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Community and Q&A

Did I goof badly? Metal bracket against exterior sheathing

Gary Dick | Posted in Energy Efficiency and Durability on

My typical wall section on part of my house is 5″ of stone, two layers of 2 1/4″ EPS rigid foam, Grace waterproofing, plywood sheathing with 2×4 studs and blown fiberglass between the studs.

At the chimney it’s the same but only one layer of exterior foam faced with 5″ of stone. I needed to mount some heavy steel brackets to the chimney made of 1/4″ plate steel. The contractor was wary of mounting these with lag bolts to the face of the foam and wanted to put the face of the brackets directly against wood to be sure there would be no deflection. (I was arguing that the foam is good for 25 PSI but not prevailing).

I conceded and we mounted 2 brackets measuring about 36″ x 6″ to the wood sheathing. Now I am worried that steel, being an excellent conductor, will bring winter temperatures directly to the wood sheathing and the studs and the dew point there will cause the wood to rot.

Am I over thinking this? I still have the chopped fiberglass between the studs (which is all most houses would have). On the other hand, the flue from the gas fireplace on the other side of the wall will create a strong temperature gradient on the other side of the wall. I have three options:

1) leave well alone
2) take the brackets down, put the foam back and reinstall before the mason gets further up the wall with exterior stone (not easy and would require cutting 2″ out of the brackets and re-fabricating)
3) Add a 4′ x 4′ layer of foam behind the brackets inside the chimney structure (although that will not be continuous and will not address warm air getting behind it.

Any advice appreciated – oh this is in south west CO – alpine desert climate zone 4 with winter night temps often in the minuses. Thanks for any suggestions you can give me……………..Gary

Brown painted box shaped brackets on the wall cut into the foam:

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  1. User avatar GBA Editor
    Martin Holladay | | #1

    What are these brackets for?

    There are at least two problems with these brackets: the one you described (cold steel encourages condensation and moisture accumulation at the sheathing); and the flashing problem.

    Depending on what these brackets are used for, they could conceivably be a conduit for rain. They will be tricky to flash.

    We need more information on how exposed these brackets will be, and what they will be used for.

  2. Gary Dick | | #2

    The brackets will support a steel chute for water to spill on to the top of a waterwheel which will be in a pond next to the house. The sheathing is covered with Grace waterproofing from the pond (grade basically) all the way up to above the spillway and brackets. The water is recirculated from the pond up to the chute with a pump and filter system.

    The in wall part of the brackets shown in my drawing below (and the photo above) are what has been installed so far

  3. Gary Dick | | #3

    The in wall brackets are 7" deep and mounted to the sheathing (with waterproofing between them and the wood). adjacent to them are 2.2" of foam and then 5" of stone so they will end up flush with the stone face. Once the wheel is installed, the visible portion of the brackets with the spillway attached will be mounted.

  4. User avatar GBA Editor
    Martin Holladay | | #4

    This is a tricky detail for water management and thermal management. There are a lot of opportunities to screw things up.

    First of all, this is a wet area. A little bit of splashing and water spray can be anticipated when it's windy, right?

    I'm not going to suggest details here. This calls for a site visit and a lot of thought.

    You probably know that stone veneer is one of the riskiest types of cladding from a moisture-management perspective -- especially when installed on a wood-framed wall. Lots of alarm bells are going off in my head right now.

  5. Gary Dick | | #5

    Well - I was thinking that where most of the water is going to be hitting the wall, I have the stone, then two layers of foam taped foam and then grace waterproofing before I get to any wood. Which seems like a lot of waterproofing / deflection of water. The brackets are the only place I penetrated to the wood and the membrane and they are above and behind the splash zone. On seriously windy days when that area of stone would get wet, I was not going to run the pump because there would be water everywhere and too much evaporation etc.

    So, unless the Grace membrane (and the foam) is not up to the task, I don't think the wood should get wet. The stone will - but it should dry out fairly quickly once the pump is off. I plan to run it 6 months of the year - it's too cold at night and the plumbing would freeze at other times.

    If that is all true, my main worry is the brackets and whether I should do anything about them or whether the air space on the inside of the chimney will dry any condensation in the wood studs better if left alone as is.

  6. User avatar GBA Editor
    Martin Holladay | | #6

    Is there any chance that the waterwheel and the steel water chute could be supported by independent concrete footings and some type of steel or wood posts?

  7. Gary Dick | | #7

    The wheel is on independent footings / pillars. The axle goes only a couple of inches into the wall ( we placed a 4" black plastic pipe there in the masonry so it will look like the axle goes into the house and does something - but it doesn't ).

    The spillway has to be supported off the wall brackets at this point. I was thinking about a big timber trestle but it won't fit in the space and I don't have the base to support one now.

    I am at the site now - will see if I can post a picture from my Iphone.

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