economical wall consrustion

[Greg Barrick]

I read often where people will route out 3/4" plywood to save weight and fill voids with foam. Then skin both inside & out with more ply. This sounds extremely strong but quite exspensive routing 3/4 ply. Ripping 2x4 both ways for studs (actual 3/4 x 1-1/2) or even using 1x2 seems a whole lot more economical than swiss cheeze two 3/4 plywood panels. What am I not understanding?

[aggie79]

You are corect in that cutting plywood to make framing is more expensive than framing with dimensional lumber (except perhaps if poplar is used for the framing.)

The main reasons plywood is used for framing are:

1. Ease of construction, particulary if your profile has a curves. Curves can be difficult to cut from dimension lumber and assemble.
2. Speed. Cutting plywood is subtractive, but when the cuts are complete, so is the "framing". There are no additional processes to join segments of dimension lumber together.
3. Squareness and repeatability. (Good) plywood is generally square from the factory and this squareness provides a good basis for laying out your profile. Once the first sidewall framing is complete, it can be used as template to cut the second sidewall framing using a router and will result in the two being matched.

Plywood has some negatives as does any method. The two biggest negatives are that the endgrain plywood can wick moisture and is hard to seal, and endgrain plywood can be problematic in holding screws and other fasteners.

[CarlLaFong]

A lot of people have a strange way of looking at this. It is perceived as a "waste" of materials when a sheet of ply is skeletonized and all of that wood is left in a pile. Would they feel better if the wall was made from a solid sheet? There is waste in any type of construction. All we can do is minimize it the best we can. Should we sweep up all of the sawdust and make particle board with it? Actually, cutting out the ply leaves scrap that can be cut into cleats, nailers, shelf supports and all sorts of odds and ends. It may turn out to be cheaper in the long run to Swiss cheese the walls.
BTW, you can take your sawdust, mix it with odorless paint thinner (just enough to slightly moisten it) and you've got an excellent sweeping compound for your shop.
"It's a good thing"

[Oldragbaggers]

Carl, you are so right on. I used the scrap from my wall cut outs for other things. My nailer blocks are all made from it for starters. I have ripped pieces of it up for many uses, and not just for the teardrop. When the teardrop is all done and the pile of what's left is too cut up for even projects around the house, it will be thrown into the outside fire pit and will make a delightful fire on some cool fall evening. No worries. A sheet of plywood, even good ply, is only about $40. Can you not spend that much on dimensional lumber??

For me, not being an experienced woodworker, the idea of trying to construct a flat, plumb, true, strong frame from dimensional lumber seemed a lot more intimidating than cutting up my plywood walls.