Speaking of issues with downpipes, had one I wanted to post here as well, we need to run a downpipe through some retaining timber at the side of the house. It'll be going down through the black plastic grating, which covers the required ventilation gap between the ground/retaining wall and the house:

 

 

 

 

The idea was to put an elbow on it, run it through the wooden retaining wall timber and then under the crushed-concrete scoria on the other side. It can't run under the grating because there's supports and posts in the way.

 

 

Will penetrating the retaining timber to carry the downpipe be non code-compliant? The guttering guys weren't sure, they were just going to use a hole saw and silicone it in place to make it watertight, or perhaps a Wallace seal, but before I give the go-head I wanted to check that's not going to make it impossible to get sign-off.