RV wood framing, types of lumber used

All the ones I've torn apart or repaired over the years have been constructed with KD spruce. And when I worked at a trailer factory in the early 70's, we built with spruce.

No fir as it weighs a lot more than spruce. Spruce is strong enough yet a lot lighter than fir. Once it is all fastened together, glued, stapled together etc it makes for a strong lightweight unit.
Fir gets very hard with age and is more prone to splitting with flexing and movement. That's one of the reasons fir is not suitable for RV application.

When they KD (kiln dried) the spruce, the moisture content is largely gone and it does preshrink somewhat, but it is very prone to twisting warping etc. More so than fir. So it's important to buy it straight, store it out of the sunlight and use it ASAP. Once in place in a wall or whatever, it is held in place by the structure it is being used for and will stay there with minimum warping.

But it will fly to pieces in a serious collision or rollover.

The few times I've repaired a TT frame, the framing has been typical S-P-F, an inclusive rating of lumber (Spruce, Pine, Fir).

My old Starcraft has 1" x 2" (nominal) studs. Actual dimensions are 1 1/4" x 1 5/8".

I was being a bit tongue-in-cheek in my "it doesn't take much to demolish" answer, to a point. I understand exactly what you're saying; mine was more of a "look how fast they become toothpicks" when they hit something statement. They may hold a light snow load (and where we live 2 feet is a light load), structurally they're not really all that strong.

Bruce Brown wrote:
^^^ Even leaving the paneling and siding on it doesn't take much effort to demolish a typical wood framed RV.

As far as the type, as has been noted, the cheapest, lightest stuff they can find.

When I rebuilt our TT I went to the local lumber yard and bought 2x2's by the bundle. I glued and screwed everything back together, double and tripled sealed everything, beefed up where I could without adding unnecessary weight and it's held up well.

Actually, RVs are a lot stronger than you would think and that IS because of the paneling creating a structural truss.. Without the paneling there is no way that 2x2s would be able to withstand 1ft to 2ft deep snow loads..

I have seen 2ft+ snow and ice drifts on top of my TT and it has not suffered any structural damage.

Take the paneling and siding off and 6" of snow would easily collapse the framing..

It should also be noted, harder wood does not necessarily make a structure stronger.. Many hardwoods can shatter/break under loads when softer pine species will simply flex..

You DO want some flex or give to the structure otherwise something else will have to give..

^^^ Even leaving the paneling and siding on it doesn't take much effort to demolish a typical wood framed RV.

As far as the type, as has been noted, the cheapest, lightest stuff they can find.

When I rebuilt our TT I went to the local lumber yard and bought 2x2's by the bundle. I glued and screwed everything back together, double and tripled sealed everything, beefed up where I could without adding unnecessary weight and it's held up well.

shermy1987 wrote:
Hi to all.

Does anybody know what common types of 2x2 lumber is used for constructing RV walls?

I can find so many posts about wood vs aluminum etc, yet nothing about what actual types of wood is being used in modern RV framing construction.

The "type" of 2x2 wood used does not really make a difference in the strength.. That is because the walls, roof and floor are actually "truss" systems.

The paneling on the walls are glued and stapled to the wall framing, this makes a strong but yet lightweight truss..

Take the outside siding off and the inside paneling off and it would not take much effort to demolish a RV..

The RV industry uses what ever evergreen type of wood (generically called "pine") they can get at the lowest price and it depends on the availability of species closest to them.. It is light weight, fairly strong and inexpensive compared to many other woods like cherry, oak, maple..

Ivylog wrote:
The cheapest soft wood they can buy...rarely is it pine and never pressure treated.

X2 and luan for the roof decking.

I suspect cardboard would be used if they could get it to last until the warranty expired.

Most of what I have seen looks like common fir.

The cheapest soft wood they can buy...rarely is it pine and never pressure treated.

Construction Fir is good. About the same as pine except... it shows more grain
and is heavier in weight if you compare it to pine.
Brian