OT: Radiant Barrier in Attic

Funny you should ask because I was just looking into this. I read somewhere that it does cause the shingles to bake and that a roofer had noticed that over areas with the radiant barrier the shingle were worse than the areas that didn't have it.

As to how much it really helps, I don't know but would sure like to find out. If it would knock 10 or more degrees off the attic temp then it might be a good thing but otherwise it seems like it would be a waste.

Save the money and use it for an attic fan.

We installed the stuff after the house was built and couldn't see a significant difference.

It would work esp. well if you could install it 3 1/2 inches above the present roof. Always wanted to try that.

In Texas there's no such thing as *too much* insulation.

If you can get them to do it, have them install batt insulation between the rafters as well as whatever you're having put over the joists.

You'd be shocked at the summertime temperature in an attic with only joist-covering insulation.

BTW, don't forget to vent the attic...

I used some of the foil backed Kraft paper in a storage building/workshop along with ridge vents and it made a significant difference. Even in mid-summer in Houston you could tolerate it for a little while and a small window unit had no problem keeping it comfortable - even with no insulation. I'm hoping to build a beach house next year and plan to use it there.

With powered blowers at each end. One to suck, one to blow if the spaces are large.

Gunner, one time alarm installer in the desert.....gack...

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

We used turbines in my parents roof. They were very happy. Karl

With a shingle roof, it may not help much...

I put metal roofing on my house, and later on my (new) garage/shop. I installed a radiant barrier on the top of the sheathing, attached 1x purlins on top of that, and screwed down the (brick-red) roofing to the purlins. In the sun, the dark metal gets HOT!, as you would expect. The radiant heat strikes the reflective surface below, and is reflected back to the roofing. The ribs in the roofing help channel the heated air up and out of the roof. Direct contact of the roofing with the barrier would prevent it from working (as well as trap small amounts of moisture, which is a "bad thing" for metal), so the 3/4" air space is critical. Of course, this makes the roofing hotter, hence the caution about using it with composition roofing. Foil laminated to the *underside* of OSB would help very little, except to make the OSB real hot.

In my attic, the underside of the sheathing is no hotter than the air temp in there. With the old shingle roof, the underside was really hot, and was the main source of the heat build-up in the attic. I will never build another roof with anything other than metal. It has clean lines, sheds water & ice better, lasts a lifetime, is lighter in weight, and can be had in lengths that allow it to go from ridge to eaves in one piece.

As others have mentioned, adequate ventilation in the attic is a must, no matter what other aids you use.

BTW, I'm in South Carolina, where the heat is pretty intense in the summer.

Joe

Oh, yeah, I got my barrier from (I th> Guys, I am having a new house built in central Texas and one of the options

Joe wrote: With a shingle roof, it may not help much...

Joe, what type of metal roofing did you use? I'm in SC, lower Berkeley county, and considering the radiant back OSB when my HUGO roof needs replacing. I've got old warehouse siding metal on my shed but I know swmbo would kill me if I tried to put it on the house. Joe

What type? Hmmm... I bought it from Metal Building Supply (in the upstate - I live in Pickens Co, but they have other locations, as well). When I reroofed the house, there was precious little (zip) in the way of metal roofing options. Couldn't even find anyone who knew how to install it for me, so I figured out how to do it myself. MBS sells materials for putting up entire metal buildings; there are lots of other suppliers now, specializing in metal roofing. Despite being intended for metal bldgs, it looks *really* good. I also used it in forest green to reroof a small cabin I own

- I was their first-ever customer for the green color (the house & shop are a brick-red). The important parameters are: thickness (I think mine is 26 ga.), galvanizing, and the quality of the paint finish. One nice feature of my roof is that the sheets can span 5 ft. between supports, since that is typical of metal building design. Makes for a fairly rigid roof, although I spaced the purlins about 30 inches, or so - it's been 9 years, so I can't remember exactly. Now there are lots of options in the profile of the metal; some even simulate standing-seam roofing. Check with some of your local suppliers - the ones contractors use, not the yuppie "superstores" (although they offer some styles, too).

If you want more details, you can email me off-list (note correct address, below). I find that, even now, many contractors don't understand the basic function of radiant barriers. I even fabricated my own vented ridge cap for my 2-story shop (no special tools required), since there was nothing available on the market.

A couple of other points: The purlin spacing should be closer if you are in a hurricane-prone area (more fasteners). Use the screws the manufacturer recommends. Buy a *good*, strong power driver (not a regular drywall gun) - mine is a Milwaukee, and drives anything.

Joe (use: jdella-ferammmcom to reply)

Joe Gorman wrote:

The house I grew up in (the one I was talking about in the above message) is a standing seam metal roof. Probably about 80 years old. It's in Summerville, SC. The only damage to it in Hugo was one corner got bent up a few inches. The only maintenance was painting it twice in 40 years. The carriage house (studio above frame shop below) roof is steel also. No damage from Hugo either. If I ever build or reroof a house it will be metal probably steel. Karl