In Extreme How-To’s June 2011 issue, contributing writer, Mark Clement, explains his method for replacing windows in thick, plaster walls:

“Often when I remove plaster from a room, I’m also replacing the old windows. The overall thickness of plaster walls changes from the original wall thickness. In cases such as kitchens, where I want the window sills as deep as possible, I find it’s best to craft what I call a ‘sleeve’ that fits into the rough-opening and into which the new window fits. (It should go without saying that I map all this out before I take the plaster down and order the windows.) A sleeve is basically a 1-by box, in this case made from 1-by-12 Fypon PVC moulding. It does the double duty of weathering exterior conditions and also takes paint beautifully inside.”

Mark and Theresa Clement are the hosts of MyFixitUpLife.