Sifu
SAWHORSE
- Joined
- Sep 3, 2011
- Messages
- 3,056
2018 IBC, type V building, climate zone 5
I find the language for unvented attics is making me re-think my assumptions. I have a proposal for all insulation to be placed in the roof framing directly under the roof sheathing. It is air-permeable, batt fiberglass. There is no "ceiling" applied directly to the underside of the roof framing, and there is no airsapce (baffle) with any eave or ridge openings. So the attic spaces are "warm", and the thermal barrier is at the roof sheathing. My first comment was to ask how they are ventilating the attic per 1202. I expected them to tell me how they are going to put the baffles and ventilation in. Instead, they responded by saying the attic is "warm" so no ventilation is required. So I now must assume they are going to go with 1202.3, which would require additional rigid or sheet insulation on the roof deck. Easy right? But a closer reading of 1202 contains this for both 1202.2.1 (ventilated rafter spaces) and 1202.3 (unvented enclosed rafter spaces): "ceilings are applied directly to the underside of roof framing members". In this case, there is no "ceiling". I don't think this matters, as the intent is to prevent moisture migration through the air-permeable insulation and condensing on the underside of the roof sheathing, but it makes me wonder if I misunderstand this. Commentary doesn't help. I think this is poor semantics, but I would like to hear other opinions.
I also see an issue with applying the required R20 rigid insulation on top of the structural sheathing because the proposal is for asphalt shingle roof coverings, and I am assuming this will not work through several inches of rigid foam.
I find the language for unvented attics is making me re-think my assumptions. I have a proposal for all insulation to be placed in the roof framing directly under the roof sheathing. It is air-permeable, batt fiberglass. There is no "ceiling" applied directly to the underside of the roof framing, and there is no airsapce (baffle) with any eave or ridge openings. So the attic spaces are "warm", and the thermal barrier is at the roof sheathing. My first comment was to ask how they are ventilating the attic per 1202. I expected them to tell me how they are going to put the baffles and ventilation in. Instead, they responded by saying the attic is "warm" so no ventilation is required. So I now must assume they are going to go with 1202.3, which would require additional rigid or sheet insulation on the roof deck. Easy right? But a closer reading of 1202 contains this for both 1202.2.1 (ventilated rafter spaces) and 1202.3 (unvented enclosed rafter spaces): "ceilings are applied directly to the underside of roof framing members". In this case, there is no "ceiling". I don't think this matters, as the intent is to prevent moisture migration through the air-permeable insulation and condensing on the underside of the roof sheathing, but it makes me wonder if I misunderstand this. Commentary doesn't help. I think this is poor semantics, but I would like to hear other opinions.
I also see an issue with applying the required R20 rigid insulation on top of the structural sheathing because the proposal is for asphalt shingle roof coverings, and I am assuming this will not work through several inches of rigid foam.