Hi,
I live in the Boston area My house has no basement, just a
crawl space between the main floor and the ground. The batts of
insulation beneath the floor are drooping or worse so that there's
nothing between the breezy crawl space and the floor.

I had a guy come over and he suggested that instead of roll
insulation, I have foam sprayed between the joists to form a hermetic
seal.

Question: Is this a good idea? I like that fact that winter
winds will no longer whip up through my floor, but will the hermetic
seal cause a moisture problem under the house in warmer, wetter times?

Many thanks in advance.
Steve

--------------
Steve Silberberg

Read "We'll Kiss For Food"
http://www.kissforfood.com/

The best way to insulate a crawl space is to turn it into an UNVENTED
space. To do that, you will first need a vapor barrier on the floor
(especially if it is dirt) using 6 mil plastic, taped at the seems.
Masonry walls, plates, and other leak points can be sealed with 2
component expanding foam (material costs are NOT cheap). You can do
the joists above. To save money, I would recommend you have the crawl
space joists netted and filled with cellulose. Urethane foam give you
better insulating value, but the costs/benefit ratio is wacked for the
joists due to the high cost of foam.




Steve Silberberg wrote:
Hi,
I live in the Boston area My house has no basement, just a
crawl space between the main floor and the ground. The batts of
insulation beneath the floor are drooping or worse so that there's
nothing between the breezy crawl space and the floor.

I had a guy come over and he suggested that instead of roll
insulation, I have foam sprayed between the joists to form a hermetic
seal.

Question: Is this a good idea? I like that fact that winter
winds will no longer whip up through my floor, but will the hermetic
seal cause a moisture problem under the house in warmer, wetter times?

Many thanks in advance.
Steve

--------------
Steve Silberberg

Read "We'll Kiss For Food"
http://www.kissforfood.com/

Steve,

I agree with slumlord about sealing the crawlspace. See the following
link to a crawlspace article:

Crawlspace problems
http://www.contractingbusiness.com/C...S=&NI L=false

The foam may be a good idea to reduce infiltration though. It
depends on how leaky your house is and how high your utility rates are.
We have one contractor in my area that sprays Icynene foam (water
based foam, no nasty outgassing) for $1.10/sq ft. He does not remove
the old fiberglass for that price though.

Stretch

"Slumlord" wrote in message
Urethane foam give you better insulating value, but the costs/benefit
ratio is wacked for the joists due to the high cost of foam.


I'd use sheets of foam. Not far from the Boston area is Insulation
Technology in W. Bridgewater. They cut sheets from large billets and can
give you any size and thickness you want. Figure R-4 per inch

Look at the Building Science Corporation web site for more information
on crawl spaces.
If the crawl space is often damp from surface drainage or from ground
with high water table, a sealed crawl space can be difficult and
expensive. If it the environment is right for it, a sealed crawl space
is a good idea. Many building codes make that arrangement illegal and
some require an engineer's report. As I remember it, Steven Winter
Associates is in your area and specializes in this sort of problem.

TB

My only problem with using sheets of foam is the labor involved. Lots
of caulking to make sure all those seams are sealed. The two component
foam is just so easy to use (be sure to ventilate well during installation).


Edwin Pawlowski wrote:
"Slumlord" wrote in message

Urethane foam give you better insulating value, but the costs/benefit
ratio is wacked for the joists due to the high cost of foam.



I'd use sheets of foam. Not far from the Boston area is Insulation
Technology in W. Bridgewater. They cut sheets from large billets and can
give you any size and thickness you want. Figure R-4 per inch

Slumlord wrote:
My only problem with using sheets of foam is the labor involved. Lots
of caulking to make sure all those seams are sealed. The two component
foam is just so easy to use (be sure to ventilate well during
installation).


Edwin Pawlowski wrote:

"Slumlord" wrote in message

Urethane foam give you better insulating value, but the costs/benefit
ratio is wacked for the joists due to the high cost of foam.




