Repost: creating a BEAM from 2x8's


OK, I asked about how to make a beam from 2x8's (2x10s actually but now I'm using 2x8s), and that thread somehow grew into indicting me for murder in Canada after constructing a dangerous skyscraper. From 2x10 PT! So I'm trying to regroup and start over.
Anyhow, my question is really very simple. I'm builing a small residential deck. Its about 30 inches above elevation. My Stanley Deck Building book suggests using 2x8 and "sandwhiching" 1/4" plywood in shims between to keep water from settling between the boards.
Is this really necessary? It seems too that the extra 1/4" or so would make a poor fit in the Simpson connector? I'd prefer to just user 2 2x8's and leave it at that.
Are carriage bolts even needed?
Honest- I'm not making a skyscraper nor am I a murderer. I just want to make the best deck I can..
- BX1
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It depends on what kind of tie you get. Most of the stuff Lowes and the borg carry is BC4R and they are 4". When you build post and beam the beams sit on top of the post. To get a good fit you put 7/16 OSB or plywood in the middle. If you have BC4's then it's not needed. Just put your 2x8's together and shoot it with 3 1/4" nails in a zig zag. You could also use AC's but you need one on each side. I have never heard of 1/4" to keep water out from in between. Using the caps with bolt holes and using bolts will depend on code. Where I am at (Southeast TX) we are in a 110mph windzone and use bolts. If you use the j-nails and drive them at a down angle the bolt is really not needed if code allows.
Buell Boy wrote:

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A single 2x10 is almost the same stiffness as 2 2x8's. That means that the deflection is going to be the same with one 2x10 or 2 2x8's. Go with a 2x10 (or a 2x12 if you are looking for life behind bars) and forget about it. If you are into carriage bolts you can bolt the 2x10 onto the face of the post with a couple of them (leave the holes a bit larger to allow for differential expansion and use those big cast washers).
-j
has about the same resistance to bending as a
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Actually the reason for the space is that water will seep in between the two side by side 2 x 8's. Then it can't get out. Then it will saturate your wood so that it rots, or expands, or rusts out the fastenings. Even if it is treated wood, you don't want it always wet. The space allows for a little air movement so that the wood will dry eventually. It also makes it harder to drive the deck fastenings into wood rather than air (DAMHIKT).
There is no structural advantage gained by tightly anchoring the two 2x8s to each other, they are each acting independently. But tacking them to each other will keep them from wandering a bit. Bolts seem to be overkill to me.
Another way is to put a piece of roofing felt over the 2x8 sandwich, like a little tent roof, to keep the water out. But some water will still get in and stay there.
Did you have any idea you were such a dangerous character before you made the post?
Walt C

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For outdoor structures, a solid beam is better than a built-up beam. Less risk of water seeping in between boards and causing rot. So, you might look into using a 4x8 instead of two 2x8's.
If the span is long and you'll be working alone, the 4x8 may be to heavy to move around easily. In that case, I would probably attach a 2x8 to each side of the post and then bolt it with a couple of 3/8" bolts at each post. I used this approach to build our deck, and it's quite sturdy. If you want a little extra strength, you could switch to 6x6 posts and notch the post on each side so the 2x8's bear on the wood post. Then bolt as usual.
The spacer idea sounds good too, but I'm not sure I would use plywood unless it was pressure treated.
Anthony
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Buell Boy wrote:

I haven't used the Simpson connector, but I just used 3" deck screws to attach my 2x8s together, no lag bolts. I've done this on 4 decks so far, and haven't had one come apart yet (first one done in 1998).
--
Odinn
RCOS #7
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That depends on how deep you are building the bunker and what sort of ordinance you expect potential adversaries to use.
If EMP is a concern then you definitely do NOT want to leave a space since the space between the boards acts like a microwave caivty crating a standing wave along the edge of the perimeter.
Otherwise you should leave a space to let the air circulate between the boards so they can dry out properly when they get wet.
BTW: Good thing you decided against building that skyscraper/abatoir.
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