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Community and Q&A

Window installation — sealant offgas issues

VapourOpen | Posted in GBA Pro Help on


About a month ago, i had some windows installed in my basement. They were installed on a cold day, about -5 degrees Ceclcius (20-25 Fahrenheit). The weather here has gotten unseasonably colder. The sealant used to put the windows in place was Mulco’s supra expert, and seems to be dry on outside, but some areas are still soft.

Ever since the windows were i basement, the back of my throat is slightly sore, but only when i enter the basement. At the first week, there was a definite solvent smell, but the smell went away, after i attempted extreme air sealing and removed the clear sealant from one of the 5 windows (where i think it was coming in from. The smell has not come back. The sore in my throat only occurs on some days, not all. My theory, is that this is only occuring on cold days where the furnace is blasting. It is an old house that uses concrete block, the hollow cores are where the leakage is coming from, the mortar joints aren’t the best either. (the basement is in the process of renovating).
All other materials have been ruled out.

THe flashing for the windows have not been installed yet (windows are covered with board temperorarly) thinking it needed to air out. I havnt aired out the space that much becuase of the temperatures.

I am not sure at this point, if the cold weather has not given a chance for the sealant to cure, or if i have a sensitivity to something in the sealant. Either way i don’t really know what to do.

I need to know two things.
1. Are there more environmentally friendly alternatives to thermoplastic sealant for this application, or one that has low voc’s
2. What should I do? Is there something simple i am missing. I want to be able to work and live in my house.

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  1. GBA Editor
    Martin Holladay | | #1

    If you are looking for low-VOC caulks or environmentally friendly caulks, a good place to start is the Caulks and Adhesives section of the GBA Product Guide.

  2. VapourOpen | | #2

    Okay, i can find a low voc product, but what about dealing with the sore throat issue in the basement. Part of me wonders if i just have really dry air there. should the old selant be removed enitrely? would just being able to air out the basement solve the problem?

  3. GBA Editor
    Martin Holladay | | #3

    GBA is a good website for answering questions about energy, construction details, and materials specifications -- but not for answering medical questions.

    If you have medical symptoms, it's best to consult your doctor.

  4. adsingl | | #4

    You could try humidifying the air with some sort of cheap/diy solution for a short period on cold days and see if that resolves the throat issue. Can't add anything to your caulk/voc selection question.


  5. VapourOpen | | #5

    I rented a ppb Minirae VOC detector. It has confirmed my suspicions, that VOCs are entering the building in the basement through the new windows. All window wells have an elevated level of VOCs in comparison to the rest of the rooms. Specifically, the air comes in between the window joints and the typar (which are not airtight, marvin integrity).

    I am thinking, instead of reinstalling the windows with different sealant, would it be a good idea to change the furnace from a exhaust ventilation system to a supply ventilation system? The reason for me thinking this, is I have made the basement really airtight which is where i installed the winodws. The leaks in the frame are acting as the air intake in the worst possible location, right where the sealant is.

    the only advantage of replacing the window, is i can install a proper pan, but it will take alot longer

    is it a good idea to change the ventellation method?

  6. KeithH | | #6

    I'm just a DIYer but I've been doing some air sealing with both caulk and canned foam lately so I'm familiar with the odors that they can produce.

    I have no idea if you could be smelling the small amount of foam sealant used around the windows many days later or experiencing respiratory irritation. I'd seek medical attention.

    But ... both caulk and canned foam produce an odor when first applied that does persist for awhile.

    Another idea for you would be to get a VOC free sealing tape and seal the interior edges of the windows using this tape. Google Siga or Tescon Profil tape. It's expensive but might be a very cheap solution compared to other options. If you install it properly, your drywaller should be able to cover the tape on the window edge with the drywall. Or ask your drywaller to install it. These tapes are air tight but not vapor tight so it is possible they would only reduce the smell.

    For that matter, the drywall, which should be airtight once installed, may cut down on the odor. You may want to consider specifying a low VOC or non VOC caulk for caulking the drywall to the window. I've found considerable difference in odor even among the products by the same company stocked at home depot.

    Last, one of the most noxious smells, in my opinion, is construction adhesive. Many brands have strongly word warnings for people with respiratory problems. Not to pick on one product, but here is an MSDS for liquid nails subfloor adhesive. If a lot of subfloor adhesive has been used, you might be focusing on the wrong item.

    Just a few idea for you...

