Radical Roof Insulation Design

Tony Adrian’s house is unusual to say the least. It is self sufficient: off the commercial electrical grid, uses filtered rainwater and has no air conditioning. All this in Louisiana, a state not known for cool weather. How does he live there? Quite comfortably because his house was designed to maximize the possibilities of insulation, solar energy and the surrounding environment. A complete article including pictures of the house can be found the here in the Daily Advertiser as well as another article here. However, Home Building and Remodeling News corresponded with Adrian to ask about one of the most intriguing parts of the design: the roof.

We obtained this diagram (rotating the diagram may be required via View->rotate in Acrobat, here is a lower quality rotated diagram) of the roof construction. Adrian had this to say about how it is constructed:

 

Radiant Barrier: Here’s how our roof is set up from top outside to
the inside ceiling. We do have a ridge vent. (We live in an non
air-conditioned house in South-Central Louisiana.)

Top Layer: Galvalume type steel roof with 30% higher peaks and 30%
lower valleys than typical commercial type steel roofing. It is
screwed to 2X4 sleepers crosswise over the 12″ rafters (air space #1).

Second Layer : Plywood decking nailed to the 12″ rafters with radiant
barrier stapled to it – shiny side down.

Third layer: 12″ Rafters with high density (AKA Cathedral Ceiling) fiberglass insulation. Timbor was applied to the insulation. The fiberglass insulation is about 8″ thick. This left about 2″ of air space between the radiant barrier and the insulation. The result is our second air space. Outside where the fascia hit the rafters we drilled holes and inserted circular, screened galvanized air vents. These vents are below the radiant barrier but above the fiberglass insulation. Air can now pass directly under the steel roof AND between the radiant barrier and the fiberglass insulation.

Fourth Layer: Tyvek brand barrier under the rafters. Nailed and caulked.

Fifth Layer: Pickled mahogany 4’X8′ luan. All four edges were beveled with a router. Makes for a nice, airy effect & decreases the need for lighting. The luan is held up with nice steel wood screws.

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Folks – this arrangement works. It just plain works. Some would consider it a drawback that with that much high density insulation and two air spaces we do not get the rain-on-a-metal-roof sound many are fond of. A large number of talented carpenters, designers, and architects have toured the place and all seemed pleasantly surprised at the functionality and appearance.

One last note: Make sure you get high density insulation – often labeled as cathedral ceiling insulation. It is usually special order. It is significantly heavier and is more expensive. Go thru the effort and expense of doing this right. Also – use the Tyvek brand. We returned the Tyvek knockoff. Bite the bullet, pay the price. Don’t try to scrimp on the roof.

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