Condensation or a Roof Leak?

[Oddjob66]

At the beginning of November I noticed a mark on the ceiling. Suspecting a leak, I got a roofer in to trace the source. He confirmed that the valley was defective and would need replacing. As the house was under 10 years old, I lodged a claim with the NHBC. The inspector from the NHBC said the mark was due to condensation.
How do I know which diagnosis is correct, please?

 

[JohnD]

if it is condensation it will be all over the loft, mostly on the upper parts, and will be worse in cold dry weather and at night when the roof is cold.

If it is a leak it will be in one area in particular, and will be worse after rain even if the weather is mild.

Take lots of photos.

 

[catlad]

If your house is new then it will probably have fibreglass valleys and there was someone complaining recently about them causing condensation on his new roof.

 

[Oddjob66]

The NHBC Report does mention a glass reinforced plastic valley gutter. This is damp and mildewy.

How much condensation would there need to be to create enough liquid to stain the ceiling, please? And why would the stain suddenly appear rather than gradually build up, please? And at a relatively warm time of year?

 

[JohnD]

photos please

//www.diynot.com/forums/viewtopic.php?t=129539

 

[roofspecialistsLondon]

You should have breathable felt installed running down the valley before the valley troaths are installed. My guess off the top of my head would be to check if there is a lead saddle installed at the top of the valley

 

[Oddjob66]

Sorry for the delay in replying.
I have attached a picture of the mark caused by the leak.
I know it is quite faint but I want to prevent it getting any worse.
Thanks for everyone's help.

 

[Oddjob66]

Well I thought I had

Mark on Ceiling

• Oddjob66
• 12 Jan 2015
• 1