Do it Yourself: [DIY] Good Crawl Space Construction (Part I)

25 September 2014

[DIY] Good Crawl Space Construction (Part I)

Posted by: wduke2@aol.com

> We are building our own home in Wyoming.

Hello (name?)

While Wyoming does not have a mandatory statewide
residential building code, you should still use the IRC
or similar code as your minimum standard. In general,
the codes are a good minimum. But, for crawl spaces,
due to the dangers they can cause, to your house, and
to your health, even code minimums are often not
good enough.

> The water table is pretty high so we opted for a 4'
> crawl space instead of a basement.

You might consider pouring a slab floor in it, and maybe
adding a course or two of block, so that it can function
as a storage space, like a low-ceiling basement. Make
sure, if it is below grade, that there is ample drainage.

> Do we need to lay down plastic and then gravel
> on all the open spaces?

Definitely the plastic...definitely definitely definitely definitely.

Without it, your crawl space can be an extremely nasty place,
that can rot out your floor and spread its nastiness up into the
air of your living space (and you family's lungs) all heating
season, when the warmth of the house (and the crawl) acts
like a chimney. The plastic should be continuous (all joints
lapped 6" and taped) up the sidewalls to the underside of
the floor. The crawlspace side walls should probably also
be insulated (details may vary). Treating the crawlspace
as a low ceiling basement is the best strategy. Vent it to
the house instead of to outdoors.

> over the gravel

Usually gravel is not necessary, and gravel on top of the
plastic may put it at risk of punctures, as also does gravel
under it if you walk on it. So, use heavy plastic (min 6mil)

> Do we need to vent it if we do?

A crawlspace needs to be vented, either to outdoor (the
traditional way which is inferior, and is not backed by any
science) or to the house interior, with the crawlspace insul-
-ated around the perimeter, like a basement (much better).

> Posted by: "Ron Johnson" l0c0l0b0@hotmail.com

> A vapor barrior is important when the water seeps
> up like that.

You are correct, and it is always important for house air quality.
Exposed ground and ground moisture can release molds, and
radon. If radon is prevalent in the area, it would also be wise
to install vented tubing under the plastic, to vent to outdoors.

> Yes, I would vent it. Because of the high water table,
> you may even have floods down there on rainy years.

If it is at risk of flooding, and there is not potential
to "drain to daylight" a sump pump should be installed.

Posted by: "Dale S" dalu@hbcomm.net

> houses can be entirely too tight in my opinion,
> but that is just me.

> Dale in the Flatlands. "Why waste time
> learning when ignorance is instantaneous."

Hi Dale;

It is just you. I recommend doing a little "learning" on
this subject. Then, I suspect, as the intelligent person
you are, that you will stop making that comment.

Briefly, let's look at the characteristics of a "tight house"
It means a house that doesn't leak moist air through walls
and other places that are inappropriate for ventilation. It
doesn't mean that the interior is unventilated. Tight houses
are house that are ventilated in healthy ways, rather than
by unhealthy leaks. Leaky houses are unhealthy houses,
because they allow warm humid air to get inside of the
walls and ceilings, to colder surfaces (below the dew
point temperature) to deposit moisture, and grow mold,
mildew, rot, and feed vermin. Radon may be another
unhealthy feature of a leaky house. Of course, having
a very drafty house, with no insulation, and an inefficient
old furnace, also may not feed mold. But, it will waste
several times more fuel to heat, and will clean out your
wallet, while contributing to damaging the environment..

> I like a little fresh air exchange during the winter instead
> of waiting for a warm day to air out the house.

Then, what you want is a "tight house" so that you do
not have to breath moldy air that comes in through leaks
in damp floors and walls. Try researching what a "tight
house" actually means, before you make comments that
could mislead others in to think things that simply are not
true. Tight houses are not unvented houses. Instead, they
are healthy ventilated houses, that don't rely on careless
inconsistent leaks, through walls and ceilings,to ventilate
them (which will inevitably create mold issues, in most
climates). Leaky homes also let in pests, through their
cracks.

Tight houses have vent systems, often with heat exchangers
to remove heat, from the out going stale air, and transfer it
to the incoming fresh air (and exchange cooling in Summer).
These HRVs (Heat Recovery Ventilators) are already
required in some code jurisdictions, along with a require-
-ment for the houses to be built tightly, and even have to
pass a blower door test. These construction standards
will likely be required in all code jurisdictions, soon.

All bathrooms and kitchens should have vents to
outdoors, to exhausts excess moisture, These vents
should be used every time that moisture producing
activities take place (showers, stove cooking, etc).
The focus of healthy houses is on moisture control.
They are not dry in Winter, and use the ventilation
systems to keep their humidity levels healthy, for
both the occupants, and the house. A house will
not be healthy if it has leaky insulated walls and
ceilings. Excess moisture should be exhausted
from the living space, via ducts rather than ending
up condensing inside of walls and ceilings, to feed
mold. A leaky house is either an unhealthy house,
or an extremely energy wasteful house, or a mix
of the two problems. Only a "tight house" (meaning
minimal uncontrolled air leakage through the insulation
envelope) can be a healthy house. Leaky walls and
ceilings lead to mold, mildew and rot. Radon should
also be dealt with, by dedicated venting, before it
enters the living space, and your breathing air.

Here is an article on "How tight is tight enough?"
As is mine, their conclusion is, for new houses,
"a house can never be too tight" and for existing
houses, a more complicated, individual, economic
formula needs to be used, in deciding what to do.

<
http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/52450/How-Much-Air-Leakage-in-Your-Home-Is-Too-Much >

Good Crawl Space Construction (Part II) to follow...........

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