. While it does work like a vapor barrier, it is more insulation. Your roof membrane that is glued to the roof decking may be TPO or PVC material. They do not use EPDM rubber much anymore. Regardless of which membrane, all moisture trying to escape stops at the membrane as it is impermeable to water.

Have a look and feel if it has a bubble wrap feel to it, if you push up. I'd like to know how well they sealed the edges or any seams of the silver insulation. Please be sure to look for that too. Any moisture can find its way up to the roof decking above the insulation through any hole or seam in the silver material and get trapped there. Granted, come the hot days of summer, it may dry out by coming back down into the camper.

Next, I have a question: I do not see any air conditioning ducts in your attic. Did you take them down, or are they just not in the picture you posted?

And you said this:

Also I should mention now that I am aware of this issue I realize that the front and back are also batting with no barrier as well and now I am happily looking at planning to remove the front and back end caps (easier than demo the interior)so then I will join the vapor barrier the whole length and properly insulate as well

Yes, the front and rear walls have large fiberglass caps. I have not seen any extra vapor barrier in them, but let me explain some on the wall structure, and you tell me what you have. You may not have to take those front and rear caps off.

What brand, model, and year of camper do you have? I can look them up and see if I can find any information about them.

Here is what I have found on the campers I have worked on, how they are built, and what that means to moisture.

Let's start with the walls. In the old days, and most all the newer Sunlines, the walls and ceiling board was 1/8" luan plywood with thin "vinyl" wallpaper bonded to the wall board. The wallboard and ceiling were glued and stapled to the wood wall studs and the ceiling to the bottom of the wood rafters. Batt-type fiberglass insulation was used in the wall cavities and in the attic.

On other brands with aluminum box tubing wall studs and foam board insulation between the studs, the inside wall board may no longer be luan, some use Adzel and some still use luan plywood wall board glued to the aluminum wall studs. With the smooth fiberglass siding, the wall is all glued together as one big structure. There is most likely a 1/4" wall board outside for the thin fiberglass to glue to the thicker wall board and the 1/8" wall board inside. Glue holds the whole thing together. What I do not know about your brand is whether the inside wallboard has vinyl paper.

What I am getting at is that if your wall board has vinyl paper on it, the vinyl creates a vapor barrier. As such, the front and back wall and the long side walls have a built-in vapor barrier that is pretty tight with no air leaks other than at the doors and windows cutouts that the windows or doors fit into the rough opening. You may not need to take the front and rear caps off, and if you do, how do you vent those spaces?

In repairing the water-damaged campers, I have not seen wall moisture or mold like the attic moisture and mildew. The vinyl-papered walls stop the vapor well enough that I have not found vapor damage. The moisture wants to go up or wherever it can try to get outside. Point being, the walls are pretty tight. But again see what your walls are made of.

This now leaves us with the attic, where the problems come when camping in cool weather with people inside and the way most campers are built.

Any opening in the ceiling board or in the AC ceiling duct system is a leak path. This allows moisture to migrate into the attic without a way out, where it festers. Radio speakers, lights, shower steam domes, rooftop antenna cranks, 14" x 14" crank up roof vents opening, and AC ducts are all moisture leak points to the attic space.

I'm not sure if, given the camper design already built, you can practically seal up the ceiling and all its penetrations to prevent moisture from getting in. But, you may be able to help seal off some of it. And add attic roof vents to let out the vapor that will still get up there.

Moisture control in the camper is also needed. The best way to lower the moisture is a dehumidifier. Get one or two large enough for the square footage and quiet enough you can live with it. A moisture gauge is also needed to see how good or bad the moisture level is. Next is leaving the crank up roof vents cracked open to let some moisture out. And yes, heat goes out with it too. But you have to get rid of the moisture in the small living space of a camper, or it will build up, create dripping wet walls, and get up into the attic.

For the attic build, fiberglass batt insulation can work, and I have used it. It allows moisture to pass through it, stopping at the roof line, where it can't escape. Next are the attic vents, which will enable the moisture to escape. This is not a perfect setup, but it is practical to do with what we have to work with.

I have no objection to the breathable barriers you mentioned, but again, can you create a perfect seal on the walls and all the openings into the attic? And then there is the ceiling board. What is your plan for the ceiling board? If you can acquire the vinyl-covered ceiling board, the vinyl can be part of the vapor barrier. Or do you have a non-vinyl ceiling board and use your breathable vapor barrier? If you can find that breathable barrier, install it on the bottom of the rafters, then put the non-vinyl ceiling board up. Granted, there still may be leaks in some of the ceiling penetrations, but you try to seal them up as best you can. Whatever moisture gets up there, it can breathe through the insulation, migrate to the attic vents and get out.

If you use the fiberglass batt insulation, do not pack it tight. As you said, the outside walls are only 1 1/2". Fill it full (but not packed tight) at the wall ends and then go thicker towards the centerline of the camper. At the center, leave some small air space at the centerline of the camper to allow vapor to pass to the attic vents. Please don't pack it tight so the moisture cannot flow through it. You are looking for a breathable insulation. Right now, I cannot think of a better type; the fiberglass will breathe if not packed, and the vapor will not damage the material. It will lose a little R value when damp, but it can dry out and still be OK. Maybe someone else knows better material.

