Hello! I’m in a bit of quandary here in regards to how best to approach insulating the roof of my 1842 brick home.
Simply put, we have a third story that we don’t use. We don’t use it because it is in a state of disrepair. It has been on the project list for years and my wife and I have decided to get serious about it this year. I have plans to renovate it, not as a living space but as a clean and comfortable area for storage and space for my wife’s various crafts. The current roof system is as follows: typical a frame, rafters, purlins, original cedar shakes nailed directly to purlins, standing seam metal roof applied directly over original cedar shakes. No roof insulation. I’m not sure when the metal roof was installed, but I have to assume it’s old. No ridge vent, no soffit vents, no roof box vents, no gable vents, no venting whatsoever. How can I insulate this? I’ve read plenty of things online regarding this issue, I’ve spoke with my local building inspector, a residential architect, and the cedar shake bureau technical rep. The idea of not installing vents and applying closed cell foam to the underside of the original singles (possibly with a contact barrier in between) is debated. Some say you can, others say you can’t. My options are to explore this route (waiting to hear back from a reputable insulation contractor) or to have a ridge/soffit system installed and use fiberglass batts.
That comes to my second quandary. Current code in my area (NJ climate 4a) states roofs must be insulated to R-49. This can be achieved with fiberglass batts at 14” thick. As far as I know, my 180 year old roof rafters are 4-6” thick. There’s no way that could work. And I seriously do not want to extend my rafters by 10 inches - it would have a huge spacial and visual impact on the third story (sloped walls/knee walls and chimneys coming through). Even with closed cell foam, using the max allowable thickness of 4-5 inches (I believe) I would fall quite short. I’m looking at the NJ rehab sub code which I believe states an exception in my case - stating that if recommended R value cannot be achieved due to space constraints, fill the available cavities. Which I interpret as put as much insulation as you can in there. But, unfortunately the inspector may interpret it differently and state I “could” achieve this by undertaking more construction and increasing the depth of my rafter bays.
Any thoughts at all would be welcome!