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We are building the “dreaded”(from an insulation/sealing perspective) 1 1/2 story house with large dormers, side attics, floor/kneewall transitions, leaky built-in furniture and a cathedral ceiling. The location is Northern California, so summers are hot ~90’s but dry and winters are mild ~40’s and wet with no worries of roof dams. The roof is a hipped roof with 2X8 rafters on 16in centers, the dormers are California framed over the hipped roof. The roof requires venting per my builder and roofer, so we are going to put soffit vents in the eaves and a continuous ridge vent.
How should be insulate this beast? Should we define the thermal envelope at the roof slope, or at the kneewall and side attic floor? How should it be sealed? Thanks in advance for your insights.
Larry
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Fred,
I was hoping you would have some answers....oh well. The vents are slated to be along the main ridge and the dormer ridge lines. More details: the rooflines of the dormers(the dormer roofs are also hipped) intersect the hips. Sorry, I don't have the tools to post a drawing.
After posting, I found your article and others in the Home Energy magazine website regarding insulating around kneewalls. I think the safest thing to do is to place the insulation at the building perimeter along the roofline. Would you recommend packing the bays tight and not venting, or rigging some sort of vent channel that runs in the bays between the sheathing and the FG insulation?
What do you think of the spray in place foams (Icynene??)that could be blown in to the roof bays? Is there another better solution? Thanks.
Larry
*Probably the MOST important thing is to insulate before you build the knee walls.
*Fred,I believe he is going to cut 1/2 in. deep notches 3 in. long into the tops of the jack rafters, where they abut the hip rafter.Larry
*Larry the Energy Efficiency and Renewable Energy Network has a truckload of information on the same subject that you are researching.