A healthy home requires exchange or displacement of air within the building.
There are two ways of achieving exchange or displacement.
- natural ventilation
- mechanical ventilation.
Sometimes a combination of both are used to achieve proper air exchanges.
Most buildings in the Northwest are broken into three parts.
- the crawl space under the house
- the living space we live in
- the attic above the house
Each of these spaces need to be vented to control air pollution, moisture and heat. Even though there are codes and formulas to calculate the air exchanges needed for each space, there are many additional factors that need to be taken into consideration.
Crawlspace Ventilation
A dry crawlspace can have as little as 1 square foot of vents per 1000 square feet of crawlspace. Vents need to be located on all corners of the crawlspace, to allow proper cross-flow. This changes drastically if there is moisture present. The relative humidity should never go above 55% in your crawlspace. This poses a major issue in the northwest for the following reasons. We have a tremendous amount of liquid moisture that raises moisture levels in soil. Even though there is a foundation wall separating the crawlspace from the outside soil, the soil acts like a sponge wicking moisture from high to low or wet to dry. The concrete foundation also is porous wicking the moisture to the inside of the crawlspace. Having a properly installed vapor barrier can help reduce the moisture transfer from the soil to the air. In addition to the soil moisture issue, a lot of crawlspaces also have an actual water issue that require drainage and or a sump pump to control that issue.
The other reason is that in the warmer months our water content of the air is higher outside then inside. Warm air holds more moisture then cold air and as this air is drawn into crawlspace with an average temperature of about 55 degrees Fahrenheit it will condense on the surfaces of the crawlspace. This can cause rot, mold, rust on iron piping, rusting of HVAC ducting and provides a perfect environment for ants, mosquitos and other insects. This attracts spiders that feed on them. Spiders are the good guys eating the bad insects. Having a lot of spiders in the fall in your home is an indicator that you may have some other issues with your structure. If natural ventilation cannot achieve moisture control in the crawlspace, then other ways like dehumidification, crawlspace encapsulation, controlled mechanical ventilation or a combination should be used. If there is radon gas in a crawlspace an encapsulation with negative air is must. Radon is the second leading cause for lung cancer next to smoking.
Living Space Ventilation
Living space ventilation controls the air we and our pet’s breathe. We need to create enough air exchanges to remove moisture, co2, VOC’s and other pollutants. The amount of people and animals in a building play a big part of figuring out how much fresh air we need to bring into our living space. There is a balance between temperature control and air quality control. In most cases we bring in unconditioned air from the outside to replace the conditioned air from inside the living space. This happens naturally through a phenomenon called stack effect. Stack effect is what causes most of the natural ventilation in a home. As warm air rises in your home it creates a positive pressure on the ceiling. This positive pressure pushes the air into the attic through penetration points, outlets, ceiling lights etc. As the air escapes it creates a negative pressure(vacuum) on the lower level pulling in air from the crawlspace and outside. Up to 50% of the air in your home can come from your crawlspace. If there is a problem in the crawlspace it will affect the air quality in your home.
Attic Ventilation
Attic ventilation controls both temperature and humidity in the attic. The temperature in attics range from the coldest temperature in your region to 160 degrees or higher depending on region. In addition to having to deal with these extreme temperatures it has to vent out all the moisture that ends up in the attic from crawlspace and living space. Even with proper ventilation, if there is excess of moisture or heat, the attic can struggle controlling these elements. The best way to control moisture in the attic, is to vent it out directly and control the humidity in the home. To control the heat in the attic, you can add additional vents and make sure there is a 50/50 balance between intake vents and exhaust vents. You will want to make sure that none of the vents are blocked and all bath room and kitchen exhaust fans are vented directly to the outside with a roof jack. The same goes for a dryer should in case it is vented through the attic. If natural ventilation cannot control the heat and/or humidity mechanical ventilation is an option. We recommend a smart ventilation system that measure outside and inside air and uses parameters in its control of the ventilation to prevent ice damming on the roof sheeting or bringing wetter air then is inside.
Summary
Without proper ventilation your house will have issues and can be a very unhealthy place to live. Even though the basics of ventilation is pretty simple, figuring out the calculation based on all the factors is very complex and should be done by someone that understands your building and how it functions. I have seen professional close off vents in a crawlspace without addressing the moisture in the crawlspace and mold overtook the home. Adding to much ventilation to a living space without the use of an HRV (heat-recovery ventilator) will increase your energy consumption to condition your home. We are a crawlspace and attic expert that understand the symbiotic design of your house and how it is supposed to function. We can help you resolve issues in the crawlspace and attic and help identify other issues and give you recommendations.