Subscribe or Renew Membership Subscribe Renew

Is Adding More Joist Space Worth It To Add More Insulation?

1chipster's picture

I am planning on replacing very old fiberglass batts with mineral wool batts and the joist spaces are 8" deep.

Is it worth it to add 2' more to these spaces in order to increase the amount of insulation I can put in there?

I have read that after a point, the amount of insulation added has diminishing returns.  Also, if this is ad-

visable, what is the best way to go about doing this? Thanks

Where do you live?  How old (post #206899, reply #1 of 5)

Where do you live?  How old is the house?

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

The house is a 2 family, (post #206899, reply #2 of 5)

The house is a 2 family, built in 1930 and I live in the greater Boston, MA area. I'd really like to maximize

the insulation in the house. Thanks

Radiant Barrier (post #206899, reply #3 of 5)

You could always add radiant barrier to help your existing insulation. It costs less, is a lot easier to install and you will notice the difference right away. Stapling it under your rafters reflects the radiant heat back out in the summer months while laying it over your floor joists (and existing insulation) keeps your heat in during the winter months. Definitely your best return on your investment.

BRANDI (post #206899, reply #4 of 5)

You have succeeded in posting several messages pertaining to insulation with this link to a radiant barrier (sic) company.

If you are an employee of the company, please either explain the system in something more than the usual and give us the science behind it.

If you're a spammer, stay away.

If you just found the above company and don't know diddley about the subject, then please say so.


Spreading disinformation and / or inserting non paid for links is not welcome here.


A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


If these are ceiling joists (post #206899, reply #5 of 5)

If these are ceiling joists in the attic, you don't want to add wood to them for insulation. Minimum recommended attic insulation is R-40 or roughly the equivalent of 12" of fiberglass batts. The joists themselves have little insulation value. Typically, the joists are filled and a second layer of batts is laid perpendicular across the joists. You won't reach diminishing returns until you get around 20" since the weight of the material will compress. Insulation itself doesn't insulate, it captures air and that's what provides the insulation, it needs to expand to full loft, not be tucked in or compressed.

Beat it to fit / Paint it to match