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Closed cell spray foam applied over wood plank with Tyvek WRB/Hardie Board covering

234John | Posted in General Questions on

Good Afternoon –

I am renovating a 100 year old home.

The insulation man chose on his own accord to apply closed cell spray foam to the inside of the first floor area under my bump out staircase of my home.  There is a wooden frame staircase built off the side of my house that is framed with wooden studs, and 1 inch thick or so planks which extends from the first floor to the second floor and ends as a peak on the third floor.  The first floor is stone and the reminder of the house is wooden framing.  

Under the wooden bump out he sprayed 2-3 inches of closed cell spray foam over the wooden plank on the inside portion under the first floor staircase rather than Rock Wool per my request.  It covers about a 6 foot by 6 foot area.  The exterior of the house has Tyvek WRB with a Hardie Plank covering. No new decking material or plywood sheathing was applied as the installer said he had enough surface area to apply his Tyvek.   There are gaps of a few inches in some spots between the horizontal 3/4 to inch wooden planks.  I am not sure why he chose to do this as it was not specified in my contract.

Will this be a problem?

Also – There is a flat EPDM roof 6 foot x 6 foot section on my second floor ceiling on the back bedroom corner of the house.  The valley of the roof comes down to this small section with a flat gutter and drain s down the side of the house.  I had requested close cell spray foam applied to this area in my contract.  The contractor took it upon himself not to spray this section and placed a Pink Fiberglass R-30 insulation there.

Will this be a problem?

He has installed 4 inches of closed cell spray foam to the roof cathedral ceiling as an insulator and vapor barrier.  He instructed me not to place more insulation into the open knee wall as this will need to breathe to “dry out” the under sheathing???  (WHAT- not sure what he is thinking…) ( I was not pleased that he did not follow our contract – And he said he had to spend $1500 more for insulating the old house because nothing was uniform – complaining to me)

The third floor walls and peaks are Rock wool.

The second floor walls are RockWool.

The front bedroom EPDM flat rood was sprayed with 4 inches of closed cell spray foam, as well as the first floor interior stone walls (after parging).

The back of the house addition has an old kitchen porch roof that has EPDM, new decking, over the original planks.

Thank you.

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  1. user-2310254 | | #1

    I'll give your post a bump and ask a question. Where are you located?

  2. 234John | | #2

    I am located outside Philadelphia....

    I get nervous because there are so few qualified contractors- Some have walked out on their work and another has to correct all their mistakes...

    I have put over a million into this stone 3?story house..

    So I ask many many questions.....

  3. user-2310254 | | #3


    You're in CZ4. You have a historic home, and it sounds like some of the exterior is stone. Is that stone cladding or is it structural? For your roof and wall areas, it would be helpful to describe each stack up. For example, let us know if a wall is stone cladding, air gap, board sheathing, 2x4 framing, and plaster (or whatever).

    It also sounds like you have some attic areas with knee walls. In general, a sufficiently thick layer of closed cell foam applied to the wall or roof sheathing is safer than open cell foam. In knee-wall assemblies, it is often the only way to effectively insulate hard-to-get-at spaces.

    But let's see what the experts think.

    1. 234John | | #4

      I will abbreviate ....

      In one small section of the exterior - new Hardie plank covers Tyvek house wrap. This is over Plan 1 inch thick 100 + year solid board. A small 6x 6 section was covered with 4 inches of closed cell spray foam.... from the inside...

      Is this okay?

  4. user-2310254 | | #5

    I don't know if it's safe. But it would be better if the siding was attached to furring. This gap would facilitate drying for the siding and board sheathing. Was the house wrap taped?

    I assume you have drywall on the interior. Was it installed in an airtight fashion (adhesive at the perimeter of each sheet and caulking to plug openings in any electrical boxes).

    Do you know your indoor humidity levels?

    1. 234John | | #6

      Hello Steve,

      ThevTyvek was tapped and flashed with tape. This bump out did not use the Tyvek flex wrap- so I insisted on flashing every new wooden Marvin replacement window on the remainder of the home.

      Winter humidity 32%. Summer about 55 % . Commercial dehumidifier in the basement. I don’t get water penetration in the basement. “French drain in place “

      Dry wall performed with typical paper tape and sparkle. There are no wall penetrations.

      The bump out is only a wooden floor.

      I assume I need to seal this from the outside with polyisocyanate board and caulk??

      Am I correct??

      Thank you,


  5. user-2310254 | | #7

    I think you are on the right track with managing your indoor conditions. For the cantilevered floor, you could follow this approach:

    There seems to be some debate about whether to fill the cavity completely or leave an air gap between the fluffy insulation and the subfloor. In another GBA post, Martin reported on a call he had with Joe Lstiburek. Basically, Dr. Joe said the gap promoted comfort but wasted more energy. (For more on this stackup, see Figure 1 and Figure 2 at Note that you would replace the gypsum with pressure treated plywood or some other durable sheathing.)

  6. Expert Member
    BILL WICHERS | | #8

    I think you're unlikely to have issues with the spray foam around that staircase. Hardie plank isn't air tight, it's actually pretty leaky (hopefully no one tried to caulk the planks together), so that helps with drying to the exterior. If the hardie plank was installed off the wall a bit with furring strips, or if you have a "real" rain screen, then that's even better for drying.

    Can you provide a drawing or some pics of the knee wall that "needs to breathe"? That sounds odd. Spray foam under a cathedral ceiling, if applied directly to the underside of the roof sheathing in an unvented roof, is usually a pretty good way to insulation an area like this. Sometimes you have vented roof areas that have no intake venting due to the way the roof comes together, so maybe this is what's going on with the kneewall in the insulator's mind? You don't want to let the house leak to "vent" the attic space though. A drawing or some pics would help to see what's going on, otherwise it's a bit confusing and hard to give you good advice.


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