Flat roof and ceiling issues

[arosindale]

Hi all,
Apologies if this is not the right area tk post this question.

Ok here is my problem:
Had a new deck and flat grp roof put on last summer with no issues, however over tbe last 6 months there seems to be a strange group of dark patches appearing on the bathroom ceiling below, almost like gbe roof is leaking in that spot, there are 2 main areas where this is happening, will supply photos for appearance and colour.

The roof is made up of these layers from top to bottom:
1.flocoat
2.grp x2 layers
3.osb deck
4.50mm ventilation cavity
5.100mm kingspan insulation
6.20mm kingspan insulation over the 100mm and joists (all joints foil taped for secondary vapour barrier)
7.12.5mm plasterboard tapered edge
8.3x coats of waterproof white paint (vapour barrier)

I am bemused as to what is causing the marks.
Have tried repainting with acrylic waterproof paint (I thought I may have applied a bit thin in these areas) but the marks keep coming through.

Have inspected the roof and all seems ok, it would take a serious amount of bad luck to not have layed the grp in these areas.

Bathroom is also ventillated witn a pir twin vents.
All penetrations (lights, vents etc) through the ceiling are sealed against the waterproofed ceiling via silicone, unlikely there is moisture entering the roof cavity from below.

Note, the marks are definately ABOVE the paintwork.

Any help or advice welcome,

Thanks in advance,
Ash

Untitled

• arosindale
• 9 Jun 2014
• 1

Untitled

• arosindale
• 9 Jun 2014
• 1

 

[arosindale]

Anyone??

 

[tony1851]

Could be black mould due to localized condensation.
Maybe a break in the insulation, or some small cold bridge?
Ideally the vapour barrier should be a taped sheet applied before the plasterboard.

 

[freddiemercurystwin]

Hmm, that first photy does look like classic condensation.

 

[wakey77]

hi mate,
where did you get your white vapour barrier paint from.

 

[arosindale]

Agreed, it does. Have even tried to scrub the area to see if I can remove the marks but as it's above the paint it will not budge...

Google this to find the paint : Technoseal white water proof paint 5L (£35 approx)