Insulating a sloped open space
John Ranson| Posted inGreen Building Techniqueson
How would one place cellulose in a large 2′ tall sloped (4:12) under roof space with a smooth sloped floor and ceiling and no internal framing? Assume that ventilation is taken care of elsewhere. My biggest concern is keeping the insulation where it belongs.
–John
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Replies
John,
You haven't provided a clear description of this space, but here are the relevant principles:
1. Unless this roof assembly includes an adequately thick layer of rigid foam above the roof sheathing, building codes require that you include a ventilated air space between the underside of the roof sheathing and the top of the cellulose insulation.
2. If the cellulose is going to be installed in a sloped roof assembly, then you need to encapsulate the area before blowing in the insulation. If these are deep rafters, then you would need to install site-built ventilation baffles to enclose the insulation at the top, and some type of material -- InsulWeb, drywall, or rigid foam -- on the underside of the rafters to enclose the insulation at the bottom.
Here are links to two relevant articles:
Site-Built Ventilation Baffles for Roofs
How to Install Cellulose Insulation