radiant insulation

Hi All, Would appreciate opinions on foil insulation. Here is where I started. http://www.radiantbarrier.com/physics_of_foil.htm
Thanks, john

"John & / or Maryln" wrote in message

Hi All, Would appreciate opinions on foil insulation. Here is where I started. http://www.radiantbarrier.com/physics_of_foil.htm
Thanks, john

Most of the claims are just that. Call your utility and see what they recommend. I would want the name and number of any contractor that they recommend. Please post it here. The government pages I have been to do not list radiant foils as a method of insulation.
Insulation works cause there is trapped air in it. The more volume the better the insulation. Fiberglass, and cellulous are the ones used by the home builders. Rock wool not so much now days. So what is a couple of inches of Mylar doing to trap? Ahh you say but what about the radiant energy? I say bunk...
If this stuff really worked, then why are the new home builders using it? Could it be that there are alternatives for less money? Or will FHA even accept this product? Tyvek the house wrap was not instantly accepted in the beginning. These claims have been around for 10 years, obviously some one is keeping the industry alive.
Why would you be worried about radiant heat anyway? If you have good insulation above the ceiling it is not a problem.
I added R-30, about 8 inches, of cellulous to my attic last July, cost ~$245. I signed a check. August's a/c bill was 50% less than July. I live in the southwest desert.

SQLit wrote:

"John & / or Maryln" wrote in message Hi All, Would appreciate opinions on foil insulation. Here is where I started. http://www.radiantbarrier.com/physics_of_foil.htm
Most of the claims are just that.

Having used reflective mylar "space blankets" for personal use, I can't see why a foil shouldn't work on a house. I use one on my unheated waterbed. It doesn't stop the bladder from cooling down, but it prevents the temperature of the bladder from cooling _me_.

Insulation works cause there is trapped air in it. The more volume the better the insulation. Fiberglass, and cellulous are the ones used by the home builders. Rock wool not so much now days.

ime, the problem with rock wool has nothing to do with insulative ability and everything to do with availability (which, in turn, is limited because of shipping costs). I did my entire last house in Roxul, but it's unavailable here because you can get 2-3 times as much fiberglass insulation in a truck to send it out here (Rock wool basically doesn't compress).

So what is a couple of inches of Mylar doing to trap? Ahh you say but what about the radiant energy? I say bunk...
If this stuff really worked, then why are the new home builders using it?

I think that must have been "why aren't..."?

Why would you be worried about radiant heat anyway?

Because all heat loss is radiant? -- derek

"John & / or Maryln" wrote in message

Hi All, Would appreciate opinions on foil insulation. Here is where I started. http://www.radiantbarrier.com/physics_of_foil.htm

Radiant insulation *can* work, in very specific circumstances. But most of the claims are over-inflated and don't really reflect 'typical' performance. The DOE has done some studies with these and came to same conclusions. Trying to assess its performance by claiming some 'R' value is usually useless. Manufacturers set up the most promising conditions, measure the performance and publish the 'R' value that would correspond to that. But other operating conditions can cut the effective 'R' by a factor of five.
The radiant surface must *not* be in direct contact with other material on one side. It is important to be able to fasten it *under* the rafters in an attic, *not* over the flooring (dust accumulation can make the foil about useless in just a couple of years if allowed to accumulate).
Most homes lose a lot of their heat via convection and foil doesn't stop that. It can keep an attic cooler in summer to help A/C costs.
daestrom

"daestrom" wrote:

Most homes lose a lot of their heat via convection and foil doesn't stop that. It can keep an attic cooler in summer to help A/C costs.

Unless there is a continuous ridge vent, this can be counterproductive by shortening the life of the roof and increasing roof replacement costs. Excess heat vaporizes the volitiles out of the roofing paper and shingles.

Harry Chickpea wrote:

"daestrom" wrote:
Most homes lose a lot of their heat via convection and foil doesn't stop that. It can keep an attic cooler in summer to help A/C costs.
Unless there is a continuous ridge vent, this can be counterproductive by shortening the life of the roof and increasing roof replacement costs. Excess heat vaporizes the volitiles out of the roofing paper and shingles.

What if you don't have tar-paper shingles? I've heard both clay and metal roofing products are popular.
Anthony

Anthony Matonak wrote:

Harry Chickpea wrote: "daestrom" wrote:
Most homes lose a lot of their heat via convection and foil doesn't stop that. It can keep an attic cooler in summer to help A/C costs.
Unless there is a continuous ridge vent, this can be counterproductive by shortening the life of the roof and increasing roof replacement costs. Excess heat vaporizes the volitiles out of the roofing paper and shingles.
What if you don't have tar-paper shingles? I've heard both clay and metal roofing products are popular.
Anthony

Roofing tiles (clay or cement) have a waterproof membrane of roll roofing underneath, so the same would follow there. Metal might not, but I've never torn a metal roof apart.

Metal sheeting or stripping = about $ 2-3 times good asphalt shingles. Metal shingles for a better look = $ 4-5 times good asphalt shingles.
"Anthony Matonak" wrote in message

Harry Chickpea wrote: "daestrom" <daestrom@NO_SPAM_HEREtwcny.rr.com wrote:
Most homes lose a lot of their heat via convection and foil doesn't stop that. It can keep an attic cooler in summer to help A/C costs.
Unless there is a continuous ridge vent, this can be counterproductive by shortening the life of the roof and increasing roof replacement costs. Excess heat vaporizes the volitiles out of the roofing paper and shingles.
What if you don't have tar-paper shingles? I've heard both clay and metal roofing products are popular.
Anthony

Harry Chickpea wrote:

"daestrom" wrote:
Most homes lose a lot of their heat via convection and foil doesn't stop that. It can keep an attic cooler in summer to help A/C costs.
Unless there is a continuous ridge vent, this can be counterproductive by shortening the life of the roof and increasing roof replacement costs. Excess heat vaporizes the volitiles out of the roofing paper and shingles.

Cite? Everything I've read suggests that's an urban legend (probably because any increase in temperature is small compared with the normal situation). So I'd like to see an actual study if you know of one.
-- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form che...@prodigy.net.

CJT wrote:

Harry Chickpea wrote:
"daestrom" wrote:
Most homes lose a lot of their heat via convection and foil doesn't stop that. It can keep an attic cooler in summer to help A/C costs.
Unless there is a continuous ridge vent, this can be counterproductive by shortening the life of the roof and increasing roof replacement costs. Excess heat vaporizes the volitiles out of the roofing paper and shingles.
Cite? Everything I've read suggests that's an urban legend (probably because any increase in temperature is small compared with the normal situation). So I'd like to see an actual study if you know of one.

This is one where I go by my own real world experience and extrapolate from that. I live in South Florida and had to replace a cement tile over roll roofing roof a few years back. I replaced it with a shingle roof, and during the summer months I water that roof to cool it with an automatic system sprinkler four times a day. I also have turbine vents. When hurricane Wilma came through, over half my neighbors lost shingles and had leaks. I lost about six shingle ends where the wind was funneled, but other than that had no roof damage. I attribute it to the shingles not being dried out and ready to split and lift. When I walk on the roof, the shingles are still supple, unlike other roofs that have been around for a few years.
There is no way that I would intentionally increase the heat load on my shingles.

Harry Chickpea wrote:

CJT wrote:
Harry Chickpea wrote:
"daestrom" wrote:

Most homes lose a lot of their heat via convection and foil doesn't stop that. It can keep an attic cooler in summer to help A/C costs.
Unless there is a continuous ridge vent, this can be counterproductive by shortening the life of the roof and increasing roof replacement costs. Excess heat vaporizes the volitiles out of the roofing paper and shingles.
Cite? Everything I've read suggests that's an urban legend (probably because any increase in temperature is small compared with the normal situation). So I'd like to see an actual study if you know of one.
This is one where I go by my own real world experience and extrapolate from that. I live in South Florida and had to replace a cement tile over roll roofing roof a few years back. I replaced it with a shingle roof, and during the summer months I water that roof to cool it with an automatic system sprinkler four times a day. I also have turbine vents. When hurricane Wilma came through, over half my neighbors lost shingles and had leaks. I lost about six shingle ends where the wind was funneled, but other than that had no roof damage. I attribute it to the shingles not being dried out and ready to split and lift. When I walk on the roof, the shingles are still supple, unlike other roofs that have been around for a few years.
There is no way that I would intentionally increase the heat load on my shingles.
I'd like a reading from a test case which doesn't include watering

the shingles four times a day.
-- The e-mail address in our reply-to line is reversed in an attempt to minimize spam. Our true address is of the form che...@prodigy.net.

Harry Chickpea wrote:

[...] I live in South Florida and had to replace a cement tile over roll roofing roof a few years back. I replaced it with a shingle roof, and during the summer months I water that roof to cool it with an automatic system sprinkler four times a day. I also have turbine vents. When hurricane Wilma came through, over half my neighbors lost shingles and had leaks. I lost about six shingle ends where the wind was funneled, but other than that had no roof damage.

Question: how many of your neighbor's had roofs that were older than "a few years back"? Over half?

Harry Chickpea wrote:

[...] I live in South Florida and had to replace a cement tile over roll roofing roof a few years back. I replaced it with a shingle roof, and during the summer months I water that roof to cool it with an automatic system sprinkler four times a day...

Well, what's a roof for? Snow and steepness aren't factors in Florida. Wind and dehumidification are. New houses might be happier with flat EPDM roofs under a few inches of sand or stone, with some water. A few plants might provide more shade, but the water they evaporate does more to keep their leaves cool than to keep the house cool.
An airtight Florida house might have a LiCl roofpond under a plastic film greenhouse to concentrate LiCl during the day and let it absorb water vapor from the house at night to keep the house cooler and drier. Nick

"Derek Broughton" wrote in message

SQLit wrote:
"John & / or Maryln" wrote in message Hi All, Would appreciate opinions on foil insulation. Here is where I started. http://www.radiantbarrier.com/physics_of_foil.htm
Most of the claims are just that.
Having used reflective mylar "space blankets" for personal use, I can't see why a foil shouldn't work on a house. I use one on my unheated waterbed. It doesn't stop the bladder from cooling down, but it prevents the temperature of the bladder from cooling _me_.
Insulation works cause there is trapped air in it. The more volume the better the insulation. Fiberglass, and cellulous are the ones used by the home builders. Rock wool not so much now days.
ime, the problem with rock wool has nothing to do with insulative ability and everything to do with availability (which, in turn, is limited because of shipping costs). I did my entire last house in Roxul, but it's unavailable here because you can get 2-3 times as much fiberglass insulation in a truck to send it out here (Rock wool basically doesn't compress).
So what is a couple of inches of Mylar doing to trap? Ahh you say but what about the radiant energy? I say bunk...
If this stuff really worked, then why are the new home builders using it?
I think that must have been "why aren't..."?
Why would you be worried about radiant heat anyway?
Because all heat loss is radiant? -- derek

Admittedly, the idea of a new kind of insulation has it's charms for me. And when I read that mass insulation just soaks up the heat as much as it can hold but then it has to give it up whereas the foil bounces those invisible infrared rays right back at you.Well I'm thrilled, but then when I came to the bottom line of what percentage of savings I could expect, the numbers don't seem to correspond to the theory. So ... I think I may play with it as nitetime window covers, but I'm not ready to bury it behind drywall until I understand more. thanks for your responses,
John,
..

nicksanspam@ece.villanova.edu wrote:

Harry Chickpea wrote:
[...] I live in South Florida and had to replace a cement tile over roll roofing roof a few years back. I replaced it with a shingle roof, and during the summer months I water that roof to cool it with an automatic system sprinkler four times a day...
Well, what's a roof for? Snow and steepness aren't factors in Florida. Wind and dehumidification are. New houses might be happier with flat EPDM roofs under a few inches of sand or stone, with some water. A few plants might provide more shade, but the water they evaporate does more to keep their leaves cool than to keep the house cool.
An airtight Florida house might have a LiCl roofpond under a plastic film greenhouse to concentrate LiCl during the day and let it absorb water vapor from the house at night to keep the house cooler and drier.
Nick

Roof water is sometimes used on commercial structures here. It makes sense, sort of. Even when cleaned regularly there is algae growth, making walking on the roof _extremely_ hazardous. You can't use shoes with cleats because of the possibility of puncturing the membrane. You also have to be extremely careful when doing even the most basic electrical work.
LiCL sounds like a good deal at first, but it heats up while absorbing humidity, which is about the last thing you want if you are trying to cool down.