Need advice on low-to-ground deck construction... - DIY Chatroom

DaveNJ · 10-31-2009, 01:29 PM

I'm building a low-level (but not ground-level) deck (22.5" from door threshold level at house to grade at the point of the first pier). By my calculations (below), that would only leave me between 4" and 5" of post height (pier to beam) if using 2x8" framing and a traditional joist over beam construction. I'd really like to use 2x10" framing which would mean the beams would sit right on the concrete piers (no posts). Not sure what the code is on that.

22.5" Threshold height
-1.0" Lower ledger by 1" to prevent water rotting subfloor
-1.25" Decking 5/4"
-7.25" Joist (actual 2x8" depth)
-7.25" Beam (actual 2x8" depth)
-1.0" Post/footing standoff
-------------------
4.75 Post height

22.5" Threshold height
-1.0" Lower ledger by 1" to prevent water rotting subfloor
-1.25" Decking 5/4"
-9.25" Joist (actual 2x10" depth)
-9.25" Beam (actual 2x10" depth)
-1.0" Post/footing standoff
-------------------
0.75 Post height

Not sure how to approach this, I had some plans drawn up for me by an online plans seller. They came back with a non-catilevered plan (just beams on posts level with the joists) but I can't for the life of me figure out how to attach the joists/beams and posts at some of the points of connection. If you look at the plan (for example, the lower pier in the image below), there are 5 pieces of lumber (2 doubled up 2x's and a joist) coming together over a single 6x6 post.

I'm curious if any of the experts here can look at these plans and tell me if they're workable or if I need to start from scratch. Thanks very much.

DaveNJ · 11-03-2009, 07:45 AM

Anyone?

CustomBuild · 11-03-2009, 10:05 AM

Hi, I am a journeyman framer from St. Louis, and most recently framing in Upstate New York. The plans you have resemble any typical plan drawn up that I have ever worked with. What I would normally do with 6x6 posts is kerf them where the band board would be inset, rather than cut your post at the bottom of the joist. This will allow the post to support your handrail also. Where there is a 45 degree turn over a post, it takes careful layout of how deep, and what angle to kerf the post. A 10" circular saw is usually required to get the depth you need. Sometimes a saw-zall is needed to finish the cut. When you are installing the band board, try to use 45 degree cuts, and have one board run by the other, instead of using 22-1/2 degree cuts and butting them together. Since it is calling for a double band, I would use the 45 degree cuts on the inside band, and 22-1/2 on the outside band for aesthetic reasons. This will allow you to bear the short board over the post more. You want to shoot for 2-1/2" bearing if possible. It is a little difficult to determine if I am answering your question directly, because I can only imagine what the elevation looks like. If this doesn't answer your question, please post the elevations.
Also, On the corners of the main deck, I would rotate the posts 45 degrees, to help simplify stair rail installation, otherwise, you will end up with a difficult compound miter cut at the top of the rail.
The exact location of the common joists is not important. So you can plan your layout so a joist doesn't land on a post. Just make sure you don't omit a joist in the process. Too few joists is a reason to fail an inspection. If that is unavoidable, then you can hanger the joist right to the post. Hope this helps.

DaveNJ · 11-03-2009, 02:58 PM

CustomBuild --

Thanks for the detailed reply -- I really appreciate it!

Although the plans call for a corner post, flush beam framing (where the beams are on the same plane as the joists), I'm wondering if I can squeeze in a more conventional joist OVER beam framing -- especially as the grade drops toward the outer edges. The height of the deck at the house is about 22", but goes to about 25" at the end of the main deck and about 27" at the end of the octagon about 26' away. My concern with the current design is that most support 6x6 posts are exactly where I want to put the 4x4 railing posts, which I want INSIDE the rim, not external to it.

I understand what you're saying about the kerfs. I'm now thinking that I would make the inside supports kerfed, with the beams set into the posts (flush beam with joists) and the outside supports framed using catilevered beams with support posts set inside the outer rim. I really don't want to use 6x6 railing posts, which is what I think I would need to do to keep the support posts at the edges and making the supports and posts one continuous 6x6.

