Go big or go home:

[MTVR]

The framing for all four windows is done. We plan to have a house raising tomorrow...

 

[MTVR]

I hope the gun safe is not too close to the hot tub as far as moisture in the safe goes.

It's actually right across the entryway from the bathroom, but the bathroom is well-ventilated to the outside, the safe door fits tightly, and we plan to keep desiccant inside the safe.

We have less than 125 square feet of living space, so there is no place to put the safe where it would be very far from the bathroom...

 

[MTVR]

Adhesive will do nothing on end grain. The strength will come from the plywood bond.

Joe, I had a little chuckle today about your post.

While framing our bedroom window today, I needed to cut and remove the top 27" of two studs. I backed out the four screws running through the header into the tops of the studs, and after reading your post, I expected them to just pop apart with the slightest lateral pressure.

They didn't.

I pushed harder, but neither one would come free.

Then I sat down, braced my back against the adjacent framing, and pushed with both legs, which simply made the framing deflect.

So I decided to find out exactly how strong an end-grain bond is, when using PL Premium Fast Grab- I got some padding for the small of my back, grabbed onto the header with my hands, and pushed harder, and harder, and harder with both legs...until the header broke.

Ultimately, I had to use the circular saw to cut the studs off the header.

And fortunately, I had more of the same urethane construction adhesive on hand, and was able to bond the header back together.

 

[CampStewart]

Why did you choose to use white pine 2x4's for all of this?

 

[MTVR]

The framing is made out of 2x4s, 4x4s, and 4x8s. I didn't grow the trees, I just placed my order from a local lumber yard. They told me that multi-million dollar mansions are built out of whatever this is, so I figured it would be good enough for us...

 

[Alloy]

The framing for all four windows is done. We plan to have a house raising tomorrow...View attachment 604086View attachment 604087

hmmmm....no king studs or headers...the corner and 2 studs support the roof = sills will deflect over the cripples....the framing will dry/shrink which needs to be accounted for in the sheething......might be better to go with thicker plywood and leave the wall framing out.

 

[MTVR]

I guess we'll find out.

I'm not worried about the cripples or any drying out- the roof is not heavy, the 3/4" thick plywood is screwed and bonded to it inside and out with urethane construction adhesive, the stud bays will be filled completely with 3.5" thick 25psi polyiso rigid foam board, foamed around the edges to make it airtight (zero airspace inside the walls), and the entire structure will be completely encapsulated inside and out with multiple coats of marine-grade epoxy before painting.

 

[CampStewart]

The framing is made out of 2x4s, 4x4s, and 4x8s. I didn't grow the trees, I just placed my order from a local lumber yard. They told me that multi-million dollar mansions are built out of whatever this is, so I figured it would be good enough for us...

100k houses as well as 1m houses use white pine 2x6s primarily for wall construction today but no one I have ever met who knows anything about construction uses 2x4 for flat roofs except for kids in back yard forts. Are you getting your advice on how to build this from a guy at a lumber yard? No building codes that I know of allow for 2x4's on 8 ft spans for flat roofs. I have seen walls like those without headers or king studs when doing remodeling work. They were always reframed and are not up to any building codes that I am aware of. Why are you using those substandard construction methods, you surely must have known about those deficiencies from any kind of established construction standards and had some good reason to proceed anyways? These 4x4's that you are using to mount winches to, are the loads going to be inline or perpendicular to the length of the boards?

 

[rruff]

the stud bays will be filled completely with 3.5" thick 25psi polyiso rigid foam board, foamed around the edges to make it airtight (zero airspace inside the walls), and the entire structure will be completely encapsulated inside and out with multiple coats of marine-grade epoxy before painting.

I'm not worried about your structure in the slightest! Assuming you have a torsion-free mount for it?

Campers are typically made with stressed skin construction, with nothing but 2" of light foam in the core and 2mm FG face sheets! There are no issues with 8' roof spans. Yours is similar only 10x more robust (and heavier). The 3/4" ply isn't sheathing, it's the skin of a panel!

An example... the camper I built 20 years ago was similar to yours, but mounted directly to the truck frame in 4 spots. The bottom (floor) piece was 5mm luan skins over 1x2s laid on edge and 1.5" foam (with 2x4s under the mount locations). The rest was 2.5mm luan and 3/4" core. It was plenty strong... never had an issue with it.

One thing I would suggest is adding fiberglass to the encapsulation. It will make it much more resistant to scrapes and gouges that might penetrate the epoxy.

 

[MTVR]

100k houses as well as 1m houses use white pine 2x6s primarily for wall construction today...

In the past, homes were built with 2x4 walls. I'm sitting in right now that's 50 years old and has survived numerous earthquakes.

...No building codes that I know of allow for 2x4's on 8 ft spans for flat roofs.

There are no building codes for stick-built RVs.

I have seen walls like those without headers or king studs when doing remodeling work. They were always reframed and are not up to any building codes that I am aware of.

