Hi, I’m planning a fairly simple, L-shaped deck, around 500 sq. ft., that wraps around one corner of the house. Height from grade to decking is around 23 in. on average. Snow load in my area is 50 psf. I was hoping to use a dropped beam construction, with 48″ deep concrete piers, 4×4 posts, 2-ply 2×10 beams, 2×6 joists and 5/4 in. decking. BUT – as I do the math, I’m finding I may not have quite enough height for a dropped beam construction, AND many people are telling me I should really use something beefier than 2×6 joists. All this makes me think I may need to switch to a flush beam construction and use all 2×10’s for ledger, beams, and joists. My biggest joist span in the current plan was going to be 7’11”, and my biggest beam span was going to be 9’0″ (the max span according to the IRC tables). I was also planning on joist spacing at 16 o.c. but am considering switching to 12 o.c. for more stability.
I would way rather do dropped beam…for a first time deck-builder the process just seems more straightforward rather than having to worry about all those added joist hangers and sizing the joists perfectly. Wondering if anyone has any thoughts on this and if I should definitely switch to a flush beam plan?? Attached the plan my father-in-law (he’s an experienced but non-professional builder) drew up for me for reference…thank you!
Replies
Hey there,
First off, the plans as drawn look good and your lumber sizing is to code. 2x6 joists at 16" oc are properly sized for spans up to 9' assuming you are using pressure treated southern yellow pine. The only reason to go bigger with the joists or tighter with the spacing would be if you were planning some large concentrated loads like a hot tub, in which case you'd want some professional engineering done.
As for the beam being flush or under the joists, the overall height of the deck above grade is definitely a determining factor. If you are considering using concrete piers and posts as shown and the deck is only about 23" above grade, those posts will be only about 4-5".. this does not allow for enough material to make a great connection between the posts and beam. The flush beam approach will add the beam height (9.25" for a 2x10) to the post length and make it much better/easier to make the post to beam connection. The framing for either scenario is mostly the same before cutting the actual joists (the easy part). The ledger, rims and beams are all framed first and the tops set to the same elevation. The joists are infilled and need to be fit fairly accurately, but since they will sit in hangers there is some wiggle room.
A third option, and probably the best in my opinion depending on how flat and level the grade is, would be grade beams. The tops of all of the concrete piers would be formed and poured level to each other and the beams would sit on them without posts. Then you are back to your beams under the joists plan which allows for more leeway cutting and lapping joists, and less hardware overall.
Fourth option.... Stone steps to stone patio... As a carpenter, I talk people out of decks in favor of patios all the time. Decks are maintenance and need frequent replacement. Patios are more expensive up front, less fun as a DIY job, but a much better value long term since they are more or less permanent and almost no maintenance. Last thing, if you decide to build the deck with built up wood beams, omit the plywood between the layers. That extra thickness can be needed to match an interior 2x4 wall, but it's not a great exterior detail as even PT plywood will rot/delaminate outdoors in that orientation. If you need to build up the beam thickness to accommodate a specific hardware (Simpson post base for example) use a scrap of 1/2" PVC. Good luck!
Thanks so much for these very clear and helpful suggestions! I think I'm going to go with the flush beam plan, all 2x10's beams (3-ply) and joists. It's pretty wet in my area, and I like the idea of having a little extra space for air circulation under there. I also worry about getting the pier surfaces exactly level with each other with the grade beams.
I'm also looking at losing the middle beam in section B of my drawing, and just going with a 12' joist span there, which is within the 14'0 max span per the IRC. Any issue with doing a span that long as long as I use decent joist hangers? Thanks again for the advice!
I would use midspan blocking at any joist spans over 8'.
Hi dmettler,
I agree with everything that fine finish has to say. Have you considered GluLam or treated LVL for the beams? The time that you save with reduced footings resulting from longer spans would be well worth the additional costs for the lumber. With reduced depth of beam you may be able to do a drop beam? You can also order them as long as you are comfortable handling.
Why the double row of footers/ beam in the 12x18 section, you can easily span the 12'
8" footers are probably not wide enough, especially if you are going to reduce the number of them.
If you can install post base after the concrete is set with epoxy or expansion anchors it will give you another shot at getting your post base' lined up
4x4 post are not allowed to be notched. I would consider a ThruLok for the railing post connection
https://www.jlconline.com/videos/railing-post-connections-with-mike-guertin_o
-max out your cantilevers to L/4 to reduce spans.
-why not ledger of the 16' side of house and save some footers there as well (that are technically in "disturbed soil" being that close to the foundation. You would have to change the direction of decking.
12" OC is nice.. but more of pain to work- think trying to squeeze your tools and body in the narrower space.
This is so helpful, thanks for all this! I think I will take your advice and lose that middle row of piers and the middle beam in section B. If I switch to a flush beam setup, and use 2x10 joists, my joist span can be up to 14', so you're right, can totally span that 12' there. There's no issue using joist hangers for a 12' span of 2x10 joist is there?
I think I will also switch the direction of section C, and again, since I'd be doing a flush beam setup, my piers and beam would now be along that 16' left edge of the deck, making for another 12' joist span from there to the ledger board, which should be fine with 2x10 joists.
My building inspector only requires 6" diameter piers at 48" deep, but that seems way too small to me, especially if I'm using 6x6 posts (which I'd want to do with this new setup to match up with the 3-ply 2x10 beams. So I'm thinking I would go with 12" diameter piers, since there would now be fewer of them. Does that sound right?
Anyway, thanks again for the advice I really appreciate it!
Not entirely on topic, but I just built a deck using helical piers. They saved a ton of labor and the installer was done in a couple of hours. You should consider them instead of concrete.