Hazards And Solutions of Moisture Problems

Air Barrier

Humidity Effects on Health

The U.S. Centers for Disease Control and Prevention (CDC) and the Institute of Medicine (IOM)

of the National Academy of Sciences convened a committee of experts to conduct a comprehensive survey of the adverse health effects of indoor humidity and mold.The results indicate that some of the adverse effects of indoor humidity on the initiation of epidemic diseases and physical health include:

Upper respiratory symptoms (including nose and throat)





Studies have also shown that indoor humidity correlates with the following factors:

Difficulty in breathing

Lower respiratory tract infection (mainly in children)



Details of the investigation were published in a report in 2004.One important idea is the effect of mold to the body's immune system.In hospitals, for example, dampness can increase a patient's risk of fungal infections.There have also been reports that the presence of moisture and mold increases the risk of various respiratory diseases.A comparative study also found that 21 percent of the 4.6 million asthma cases were attributed to indoor humidity and mold.


Building Wrap

Humidity Effects on Buildings

1. Prolonged damp conditions can expose building materials and HVAC systems to mold, fungi, wood decay, and insects (including termites and carpenter ants).

2. Some chemical changes are more likely to occur indoors. For example: structural fasteners, wiring, metal roofs and conditioning coils are more likely to corrode, floor and roof adhesive can become fail.

3. Water-soluble material (e.g. plaster will absorb moisture and peel from the wall )

4. Wood products will warp, swell or rot..

5. The R value of the insulation will decrease.

Air Barrier


Solutions For Moisture Problems:

1. Control the leakage of liquid water

The first way to prevent moisture intrusion is to prevent liquid water from entering the building.Several key parts include the roof, wall, foundation, etc.External liquid water mainly has the following forms:

Rain, melted snow, ice and frost

Underground and surface runoff

Water from the indoor plumbing system

During the construction process, moist materials are contained within the building


2. Control Moisture From Designation

If you want to build a building with long service life and good indoor air comfort, you must follow the following three principles:

1) control liquid water

2) control the indoor humidity so that it is not too high.To prevent moisture from condensing on cold surfaces and being absorbed into cooler materials.

3) During construction, choose anti-moisture materials for unavoidably wet locations.


3. Roof and Cladding for drainage

There is usually an air layer on the back of the roof and cladding. Then there is a drainage layer.Most of the water that seeps behind the cladding is held back by this layer of drainage.

1) Roof: asphalt or shingles, metal plates or elastic materials, etc

2) Walls: wood or vinyl cladding, stucco, concrete panels, brick, concrete masonry units and stone

veneers are common materials for external walls

3) Drainage layer: house wrap, breathing membrane, building wrap, etc.


What is a house wrap?

House wrap is a new product for controlling moisture.It is usually used inside the cladding to act as a drainage layer.Very suitable for wall and roof applications.


Performance of House Wrap:

1. Waterproof: the basic performance of the house wrap is to act as the second drainage layer of the house.Drips of water on the house wrap is just like a water drip on the lotus leaf and will not be absorbed

2. Permeability: the most important performance of house wrap is its water vapor permeability, which is also the key method to solve the moisture problem.No matter how tight the waterproofing system is, it will produce water inside the wall system.Because indoor life itself produces a lot of moisture, it can't easily escape the building structure.If the building is equipped with house wrap, the indoor moisture can be gradually discharged to the outside of the building within about one month, which can reduce the accumulation of moisture inside the building.

Building Wrap


Waterproof Membrane

3. Windproof performance: no matter how tight the wall cladding is installed, it is difficult to avoid the invasion of small airflow.Waterproof membrane is very light and easy to install, so it is  easy to deal with some details of the house. Houses applied waterproof membrane can be much more air tight and more comfortable to live in.

The Installation of Breathable Membrane:

If the insulation layer is installed inside the wall cavity, then the breathable membrane is generally installed outside the sheath wall.In this case, the breathable membrane is usually fixed outside the sheath wall with wood strips which are directly fixed to the wall by long screws or insulation screws.If external insulation is installed outside the sheath wall, the breathable membrane is usually installed outside the insulation.They are still held in place by wooden strips, but the nails should be long enough to pass through the strip, the insulation and be firmly attached to the interior wall panels.

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