Radiant Barrier (Austin, Amherst: how much, house, heat pump)

[m00se]

Has anyone had experience or opinion on radiant barrier and its effectiveness. I've seen discussion here about the cost of energy but have not seen anything regarding radiant barrier. I'm about to have this installed in a new build and I'm wondering if this is a wise investment. Thanks.

[lh_newbie]

I have had a home with and a home without it. Here's my experience, mixed in with some research I've done:

Two technologies seem quite promising:
- Roof decking with an aluminum foil attached to the back side
- Aluminum foil, stapled to the underside of your roof rafters

Both technologies block over 75% of the heat from getting into your attic. Keeping the heat out of the attic means your ducts and HVAC equipment aren't getting heated up (read: raising your cooling bills).

The one technology that I feel is a waste is the spray on barrier. They only block about 25% of the heat. Not enough to really make a difference.

Beyond the barrier, it's really important to have adequate ventilation, as heat WILL get up there no matter what you do and it's important to allow heat to rise out the top and fresh, cooler air to get in to replace it.

You made a good choice. When our roof needs to be replaced - we will pay the upcharge to get the decking redone with a radiant barrier.

Brian

[bricor]

I've been doing a little research on this as well.
If building or getting a new roof, the way to go is with foil backed decking (cool ply, themo ply, etc)
Second best seems to be the foil on the back side of the rafters approach. The foil is supposedly 97% reflective.
The most expensive and least effective is the spray on radiant barrier. The best ones are 75% reflective. And that's for the best spray on ones.

[loves2read]

have been in homes w/radiant barrier decking in attic and without--there is always a different in heat in attic--we replace our wood roof with composition about 8 years ago and missed the opportunity to add the radiant barrier decking--will always regret that--now to take up the plywood decking to add the radiant barrier would be cost prohibitive...we have talked about adding the foil to attic rafters but you have to have a really good crew for that and your attic has to be designed to make it fairly easy to install---
I think ours would be because it has a lot of vaulted space...

if there is any way to have radiant barrier added to your walls as exterior sheathing, think that would definitely be something to consider--most people cannot afford to have foam insulation but using radiant barrier (and now there is a wrap like Tyvek which is a foil but don't know what the R-factor is for that....
big heat gain/loss on side walls are window areas (which is why vinyl E2 windows are the way to go) and where the wood studs hit the brick or siding--if you sheath the wall outside the studs with the radiant barrier in addition to the insulation in between the studs you have given your house a much more effective heat gain/loss barrier than just plywood or OSB board that is typically used--they have minimal R-factor and are pretty conductive for heat gain/loss...
some builders dont like to use new technology and tract builders are really not eager because they don't know how to bid it...you might wind up paying more than just the material costs because it is a special order/special oversight thing...but there are couple of independent builders in Tarrant co that have gone to using the radiant barrier on house walls as well as roof decks and they sware by its effectiveness...

[justsomegal]

Originally Posted by m00se

Has anyone had experience or opinion on radiant barrier and its effectiveness. I've seen discussion here about the cost of energy but have not seen anything regarding radiant barrier. I'm about to have this installed in a new build and I'm wondering if this is a wise investment. Thanks.

Here are some really great websites that sould get you going:

BuildingScience.com

File not Found - BM&WT - UMass Amherst

[justsomegal]

Make that

Building Materials and Wood Technology - UMass Amherst

[johnrex62]

Yes, I have installed the SolarShield brand of decking when I built my house in 2001 in Austin Texas. I am extremely pleased with it.

My house is approx 2500 sqft and my wife likes to keep it cooled to 65-67 degrees. My highest elect bill has been under $200. Compare that with a similar floorplan I lived in a few miles away that was built without a radiant barrier. My bills were routinely close to $300 and a few time near $400 a month.

I also built a small shed next my house, but did not put the radiant barrier decking in it since it was an after thought project and I had not purchased enough decking. I put thermometers in the attic and in the shed one summer to compare. The highest outdoor temp got to 102, the peak attic temp was 96 and the peak shed temp was 116.

Even in the hottest part of the summer I can go into my attic and be no warmer than the outside temperature and often be somewhat cooler due to the convection currents provided by the soffit and ridge venting system.

I highly endorse radiant barrier decking.

I would also suggest looking into ground loop heating and cooling systems. I did not go that route due to the increased cost and have greatly regretted not biting the bullet at the time. I figure that the roi on that system would have been less than 5 years. At the time the extra 2 grand was enormous, but now it seems like such a dumb decision to pass on it since it could have brought my summer bills down by another $30-$60 per month

[lh_newbie]

By ground loop, I'm assuming you mean a geo heat pump? 2 grand extra for the equipment... then 2.5 grand for each hole they have to dig... and you need one for every ton of HVAC. I got a quote from two companies. Here were the costs, as compared to a "regular" HVAC system:

Geothermal HP - Quote #1: 21K
Geothermal HP - Quote #2: 25K
16-SEER Dual-stage HVAC: 6.6K

I went with the 16-SEER HVAC unit.

[Rane84]

First of all, hi everybody. This is my first post. I know this discussion is over a week old, but I have radiant barrier installed in my attic and I think I can help.

I agree that it is a huge energy saver. My energy bill went down by almost 25%. From what I've been told, the radiant barrier blocks 97% of the heat, which explains why the second story isn't hotter than the rest of the house, like it used to be. I'm sure that radiant barrier decking and radiant barrier paint work, but they are so much more expensive. I just bought rolls of radiant barrier online and spent under $200. I also saved on installation by installing it myself. I would suggest googleing "radiant barrier" like I did and see what comes up.

Well, that's my 2 cents.

[KantLockeMeIn]

Did you staple it up to the rafters in the attic, or lay it down on top of the insulation?

The one concern about stapling it to the rafters is that you have to really analyze your airflow in the attic. If you have soffit and ridge vents, you're safe. Otherwise you're negatively impacting the airflow and could severly shorten the life of the shingles.

If you laid it down on top of the insulation the efficiency over the first few years is good, but once dust settles it's reduced.

I'm leaning towards getting the foil stapled to the rafters. We already have soffit vents, we just need ridge vents added and the existing vents sealed. I'm just not sure how much $ that's going to set us back.