One of the downsides of do-it-yourself radiant barrier installation is that you'll probably be doing it in an uncomfortably hot attic. You can try to work mostly during the cool early morning hours or after dark, but that does not work for everyone. Fortunately, there are a couple of different ways to keep yourself cool while installing your radiant barrier during the heat of the day.
The first and simplest way is to run a sprinkler on top of your roof while you're working in the attic. The water falling on the roof will have the same cooling effect as a rainy day, and the run-off can water your flower beds at the same time!
The second way is to disconnect an air duct so it will blow cold air into your workspace. This is an old trick used by air conditioning technicians and is surprisingly simple. Here's how to do it:
First, be sure to open a window inside your home that is near a return vent. Two to four inches should be sufficient to provide what is known as "make-up air." This is air that needs to move into your home to counteract the negative pressure caused by blowing the cold area into your attic. Without it, air will be pulled from your chimney or hot water heater vent into your living space.
Next, go up to your attic and choose an air duct long enough to move around your attic to the areas you will be working. A 6-10 inch duct is ideal, although any size will work. Use wire cutters to cut both the inner and outer Panduit straps around the inner and outer linings of the duct. These are the large ties that fasten the duct to boots in the ceiling. These can be found at most home improvement stores or air conditioning supply companies, and you'll want to have a few extras around.
Then, remove the air duct and use it to blow cold air into your workspace. Move it with you as you move around the attic. If you turn the fan switch on your thermostat to "on," the fan will blow continuously.
If you do not finish in one day, simply slide the duct back over the boot without fastening it so you can easily remove it when you resume work. When you're completely done, you'll want to reattach the duct more permanently. First, apply some sealant to the boot, then pull the duct's inner lining over the boot at least a few inches. Next, fasten a new Panduit strap around the duct, and use pliers to tighten it. Then, pull down the insulation and outer lining and fasten with a second Panduit strap. Trim any excess length from the strips. Finish by piling some blown-in insulation around the boot.
You can use these methods separately, or at the same time. Either way, you'll keep your attic cool so that you can be comfortable working in it for as long as you need to while installing your radiant barrier.