How could I insulate this metal roof?

Bill Spikowski
1/7/2018
In the early 80's, my wife and I built an off-grid home on a small island near Fort Myers, FL. We lived there for twenty years and now use the home as a weekend getaway as it’s just a short drive and even shorter boat trip from our house in Fort Myers. The house has an aging PV system for electricity; a propane stove and refrigerator, and water is collected off the roof and stored in large tanks. Now that we’re approaching retirement, we’ve been considering some upgrades so we could spend more time out there, especially when the weather gets hot. We’ve been considering a limited amount of air conditioning with small, high-SEER ductless mini-splits, which we could power by expanding the PV system. The big stumbling block is our uninsulated metal roof. The roof has about a 5:12 slope and is a single layer of thin white aluminum panels that sit on purlins atop beautiful site-built heavy beam trusses. The roof panels are through-fastened with about a jillion stainless steel screws with covered neoprene washers, which amazingly have held up this whole time. (I’ve had to tighten some screws over the years and replace a few others, but that’s about it for maintenance.) The bottom of our roof panels became an exposed sorta-decorative ceiling; but in hot weather, that ceiling gets REALLY hot, making the house uncomfortable 4 or 5 months a year. It doesn’t get that cold down here so cold weather is not a big problem. I had always intended to insulate the roof but never figured out a good way to do it. I’m still stumped, and am looking for advice. Since the existing roof has survived two hurricanes, including one Category-5 direct hit, I had been thinking about leaving it in place and adding foam insulation over it (either sheets or spray foam) and then another metal roof on top; but the complexity of doing all that in such a remote location is daunting. Another solution, putting the insulation below the existing roof, would mean covering up the heart-pine purlins and part of the trusses, then building a new ceiling to cover the insulation – also a very major undertaking, with negative aesthetic results from our point of view. Somewhere in my research I ran across a metal roofing company that made sandwich panels with foam inside that’s completely encased in metal. With panels like that, I’m thinking I could replace my existing metal roof entirely. We’d end up with an exposed metal ceiling like we have now; good insulation (FINALLY!); and a new roof surface – all with a single panel installed by a single contractor. I’m looking for advice on using this approach. Even if it would make sense, I see several hurdles; for instance, would companies who make those panels supply them for a small residential job; would a local contractor know how to install them and be willing to do the job on an island; and would this roof be able to withstand hurricane winds at least as well as my existing roof. The bigger problem perhaps is that I haven’t found a company that makes such panels in aluminum. I have severe reservations about using steel in this coastal location. My experience with steel has been terrible, even when galvanized; the only steel that has held up are some triple-hot-dipped galvanized joist hangars I bought from Simpson. Stainless steel and copper hold up great; painted aluminum holds up OK; unpainted aluminum is much better than steel but still not great. (I know nothing about terne or galvalume or other treatments that might make steel hold up in our salty environment.) Ideas???
Info @windowsonwashington.net
An informed customer is our best customer.
1/7/2018
How much square footage we talking about here? The reality is there is no "good" answer here.
Guest User
1/8/2018
This roof is about 1,110 square feet.
Info @windowsonwashington.net
An informed customer is our best customer.
1/8/2018
With that modest area, I would look into removing the roof panels and doing the work from the top down.
Bill Spikowski
1/10/2018
I'm definitely leaning toward working from the top down.... If I RETAIN the existing roof, I've come up with a couple of decent methods for adding foam insulation on top of it and then adding a new metal roof over the insulation. That's two separate jobs (but both are outside my competence and physical abilities). If I REMOVE the existing roof, I understand I'd have to cover the bottom of new foam insulation for fire reasons. That leaves me with probably a new layer of metal, then layers of foam board, then a new metal roof. Now I'm up to THREE separate jobs -- which could be simplified to just one job if I could use insulated roof panels that include the new bottom layer of metal, 2" to 4" of foam built-in, and a new and better metal roof on top -- all in a single panel. But no one I've talked to so far has worked with insulated metal panels, so I don't have any verification of their suitability for this application. The manufacturers don't want to deal with homeowners at all; and I hesitate to start calling roofing contractors without feeling somewhat comfortable that this solution might be viable for my application, and hopefully for them as a business proposition for one small house.
Info @windowsonwashington.net
An informed customer is our best customer.
1/10/2018
What kind of metal roof is on the top as of right now?
Bill Spikowski
1/10/2018
The roof right now is a single layer of aluminum, painted white top and bottom. It was the bottom-of-the-line siding/roofing product for farm buildings that Alcoa was selling in the early 1980s. I had run out of money and needed to close in the building before our rainy season began! I attached a couple of photos to my earlier posts; the panels are screwed down to purlins, with the purlins and the underside of the aluminum being the ceiling for the rooms below. Now 35 years later, I sit here and marvel about two things: (1) how I could ever have thought that such a thin uninsulated roof might be acceptable for a house, even for a couple of years until I could afford to upgrade it; and (2) that the roof has held up all this time, even through two hurricanes!

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