Bending plywood for roof

DrewE wrote:

Gdetrailer wrote:

You do realize "EXTERIOR GRADE" plywood simply means it is another name for BC grade plywood? BC grade is very rough texture on both sides with one side being lightly sanded.

Exterior grade plywood glue is not moisture resistant, get it wet or damp and it WILL eventually come apart, to get moisture resistant glue you have to MARINE GRADE and that is not sold in big box stores.

Everything I've read has said that exterior grade plywood means it uses waterproof glues, while interior plywood uses merely moisture-resistant glues. That's the main differentiator. Exterior plywood can come in many different face grades (as can interior plywood), though BCX is the most readily available one. Plain BC plywood (as opposed to BCX) is not exterior grade; that's what the X indicates.

Marine plywood is a higher grade for sure, and costs correspondingly more.

Drew I agree with you it's all about the resin or glue.
BC refers to the grade of the sides BC is basically one good side one rougher side. Sheathing grade plywood is often CDX. This is two sides that are relatively rough generally used where a smooth side is not required like a roof. Most construction grade plywood is pine or a softer wood however Fir and other woods are used for construction when more strength is desired.
Luan is general made with interior use in mind. The glue between the plies is interior grade. If the plywood gets wet the glues will dissolve and the plies will separate. This is classic delamination.
On the other hand Luan is desirable because it is a hardwood which gives it added strength. Luan is also very smooth. More importantly it is cheap which is why the RV industry uses it. Cheap is the magic word in the slap together RV world.
If it stays dry Luan works well. If it gets wet it delaminates easily however roof leaks generally come later after the warranty has expired.
There are products like advantech that is made with high grade exterior resin that hold up much better to moisture.
Pick your poison and your price point.