diy ply / foam panels

[wait]

Hi all - I am new to the space. Thanks to everyone for contributing. I am finalizing plans to proceed with a fairly generic wedge style oversized canopy for the back of my midsize Xtra cab 6.5ft bed pickup. I will be making my own panels save for the roof, which will be a hard tonneau cover off of a full size long bed. I will follow the stitch and glue method to adhere the panels together.

My specific inquiry has to do with ventilation. I have gone back and forth on a number of details for the specifics of my panels. At present I am intending to proceed with 1/8 ply interior and exterior faces, with 1x2 stringers and 3/4 board insulation in between. I have been planning to generally follow the method lined out and executed by traveling-together-journal in utilizing 6oz weave and a light epoxy, but have wondered at deviating in a couple of directions.

For starters I will be drilling 3/8in ventilation holes along the roof facing perimeter of the side/rear walls and spacing the tonneau cover 3/8in inward from the exterior of the side panels. The tonneau cover has a lip designed to overhang the sides of a truck bed. In my application I will use that to overhang to conceal these ventilation holes. This will create adequate exhaust airflow for the space and illustrates that I am not striving to build vapor / air impermeable panels.

I have spent time in the construction space and have been fairly influenced by the work of Lsitbutek. https://www.buildingscience.com/documents/insights/bsi-001-the-perfect-wall

Lsitbutek worked extensively with sips panel construction when they first came out, and comfortably allows that within sips construction, practically achieving air / vapor barriers is very very difficult, and the risks are great. What he arrives at is the worth of ventilating the roof even within structures that are designed to be completely sealed. Ventilating the roof allows unwanted moisture will penetrate structures, and gives it somewhere to exit.

Concerning ply diy panels: Fiberglassed and glassed plywood sandwiches are not going to breathe. Moisture that finds it's way in does not have an engineered way to exit. Others have occupied this query, and metal stringers are a consideration I have thought about. Consider though - what if the exterior skin received glass / fiberglass on both of it's faces, and the inner were left untreated? Glass and address all the corners and seams, but leave the bulk of the inner face of the panel free of glass/fiberglass. This would allow the panels to dry to the interior by design. The 3/8in ventilation holes while engineered for the entirety of the space do function open up and let the panel itself breathe too. Maybe that's sufficient enough?

Any thoughts on this? Truthfully I'm not terribly worried about it. I don't think I'm looking at a catastrophe either way. I suppose essentially I am wondering to myself if the structural integrity I stand to lose at not glassing the interior face of the panel is worth the trade off in ventilation. If I were further concerned I've thought I could increase the diameter of the ext skin to 1/4in ply.

Thanks in advance, and apologies I am sure for gumming of some of the fiberglass / epoxy language. This is s a new method for me and I am sure I am misusing terminology, but I hope the basics of my query still come through.

 

[rruff]

These 3/8" holes are ventilating the walls how, exactly? Isn't the interior of the wall completely taken up by foam, wood slats, and glue?

If you wish to leave the inner ply face permeable, that is fine. That's what I did on the camper I built 22 years ago. If you encapsulate the outer face by glassing both sides, then wouldn't it deteriorate if moisture entered?

Stitch and glue seems like an odd way to join 1" thick rigid panels. Normally this is for single sheets of plywood, and they are curved and segmented to provide rigidity.

It might make more sense to use a FRP skin at least for the outer surface. If your panel cores have wood slats anyway, then have a perimeter of wood in the core, and use glue and screws to join them. Then add a protective external corner piece made of aluminum or FRP angle.

 

[wait]

The 3/8 holes would vent the interior space, but as they are penetrations in the panels they also in a respect vent the panel. Unless of course you glass/seal at penetration. Have thought to use board insulation rather than pour-foam in part so that I could glue it all ddown with air gaps in place.

Yes if I fully encapsulate the outer skin and moisture penetrates it there's nowhere for it to go, true. But it would yield some structural integrity and I've felt better at the prospect of waterproofing just the exterior skin and leaving everything else more or less permeable.

Wondered about frp. Am unfamiliar with the uv stable stuff.

Appreciate the feedback. I've spent time with some of your build notes, rruff, and wondered at abiding by your protocol wherein you glassed all the wood, yes? Both sides of both skins, and the timber on the interior? But I don't really need something that heavy duty. I think my whole structure will be around 400lbs.

I suppose I use stitch and glue a little out of place. I'll tack the panels together with screws and wood glue, while recognizing that ultimately the glue in the equation is where the strength of the structure comes from.

 

[rruff]

Appreciate the feedback. I've spent time with some of your build notes, rruff, and wondered at abiding by your protocol wherein you glassed all the wood, yes? Both sides of both skins, and the timber on the interior?

Only the exterior of the outer sheet was glassed. That's where you need extra durability.

I only stayed in moderate temperatures in the western US, and did not use a heater, so I don't think it was a good test case for moisture and condensation issues. Idasho would be a better resource if you wanted to use wood... I think his rig is about 10 years old now.

