Options for insulating the walls of an existing home?

[jeff47]

3. Depends on where you live and just how much you want to take off the outside.

Your siding attaches to sheathing (usually plywood or OSB today, planks on older homes). If you want to replace that, your options are basically anything because the wall will be open. Alternatively if you're already doing a lot of improvements, you may want to go ahead and redo the interior walls, especially if you are good at drywall. If the old windows use counterweights, be sure to open 'em up and insulate the weight pocket.

If you're not going to open the wall, you are correct in your two options. Though I wouldn't recommend normal DIY'ers do blown-in cellulose in a wall that is not opened. It's very tricky to get it to pack properly on a closed wall. It's much harder than blowing it into your attic. In fact, if your house was built after about 1930-ish and seems uninsulated, it is likely that your walls are insulated with cellulose that wasn't packed properly.

Which one I'd personally pick would depend on the climate where I live. In areas like the Northeast, northern Michigan, the Dakotas, Montana, etc. I'd pop for foam. Warmer areas won't receive as much of a benefit from foam, since it doesn't get as cold. Alternatively, if my heat source was very expensive, foam might be worth it.

Foam on the outside would be the quickest and easiest, but unless you live in the Southwest it's not going to be much of an improvement. Also it's not really going to stop air infiltration itself - the joints between the panels won't stop air. The housewrap will though.

Long story short - get some bids so you really know what the difference in cost is, so you can calculate ROI.