On 9 Oct 2006 13:02:23 -0700, "Heathcliff"
wrote:

Thinking about adding insulation to the attic, which is floored over.
The easiest thing would be to put insulation on top of the flooring.
However, I need part of the space up there for storage. If, say, I put
insulation all around except for an area in the middle, would that
eliminate most of the gains of insulation? In other words, if I leave
20% of the space uninsulated, do I cut heat loss by 80% (of what I
would by insulating all over)? -- H

Right now the 20% of the floor that you're going to not-cover
looses 20 units of heat, and the 80% that you are going to
cover looses 80 units of heat. If you double the insulation
on the 80%, you halve the heat loss there, so you'll
be loosing 20 + 80/2 = 60 units of heat. Still worth doing,
but:

Put foam insulation covered by plywood over the part you want
weight/traffic on, and use cheaper insulation (of your choice)
everywhere else.