You may have seen FRAMING similar to this, but you probably haven't seen WALLS like this.

Why are you using those substandard construction methods, you surely must have known about those deficiencies from any kind of established construction standards and had some good reason to proceed anyways?

Yup.

Due to the fact that we are filling the stud bays with 25psi rigid insulation, foaming the gaps, screwing and gluing 3/4" plywood inside and out with that urethane construction adhesive, and then epoxying the interior and exterior plywood, the framing has little to do with the strength of the structure- the strength is almost all in the skin- it's a composite wall, which is MUCH stronger than the individual components. This is not just a pile of sticks held together with nails.

We stripped down the framing to reduce thermal bridging- more insulation, less wood. The framing is mostly just spacers to give each panel a shape prior to putting all that other stuff into/onto it anyway.

We have already built the floor using these methods, and it is monstrously strong- we can jack up one corner, and it doesn't deflect at all, diagonally across 16 feet to the other corner.

These 4x4's that you are using to mount winches to, are the loads going to be inline or perpendicular to the length of the boards?

The 4x4s aren't carrying the loads- the loads are being carried inline with the composite walls, except for the front winch, which really isn't seeing any significant loads at all- at the most, it's pulling a 400-pound motorcycle up a 16-foot ramp.

Look at it this way- RVs made out of paper-thin corrugated metal stapled to wispy wood framing, survive for decades. When we're done, I'd back this into one of those, and we'll see which one folds.

 

[MTVR]

I'm not worried about your structure in the slightest!

Neither are we.

Assuming you have a torsion-free mount for it?

The MTVR already has one built in from the factory- the bed is rigid, but the frame is free to twist beneath it.

Campers are typically made with stressed skin construction, with nothing but 2" of light foam in the core and 2mm FG face sheets! There are no issues with 8' roof spans. Yours is similar only 10x more robust (and heavier). The 3/4" ply isn't sheathing, it's the skin of a panel!

Yup.

I think some people are looking at this as if it were just a bunch of sticks held together with nails, but what it really is, is a very heavy and well-insulated composite wall construction.

An example... the camper I built 20 years ago was similar to yours, but mounted directly to the truck frame in 4 spots. The bottom (floor) piece was 5mm luan skins over 1x2s laid on edge and 1.5" foam (with 2x4s under the mount locations). The rest was 2.5mm luan and 3/4" core. It was plenty strong... never had an issue with it.

One thing I would suggest is adding fiberglass to the encapsulation. It will make it much more resistant to scrapes and gouges that might penetrate the epoxy.

Glassing it has always been an option, but it's not part of our initial plan.

If we had simply butted the plywood sheets up against each other, the stressed skin would not have been as strong- but when we use the urethane construction adhesive to bond the tongues and grooves together, they are MUCH stronger. As we learned yesterday, any wood we bond with that stuff isn't going to fail at the joint.

 

[rruff]

the framing has little to do with the strength of the structure- the strength is almost all in the skin- it's a composite wall, which is MUCH stronger than the individual components. This is not just a pile of sticks held together with nails.

Exactly. It's built like a tank, relative to typical camper construction. Which is appropriate considering what it's mounted on...

I'd like to add that decent wood is actually quite a good composite material for strength/weight and definitely for cost, and the low density makes it ideal for many applications. I think for a lot of people it's ideal for DIY camper builds. You just need to make sure water doesn't get to it...

 

[Alloy]

I guess we'll find out.

I'm not worried about the cripples or any drying out- the roof is not heavy, the 3/4" thick plywood is screwed and bonded to it inside and out with urethane construction adhesive, the stud bays will be filled completely with 3.5" thick 25psi polyiso rigid foam board, foamed around the edges to make it airtight (zero airspace inside the walls), and the entire structure will be completely encapsulated inside and out with multiple coats of marine-grade epoxy before painting.

Didn't realize that the skins are 3/4"ply .....you'll be good for 100years.

 

[MTVR]

Exactly. It's built like a tank, relative to typical camper construction. Which is appropriate considering what it's mounted on...

I'd like to add that decent wood is actually quite a good composite material for strength/weight and definitely for cost, and the low density makes it ideal for many applications. I think for a lot of people it's ideal for DIY camper builds. You just need to make sure water doesn't get to it...

We read much of the Gougeon brothers book on wood boat construction, and came to the same conclusions.

Powerboats made out of single sheets of 6mm plywood and epoxy, get pounded over waves for decades without losing any structural integrity. We're using six times that much plywood, plus rigid foam, in 5" thick composite walls.

We are storing the wood stacked indoors to keep it dry, and carefully watching temperatures and humidity before pulling the tarps off our project to work on it. Once it's encapsulated in three coats of West System marine grade epoxy inside and out, there will be zero moisture entering or leaving the wood- it will be dimensionally stabilized...

 

[rruff]

Once it's encapsulated in three coats of West System marine grade epoxy inside and out, there will be zero moisture entering or leaving the wood- it will be dimensionally stabilized...

How will you deal with penetrations?