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Community and Q&A

Renovating an older home

nvman | Posted in Green Building Techniques on

We are renovating our house in North Vancouver, BC.
This area gets about 2500 mm of rain per year.
All the siding is removed and underneath, are 1×8 ship lap boards over 2×4 framing.
I removed the old building paper and covered with Typar for the winter.

I was thinking of installing inch and a half Roxul Comfortboard over top the Typar and under the rain screen but I understand that the bottom edge of the air barrier should not be sealed so that any water that gets behind it, can drain.

However, with the board sheathing, I don’t get much in the way of air sealing.
Should I remove the Typar and apply a layer of plywood over the board sheathing? I would tape all the edges of the ply. (Most likely 3/8″ spruce)

And should I overlap the top of the concrete foundation with the plywood and seal the new sheathing to the concrete with caulking?
What type of caulking is acceptable, silicone, polyurethane?

I would reapply Typar over the new sheathing.

We are also adding a short extension onto the home.
I would add 3/4 inch sheathing to match the existing 1×8 sheathing. The question is would it be ok to continue with the 3/8″ ply overtop the 3/4 inch ply so the exterior is on the same plane?

I need to fur out the original 2×4 framing to match the new 2×6 framing so I can’t make any adjustment on the interior.

All suggestions are welcomed.


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  1. Expert Member

    Aaron, I wouldn't worry about sealing the Typar at the base. If you have enough bulk water intrusion that it can run down your sheathing, you have much bigger problems than whether it can easily drain at the bottom. That said, I'd suggest not relying on the Typar as your primary air barrier. You will be furring out the existing 2"x4" walls to match the new framing. Why not include an air barrier behind the furring where it is protected from mechanical damage? Unless you are particularly worried about seismic concerns I also wouldn't sheath the existing walls. The Typar, sealed at the base or not, will shield against wind washing of your insulation. I'd situate the framing for the new addition so that 1/2" plywood sheathing matches the existing shiplap and adjust the interior furring as required.

  2. GBA Editor
    Martin Holladay | | #2

    It good that you are thinking about air sealing. There are lots of ways to seal air leaks, so there is no single answer to your question. The answer depends in part on what type of insulation you have between the studs -- is it a type of insulation that allows a lot of air movement, or a type of insulation that reduces air movement? -- and the tightness of your interior finishes (usually drywall) and electrical boxes (usually, but not always, leaky).

    Plywood sheathing with taped seams usually leaks less air than Typar over board sheathing, although it's worth pointing out that some installations of Typar are sloppy, and other installations are quite good.

    Leaving Typar exposed to the weather for the winter is likely to make it leakier than it would otherwise be.

    It's OK to seal Typar at the bottom. There is no reason to think that you have to handle liquid water behind the Typar.

    If you want to use a barrier that will achieve better airtightness than Typar, you might consider using one of the European air barriers / WRBs sold by 475 High-Performance Building Materials or Small Planet Workshop.

  3. nvman | | #3

    Thank you Malcolm and Martin for your answers.
    Malcom, if I am not to use Typar as my air barrier, what do you suggest I use?

    And does anyone have a suggestion as to what is a good caulking for sealing the Typar or any sealant for general use? I know that Typar has their own brand of compatible sealant but most places don't sell it. I have yet to find one that does so I would rather stick to something readily available.


  4. GBA Editor
    Martin Holladay | | #4

    Q. "If I am not to use Typar as my air barrier, what do you suggest I use?"

    A. I already suggested that you could use one of the European membranes. Here is a link:

    Q. "And does anyone have a suggestion as to what is a good caulking for sealing the Typar or any sealant for general use? I know that Typar has their own brand of compatible sealant but most places don't sell it."

    A. Typar tape is readily available online, if for some mysterious reason your local supplier is all out. Here are some links:

  5. nvman | | #5

    Thank you Martin.
    I thought maybe Malcom was suggesting to use something in addition to Typar because he said to use it as my 'primary' air barrier, suggesting that it would be a secondary air barrier.

    Home Depot only carries the wrap, not the tape or sealant, as most other building supply companies.
    As for ordering from an online company from the US, shipping is never free, only expensive and the same with the exchange rate.

    That is why I was hoping to find an equivalent generic product.
    I will do my own research.


  6. GBA Editor
    Martin Holladay | | #6

    You can certainly have more than one air barrier. For example, if you do your best to make your Typar layer airtight, you can also do your best to make your drywall layer airtight. Having more than one air barrier will usually improve the airtightness of your wall assembly.

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