Attaching deck to double stud wall
A lot of good (and fairly recent) information is available on attaching decks to conventionally framed walls. I have not found anything on attaching one to a double stud wall in which the rim board and floor joist ends rest on the inner wall and do not extend to the outer stud wall.
I have attached a sketch of a double wall and a proposed deck attachment. The inside floor and roof loads are borne by the inner wall. The outer wall supports only itself, except that for the section that must support half of the deck.
To provide attachment for either a 2x ledger (shown) or perhaps the Maine Deck Bracket (not shown), a rim board (“A”) is let into the outer wall studs. The nailing of this board into the studs is not adequate to resist lateral pullout from the wall. Accordingly, board “B” is mounted on the inside of the outer wall studs.
One way of bolting through to “B” would be to bolt the ledger or deck brackets through “A” to “B”. Thus “B” would have to be of sufficient height to accommodate vertical bolt spacing.
Another way of bolting would be to bolt the ledger or deck brackets to only “A”. Separate bolts would connect “A” and “B”. In this case, board “B” might be smaller, perhaps even a 2×4.
In either case, boards “A” and “B” sandwich the outer wall studs. To have the deck separate from the wall would require ripping apart the whole outer wall.
I’m looking for opinions, alternative ways of attaching the deck, or whatever, anything short of drift into the evolution of decks or the true meaning of decks in American life.
Replies
I make the outside wall the load bearing wall since it has the windows and doors in it. so the floor system runs over the inner wall and bears on the exterior wall, Makes the plumber and electrician happy, simplifies fire blocking at the top plate and floor ply since we just use a 2x12 upper top plate and run the floor ply to the exterior. This would simplify your deck attachment problem as well.
But the detail as drawn is fine other so long as the outer wall is capable of bearing the load. I'm not keen on single top plates and would question how you plan to get insulation in outboard of your rim joist. So long as you are not in a hurricane area this will probably work fine.
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"You cannot work hard enough to make up for a sloppy estimate."
Edited 4/19/2009 1:13 pm ET by ShelterNerd
I may be missing something here, but I fail to see the necessity for the 'rim boards' you've designated as A and B. Assuming the outer 2x4 stud wall is sufficiently strong (it should be, barring any special circumstances you didn't mention), you should be able to just lag-screw the ledger through the sheathing directly into the studs, the same as you would into a single-stud exterior wall.
I don't have the numbers handy, but the pull-out on lag screws is quite appreciable. If you run two 5/16" lags 1½" into each stud through a 2x6 ledger, the force required to yank that ledger off the wall will far exceed that required to pull the joists off the ledger, no matter what method you use to attach them.
Another consideration is that by notching the 2x4 outer studs to accept that rim board or sub-ledger or whatever you might call it, you will be appreciably weakening the stud wall itself--not a particularly good idea, IMO.
Dinosaur
How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....
"Another consideration is that by notching the 2x4 outer studs to accept that rim board or sub-ledger or whatever you might call it, you will be appreciably weakening the stud wall itself--not a particularly good idea, IMO."Yes, that was my own first criticism of what I drew. I think I have been inclined more toward the deck brackets for mounting the ledger, to avoid the issue of getting the ledger mounted and flashed properly for maintaining long-term integrity of the attachment. It would seem that getting the brackets flashed well would be easier than a long stretch of ledger. Since the bracket bolt spacing would span the width of the stud, I need something to bolt the bracket onto. If I bolt a ledger onto the surface of the studs, then why do I need brackets?I suppose I could make the outer wall studs in that area be 2x6, to counter the weakening due to letting the board in to be flush.The jury is still out. I'll await further comment.
You don't need any brackets to attach the ledger to the wall. Just lag-screw it right onto the sheathing, two lags into each stud. 2x4 studs should be sufficient. The only advantage to using 2x6 would be to gain additional wallt thickness for insulation.
You should not have any trouble installing proper flashing to protect the house, especially since this is new construction. Bolt on your ledger; then trowel on a coat of roofing pitch joist-high up the wall and also on the top edge of the ledger.
Have your metal fabricator put a 45º kicked-out hem on the bottom of your flashing--like on a commercial roof drip-edge--and make sure it goes a couple of inches down the face of the ledger and up the sheathing for a good 12". Don't nail it to the ledger, just to the wall sheathing.
You drop your deck joists on top of the flashing, and the pitch under and behind it seals the nail penetrations when you toe-nail the joists in place.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Dick...
Read your question this morning and it has been bothering me all day. So... As a rule, I avoid hanging the inboard end of a deck off the house unless the wall has been engineered to take the weight or the stress - especially if the house is in a heavy snow-load region. In your case, I'd question the 2X4 outer wall as it is. If you go ahead and notch it, as suggested, it'll only get a lot weaker. I'd prefer to spend a little more for labor and materials to pour proper footings and erect the same size posts being used to support the outboard end of the deck. If you really have to hang it off the wall I'd recommend reading an article by John Spier in the summer 2007 issue of Fine Homebuilding's special issue on deck-building. He shows some great techniques for waterproofing and making a strong joint between the house and deck as well as other good framing ideas. (No, I don't work for the magazine - it really is a good piece.)
Good idea to think your way through the project carefully before putting saw to wood.
Thanks for your thoughts on the strength of the 2x4 outer stud wall, particularly if notched. As I replied, earlier, that bothers me as well, and I am indeed inclined to use 2x6 for that part of the wall that supports the deck, if I do attach the deck to the house.Making a deck freestanding is always something to consider, although it trades the advantages of removing wall strength and flashing from the equation at the expense of bracing the deck structure that in this case will be 8 feet or so above grade.