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Several of us are trying to reduce the summer heat build up in attics. We're exploring the use of radiant barrier material. Here's a good basic explanation of the basic science of heat gain and loss in a roof/attic system. Here's one very good example of radiant barrier supplier. Radiant Barrier Material
The Brennans did a 30'x30' attic in their two story colonial home in June 2008. This is the upper attic above all the bedrooms. The problem we were trying to solve was reducing the heat from the attic that was making the bedrooms hot from the late afternoon to well into the early hours of the morning.
We decided to use the technique of installing the material over the top of your insulation on the attic floor. We have about an R25 level of blown in insulation in the attic already. The couple of benefits of this approach are:
- Lower material costs because its a small area to cover versus installing it under the rafters.
- Slightly easier installation because there is no stapling of the material
- There are some winter energy savings with the blanket over the insulation
The main potential drawback of installing the barrier on the attic floor, is the radiant barrier will loose its effectiveness if dust settles on it. A government study showed that this could reduce its effectiveness up to 50%.
We didn't add any additional attic ventilation after determining that we have more than enough using the "1 sf of ventilation for 300 sf of attic" method.
We ordered 1000 sf of the Radiant Super R Supreme material in a 4ft roll (250ft). The cost was $150 + shipping. It arrived within 5 days. When installing it the more shiny side goes up and the less shiny is down. Theere is a rip-stop nylon threading in the material to keep it from tearing
The material needs to be installed with the shiny side facing up. We hired Dunbar Construction to install it. It took two men 4.5 hours to install it. The main difficulty is working around the vertical members of the truss. You need to cut small pieces to lay between the truss joists. This just takes time. It is something the a homeowner can do themselves depending on how complex the attic structure is.
Here are the manufacturer's installation tips.
The difference on the first day was quite remarkable. It was a sunny day with the highs in the mid-80's. So at 7pm I walked up stairs and found no discernible difference in temperature between the first and second floor. It is normally 7 - 10 degrees hotter upstairs. Typically you can feel the difference going up the stairs. This means that we will not be turning up the A/C this summer. The real benefit is just the comfort at bedtime and though the early hours of the morning. Our ceiling/rooms would stay quite hot during this time, probably because the attic insulation was keeping the ceiling hot by preventing the heat lose back into the attic. We'll keep checking this as we going forward, but the initial results are really promising.
We've now lived most of the 2008 summer with this material and it makes all the difference. There continues to be little to no difference between the first floor and second floor temperatures, even on the hottest, sunniest days. This is a real winner for the Brennans.
For August update, see A Cool Roof on our blog.
Green roofs are sprouting up (literally!) everywhere. Here are a few examples of green roofs being used locally in Michigan:
- Selecting Plants for Green Roofs MSU Extension Publication by Prof Brad Rowe from MSU. This is an excellent resource for our Michigan area. He also thought the little blue stem might work with the proper depth soil. He did have spiderwort work on a roof at MSU.
- Green Roof for Fraser School, shown below.
- Kresge Foundation When the Kresge Foundation decided to remodel their headquarters in Troy, MI, they went green (see Kresge Case Study in Green. You can see a picture of their green roof on p.8, along with a brief description. See one part of the roof, below.
- The Ford Rouge Factory has undergone extensive remodeling and is now an example of green efficiency. It boasts the largest living roof, pictured below.
Urban Rooftop Farming
Urban Rooftop Farming Will Save The World from No Impact Man blog.
- Green Roofs Offer More Than Color for the Skyline NYT Aug 28. Some good basic information on this page.