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jbeuckm 09-29-2010 12:56 AM

Insulating Below Rafters in 1-1/2 Story House
Our 1956 1-1/2 story house is in Minneapolis. The ceilings and knee walls are insulated but the side attics are outside temperature, causing the 2nd level to be cold all winter. The roof above the second level interior space is insulated with no space for ventilation between the side attics and ridge, which appears from outside to be vented. (Isn't that going to cause ice dams at the knee walls?)

There are only two roof vents on each side attic and vents along the eaves. After some reading, my plan is to install short lengths of furring strips on the underside of the rafters - spaced apart for ventilation. Then I would sheath the whole underside of the roof with pink foam boards and tape the joints.

I haven't read about that solution so I assume there is a problem with my design. Thanks for your advice.

Michael Thomas 09-29-2010 10:20 AM

Take a look here, the discussion is of insulating above a garage, but any under-roof conditioned space with knee walls has similar considerations: 09-29-2010 12:59 PM

Insulating Below Rafters in 1-1/2 Story House
The original method of insulating is correct; you normally keep any unused attic space cold to prevent ice dams. I was not sure from your description, but I assume that there is insulation between the floor of these side attics and the lower floor. If this is the case I would recommend you just increase the side wall insulation, just be careful that you don,t create a vapour barrier on the cold side of the wall.


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