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I live in south Florida and am insulating the roof by placing batts between the rafters. I'm not sure if placing the batts up against the edge where the beams and walls meet is ok or not.

The rafters that correspond to the ventilation grills in the softit will have plenty of space for air flow.

Should I back the batts off from the edge? If so how much, 6" alright?

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  • Can you show a picture(s). It would help to visualize a lot. – Michael Karas Sep 11 '15 at 4:36
  • Michael Karas, I've updated the post with pics. – mmlb Sep 11 '15 at 12:44
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The distance to the wall isn't the concern. You need some space for airflow between the insulation and the underside of the roof. There needs to be a path for air to enter in the soffit vents and out the ridge vent, passing under the roof. They make baffles that you can install between the rafters and top plate of the wall if you are concerned about pushing the insulation too far back, these are commonly used with blown insulation. You do want the insulation as far over the wall as possible without blocking the soffit airflow. This creates a continuous insulation envelope around your home and avoids cold/hot spots in the corners.

See this blog post for more details.

  • Most of my confusion lies with the softit vents I have. There only a few of them spaced about 8' apart and as far as I can tell the beams extend down to the soffit, restricting inter rafter airflow already. – mmlb Sep 11 '15 at 13:36
  • That's either not enough ventilation, or they designed the vents with the idea insulation would be between the joists, rather than the rafters. In FLA, the risk is that your roof will just get very hot making your AC work harder, rather than the risk of an ice dam faced by those in colder climates. – BMitch Sep 11 '15 at 13:42
  • Yeah that makes sense – mmlb Sep 11 '15 at 13:43
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I see. So the attic is going to be a finished or conditioned room? That's why you are installing the insulation in the roof rafters? If so you are correct you will need to create vent openings in each soffit bay and to allow for air circulation, in each rafter bay, between the bottom of the sheathing and the batts. Try to max out your R- value. It is wise to be meticulous when installing roof insulation (you want to have the batts expand and fluff out to the fullest and not be compressed). When you drill circulation holes in the soffit bays you should do the same at the ridge board to allow for soffit to soffit air circulation.

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