Air Tightness

Telephone: 08456 035 532

Testing Information

The part L1A regulations require that:


The Number of tests required;

Most larger developments include different dwelling types i.e 2,3,4 bed detached, semi-detached, terraced etc. The specific dwellings making up the test sample should be selected so that about half of scheduled tests for each dwelling type are carried out during construction of the first 25% of each type.

If the dwelling tested fails to achieve the required “Design Air Permeability Rate”, remedial work will be carried out, followed by a retest. One additional test on the same dwelling type will be required.

NOTE: See “WHAT BUILDING REGS SAY…. on this page, to the right.
b. option ii. This means that in order for untested dwellings of the same type to achieve an assessd air permeability less than the limiting factor of 10 m3/(h.m2) @50pa, the design air permeability should at most 8.0 m3/(h.m2) @ 50 pa.
If the design is aiming to achieve a low design air permeability, then the margin under paragraph ii will have a sgnificant impact on the calculated DER.

BINDT Registered

NHER Registered

What Building Regs Say…

To comply with regulation 17C, the DER must be no worse than the SAP calculated TER. The final DER calculation must be based on the building as constructed, incorparating: a, any changes to the list of specifications that have been made during construction; and b. the assessed air permeability shall be determined as follows: i. where the dwelling has been pressure tested, the assessed air permeability is the measured air permability; ii. where the dwelling has not been tested, the assessed air permeability is the average test result obtained from other dwellings of the same dwelling type on the development increased by a margin of +2.0 m3/(h.m2) @ 50pa.

ATT SOUTH WEST, Gorsey Leaze, Perran Downs, Goldsithney, Penzance, Cornwall, TR20 9HJ
t. 08456 035 532 | m. 07890 895671
Web Design Cornwall by Creative Steam