Case Study: 76 dwelling housing site, Derry

The site had been classified as a characteristic situation 3 risk site with elevated levels of methane and carbon dioxide. GQA Environmental was employed to provide a validation plan and strategy for the verification requirements on site.

By looking at the design, gas risk, type of structure and installer competency, a risk assessment was used to determine the full verification strategy. The main contractor employed a local specialist to install the gas membrane system. The validation plan consisted of:

  • Independent inspection to the passive vent system used by the block and beam floor
  • Independent inspection visits to the perimeter installation of gas membrane prior to the infill
  • Independent inspection and integrity testing by air lancing to ASTM D4437 of all seam joints and penetration details.

This was completed for the first 5 plots and then 1 in 4 plots thereafter if the installation was acceptable. With the balance of housing inspected by the main contractor under their own CQA.

The procedure used meant that the installation had to be kept to a high standard across the full site whilst also keeping the amount of independent visits down from a cost point of view for the contractor.