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

Insulating a 1-1/2 Story House

GBA Editor | Posted in Energy Efficiency and Durability on

I am about to begin construction on a house in central North Carolina. It is a basic rectangular gable roofed story and a half with dormers on the front. Due to the design of the house it will have the HVAC for the second floor in the attic. This obviously means I will need a sealed/conditioned attic. I do not want to use spray foam in the attic because I feel there are too many unknowns with it. I believe cellulose is the best way to go but do want to maintain an airspace in case of a roof leak that always seems to occur at some point. I also like the idea of using the exterior sheathing as an air barrier as described in a recent blog post at https://www.greenbuildingadvisor.com/blogs/dept/musings/airtight-wall-and-roof-sheathing.

My thinking was to follow the approached shown in the mentioned blog. On top of the sealed roof sheathing I would apply furring strips followed by another layer of osb/plywood. Any water that leaks past the top layer of sheathing would be caught by the second layer. In addition I think it would make it easier to vent the valley areas where the dormers and main roof meet.

My question is what potential problems have I overlooked in this design? Will I have any problems with not having an airspace between the cellulose and the first layer of the roof sheathing? Do I need to have an air barrier like drywall or thermaply over the exposed insulation in the attic rafters? Any other issues I should be aware of?

Thanks for your input.

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.

Replies

  1. GBA Editor
    Martin Holladay | | #1

    Andrew,
    Your plan will work well.

    If you can afford it, you might consider adding a layer of rigid foam on top of the lower layer of OSB roof sheathing. The foam will reduce thermal bridging through your rafters.

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |