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Ventilation in crawl space Dejola 08-26-2006
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Posted by Dejola on August 26, 2006, 3:36 pm
I live in northern Westchester County, N.Y. My house is built above a
crawl space with a dirt floor. Last year I had expanding foam
insulation installed between the floor joists above the dirt floor. The
height between the dirt floor and the bottom of the floor joists varies
from a high of about five feet to a low of about six inches (the house
is built on a slope).

I have heard conflisting theories about ventilating a crawl space. One
theory says keep vents open in winter and closed in summer. That seems
counter-intuitive to me.

At one end of the house I have a window opening to the crawl space
measuring about three feet by three feet. In spring, summer and fall I
place a screen in the opening. During winter a place a solid door in
the opening.

At the other end of the house there is a small window (27 x 17). In
spring summer and fall it is covered by a screen. In winter by a solid
board.

Here's my question.

Should I cover the two aforementioned windows with the screen, or solid
covering, in the spring, summer, and fall? What about winter?

Is it necessary to cover the dirt floor with polyurethane?

Thanks.


Posted by Joseph Meehan on August 26, 2006, 3:58 pm
Dejola wrote:
> I live in northern Westchester County, N.Y. My house is built above a
> crawl space with a dirt floor. Last year I had expanding foam
> insulation installed between the floor joists above the dirt floor.
> The height between the dirt floor and the bottom of the floor joists
> varies from a high of about five feet to a low of about six inches
> (the house is built on a slope).
>
> I have heard conflisting theories about ventilating a crawl space. One
> theory says keep vents open in winter and closed in summer. That seems
> counter-intuitive to me.
>
> At one end of the house I have a window opening to the crawl space
> measuring about three feet by three feet. In spring, summer and fall I
> place a screen in the opening. During winter a place a solid door in
> the opening.
>
> At the other end of the house there is a small window (27 x 17). In
> spring summer and fall it is covered by a screen. In winter by a solid
> board.
>
> Here's my question.
>
> Should I cover the two aforementioned windows with the screen, or
> solid covering, in the spring, summer, and fall? What about winter?
>
> Is it necessary to cover the dirt floor with polyurethane?
>
> Thanks.

The reason for ventilating is to reduce moisture build up. Since
different areas will need different amounts of ventilation, you are going to
hear different responses and they all are likely right, at least where they
started from.

Personally I would want ventilation. I would never want to seal it up
even if it were in a dry area. You are not going to gain much insulation
from sealing it up, if you have insulation above the craw space. Trapping
moisture there will mean rot and mold. Of course I live in an area that is
a little moist.

As for the dirt floor, I would say the same there. Different local
conditions would give you different answers. I see no reason not to cover
it however. You got to win there.

--
Joseph Meehan

Dia duit



Posted by Phisherman on August 26, 2006, 5:21 pm
wrote:

>I live in northern Westchester County, N.Y. My house is built above a
>crawl space with a dirt floor. Last year I had expanding foam
>insulation installed between the floor joists above the dirt floor. The
>height between the dirt floor and the bottom of the floor joists varies
>from a high of about five feet to a low of about six inches (the house
>is built on a slope).
>
>I have heard conflisting theories about ventilating a crawl space. One
>theory says keep vents open in winter and closed in summer. That seems
>counter-intuitive to me.
>
>At one end of the house I have a window opening to the crawl space
>measuring about three feet by three feet. In spring, summer and fall I
>place a screen in the opening. During winter a place a solid door in
>the opening.
>
>At the other end of the house there is a small window (27 x 17). In
>spring summer and fall it is covered by a screen. In winter by a solid
>board.
>
>Here's my question.
>
>Should I cover the two aforementioned windows with the screen, or solid
>covering, in the spring, summer, and fall? What about winter?
>
>Is it necessary to cover the dirt floor with polyurethane?
>
>Thanks.


This all boils down to mold/mildew issues which grows best with warm
temperatures and moisture. I think what you have been doing makes the
most sense, especially for your location having cold winters. The
exception would be if there is excessive moisture (water puddles),
then you'd want to vent all year round. I do not believe a plastic
ground cover is necessary.

Posted by Jack on August 26, 2006, 6:38 pm

Dejola wrote:
> I live in northern Westchester County, N.Y. My house is built above a
> crawl space with a dirt floor. Last year I had expanding foam
> insulation installed between the floor joists above the dirt floor. The
> height between the dirt floor and the bottom of the floor joists varies
> from a high of about five feet to a low of about six inches (the house
> is built on a slope).
>
> I have heard conflisting theories about ventilating a crawl space. One
> theory says keep vents open in winter and closed in summer. That seems
> counter-intuitive to me.
>
> At one end of the house I have a window opening to the crawl space
> measuring about three feet by three feet. In spring, summer and fall I
> place a screen in the opening. During winter a place a solid door in
> the opening.
>
> At the other end of the house there is a small window (27 x 17). In
> spring summer and fall it is covered by a screen. In winter by a solid
> board.
>
> Here's my question.
>
> Should I cover the two aforementioned windows with the screen, or solid
> covering, in the spring, summer, and fall? What about winter?
>
> Is it necessary to cover the dirt floor with polyurethane?
>
> Thanks.


If the crawl space ground stays ,moist the I say cover with poly, If it
stays dry there is no need. But do ventilate in warm months and close
off for winter for sure. unless you live in tropics.
Jack


Posted by Dejola on August 27, 2006, 12:54 pm
Many thanks, Joseph, Phisherman, Jack, and Jay, for your responses to
my questions.
This is a very confusing issue indeed. I'm happy to say that the dirt
floor below my floor joists is cool and dry. No sign of water
infiltration.

For now I will continue to vent from spring to fall and close things up
for the winter months.

I am especially grateful, Jay, for the link to the various crawl space
studies. Thanks.


Dejola wrote:
> I live in northern Westchester County, N.Y. My house is built above a
> crawl space with a dirt floor. Last year I had expanding foam
> insulation installed between the floor joists above the dirt floor. The
> height between the dirt floor and the bottom of the floor joists varies
> from a high of about five feet to a low of about six inches (the house
> is built on a slope).
>
> I have heard conflisting theories about ventilating a crawl space. One
> theory says keep vents open in winter and closed in summer. That seems
> counter-intuitive to me.
>
> At one end of the house I have a window opening to the crawl space
> measuring about three feet by three feet. In spring, summer and fall I
> place a screen in the opening. During winter a place a solid door in
> the opening.
>
> At the other end of the house there is a small window (27 x 17). In
> spring summer and fall it is covered by a screen. In winter by a solid
> board.
>
> Here's my question.
>
> Should I cover the two aforementioned windows with the screen, or solid
> covering, in the spring, summer, and fall? What about winter?
>
> Is it necessary to cover the dirt floor with polyurethane?
>
> Thanks.


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