Dot and dab cold spot / damp?

[Guyray]

Hi All,

This could be an easy one for the experts out there to close out. My house is a late 1800s mid terrace. My attic wall (loft built to regs) has damp patches that have penetrated through the dabs. The other side is my neighbours non insulated , non converted attic room (no cavity between us, I don't think). See pics. I've hacked off all the plaster. There was no insulation between the wall and plaster. There are loads of gaps in the mortar between My neighbour and me. There are no vents in the wall. The plasterboard over both chimneys is brown feels a little damp. One is operational the other is capped.

Are these damp patches caused from cold spots? My builder says just re-board with insulated board using dot and dab. However, I think re point all gaps, salt neutralise chimneys, batten and re board with insulated board. Maybe insert vents? Is that sensible?

We have spent a lot and time and money ensuring the roof is ok and no water can be getting through... please help experts!

Thank you
Guy

 

[Guyray]

 

[Jadele]

Cant See any pics but if enough moisture is present to some through what you say then its unlikely to be cold spots and more likely wet brick work. If your chimney and roof is good then maybe nextdoor has an issue and the motor is being wet on their side and tracking through to yours.

 

[Guyray]

Cant See any pics but if enough moisture is present to some through what you say then its unlikely to be cold spots and more likely wet brick work. If your chimney and roof is good then maybe nextdoor has an issue and the motor is being wet on their side and tracking through to yours.

Thanks jadele. Can you see pics now?

 

[Jadele]

yes there now

 

[Doggit]

Get the carp of the wall, batten it with 25x40 tantalised battens with a dpm behind them, then put up a VCL, then use insulated plasterboard. If you put in ventilation, then that'll allow any moisture to come through to you. You could paint the wall with a liquid dpm first if you wanted to make sure nothing comes through.

 

[Guyray]

Get the carp of the wall, batten it with 25x40 tantalised battens with a dpm behind them, then put up a VCL, then use insulated plasterboard. If you put in ventilation, then that'll allow any moisture to come through to you. You could paint the wall with a liquid dpm first if you wanted to make sure nothing comes through.

Thanks Doggit. What do you think could be causing this. Shall I repoint the large gaps in the mortar?

 

[noseall]

If it is very humid in your loft and very cold in your neighbours loft then you will get cold bridging and condensation occurring where the dabs are in contact with the cold wall.

There is evidence of black spot mould on the back of the plasterboard which would corroborate what I've said above.

A robust method (as said) of insulating, joint sealing, VCL and loft ventilation will enure this does not happen again.

 

[Guyray]

Thanks noseall! Really useful to be getting some consensus. How do you suggest I loft ventilate? Vents in loft ceiling? This room is en suite but has a suitable fan in the bathroom, and the room in question has two veluxs

 

[noseall]

Do you have breathable membrane on the roof?
Keep the trickles open on the Velux. It's probably more a case of insulation and a robust method of achieving a VCL.

 

[vinn]

There's definitely (as above) black spot condensation on the back of the p/b.
There are also very damp looking areas on the party wall brickwork - centre high being the most obvious one to me.
The RH c/breast brickwork appears to be damp.

OP, can you post pics of the front and rear roof planes from eaves to ridge also showing chimney stacks?

Have your chimney flues been swept and ventilated top and bottom?

 

[Guyray]

Thanks Vinn. Chimneys haven't been swept. One chimney is operational (left) the other is not, but capped. Will try And get some photos from outside tomorrow.

My neighbour claims his side isn't fine, not damp. Ive just finished a rear extension where he was difficult so I'd like to keep him out of it if possible. We have both had the party parapets above the wall done, so no ingress from there. Will recounting stop more water getting through? Plan is to then batten and board.

Thanks again,
Guy

 

[vinn]

The mention of party wall parapets brings a possible whole new ball game into sight esp. given that you have a 9" loft party wall. Close-up or good zoom pics of the parapets on your house side, and the neighbour's side would help.

Is the operational flue being used for solid fuel or gas?
Best practice is to open up fireplace openings if closed, & sweep all flues from all possible fireplace openings.
All flues must be vented top and bottom.
Capping typically means slamming a flag stone over the terminal opening, and disregarding any idea of venting the flue.
Do you know the condition of your stacks and flaunchings?

Your house is most likely a late 19thC build.

 

[Guyray]

Operational chimney is gas. The other is a vented cap, and open below. It's the damp in the middle of the wall which has thrown me. It must be coming from my nieighbours side right? Stacks and flaunchings all good. Roof new 8/9 years ago, lead work good, tiles good. Had 3 roofers up there, none can find any issues / potential for ingress. Thanks for taking the time to respond.

 

[Guyray]

Removed dab from left chimney. Plan is to clean it all up, point, dpm, batten, board etc...