Insulating a loft roof will decrease draftiness and increase energy efficiency. With a few basic tools, nearly anyone can insulate a loft’s roof in a few hours. Several options in insulation exist, from the traditional fiberglass batt to solid foam. The kind of insulation you choose may depend on whether you plan to leave the insulation exposed, or cover it with drywall or other wall material. The familiar pink fiberglass can be used to insulate a space. Always follow your local building codes and safety practices.
Measure the size of the area to be insulated. Insulation comes in rolls of batting designed to fit between studs and joists. How much you will need depends on the size of your loft. Insulation is designed to be stapled to studs or joists, and then wall or ceiling material is to be installed over the top of the insulation. If there are no exposed joists, stop. Have a professional inspect the loft, advise you, and install joists if needed.
Go to your local home improvement store, and purchase materials and any tools you may need. Save the receipt, because most stores will accept any unopened rolls of insulation for a refund or store credit.
Don protective eyewear and a filter mask. Open and unroll just one package of insulation at a time. Allow it to rest and expand for a few minutes while you lay out the tools you'll need. Allow the other rolls to rest and expand while you are working with the previous roll. Spread the drop cloth in the area where you'll begin, and set up the ladder or scaffolding on top of it, so that you can reach the highest point of the ceiling. Most people find it best to begin in a corner and proceed around the room to the right.
Install the first strip of insulation. The vapor barrier (in this case the paper backing) must always be toward the living area, so you'll be installing it with the "itchy" pink side away from the living area, toward the sky. Staple through the edges of the vapor barrier into the wood of the joists. Place staples 6 inches apart. Start by stapling the end of the strip at the top, or the highest point on the ceiling. If the ceiling is flat, just staple from one wall, across the ceiling, to the other wall. Staple down the length of the insulation strip, working on each side of the insulation strip as you proceed.
Cut off any excess batting with the utility knife. Some people find that it's easier for them if they cut the paper backing with the utility knife, then use a dull saw or a pair of scissors to cut through the pink batting. Just try to cut it evenly, whichever method you choose. Some prefer to measure and cut the insulation on the floor, then begin stapling up the cut length of insulation. Others prefer not to cut until the insulation strip is in place, to avoid cutting it too short. You may want to try both ways and see which is more convenient for you.
Repeat Steps 2 through 5 until each section between joists is filled. Open another roll of insulation a few minutes before it is needed, and allow it to expand. When finished, clean up the entire area carefully and store or dispose of any partial rolls of insulation.
Install drywall sheeting, paneling or other material over the insulation. This will keep the insulation from being exposed and make for a more finished look. Some loft dwellers may prefer to staple fabric to the joists to cover the insulation, instead of installing a ceiling material such as drywall. Applying a tightly woven and opaque fabric certainly can be quicker and less costly than having drywall installed, but local building codes and what you want the finished loft to look like will determine which choice you make.