20×20 deck, should I lap or butt joists on the middle beam located at 10′?
sfortier
| Posted in Construction Techniques on
Hello,
Building a 20’x20′ deck. I’m using 2″x10″x12′ treated wood for joists and I have a beam 6″ wide at 10 feet from the ledger. My question is: should I lap the joists or butt them (effectively supported by 3″ each on the middle beam)? And if butt, how do I tie them to the beam below? Maybe I need a transversal “joist” where joists on both sides are connected using joist hangers like the ledger?
See attached image for lap joint.
Replies
I would let them lap. It's a lot less cutting and you don't throw away all that wood.
Thanks 2sheps. I would not throw away all that wood, I do need minimally 2 bridgings (or maybe 3) on 20 feet but I have been trying to find an article describing the best practices to extend joists to 20' and have not been able to find anywhere... Fine Homebuilding has quite an extensive section on deck building but no word on sistering/overlapping or butt joints to extend the length.
Anyone found such an article?
Are you securing deck boards with exposed fasteners? If so, your fastener line can stay consistent if you butt the joists together. It'll jog to follow joists if you lap them.
No, going with Trex boards with hidden fasteners so lapping joists will not show (which I agree would look bad with exposed fasteners). Trex makes 20' feet boards which is nice, no need to have a joint in the middle.
Why not use 20 ft. long joists? Then there's no joint.
And if you use 2x12s instead of 2x10s you can eliminate the center beam and just have one beam set 3'-6" back from the end of the deck. The allowable span for 2x12s at 16oc is 16'-6" with a cantilever max of 4'. When you figure the cost of footings, posts, solid blocking and lumber for the center beam that may cover the extra cost for the 2x12s - and you save the labor.
And if you stick with the center beam at 10 ft then you don't need to use 2x10s for joists. 2x8s SYP can span 11'-10" at 16 oc and HemFir / Dfir can span 11'-1". And you can purchase 20' joists which will actually be pretty stiff resting over a center beam since they'll be in multi-span condition instead of simple span (the effect of deflection / reaction of multi-span joists improves stiffness).
To answer your specific question: Either way works - lap the joists or cut and butt them over the beam. Since your beam width is 6 in. you have more than the required 1-1/2 in. min. bearing for the ends of joists that butt one another if you decide to cut them. If you do cut the joists to meet in line you do need to install blocks alongside them to tie them together (IRC R502.6.1) If you decide to lap the joists over the beam you just need a minimum of 3 in. overlap. So you could use 2x10x12 from one direction and 2x10x10 from the other direction - the 10ft joists will still have plenty of bearing and the 12 ft joists will provide plenty of overlap to meet the 3 in. lap requirement.
Mike, awesome details! I already bought the 2x10x12 last summer, used them to form the cottage footing (protected them with polyethylene before pooring concrete so they are fairly clean). And the deck footings were also poored last year. Somewhat made a mistake, I have a row of 3 sonotubes at 10' from the ledger and another one at 20'... should have installed them at 9, and 18' instead but too late now.
The only concern I have with lapping them 4 feet is the tail ends rising in time so with the info above I will remove 14 1/2' from each joist (which I will use for bridging) and then the lap will be about 19 in, plently over the 3 in lap requirement. It is a little more work but will save some wood while being inside code.
One last question: should I use lag screws/bolts to assemble lapping joists or nailing them is sufficient?
The code just requires 3 - 10d nails at the overlap of joists. No need for screws or bolts. I'd drive in 3 nails about 3 in. to 4 in. in from the end of each joist (figuring you have the 19 in,. overlap) That'll be plenty.
And your idea of cutting the 14-1/2 in. off the joists is ideal since you are required to install solid blocking between joists that bear on a beam. So those blocks will be put to good use. Because of the overlap of the two joists the actual block length will be around 13 in. so you can cut the block length off the joists rather than resawing the blocks from 14-1/2 to 13.
OK, so I'm further away, followed Mike's expert opinion and you can see the results in the second pic.
One question: my 2x10 treated ledger board is attached to my ICF wall with 6" Dewalt Screw Bolts+, so about 2 inches in the concrete. Do I still need 2 tension ties and how far in the concrete those ties would need to go? Feeling like 20 screw bolts+ for a 20' ledger should be sufficient but want to be up-to-code. Thanks.
I’d be more concerned about the 6x6 post that appears to be on something like an 8” footing.
They are 8x8 posts on 12" "sonotube" footing, with a "bigfoot" base, sitting directly on bedrock and armed with 15M rebars vertically, hopefully this is enough! (but I guess the post not being centered on the footing is what concerns you, unfortunatelly I had to pour the footings last fall when the escavator was on site...) There is a 1 inch bolt x 1 foot deep in the footing to hold the post in place (see picture).