Hi all
First post here. I've searched around everywhere for someone with a similar set up to my place and found nothing so had to ask for myself.
I have a ground floor flat of a converted pub built circa 1905 and converted in the mid 90's. It's solid brick wall construction, single glazed sash windows, cement based (I assume) rendered outside, gypsum plastered inside. It has a very large basement, none of the basement comes above ground level which is fairly unusual it seems. We have damp problems from ground floor up to about 1m around most of the external wall areas ranging from a bit patchy to very wet but there is no visible mould, just tide marks. The pavement is a little higher than I expect it was when originally built but it all slopes away from the building quite dramatically and never has any pooling water outside. There are airbricks / grills that are mostly covered by the render and are full of grime making them pretty much ineffective at the moment.
Now I know what a lot of people will be thinking already; cement render, gypsum plaster, old building, blocked air vents. Lots of causes for damp already that seem pretty obvious. However.....
The blocked airbricks I mentioned are ABOVE the internal ground floor level (roughly 25cm above the finished floor). They appear to vent down into the basement via small cavity in the solid wall. It's similar to a periscope vent setup but this is not a cavity wall. It's basically a periscope vent to the basement from above the ground floor level but it's directly built into the brickwork. I'm fairly sure that the closed portion of the vented cavity above the ground floor is only covered by a bit of plasterboard / ply or something and skimmed over. I haven't yet confirmed this though as all the areas with vents are covered by radiators. If this is right then the only thing between the internal wall and the outside air in my living room is a bit of board and plaster! See my illustration of what I think is going on below:
The other thing I have noticed is that the only place we have damp is where the vents are located. The only 2 bits of external wall that have no vents are bone dry. The basement itself is a little musty but not visibly wet and usually stays fairly warm. It has a plastic drainage membrane around the perimeter but the damp above was there long before I installed that. If anything it's got slightly better since the membrane went in. Even behind the membrane it's fairly dry and drains freely. This tells me that the vents must be the main issue for some reason but I expect the cement render outside and gypsum plaster don't help the situation. It definitely gets most visibly wet when it's cold outside and the windows are kept shut so I'm fairly sure condensation is the main culprit.
This is leading me to a couple of possible conclusions:
1 - The lack of any solid wall to the outside where the air brick is located is created big cold spots where moisture coming up from the basement and within the house is condensing around leading to concentrated damp patches.
2 - There may be penetrating damp coming in around the vent where the wall is thin and the pavement raised condensing on the back side of the wall inside the vent flu cavity and saturating the walls from within.
I think I'm first going to try and un block the vents and get some air flowing to see if that makes any difference first. If that fails then I might have to fully seal the vents and fill the cavities and put some kind of mechanical ventilation in the basement / house to mitigate the condensation more effectively. Last thing I want to have to do is re-do the rendering and plaster with lime if I can help it. The fact that there are dry areas with no vents tells me this shouldn't be necessary and it's the vents combined with the condensation that are actually causing the problems.
Has anyone ever come across a set up like this? Anyone got any better solutions than my approach? Googling around and scouring forums has lead to finding nothing similar to this setup and specific issue.
Thanks
Will
First post here. I've searched around everywhere for someone with a similar set up to my place and found nothing so had to ask for myself.
I have a ground floor flat of a converted pub built circa 1905 and converted in the mid 90's. It's solid brick wall construction, single glazed sash windows, cement based (I assume) rendered outside, gypsum plastered inside. It has a very large basement, none of the basement comes above ground level which is fairly unusual it seems. We have damp problems from ground floor up to about 1m around most of the external wall areas ranging from a bit patchy to very wet but there is no visible mould, just tide marks. The pavement is a little higher than I expect it was when originally built but it all slopes away from the building quite dramatically and never has any pooling water outside. There are airbricks / grills that are mostly covered by the render and are full of grime making them pretty much ineffective at the moment.
Now I know what a lot of people will be thinking already; cement render, gypsum plaster, old building, blocked air vents. Lots of causes for damp already that seem pretty obvious. However.....
The blocked airbricks I mentioned are ABOVE the internal ground floor level (roughly 25cm above the finished floor). They appear to vent down into the basement via small cavity in the solid wall. It's similar to a periscope vent setup but this is not a cavity wall. It's basically a periscope vent to the basement from above the ground floor level but it's directly built into the brickwork. I'm fairly sure that the closed portion of the vented cavity above the ground floor is only covered by a bit of plasterboard / ply or something and skimmed over. I haven't yet confirmed this though as all the areas with vents are covered by radiators. If this is right then the only thing between the internal wall and the outside air in my living room is a bit of board and plaster! See my illustration of what I think is going on below:
The other thing I have noticed is that the only place we have damp is where the vents are located. The only 2 bits of external wall that have no vents are bone dry. The basement itself is a little musty but not visibly wet and usually stays fairly warm. It has a plastic drainage membrane around the perimeter but the damp above was there long before I installed that. If anything it's got slightly better since the membrane went in. Even behind the membrane it's fairly dry and drains freely. This tells me that the vents must be the main issue for some reason but I expect the cement render outside and gypsum plaster don't help the situation. It definitely gets most visibly wet when it's cold outside and the windows are kept shut so I'm fairly sure condensation is the main culprit.
This is leading me to a couple of possible conclusions:
1 - The lack of any solid wall to the outside where the air brick is located is created big cold spots where moisture coming up from the basement and within the house is condensing around leading to concentrated damp patches.
2 - There may be penetrating damp coming in around the vent where the wall is thin and the pavement raised condensing on the back side of the wall inside the vent flu cavity and saturating the walls from within.
I think I'm first going to try and un block the vents and get some air flowing to see if that makes any difference first. If that fails then I might have to fully seal the vents and fill the cavities and put some kind of mechanical ventilation in the basement / house to mitigate the condensation more effectively. Last thing I want to have to do is re-do the rendering and plaster with lime if I can help it. The fact that there are dry areas with no vents tells me this shouldn't be necessary and it's the vents combined with the condensation that are actually causing the problems.
Has anyone ever come across a set up like this? Anyone got any better solutions than my approach? Googling around and scouring forums has lead to finding nothing similar to this setup and specific issue.
Thanks
Will