I'd use sheets of foam. Not far from the Boston area is Insulation
Technology in W. Bridgewater. They cut sheets from large billets and
can give you any size and thickness you want. Figure R-4 per inch


Hi,
Tape is no good?
Tony

Slumlord wrote:

My only problem with using sheets of foam is the labor involved. Lots
of caulking to make sure all those seams are sealed...

If you seal up the floor above, where will the water vapor from
the imperfect vapor barrier on the ground go?

Automatic foundation vents could help, but that's more complex
and less energy-efficient.

Nick

Nick,

If foam insulation is used in the floor, the water vapor will not go
into the house, that is for sure The water vapor won't hurt the
block/rrick foundation, but it can hurt the wood floor. If the joists
amd floor is covered by foam insulation, the wood will be OK. Put a
dehumidifier in the crawlspace and drain it to the outside. If the
crawlspace is low or coners a large area. put in a fan to circulate the
dry air so the dehumidifier dries the entire crawlspace. According to
ASHRAE fundamentals, with a high water table, the ground can evaporate
10 gallons per day per 1,000 Sq. Ft. into the crawlspace with bare
dirt. If you put down 6-mil plastic, overlapped 12-inches, and
fastened to the foundation walls, that drops to about 1 quart per day
per 1000 Sq. Ft. (per Craig DeWitt, PhD, PE, RLC Engineering, Clemson
SC. www.rlcengineering.com )

Nick, automatic vents open when it is warm, which is when the outdoor
humidity levels are highest. That makes the crawlspace worse not
better. Dehumidistats installed in the crawlspace will bring on fans
hwen it is humid inside, but if it is humid outside, they never shuts
off and the crawlspace gets wetter, not drier.

Stretch

On 5 Jun 2005 17:43:29 -0700, "Stretch" wrote:

I agree with slumlord about sealing the crawlspace. See the following
link to a crawlspace article:

My crawlspace actually is sealed, but not very well. I live in across
the street from Boston Harbor and winds come whipping in over 50 MPH
gusts several times during the winter. When this happens, I can feel
the wind come up into the living room through the old hardwood floor.
So while it's sealed in theory, wind gets in pretty easily.

In the summer, winds die down and it gets humid. I haven't seen any
rot under there, but it's hard to access, so I haven't looked in a
year.

The foam may be a good idea to reduce infiltration though. It
depends on how leaky your house is and how high your utility rates are.

I'm actually in the mood to fix it "for good", so while price is a
consideration, staying warm in the winter (and not getting rot in the
summer) are my primary motivations here.

So I guess I should re-phrase the question as "Is there a reason NOT
to use the foam?" or How can I insure it won't get too humid under
there if I use foam?

Thanks for all your replies.
Steve
--------------
Steve Silberberg

Read "We'll Kiss For Food"
http://www.kissforfood.com/

I'm actually in the mood to fix it "for good", so while price is a
consideration, staying warm in the winter (and not getting rot in the
summer) are my primary motivations here.

So I guess I should re-phrase the question as "Is there a reason NOT
to use the foam?" or How can I insure it won't get too humid under
there if I use foam?

My understanding is that the way insulation combines with
water-vapor to create a problem is if there's water-vapor
that enters from the warm side, migrates through the insulation
to the cold side, hits an impermeable and/or cold barrier, and
condenses there.
If you put fiberglass under the floor, and covered it with
plastic sheet, *THAT* would cause a problem when the crawlspace
was colder than the house. If you put permeable insulation in
WITHOUT covering it with plastic, then that would cause a problem
when the floor is colder than the crawlspace. (during the
AC season.)

Since spray-applied foam *IS* the vapor barrier, you shouldn't
get any significant water migration through it, and any water
that condenses on one side or the other should be able to
get out the way it got in.

http://www.ncfi.com/Insulation/JLC_SPF_Artcle.pdf

--Goedjn