Best retrofit wall for eastern Washington
I live in southeastern WA state (5B). Summers are hot/dry, winters can get fairly cold and come with snow/rain. I’m looking at a house that has some mold issues, mostly from a poorly installed roof. It needs new roof, sheetrock, and siding (and I’m assuming sheathing all around). I would also assume it has 2×4 walls, and I would probably put in all new vinyl windows. So basically a total retrofit of the exterior.
My goals for this house are:
1. Insulation up to code (R-19) at minimum. This means that I need something in addition to the R-13 that will fit in the wall cavities, which has lead me to start looking at foamboards on the exterior, which lead me to the confusing world of vapor barriers.
2. Hold this property for at least 5 years and build it so the tenants or next owners won’t ever have an issue.
3. Do the renovations on a budget. Total wall area is about 1600 sq ft. My plan was to put R-13 in the wall cavities, and one layer of 1″ R-max R-6 foamboard on the exterior of the sheathing, getting me to the required R-19. This would cost me roughly $2000.
So after getting all kinds of conflicting information on the internet from seemingly legitimate sources, my head is swirling with confusion.
Do I need a house-wrap, and does it need to be a vapor barrier?
Do I need a vapor barrier between the sheetrock and the insulation/framing?
If it gets down to 10 deg F for a few weeks, is the R-6 enough to prevent condensation on the sheathing?
The foundation is not too far above ground, how to I keep pests and wet air from coming up behind the foamboard or getting behind the foamboard at the top?
I have done a lot of research on this topic, but still have no clue, any help is greatly appreciated!
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Replies
Where to start? If you want to make the house more energy efficient and eliminate the mold, you need to do as much air sealing as possible. Here is an article on that topic://m.etiketa4.com/blogs/dept/musings/getting-biggest-bang-your-air-sealing-buck
You can achieve your insulation goals for the walls by combining exterior insulation (1.5 inches of EPS) with air permeable insulation installed between the studs. Here is an article on that topic://m.etiketa4.com/articles/dept/musings/combining-exterior-rigid-foam-fluffy-insulation
I would not replace the windows unless absolutely necessary. They may be fine as-is (with air sealing) or with the addition of storm windows. The payback time on new windows is typically very long.
Where is your HVAC system located? What type? Ideally, it and any supply and return lines should be inside the home's conditioned space.
If you make the home tighter, which you should, you will need to consider ventilation. Here is an article on that topic://m.etiketa4.com/blogs/dept/musings/designing-good-ventilation-system
Thanks for your responses!
-I do plan on completely re-insulating the attic, at which time I will seal up any leaks. The article you posted on combining the two types of insulation, along with one that it linked to on the thickness needed to keep the sheathing dry, was perfect. It suggests R-5 foamboard in my zone, so I will likely go with R-6 or R-7.7
-I will most likely replace the windows, should only cost me $2500 for the whole house, and will make a difference on the rental/resale value in my opinion. If some look great when I go to replace the sheathing, I will consider re-paining and re-using them.
-Unfortunately there is no HVAC system. The home currently has baseboard heating and a giant squirrel cage fan rigged to a window. The crawl space is very small. I will put in a heat pump with the ducting well insulated in the attic.
-I will also consider a ventilation system, though I have no experience there. I will do some research. Thanks again!
NA,
Q. "Do I need a housewrap, and does it need to be a vapor barrier?"
A. Every wall is required by code to include a water-resistive barrier (WRB). Housewrap is probably the most common material used as a WRB, but there are other options, as explained in this article:All About Water-Resistive Barriers. The vast majority of WRBs are vapor-permeable. In almost all types of wall assemblies, you don't want to choose a WRB that is a vapor barrier unless that material has a high R-value (for example, some type of rigid foam).
Q. "Do I need a vapor barrier between the sheetrock and the insulation/framing?"
A. No. According to most building codes, cold-climate builders only need a vapor retarder, not a vapor barrier, at this location. Vapor-retarder paint will work. For more information on this topic, see these two articles:
Do I Need a Vapor Retarder?
Vapor Retarders and Vapor Barriers
Q. "If it gets down to 10 deg F for a few weeks, is the R-6 enough to prevent condensation on the sheathing?"
A. Yes. For more information on this topic, seeCalculating the Minimum Thickness of Rigid Foam Sheathing.
Q. "The foundation is not too far above ground. How to I keep pests and wet air from coming up behind the foamboard or getting behind the foamboard at the top?"
答:你需要一个最低年级的8英寸the lowest wooden components of your building. If this measurement is less than 8 inches, you need to lower the grade. You keep pests from coming up behind the rigid foam at the base of the wall with metal flashing and airtight installation techniques. You keep pests from getting behind the rigid foam at the top of the wall with a soffit and a roof.