As part of the "Homes Behaving Badly" project, 4 local homes received air tightness testing. The results from these 4 case studies can be found in the HOBBS Report.
Two further case studies were tested by Midland Energy Services just last week, and the results are in!
The 1930's solid wall detached house (see HOBBS report) has undergone significant improvements to reduce energy use, and has achieved an air tightness figure of 7.44 m3/hr/m2 at 50 Pascals.
This is a respectable figure, given that the average new build must now achieve less than 10 m3/hr/m2 at 50 Pascals and most 1930's houses would be far more leaky than that! However, the owners have made a note of the locations where the test revealed draughts, and will be addressing those to improve the air tightness further.
The other case study to undergo an air tightness test last week was the 1950's solid wall detached house. This house is being refurbished to become an ultra-low energy home (to passivhaus refurbishment standard). It will receive a number of air tightness tests during the works, this being the first (preliminary) test with a result of 4.4 m3/hr/m2 at 50 Pascals.
Following this test, the real air tightness work begins, including plastering of the walls and installation of air tightness tapes and membranes around windows, in the attic etc. This internal layer of air tightness will be the key factor in determining the eventual air tightness of this particular house. For this Passive House refurbishment, a figure of less than 1 m3/hr/m2 at 50 Pascals is required (quite a challenge!)
It should be said - while the fabric of this 1950's house is being made extremely air tight, this does not mean that there won't be good ventilation. A ventilation system (Mechanical Ventilation with Heat Recovery, or MVHR) will be installed to deliver a constant supply of fresh air to the house, and extract stale air from kitchen and bathrooms continuously. Heat from the stale air will be transferred to the incoming fresh air via a highly efficient heat recovery unit. This kind of system becomes energy efficient in houses with an air tightness of ~3 m3/hr/m2 at 50 Pascals or lower.