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Old house insulation, vapor retarder & ventilation

user-5830971 | Posted in Energy Efficiency and Durability on

Good morning,
Having read your articles for years, I want to confirm my understanding of the literature with you, as we proceed with a remodeling project in our 1897 home in south/central eastern Iowa. Our balloon construction house has more than 6400 sq ft of living space, with gambrel style roofs on three sides. There is no soffit for ventilation, except near a bay window covered with a low, flat almost turret roof. There is no insulation in the rest of the house.

We are trying to renovate our third floor. It is 1900 square feet of 3rd floor space, with knee walls throughout, no soffit for ventilation. The attic above has gable ends which we can close with windows or open with louvred vents on the east and west ends. Our HVAC team placed our ductwork mostly in the unconditioned attic some years ago. I had requested that it be sealed properly, and it is triple wrapped with foil (R 9?), taped and now buried in R 49 blown in fiberglass.

Our contractor air sealed penetrations with foam as best he could, (though clearly we are not air tight and probably never will be). Then, he insulated yesterday, placing R49 blown in fiberglass in the attic and on one small, low, flat turret area in the third floor. He also placed R 13-19 friction fit in the stud walls, depending on the stud space. The contractors stapled 6 ml polyethylene over all the sloped ceilings and exterior sidewalls. Unfortunately, we cannot say that we are well air sealed. The drywallers are coming this morning to begin hanging the drywall they just delivered.

My questions:

I would like to remove the polyethylene over the sidewalls and sloped ceiling, and instead use a Vapor Retardant paint with a perm of 0.45 to less than 1. Would that be the right thing to do?

Do you recommend we leave the gable vents open from April through October and closed with glass in the winter, OR should the gable vents be open year round?

Do you have any recommendations for specifics on air sealing our old house? I know this is a huge issue but many folks don’t seem to even
attempt to air seal these old homes.

Are there any specific articles I can read about the outcome of using this polyethylene in southeastern Iowa in an old house that is not well air sealed? All I have read on your web pages and my gut tell me to get rid of it.

Our old house has been breathing a bit too well for more than 119 years now. I feel the plastic is a huge mistake. Our hope is to keep this old home standing for years to come for the community and future families. Thank you very much for your help with my question.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Denise,
    Q. "I would like to remove the polyethylene over the sidewalls and sloped ceiling, and instead use a Vapor Retardant paint with a perm of 0.45 to less than 1. Would that be the right thing to do?"

    A. In your climate zone (Zone 5), I would probably remove the polyethylene if I were you, and install the vapor retarder paint. Remember, though, that the most important way to prevent moisture problems in your walls is to pay attention to airtightness. Ideally, that means using airtight electrical boxes and sealing all penetrations. If you don't have airtight electrical boxes, you'll need to seal the boxes as best you can.

    Moreover, it is essential that your builders include an air barrier on the exterior side of your insulated kneewalls. You could use rigid foam, drywall, or OSB as an air barrier.

    Q. "Do you recommend we leave the gable vents open from April through October and closed with glass in the winter, OR should the gable vents be open year round?"

    A. If the gable vents are located above the insulation level (in a vented unconditioned attic), it's OK to leave them open all year 'round.

    Q. "Do you have any recommendations for specifics on air sealing our old house? I know this is a huge issue but many folks don't seem to even attempt to air seal these old homes."

    A. Air sealing work needs to happen before insulation improvements, not after, so now is not the best time to ask these questions. (It's a little late.) You may want to read these two articles:

    Air Sealing an Attic

    Air Sealing a Basement

    Q. "Are there any specific articles I can read about the outcome of using this polyethylene in southeastern Iowa in an old house that is not well air sealed? All I have read on your web pages and my gut tell me to get rid of it."

    A. Here are some links to articles on the topic:

    Do I Need a Vapor Retarder?

    Vapor Retarders and Vapor Barriers

    Forget Vapor Diffusion — Stop the Air Leaks!

  2. GBA Editor
    Martin Holladay | | #2

    Denise,
    One more point: It's a mistake to insulate unvented sloped ceilings with fiberglass insulation. You can only use fiberglass insulation in a sloped roof assembly if there is a vent channel between the top of the insulation and the underside of the roof sheathing. This vent channel needs to be connected to a soffit vent (as an air intake) and either a vented attic or a ridge vent (at the top).

    For more information on this issue, see How to Build an Insulated Cathedral Ceiling.

  3. user-5830971 | | #3

    Thanks for all your responses, Martin. We have done as much air sealing of all holes and penetrations, though clearly this is an old house. We will remove the poly, if that is your recommendation. If you have any other recommendations, I welcome them and I remain grateful for your help.

  4. user-5830971 | | #4

    Thank you, again for your recommendation. I too am concerned about the sloped ceilings and appreciate your thoughts. These sloped ceilings are almost upright, so the team's thought was to treat these as more like walls. I remain concerned.

    I agree soffit and ridge vent would be ideal, though as stated, we have no soffit. When we reroof in the very near future, do you have a recommendation that might help at that point? I have read about gable vents and ridge vents. Would you recommend gable vents remain, since any ridge vent we could add would not have soffit to help with ventilation. Also, is it possible (though clearly not ideal) to better insulate the sloped roof from the exterior?

    Again, thank you for your help.

  5. GBA Editor
    Martin Holladay | | #5

    Denise,
    The steeply sloped roofs you describe are roofs, not walls. If these rafter bays are unvented, the best way to insulate (assuming that you have to insulate from the interior) is with spray polyurethane foam, or with a combination of spray foam and fibrous insulation.

  6. charlie_sullivan | | #6

    Insulating the roof on the exterior, while you are re-roofing, is a great solution. I think Martin will agree and he may just have missed that suggestion. With enough foam added, you can leave the fiberglass in place with no venting needed.

  7. GBA Editor
    Martin Holladay | | #7

    Charlie,
    I agree, of course, that exterior rigid foam is the best solution. If the attic is all opened up right now, however, it might make more sense to insulate these roof assemblies from the interior rather than to delay the work until some future time.

    That said, adding rigid foam on the exterior side of your roof sheathing is always the preferred approach. Here is a link to an article with more information: How to Install Rigid Foam On Top of Roof Sheathing.

  8. user-5830971 | | #8

    Charlie and Martin,

    Thank you both so much for your responses. We are planning to reroof much sooner than later. Clearly, I need to continue to inform myself so as to make the best choices for this old house. Again, thank you, both, very much for your thoughtful recommendations.
    Denise

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