Expert: Ted Barnhill (Principal, Design45 LLC) - 6/29/2008

Question
I recently bought a small, 850 sq. ft.,concrete block home for my son. It is 60 years old with a flat roof and no insulation. It is presently gutted, no ceiling, and I wanted to know the best type of insulation to use on it, in NW Ohio. There are currently no vents in the overhangs.
Thank you for any help.
Linda Barker

Answer
Linda,

Most would agree that a spray foam insulation is your best choice for performance - it will seal any air leaks while providing a high R-value.  If you are concerned about resource usage, note that these are often petrochemical based products (though there are some bio-based products that use soy or other natural elements).

Damp-spray cellulose is another good choice.  It will provide less insulation per inch, but if your roof structure is thick enough to get adequate depth, cellulose is a more natural product and generally will be significantly less expensive.

Even though you currently have no soffit vents, you would be advised to add proper venting before applying new insulation.  It will keep the roof cooler in summer, minimize ice damming in winter, and, most importantly, will provide a means for the roof to dry out if it gets wet from interior condensation or leakage/seepage from the roofing or flashing.  As you have overhangs, venting through the soffit is your best approach; if this is troublesome for some reason, it is also possible to vent directly through the flat roof membrane.

Good luck, and feel free to follow-up with additional questions.  -Ted