Insulate below a floor or not?

Posted by Steve Barker LT on November 10, 2006, 10:28 pm

I've mentioned in other posts about our 135 yr old house we're working on.
At this point I'm rebuilding the floor on the lower level. This house
basically sits on the ground. My new joists will be about 4" off the dirt.
I've been through the "to vent or not to vent" threads about crawl spaces.
I've decided not to ventilate. It's been closed for 135 years, it can keep
being closed. My question is, IS there any reason why I shouldn't fill this
space will insulation? Whether it be fiberglass or blown cellulose? In a
few days I'll have all new joists and proper center support and will
probably insulate unless there's some reason I shouldn't.

thanks!

--
Steve Barker

Posted by RicodJour on November 10, 2006, 11:05 pm

Steve Barker LT wrote:

> I've mentioned in other posts about our 135 yr old house we're working on.
> At this point I'm rebuilding the floor on the lower level. This house
> basically sits on the ground. My new joists will be about 4" off the dirt.
> I've been through the "to vent or not to vent" threads about crawl spaces.
> I've decided not to ventilate. It's been closed for 135 years, it can keep
> being closed. My question is, IS there any reason why I shouldn't fill this
> space will insulation? Whether it be fiberglass or blown cellulose? In a
> few days I'll have all new joists and proper center support and will
> probably insulate unless there's some reason I shouldn't.

4"? Did you use treated lumber for everything within 18" of grade? I
would never stuff the space entirely with insulation no matter how
tempting that might be. It would end up being a perfect nesting place
for vermin, you wouldn't be able to inspect underneath to make sure
everything is copasetic, and it'd end up being a mold breeding ground.
Rigid insulation would be a good choice in your situation. Cut it to
fit with some expanding foam as needed to seal the edges. It's a
little more expensive, but the higher R-value will give you whatever
level of insulation you want and keep it within the depth of the joist
bay.

R

Posted by longshot on November 11, 2006, 6:17 am

> Steve Barker LT wrote:

>> I've mentioned in other posts about our 135 yr old house we're working
>> on.
>> At this point I'm rebuilding the floor on the lower level. This house
>> basically sits on the ground. My new joists will be about 4" off the
>> dirt.
>> I've been through the "to vent or not to vent" threads about crawl
>> spaces.
>> I've decided not to ventilate. It's been closed for 135 years, it can
>> keep
>> being closed. My question is, IS there any reason why I shouldn't fill
>> this
>> space will insulation? Whether it be fiberglass or blown cellulose? In
>> a
>> few days I'll have all new joists and proper center support and will
>> probably insulate unless there's some reason I shouldn't.

use KRAFT FACE R-19 between the joists

Posted by M on November 11, 2006, 7:47 am

> 4"? Did you use treated lumber for everything within 18" of grade? I
> would never stuff the space entirely with insulation no matter how
> tempting that might be. It would end up being a perfect nesting place
> for vermin, you wouldn't be able to inspect underneath to make sure
> everything is copasetic, and it'd end up being a mold breeding ground.
> Rigid insulation would be a good choice in your situation. Cut it to
> fit with some expanding foam as needed to seal the edges. It's a
> little more expensive, but the higher R-value will give you whatever
> level of insulation you want and keep it within the depth of the joist
> bay.
> R

hmmm... I too am doing something similar. I am between 12" and 24" above
grade however. I was thinking of making a 2" foam skirt around the
perimeter and make it removable so as to let it breath in warmer months. I
was also going to stucco the exterior faces. You mentioned solid
insulation. Would that be foam or lumber?

Posted by Matt Whiting on November 11, 2006, 8:45 am

Steve Barker LT wrote:

Insulating between the joists would be a good idea, using rigid foam
board, but you'd have to do so before you install the flooring as it
sounds like you don't have clearance to work under the floor.

If you are talking about just blowing insulation on top of the dirt and
up under the floor, I'd be hesitant about that. I'd fear that this
would just provide a path to conduct ground moiste up around your floor
joists.

Personally, I'd insulate between the studs and then ventilate the space
under the joists. Then again, if you live in the desert of AZ, never
mind the ventilation.

Matt

Similar Threads	Posted
Insulate under floating floor below grade?	December 11, 2006, 4:14 pm
How to Insulate Front Door	January 20, 2009, 1:08 pm
What is the best way, what material to use to thermally insulate 12 meters of sewer pipe	October 14, 2007, 8:01 pm
Building stud partition onto tile floor with under floor heating	July 12, 2006, 2:54 pm
Learn how floor tile patterns affect the look of your new floor.	October 11, 2007, 3:39 pm
Nailing floor with glue versus screwing floor without glue--which is better?	October 3, 2006, 9:36 am
floor	January 27, 2007, 12:46 pm
New concrete floor	November 17, 2006, 4:08 pm
Raising a floor	November 30, 2006, 1:05 pm
Floor estimate help.	December 24, 2006, 1:38 am