I’m considering installing a 50mm flag base for Lean-To greenhouse against the existing single leaf garage wall, however the damp proof course (DPC) is below the surrounding ground. I understand that to conform to building regulations the base needs to be at least 150mm below the DPC, meaning that it would effectively be in 350mm deep pit requiring step access, which is less than desirable from a safety aspect, taking more space from the garden, whilst introducing the potential for flooding.
Please can you advise if there a recommended method of installation which complies with building regulations, allowing the Lean-To floor to be higher without compromising the existing garage DPC?
I have considered installing a dry trench as suggested, but depending on the required width? this too may be undesirable both inside and outside the lean-to without some form of grating just below the DPC?
What do you recommend?