Self-build diary: fitting the methane membrane

Written by Craig and LB – Plot 2 (Manuka Cottage) homeowners


Our initial steps

We must admit, the gas membrane is one of the things that’s thrown us the most so far on our self-build journey!

It sits above the block and beam floor, not only acting as a gas membrane but also doubling up as our airtightness barrier, so, it was imperative there were no holes. Having a gas membrane isn’t a normal requirement for a house build, however, given there used to be a tip around 800m from our site 30 years ago, as mentioned in an earlier blog, it was part of our planning conditions from Herefordshire Council.

It all started with the requirement of a full soil and gas technical specification which needed to be written by a specialist. Finding one proved to be very problematic, so Craig decided to take on the specification himself with a little help from Google, a local Geologist and the membrane company. After three or four reiterations and roughly eight months, we could finally submit the condition to the Council. As a result, a subsequent condition was put in place that there had to be a gas membrane fitted and signed off by a third party verifier. This was easier said than done as it’s a pretty rare condition: a more common occurrence would be for a radon barrier to be fitted.

Craig making progress with the membrane for Manuka cottage

Fitting the membrane

We decided to take on the fitting of the membrane ourselves as the cost from the supplier was pretty substantial. We were given no instructions other than a threat from the third party verifier that there better be no holes in it!

We sent off the floorplans for the house to Butec Landlines and the membrane was made to order. It arrived all folded up and we didn’t know where to begin: it looked more like a slip and slide mat than any form of barrier. The membrane came with a special type of tape and within the first five minutes we had stuck half a roll to the top of the block and beam edge, which turned out to be a huge mistake.

Over three nights we slowly began to get there. After night one, Craig managed to befriend someone from the supplier and sent him a photo. The man kindly replied and informed Craig it was very neat but he was using far too much tape! Once the membrane was down, we then had to book the third party test verification. If the membrane didn’t meet the requirements, we wouldn’t get the condition passed by planning and the build couldn’t commence.

The test focuses on three main areas:
1. Jointing
2. Corners
3. Bumps in the membrane that are usually caused by cement snots under the membrane and could puncture through.

Thankfully we passed with flying colours and the third party verifier even said it was the best fitted membrane he’d ever seen!


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