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Comment by endisneigh | Hacker News Reader

Cheapest thing to do is remove all exterior drywall, spray foam everything and call it a day.

Spray foam is expensive. It’s considerably cheaper to install mineral wool or blown cellulose or fiberglass. And you can blow in insulation without removing the drywall.

Aren't the tops of walls capped usually? How does one blow in insulation without removing drywall?

Serious question.. I'd have thought it not practical to remove the cap on the wall (and that's assuming you can access it from the attic).

edit: "top plate" is the term I couldn't remember. substitute for cap in my comment.

> How does one blow in insulation without removing drywall?

We got blown insulation in the floors (ie between roof and floor), he drilled a 2 inch hole every two feet or so. We added our parquet floor right on top, with just some thin XPS sheets inbetween for noise.

Not sure about drywall, but I'd imagine it's similar. Easiest would be to just put some 6mm plasterboards on top to cover the holes, saves you handling each one individually.

You drill smallish holes in the drywall in each stud bay, blow the insulation in through the holes, and patch them. This is much less expensive and less messy than removing and replacing drywall. It can be done with cellulose insulation, with fiberglass (the loose fluffy kind, not batts), and possibly some other products.

Ah ok that makes sense. Thanks!

Spray foam is expensive, but it pays for itself pretty easily. You can diy drywall hanging simply enough so you’re really just paying for the foam and someone to plaster, you can paint yourself.

A cheaper option is rigid foam with canned spray foam around the perimeter.

Where do homes have "exterior drywall"?

I guess they meant demolish the interior finishes of exterior walls, spray foam the wall cavities.

That's certainly a way to retrofit an older building, but you still need a heat pump.

Ah, thanks. I get what they mean now. It doesn't sound like a good idea, but I get what they mean. :)

You really don’t. I’ve been in a house in Maine with spray foam in 20 degrees with no heat turned on and interior temp was around 65. It was pretty amazing actually.

A heat pump isn’t cost effective compared to Reno with spray foam. An average heat pump probably takes a decade minimum to pay off.

drywall on the interior of exterior-facing walls

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