  7. GBA Editor
    Martin Holladay | | #7

    Q. "Instead of reinstalling the windows with different sealant, would it be a good idea to change the furnace from a exhaust ventilation system to a supply ventilation system?"

    A. While it is true that a supply-only ventilation system will slightly pressurize a house with respect to the outdoors, and that an exhaust-only ventilation system will slightly depressurize a house, the airflow rates required for ventilation are quite low -- usually in the range of 50 cfm to 80 cfm -- and these air flow rates are easily overwhelmed by the stack effect and wind. So installing a supply-only ventilation system is no guarantee that you won't have continuing infiltration through cracks around your windows.

  8. VapourOpen | | #8

    What about an HRV instead of supply ventilation? would this produce the same effect as supply only?
    I spoke to my HVAC guy, and he said that supply ventilation can crack the heat exchanger prematurly in cold climates. I wouldn't have thought about that.

    it is interesting what you said about the tapes. I was using 3m 3015 Air/vapour barrier tape in the windows instead of tuck tape in most areas (that is what i could get my hands on). Do tapes off gas as well?

  9. GBA Editor
    Martin Holladay | | #9

    Your HVAC contractor is wrong; supply ventilation systems will not crack a furnace's heat exchanger in a cold climate. To learn more about this issue, see Designing a Good Ventilation System.

    In that article, I wrote, "Assuming a high outdoor air fraction (15%) and a low outdoor temperature (-30°F), a furnace equipped with a supply-only ventilation system will experience mixed return-air temperatures no colder than 55°F, as long as the thermostat is set to 70°F."

  10. VapourOpen | | #10

    Would an HRV be able to counter the stack effect (obviously harder to positive pressurize basement windows opposed to ground floor ones).
    Really what i am asking, is will an HRV be a better choice for what i am going for?

  11. GBA Editor
    Martin Holladay | | #11

    Q. "Would an HRV be able to counter the stack effect?"

    A. No. To reduce the stack effect, you need to perform air sealing work, starting in your attic and your basement. For more information, see these articles:

    Air Sealing an Attic

    Air Sealing a Basement

    Q. "Will an HRV be a better choice for what I am going for?"

    A. I'm not sure what you are going for. To learn about different options for providing mechanical ventilation, see Designing a Good Ventilation System.

  12. VapourOpen | | #12

    Those were helpful links, especially designing a good ventellation system.
    I have a question about a multi-point HRV (fully ducted return) with Partial supply connection to air handler (at least that is the plan).

    First off, I wanted to ask about placement of those new returns for the HRV. My existing HVAC ducts have returns in two common areas at different ends of the main floor and two in the basement basement 2x2=4 returns total. When installing new returns, should i be using only one return for the basement and one for the main floor? Is more than one per floor unnecessary? I was thinking of placeing new returns near the same location as the ones for heating/cooling.

    About duct sizing question
    The size of the system should be ~65-70cfm. Since the airflow is so small (split between 2 returns) can this be ducted without a trunk (just 6"rigid metal or smaller)?
    The system would have very few elbows, one return duct would have to be about 15 feet, and the other return duct about 30 feet.

    One more side question. I am going to reset my new flanged windows in the opening and replaceing the sealant. I was wondering due to trying to reduce chemicals for this install (nice article this week btw about chemical sensitivity). WHen the windows are shimmed in place, is it possible to use backer rod to air seal the windows in place as opposed to canned spray foam? or does the backer rod need some sealant in front of it. It is only for air sealing after all

  13. GBA Editor
    Martin Holladay | | #13

    Exhaust air for an HRV is usually pulled from your smelliest or most humid rooms -- usually your bathrooms or laundry room, and sometimes your kitchen (but never from a range hood).

    For more information on ducting your HRV, you should consult the installation instructions that came with your HRV, or you should read this article: Installing a Heat-Recovery Ventilator.

  14. VapourOpen | | #14

    What about the final question about using backer rod instead of spray foam for air sealing around the window?

  15. GBA Editor
    Martin Holladay | | #15

    Backer rod is not intended to create an air seal; it just provides a material that you can install caulk against.

    If you want to create a better air seal than can be achieved with spray foam, use one of the European tapes sold by Small Planet Workshop or 475 in Brooklyn.

  16. wjrobinson | | #16

    I am logic driven Cory. VOCs bother you. Get rid of the VOCs. Simple compared to the rest of this thread.

  17. Deleted | | #17


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