insulating only part of attic

[Heathcliff]

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

 

[scott21230]

What you say is true to an extent since heat loss is a function of the
area times the R-value, it's perfectly fine to inculate part of the
attic better. However, a better way to do it would be to put in joists
going cross the direction of the existing ones, then insulate that
whole area, then put the floor on top of that, effectively raising the
floor.

 

[Guest]

What you say is true...

Who's "you"?

since heat loss is a function of the area times the R-value,

No. Heat loss is proportional to ared DIVIDED BY R-value.

Better to inculate all of it.

Nick

 

[Goedjn]

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.

 

[Phisherman]

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

The floor itself offers some insulation. The insulation property is a
factor of material, coverage area, and thickness. You could add a
thick underlayment and carpet to the floor. Often you can find used
carpeting and underlayment for free.

 

[Pat]

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

Something to think about. Part of you house is probably warmer than
others. Often people want their livingrooms warmer than their spare
bedrooms, etc. If that's the case, it might help to insulate over the
warmer areas if you're only going to insulate part of it. Also, I
would stop at wall lines to provide insulation over an entire room, not
stop in the middle of a room.

I'm sure someone can produce tons of formulas saying it doesn't matter,
but I would be that it does and do it that way.

 

[buffalobill]

since household junk expands into every available cavity of the home
and forces its way into a second garage, nip it in the bud right now
with a garage sale.
then take the money and remodel the fully insulated new attic space.

 

[Noozer]

If I cover 80% of the holes in the bottom of a sieve, does that mean it will
hold 20% of it's water?

 

[Heathcliff]

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.

I like the foam boards covered by plywood idea. That would have some
advantages over raising the floor with cross-joists, which would reduce
clearance (at a premium) and would be awkward at the access point
(access by stairs). How thick does the plywood have to be to stand up
to light foot traffic, when on top of the foam board? Does it matter if
the foam board is the expanded kind or the extruded kind (i.e. is one
kind stronger)? thanks, -- H

 

[Art Todesco]

I like the foam boards covered by plywood idea. That would have some
advantages over raising the floor with cross-joists, which would reduce
clearance (at a premium) and would be awkward at the access point
(access by stairs). How thick does the plywood have to be to stand up
to light foot traffic, when on top of the foam board? Does it matter if
the foam board is the expanded kind or the extruded kind (i.e. is one
kind stronger)? thanks, --

I did a similar thing. I used 2 3/4"
sheets of foam board, one on top of the
other, in a 2' wide path going down the
center of the attic at the highest point.
On top of that, I put 1/2"+ plywood that
is used for sheathing (not OSB or
the like). The truss/joists are at 2'
centers. It is a bit springy, however, for
storing boxes, etc. it works quite good.
I only have about 3 1/2' of height.