I’m planning a 12X26 shed roofed addition to be attached to our 24X26 cabin. My plan was to use a row of sonotubes + posts for the outboard foundation and to use the cabin itself for the inboard foundation — like a deck. And, like a deck, I was going to attach a ledger, use joist hangers etc. Now I’m nervous about ledgers. Many BTers have cast doubt on lagged ledgers, preferring to through-bolt. So, should I through bolt through the band joist of the cabin?
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A. Use thru bolts being sure your existing cabin foundation is sized sufficiently to handle the bolts as well as the weight of the new addition.
or
B. Use a product such as "Ledgerlock" structural screws made by FastenMaster (www.fastenmaster.com) and recently written up in the Journal of Light Construction. I think they have also been advertised in Fine Homebuilding. They're 1/4" self drilling coated scews specifically designed for attaching ledgers. They supposedly have greater shear strength than lags, they are less expensive than lag screws, and they are much easier to install then lags or thru bolts.
The question I have is what is between the existing rim joist and the ledger? If it is foam sheathing, lags would concern me, If it is wood or plywood lags are fine. With a 12' span and all the roof load on the piers and existing foundation, lags firmly secured at the proper depth should do fine.
Woody
It's wood - T111. Thanks for your response (and thanks to everyone who helped with this question!)
I would use bolts and piers where the addition connects to the house, just like the decks I build.
MES
I think Woody has it right. As long as the ledger is being fastend to soild wood and the roof loads are bearing on the concrete footings away from the cabin you should be fine.
What is the cabin sill material? What is the ledger material? Can you get to the area behind the rim (band) joist? Will the floor heights be equal? If bolts are easy to do, I'd probably go that route. Lags into a big, solid sill might be stonger than lags trough a 1-1/2" 2x rim joist.
I like the sound of those special ledger screws. I'm going to look for those.
Al Mollitor, Sharon MA
Much of the recent uproar surrounding deck ledgers has to do with the fact that they are exposed to the elements. That makes for complex design tradeoffs with flashing, offset, and such. Not so in your case.
Through-bolt is better.