Radiant Barrier?

[ziggy29]

I think it's too late in the season in Texas to install radiant barrier.

There's a company that advertises on Austin radio that they will do radiant barrier jobs for half price through the end of May. A couple of thoughts on that:

(1) I suspect what's really happening isn't a half-price job before June, but rather a double-price job during the summer months.

(2) Given the mid-July weather Texas has had over the last week, it really must suck to be charging springtime prices for summertime conditions up in the attic for those guys...

 

[Nords]

A somewhat off the wall, roof really, observation. If you have a roof largely covered with solar cell panels, presumably on brackets, then the roof is mostly in a shade. Solar panels not being highly efficient electrical generators, maybe 20% efficient, generate a good bit of heat. This heat coupled with with air space between it (them) and the roof set up some nice convective air flow.
With solar panels on standoffs, the roof is mostly shaded, the attic temperatures should be near outdoor ambient temperature.
An interesting test may be to measure temperature in the air space between solar panels and roof, attic temperature and temps between any radiant barrier and roof underside.

For anyone tempted to try this, I'd recommend not allowing any gaps between panels that could allow sunlight to hit the roof. I suspect that the sun does just fine at heating our uncovered 10% of the roof directly and allowing conduction to heat the remaining 90%...

We just put radiant foil in our south wall but we don't really have enough hot-weather data to claim victory yet. If that doesn't do the trick then the next shading step would be mounting south-facing panels on a west-facing roof, which is gonna be expensive.

 

[HFWR]

Well, in a fit of bassakwardness, I decided to proceed with putting radiant barrier in my attic. I can't get a roofer in a timely manner to redo the ridge vents, and I want to do some tidying up in the attic before blowing in more insulation. Since I'll be back to w*rk soon, and since Lowe's has been sending me 20% off coupons, I bought a 4' x 25' roll today, and installed it without much fanfare, aside from the 110 degree attic temperature...

It will take three more of the aforementioned rolls to complete the "living" wing of the house. The "bedroom" wing has more obstructions, so I think I'll buy 2' wide rolls for that.

It'll be interesting to see how this affects the attic temp. Max temp today was 136...

And I'll be doing any future work very early in the morn!

 

[Leonidas]

Since I'll be back to w*rk soon, and since Lowe's has been sending me 20% off coupons, I bought a 4' x 25' roll today,

Was the brand name Reflectix? Just checking to see if your Lowe's is selling the same stuff. Buying a couple of rolls is on my list of crap to do tomorrow.

and installed it without much fanfare, aside from the 110 degree attic temperature...

Only 110? Did you go up there at 4 AM?

 

[HFWR]

Was the brand name Reflectix? Just checking to see if your Lowe's is selling the same stuff. Buying a couple of rolls is on my list of crap to do tomorrow. Only 110? Did you go up there at 4 AM?

Yes, Reflectix. About $50 for the 4' wide roll. Basically, a roll of bubble wrap with foil on both sides.

It was 115 in the attic at 7:30PM when I started, and was all the way down to 100 by 8:30. This morning it was 80-something...