Apart from “wrapping up” the house (see here for more on this concept), another fundamental element of an energy efficient building is how well sealed it is. Airtightness is one of the key concepts we have become rather obsessed with since we began designing our house. This refers to the uncontrolled flow of air through unwanted “openings” (gaps) in the building envelope. This leakage has an important impact on the energy performance of the house.
So how do you measure the impact of air movement through these often miniscule and invisible gaps?
The concept used is called “air renovations/hour” which measures the number of times the air in the building changes in the space of one hour. The average in Chile for this indicator is 12,9 renovations/hour across all types of houses (concrete, bricks, bricks and timber, timber). And if we zoom in on the specific building type that we are using (timber), the rate is 24,6 renovations/hour.
This means that in winter, while you are heating the air in the house with gas, paraffin or electricity, you have to heat “new air” approximately 13 or 25 times in one hour to maintain the warmth.
Conclusion: we are constantly losing the air we have spent money on to heat.
To give you a comparison, the Passivhaus Standard permits a value of 0,6 renovations/hour to be able to certify the building, no matter what material is used. That is 96% less than the Chilean average and 98% less than a wooden house in Chile. To date, and according to our knowledge, no house in Chile has reached this incredibly demanding number. The closest a house has come in Chile is 1,1 renovations/hour.
Current Chilean building regulations do not have a specific requirement relating to air infiltration, although the CEV standard incorporates the concept in its calculation and recommends reducing the infiltration level as much as possible.
So what is the solution to the airtightness challenge? Make sure the house is well sealed.
How? Achieving airtightness depends on the material used to build the house. In the case of a house made of wooden panels it is particularly important to seal the tiny cracks that are inevitable between panels. In a “business as usual” wooden house, these tiny cracks are hidden by the exterior siding and interior wall coverings, but this does not mean that the cracks are sealed and air filtration still occurs. To seal these gaps we investigated a number of options and finally decided on an adhesive membrane that is applied to the exterior of the house. We imported this membrane from a company, Proctor in Scotland.
We will write more on the properties of this membrane and the airtightness concept in future posts when we apply more insulation to the exterior and the final siding and when we do the blower door test to determine the number of infiltrations/hour.