Line of yellow discoloured paint appearing on original wall/new loft wall boundary.

GermanderSpeedwell

Last year we had a loft extension on our semi-detached house. Following the recent freezing weather, the paint on the boundary between the top of the original wall and the start of the new loft extension wall has started to turn yellow in pretty much a straight horizontal line along it (this is on the side wall of the house where we get the most wind/rain). We told the contractor and he came to see it, said it was damp, then suggested painting over the walls again in spring/summer when the walls have dried out.

We obviously don't want to go just on what the contractor suggests and so would like to get a second opinion on the extent of the problem and what should be done to fix it. What type of surveyor/professional would be best placed to investigate this issue?

ThisIsWeird

Photos, please.

And do you have a copy of the plans that were submitted to BC so we can see how it was meant to be built? Things like insulation levels. Type of construction. Outer skin material. Etc.

It sounds worrying. And the contractor's response seemingly inadequate. Ie - I cannot think of a 'good' cause for this.

GermanderSpeedwell

Thanks for your reply. My camera doesn't pick up well the contrast between the yellow/white paint but anyway I've attached a photo. Also a section of the plans (the photo was taken above the new staircase on the left side of the landing), and the specification of the plans. The last photo clearly shows the join between the existing house/loft where the yellowing has appeared. By the way, it's a 1940s house with single brick walls. 

ThisIsWeird

I'm going to struggle to help with this - really beyond my knowledge. But there's some folk on here who I hope can.

stuart45

If it's penetrating damp, waiting for it to dry out in the summer, and then painting over isn't the answer. Is that a timber stud wall on top of a 9 inch brick wall?

GermanderSpeedwell

It's blockwork - this is what's written in our construction contract:

'Raise up the new gable wall in solid blockwork and apply a cement render and 2No coats of white masonry paint. Total allowance is 12m^2.'

Doozergirl

I wonder if it's just a bit of staining where the top of the wall may have gotten wet between the roof coming off and the gable being raised. 

If it isn't wet now then it probably isn't an ongoing issue.  

I think I'd have rendered the whole gable wall though.  There is a potential week point across the joint for water ingress.  We can't really see the detail from that distance but it looks both more distinct and less distinct than it should, depending on one's choice of dealing with the rendering - making it on smooth wall or opting for a bell bead to overhang the join and take water away from it.  

ThisIsWeird

I'm confused. Which 'gable wall' has been 'raised up'?

The gable wall with the dark-coloured window is surely original, and the only addition made for the loft is the dormer shown to its left in that picture, and that is timber construction, with tile-hung or cladding (can't make it out)? What's been made in 'solid blockwork'?

Doozergirl

ThisIsWeird said:

I'm confused. Which 'gable wall' has been 'raised up'?

The gable wall with the dark-coloured window is surely original, and the only addition made for the loft is the dormer shown to its left in that picture, and that is timber construction, with tile-hung or cladding (can't make it out)? What's been made in 'solid blockwork'?

Raise up the new gable wall in solid blockwork and apply a cement render and 2No coats of white masonry paint. Total allowance is 12m^2.'

The gable we're looking at was originally a hipped roof.  

ThisIsWeird

Doozergirl said:

ThisIsWeird said:

I'm confused. Which 'gable wall' has been 'raised up'?

The gable wall with the dark-coloured window is surely original, and the only addition made for the loft is the dormer shown to its left in that picture, and that is timber construction, with tile-hung or cladding (can't make it out)? What's been made in 'solid blockwork'?

Raise up the new gable wall in solid blockwork and apply a cement render and 2No coats of white masonry paint. Total allowance is 12m^2.'

The gable we're looking at was originally a hipped roof.  

Ah! I see. Thanks.

Man, it looks in an awful state for something painted last year. :-(

stuart45

Doozergirl said:

I wonder if it's just a bit of staining where the top of the wall may have gotten wet between the roof coming off and the gable being raised. 

If it isn't wet now then it probably isn't an ongoing issue.  

I think I'd have rendered the whole gable wall though.  There is a potential week point across the joint for water ingress.  We can't really see the detail from that distance but it looks both more distinct and less distinct than it should, depending on one's choice of dealing with the rendering - making it on smooth wall or opting for a bell bead to overhang the join and take water away from it.  

I think you could be right about the cold joint in the render. It often causes a slight shrinkage at the joint, unless a bonding agent is used. Using a smooth finish above a roughcast, or tyrolean probably makes the joint more difficult. 
Being a solid wall penetrating damp is more of a issue with cracked render.
Is the inner wall insulated?