Replies

1. GBA Editor
   Martin Holladay | Oct 08, 2015 04:27am | #1

   Deb,
   You didn't tell us your location or climate zone. In this case, location matters.

   If you live somewhere that gets snow during the winter, the situation you describe is a classic problem leading to ice dams. However, if you live in Florida, ice dams are unlikely.

   Probably, the house no longer looks like it did when the photo was taken. I'm guessing that new roof sheathing and roofing have already been installed. Is that right?

   If so, it's already too late for the best solution. (The best solution would have been to install a substantial layer of rigid foam insulation above the roof sheathing, followed by a second layer of roof sheathing and new roofing.)

   The best of the remaining approaches -- all of which are bad choices -- would be to insulate the perimeter of the attic with closed-cell spray polyurethane foam, installed under ventilation baffles. This approach might work in Florida or southern California. In Maine or Minnesota, however, the homeowners can anticipate ice dams.

2. 
   proo | Oct 08, 2015 09:17am | #2

   Thanks for the reply. You are correct, it is too late as the new roof is already installed, and we are in a northern region that gets about 50in of snow per year on average. Is there a way to check for leaks due to ice damming before it causes damage to insulation/sheathing? We have some ice/water shielding, but only 3'.

   Can you comment on the proposal of applying closed cell spray foam on the entire attic floor to form a vapor barrier and eliminate the need for intake ventilation? I don't prefer this as it is messy to "undo", expensive, and permanently covers up access to wiring and ceiling fixtures.

   Are ventilation baffles recommended on every rafter around the perimeter or only periodically spaced?

3. GBA Editor
   Martin Holladay | Oct 08, 2015 09:35am | #3

   Deb,
   I'm not sure whether you are the contractor or the homeowner. In either case, this isn't the only home with this problem -- not by a long shot -- so you (or the homeowner) will probably just have to live with the problem until the next time someone wants to install new roofing and get the details right.

   The likely problems include excess heat loss (which increases energy bills) and ice buildup. If you have Ice & Water Shield that extends at least 3 feet above the imaginary line formed by the intersection of the exterior wall plane and the roof, that would help a little. Not all instances of ice build up result in leaks.

   Q. "Can you comment on the proposal of applying closed cell spray foam on the entire attic floor to form a vapor barrier and eliminate the need for intake ventilation?"

   A. I think you misunderstand code requirements for attic ventilation. All attics with insulation on the attic floor are required by code to be vented. If you want to create an unvented attic, you have to install insulation along the roof slope. That's possible, of course; however, it won't solve the ice damming problem unless all of the required insulation (ideally, rigid foam) is installed above your roof sheathing -- a solution that would require the removal of the recently installed roofing.

4. 
   proo | Oct 08, 2015 10:55am | #4

   I'm just a homeowner trying to reconcile the various advice from experts, roofers, and insulation salespeople. The suggestion came from a spray-foam insulation company.

   Also, the tone of your blog article on attic ventilation suggested that although it is required by code, properly sealing the attic from internal air/moisture produces a much greater benefit than ventilation. I know you were not saying that ventilation is unnecessary, but given that we have a choice between insufficient intake (via baffles) and insufficient insulation around the perimeter, I'm just weighing the trade-off.

   I think you answered that putting the baffles in and doing as much as we can to seal the perimeter with spray-foam was the best (least bad) option at this point. I was just concerned about the potential problem of condensation in the wall/ceiling around the perimeter if it drops below dew point.

   Thank you

5. GBA Editor
   Martin Holladay | Oct 08, 2015 11:06am | #5

   Deb,
   You are quite right that it is always a good idea to seal air leaks at the ceiling plane. I certainly urge you do to that if you haven't done that already. However, it isn't necessary to install spray polyurethane foam over 100% of your attic floor -- all you have to do is address the areas that are known to leak (including plumbing penetrations, electrical boxes, and the cracks between partition top plates and partition drywall).

   For more information on this issue, see Air Sealing an Attic.

6. 
   proo | Oct 08, 2015 03:24pm | #6

   Do you recommend using Touch N Foam DIY products for plugging and sealing these soffit gaps all the way around the attic perimeter, or is professional worthwhile/necessary? Are the polystyrene baffles from Home Depot or Lowes sufficient or are there better ones?

7. GBA Editor
   Martin Holladay | Oct 08, 2015 03:47pm | #7

   Deb,
   I have no knowledge of your level of skill or experience, so I can't judge whether you can do an adequate job of air sealing your attic, or whether you need to hire a contractor. If you have lots of spray foam work to do, a two-component spray foam kit (something that comes with large containers of chemicals) would make more sense than the small cans of foam from a hardware store.

   There are better brands of ventilation baffle than the flimsy ones made of polystyrene. One brand that has a good reputation is SmartBaffle. Read more about ventilation baffles in this article: How to Build an Insulated Cathedral Ceiling.

   Another option is to make your own baffles. For more information on this approach, see Site-Built Ventilation Baffles for Roofs.