Wall insulation

​​Most houses and buildings have some kind of interior wall insulation. Wall insulation is one of the 'low-hanging fruit' options to reduce the draftiness in a building, keep heat down in the summer and cold out in the winter. And the most common of insulation type used for wall insulation is fiberglass insulation. This is because fiberglass insulation is inexpensive, plentiful, and easy to install. Though it is cheap and easy to install fiberglass insulation is not always the best choice for wall insulation.  Installing fiberglass involves opening up the walls, that is removing the sheet-rock finishing of a wall and putting the insulation in behind that. The batts of insulation are unfurled and stuffed into the studs that make up the wall. 

There are other choices for wall insulation besides fiberglass. One such choice is so called drill and fill insulation, which does not involve removing drywall finishing. Drill and fill insulation is a kind of blown in insulation usually made of cellulose. Cellulose is insulation made of old newspapers and treated with chemicals to make it fire resistant and unappetizing to critters and mold. The reason cellulose is a good kind of insulation for drill and fill applications is because it is made up of loose particles. These particles will bounce around while they are blown in and stack up to fill the wall cavity. Other kinds of insulation do not have this property.

Drill and fill l insulation method can be used to insulate exterior and interior walls.  It involves involves cutting three holes  in the wall large enough to accommodate  a nozzle connected to a hose. The hose then pumps in the the insulation into the wall. For buildings with siding panels made of vynl or aluminum a layer of siding is taken down and a hole bored into the the space between each wall stud, the insulation is then blasted or pumped into the space through the hole until it is completely filled.  After that the hole is closed up and the siding reinstalled.
For buildings with brick exterior walls, three holes are bored through the mortar into the area between each wall stud. The holes are at the top, middle and bottom of the wall and are covered over with new mortar once the installation is complete. 
One downside of drill and fill insulation is the potential for mold problems. Since the wall is not opened, there is no way to install a moisture barrier. This can be mitigated with insulation that is water-resistant. 

Another insulation type that is good for retrofitting insulation into walls is spray foam insulation. Spray foam insulation is good for already existing walls because it has several advantages over other kinds of insulation. It generally has a higher R-value than fiberglass batts. It can expand to accommodate the quirky spaces in homes built to different standards than newer homes today. On disadvantage of using spray foam insulation for walls is that the drywall will need to come down to have the best effect. Also during the insulation process, the building will have to be empty for 24 hours after the insulation has been installed in order to allow it time to set.