Wood Ledger Attachment 1

[msquared48]

Got a project where the owner has erected a deck (8' up) with a large roof structure over it without a permit... New situation for allof us, huh?

Anyway, my problem is that he has attached this deck to the existing house with a 2X ledger over 4" bevel siding, over 1/2" fiberboard to a 2X rim joist. This leaves an effective 1" gap to span between the ledger and rim board as the siding and fiberboard are non-structural.

I would like to bridge this gap with either lag screws or thru-bolts as to do otherwise would mean tearing out the whole deck and replacing it. Does anyone have any design guidelines for the bolts, as to capacities in this circumstance for either the lags or thru-bolts?

I would prefer thru-bolts as the inderside of the rimjoist can be exposed to install the bolts as there is a 2' floor joist cantilever from the bearing wall of the story below to the rim joist.

I am thinking of installint an angle that would mount on the backside of the rim joist and extend forward to let the rim joist bear on the angle rather than rely on bolt bending. Themore I think about this detail, the more I like it to avoid the bolt-bending and deflection / prying / bearing problems.

Any thoughts?

Mike McCann
MMC Engineering

 

[JAE]

Avoiding - or minimizing at least - bolt bending is of course preferred.

 

[HouseBoy]

I think I understand your detail. You are fastening to the rim board at the end of cantilevered floor joists . The angle doesn't seem like much of an improvement (at least the way I understand it). Yes, the new ledge will have something to sit on but the connection to the rim is still going to be the bolt that connects the angle to it. In fact, you might be inducing bending across the grain of the rim (if the vertival leg of the angle is not full depth of he joists) which is a no-no.
I wonder how well the rim board is fastened to the joists. That seems like the weak link.
Maybe I don't unsterstand your detail but that's how it seems to me. Is it possible to provide a sketch?

 

[SteveGregory]

Adding more load to a 2 foot cantilever concerns me without knowing the whole story.

To avoid relying on the connection to the rim joist, could you put a few posts down under the edge of the deck that is attached to the house?

 

[msquared48]

No posts here...

The angle will allow the new rim to bear on the leg of the angle, taking the load thru the angle to the existing rim joist. This negates any structurally significant bolt bending.

I have already thought of adding hangers to the existing houise joists to better support the existing rim joist.

Thanks all...

Mike McCann
MMC Engineering

 

[HouseBoy]

Two things:
How is the angle fastened to the rim?
Will the hangers be installed upside down or will you just count on the uplift capacity of the hanger?

 

[concretemasonry]

Way beyond the pure structural consitions/solution, are you going to open up any liability by signing/approving a design that does not address the potential liability for either continued moisture intrusion and/or mold?

The connection of decks to attached ledgers is prohibited by many local codes and is the source of most failuers - moisture or deterioration of the connection in general. Flashing and associated details become a part of most litigations. Because of this, only free-standing decks are permitted for obvious reasons.

Dick

 

[SteveGregory]

houseguy, Excellent question!

 

[msquared48]

Houseguy: The angle will be bolted to the rim with two bolts at 4" OC vertically, spaced 16 to 24" on center, maybe up to 4 feet if the loads allow, and, since it will not be possible to mount the hangers upside down, I will have to rely on the uplift values for the vertical support of the existing rim.

Concretemasonry: The attachment of decks to existing rim joists is not a problem here. The new deck is not waterproof and water intrusion / venting will not be an issue - plus, there is an Architect involved to to help with any flashing detailing if needed. I also intend to have them install soffet vents at the underside of the joists where the ledger and rim joist meet, pushing up the floor insulation as needed for venting.

Mike McCann
MMC Engineering

 

[druminman]

Mike,

Doesn't one of the failure modes in the NDS account for bolt bending? I'm thinking so, because the tabulated values are a function of the thickness of the attached member. Perhaps you could find a weighted Gs for the siding/sheathing/rim board sandwich and use that to find your connection capacity? Could simplify further and assume Gs is zero for siding.

The first option I thought of, though, was to hack the siding/sheathing out (You can do a lot with a Sawzall) and install a length of 5/4 decking as a shim. Then screw the now thicker ledger on with 1/4" SDS screws. The first time I saw SDS screws in action I stopped specifying lags for ledger attachment. The contractors I work with love them, and they're a lot more reliable than lags.

 

[msquared48]

druminman:

I thought about selectively removing the siding and fiberboard, but thought it too labor intensive, even with a sawsall. Besides, as the angle will have to be an 8X4, 4 to 6" long, probably 1.4" thick, LLV, that would be a lot of material to remove. Nevertheless, I will think about this further.

Regarding on the bolt bending issue, yes it is one (close), if not more of the scenarios, but, in thinking about it, as JAE originally said, I would rather avoid the issue entirely. With the angle lower leg serving as a bearing surface, the bending will not happen if the thickness of the angle is great enough. Hence - non-issue.

Mike McCann
MMC Engineering

 

[HouseBoy]

Seems like the eccentricity on the angle will not be a good thing. Perhaps not insurmountable but I wonder if it causes odd behavior of the ledger or the bolted connection of the angle. What size angle are you expecting to use?
I'm wondering too if you will want/need to have some way to impose a "tension" capacity or otherwize provide a tying capability to tie the deck into the house floor system (horizontally).

 

[msquared48]

Yes- I am thinking of Simpson LTT's bolted to the top bolt a very 4 to 6 feet or so... Still have to run the numbers.

Not really worried about the eccentricity here as I can compensate for it with the LTT's

As I previously said, probably angles 8 X 4 X 1/4 or so, LLV.

Mike McCann
MMC Engineering

 

[H57]

My only caution would be the attachment of the rim board to the ends of the joists. Typically these are nailed into the endgrain of the floor joists. When this occurs on a bearing wall not an issue as the rim board is supported. In a cantilever you may have to consider how you will transfer the load to the joists - not only the rim board.

 

[RockEngineer]

Fastenal did a bunch of testing on various deck connections just like you are talking about a couple years ago. They tested their own brand of lag screws with various materials between the rim board and the deck ledger. When I get back I will look in my office to see if I can find it but you may be able to contact them and get the testing data. Some of the results I know were published in Professional Deckbuilder Magazine because I was a consultant on the article. I hope this helps in pointing you in the right direction. I'm out of my office so I don't have easy access to my files.

 

[RockEngineer]

Here is and article from the test data I was talking about for engineering deck ledger attachments with material between the ledger board and the rim board.

http://mfboweb.org/Documents/deckledger.pdf