EcoHouse Research

Jerell Gill (MEng, 2013)

 

The field of building physics is one often dominated by energy, be it from the viewpoint of reduced mechanical loads, or occupant comfort levels. This focus is partly a symptom of the growing importance of global warming and depleting sources of non-renewable energies. Another important, interlinked but often overlooked factor in the determination of building performance, however is moisture control, and it becomes of ever greater importance as building envelopes improve.

The presence of unwanted moisture is found to have 3 primary negative effects in buildings. The first is due to the absorption of water by building construction components. Historically, the single greatest factor affecting the durability of buildings has been excessive moisture.

 

The absorption of water by materials can have a significant effect on their properties, including their ability to perform structurally. Timber provides a common example: high moisture content will often lead to wood rot, but also result in the expansion and warping of the wood. Excessive moisture can cause metals to corrode, coatings to separate and masonry to flake.

 

Moisture control is also essential for the prevention of mould growth and dust mite colonisation. Dust mites, which can trigger allergic reactions, can survive in warm conditions with relative humidity above 50%. Mould has been linked to adverse health effects. Certain fungi found in indoor air can even produce mycotoxins which have been found to be carcinogenic (induces cancer), teratogenic (induces birth defects), immunosuppressive (reduces immune system performance), and oxygenic (poisons tissues). Depending on the type of mould, different combinations of temperature and humidity can cause it to germinate and grow, but as a general rule, the higher the humidity, the higher the risk of mould growth.

 

Finally, moisture has both direct and indirect effects on the comfort of building occupants. For a given temperature, higher moisture content in the air increases relative humidity and can make it harder for people to benefit from evaporative cooling in hot climates. Additionally, a higher moisture content inside building components causes an increase in thermal conductivity and therefore usually an unwanted increase in heat loss or gain.

 

Excessive moisture in building materials (and the associated problems) is a significant risk in low-cost “transitional housing” that has been, and continues to be, constructed across Latin America. TECHO, a Latin American Non-Governmental Organisation (NGO) founded in 1997, coordinates the construction of thousands of transitional houses by unskilled volunteers every year. These houses are built for families in clear need of an improvement in living conditions; they provide a low-cost, but temporary, housing solution (with an estimated life span of 5 years), intended to bridge the gap to more permanent homes. Consisting of locally pre-fabricated panels, it is possible for a group of 6-8 unskilled volunteers accompanied by one or more experienced volunteers to build a transitional house in 2 days. Construction occurs in a range of climates; in Ecuador alone, this ranges from the hot and humid coastal areas, “La Costa”, to the dry and windy mountainous regions, “La Sierra”.

 

It was during visits to existing housing in Ecuador in 2011, by members of the EcoHouse Initiative, that moisture damage was first identified as a significant problem. Few engineering principles have been used to design the transitional house that is currently predominantly built by TECHO in Latin America; hence there is much room for improvement in its moisture related performance.