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Double-brick house in Toronto – how to deal with high indoor humidity after insulating?

Leif Schumacher | Posted in General Questions on


First time posting, but I have learned tons from reading many of the excellent articles and postings on this site.

Here’s our situation. We live in a double-brick one and a half story house in Toronto that was built in 1949. We have done a number of energy efficient upgrades and are now experiencing consistently high indoor humidity (60%+) which leads me to believe that we have a ventilation problem.

The upgrades we have done:
-Closed cell spray foam insulation on basement walls (R12-R24). This was done after complete exterior waterproofing and weeping tile replacement around perimeter of house. Basement is dry.
-New high efficiency furnace (95%)
-3″ closed cell spray foam on underside of roof between rafters. Spray foamed over rafters behind knee walls and at peak of ceiling. Put one inch (R5) of XPS rigid foam on top of spray foam where drywall was going on top. Roof is airtight where before there had been huge gaps – needed space heaters to keep room beside bathroom from freezing.
-No insulation added on main floor, but extensive air sealing has been done. Still a little leaky and drafty, though.
-Sealing of all ductwork that was exposed during renos.
-Home Energy inspector gave us a 75 EnerGuide rating after the latest upgrades (attic).

These upgrades have been done over the last three years. We always thought humidity was a little high in the house (no known plumbing leaks), but at least in the fall and winter it would drop into the low 40s or high 30s. Now it is consistently around 60%, and I’m getting concerned about mold. One cold night when it dropped down to around 0 degrees centigrade (32 F) we already had condensation build-up on our windows.

What we haven’t done yet is fix the ductwork going to the second floor. Two rooms up there (bathroom and kids’ bedroom) have adequate supply, but the third room (master bedroom) has hardly any air coming out. No return air on second floor. Plan is to install a new supply run to the master bedroom, relocate supply to kids room to terminate below window instead of middle of the room and install cold air return near ceiling in central hallway between the two bedrooms. This should at least circulate the air in the house better, but will probably still not take care of the humidity issue.

I also suspect that some cracked mortar between the exterior bricks contribute to more moisture entering the building envelope when it rains, so some repointing is planned and I have also considered sealing the exterior brick using a siloxane or silane based water repellent.

Now, I’ve considered an HRV, but after reading the following articles by Martin Holladay I’m not so sure:

An HRV might make my situation better, but there’s no way that I can install it properly as outlined in those articles (separate ductwork hooked up to bathroom fans). I could install better bathroom fans (currently fairly noisy 70CFM units) in our two bathrooms and run them all day to create an exhaust-only ventilation system, but I’m worried that this might not be enough to benefit the whole house. I could of course also just open a couple of windows, but then why did I install all the insulation and do all the air sealing in the first place???

Anyway, I’m a little worried and frustrated at this point, so any advice would be greatly appreciated.

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  1. GBA Editor
    Martin Holladay | | #1

    The first way to address your problem is to be sure that you have addressed all of your moisture loads.

    Is moisture entering your house through your basement floor?

    Does everyone in the house always use the bathroom exhaust fan when showering?

    Do you introduce extra moisture in your house via lots of houseplants, or fish tanks, or drying laundry indoors, or bringing green firewood indoors?

    Assuming you have addressed these issues, there is nothing wrong with upgrading your bathroom exhaust fans to Panasonic units (they are quiet) and running them as needed to lower your indoor humidity level during the winter.

  2. Leif Schumacher | | #2

    Thanks for the reply, Martin.

    Basement is finished and we put down a vapour barrier on the floor before putting in laminate, so there shouldn't be a problem there.

    We use bathroom fans excessively, and usually leave them running for at least 30 minutes after taking a shower.

    We do dry laundry indoors sometimes (about once a week) and obviously I notice a spike in humidity at that time. However, I figure that within a week it should return to normal levels, but it's still around 60%.

    No problem with upgrading the fans and leaving them running. I just wonder if that will be enough to pull in air from other rooms in the house?

    Also, do you categorically recommend against installing an HRV that is connected to the existing ductwork for the furnace?

  3. GBA Editor
    Martin Holladay | | #3

    Running your bathroom fans for more hours per day during the winter will definitely lower your indoor relative humidity. After all, whenever a volume of air leaves your house, an equal volume of outdoor air enters your house to replace it.

    The RH in your home will drop, even in rooms without a fan. Try it for a few days and see if your hygrometer can register a reduction in indoor RH; I predict you'll see a difference.

    Of course, this ventilation incurs an energy penalty (although the energy penalty is not as severe as that exacted by a dehumidifier). Don't overventilate; only ventilate for as long as you need to to control your indoor humidity.

  4. Leif Schumacher | | #4

    Thanks again, Martin. I ran both bathroom fans all night last night with the bathroom doors wide open. Humidity did actually drop around 3-4% (down to 55%). Started creeping up again this morning as daily activity started - natural I suppose. I'll keep doing this for a few days to see what happens. This would obviously be the cheapest solution, and I don't mind the energy penalty, especially right now with such cheap natural gas prices. I assume I could run these fans for many years with the energy penalty for the price of installing an HRV!

    Thanks again. I'll report back after a few days of running the fans.

  5. GBA Editor
    Martin Holladay | | #5

    One more observation: it's always possible that you have a faulty hygrometer. It may be worth buying another one to double-check your RH readings.

  6. Mika L | | #6

    #5 by Martin is something that I found to be worth checking.

  7. Leif Schumacher | | #7

    Hi there,

    Just thought I'd follow up to let you know what I have observed so far after running my bathroom fans 24/7 for a couple of weeks.

    Humidity has dropped. It actually dropped to around 52% (from 60%) within a few days. During those days we did not do much cooking and didn't hang any clothes to dry. Once we resumed those activities, humidity quickly climbed up to around 60% again within a few days.

    So, we've changed some things. For example, we only hang wet clothes in the bathroom now, with the fan running. We also leave the kitchen fan on longer after we are done cooking.

    The interesting thing is that the humidity level seems to have stabilized around the 54-55% mark over the last few days, even though it's been raining steadily outside. I thought that the humid outside air would be pulled in by the fans and would increase my indoor humidity, but that doesn't seem to be happening.

    I'll obviously monitor this closely going forward, but so far, the simple trick of running the bathroom fans seems to be working. Thank you everyone!

    And btw, I have double-checked my hygrometer with another model and it does seem to be fairly accurate.

  8. Stacy Kim | | #8

    Hi there,
    Keeping the right humidity levels in your house is actually very important. Usually it's between 40 - 50%. Depending on where you live. Because of your high humidity you probably also have squeaky floors, since the wood contracts and expands in different seasons. I had that problem in my house too, so we fixed the humidity levels and found a firm that fixes the squeaks in our hardwood floors. If you do also have that problem google them. I believe they were called silent floor.
    Cheers! Good luck.

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