I'll soon be replacing some of the double-hung windows on the north side of a 100+ year-old farmhouse. I've read up on how to do it and have been looking through this forum. And I've watched the video on thisoldhouse.com. But I have a question: The void outside the frame where the window weights hang is huge. If I'm screwing the replacement window to the frame of the old window is that going to be strong enough to hold the window? Or should I use screws long enough to span the void and screw into wood on the other side of the void? I was also thinking of filling the void with blocks of wood and screwing them to the house framing, then attaching the new windows to them. Any thoughts or suggestions?
In the video, Tom Silva fills the window weight void with spray foam. In addition, he drills holes in the bottom of the frame and fills under the sill. I've been reading about not using expanding foam, but instead use the mildly expanding type for windows and doors. With such a large void, am I going to need multiple cans of foam per window? Or can I use the greatly expanding foam for the voids on the sides and the other type for around the window itself?
Others have written to use insulation to fill the voids, but that's not going to stop the drafts. So I'm definitely looking towards using the foam.