Replies

1. GBA Editor
   Martin Holladay | Oct 27, 2015 09:23am | #1

   Nicholas,
   It's impossible to vent a hipped roof. If you want the insulation to follow the roof slope with this type of roof, you need to choose one of the unvented approaches.

   For more information on unvented insulated roof assemblies, see How to Build an Insulated Cathedral Ceiling.

2. 
   CTSNicholas | Oct 27, 2015 07:09pm | #2

   Hmm...Well.. I have a continuous ridge vent and have insulation baffles along the rafters that they fit in. I only have problems with the corners. Should I just block the corners off? Or should I leave just a tiny gap that would allow air flow and just not install insulation past that height (raised heel roof, so I may not need insulation to that height).

   There has to be a standard method because this is how all the houses o see are done. I never see the baffles but I always see a ridge vent and soffit vent on hip roofs.

3. GBA Editor
   Martin Holladay | Oct 27, 2015 07:47pm | #3

   Nicholas,
   Hipped roofs have ridge vents because most hipped roofs have vented unconditioned attics. These attics are easy to vent.

   Once you start stuffing insulation between the rafters, however, things get complicated.

   I don't doubt that some ill-informed builders have tried to install ventilation baffles in hipped roofs. But you can't do it. If you do, you risk moisture accumulation and rot -- unless you switch to spray polyurethane foam.

4. Expert Member
   MALCOLM TAYLOR | Oct 27, 2015 08:48pm | #4

   Nicholas,
   I'm confused - and maybe Martin is too: Are you insulating each bay, or just the ceiling of the attic?

5. 
   CTSNicholas | Oct 27, 2015 10:36pm | #5

   Haha, I am sorry....I am insulating the attic floor! I am just not sure how I can get the required 1 to 2" gap between roof sheathing and my insulation in these corners of the hip roof since my baffle does not work there... After your second post Martin, I realized you misunderstood and Malcolm made it apparent.

6. Expert Member
   MALCOLM TAYLOR | Oct 27, 2015 11:54pm | #6

   Nicholas,
   Don't worry about it. That small area will dry even if in contact with the roof sheathing. If you look at professionally insulated roofs they often only place baffles in every other truss bay - and this doesn't present any problems as long as the required volume of ventilation necessary at the soffits is met.

   Edit: Looking at your pictures again, I'd be tempted to remove the baffles in the second bay too, as there is nowhere at the peak for the air to exit.

7. 
   CTSNicholas | Oct 28, 2015 12:03am | #7

   Malcolm, I was planning on trimming the baffle some more on the second bay. I just trimmed the angle to get it installed. I think my insulation height will only touch about halfway up the insulation baffle. I have to meet code R-38 in zone 5. I'd like to do R45 or R50 if time/money permits. That will require 12 to 16 inches of space. I really don't want to leave the 3.5" of void between roof sheathing and wall sheathing. Can I get away with completely sealing those corners or should I still try to get some air space? I am thinking I could put some osb up to cover the 3.5" x 22.5" air gap that either the baffle or 'bird blocking' would typically fill and then stuff the corners full of insulation.

8. Expert Member
   MALCOLM TAYLOR | Oct 28, 2015 12:27am | #8

   I think you are better off filling them with insulation. The moisture is going to diffuse through the cellulose and dry into the air in the attic. There is no real benefit to supplying an air space unless it has air movement through it.

9. 
   CTSNicholas | Oct 28, 2015 12:46am | #9

   Okay. I will block off the kneewall in the immediate corners. I suppose I better leave the second rafter bay over the way I have it with some venting as long as I cut the baffle back 8 to 10 inches so air has a channel. Thanks!

10. GBA Editor
    Martin Holladay | Oct 28, 2015 06:35am | #10

    Nicholas and Malcolm,
    Yes, I misunderstood. Thanks, Malcolm, for clarifying the issue.

    Malcolm is right -- if you are installing insulation on the attic floor, it isn't essential to have a ventilation baffle in every rafter bay. Ventilation in this situation is much less important than it would be if you were insulating the sloped roof assembly.

11. 
    CTSNicholas | Oct 28, 2015 10:08am | #11

    Okay. Just some food for thought. I have so far installed baffles along the entire length of one side. If I were to start doing every other, would this likely cause an issue with unbalanced venting?

    I was reading articles about air sealing the baffle or it isn't really worth using. Is the quickest way to do this by using expandable foam on the corners and cracks of the baffle?

12. GBA Editor
    Martin Holladay | Oct 28, 2015 10:31am | #12

    Nicholas,
    Canned spray foam is indeed useful to seal air leaks around these ventilation baffles.

    For more information on these issues, I suggest that you read these two articles:

    All About Attic Venting

    Site-Built Ventilation Baffles for Roofs