Whether you are building a load bearing support beam for your wall or a deck beam, you probably wondered about adding a 1/2″ plywood strip in between 2x lumber.
As a non-engineer, I always err on the cautious side and “over build” so I’ve ALWAYS added a strip of plywood.
Now thanks to GBrackins from DIYchatroom.com, I found a very well written article from Fine Home Building that you should definitely read. (link – if the link is broken, email me).
The article is written from an ex-framing carpenter who became a structural engineer so you know right off the bat that he knows what he is talking about.
After reading this article, I felt good about my always-add-plywood-strip approach and I will probably continue on with that “tradition” (unless I decide to use steel beams!)
if you bollt 2x beams together. can you use galvanized washers for spacers to build up beams to 3.5 inches for sitting on 4×4.
No more rot from PT plywood.
yes, I suppose you can do that. But I normally spike staggered screws or nails every 6 inches of so (in addition to any structural bolts) which would mean a lot of washers.
also, if you are worried about plywood rotting, you can lay down a strip of ice dam shield on top (has sticky bottom).
for built up beams using plywood, i followed the link and gave a read. its convincing, but is the author talking about outdoor weather exposed beams? if you’re going to use built up beams exterior, i would say as a minimum you need PT plywood (not cheap!) and graceshield over the top to keep the water out.
remember, PT wood is rot resistant, not water proof
I read the article but seem to have come to a different conclusion. Kevin, you feel that the article supports the use of plywood? I did not get that message at all. Jim suggests that there is little reason to do this and that one exception would be just to pack out a beam to match the lumber it is sitting on. I do not believe that Jim Thompson is very supportive of the idea at all. HighHopes – you bring up some good points – from your comments and Jim’s answer I do not think plywood lamination would be a very good idea for a deck. You would be better adding another 2x rather than plywood if strength and stiffness was a concern.
(HighHopes – you said the article was “convincing” – in what way? It convinced me that adding plywood was not the best solution. Is that what you gathered? I think Kevin was convinced that Jim supported the idea.)
Yes Richard R, that’s what I got from the article. Not sure why the original poster came to the conclusion he did.
Plywood sandwiching makes little improvement, better to use taller beams, or add another 2x to the build-up.