Hole in wall, behind skirting board

[shell.mil15]

We have a traditional 1940s UK semi and have recently attempted to replace the kitchen skirting boards. We are not great at DIY and have discovered a problem. On removing a piece of skirting that was glued on, there is a large hole in the wall. This is an external double brick wall (no cavity) and the hole area goes to single brick, there is an airbrick in this space, and when we look down we can see the floor space beneath the wooden floor boards. The gap in the wall is about three feet in length. I am reluctant to glue a new skirts on as it will only attached by one inch at the top and simply be resting on the floor underneath. We can't brick up the hole without lifting all the floorboards (new floor now laid so not a viable option) and expanding foam won't work as it will just fall into the void under the floor. Any suggestions on how to resolve this problem would be greatly appreciated.

 

[thomp1983]

A picture will help if you can take one

 

[^woody^]

Expanding foam

 

[Ivor Windybottom]

It sounds like it's functioning as a duct for the airbrick. The airbrick is above floor height, possibly due to the ground level outside. The air blows horizontally until it hits the back of the skirting, then turns downwards to blow under the floor.

Definitely don't block it, with expanding foam or anything else. This airflow stops the floor from rotting away.

I don't see an issue with putting skirting back spanning the gap, as it was. It will be just touching at the top, but will be held by the surrounding areas to left and right so will be fine. I'd just paint the back of the skirting in this area (and beyond), with primer then a couple of topcoats to ensure that damp air blowing in hopefully doesn't make it bend or cup (or rot).