I read the article by Mike Guertin in the latest issue, about deck building strategies. Since I am going to be putting a deck on my house sometime later this year, any article about deck building is helpful.
However, I have a dilemma. My house is a timber frame with 5-1/2″ thick structural insulated panels (SIPS) as a skin on the frame. I do have a traditional rim board and deck system on my first floor. I really like the idea of the “deck brackets” that Mike used in his article, but in my case, I can’t see how it would be possible to use them, since I have 5-1/2″ of FOAM between the rim board and the sheathing. I checked the manufacturer’s web site and they gave virtually identical instructions for their installation (as well they should).
I can only imagine that bolting these things to the outside of the SIPS is going to squeeze the foam to the point where the brackets will always be loose. I wonder if any of you can give me some ideas on how to do something similar, use this product or otherwise attach a deck to a SIPS house without creating problems.
Replies
What's the exterior finish on the SIPs?
exterior of the sip is hardie plank but that's irrelevant, since the brackets need to be bolted directly to the rim.
any reason why you can't make the deck free standing and independent of the house?
john, that's been my foremost thought, making the deck freestanding, but my concern has been stability. I guess it's probably appropriate to apply some of the timber framing principles I learned by building the house, to a deck project, but even so, I worry that it will not be particularly solid.
Any resources or references on building a free-standing deck?
IIRC FHB did an article on FS decks not too long ago but if you know/understand timber framing I'd think you could figure how. A couple of things... not sure how long buried posts last there but here they last a long time (long enough) without being set in CC (CC footer @ the bottom though). The larger the post the less they deflect. Not hard to get diagonals 2 ways on the vertical axis from beefy posts and a good rim joist/girder. I'd consider bracing (diagonals) for every post especially if you chose not to set the post in holes and use post brackets in CC.
How high off the ground is this going to be?
Different heights, depending on where it is, the height at the building varies from four to six feet, twenty feet away it drops off by as much as three more feet. So the highest it will be is about nine feet above existing grade. I can fix that a little bit but not much more than 12-18". I am planning on a deck with multiple levels, though, so in some places it will not be much more than three feet off the ground, maybe even less.
Since these brackets require through-bolts I would think a beefy ferrule would work. Something like a length of 1/2" steel pipe that extended from the back of the bracket to the large washer on the nut end of the bolt. Cut it just a hair short to ensure that any gaps in the SIP panel and the ledger are clamped shut when the bolts are tightened.
I don't know what the compressive strength of a SIP would be but I would skip the cutout in the outer panel as shown in the article so that the ferrule would have the panel to take up the shear load.
Another idea would be to cut out a section of the panel all the way to through the foam to the back panel and install a large bearing block to completely fill the resulting hole. Then drill through and mount the bracket.
re: the pipe idea; I can't imagine that nearly all the force of the deck's weight would still be bearing vertically on the panels. Maybe a small percentage on the rim, because you're not really bolting to the rim with a snug connection, you just have a bolt going through it with a nut on the end. The instant that the SIP compresses enough to make the pipes relevant, most of the deck bears on the SIP. Not gonna make me happy when my panels tear off the house (not likely, but I'm not taking any chances).
I like the idea of the large bearing block much better, except that I'm not cool on cutting big holes in my panels to install the block.
Free standing is easy if you add some diagonals to the "legs".
I'd build a freestanding deck in this type of application, but lay the decking on the diagonal for stiffness and still bolt the ledger. That way, the wall would not need to provide support, just stability from horizontal motion.
Mike Hennessy
Pittsburgh, PA
I had the same problem, Jon. I would have liked to use the Maine Brackets but was worried about the compression on the outer 7/16" of OSB of the SIP. I considered the free-standing deck, which in my opinion is ideal, but I rejected this because the deck was too extensive, wrapped around the house, and the extra diag braces would have been hazards to anyone walking under the deck.
What worked for me was that I had slightly oversized the sill plate, so it was 3/4" wider than the bottom of the SIP when the panel was positioned on top of the sill and on the outside of the rim joist. I went with a double ledger, with the two ledgers separated by 1/2" PT ply spacers, then bolted with 1/2" x 10" galvie carriage bolts through the whole package.