Best layers in above-deck system

Elton Johnson
Elton
8/31/2015
Aloha! Just did the tear-off on our 1965 low-pitch (2.3) 2,500 square foot roof. Before we install the standing seam aluminum (Surelock by Hawaii Metal Roofing), I need to get my mind around best practice for the entire above-deck system. Trying to keep the sun's heat out of the home to the extent possible. Q1: I was thinking that insulation (Polyiso) would help keep the house cooler, but now I'm wondering if I misunderstand the function of above-deck insulation! Maybe its function is not to reduce the transfer of the sun's heat into the home, but rather just to maintain home temperature for those who heat their home in winter or use AC in summer (we do neither) . . . Help! Q2: If that is correct--i.e., no need for above-deck roof insulation for our screen-windowed house that is never sealed for heating or AC--then is there something better than the following sort of roof system, to keep out some of the tropical sun's heat: e. Aluminum standing seam d. PolyGlass MTS underlayment c. TechShield (0.5"), shiny side in b. Protecto Wrap Ice & Water Guard a. Wood deck Any above-deck recommendations for what to put under an aluminum roof in a sunny/rainy tropical climate would be much appreciated. Thank you.
Dick Bus
9/1/2015
Elton, you are headed down the right path. The only thing I would add is above sheeting ventilation. Create an airspace under the aluminum roof using either raised clips, furring strips or shims. The panel should be raised 3/8 to 3/4 of an inch. allow for intake at the eave and exhaust at the ridge. tests have proved that this will make the attic space cooler. I assume you are getting a PVDF paint finish on the aluminum roof.
Eric Novotny
An informed customer is the Best Customer!
9/1/2015
Above deck venting would work great here. Some foil faced ISO insulation in conjunction with a nice air gap will keep most of the heat out of the roof assembly. Above deck venting is the best of both worlds in this case.
Elton Johnson
Elton
9/1/2015
Thank you--so it sounds like polyiso would help keep heat out even though we don't use AC. Where do you think the polyiso should be applied in the system? Instead of the TechShield?
Elton Johnson
Elton
9/1/2015
Thank you--maybe furring strips would work best for the ventilation space. The aluminum does have a reflective coating. Mis-spoke earlier--using Shur Lock by HPM. Thank you for your help!
Dick Bus
9/1/2015
they are a good company.

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