An Airtight Explanation

28 April 2017
Posted by: Evolution
Time to read: 3 mins.

An Airtight Explanation

Airtightness is probably the most difficult concept to explain when describing the elements that contribute to creating an energy efficient house.

Oxygen is an integral part of our survival and our vocabulary abounds with positive connotations reflecting our love of air, including words like “breezy, airy, spacious and breathless.”  So, selling a homeowner on the advantages of living in an airtight space requires a solid explanation.

Here it goes:

Let’s start by replacing the word “airtight” with “draft-free.” 

An essential aspect of creating an effective thermal envelope is ensuring no unwanted air leakage occurs.  From the dweller’s perspective, this means no drafts or heat loss. 

BRANZ estimates that most modern New Zealand homes built to the minimum code experience 6 – 9 air changes per hour (ach).  In other words, the warm inside air is leaking out through gaps, such as unsealed joints, and being replaced by outside air that requires temperature control.  During the winter, a continuous heat source needs to operate to heat up the air that has infiltrated from the outside through weaknesses in the thermal envelope.

Next, think control.  We’re not talking about keeping air out of the house, but rather controlling the quantity and quality of air entering and leaving the home.

When air infiltrates through walls (especially when the insulation has not been expertly installed) and around doors and windows, the quality can be compromised as it may be picking up toxins and unhealthy particles.  BRANZ’s research revealed that “in New Zealand, poor air quality is estimated to cause over 1,000 premature deaths yearly, with associated costs of over $4 billion.”

Airtightness can be achieved through various means; a common method is by installing a vapour check membrane, like Proclima's Intello, in exterior walls and ceiling.  An added advantage of this membrane is that it protects exterior walls from potential internal moisture issues, much like Proclima's Solitex wrap protects from exterior moisture.  This ensures moisture doesn't compromise the performance of the insulation.  

Another way to think about airtightness is Indoor Air Quality Control.

We do need fresh air in our homes.  The humidity that builds up in our living spaces, through cooking, showering and breathing, needs to be expelled.  However, in this modern day and country, we can do better than simply cracking our windows open in winter.

One component of controlling our air quality is efficient exhaust fans, particularly in the range hood and bathrooms. Not only do we specify these in the homes we build, but we also ensure they have dampers that prevent air from leaking into the home when the fan is not in use.

Mechanical Heat Recovery Ventilation (MHRV) is the ideal system for bringing in a constant supply of filtered fresh air which recuperates the heat of the exhausted stale air. 

JFK 1826 51 Medium

Mechanical Heat Recovery Ventilation System 

Achieving <1ach and installing a MHRV is the basic principle behind the Passive House standard.

At Evolution, we understand that building to Passive House standards may not be achievable for every home as budget and design limitations exist.  What we offer is our expertise in applying our knowledge to your needs and wants to achieve the best balance.

A good level of airtightness is highly important if you are considering building because it is one of the most difficult aspects to address retrospectively. 

Interior fittings can be easily replaced, and most likely will need to be as tastes change.  The structure of your walls and foundations, on the other hand, need to be done correctly and should last through decades worth of fashion trends.

Fresh, clean air in the home at a comfortable temperature will never go out of style.

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