Deck connection to building
Deck connection to building
(OP)
In this heavy snow area (100 psf) deck ledgers often fail, and the fasteners (lag bolts, SDS screws) just do not calc out except for the smallest decks. For that reason, I've specified that the deck hangers are to be nailed through the siding (usually T1-11) into the rim joist, with blocking between the joists at that point, so there is no ledger.
The inspector just questioned this method, stating that the Simpson catalog shows hangers fastened directly to a header or other wood member without the intervening siding. He does not feel we would get the full value of the hanger this way.
Any suggestions or comments would be appreciated.
John
The inspector just questioned this method, stating that the Simpson catalog shows hangers fastened directly to a header or other wood member without the intervening siding. He does not feel we would get the full value of the hanger this way.
Any suggestions or comments would be appreciated.
John





RE: Deck connection to building
Call Simpson - or whoever is the hanger manufacturer - and they will confirm this.
RE: Deck connection to building
RE: Deck connection to building
There is a "prescriptive" deck construction code that details this pretty well. try googling it and you should find it.
RE: Deck connection to building
If you have already contacted Simpson you will have learned that they have quiet a bit of information about options for attaching decks to the house. Also try AFPA, I think they just came out with a new publication on decks.
The detail you describe is not the best detail from a moisture stand point. Details that provide a space between the rim joist and the ledger are better details.
The challenge you face is the high load on your fasteners. Their is a company that makes a thick steel washer that nails to the rim joist as a spacer. However the nailing to the rim joist only holds the washer in place. I have tried to think of a detail where the washer would transfer the vertical deck reaction to the rim joist.
My best idea would be to use shear plates where the first shear plate takes load out of the ledger, the next shear plate is a spacer the third shear plate transfers the load into the rim joist. This solution has two problems. The first is that shear plate cutters are not a standard builder tool. The second is that you get bending in your bolt.
RE: Deck connection to building
I know the IRC specifically prohibits it but I also know that it is done routinely in many areas.
RE: Deck connection to building
How about doubling the amount of fasteners - they are cheap - and just go from there....
RE: Deck connection to building
Another option would perhaps be to use only, say 80% of a hanger's rated capacity when installing over wood siding. How could that be determined?
RE: Deck connection to building
With T-11 it is nailed to the rim joist and its ability to resist the vertical load would depend on the number of nails into the rim joist. Also most T-111 has some sort of grooves. A nail falling in the groove would have less strength.
RE: Deck connection to building
A STHD8 over 3/8" diaphragm gives 0.032" deflection; over 5/8" it is 0.083. It is in their Technical Bulletin "T-Plywood08".
Likewise, if we use the ledger-over-siding approach with lag bolts, I am sure there would be deflection at that connection as well as the deflection at the hanger, for a compounded deflection. I suppose the question now is; would that compounded deflection be more, less, or equal to the hanger-on-siding deflection?
RE: Deck connection to building
I believe that the code requires deck ledgers to be fastened positively with fasteners not subject to withdrawal (no nails). I don't think omitting the ledger would eliminate the need for similar fasteners.
The hanger straight to siding (sheathing?) sounds like a bad idea in general to me. But that's just my opinion.
RE: Deck connection to building
RE: Deck connection to building
As I indicated before both Simpson and AFPA have some good publications available on deck design. Also "Wood Design Focus" has had several good articles.
To me the main problem with deck ledgers is the low fastener values perpendicuar to grain in the rim joist.
RE: Deck connection to building
Never, but never question engineer's judgement