Inspect and measure the thickness (inches) of any insulation in unfinished basement ceilings and walls, or above crawlspaces. If the crawlspace isn't ventilated, it may have insulation in the perimeter wall. If your house is relatively new, it may have insulation outside the basement or foundation walls. If so, the insulation in these spaces won't be visible. The builder or the original homeowner might be able to tell you if exterior insulation was used.