Insulating Low Pitch Attic

Using spray foam insulation in an unvented attic application.

Insulating low pitch attic.

Multiple jurisdictions have indicated that even though we are utilizing 4 or more of polyiso rigid insulation on the exterior side of the roof sheathing low slope roof the 24 open web parallel chord roof trusses form an attic space and they have been requiring us to vent the low slope application. Start with the attic floor. Suggestions for un vented or hard to vent building roof cavities. How to avoid condensation leaks attic mold insulation mold structural damage to roof framing when roof venting is not possible cathedral roof and knee wall insulation venting air path options in older homes hot roof designs.

Worries about the hot roof un vented cathedral ceiling designs how to. Although some builders insulate a low slope roof with the same techniques used for a house with a big attic they should be using a different approach. Because the simplest and cheapest way to insulate an attic is to add material to the floor. If it is and you plan to provide heating and cooling to the finished attic space you need to remove.

Current air sealing and insulating methods. The attic floor which is the ceiling of the living space below often already is insulated. The most common practice is to blow in loose fill or wet blown insulation if you are insulating the ceiling where there is a cavity. Blow or pour in loose fill between ceiling joists and outer attic rafters behind kneewalls.

If the roof is vented the ceiling must be air sealed to prevent moisture laden air from reaching the attic. Now that i ve cut into the attic space i see that much of the roof has 2x4 joists that rest on the top of the exterior walls and due to the low slope of the roof there isn t the requisite 15 of space for blown cellulose until you get almost 3 in which means the effective r value is going to range from about r12 up to r49 over that stretch. Both low density open cell and medium density closed cell spray foam can be used in an unvented attic to provide the needed thermal resistance and airtightness. But if the floor is covered in plywood you can t stuff enough insulation beneath it to do the job sufficiently not even in warm climates.