Replies

1. 
   BrianPontolilo | Dec 29, 2018 07:23pm | #1

   Andrew,

   First of all, I'd see if you can find an insulation installer to take this project on. It may be that the two you spoke to are busy enough with new construction and easier retrofits that they are blowing you off. I've heard that tale a lot over the years (or they quote a super high price).

   Here are a few of questions that will help you get the answers you are looking for:

   Where is your house? This will determine if the R-values you are proposing are sufficient for an unvented roof.

   Do you intend to keep the cellulose insulation tight to the roof? Since you have not included venting between the sheathing and the rigid foam at the eaves, it seems that you are planning on an unvented attic, which means that the cellulose is going to continue up the roof plane. In this case, you'll want to close up the gable vents and insulated the gable walls too. Of course to do this right, you need the appropriate R-values, which brings us back to the first question.

   Also, this article may be helpful:
   https://www.finehomebuilding.com/2015/03/04/insulating-a-low-slope-shed-roof

1. 
   user-1110970367 | Dec 29, 2018 09:31pm | #2

   Thanks for the reply. I will look over the link you sent me. I am in Norfolk, VA, Zone 4. Zone 3 is about 30 minutes south of me.

   Also, the two insulation companies I spoke with were good with air sealing the deck of the attic, and putting in blown in cellulose. However, neither really had an idea for the eves. From my point of view, it may take too much time to be profitable.

   I would have both the rigid insulation and the cellulose(loose) touching the attic roof. There are two large gables vents on the south and north sides of the attic. The east and west side, which is low slope, have no soffit vents.

   My concern is that most drawing I have seen show an air gap between the attic roof and any insulation. You are correct I will not have an air gap.

   Does it make sense to have an air gap if there is no soffit vent?

   Thanks
   Andrew

2. GBA Editor
   Martin Holladay | Dec 30, 2018 05:34am | #3

   Andrew,
   For an overview of your options, see this article: "Insulating Low-Slope Residential Roofs."

   Using cellulose only works if you can create a vented assembly, and with a low-slope roof, a vented assembly needs a high attic, with room for at least 6 inches of air above the top of the cellulose. If you don't have that much room, you need to take an unvented approach.

   In your case, the best approach will probably involve new roofing. If you can install several inches of rigid foam above your roof sheathing, followed by a cover board and new roofing, that would be ideal.

1. 
   user-1110970367 | Dec 30, 2018 06:36am | #4

   Got it thanks! I guess there are no short cuts when you want to do it the right way.

   Thanks
   Andrew