When you're building a house, it's not hard to add additional insulation on either side of the framing. Not terribly expensive, either. You also save on the ins

When you're building a house, it's not hard to add additional insulation on either side of the framing. Not terribly expensive, either. You also save on the installation of the furnace (and AC) because it just requires very little heating and cooling. Since insulation is low maintenance, you'll get those savings over the whole lifespan of the house. Now, if you're in an existing house, it likely doesn't make sense to tear down all your siding and drywall just to add insulation, since you're having to both demo and build.