CustomBuild · 11-04-2009, 12:10 AM

In the end, there really is no substitute for being there, first person to assess the situation. While I do agree that cantilevering a deck is more practical and attractive, the plans may need to be altered, So the print and the construction coincide. Also, a deck of this size has the potential for an enormous live load. Any deviations need to be approved by the engineer, so the loads can be recalculated.

GBR in WA · 11-04-2009, 01:19 AM

I would get a permit for this deck. Your span of the joists need to be Southern Pine - 2x10, or Doug-fir larch, hem/fir, spruce/pine/fir - in 2x10 would be at max. using the 2006 deck code: http://www.awc.org/Publications/DCA/DCA6/DCA6.pdf
I did not check your footing sizes or ledger attachments- spacing, etc. as listed in the article. If using composite, you will want to reduce the "on center" to 14" or so. Be sure to put the footings below your local frost depth to protect against frost heave.
You don't need any beams, just the doubled joists with hangers on all the joists. That drops it all 7-1/2".
Be safe, Gary

DaveNJ · 11-04-2009, 06:48 AM

Gary,

Thanks. The permit was issued on the plans shown. All framing is specified as 2x10 SYP, joists 12" OC with 6x6 post. The smaller footings are 16" in diam, 30" deep (per code for my area), except for the two inner piers which are 22" in diameter.

So, assuming I go with these plans and don't revise and resubmit...

Is there a way to work the railings so they're inside the rim? With the beam posts at the corners, that space seems to be occupied. One thought would be to make the railing post and beam post all one piece (with kerfs for the beam insets), but that would give me massive 6x6 railing posts.

DaveNJ · 11-06-2009, 09:18 PM

Quote:

Originally Posted by CustomBuild

...When you are installing the band board, try to use 45 degree cuts, and have one board run by the other, instead of using 22-1/2 degree cuts and butting them together. Since it is calling for a double band, I would use the 45 degree cuts on the inside band, and 22-1/2 on the outside band for aesthetic reasons. This will allow you to bear the short board over the post more. You want to shoot for 2-1/2" bearing if possible. It is a little difficult to determine if I am answering your question directly, because I can only imagine what the elevation looks like. If this doesn't answer your question, please post the elevations.
Also, On the corners of the main deck, I would rotate the posts 45 degrees, to help simplify stair rail installation, otherwise, you will end up with a difficult compound miter cut at the top of the rail.
The exact location of the common joists is not important. So you can plan your layout so a joist doesn't land on a post. Just make sure you don't omit a joist in the process. Too few joists is a reason to fail an inspection. If that is unavoidable, then you can hanger the joist right to the post. Hope this helps.

I tried rotating the angled corner posts to see how I could also use inside-the-rim posts. Since the beams lie on the outside (no cantilever), they're double 2x10's, so the posts will be inset 3". Not sure aesthetically how that would look, but it looks like everything will line up OK. Does this make sense?

CustomBuild · 11-09-2009, 06:21 AM

[IMG]file:///C:/Users/Owner/AppData/Local/Temp/moz-screenshot.png[/IMG]For a large deck, I think 6x6 posts are gorgeous. I have used them on large decks before, and they seem to stay in proportion to the size of the deck. I would run them about 8" above the height of the top handrail, cut a 3/4" chamfer at the top of the post, and 6" down cut a 3/4" "V" out, all the way around. Those cuts dress the posts up with a squarish ball at the top. Then to really make them pop, a copper solar light with a drive-in-the-ground type spike set into an appropriately sized hole drilled down into the top of the post would be the icing on the cake. But that's just me, and tastes differ from person to person. I have included a link to a drawing I did. I did it in paint, so nothing is straight, square, or drawn to scale, but I think it would work. Although, you would lose some square footage on the deck. The blue squares would be the 4x4's, and they would run alongside the 6x6's, and get lagged together. You would end up with 5-1/2" of deck outside of the railing, but I think, considering the size of the deck, that too, would be in proportion.