DIY Doctor UK DIY Forums

Hello all – I hope you can help, and sorry for the essay!

I have some damp issues in a half-brick thick lean-to. I think it is a combination of condensation and some penetrative damp and would like your opinions on what I think are possible solutions – I’m no expert by the way.

Firstly, the condensation. Within a month of moving into my new house I noticed black mould growth in the corners of the lean-to. To tackle this I turned up the heating in the room slightly and locked the windows in a slightly open position to improve temperature and airflow. So far, this has appeared to mitigate things somewhat – but does anyone think perhaps installing some airbricks, maybe high up, would be a better long term solution than having the windows permanently open?

Secondly, possible penetrative damp. On the wall of the lean-to that faces the garden, paint and plaster has blistered and fallen off along the length of the wall at around 50cm high – almost like a tide-mark (with some mould growth as well). I do not believe that this has been caused by condensation alone. This is because the garden patio, which runs right up to the lean-to wall, is a higher level than the floor in the lean-to (which also has some damp patches near the wall). I think that this is the primary source of the damp issues on this wall. Rather than some sort of DPC, I thought that digging a French drain around the external walls of the lean-to, thus preventing water lapping up against this wall, would reduce most of the damp in this wall – does anyone agree/disagree?

I can upload photos if anyone feels this is necessary

Huge thanks to anyone’s input – as I said above I am no expert but I have done some research.

John

the damp is caused by 2 issues,
1.the cold walls,even though your heating the room the outside temperature is conflicting with the single skin wall and no insulation will cause moisture on the wall and black mould occurs.
2.The exterior ground is higher than the internal floor height.
To resolve this I would paint the internal walls with buitumin paint,then dryline the walls with insulated plasterboard.
The exterior of the property needs a drainage system installed, like ACO drainage channel system
to eliminate water ingress.

thanks for you quick and helpful reply!

Just a quick follow-up question - presumably an ACO drainage channel needs to go towards the main drain, but if it is not possible/easy to get to a drain would a french drain down to the soil suffice?

Thanks again.

John

If you cant connect to a surface water drainage system,then pipe it away from the building as far as possible and dig a large pit and fill it with 6mm stone chippings.