I've had a bad smell in my first floor front bedroom for perhaps a year. It comes on overnight. After rain it's a damp, almost mildewy smell. When it's dry it's more musty. There is no visible sign of damp.
The house was built in the 1890s. It's a typical two storey London terraced house with solid brick walls and a bay window at the front. The front wall had cement pointing removed and replaced with lime pointing about 3 years ago. The house faces south and rain overwhelmingly comes in from the south west. The plaster is almost certainly gypsum but I'm not 100% certain on that. I'm 99% sure the paint isn't breathable. The ceilings above and below the smelly room are the original lath and the there are floorboards in the bedroom and hallway, with the cracks unfilled. The roof underlay was partly replaced about 3 years ago and we haven't noticed any leaks since then. The roof flashing looks fine from ground level. The chimneys are on the opposite side from the smelly wall.
The parapet between my neighbours' house and mine is rendered with cement on my neighbours' side. On my side the pointing has patches of both cement and lime mortar - it was only partially repointed when the front of the house was done 3 years ago. It's possible that some of the cement mortar up there which looked solid 3 years ago is now loose - I haven't been up to check. There are dark vertical streaks on both sides of the parapet below each coping stone joint, suggesting the pointing between the stones is letting quite a bit of water through. You can see pictures of the parapet here: https://photos.app.goo.gl/GoK9u3MZssyiBN7L9
The smell seems to come a party wall, most strongly from around floor level in the back corner of the room - i.e. nowhere near an external wall. I've had the floorboards up and the subfloor timbers are all bone dry. No plumbing in the area. The neighbours on the other side of the wall don't have any problems. The smell is also quite strong inside a fitted cupboard in the hall, just outside the bedroom. I occasionally get a damp smell on my stairs outside the room too.
I'm aware of moisture meters' flaws but I'll share my readings anyway. I get 16%ish damp in the bricks and mortar behind the skirting board in the smelliest areas. 12% damp in all of the bedroom's plaster (except below one bay window which faces into most of our weather, which read 17%). The plaster elsewhere in the house tends to read 3-6% damp.
Humidity in the bedroom (and elsewhere) is normally around 50%, occasionally 60% but never higher, and the air temperature never gets anywhere near the dew point. I don't have a surface thermometer but the smelly wall is internal so I wouldn't expect it to be particuarly cold. Several windows are left open in the room every night, year round.
I'm guessing that the problem may be caused by water getting in through the parapet at the top of the smelly wall. The wall just under the roofline in the loft is visibly damp and measures c. 23% damp, although that falls to 3-6% at loft floor height (i.e. well below the readings I'm getting one floor below). The loft is well ventilated and extremely warm in summer. There are no chimneys on the smelly side of the house. The flue on the other side gets a lot of rain down it - the bricks are pretty saturated in the top section of the flue but seem quite dry below the point it splits towards two separate fireplaces (each of which is open but not in use on one floor of the house). I haven't had any damp problems below loft level on that side of the house.
My current plan is to get someone up on the roof to check the pointing and flashing on the parapet, and repoint if necessary. Also consider getting rain caps/cowls fitted to the chimney pots. Someone on another forum suggested rendering my side of the parapet like my neighbours but that feels like the wrong answer.
If the problem is just the parapet, I'm also confused about how the wall is drier at floor level in the loft than at floor level one floor below. And why the plaster is relatively damp (compared to the rest of the house) in the bedroom on all the walls, not just the smelly wall below the parapet. Might that suggest there's a condensation problem too/instead, even though the RH never seems high enough?
Sorry for the long post. Any advice very gratefully received!
The house was built in the 1890s. It's a typical two storey London terraced house with solid brick walls and a bay window at the front. The front wall had cement pointing removed and replaced with lime pointing about 3 years ago. The house faces south and rain overwhelmingly comes in from the south west. The plaster is almost certainly gypsum but I'm not 100% certain on that. I'm 99% sure the paint isn't breathable. The ceilings above and below the smelly room are the original lath and the there are floorboards in the bedroom and hallway, with the cracks unfilled. The roof underlay was partly replaced about 3 years ago and we haven't noticed any leaks since then. The roof flashing looks fine from ground level. The chimneys are on the opposite side from the smelly wall.
The parapet between my neighbours' house and mine is rendered with cement on my neighbours' side. On my side the pointing has patches of both cement and lime mortar - it was only partially repointed when the front of the house was done 3 years ago. It's possible that some of the cement mortar up there which looked solid 3 years ago is now loose - I haven't been up to check. There are dark vertical streaks on both sides of the parapet below each coping stone joint, suggesting the pointing between the stones is letting quite a bit of water through. You can see pictures of the parapet here: https://photos.app.goo.gl/GoK9u3MZssyiBN7L9
The smell seems to come a party wall, most strongly from around floor level in the back corner of the room - i.e. nowhere near an external wall. I've had the floorboards up and the subfloor timbers are all bone dry. No plumbing in the area. The neighbours on the other side of the wall don't have any problems. The smell is also quite strong inside a fitted cupboard in the hall, just outside the bedroom. I occasionally get a damp smell on my stairs outside the room too.
I'm aware of moisture meters' flaws but I'll share my readings anyway. I get 16%ish damp in the bricks and mortar behind the skirting board in the smelliest areas. 12% damp in all of the bedroom's plaster (except below one bay window which faces into most of our weather, which read 17%). The plaster elsewhere in the house tends to read 3-6% damp.
Humidity in the bedroom (and elsewhere) is normally around 50%, occasionally 60% but never higher, and the air temperature never gets anywhere near the dew point. I don't have a surface thermometer but the smelly wall is internal so I wouldn't expect it to be particuarly cold. Several windows are left open in the room every night, year round.
I'm guessing that the problem may be caused by water getting in through the parapet at the top of the smelly wall. The wall just under the roofline in the loft is visibly damp and measures c. 23% damp, although that falls to 3-6% at loft floor height (i.e. well below the readings I'm getting one floor below). The loft is well ventilated and extremely warm in summer. There are no chimneys on the smelly side of the house. The flue on the other side gets a lot of rain down it - the bricks are pretty saturated in the top section of the flue but seem quite dry below the point it splits towards two separate fireplaces (each of which is open but not in use on one floor of the house). I haven't had any damp problems below loft level on that side of the house.
My current plan is to get someone up on the roof to check the pointing and flashing on the parapet, and repoint if necessary. Also consider getting rain caps/cowls fitted to the chimney pots. Someone on another forum suggested rendering my side of the parapet like my neighbours but that feels like the wrong answer.
If the problem is just the parapet, I'm also confused about how the wall is drier at floor level in the loft than at floor level one floor below. And why the plaster is relatively damp (compared to the rest of the house) in the bedroom on all the walls, not just the smelly wall below the parapet. Might that suggest there's a condensation problem too/instead, even though the RH never seems high enough?
Sorry for the long post. Any advice very gratefully received!