Radiant Barrier

[Lomag]

I'm thinking to install radiant barrier in our attic, will this affect the solar panels in anyway? I read the barrier makes the shingles around 5 F hotter so there maybe some extra heat around the panels but minimal. I wouldn't think there'd be any effect but I figure I'd ask(?)

When the panels were installed our attic temp fell a bit, I think it was around 5-10 F, since they cover a good portion of our front roof. I'd like to install the radiant barrier along the entire roof in the attic and on both gable ends which should help dramatically lower the attic temp and hence our 2nd floor temp. More of a comfort issue in the summer time. A buddy of mine recently did it and said it's cheap too, so I figure why not?

[SunEagle]

I'm thinking to install radiant barrier in our attic, will this affect the solar panels in anyway? I read the barrier makes the shingles around 5 F hotter so there maybe some extra heat around the panels but minimal. I wouldn't think there'd be any effect but I figure I'd ask(?)

When the panels were installed our attic temp fell a bit, I think it was around 5-10 F, since they cover a good portion of our front roof. I'd like to install the radiant barrier along the entire roof in the attic and on both gable ends which should help dramatically lower the attic temp and hence our 2nd floor temp. More of a comfort issue in the summer time. A buddy of mine recently did it and said it's cheap too, so I figure why not?

I can't answer your question about how a radiant barrier affects your solar panels but I can tell you that it does drop the temperature in my attic by at least 30 F. My barrier did not go to the peak of the roof so I needed to install vent fans to get rid of the heat that builds up at the peak.

Some people use roof vents or roof mounted fans but I did not want to penetrated the roof so I mounted two in the openings on the side of the house near the peak. They were about 16 inch in diameter and ran off of a 10 watt solar panel that I mounted on the roof. They only run when a thermostat in the motor circuit gets to 75 F but they do get rid of the heat. Got them at Costco for about $215 each but I have seen them in other places for less.

[Lomag]

WOW a 30 degree drop? Nice! I'm expecting some sort of drop but don't know how much. The previous owners of our house put up a new roof recently and thankfully they had a ridge vent installed.

I'm guessing it won't affect the panels. It'll only cost like 300 bucks and I think it'll make a world of difference in the heat level up there.

[SunEagle]

WOW a 30 degree drop? Nice! I'm expecting some sort of drop but don't know how much. The previous owners of our house put up a new roof recently and thankfully they had a ridge vent installed.

I'm guessing it won't affect the panels. It'll only cost like 300 bucks and I think it'll make a world of difference in the heat level up there.

As long as the heat has somewhere to go it won't build up in the attic and migrate to the rooms below.

I would see temperatures > 110 F in the summer before I put in the barrier. Now it stays in the low 80's as long as the fan is doing it's job. I also blew in more insulation which really keeps the temp down in the house so my AC doesn't run as much as it use to.

[inetdog]

I'm thinking to install radiant barrier in our attic, will this affect the solar panels in anyway? I read the barrier makes the shingles around 5 F hotter so there maybe some extra heat around the panels but minimal. I wouldn't think there'd be any effect but I figure I'd ask(?)

The radiant barrier in the roof around the panels may increase the temperature of the roof, but the radiant barrier under the panels cannot cause the roof under the panels to get any hotter than the air temperature in the space in between. The effect, if any, should be small.

Remember that the greatest effect will come if you install the radiant barrier in two layers, with spacing, inside each rafter cavity. Make sure you provide the recommended ventilation at top and bottom so that you do not create a moisture problem under the roof. The effect of heated air rising between the radiant barrier layers will be minimized if you have a ridge vent to exhaust that hot air more or less directly.

[peakbagger]

One comment is that "vent a ridge" systems are far more effective than gable end vents to ventilate a roof. I used to have a gable end fan and my attic temps were higher until I installe passive roof vents. I need gable end vents anyhow as in the winter the vent a ridge gets covered with snow.

The other caveat is that most builders install far fewer soffit vents than needed for good roof insulation. Generally a continous 4" wide screened slot the entire lenght of the roof is needed. The cut in cricular or rectagular vents just dont flow enough air. The other hassle is that many folks block air flow with insulation down near the intersection of the roof and the wall. You can buy "proper vents to slip down in this spot to keep the air flow going.

[cyph]

I installed reflective barriers but not directly under the panels since the panels already act as reflective barriers. My attic is now 5-10 degrees warmer than the interior around 4pm when it's hottest. It never goes over 95 degrees when the weather is in the 80's. I also use an attic fan I only turn on around 7pm when the outside temperature is cooler. It doesn't seem to make a difference in the day time. However, it does work at night to help cool down the attic faster than just letting it cool on its own.

[inetdog]

I installed reflective barriers but not directly under the panels since the panels already act as reflective barriers. My attic is now 5-10 degrees warmer than the interior around 4pm when it's hottest. It never goes over 95 degrees when the weather is in the 80's. I also use an attic fan I only turn on around 7pm when the outside temperature is cooler. It doesn't seem to make a difference in the day time. However, it does work at night to help cool down the attic faster than just letting it cool on its own.

If it gets comfortably cool outside at night, consider using a whole house fan to draw cool outside air into the house through your windows at night while discharging it into the attic and cooling the attic that way. Larger than normal exit vents from the attic are required, of course.

[russ]

Roof insulation is a good thing - in warm climates it should be at least R49 - that is about 150mm of Dow XPS foam.