Consider all the above as ideas to build on. We can bounce ideas back and forth to find a better solution. I'm very open-minded, I share what I have done and know, and our members often take it to the next level, and all is good.

I hope this helps. Please let us know how this comes out and if you can find a source for that breathable vapor barrier.

John

 

[Kingerna1]

Thank you for the reply
The unit I have is a 2024 sabre 37fll. The barrier that is shown in the picture is not reflectix but a very thin radient barrier. It was installed as sub par as everything as they left gaps on some ends but all the moisture did stop at it and left the plywood roof on the other side dry.

Yes the walls are filled with foam and act as a barrier and were fine, we did get some frost forming on areas with lack of air circulation but we have a system that we use defrost those as it gets cold

But the front and back end caps im not so sure. In the back we removed the loft cabinets in the kids room and left a hole before we fnished it and I just seen a yellow batting with no vapor barrier and the walls are not acting as a barrier. The front is the tv and fireplace and cubpoard set up, when i took off the ceiling I can reach in there and dont feel anything. When I first found the water dripping I could here chunks of ice dropping into a pool of water in the front cap so Im not sure. The back cap cant be vented I guess but the front would be connectted to the air gap on the ceiling therefore be able to vent with the new vents as I could put one very close maybe?

Yes I had an ac duct system but I removed it when I ripped everything out because I previoulsy removed the ac units on the roof to accomodate my solar panels and will be finishing the install of a large mini split next month now that I have a new project. lol

I purchased the Siga Majrex 200 and will be using this, I am still waiting on vents so when I get those I will go get the insulation. I figured the small air gap would be better so I guess I will get rockwool batting and leave a small space at the top. I wont be able to on each end but should still be allowed to breathe towards the air gap and vents. The idea will be to use the tape and seal off that vapor barrier 100% or the best we can. We will put extra time for that. We havnt decided yet but we may be replacing our ceiling with metal, so nothing that seals it off completely. My thoughts were that vapor barrier is supposed to open and allow any moisture to come back if needed so dont want to seal it off completely. Also without the ac on top we have far less openings now.

I could be wrong but I believe we have good control of moisture and spent some time adressing this before we attempted this. Along with our insulated skirting we have slide wraps and we buiilt panels for all the windows that snap outside. This prevented any moisture form ever building on the windows. We plumbed 2 diesel heaters to use when it gets cold for drier heat. Our main source of heat also is a wood stove. We vent when we cook and monitor the humidity and never found it too high this winter at all.

I understand the limts we are pushing as its not designed for this but 1. I believe it can be done you just have to swear a bit when you miss something lol and 2. I think I would have had moisture issues even if I was using it in the fall the way it is set up

Thanks so much for the input!

 

[JohnGB]

Thank you for the reply

Snip...

But the front and back end caps im not so sure. In the back we removed the loft cabinets in the kids room and left a hole before we fnished it and I just seen a yellow batting with no vapor barrier and the walls are not acting as a barrier. The front is the tv and fireplace and cubpoard set up, when i took off the ceiling I can reach in there and dont feel anything. When I first found the water dripping I could here chunks of ice dropping into a pool of water in the front cap so Im not sure. The back cap cant be vented I guess but the front would be connectted to the air gap on the ceiling therefore be able to vent with the new vents as I could put one very close maybe?



I understand the limts we are pushing as its not designed for this but 1. I believe it can be done you just have to swear a bit when you miss something lol and 2. I think I would have had moisture issues even if I was using it in the fall the way it is set up

Thanks so much for the input!

Hi Kingerna1,

First off, you are very welcome, glad to help as I can.

I have a few thoughts for you. Not seeing your camper makes it difficult to provide a better way to vent the front and rear cap areas, but I will offer some ideas that you can build on.

I looked up the Forest River brochure for the 2025 model and sense that yours is similar, if not identical. They categorize the Sabre as "extended season" instead of using the term "four-season.“ Some brands advertise as four-season, with the Northwood Arctic Fox being one example. However, the floor plans and your bunk beds for kids might pose a concern. They construct four-season campers differently from those labeled as extended season.

Now that you have a handle on the situation, here are some thoughts.

On venting the front cap and utilizing an attic vent to address this, I have a preconceived notion that while it can vent the front, water will get into that area through the vent on the roof when towing down the road in wet weather without some kind of air dam in front of the vent.

The front wall air blowing directly on those attic vents is significant even without wind blowing outside. Towing down the road creates a wind at 55 mph, which may try to beat the water into that vent. And towing into the wind is even stronger, trying to get in.

When I installed the attic vent, there was always something on the roof acting as a windbreaker—a crank-up roof vent with a Maxx air cover, an AC unit, etc. If you add one at the front, consider creating an air dam to divert the wind away from hitting the vent directly.

You might be able to run a duct hose or several smaller ones from the cavity area up into the attic and let the attic take care of the venting. You may need to create a decorative cover in the living space to conceal the ducts. Additionally, consider how to prevent vapor from entering the area in the first place if at all possible. None of this will be simple as you are doing all this after the fact in the way the camper was built.

And I fully agree, you would of had moisture issues even during fall or spring season and not winter. The lack of any prep by the RV manufacturer to not have roof vents to start with is problem one. Any camper should have them, even non extended season, as they help on things other than venting moisture. And sadly, they do not cost that much at the OEM level when they are building it. This is an issue across the RV industry.

Hope this helps, and please let us know how you make out.

John