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Community and Q&A

How to Insulate a Three-Season Cottage

CanadianCottager | Posted in General Questions on

I’ve read many GBA articles and blogs pertaining to interior/exterior wall insulation guidelines pertaining to rigid board insulation as well as other (fiberglass etc.) insulating materials and the focus being on reducing or eliminating moisture accumulation throughout the entire wall structure.

Unfortunately the more I read, the more I’m confused. Perhaps someone can provide some guidance and clarity to me regarding my insulation needs.

I have a two story 2400 sq. ft. 3 season cottage located on an island in Northern Ontario or Zone 6. Because we are on an island access is limited to approx. 6 months of the year between May 1st (just after ice break-up) and October 31st (just before the lake freezes over).  We stay at the cottage until the temperatures reach 0 degrees Celsius or 32 degrees Fahrenheit.

We use a woodstove to heat the cottage for May, June, September & October.
6 months of the year the cottage is vacant from Nov – Apr.

We will be installing new siding in the spring of 2021 and wanted to add some insulation as currently we have none. The current siding is wood which will be taken off and most likely replaced with an engineered wood siding product.

Many thanks in advance for any suggestions and advice.

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  1. Expert Member
    NICK KEENAN | | #1

    I'd say the "how" is the same as insulating any other building, the key question is "how much."

    Two ways of looking at it: Do you have historical weather information available for someplace nearby? If your winter was just May, June, September and October, how many heating degree-days per year would you have? What level of insulation do people who live in climates with comparable heating seasons have? That may be tough because mostly those are going to be cooling-dominated climates and people have insulation for cooling too.

    Second, how much do you spend on wood per year? How much insulation would you need to cut that by a third, in half? How much money would that save? How long of a payback do you expect? How much insulation can you get for that money?

    1. CanadianCottager | | #3

      DCC my total heating days would be approx. 100 days for the 4 months mentioned above.
      My wood is essentially free as we a large supply of trees on the island. I'm not really too concerned about the payback, just want a guideline of how best to insulate and how much and what kind of insulation to use.

  2. Expert Member
    Michael Maines | | #2

    Casey, one suggestion is to simply follow the building code for conditioned homes in your area, even if you aren't required to. Insulation is not particularly expensive, this is the only chance you'll have to insulate it for many years, and insulation will make the building more comfortable in all seasons.

    If you want or need to skimp on insulation, you could figure out the heating degree days for the time period you are using the cottage. By skipping the coldest part of winter, I bet your heating degree days are something like an IECC climate zone 2 or 3, which requires R-13 to R-20 in walls and R-38 to R-49 in ceilings.

    As for type of insulation, when replacing siding it's a good time to blow insulation into the wall cavities. I prefer cellulose but blown fiberglass or mineral wool are other options. You could DIY it but it's probably best left to a pro.

    Alternatively, or additionally, you could install continuous exterior insulation, in the form of foam, rigid mineral wool or rigid wood fiber. Each has pros and cons but any can work with proper detailing.

  3. CanadianCottager | | #4

    Thanks Michael for your suggestions, very much appreciated. I don't necessarily need to skimp on insulation, (mind you the cottage will always be vacant between Nov - Apr) however for the 4 cold months that we will be there, would like the cottage to be warm and cozy versus cold and drafty. Since we're on an island blown insulation provides a bit of a challenge logistically and this would most likely be the most expensive option. Regarding the other options that you provided, what would you recommend insulation between the wall cavities or exterior insulation.

    1. Expert Member
      NICK KEENAN | | #5

      For the most part the methodology around insulation revolves around economics and not comfort, so you probably aren't going to get hard factual answers.

      I would think a thorough air-sealing -- which is separate from insulation -- would be the first step in making things cozier. Depending on your type of wood stove this might cause problems, and you might have to add some way of providing replacement air for the stove or even buy a new stove. If your stove produces any smoke a tight house is going to be unpleasant.

      Conventional heating systems will typically have an outlet in every room and multiple ones in large rooms. The reason is that heat doesn't travel particularly well around the inside of a house. A point source like a wood stove is going to have trouble keeping a building comfortable all over. The time-honored solution was to have a stove in every room but that has its own drawbacks. There are forums devoted just to woodburning, you may want to ask there. People make up elaborate ways to distribute heat around the house, such as the stove warming water which is pumped around the house into radiators.

      One of the things about wood stoves is they tend to be tough to run on low heat. You may find that with some air sealing and some way of distributing heat the stove puts out more than enough heat and you don't need much in the way of insulation.

  4. CanadianCottager | | #6

    Thanks DCC I will take into consideration all of your comments as I formulate a solution that hopefully addresses my cottage insulation challenges.

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