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Built-In House
Moisture Control Features

A house is designed to shed rain and control moisture vapor. Roofing, siding, foundation water proofing, grade drainage, vapor barriers, mechanical ventilation, heating & air conditioning all work together to limit or prevent moisture damage and mold growth. Stopping moisture stops mold growth.

Home Performance Issue. Moisture control is one leg of the Golden Triangle of home performance: energy efficiency, indoor air quality, and moisture management.  All the house subsystems contribute to it, including structure, electrical, plumbing, fuel gas, mechanical, storm water drainage, and energy efficiency. 

When everything else is installed correctly, the mechanical system effectively manages indoor moisture levels: the heating, ventilation, and air conditioning (HVAC) systems.

When trying to control mold in a house, all the subsystems need to be considered together to stop it by managing moisture levels in the house.

Built-In Moisture Control Features

To control mold growth, indoor humidity levels should be set to between 35-40%.  When relative humidity levels increase above 60%, mold growth can start.  Once it starts, 50% can sustain it.  Whatever the weather, we need to control indoor moisture!

Ventilation.  The most overlooked system in a house is ventilation.  Not only that, we tend to spend the least amount of money on it.  Have you ever noticed how loud your bath area fan is (assuming you have one)?  Ventilation is provided by windows, doors, exhaust fans, and fresh air intakes.  We accidentally get it from air infiltration: air that leaks into our house through cracks in wall, floors, and ceilings.

Besides ridding our house of foul odors and stale air, a primary purpose is to get rid of the moisture we put into our houses just by living there: cooking, cleaning, bathing, toileting, breathing, perspiring, etc. 

Did you know that every time we take a shower, we put a cup of water in the air?  Opening a window often doesn't help much because temperatures inside are close to those outside, so air doesn't move.  Newer houses have bath area fans in them, but who really uses them?  Until I figured out what they were for, I left them off thinking I was saving energy and avoiding noise.  The best thing to do here is put a humidistat or timer on the fan.  When timers are used, they should run 10 minutes after your bath or shower

Air Sealing.  As a nation, we might finally be getting it.  To control energy costs, we want to seal holes through walls, floors, and ceilings.  The good news is that this approach tends to keep the weather out.  However, it also tightens up the house so moisture we generate inside the house doesn't get out.  Kitchen and exhaust fans become important as does the need for mechanically supplied air, such as through fresh air dampers.

See the EPA's do-it-yourself (DIY) guide to air sealing.

Humidity Control.  When most of us think of humidity, we think of the Southeast.  Yes, it's hot and humid here, and everyone runs air conditioners.  Mold doesn't grow because an air conditioner is both a refrigerator and dehumidifier.

Many in our area believe they can save money when they go on vaction or any other time a house is vacant by turning off the air conditioner in the summer time.  When they do, they're surprised when mold is found all over everything.  This is the extreme.

Similar thinking leads folks to keep a warmer house so the air conditioner doesn't run as much.  This works to a degree, but we've been in more than one house people are living in with mold growing all over the place.

The giant dehumidifer, the air conditioner, must run to keep moisture levels down.  The other option is to open windows.

Temperature.  When we lived in New Zealand, we lived in a marine environment similar to California's.  They didn't use heat much at all, so there houses were always cold.  Did you know they also have the highest asthma rates in the world?  If you look at the walls, slime grows on them, just as we've seen here.  Any money saved on power bills was spent on doctor bills.

Atlanta also has high respiratory issues.  Why? The air conditioners are either oversized, the ductwork is too small, or both.  Oversized air conditioners can keep a house cold without removing much humidity.  This moisture is available to promote mold growth.

To be scientific about it, sort of, use measure relative humidity and maintain temperature accordingly.  If at anytime over the year the relative humidity exceeds 50-60%, the services of a home performance contractor are needed to find out why and to solve it.

Roofing & Siding.  If there are holes in the roof or siding, fix them!  Unfortunately, water knows about holes we don't think about.  We find water getting between the siding and interior wall structure every day!  The problem is bigger with stucco clad homes because once the water gets in, it's hard to get it back out.  In addition, water gets through window and door sills to.  The number one hole? At a kickout location, where a gutter meets a wall.  Think like a rain drop!

Windows.  Besides being a means of ventilation most people don't use when it hot or cold outside, windows contribute to moisture control.  The insulation value of a single-pane window might be R-1.  When warm, humid air meets it, moisture in the air condenses out it.  Often this moisture gets trapped between the window and curtains.

When dual-pane windows or storm windows are used, the potential for condensation is greatly reduced.  The exterior pane is closer to the outdoor temperature, while the interior pane is closer to the inside temperature.  Therefore, less moisture drops out of the air.

Another strategy used to avoid window condensation is for ceiling air supply ducts to blow down in front of them.

Insulation.  Insulation plays a major role in moisture control too.  Most of the mold found on walls is behind furniture and personal items, where they lean up against them.  The cold wall condenses moisture out of the area that collects on the walls.

Often, batt insulation is put into walls with vapor barriers on them. The instructions are to put the vapor barrier on the warm-in-winter side of of the wall, which in the Metro Atlanta Area means against the interior wall. Unfortunately, in our climate, the vapor barrier is in the wrong place half the year.  It should be on the exterior wall in the summer time.  There are many who believe Altanta residents should not use insulation vapor barriers.

To avoid condensation along walls, either fill the walls with insulation or keep personal items away from exterior walls.

Crawlspace Vapor Barriers. Crawlspaces and basements are popular in the Metro Atlanta Area, for a variety of good reasons.  With crawlspaces come soil evaporation.  Since water vapor is a gas, it will go right through the floor and carpet.  The moisture from the crawlspace will also be drawn through the house through holes in the floor and walls as attic temperatures rise and wind blows.

Keeping moisture in the ground is also important for house built on clay soils to protect the soil from drying out around the foundation.

When water isn't flowing into or through the crawlspace, a vapor barrier needs to be installed.  Placing a vapor barrier over saturated soil will make mold problems .  The vapor barrier should be sealed at seams and to the walls.

Foundation Sealing. 30-60% of all houses with basements in the United States have moisture problems.  That's why the wet basement smell, the musty odor, is so familiar.  Much of the time its because the walls are damp-proofed, rather than water proofed.  The membranes dry out and crack over time.  In addition, expansive soils and normal concrete drying can crack a foundation wall.

Ideally, the fill dirt should be removed to install waterproof barriers.  In the process, footing drains need to be repaired, replaced.  Many of them are installed incorrectly or clogged, if they are there at all!

The best recommendation for foundation leaks is to consult with a dry basement specialist.

Storm Water Management
. We tend to let water pool in puddles around the foundation at downspouts.  Often, this water flows through the foundation, into the basement or crawlspace.  Some of this occurs because the ground is flat or sloped toward the building.  It's not uncommon to find roof water runoff collecting in a crawlspace.

One strategy is to discharge downspouts into buried drains or collect water in rain barrels.  A landscaper can help with that.  Another strategy is empty downspouts 5 ft or more from the foundation.  Another is to not use gutters, but rather deflectors, to spray water evenly 3-5 feet away from the foundation.  We installed these ourselves in one day.


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