Deck connection to building

[josta]

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

 

[JAE]

You do not get the full value when nailing through siding. The inspector is correct.

Call Simpson - or whoever is the hanger manufacturer - and they will confirm this.

 

[josta]

Thanks for your response. So what do others do in the heavier snow load areas other than running another girder close to the building?

 

[HouseBoy]

The effective "gap" that is created by the space of the siding and sheathing means that any bolt or screw connector has to cantilever across that distance. I've seen much discussion about how some strength value might be accounted for but it's duboius at best.
There is a "prescriptive" deck construction code that details this pretty well. try googling it and you should find it.

 

[RARWOOD]

I think the best solution is to put in post so the main deck support is free from the house. You can still tie the deck into the rim joist for lateral support perpendicular to the house.

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.

 

[HouseBoy]

Can anyone show how one might rationally justify connecting a ledger to brick vener?
I know the IRC specifically prohibits it but I also know that it is done routinely in many areas.

 

[MiketheEngineer]

I have seen some projects where the siding was peeled back - deck installed and then flashed. Not my favorite solution but workable.

How about doubling the amount of fasteners - they are cheap - and just go from there....

 

[josta]

Thanks for the responses. I can understand this if the "siding" was gypsum board, hardi-plank or of some brittle material, but T1-11 is mostly solid plywood. I'm having a hard time visualizing why the plywood wouldn't give as much structural value for the hanger nails as the rim joist here.

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?

 

[RARWOOD]

I think attaching to brick veneer is a bad idea and in most areas a clear code violation.

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.

 

[josta]

OK, just talked to Simpson. While they do not have any information on hangers through siding, they had a good analogy; where you nail a HPAHD22 or STHD holddown through the siding into the holddown post you have increased deflection.

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?

 

[rday]

I spec bolts (not lag screws) through the rim for new construction. We do have some pretty big snow loads in parts of Colorado.

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.

 

[MiketheEngineer]

I agree w/ rday - you need to go thru the rim boards

 

[RARWOOD]

As a structural engineer when I build something at home I go way over board. I have never liked the idea of lag bolts or timber screws int the rim joist to support the ledger. I always want to use bolts. When I saw the detail for using bolts attached to a Simpson hold down screwed or bolted to a parallel joist behind the rim, I thought thats my kind of detail.

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.

 

[COEngineeer]

I've been specifying "ledgerloks" screws manufactured by fastenmaster. The values are so much higher than lag screws.

Never, but never question engineer's judgement