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Deep energy retrofit

Smc1900 | Posted in Energy Efficiency and Durability on

I’m in St. John’s, Newfoundland and Labrador, climate zone 6, about 4800 he’d, wind driven rain category is Extreme. House is 25 years old and wall structure is from inside to outside
1. 1/2″ gyproc
2. Super 6 mil poly, acoustic sealant
3. 2×[email protected]″oc studs, r20 fibreglass baths
4. T&g board something
5. Tyvek
6. Vinyl siding

Electric baseboard heat, HRV ducted to every room, r32 cellulose in a vented attic.

Without any tear up, I will upgrade the attic insulation, and at the same time do air sealing. Some of the HRV ducts run through there, and ideally I’d like to move those, but I may have to settle for just ensuring they are well insulated. These are currently the flexible insulated ducts. Any suggestions on how I may improve those ducts without moving them into soffits in the rooms below?

I’d also like to do something for the above grade walls. The vinyl siding will be reused, so I don’t need or desire a rainscreen. There is an island manufacturer of EPS, so I can get type 1 or type 2 in a slotted version 9f whatever thicknes I want. If I go this route, there will be a layer of tyvek on the t&g board. Should I also put another layer over the EPS? Should I use type 1 or type 2? I am thinking the thickness will be 2-3″, so r8 to r12.

I am also considering 2 layers of 1 1/4″ r5 Rockwood comfortboard instead of the EPS. At 2 1/2″ total thickness, I won’t need strapping. Should i put another layer of tyvek over the comfortboard? I know this won’t be easy.

My windows stay where they are so they become innies and I need to deal with that.

I am also adding a mini split heat pump.

Thanks for any suggestions.

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  1. GBA Editor
    Martin Holladay | | #1

    You wrote that your house has electric baseboard heat. So I assume the attic ducts you are talking about are HRV ducts. Is that correct?

    If so, the ventilation ducts you are talking about don't really carry much of an energy penalty if they are located in an unconditioned attic -- they aren't as problematic as heating and cooling ducts. As long as these ventilation ducts have sealed seams and adequate insulation, everything is OK.

    Q. "I can get Type 1 or Type 2 [EPS] in a slotted version [9f] in whatever thickness I want. If I go this route, there will be a layer of Tyvek on the T&G boards. Should I also put another layer over the EPS?"

    A. You need some type of water-resistive barrier (WRB). Note that the WRB needs to be integrated with the window flashing, so you have to think these details through. Either (a) you can depend on the existing Tyvek and make sure it is functioning as your WRB, or (b) you can install a second layer of Tyvek (or another brand of housewrap), or (c) you can use the rigid foam as a WRB (although I don't like that approach). For more information, see these two articles:

    "Using Rigid Foam As a Water-Resistive Barrier"

    "Where Does the Housewrap Go?"

    Q. "Should I use Type 1 or Type 2 EPS?"

    A. Type 2 EPS has a higher density and more compressive resistance than Type 1 EPS, so it's fair to say that Type 2 EPS is a better choice. For more information on this issue, see these articles:

    "Choosing Rigid Foam"

    "EPS Compressive Strength"

    "Specifying Polystyrene"

    Q "I am thinking the EPS thickness will be 2-3 inches, so R-8 to R-12."

    A. In Climate Zone 6, the minimum recommended R-value for continuous exterior rigid foam over a 2x6 wall is R-11.25, so you should go with 3 inches, not 2 inches. For more information, see "Calculating the Minimum Thickness of Rigid Foam Sheathing."

    Q. "I am also considering 2 layers of 1 1/4 inch R-5 Rockwool Comfortboard instead of the EPS. At 2 1/2 inches total thickness, I won't need strapping."

    A. Really? You want to install vinyl siding over 2.5 inches of mineral wool, without any furring strips? Before concluding that your plan makes sense, you might want to consult with the vinyl siding manufacturer. Mineral wool is squishy, and your fasteners would be very long. I'm not sure that's a good idea.

  2. Smc1900 | | #2

    thanks Martin.

    Yes, ducts in the attic are for the HRV, so I'll just make sure they are well sealed and insulated.

    On the mineral wool, my thoughts were the vinyl siding needed a flat surface, thus I couldn't easily put furring strips without having to fill in between those strips. Sounds like EPS type 2 is my best bet and supports the local economy. The windows are double glazed, low E, argon, about 6 years old, I really didn't want to have to remove and move the windows to the the same plane as the EPS, so I'll have to take a much closer look at those 2 articles before making a decision on that.

    I posted the question from my tablet and it auto corrected a few words, so I went back, fixed the auto correct, and posted. I thought it wold update the post, so there are now 4 of them. You can delete the extras if you are able. Sorry about that.

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