Exterior Masonry Wall Insulation
Climate Zone 4A here! We have a triple wythe masonry wall on the top floor of our house that ended up having moisture problems. It’s exposed to the elements on the exterior. We’re having to repoint the brick in the exterior and need to completely rebuild the partitions on the interior (due to mold that was discovered and mitigated – unfortunately it seemed someone used floppy batt insulation on the wall that made contact with the wet masonry and grew mold). It is extremely important to us that the new interior partitions and treatment of the interior brick prevents any mold from occurring in the future. Our thought is that we’ll seal the interior brick with a highly permeable sealer (so the masonry can still breathe), hold any wood studs 1” off the wall, use rigid rock wool insulation and drywall over that. I know that there are plenty of other insulation methods that may be more effective but we’re trying to keep costs down. I’m so nervous for ANYTHING to make contact with the masonry (due to past mold issues) so doing any insulation up against the masonry makes me extremely nervous. I’m seeking thoughts on what product the interior sealant on the brick should be and if there are any comments/feedback on our partition re-build approach.
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Replies
If liquid water is getting through, you need to give it a path to the exterior. If the wall is merely damp, you just need a vapor barrier. I realize it can be hard to tell the difference.
What you don't want is that moisture drying to the interior, your house doesn't need the extra moisture. Basically this wall is going to be like a basement wall, where you want to keep the exterior moisture out, avoid having a cold interior surface that interior moisture can condense on, and to the extent there is drying in the interior insulation it dries to the interior.
Like a basement wall, it is best waterproofed from the exterior, but sometimes we have to play the hand we're dealt.
Addressing moisture issues in a triple wythe masonry wall, especially after experiencing mold problems, requires careful consideration of both moisture management and insulation strategies. Your approach to keeping the new interior partitions and treatments mold-free seems well-considered, focusing on allowing the masonry to breathe while minimizing direct contact between insulation materials and potentially damp surfaces. Here are some thoughts on your proposed solution:
Interior Masonry Sealer
Permeability is Key: Choosing a sealer that allows the masonry to breathe while providing some protection against moisture ingress is essential. Look for a silane-siloxane based sealer, which is highly permeable and provides excellent water repellency without sealing off the masonry completely. These sealers penetrate the surface of the brick, offering protection while allowing moisture within the wall to evaporate.
Product Selection: When selecting the sealer, ensure it's specified for use on exterior masonry surfaces and is vapor permeable. Products like Prosoco’s Sure Klean Weather Seal Siloxane PD or similar breathable masonry sealers are designed for this purpose.
Interior Partition Re-build Approach
Maintaining an Air Gap: Keeping wood studs 1” off the masonry wall is a good strategy to prevent direct contact and potential moisture transfer. This air gap can facilitate additional airflow and drying of the masonry.
Rigid Rock Wool Insulation: Using rigid rock wool insulation is a sound choice for its moisture resistance and thermal performance. Ensure that the insulation is tightly fitted between the studs to avoid thermal bridging and gaps where moisture can accumulate.
Drywall Installation: When installing drywall over the insulation, consider using paperless drywall, which is less prone to mold growth compared to traditional paper-faced drywall. Additionally, ensure that any vapor barriers or retarders used in the assembly are appropriate for your climate zone and wall construction to prevent trapping moisture within the wall.
Additional Considerations
Ventilation and Humidity Control: Beyond the wall assembly itself, maintaining good indoor air quality and managing humidity levels within the house can help prevent condensation and mold growth. Consider adding dehumidifiers or improving ventilation in areas prone to high humidity.
Exterior Repointing: Since you're repointing the exterior, ensure that the mortar used is compatible with the existing masonry in terms of permeability and strength. This will help maintain the wall's ability to manage moisture effectively.
Professional Consultation: Given the complexity of moisture management in historic or older masonry buildings, consulting with a building science professional or a structural engineer who specializes in masonry can provide tailored advice. They can help ensure that the chosen materials and strategies effectively manage moisture while preserving the integrity and aesthetic of the masonry.
Your cautious approach to rebuilding the interior partitions while prioritizing moisture management and mold prevention is commendable. By selecting appropriate materials and maintaining a clear strategy for moisture control, you can create a healthy and comfortable indoor environment that respects the building's masonry construction.