Steel brackets for deck ledger

[mjr6550]

I am looking into ways to attach a deck lager to a poured concrete foundation wall. The basement is finished and the owner does not want it disturbed. The exterior wall is stucco and the contractor does not want to touch that. I would prefer to step the deck down and attach the ledger directly to the foundation wall, but the owner wants the deck approximately level with the floor. I am looking at designing brackets using either rectangular HSS tubing or a channel with an angle welded to the top. Each bracket would be attached to the foundation using one expansion anchor.

I have run some calculations and the numbers seem fine, but I guess I'm not in love with the fact that the bracket puts the anchor in shear and tension (I did calcs for combined tension and shear). I have generally used anchors mostly for shear. I'm just looking for input as to whether this design makes sense.

 

[CANPRO]

my first choice here would probably be to build the deck independently of the house with posts and bracing - if this is an option.

If you have to use the foundation wall as a support, instead of using a series of single brackets, I would look into using a continuous ledger - steel angle or maybe a 2ply timber member with staggered fasteners. Don't be afraid to specify a tighter spacing on the anchors if it makes you feel more comfortable - you have to consider the condition of the concrete and the quality of construction for residential foundations.

 

[mjr6550]

Posts and bracing is not an option.

Because of offsets in the rear wall there are a series of ledgers. Most are relatively short and the loads are not really very great. For those I was thinking one bracket near each end would be fine. For one longer span I was thinking of adding a couple extra brackets even though two would work. I don't like the idea that failure of one bracket would lead to collapse. There is an option to lower the section of the deck with the longer ledger. If that happens I can use a staggered bolt pattern and just attach the ledger to the foundation wall.

 

[chicopee]

Per your sketch, it appears that each bracket has one anchor to the concrete wall and that anchor would be primarily under shear but would also be under tension. If I am looking at this drawing correctly, there will be some prying at the bottom of the brackets putting the anchor under tension, therefore, I would us two expandable anchors instead of one. Many failure of decks and balconies result from underestimating the load that would take place during unusual concentration of people that under normal circumstances would not exist.

 

[dhengr]

Mjr6550:
That’s not a particularly good or well thought out detail. Where is the stucco that you are building over; what does the wall framing and sheathing look like; the floor framing diaphragm; the dimensions; the loads and deck framing; all of the flashing details; etc, etc. How is the rim joist attached to the fl, framing, and in particular nailed to the sill pl. and the fl. sheathing. This prevents it from being pulled out of the bldg. under lateral loading. What is the framing at the other end of the deck joists and how are lateral loads accommodated? What prevents those brackets from just rolling over, rotating about the anchor if a lateral load is applied? It would be good to see a plan of the house ext. wall and deck in this area. Sometimes, if you want to do it right, the Architect, Contractor and Owner can’t have everything they want. They just want it quick and cheap, never mind poor detailing or the fact that it might not be water tight. I would cut a pocket in the stucco and attach the ledger to the rim joist and fl. framing diaphragm. Cut the stucco out to fit the ledger, plus .25" all around, flash that pocket, up and behind the water/wind/drainage plane membrane and out under the ledger, including end dams full height in the pocket; then set the ledger and flash over and around it, and caulk around the ends. Cover the deck joists with 2" wide peal-n-stick (ice-n-water shield type) tape and also cover the outer beam with peal-n-stick tape, particularly when it is a multiply member; keeps water out from btwn. the plys. If the decking runs parallel to the ledger, consider setting the first full piece, at the ext. wall, on treated wedges so it drains away from the wall and the ledger, about .25" high at the wall.

 

[hokie66]

A fastener that close to the edge of the wall will do little good, and is unreliable. If you can take the joists in a little bit as shown, why not take them in further? Since the deck is to be level with the floor, I assume the deck has a roof, and the watertightness will be other that at the floor level.

 

[mjr6550]

There is no roof. Contractors are reluctant to touch stucco doe the leakage concerns. Installation flashing properly with an existing house is not easy.

I placed the anchors down far enough on the foundation to meet critical edge distance. I am accounting for the prying action in the tension forces, although predicting actual lateral loads is difficult.

Lateral movement side to side should not be an issue since there are offsets in the rear wall with the flat seats on the brackets. Longer brackets to accommodate additional anchors is not practical because of some doors and windows.

I had intended to add some lateral connectors to meet code requirements of tying the joists to the ledger. I now think that penetrating the stucco at a few locations would be advisable. The revised sketch shows typical lateral connectors that would be placed in a few locations. With proper sealing at the hole and a slight downward angle water penetration should not be an issue.

Thanks for the input.

 

[dukengnr79]

Would it be possible to flip the orientation of the angle so that the vertical leg hugs the corner of the concrete wall (rather than sticking up above the top of wall) ? Would that allow you to still penetrate only at the top of the wall and not the stucco, but by hugging the vertical face of the wall with that angle leg remove the prying action from the picture?

 

[gte447f]

mjr6550,

I agree with most of what dhengr is saying above, and I may be missing something, but your second detail that you posted showing the lateral ties to the house joists is pretty much the same condition as using thru-bolts to attach the ledger, so what's the big deal?; why don't you just do that? The only difference that I can see is fewer holes (for the lateral ties with no thru-bolts) and a sloped rod for the lateral ties vs presumably level thru-bolts, but drilling holes is drilling holes. In my view, it doesn't matter if there are 2 or 4 or 20 holes; if the job isn't waterproofed properly they will all leak and if it is done properly none of them will leak.

 

[mjr6550]

I am trying to keep the owner happy. If I tell them they need three holes, they can probably live with it. With through bolts it would be about 18 holes. I have not seen the basement, but apparently it is very impressive and accessing and patching that many holes is not something the owner or contractor want to deal with.

I try to accommodate the owners and contractors when possible. This is a case whether I have to decide what is possible. I'd rather than touch the stucco, but for several well sealed holes I think the potential for problems is low and the level of comfort with the attachment is well worth it.

 

[KootK]

Given your particular constraints, I think that your solution is quite clever. I can't think of a better one. With the addition of the lateral ties, I think that you're good to go.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.