While retrofitting insulation into wall cavities is often a prohibitively large job, there are a growing number of options for getting inulated walls.
Wall batts are usually stiffened versions of the standard batt which makes the installation easier than using a floppier ceiling batt. If nonspecific batts are used, then additional support may be requried in the form of stapling a portion of each batt to the wall frame or studs.
The following Sustainable Living Tasmania video demonstrates one process for retrofitting wall insulation into a weatherboard house. Waterworks Valley Community also have a useful document with recommendations and instructi ons for retrofitting wall insualtion. Click Here.