Fixing Reflective Foil

Air conditioning, fans, and anything related to keeping it cool, such as insulation. This would include any posts generally discussing how to keep it cool, such as which types of blocks are better insulators.... ideal wall thickness for keeping an A/C house cool, etc.

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Fixing Reflective Foil

Postby Greenside » Mon Jul 01, 2013 2:26 pm

I'm posting this in the insulation forum in the hope that some expert will be able to answer my question. For the background, my build is being documented here. http://www.coolthaihouse.com/forum/viewtopic.php?f=3&t=3855

My efforts to find out which brand of foil is best value brought up the fact that to be effective, the foil should be installed facing an air gap on the side from which the radiation is coming from otherwise, assuming it's double sided, the only benefit will be from the low emissivity which seems like wasting half of what one is paying for. Here are some useful links about the theory and application of radiant barriers I came across during my research:

Wikipedia

US Government Guidelines

Radiant Barrier Fact Sheet

Florida Solar Energy Centre

I just ventured up into our loft to put some stuff away and thought I'd snag a sample of the Chang foil to make me feel better about paying all that extra. Having read that foil must be separated from the tiles by an air gap I was depressed to see that actually they had simply laid the foil down on the purlines and placed the tiles on top, pushing the wire through the foil to secure them to the roof. This makes me suspect that it's not being very effective as the only air barrier that could possibly be there would be in the curved part of the tile or the slight sag between the purlines - pretty insignificant, I'd say.

Image

Anyone had this applied in a way that is in line with the advice given in the radiant barrier links I posted above (ie an air gap between tiles and foil)? In particular, I'd be interested to hear from anyone who managed to find a workable way of fixing the foil to the underside of the rafters.
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Re: Fixing Reflective Foil

Postby Baht Man » Thu Jan 02, 2014 1:43 pm

Don't worry about it.
You've got a HUGE air gap between the roof and your insulated ceiling.
With your large gable vents at such a height, you should not have a heat build up problem below.
The more hair I loose, the more head I get.
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Re: Fixing Reflective Foil

Postby geordie » Wed Jan 08, 2014 11:44 pm

The small gap is sufficient the foil wiil create convection currents drawing air from the eaves and hopefully well ventilated at th peak shiny side down so theoretically minimising radiated heat as the proof is in the pudding you need reall to take a look into a none insulated roof of similar size and construction probably not going to happen :D

If you were wanting to be really finicky you could foil it again using th main prlins and double sided tape the screw a metal strip over it for the inevitable faliure of th tape i have just installed a flat roof metal with bonded insulation and as an afterthought screwed chicken wire to the purlins with 100mm of fiberglass and foil the results made it positively worth the effort from both a heat and a noise point of veiw
my comments may be wrong but never deliberately
If it aint broke, dont fix it
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