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Questions on retro insulating a 1968 Cape Cod style home in Zone 5 (northeast Penn.)

Ryan O'Rourke | Posted in General Questions on

I recently bought a 1968 cape cod style home in NE PA region 5. There is a full below grade basement, main level, and of course the upstairs bedrooms with dormers / kneewalls and a tiny crawl attic. There are hatches to enter all these spaces. The bedrooms closets occupy space between the attic and kneewalls (sloped drywall against the roof rafters at top of closets). Presently there is R-13 fiberglass batting in the kneewalls, the roof rafters above the closets, and on top of the drywall ceilings in the bedrooms. So the kneewall cavities and the attic are unconditioned. There is also R-13 in the basement ceiling joists, so the basement is unconditioned. This original portion of the house has all single pane double hung wood sash windows, and there are 18 of them, plus 5 single pane basement windows which I may remove and replace with block prior to insulating. Debating whether to replace the house windows or if it’s feasible to add storm windows. This winter we may just tape plastic over them.

There is also an addition with a family / fireplace room with a crawl space underneath, and then an attached garage on a slab. Both of these rooms have a large full attic. Presently there is R-13 fiberglass in the ceiling joists over both of these rooms, as well as over the crawl space (under the fireplace room). We want to create a storage deck over the addition room (fireplace room). Presently there is R13 in the joists above this room. We are debating whether to install rigid foam board and lay plywood over top of this, or to run perpendicular joists and add R30 into them and then sheath over those joists. An insulation contractor suggested removing the fiberglass and spraying 4 or 5″ of closed cell spray foam right on the drywall ceiling and then sheathing over that. Not sure on the best option.

In the main attic, we were proposed to remove the existing R13 fiberglass, then spray 6.5″ lapolla 4G open cell spray foam in the roof rafters from soffit to ridge. With exception of the closet between the kneewalls and attic, would get 6.5″ open cell lapolla injection foam. Problem is I only achieve R28 using this method, and there are debates of sheath rot. I do like the idea of incorporating the attic space into my envelope, as I don’t have to worry about installing ceiling lights, speakers, or perhaps mini duct cassettes if need be.

We’ve decided to encapsulate the crawl space and remove the fiberglass. So on 3 walls we will use 2″ closed cell spray foam, with 3″ in the band joist. The floor will have either fiberglass reinforced plastic, or cleanspace liner with drainage matting depending which contractor we use. The 4th wall is adjacent to the full basement and so will only have about 1″ of closed cell to seal off the flooring. I’m going to attach a manual J that I had done, which at the very bottom has a not-to-scale sketch of my house, but gives a good idea of the layout.

Then in the basement, again, we would do 2″ of closed cell on the walls with 3″ in the band joist. It will be difficult to spray foam behind certain areas, such as the electrical utility area, and some areas with copper water pipes. Assuming we do not have an unlimited budget, what is the best way to handle these areas? (Primary question #1)

We are debating if we should frame out the walls prior to or after spray foam. If we frame prior, then I would leave a 1″ gap so to have a continuous layer of insulation, and also save some interior wall space. However it also slows us up in getting the insulation done as it gives me a good amount of legwork. And it also makes the framing semi-permanent, difficult to replace if need be. Is it better to simply have the spray foam done first and foam later? Or is there benefit to framing first and leaving a 1″ gap, beyond just saving an inch or so of space?

I have some more questions but this is a good place to start.

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  1. GBA Editor
    Martin Holladay | | #1

    If you have copper pipes and electrical boxes close to your rim joists or your basement walls, the best way to proceed is to have a qualified plumber and a qualified electrician move the pipes and electrical boxes to make room for the insulation. If you can't afford this work, I suppose that you would end up with areas that aren't insulated. The downsides to that approach are (a) increased air leakage, (b) higher energy bills, and (c) the risk of frozen pipes.

    If you plan to install both spray foam and stud walls in your basement, the usual method is to install the stud walls first, and then the spray foam, but there is no real reason that you can't install the spray foam first, other than the fact that you will lose more basement area.

