Download Moisture NC Version - Keystone Building Group

Crawlspace Moisture Management
The smart and scientific way to manage moisture in the crawlspace.
NC Building Code:
Wall Vented Crawl Spaces


R408.1.1. Foundation vent sizing.
The minimum net area of ventilation openings shall be
not less than 1 square foot for each 150 square feet of
crawl space ground area.
1500 Square Foot Home
Wall Vented Crawlspaces

Natural ventilation works under these
conditions:
No outside groundwater or water intrusion.
 Good height of airflow. Natural crossventilation of air. No blockages.
 Crawlspace stays reasonably warm.

Moisture in Crawlspace
Understanding dynamics of
moisture in a crawlspace is
not so simple.
What is healthy for a
crawlspace?
Most research out today agrees wood
moisture for a substructure should be
10%-16%.
12% is generally ideal for wood.
Outside Air Supports This
Equilibrium moisture content (EMC) of wood exposed to outdoor atmosphere:
State - City
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
NCCharlotte
12.8
11.9
12.0
11.4
12.4
12.8
13.1
13.8
12.8
13.0
12.9
12.8
SCCharleston
13.3
12.6
12.5
12.4
12.8
13.5
14.1
14.6
14.5
13.7
13.2
13.2
VARichmond
13.2
12.5
12.0
11.3
12.1
12.4
13.0
13.7
13.8
13.5
12.8
13.0
TNKnoxville
14.2
13.4
12.8
12.4
13.7
14.0
14.4
14.7
14.7
14.1
14.0
14.4
MABoston
11.8
11.6
11.9
11.7
12.2
12.1
11.9
12.5
13.1
12.8
12.6
12.2
OK –
Oklahoma City
13.2
12.9
12.2
12.1
13.4
13.1
11.7
11.8
12.9
12.3
12.8
13.2
CASan Francisco
15.2
14.7
14.0
13.6
13.8
13.6
13.9
14.3
13.6
13.4
14.3
15.1
Source: William Simpson, Research Forest Products
Technologist
Forest Products Laboratory, Madison, Wisconsin
Wood Moisture stays fairly consistent in most geographic climates in U.S.
Why is wood moisture a better
judge of moisture levels?



Humidity sensors vary greatly in accuracy
Humidity can vary greatly with just a few
degrees of temperature
Wood moisture directly relates to humidity
levels in a measured area
Wood Moisture Table
Dependence of equilibrium moisture content (EMC) of wood on relative
humidity (RH) and temperature:
Temp
(F)
10%
RH
20%
RH
30%
RH
40%
RH
50%
RH
60%
RH
70%
RH
80%
RH
90%
RH
30
2.6
4.6
6.3
7.9
9.5
11.3
13.5
16.5
21.0
50
2.6
4.6
6.3
7.9
9.5
11.2
13.4
16.4
20.9
70
2.5
4.5
6.2
7.7
9.2
11.0
13.1
16.0
20.5
90
2.3
4.3
5.9
7.4
8.9
10.5
12.6
15.4
19.8
110
2.2
4.0
5.6
7.0
8.4
10.0
12.0
14.7
19.1
130
2.0
3.7
5.2
6.6
7.9
9.4
11.3
14.0
18.2
150
1.8
3.4
4.8
6.1
7.4
8.8
10.6
13.1
17.2
Source: William Simpson, Research Forest Products
Technologist
Forest Products Laboratory, Madison, Wisconsin
Understand Moisture Problem

Which has more moisture?
95 Degrees
45% Relative Humidity
70 Degrees
90% Relative Humidity
Understand Moisture Problem


Dew point is a better measurement of moisture.
In this illustration, there is actually more moisture outside than in
the crawlspace.
67 Degree Dew Point
70 Degree Dew Point
95 Degrees
45% Relative Humidity
70 Degrees
90% Relative Humidity
Why Dew Point Matters

Dew point is a measurement of
the moisture in the air




Humidity levels can trick you.
Humidity is relative to the temperature
Once you get to 100% relative
humidity at a given temperature
the capacity of moisture in the air
has been reached
This is when you get condensation.
Why Dew Point Matters


The warmer air is the more water
it can hold.
For example take and air mass
the size of an average 2000 sq
foot crawlspace that is 3 feet high.


That crawlspace at 68 degrees can
hold around 185 cubic inches of
water in the air before it is full of
water.
The same amount of air at 95
degrees can hold up to around 420
cubic inches of water before it is full.
Why Dew Point Matters
Think about it?
95 degree air can hold over twice
as much water as 68 degree air.
Crawlspace Moisture

What is causing the moisture?
Water intrusion
 Ground moisture
 Limited height and airflow
blockage
 Decks and porches
 HVAC systems
 Sprinkler systems

Crawlspace Moisture

What is causing the moisture?

Water intrusion
 Water
intrusion problems are
always better solved on the outside
of the home but often you have to
use an interior drain system.
 Whenever you use an interior
system you will have moisture you
will have to deal with.
Crawlspace Moisture

What is causing the moisture?

Ground moisture
 This
occurs when the ground of the
house has a high water table, the
outside dirt is higher or the lot
naturally allows water to push back
up.
 It is hard to ever waterproof this
problem outside of the crawlspace
and often this water has to be
managed rather than eliminated.
Crawlspace Moisture

What is causing the moisture?

Limited height and airflow
blockage
HVAC is cooling
this area and its
limited size and
height allows it to
cool and handle
very little moisture.
Crawlspace Moisture

What is causing the moisture?

