GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Townhouse Deep Energy Retrofit

eyremountllc | Posted in Energy Efficiency and Durability on

I recently purchased a 1970s townhouse in northern VA. The property was neglected for about 20 years, the T-111 siding had holes that various animals large and small had made over the years. Roof has several leaks judging the the interior and from the degree of wear on the outside. Other than that, the house is actually in surprisingly good condition.

I do not plan to rehab it to passivhaus or Enerphit but trying to devise an approach that is effective at significantly increasing energy efficiency and comfort while doing it at a modest cost. In addition, I want the neighbors to know that energy efficiency, comfort and better indoor air-quality are not out of reach with a modest budget.

So, here are some of my thoughts, please let me know if I am on the right track and feel free to offer suggestions.

I’ve already ordered some decent American made windows and doors, nothing spectacular like the European ones but I want them to be something that people can easily source locally.

For the roof, I plan to cut off the overhangs to provide the smoother transition between the roof and the walls (chainsaw method). Then, I would remove damaged sheathing and add more cellulose insulation into the attic space. I am thinking R-50 if there’s enough space. Replace sheathing and use a high quality solid-acrylic tape like the Siga Wigluv if the sheathing is OSB (Yes, I read Martin’s article: Backyard Tape Test).

For the walls, I plan to remove the T-111, remove damaged sheathing and insulation, replace it with roxul batts or rockfill, replace sheathing and tape the seams like the roof.

I think by doing the above I would have established my air-tight layer on the exterior. Then underlayment and shingles on roof and housewrap the house. Depending on what PHPP tells me, I would add 2-3″ of Roxul comfortboard to the exterior of the housewrap. Then put on cladding.

Anything wrong here?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    1. After you have finished taping the wall sheathing and roof sheathing, don't forget to rebuild your roof overhangs (at the rakes as well as the eaves).

    2. If your ceiling insulation is located on the attic floor, it makes no sense to locate your air barrier at the level of the roof sheathing. Your air barrier always needs to be directly adjacent to your thermal barrier. There are two possible solutions. Either (a) Insulate the sloped roof (using an unvented approach) or (b) move your air barrier to the ceiling below your attic insulation.

  2. user-626934 | | #2

    Is there other sheathing behind the T-111? I've only come across T-111 a few times so far on multi-family buildings (of roughly the same vintage), but in these cases there was nothing behind it except for the 2x4 studs and some fiberglass.

  3. eyremountllc | | #3

    Yes, I forgot to write the step about rebuilding the overhangs. I was wondering about the exterior airtight layer being on the sheathing level. What is the reason that the air barrier needs to be directly adjacent to thermal barrier? By cutting off the overhangs, my soffit vents are gone too. I assumed the attic would then become a unvented roof.

    From the parts we've removed, there are. However, that was something we were wondering too.

  4. eyremountllc | | #4

    I got it! By moving the airtight layer to the roof level instead of the ceiling level, I've created an uncontrolled condensing surface!

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |