Radiant barrier (1 Viewer)

[cosjobs]

I am getting cellulose blown in my attic to r-38.

They have offered to add in a radiant barrier for an additional $1200 (about 2000 Sf house).

With that much insulation, I do not think the RB will have a big impact. But I'd get a 30% tax credit, amking it cost under 900, so its very tempting.

Also, I could get blown in fiberglass instead of cellulose - and save 500 there- any thoughts on pro/cons of Fiberglass v. cellulose?

 

[Chemical X]

i am not familiar with a radiant barrier.....is it a locale situation?

 

[culdeus]

I am getting cellulose blown in my attic to r-38. They have offered to add in a radiant barrier for an additional $1200 (about 2000 Sf house).With that much insulation, I do not think the RB will have a big impact. But I'd get a 30% tax credit, amking it cost under 900, so its very tempting.Also, I could get blown in fiberglass instead of cellulose - and save 500 there- any thoughts on pro/cons of Fiberglass v. cellulose?

The better thing to do at least IMO is to get a solar powered attic exhaust fan. Or two. That's a much better way of removing the heat in the attic. Radiant barriers work for awhile ok, but then they get dusty and to operate at max efficiency they practically need to be glassy.

 

[cosjobs]

I am getting cellulose blown in my attic to r-38. They have offered to add in a radiant barrier for an additional $1200 (about 2000 Sf house).With that much insulation, I do not think the RB will have a big impact. But I'd get a 30% tax credit, amking it cost under 900, so its very tempting.Also, I could get blown in fiberglass instead of cellulose - and save 500 there- any thoughts on pro/cons of Fiberglass v. cellulose?

The better thing to do at least IMO is to get a solar powered attic exhaust fan. Or two. That's a much better way of removing the heat in the attic. Radiant barriers work for awhile ok, but then they get dusty and to operate at max efficiency they practically need to be glassy.

If you lay them on top of your insulation, that can be a problem. But if you attach tehm to the rafters, not so much.I have been looking into an attic fan- but there is much debate as to their effectiveness. Many experts are saying the coolness they suck from your home offsets any gain. I'm still researching.... If I do go for one, I think I will do a gable fan, mainly because I hate penetrating the roof and opening the possibility of leaks.

 

[cosjobs]

i am not familiar with a radiant barrier.....is it a locale situation?

It used reflectivity top direct UV heat away from the house. They are used nationally, but more in the hotter climes.Its basically a thin sheet wit a couple layers of aluminum, some air bubble and then laminated. When the UV ray emanate from the sun, rather than penetrating thru to the attic space, they are reflected back outside the house.My initial research show them to be very effective with r-11 or less insulation, but with the R-38 I am putting in, their usefulness may not be worth the price.

 

[moleculo]

my uncle is a PE that has 20+ years experience doing HVAC in orlando, for really big buildings. Right now he is working on some new building for NASA on the coast.

I asked him about this several years ago, and he said that radiant barriers are one of the most effective things you can do.

Here's the heat transfer chain: sun -> shingles (radiation) ->inside surface roof (conduction)->top layer of insulation (radiation)->through insulation to ceiling (conduction). The top layer of insulation is also cooled some by air flow (convection).

The hottest point of an attic will be the inside surface of the roof, followed by the top of the insulation. moving more air through there really doesn't impact how much heat goes into the ceiling.

A radiant barrier prevents the radiation from the roof to the insulation.

I think it's probably worth it, especially if you are talking new construction.

 

[culdeus]

I am getting cellulose blown in my attic to r-38. They have offered to add in a radiant barrier for an additional $1200 (about 2000 Sf house).With that much insulation, I do not think the RB will have a big impact. But I'd get a 30% tax credit, amking it cost under 900, so its very tempting.Also, I could get blown in fiberglass instead of cellulose - and save 500 there- any thoughts on pro/cons of Fiberglass v. cellulose?

The better thing to do at least IMO is to get a solar powered attic exhaust fan. Or two. That's a much better way of removing the heat in the attic. Radiant barriers work for awhile ok, but then they get dusty and to operate at max efficiency they practically need to be glassy.

If you lay them on top of your insulation, that can be a problem. But if you attach tehm to the rafters, not so much.I have been looking into an attic fan- but there is much debate as to their effectiveness. Many experts are saying the coolness they suck from your home offsets any gain. I'm still researching.... If I do go for one, I think I will do a gable fan, mainly because I hate penetrating the roof and opening the possibility of leaks.

You shut them down in the winter. There's hardly a time from May to October where ambient air is under attic air. Maybe a total of 300 hours tops.

 

[cosjobs]

I am getting cellulose blown in my attic to r-38. They have offered to add in a radiant barrier for an additional $1200 (about 2000 Sf house).With that much insulation, I do not think the RB will have a big impact. But I'd get a 30% tax credit, amking it cost under 900, so its very tempting.Also, I could get blown in fiberglass instead of cellulose - and save 500 there- any thoughts on pro/cons of Fiberglass v. cellulose?

The better thing to do at least IMO is to get a solar powered attic exhaust fan. Or two. That's a much better way of removing the heat in the attic. Radiant barriers work for awhile ok, but then they get dusty and to operate at max efficiency they practically need to be glassy.

If you lay them on top of your insulation, that can be a problem. But if you attach tehm to the rafters, not so much.I have been looking into an attic fan- but there is much debate as to their effectiveness. Many experts are saying the coolness they suck from your home offsets any gain. I'm still researching.... If I do go for one, I think I will do a gable fan, mainly because I hate penetrating the roof and opening the possibility of leaks.

You shut them down in the winter. There's hardly a time from May to October where ambient air is under attic air. Maybe a total of 300 hours tops.

the ones I am looking at (attic fans) are thermostatically controlled, so they only turn on when heat is high.But as I said, a lot of recent research and articles I've read question their effectiveness. While they do move around the hot air, evidently they also suck up the air you cooled from your house. I have no horse in this race, I am just reading and trying to figure out what's best. I have a call into the Austin energy conservation dept., and I will get their 2 cents, as well.

 

[Urinal Mint]

They must work. They advertise on local radio 22 solid hours out of every day.

 

[daddo39]

We have gone to installing turbines. They cost less than a hundred bucks and use no power. Just put 2 in a 1250 sq ft rancher and they almost instantly cooled the attic 20 degrees. The data on power vents is what i'm hearing to. They aren't compatible with ridge vent and cause more harm than good.

 

[matttyl]

Anyone installed a radiant barrier and have any insight on if it's been doing any good for them?