Decks and porches

Decks and porches allow water under
them. When the sun hits them the air
underneath heats up and allows moisture
to evaporate. When this air drifts back into
a crawlspace and meets colder air, it
immediately condenses allowing moisture
to form.

These decks also contribute to air
blockage.
Crawlspace Moisture

What is causing the moisture?

HVAC systems
 This
cools the crawlspace to a
lower than normal level which as
discussed earlier doesn’t allow the
air to handle water in volumes
necessary.
Crawlspace Moisture

What is causing the moisture?

Sprinkler systems
 Improperly
installed sprinkler
systems pour water against the
foundation allowing water intrusion
and makes for higher levels of
moisture around vents in house.
Dealing with Problems

What are the options?
Vapor Barrier
 Temperature sensitive vents
 Fans on humidistat or timer
 Closed crawlspace with dehumidifier
 Conditioned crawlspace with HVAC
 Controlled ventilation system

Dealing with Problems
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Vapor Barrier Benefit


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Slows evaporation of moisture from ground
Listed in NC Code (Section R408 – Wall
Vented Crawl Spaces)
R408.2. Ground vapor retarder.

Requires full coverage ground vapor retarders for all
wall vented crawl spaces. Wall vented crawl spaces
shall be protected from water entry by the
evaporation of water from the ground surface. . . .
Dealing with Problems

What are the options?

Temperature sensitive vents
 These vents are designed to save
energy and protect pipes. They were
never designed to dry a house as their
primary function.
 They start to close up during the
driest times outside and open during
the highest humidity weather.
Dealing with Problems

What are the options?

Fans on humidistat
This may be the worst thing you can do
on an air conditioned house. You
cannot put a wetter air mass into a
crawlspace and improve it.
For example

How a dehumidifier works.
A dehumidifier pulls air into a refrigerated coil
which causes the air to cool.
 This air is now colder and the moisture must
condense out of the air.
 Then the air exits the dehumidifier after the
motor heats the air back up making it a lower
humidity

Building your own
dehumidifier for the outdoors

When you pull air with a higher dew point across a surface colder
than the dew point the surface acts like a coil in a dehumidifier .
The fan running is working to help pull that air across the surface
creating a dehumidifier for the outdoors.
67 Degree Dew Point
73 Degree Dew Point
95 Degrees
50% Relative Humidity
70 Degrees
90% Relative Humidity
Dealing with Problems

What are the options?

Closed crawlspace with dehumidifier
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No fresh air (which can just as easily lead to air quality
issues)
Dehumidifiers are costly to operate.
The humidistats in dehumidifiers are not consistent .
Radon concerns
Gas leaks (If gas system is improperly vented)
Can overdry the wood in a home.
Dealing with Problems

What are the options?

Conditioned crawlspace with HVAC






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No fresh air
Air must return to the cold air return or be pushed out of
the house to dehumidify the air
HVAC system must be working to dry the house
Radon concerns
Gas leaks/combustion problems
Many cases of problems with new construction
Cold air from A/C being pumped into crawlspace allows
for a cooler environment meaning air can hold less
moisture.
Dealing with Problems

What are the options?

Controlled Ventilation System
 Use
the outside air only when it will improve the
conditions in a crawlspace.
 Enhance cross ventilation through use of fans.
 Can integrate a dehumidifier as needed.
Cross Ventilation is Key



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Section R408.1.1 of NC Building Code lists minimum
number of vent openings.
“Exception: The total area of ventilation openings may
be reduced to 1/1,500 of the crawl space ground area
where the required openings are placed so as to provide
cross-ventilation of the crawlspace. The installation of
operable louvers shall not be prohibited.”
Fewer vent openings are allowed with
cross ventilation.
Air movement is critical to reduce moisture.
Crawlspace Environment


Crawlspaces need to be
kept in balance for a
healthy home.
Crawlspaces need
PROPER ventilation.
How A Controlled Ventilation
System Works


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Controls use sensors to
measure dew point inside
and outside the crawlspace.
The system knows when to
ventilate to improve
conditions.
It is completely automatic
and adjusts for temperature
conditions and time of year.
This conserves energy by
not pumping extreme
temperatures into the
crawlspace.
Fans


Fans create a cross
circulation of natural
air flow
Fans are extremely
quiet
Vent
opening
fans are
either intake
or exhaust.
UL AC-Fan
DC-Based Fan
Joist-mounted
fans are
mounted
internally for
“dead corner”
ventilation.
Dehumidifier Option



In very humid climates in certain homes, the crawlspace
may need supplemental drying.
A controlled ventilation system can incorporate the use
of a dehumidifier when fans alone are not enough.
Energy efficient use of a dehumidifier by only using
when absolutely necessary.
Crawlspace Environment

The principle of a controlled
ventilation system is very
simple. Use the outside air
when it is drier and it will
improve the crawlspace
conditions. If a house is
getting too much moisture
during peak humidity times,
the system can use a
dehumidifier to dry the area
until the system can use the
outside air again.
Healthy House


Think of a controlled
ventilation system as an
automatic system that knows
when to open and close your
windows.
It will only open the windows
when the air outside will
improve the air quality and
dry the home.
Modular Solution



Every crawlspace is
different.
A controlled ventilation
system is easily adapted
to unusual crawlspaces.
These systems can be
modified to
accommodate
crawlspaces as needed
through various systems
and fans.
Keystone

For more information:


Office: 866-588-0315
Email: