Q&A: A Forum for Green Building Experts and Beginners

My wife and I recently bought an old (1880's) two-story duplex with separate apartments on each floor, each about 750 square feet and very poorly insulated. We have long-term renovation plans, but our primary near-term complaint is the inability of the apartments (especially upstairs) to cool down at night -- even with our quite cool summer nights here in Northern Colorado and all the windows open. We don't want air conditioning, but we would like to improve night-time ventilation.

As a long time visitor and few years member, I have tried to absorb the lessons, opinions, science and conjecture presented here. However, I now find myself confronted with conflicting theory regarding unvented roof profiles.

For my own project, (high altitude, dry, -10 to 90 F) I have regarded the "top" layer of sheathing in an unvented assembly to be essentially in dead space - not exchanging air or moisture - the underside in contact or glued to impermeable insulation, the top side sealed off from all contact with the locally required ice and water shield over the entire roof.

I put the cart before the horse, and selected the house depicted below to build in the Adirondacks, NY. After working out the design details inside the house, I moved to the outside. I questioned the building designer about the low profile 3/12 pitch roof and how it is vented on the high edge, and the reply was "this home uses water impenetrable closed cell urethane insulation, sprayed in to fill the cavity from below prior to drywalling, and it therefore unvented.

I had a new central air installed, and the gas line is against the flue on the heater.