To insulate your attic, one solution is closed-cell foam. It is applied by spraying a liquid into the spaces in walls and attics. This then dries out, forming a very hard foam, which is resistant to moisture and insects. On the downside, closed-cell foam is considered to be slightly less moisture-resistant than the open-cell form, and it is expensive to have installed. With the right equipment, though, you should be able to do this job yourself.
Clear the Attic
Before you start installing the foam, clear out your attic. You will be applying the foam with a large machine, so you will need plenty of room to maneuver. After that, sweep the attic and check the walls and floors for holes and gaps. These holes and gaps could allow the foam to penetrate into the storage space of your attic and need to be repaired before you begin.
Seal off the Attic
To seal off these gaps, add a good lump of caulking mixture to the hole, or use some wood glue to form an impenetrable layer. For larger problems, simply nail some boards over the spaces to prevent the foam from escaping. When this has been done, you will be ready to apply the closed-cell foam.
Along with the foam, you should have rented a spraying suit. This looks a little like a hazard suit and runs from your feet to your head. Put your feet into the suit and pull it up, putting on the arms when you reach that point. Zip up to the neck. Pull the hood over your head and seal the mask at the front. You are now ready to spray.
Spray the Foam
Plug your spray machine into a nearby outlet. Take it up the stairs and pull it into the attic. You should be able to fit the nozzle around the side of the attic walls and pump the foam into the holes. You don't need to fill the spaces up to bursting, as the closed-cell foam will expand as it dries. When you have pushed the foam into all of the areas of the attic, leave it to dry. Remove your spraying suit and return it along with the machine.
Make sure your house stays warm with this guide: Heat Saver: Preventative HVAC Care Tips.