I am in the process of constructing an extension and would like some advice please on how to waterproof part of the external wall which will be below the level of the adjacent garden. To clarify, the garden slopes upwards away from the house and I have dug out to allow for footings etc. and am now laying the first courses in engineering brick up to DPC/DPM level. Part of the extension will be around 1.2m below the level of the garden. As this section will never be seen, my thoughts are that in order to reduce moisture ingression, I could use engineering bricks in this location and then place a DPM against the finished wall prior to backfilling. Is this an acceptable method or am I being too simplistic?