How best to Insulate an old Craftsman style house.
I recently purchased a craftsman style home that was built in 1918. All interior walls are covered with 3/4” shiplap throughout house. There is no insulation in the walls and it has wood siding attached to the exterior of the studs. The siding has been covered with 1” rigid foam board which is covered with vinyl siding. Original siding is deteriorating and the vinyl is an eyesore. Was planning to remove siding And sheathe the exterior walls with Zip plywood and Zip tape to act as an air barrier. I was hoping to insulate the exterior walls While they were exposed before sheathing the exterior. Not sure of the best product to use for insulating and if to do it right, do I need to remove shiplap on interior side of studs and insulate from the inside.
any advice is much appreciated and thank you very much for your time.
Faydlee Baker
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Replies
Hi Faydlee there are a lot of factors to consider, one concern for you with the Zip or any foam based exterior insulation will be the lack of a vapor barrier on the interior side of your walls. A vapor barrier on the interior stops moisture from migrating into the walls from inside, generated by showers, baths, cooking, etc... The problem with a foam exterior insulation in this situation is that it will not let moisture dry to the exterior. I would suggest you take a look at Gutex (Wood Fiber based) or Comfortboard (Rigid Mineral Wool), both of these exterior insulation are vapor open. Another option to consider would be doing a Larsen truss system, there was just a great article published here by Andy Engel called the Benefit of Larsen Trusses. Basically this system uses vertical boards attached to the existing structure, creating a thicker wall and more space for insulation. One benefit of this system for you would be that you could fill both your existing walls and the space in the trusses with cellulose, which would also allow vapor to dry out of the walls both to the exterior and interior. Additionally this would allow you to put an air barrier in the middle of your wall (the existing exterior of your wall) where it would be safe from penetrations if you did future interior or exterior work.
Another very big factor to consider is that you will be taking an old house that probably has lots of air leakage, which allowed it to dry out for the last 100 years, and now making it very air tight. This is a big change for the house and if not done properly can lead to mold and moisture issues. That said its is also an excellent opportunity to take what I assume is a charming old craftsman and give it another 100 years of life!
Almost forgot what climate zone are you in?
Derek
Thank you very much for your time and thoughts.
Climate zone I believe is 3 or 3W/H. Basically 40 miles north of Little Rock, AR.
Was planning to cover interior shiplap siding with Sheetrock and a vapor retardant paint. Would this suffice as a vapor barrier on interior side of wall? Also, All the insulators I have met with, suggest that I go with open cell foam for the floor in my crawl space. I really don’t want to cover all that beautiful old growth beams and joist with foam.
Thank you,
Faydlee Baker
Faydlee,
In your climate, you can use any fluffy insulation (cellulose, fiberglass, rockwool, etc.) in the walls, with taped ZIP sheathing as the air and water barrier. Making the walls as airtight as possible is even more important than their insulation value. Pay attention to air sealing details. Bulk water management is the most important, and you will have to pay attention to flashing and other water management details while residing. The insulated and sealed walls will have less tolerance for water leakage than they did in original condition.
Interior gypsum with vapor retardant paint will be fine for the interior surface and easy to install. Both the ZIP and the vapor retardant paint have low, but not zero permeability. This gives the wall the ability to dry to both sides, albeit slowly. That is a decent wall system in your climate and relatively easy to build. If you want a higher R-value, adding an inch or two of EPS foam or wood fiberboard (ie. Gutex) would be a good choice.
user,
You might find this BSC article relevant:
https://www.buildingscience.com/documents/building-science-insights-newsletters/bsi-091-flow-through-assemblies