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Insulating a Modular Home

mbmiller34 | Posted in General Questions on

I have a early 1980s modular that I’ve been working on fixing up. Wife says we should just burn it down and start over hah. We live in central northern Alberta with damn cold winters.

Anyhow – my main goal is to have my furnace run less, rather simple concept! The main areas I’ve been tackling is the insulation. The original insulation was R10/12 yellow batts, not too itchy but enough that I could feel it. 90% of the house now has rock wool R14 for 2×4 framing. The front room with the big windows basically was all headers and stacked 2x4s no insulation to speak of.  With that in mind, instead of poly for vapour barrier I went with 1” 1/2 silver foam board using spray foam to seal it to the existing roof, subfloor and to itself, I then taped the seams and it makes a noticeable difference as there is no longer a cold breeze blowing through my walls. I am mildly concerned about the potential for moisture getting trapped inside the wall. The research I did before I started seem to indicate that while not common, it’s perfectly acceptable method of doing things. Basically turned the master into a styrofoam box. Anything I might have missed?

Second job to tackle will be the exterior, insulation and new siding. I should mention that there is an expansion gap about 3-4” wide running around the entire middle of my house.  Apparently this was done back in the day for modular construction I guess? Craziness. Plan is to fill it with spray foam as the bugs love crawling in where it is warm.

Next is the crazy happy stapler that put all the sheathing on back in the day, kept putting in 2” staples until he found a stud and then would promptly forget where the stud was and started looking for it again. The number of floating staples is mind blowing and I don’t know how the house didn’t burn down back in the day as at least 2 electrical lines were tagged and proceeded to lightly char the surrounding wood.

What are my options for covering this to make it less hole-y? Staples holes and expansion gap? Option 1 is tyvek which is probably not the best choice, the other one that has come up is aluma flash which would do the trick.

After doing the best to ‘seal’ the sheathing (I know it would be perfect but better is great). I was debating about using 2” foam board or rock wool on the outside before putting up new siding. I like the rock wool as it can breath and expel moisture but everyone seems to use a foam board on the exterior.

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  1. Patrick_OSullivan | | #1

    Always nice to see someone wanting to improve their existing structure. Some diagrams of your assemblies could be helpful to visualize. I'm not 100% clear how you installed the foam. For instance, are you saying it's completely covering the studs now and then you drywalled over it?

    You seem to be getting at an important point... air sealing is more important than insulation.

    Since you're talking about getting into the exterior as well, take a look at this article and familiarize yourself with needing to have controls for four things: water, air, vapor, and thermal energy:

  2. mbmiller34 | | #2

    Correct, secured to the studs with 4” screws through strapping. All gaps are filled with expanding spray foam so that there is no possible airflow. To seal it to the existing floor and roof (and walls) I applied more spray foam, on the face/butt of foam so pressing upwards and downwards and a beam along the joint. Can’t completely demo the interior so there are still some existing walls that I can’t replace. Drywall is hung on the strapping.

    Hmm maybe alum flash would be a bad choice as I probably should maintain the ability to dry from the outside? Since I know this place wouldn’t come close to having proper air sealing. Heck my bathroom vents are a pipe with a in-line fan it it. I can see daylight if I look up

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