    In your climate zone, the 2012 IRC calls for a minimum of R-15 insulation for basement walls. Your proposal to install only 2 inches of closed-cell spray foam won't achieve the minimum code level.

    You provided a lot of information on your kneewalls and attic, but no questions about your plans for those areas. I'm not sure why you provided all that information. However, you may be interested to know that the best way (by far) to improve the insulation levels in the attics behind your kneewalls and your insulated sloped ceilings is to install one or more layers of rigid foam above your roof sheathing, followed by another layer of plywood or OSB and new roofing. For more information on that approach, see How to Install Rigid Foam On Top of Roof Sheathing.

  2. Ryan O'Rourke | | #2

    Thanks Martin. I provided the background detail to help understand my overall situation. But my proposal for the kneewalls was covered by the plan to spray 6.5" lapolla 4G open cell (I'm not set on this, it's just what was proposed to me) in the 2x6 rafters. There are portions along the front wall that are covered in drywall though. Such as over the hall stairs, and in the closets. We were proposed to fill these with an injection positive. But I'm actually considering pulling down and redrywalling these sections if it gives us superior options. I'd prefer though not to completely tear out and re frame the bedroom closet walls if it can be worked around.

    The 3 tab singles probably have about 10-15 years left in them. It's not in our budget to change the roof early. I'll consider addingadding rigid foam board at that time but doesn't help me now.

    As for the basement, then I will frame out with 2x4 studs, 1" from my block wall, and then spray the entire wall and rim joist with 3" closed cell. I'll try to move the electric and plumbing.

    We are not looking to achieve net zero, and we are at best a medium income family, so our goals are quality and performance with the best value in mind from a practical perspective, and to avoid the realm of diminishing returns.

  3. GBA Editor
    Martin Holladay | | #3

    I may have misunderstood your plans, but it sounded to me as if you were planning to leave the triangular attics behind your kneewalls outside of your thermal envelope. If that's what you are planning, it's a bad idea. You need to bring these little attics into your conditioned space by installing insulation that follows the roof line, from the soffits to the ridge.

    The problem, of course, is that this work is tough to perform from indoors. The work is best performed by installing the insulation above the roof sheathing.

    For more information on these issues, see “Two Ways to Insulate Attic Kneewalls.”

    All of that said -- I understand that it's often necessary to make compromises when there isn't enough money in the budget to perform all of the required work.

  4. GBA Editor
    Martin Holladay | | #4

    OK, that makes sense. In your climate zone, you will need to install an interior vapor retarder (presumably, vapor retarder primer on top of gypsum drywall) to avoid problems with moisture accumulation. If you do that, your plan will work -- as long as you understand that the roof assembly will have a relatively low R-value, and will suffer from thermal bridging through the rafters.

  5. Ryan O'Rourke | | #5

    Martin, I must not be communicating clearly. We wish to spray the entire roof system from the soffit to the ridge. This would include the knee walls. The bedroom closets with the drywall on the rafters is in between the knee walls and the attic.

  6. Ryan O'Rourke | | #6

    Is there a better solution that doesn't involve removing my singles?

    Is lapolla 4g a good product or is there a better option?

    The attic is extremely tight. You cannot even sit up inside, must crawl on stomach the entire length. And one side has such a mild pitch that I'm not even convinced the spray contractor will truly be able to reach all the way to the soffit on that side of the house (the rear). And on the front I'll also need to enlarge the openings cut into the sheathing to access my 2 dormers. I imagine it will be very difficult to enter these dormers and spray the roof in there.

    Is there an easier option for a vapor barrier than drywalling the entire length?

  7. GBA Editor
    Martin Holladay | | #7

    The work will be easier, but probably not cheaper, from the exterior of the building. You are quite right to worry about access.

    If you don't want to install gypsum wallboard and vapor-barrier paint on the interior side of the open-cell spray foam, you could use MemBrain (a smart vapor retarder). But first, check with your local code official to make sure that the gypsum wallboard isn't required by local codes or fire safety regulations.

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