Water and air control strategies for retrofit applications
I have an old house with no insulation aside from 1/2″ of polyiso installed to the outside of old wood sheathing and siding and covered in vinyl. Based on previous posts and research I have decided I want to add exterior foam insulation while residing. I am trying to make a plan to get the greatest “bang for the buck” and I am encountering varying advice. Here are my observations:
– building science corp. published a deep energy retrofit builders guide based on the national grid pilot program. In this guide they use house wrap, either adhered or un-adhered as an air control layer and lapped and taped exterior foam as a water control layer.
– here on GBA comments by Marc Rosenbaum indicate that house wrap is not a good air barrier and foam is not a good water barrier (airtight wall and roof sheathing article)
– the article “where does the housewrap go” suggests that the housewrap should be aligned with the windows. BSC’s guide does not align the windows (outie) with the wrap (under foam).
– other and possibly biased sources also suggest that taped foam is not a durable wrb.
1. Is there a right way to do a retrofit with exterior foam or do a number of methods work? What is the best bang for the buck?
2. For a retrofit situation, what would be used for air and water barriers if housewrap and foam (respectively) were not.
3. What would be used as a fully adhered sheathing wrap for board sheathing? Liquid applied wouldn’t work because of the gaps. Would it be something like ice and water or enV-s?
4. BSC’s guide does not recommend folding the housewrap into the RO. Instead they use a transition membrane in the RO sealed to the housewrap with caulk. What is a transition membrane? Why not fold the housewrap?
5. Would a liquid applied flashing work as a sill flash with exterior foam?
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