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Community and Q&A

Attic insulation retrofit

New2Alberta | Posted in General Questions on

We live in a 30 year old split level house in North-central Alberta. The house faces south and gets a lot of sun in the front (1 story), but a lot of shade in the back (2 story) It has brick, aluminum siding and stucco for exterior surfaces and an asphalt shingle and tar paper roof. There is a full basement that is partially finished/insulated.

Attic #1 has fiberglass batts, with a south facing gable vent and we added a rolled ridge vent when re-shingling (asphalt and tar paper). It also meets with the south wall of the 2nd story.

Attic #2 is over the unheated attached garage with batts. It has a gable vent on the west side and we added a ridge vent. This attic is also attached to an uninsulated porch overhang with vented soffit at the bottom of a valley between attic #1 and attic #2. The garage is not well sealed and has an uninsulated wood garage door, a 2nd crudely insulated and sealed off wood garage door and wood entrance door and a steel door to the house.

Attic #3 is only over the second story and has east and west gable vents, and added roof vents near the peak with batts and blown-in cellulose over it but not to the edges as there were no baffles installed. It also contains the furnace/water heater chimney, 2 bathroom exhaust fans not vented through the rood, a heat lamp, a plumbing stack and 6 electrical boxes from fixtures as well as a wired in smoke detector that is not functional.

The cantilever is a north facing stucco wall and has a plywood bottom that is not sealed around the wood bottom and the floor is very cold in the winter.

We have plans to have an insulation contractor:

Add cellulose to R-40 and baffles to the kitchen attic
Up the cellulose to R-40 in the 2nd story
Add cellulose into the drywalled wall cavity that is within the garage attic against the east side of the 2nd story.
Spray foam the floor of the cantilever and seal the plywood soffit.

My question is – should I be doing anything prior to any of the insulation going in? Sealing around windows, etc. (I plan to replace trim anyway). What kind of vapour barrier do I need? Can the floor just be sealed at cracks and gaps? The upper attic has vapour boxes over the electrical boxes, and a crude unsealed osb box built over an existing heat lamp that we plan to remove but I’m not sure how best to seal the hole if we do remove it. There is also cellulose right up against the furnace/water heater chimney (not code, nor is it recommended by the manufacturer). I am not sure if there is an existing poly vapour barrier under the batts. From what my insulation guy said it is against code to have spray foam (and foam board exposed in an attic here and covering it with drywall is obviously impractical.

The manufacturer website for the cellulose used says “Weathershieldâ„¢’s high density dramatically reduces air leakage, controlling air and moisture infiltration.” but I’m assuming you will disagree.

We replaced the shingles last year so we won’t be adding insulation, etc to the top of the roof.

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  1. GBA Editor
    Martin Holladay | | #1

    Before any insulation is installed in your home, air sealing work should be completed, especially on the floors of your attics.

    In some areas of North America, insulation contractors understand the need for air sealing and offer this service. In other areas, insulation contractors are totally ignorant and just go up to an attic and blow insulation on the floor with a hose.

    Ask your insulation contractor a few questions about air sealing. If you are unsatisfied with the answers you receive, you should hire a home-performance contractor to do the air sealing work before any insulation is added to your home.

  2. New2Alberta | | #2

    What do you think about sealing without a poly vapour barrier? Do I need to paint the ceilings with a vapour barrier paint? I could easily complete that in the 2nd story, but the ceiling is orange peel texture in the remodeled kitchen so I don't think that's practical. It sounds like it's not code to use exposed spray foam, or rigid foam boards in an attic here due to fire regulations.

    If I can't get someone to air seal properly am I better off just not insulating?

  3. GBA Editor
    Martin Holladay | | #3

    The need for interior vapor retarders has been greatly exaggerated. For more information, see:

    Vapor Retarders and Vapor Barriers

    Forget Vapor Diffusion — Stop the Air Leaks!

    You should do your best to locate a home performance contractor (someone who owns a blower door) before you invest a penny in insulation.

  4. New2Alberta | | #4

    Thanks Martin, I'll have a look at those links. My insulation was supposed to be put in at the end of this week, but I could have him start with the cantilever floor first instead maybe. It extends the entire width of the house and is about 2 feet deep. Anything I need to prep that for? He was going to remove the plywood bottom and fill with spray foam and replace the wood. It's a stucco exterior and it looks like we have batt insulation in those walls. The spray foam should effectively seal and insulate right?

  5. GBA Editor
    Martin Holladay | | #5

    Q. "The spray foam should effectively seal and insulate, right?"

    A. Right -- as long as the contractor knows what he or she is doing.

  6. New2Alberta | | #6

    I have been reading Bruce Harley (Insulate and Weatherize and Cut Your Energy Bills Now) and he shows the same cantilever with a plywood bottom in both books and only mentions to seal them around the edges. From my previous post obviously I planned to have spray foam applied to the underside of the floor and then reattach a plywood soffit. Should I take the opportunity to add insulation, or just caulk/foam the gap that is currently there? It's costing quite a bit to do the spray foam since it spans the width of the house. Seems odd that adding insulation wasn't mentioned (or maybe just because I'm reading the air sealing sections?).

  7. GBA Editor
    Martin Holladay | | #7

    Spray foam is a type of insulation. Closed-cell spray foam has an R-value of about R-6.5 per inch, while open-cell foam has an R-value of about R-3.7 per inch. If you are aiming for an R-value of R-30 -- a good target for a floor in your climate zone -- you want to install at least 5 inches of closed-cell spray foam or 8 inches of open-cell spray foam.

  8. New2Alberta | | #8

    Hi Martin,

    I know spray foam is insulation, what I meant was that in Bruce Harley's books he doesn't mention insulating a cantilever from the outside, just sealing solid plywood soffit edges with silicone caulk or applying plywood under vented soffit to air seal. It seems like a pretty easy way to add insulation and I was surprised it wasn't suggested. I assume there may be batt insulation when we take off the plywood but obviously foam offers a greater R value and seals at the same time. It would just be much more cost effective to seal the gap with caulk.

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