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Community and Q&A

Practical Remodel Advice

tdh2106 | Posted in General Questions on

I’ve been reading up on building science articles and have even hired a building science engineer, but have been frustrated by the lack of practical advice for retrofits. I understand that the ideal solution is to take my house to studs to insulate cavities and air seal, and rewrap the house with WRB, exterior insulation and rain screen. But what about cost-effective solutions for a house that is already performing? 

Like many people, I live in a post-war home with cedar clapboard, tar paper and no insulation. The clapboard is in excellent condition, and let’s just assume that the tar paper and sheathing is as well. The home doesn’t have mold/fungi problems in large part because it is uninsulated, but the trade off is energy inefficiency. If it matters, we’re in Seattle, a mild maritime climate with lots of rain, and are converting to heat pump and HRV.

In this context, if I wanted to improve the performance and longevity of my home, what would this community recommend? I think my options are:
(1) Just go for it — Take everything down and rebuild to best practices.
(2) Take the interior to studs — Strip the interior and build back up with something like air sealing, stud cavities with rockwool or similar insulation that can get wet and dry out, and perhaps more air sealing on the drywall (and if building code requires it, vapor retarding primer or CertainTeed membrane). This would leave siding and tar paper in place.
(3) Take exterior to sheathing — Strip the exterior and build back up  with something like vaproshield, rockwool comfort board, rain screen and siding. This would leave interior cavities uninsulated.

It’d be great to get a general answer to this, as I think there are a lot of people in the same boat. But, for me, I’d also be grateful for some more tailored advice. We’re already committed to do #2 as part of a largely interior remodel (so we will do air sealing, rockwool, etc.), but we are also committed to re-side two sides of the house for curb appeal. My more tailored question is whether the exterior upgrades are sufficiently important that it’s worth also pursuing #3 everywhere (WRB, continuous insulation, rain screen siding) or leave the current system in place on two sides (tar paper, cedar clapboard). If the latter, I’m curious if combining the old exterior system (tar paper and cedar clapboard) with the new interior system (cavities insulated with rockwool) could lead to mold/fungi issues due to the cavity having less opportunity to breathe.

Any thoughts would be much appreciated. Thank you!

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  1. freyr_design | | #1

    Generally people in your boat would blow in cellulose. Though, this often results in realizing your siding is not as waterproof as you assumed…

    I think you would probably be just fine with only a rain screen on exterior when you do it, though continuous isn’t that much more work.

    Lastly, breathe is a bit of a curse word here… you should ask whether you really trust your exterior waterproofing, because if you don’t then this could certainly lead to more mold and rot issues due to limited energy flow drying the assembly. If you are worried about interior vapor condensing, this is easily remedied with a variable perm membrane on interior. Also tar paper is vapor permeable at something like 30 perms, just not airtight.

    I think your biggest challenge is going to be getting a good air barrier.

  2. BSBot | | #2

    Improving the energy efficiency and longevity of a post-war home while balancing cost-effectiveness and preservation can be challenging. Based on your situation in Seattle's mild maritime climate, and considering you're committed to interior remodeling and partial exterior siding replacement, here's how you can approach this:

    Integrated Approach for Your Home
    Since you're already planning interior work, including air sealing and adding insulation, and committed to re-siding two sides of the house, you have a unique opportunity to enhance your home's performance significantly without fully stripping it down.

    Tailored Advice for Combining Systems
    Interior Upgrades (Already Committed):

    Air Sealing: Essential for reducing energy loss and preventing moisture intrusion. Focus on sealing gaps, cracks, and penetrations in the building envelope.
    Rockwool Insulation: Installing Rockwool in the stud cavities is a great choice due to its moisture tolerance, thermal performance, and fire resistance. Since Rockwool allows for moisture to pass through, it’s less likely to contribute to mold/fungi issues when paired with proper air sealing.
    Partial Exterior Upgrades (Considering Two Sides):

    Exterior WRB, Continuous Insulation, Rain Screen: Since you're re-siding two sides, implementing a WRB (like VaproShield), adding Rockwool comfort board for continuous exterior insulation, and installing a rain screen system on these sides would significantly improve thermal performance and moisture management. This is especially valuable in Seattle's climate, where managing rainwater and allowing wall assemblies to dry are critical.
    Combining Old and New Systems:

    Potential for Mold/Fungi with Mixed Systems: When you insulate the cavities from the inside and leave the existing tar paper and clapboard on two sides, there's a potential for changing how moisture moves through those walls. However, if air sealing is done effectively and the Rockwool allows for moisture permeability, the risk can be managed. The key is ensuring that the wall assembly can dry to the outside or inside, preventing moisture accumulation.
    Proceed with Interior Upgrades: Since you're already committed, ensure thorough air sealing and consider adding a smart vapor retarder if local codes require vapor control. This will help manage moisture while allowing the wall to dry.

    Implement Exterior Upgrades on Two Sides: For the sides you're re-siding, fully embrace the WRB, continuous insulation, and rain screen system. This approach significantly enhances wall performance without requiring the entire home to be stripped.

    Assess and Decide for Remaining Sides: For the sides not being re-sided immediately, evaluate the condition of the tar paper and clapboard. If they're in good shape, you might opt to leave them as is for now, focusing on interior improvements. However, plan for future exterior upgrades to wrap the house consistently for energy efficiency and moisture management.

    Monitor Moisture: After completing the upgrades, especially where new meets old, monitor humidity levels and look for signs of moisture accumulation or mold. Consider consulting with your building science engineer to evaluate the retrofit's impact on moisture dynamics.

    Consult with Professionals: Given the complexities of mixing new and old systems, consulting with professionals (as you've done with the building science engineer) for specific recommendations tailored to your home's condition and local climate is wise.

    By carefully balancing the improvements with an understanding of moisture management and thermal performance, you can enhance your home's efficiency and comfort without compromising its integrity. This phased approach allows you to address immediate concerns while planning for long-term upgrades.

  3. gusfhb | | #3

    Love cedar and it lasts a long time, but not forever. I think I would go outside unless the interior was a wreck.
    My MCM house had a iffy interior and redwood siding, so we went from the inside. We were able to pretty much triple the insulation on average, mostly roof and windows.
    If I had been forced to lose the siding, I would have fought to repurpose it, so perhaps that is a thought for you to get past tearing off beautiful wood

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