Statistics, analysis and conclusions from 250,000 blower door tests, including ventilation types

With lower air leakage in modern homes, ventilation of homes has become more important than ever before. It seems however that we are getting it very wrong. A lack of ventilation can cause building sickness, with degradation of the physical building and also poor air quality which has a big impact on the occupants themselves. Our statistics show that designers and contractors are still not getting it right, leaving us with a generation of poorly ventilated housing stock.
The Air Tightness Testing and Measurement Association (ATTMA) introduced a lodgement system in September of 2015 that records results of approximately 85% of all air leakage tests in the United Kingdom. The Lodgement system also records the type of ventilation installed plus another 25 fields that allow us to study statistics in depth.
The ATTMA is able to therefore demonstrate that the average home is not adapted for the ventilation system installed. From the 200,000 tests, the average result between a System 1 (Trickle ventilators and intermittent extractors) and a System 4 (Whole house heat recovery ventilation) is only 0.39 m3.h-1.m-2@50Pa, the equivalent of a leaky letterbox. A System 4 ventilation type is usually designed to work with very low air leakage homes, yet the same building type and build quality is observed regardless of the ventilation strategy.
From the same data, we can also see that a staggering 58% of dwellings are still built using traditional ventilation strategy, System 1. Perhaps more concerning is the number of properties using a System 1 ventilation type but scoring a very low air leakage (less than 3.00 m3.h-1.m-2@50Pa), an estimated 10,000 dwellings a year. The percentage of System 4 ventilation types in comparison is 29%. Perhaps the scariest statistic of all is 85% of all dwellings tested with a System 4 ventilation type achieve greater than 3.00 m3.h-1.m-2@50Pa which could lead to inefficient heating because of the level of uncontrolled ventilation.
So what can we do to put this right? The legislation makes reference to the ventilation and infiltration needing to be matched but this is not regularly enforced by Building Control or Approved Inspectors. Contractors need to take the issue seriously. This may not happen until the poorly ventilated homes are exposed and building warranty providers are left with millions of pounds of claims.