Metal Roof Insulation & Whole Home Fans

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Metal Roof Insulation & Whole Home Fans

Postby kmanonmaui » Sat Apr 01, 2017 6:01 am

Curious what you all have found to be the best insulation method/product for metal roofing? While, I plan on have twin attic exhaust fans (one facing East and one West) with automatic temp. controls to kick them on when the outside air is cooler than the attic. But, keeping the heat from coming in from the tin roof would obviously be a good thing. Not so familiar with them as in Hawaii most roofs are 3/4" plywood with asphalt shingles.

I am also considering using what we call a "whole house/home fan" when the A/C is not quite needed (https://energy.gov/energysaver/cooling-whole-house-fan) . It works wonderfully over here. Basically, a large fan (or set of fans) that draw about 3,000 cubic sq. feet per minute (depending on size) out of the living space and out of the attic. I have not seen them used in Thailand but for those days when it is just a bit too hot here in Hawaii, they are perfect bringing in a nice breeze from which ever windows you leave open and, having the fans in the attic, do not make much noise at all. So, I guess two more questions I am adding, the metal roofing insulation recommendations and if any one there is familiar with a whole home fan.

Thanks in advance,
-k-
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Re: Metal Roof Insulation & Whole Home Fans

Postby Sometimewoodworker » Sat Apr 01, 2017 10:55 am

Your ideas will keep the attic cooler than the outside. Howeve in my opinion that is less important than keeping the rooms cooler than the outside. As part of a system venting the attic does no harm and probably helps, I don't know anyone who has a whole house fan.

FWIW I don't know of any tin roofing in Thailand

If the outside air temperatur e was consistently comfortable and moderately humid your system is good, but for quite a lot of the time in the north east the outside air is either too hot, too humid or both.
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Re: Metal Roof Insulation & Whole Home Fans

Postby chakayan » Tue Feb 13, 2018 10:16 am

the problem in general with attic vent fans is that unless your attic is hermetical sealed from the conditioned space below (unlikely!), they will draw air from the conditioned space into the attic. this in turn will draw air from outside into the conditioned space. the vent fans cost money to buy and use electric to operate, and cost you money by removing air you've probably paid to condition.
this applies in any climate.
continuous soffit and ridge vents are as effective as motorised fans, and are maintenence free, lasting as long the roof they are part of. coupled with a radiant barrier and proper insulation, you have an excellent passive conditioning system.
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Re: Metal Roof Insulation & Whole Home Fans

Postby Sometimewoodworker » Tue Feb 13, 2018 11:33 am

chakayan wrote:the problem in general with attic vent fans is that unless your attic is hermetical sealed from the conditioned space below (unlikely!), they will draw air from the conditioned space into the attic. this in turn will draw air from outside into the conditioned space. the vent fans cost money to buy and use electric to operate, and cost you money by removing air you've probably paid to condition.
this applies in any climate.
continuous soffit and ridge vents are as effective as motorised fans, and are maintenence free, lasting as long the roof they are part of. coupled with a radiant barrier and proper insulation, you have an excellent passive conditioning system.


We don't install ridge vents, though they were considered, because of the large amount of black dust and ash from sugar cane burning every year around this time. Think very carefully about the problems that you can create, if you don't think that it will be a problem just talk to SWMBO.
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