Insulation, to be effective, has to cover every square inch of exterior-to-interior space.
Heat seeks cold. And insulation traps air. If insulation is not trapping air in a space where heat can move toward cold, it will do just that.
On pre-drywall inspections, which are best done AFTER the insulation has been installed, I always look at how the carefully the insulation has been applied. Behind the bath tubs, does it extend all the way to the floor? Under fireplaces and bay windows, does it completely fill the cavity and does the paper backing touch the sub floor above? Are exterior gaps sealed with caulking or foam? If not, I note it and the buyers will bring it up on their builder walk through.
Here is something I see a lot.
This is the basement room under a rear sun room. That window is on an exterior wall 12' wide.
Just above the window you see the outer-most floor joist. Hard to tell from this view is that there is a space between it and the rim joist (also called frieze board) on the exterior of the house. See the holes in the joist? That space has been used for wiring. It is 8" deep.
Well, 12'x8" is about 8 cubic feet. Do they intend to insulate that space? Not doing so is the equivalent of not insulating an exterior wall between about three 8' high studs.
There are three such spaces in this particular basement. Taken together they represent a 9' wide wall without insulation. Do you think that not insulating a 9' wide wall would influence the HVAC environment in a room? Depending on which wall isn't insulated, it could influence an entire floor! Additionally, it creates a space ripe for the amplification of microbial growth (molds) which nobody wants.
There are various ways these spaces can be insulated - blown-in cellulose or Icynene - and it needs to be done!
My recommendation: On pre-drywall inspections, insist that they be done AFTER the insulation is completed. Check carefully. You might find spots that were not done!
Jay Markanich Real Estate Inspections, LLC
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560