My name is Rod and I live in Waialua on Oahu. It gets pretty hot here. We have vaulted ceilings and are about to replace the roof so we can put a new solar hot water system and 18 pv molules up there. What roof would you use to repel heat from coming in the house?
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To keep heat out of your house, you need to install a roof assembly that includes insulation.
If for some reason you don't want to include insulation, at least choose a "cool roof" (that is, roofing with high solar reflectance and high thermal emittance).
In some cases, including a vent space between the roofing and the sheathing can help -- but venting is never as effective a measure as including insulation.
The portion of the roof with the PV now has a nice shading factor on the roof-proper, as long as there's sufficient ventilation space between the PV and roofing.
A CA Title 24 compliant cool roof material or coating relevant for your roof pitch would work. The highest solar reflective index (SRI) goods tend to come in one color- BLINDING WHITE, which is restricted by code in some locations. But there are an array of pretty-good products that reflect primarily in the infra-red spectrum. There are searchable third-party tested products listed on:
The higher the aged SRI numbers, the better the heat rejection. For anything other than white you won't find anything with a 3 year aged SRI >80, but there are some off-white finishes with SRI >70.
In a HI climate adding mass to the roof can be almost as important as adding insulation- ceramic and concrete roofs do quite well, but if the house wasn't designed for it a retrofit would be a bit daunting on cost. If metal roofing is an option for you (not cheap, but not heavy like concrete roofing), there are some very high SRI finishes >80 for metal roofing out there.
This article might also be of some help to you: