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Underground FAQs

Yes, our underground drainage system is to EN 1401.

For 110mm drainage the gradient is 1:80 with 1 WC. For 160mm drainage the gradient is 1:150 with 5 WC’s.

You can either use an adaptor to the top of the pipe (B4301), (B4501) or a hopper (B1031) with the waste going into the top.


Yes part no. B3500 is the adaptor required.

Yes there are a choice of Back Inlet Roddable Gullies with 90° Outlet available to choose with choice of grid:  with Round Grid (B1001); with Rectangular Grid (B1002) and with Square Grid (.


Shallow Inspection Chambers can be installed to 600mm, which is 2 risers high.


An inspection chamber should be installed at each change in gradient, direction or pipe size.

Yes, they have a double sealed lid and can be installed in garages.

For the 280mm chamber there is a lid for pedestrian areas (B2802).  For 315mm chambers there is lid for pedestrian areas (B3153) and another for driveways (B3154*) which is rated to 35kN. For 450mm chambers there is a lid suitable for driveways (B6255*) and is rated to 50kN. (*See FAQ 'Where can driveway lids be used?)

Brett Martin's driveway lids (B3154 & B6255) are rated to A35 (ISO 15398) and are suitable for installation in private single household driveways which are not part of the road network. They are designed for occasional use only and should not be parked on. Therefore, it is necessary that they are installed outside of the line of drive and not in an area where vehicles turn as turning can generate higher wheel forces and point loads.

Larger 4-wheel drive vehicles and delivery vehicles can generate higher loading again and therefore if there is a possibility of larger vehicles entering the driveway a B125 cover (supplied by others) should be used. Driveway entrances can often be used for turning by larger delivery vehicles, if this is likely to occur a B125 cover should be used here also.

To ensure maximum performance of the driveway lid, the frame should always be installed with a concrete surround at least 300mm wide x 225mm deep. On sloping driveways, the concrete should be extended upwards to surround the frame at ground level and no tarmac should be installed on top of the concrete.

Brett Martin manufactures a range of underground drainage products, certified to EN 1401and EN 13598-1. As a result of Brexit, Brett Martin has consulted with BSI and confirmed that in the case of the Kitemark, there was no need to make any changes to certification. The above Kitemarks continue to be valid throughout the UK and Ireland. Additionally, BSI issued the following statement on this issue:

Kitemark is a voluntary 3rd party certification scheme and is completely unaffected by Brexit or the recent introduction of UKCA marking.

The certification scheme remains valid across the globe and demonstrates quality, safety and performance related characteristics backed by independent testing and regular assessment of the quality management system at the point of manufacturer.

Our Kitemark schemes are accredited by the UK’s national accreditation body (UKAS), which remains a member of the European co-operation for Accreditation (EA), International Laboratory Accreditation Co-operation (ILAC) and International Accreditation Forum (IAF).