2x deck beam construction with spacers?
gmartin1215
| Posted in Construction Techniques on
I have seen a couple of ways to build deck beams out of 2x material and like to get anyone’s opinion on what they think is the best method. The first method is screwing two 2-bys togethor and then running caulk over the top to keep moisture out. The second way is to build the beam with 1/2 inch ply spacers in between the 2-bys. To me, it would seem that the second method would be better so that air can pass through the beam and dry-out any moisture. However, I live in Colorado which is relatively dry, and wondering if all this just might be overkill.
What are your thoughts?
Replies
You could use a flexible flashing (ice and Water shield) if UV rays are not an issue.
I would try the spacers.
Why not use a conventional beam?
Wood is Good
Adam Greisz
I have built good box beams of 2x8s capped top and bottom with 2x4s, hollow center.
If these beams are going on top of 4x posts, then you're gonna need to find a way to make them 3 1/2" anyway, hence the 1/2" spacer. I use the plywood....and it's easier to simply cut the plywood something like 4" x 5" so that you just put it on a tilted axis between the 2 boards while building up your beam instead of cutting the top with 2 45 degree cuts to shed the water....serves the same purpose, and saves an awful lot of time.
Someone mentioned "Why not use solid beams instead of built-up beams....In Ohio, if you asked for a 4x10 beam, you're gonna get those "Deer-in-the-Headlight" looks from your lumberyard guys.
What's wrong with nailing 2-2x12's together with no space like I've always done and never had problems before?I've never heard of anyone doing this before. Are you guys sayimg that if you don't put a space or something on top of the joint the water/snow/moisture will seperate pt lumber?Joe Carola
Edited 7/29/2005 7:37 am ET by Framer
Joe, I hear you. If the beam in question will be used in a protected location, I agree: nail it up and be done with it.
On the other hand, I've seen too many decks where the main beam rotted out and took the joists with it because water got between the 2x's and stayed there to feed the little wood munchers. If this guy is using the beam for an unprotected deck, he needs to flash the top of it, either with 90#, IceGard, or--best way--a galvanized flashing, like this one:
View Image
(PS--don't ask why the joists are 4x4's; I'll tell you: The HO wanted them that way, and it was overkill so there were no code issues I had to worry about. He was paying the bill....)
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
It sounds like he's talking about a deck that's not covered. I've never seen a deck where the 2-2x beams nailed together rotted before and I've always done it this way and seen every deck done done this way. Once or twice while driving around I've seen a deck girder where they bolted a 2x10 on each side of the 4x4 post and then sat the deck joists on top and I also did that about 15 years ago on my friends deck.Like I said I've always just nailed the two together and seen every other deck built the same way.If you use a plywood spacer, do you use pressure treated plywood?Joe Carola
Edited 7/29/2005 7:48 am ET by Framer
I don't use PT anything unless you twist my arm up around my head two or three times and then start to go to work on my legs. Hate that stuff....
Most times I just nail two (or three, depending on the span) full-dimension (unplaned) 2x10s or x12s face to face and go to town. I used to cap with 90# felt; now that self-sealing membranes are in use everywhere I've always got scrap membrane lying around so I use that instead. If it's a critical application (north side of the house) I cap with metal flashing bedded in roofing pitch, like the one you saw in my photo.
I dunno, Joe. Maybe its regional, but here a built-up deck beam that's not capped with something or otherwise protected from the weather has got about a 7 year half-life. Local contractors and remod guys like me call it 'DIY Deck-rot Syndrome'....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Thanks for the replys guys! A lot of good advice here!
I am building this deck in Colorado and the eather here is relatively dry. The deck is being built where pine trees are closely surrounding it. So, there is some cover from the trees, but not a complete cover. The beams are being constructed out of PT 2-x's.
What about just running a bead of caulking, or silicone over the joint on the top?
What about just running a bead of caulking, or silicone over the joint on the top?
It's easier and cheaper to staple on a strip of 90# felt. And it will work better because it will also help prevent rust-rot at nail penetrations. The tar in the felt coats the nail somewhat as it is driven through, and slows this oxidation down. There is something about iron oxide that some types of wood rot just love....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
PT is all we use here just for the framing and then it all gets covered by cedar, mahogany .......etc. It must be a regoinal thing because I've see decks that I built 20 years ago and they're still standing with no seperating girders. I've never seen anyone cover the top of a girder before and I've never seen a girder open up before or have to fix a deck because of a girder opening up. I haven't put down pt decking in years. Even when I did I would nail them tight and after a week or two there was a 1/4" gap.Joe Carola
I haven't put down pt decking in years. Even when I did I would nail them tight and after a week or two there was a 1/4" gap.
Oh, yeah! I've seen that phenomenon. I swear PT lumber must go from felled tree to poisoned wood in a matter of days. The big plants pour through a million board feet in no time flat and then ship it south. A lot of the sh!t we get is cut up north of Suk-a-Frozen-Muk-Luk; 95-100% of it is jackpine. Scrappy wood, too....
I've had good luck setting KD SPF using a 20d common as a spacer. When that dries in place to its final state, it usually winds up spaced right about ¼"...which is just what I want for a deck.
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
My friends step father built his own deck in Pennsylvania and was telling me that everyone was complaining about the gaps in the decking and told me that I had to go there to see what he did because I wouldn't belive him if he told me. I drove up there to see that his step father used a cigarette lighter to space the pt decking............yes a cigarette lighter.Joe Carola
You mean a Zippo or one of those throwaway jobs?
LOL!
Well, he sure isn't gonna have any issues about insufficient ventilation of his planks. OTOH, he might have to worry about his big toe getting stuck between boards....
Dinosaur
A day may come when the courage of men fails,when we forsake our friends and break all bonds of fellowship...
But it is not this day.
Without primary concern for the space, the method I've followed does yield the space:
Cut a tennon in the top of each 4X4 so there is a ledge for each half of the beam to sit, then through bolt at each beam/post joint.
Grace makes a take off of there ice and water shield product that is for what you are looking to do. They also make it to be used with all the PT joists which I think is over kill. Also there are flexible copper rolls that must of the good builders in my area of the northeast use now, both links are below.
http://www.graceathome.com/pages/decking.htm
http://building-materials.gillroys.com/Roofing_materials/Roof_flashing/Copper_Flashing-s112143.html
>> The first method is screwing two 2-bys togethor and then running caulk over the top to keep moisture out. << Screws are overkill - unless your time is not worth anything... The caulk - it's just temporary. Any exposed wood is going to change dimensions with wetting and drying cycles and the caulk is, long term, either not gonna adhere, or crack and let water in.
>> The second way is to build the beam with 1/2 inch ply spacers in between the 2-bys. << I've used that method before when I had to make the beam 3.5", but really don't trust PT plywood. I'd really be interested to know if the PT plywood doesn't just disintegrate after about 10 years...
>> However, I live in Colorado which is relatively dry, and wondering if all this just might be overkill. << I think you are right on the money here. If you are really worried about it go get some bituminous (tar based) 'peal and stick' tape and put it on top of the beam. The Ice & Watershield is good, but more if you happen to have a part of a roll laying around - based on the fact that it is somewhat expensive (+- $100?), where as you can probably find the tape for around $12 - $20. Check a roofing store for the tape.