You would want to use FRP skins made for campers. They already have a durable and shiny gelcoat exterior, so you don't need to finish them. This is one company: https://www.vetroresina.com/en/p/3/FRP-panels.html

 

[billiebob]

Venting the panels in SIPs housing has nothing in common with a vehicle. I take it you are only venting the enclosed wall, not the camper interior. Opening the wall will allow moisture, water, rain, storms entry into the wall on the highway at 60mph. You want that space 100% sealed to water penetration.

Thinking SIPs in housing... the ventilation of the structure is not affected by 60mph winds thru a rain storm. Seal the exterior 100% just like your car is sealed. If humidity is an issue vent the wall to the interior. This is not a house.

But quite right. Completely sealed structures are a disaster every where. Ventilation, traditional construction is always the best choice.

PS, I am a building construction engineer and building envelope has been my focus for 35 years. Modern technology air tight technology is not always the best solution. Even RS2000 and the following sysyems which require active heat recovery ventilation systems in modern homes create issues.

Ventilation is key to health safety. Thinking campers, I compare them to Bed Boxes from 100 years ago. Everywhere using them had massive TB problems as several kids slept together every night.



In Canada for the past 25 years we have been building air tight homes in the Arctic. But Canadas Northern People don't live like people in Toronto. They live off the land with extended families in these incubators. A pot is always boiling on the stove. Entire families gather to enjoy the days hunting or fishing excursions and the housing our architects designed with zero regard to the end use has caused another Tuberculosis explosion in the North.

 

[wait]

Re: vent enclosed wall and/or interior space - both potentialy.

Campers are not houses maybe, but both serve as dwelling units for people and animals in all manner of climate and region. And as seen in general construction, building tighter envelopes brings risk that make the demands for air and vapor transfer more consequential, and faster. Campers and vehicles aren't expected to last as long as houses. But sometimes they do and I suppose there's no reason why they couldn't. Neither do I suggest they ought though or anything like that.

I enjoy hearing about campers that have been around successfully for some time. Such reports from foam builds and diy panels will be of particular interest as time moves forward. When the structure fails in time, what were the weak points? And are they worth addressing, or do the other details they provide (weight, ease of construction, price etc) outweigh the harm? Very interesting

Worthwhilee note on the TB. Extremely sad.

Thanks for the conversation

 

[rruff]

In Canada for the past 25 years we have been building air tight homes in the Arctic. But Canadas Northern People don't live like people in Toronto. They live off the land with extended families in these incubators. A pot is always boiling on the stove. Entire families gather to enjoy the days hunting or fishing excursions and the housing our architects designed with zero regard to the end use has caused another Tuberculosis explosion in the North.

Interesting. No heat exchangers with controlled venting?

 

[rruff]

I enjoy hearing about campers that have been around successfully for some time. Such reports from foam builds and diy panels will be of particular interest as time moves forward. When the structure fails in time, what were the weak points? And are they worth addressing, or do the other details they provide (weight, ease of construction, price etc) outweigh the harm? Very interesting

I can say my first camper built from thin ply and foam deteriorated from lack of sealing out rain. I built it under duress in someone's garage in about a week, and I didn't know what I was doing. I ditched it and built a new one after 7 years of fulltiming in it. The 2nd one would have lasted much longer I'm sure, but I only used it for 4 years (very solid in that time), and it mostly sat in a shed for 11 more before I gave it away.

If you are worried about moisture ruining the ply over time, then use FRP instead. You can avoid wood in the core also by using extruded FRP hollow square tubes, or simply using more durable foam in the core. That would probably last until someone ran into you, or you ran into something, or flipped, or...

 

[wait]

Seven years is no short amount of time in vehicle years.

I'll look into those from square tubes, thanks.

Any idea if there are permeable epoxies that could be utilized on the interior of a panel? That would be convenient.

 

[1000arms]

It was a number of years ago, and the plywood and Rustoleum paint may have changed, but, I have had good success with a plywood camper painted with Rustoleum:

A while back, I designed and built a small camper trailer to tow behind my Jeep. 45 degree angle at the back for departure angle. Same size rims and tires as on my Jeep. Same track-width. Torsion axle stubs. I welded up my frame with a receiver hitch front and rear on the trailer. Pintle ring inserted in to the front receiver on the trailer. Pintle hook in the rear receiver on my Jeep. Tongue long enough that combined with the pintle hook-ring setup, I could turn with the tongue more than 90 degrees from straight ahead towing, without Jeep body to trailer body contact. The trailer body was built out of 2x layed flat and 3/8" plywood, with 3/4" plywood floor. Silicone on every joint and sheetrock screws. No insulation or interior sheathing, so very easy to see how all the joints held up. I painted the outside with Rustoleum white metal paint. I towed it across the US. It spent a lot of time in the Pacific Northwest rain (and some snow), but had no leaks when I sold it 5 years later.

I "glued and screwed" every bit of the perimeter, on every panel, to something solid. The "glue" did the sealing and the screws pulled the panels tight and clamped them until the "glue" cured. I was careful to avoid pushing all of the "glue" out of the joints.

I painted multiple coats of Rustoleum metal paint (white) and let the ACX plywood soak up all it could, especially the edges. It was just ACX plywood from the store with the cheap orange buckets.

The camper trailer was easy and cheap to build and seal.

 

[rruff]

Any idea if there are permeable epoxies that could be utilized on the interior of a panel? That would be convenient.

I have not heard of that, no.