Insulating a Deck Ledger
I am attaching a deck for a front entry to the thickened edge of a concrete slab. It’s gonna be out of rough cut white oak, coming out 5 feet from building and 10 feet wide. Plan is full sawn 2×8 ledger into concrete and the other ledger on top of two concrete piers.
doesn’t seem like rigid foam behind the ledger is a good idea, even thin high density stuff. Do I just fasten directly, maybe with some of that foam roll behind for air sealing/little break, and have a thermal bridge there? Do I cut and cobble some rigid foam to go in between joists on top of ledger after building frame?
And tapcon or grk concrete screws 1/4” good, 2 screws every 2 feet?
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brooksbend,
How high above grade is it?
What climate zone are you in, and how is the rest of the slab insulated as is?
Zone 5, slab is insulated with 3” eps on sides and 5” underneath.
It’s gonna be roughly 1 foot above grade
brooksbend,
As Patrick said: For a deck that close to grade, there is no point attaching a ledger to the building. It's much less complicated to pour another couple of piers about 18" from the slab and have the deck free-standing.
You could look at something like the Maine Deck Bracket (https://deckbracket.com) which would allow you to space the ledger away from the slab and then infill the void with rigid foam.
The bracket is designed for installation to a wood rim joist, so you'd likely have to have a design professional specify a fastener schedule for this use.
That being said... even though this product is popular (at least here), I do wonder if anyone's ever modeled the heat flow through it vs a directly attached ledger. Even with foam between the brackets, there's no getting around the fact that these aluminum brackets will be heat funnels from one surface to the other.
> And tapcon or grk concrete screws 1/4” good, 2 screws every 2 feet?
FWIW, I'm not sure I'd trust a 1/4" Tapcon to hold up much of anything, let alone something people will stand on. I suspect I'd be looking at something like 1/2" Simpson Titen anchors, and installing them with a torque wrench so they don't snap.
Another option is to build this structure to be freestanding. Given it would be pretty close to grade, and is relatively small, your code may allow for this. It's probably the option I would go with.
Okay so if I do free standing how do I deal with the connection between deck and concrete floor? The doors are out swing (it’s a barn/farm workspace) so the threshold has to be on the plane of the siding. The wall assembly is 2 layers of 2.5” polyiso, 3/4” vertical furring, 1” vertical pine boards.
> Okay so if I do free standing how do I deal with the connection between deck and concrete floor?
I'm not sure what you mean by connection. You typically want a step down from an exterior door to the landing to eliminate or substantially mitigate the possibility of rain or snow build up encroaching on the door, threshold, or under the threshold.
There will be a roof over the area so that’s not a concern. What I’m saying is that I was imagining using the landing as a threshold for the door as well. Now that we eliminated the landing as needed to be held up by a ledger connected to concrete, we still need someway to make a threshold connected to the concrete?
> There will be a roof over the area so that’s not a concern.
I've seen wind cause rain and snow to do some funny things, at least by me.
> There will be a roof over the area so that’s not a concern.
Where is the plane of the siding relative to the plane of the slab's side insulation?
In line
brooksbend,
You can have the rim-joist of the deck where your ledger would have been if you had separated it from the slab with foam. There would be no difference, except you aren't worried about how to support it.
Thanks Malcolm, that makes sense. Is it floating or should I screw it through foam to the concrete? And should I have less foam behind it or just have it be my wall assembly behind it minus the siding?
brookesbend,
I would leave it independent of the building. I can't think of any reason to connect the two.
Ideally, If you can afford the depth and still support the threshold, I would finish the wall just as if there wasn't a deck there (siding and all), and leave a 3/4" gap to the rim-joist. This would pretty much eliminate any moisture concerns, and makes eventual replacement or future changes very easy.
Use a 2x perpendicular to the ledger board and longer screws with foam in between the screws to attached the ledger board to the concrete. You screw through the 2x as the normal screw spacing. Installing some additional piers a closer to the foundation wall as others have said is also beneficial.