Damp ceiling woes!

[Sorbustree123]

The week before last we noticed damp patches on the ceiling in our bedroom, which is located in a side extension with an old flat roof. It was about 24 hours after a day of rain and strong winds. We were able to dry the damp patches using an electric heater in the room, and by the time our insurer's surveyor came out to take a look it was no longer noticeable - they tested the areas with a moisture detector and confirmed that they were now dry.

We set about getting quotes to replace the flat roof and the work was carried out about a week later. No damp patches reappeared in the interim (it didn't rain during this time and it was relatively warm outside). We then went away for three days and came back to find the ceiling still dry - at least that's what we thought. After having been back for around 24 hours, the damp patches reappeared, despite the roof having been replaced!

I can't work it out. We will of course speak to the roofing company we used, but I'm wondering if anyone has any ideas? The damp patches don't appear like dramatic leaks, more like condensation that slowly forms patches with a sprinkling of droplets that barely drop. Could it be something to do with the temperature outside dropping and us returning home and turning the heating on?

The damp patches are in a relatively straight line across the middle of the room, from side to side.

It sounds like the damp is following a joist that supports the roof. Either the joist is cold bridging to the outside and humid internal air is condensing along the cold internal surface. Or, there is a leak and water is tracking along the joist.

I've noticed that if there is a leak from above on the ceiling it stains brown, but if it is condensation it is just wet/damp with no stain.

Are there broewn stains?

Or brown even.

Thanks @Daftasabroom and @Somanysocks for the helpful insights... there have been no stains so far, brown or otherwise, so that's really interesting to know.

was the ceiling reinsulated when the new roof was done?

@PigletJohn no, it wasn't. They checked the overboard when the old felt came off, but it was in good condition so didn't need replacing.

How old is the building?

Open the windows to dry out the damp. Tape a piece of clear plastic tightly to the ceiling (try Frog tape, which will mark the paint less than most)

If water appears on the ceiling side of the plastic, it is a leak from above.

If the covered patch stays dry, or water appears on the room side, it is condensation.

Only just seen your message @PigletJohn but will give this a go! Assuming it is condensation forming inside the room, as it doesn't seem to be linked to when it rains but more in tune with cold weather, what do you think the best solution might be? The patches of damp aren't severe and don't seem to be leaving any damage, but they do keep reoccurring which is worrying. It's worst at night if it's cold outside, the heating is on inside, and the windows aren't open. The house is 1930s, with a 1980s side extension where the flat roof with the problem is occurring. Many thanks in advance!

@Sorbustree123

if condensation, ventilate the room and reduce sources of damp, such as wet washing, nearby bathrooms without effective extractor fans, and excessive breathing. Water vapour is lighter than air so will rise from rooms below, especially if there are holes in the ceilings.

Condensation on a ceiling is rarely seen now because good loft insulation is usual, but perhaps your flat roof is poor.

Thank again @PigletJohn Do you think we'll have to take the ceiling down to access the poor roof and make improvements? Or is there a way to avoid this?

No excessive breathing in the bedroom seems a bit harsh though

probably.

it's possible to add an extra layer of insulated plasterboard to the ceiling, but this will not be as good as taking it down and adding a (much thicker) layer between the joists. When putting up the new ceiling, you can use the insulated plasterboard as this will give a bit extra, and reduce the slight risk of shadow pattern dust staining along the joists (this is not likely anyway, unless you smoke, have an open fire, or use candles) If not, I'd have the foil-backed plasterboard.

it's always worth thinking of when you have a flat roof relaid, as insulation can be laid from above while it is open.

Many thanks for your advice @PigletJohn, the roofer has returned and suggested installing mushroom vents but I'm assuming that these alone will not be enough to combat the condensation forming on the ceiling, as it's the insulation that needs improving? Dread to think how much it's going to cost to remove the ceiling. Any ideas? We're in Hertfordshire. Fortunately it's the only room in the house that's not yet decorated and with new carpets due in the future.

Plasterers charge a few hundred pounds for a room. There will be extra work in pulling down the old and adding the insulation.

@Sorbustree123

Only just seen your message *@PigletJohn* but will give this a go! Assuming it is condensation forming inside the room, as it doesn't seem to be linked to when it rains but more in tune with cold weather, what do you think the best solution might be? The patches of damp aren't severe and don't seem to be leaving any damage, but they do keep reoccurring which is worrying. It's worst at night if it's cold outside, the heating is on inside, and the windows aren't open. The house is 1930s, with a 1980s side extension where the flat roof with the problem is occurring. Many thanks in advance!

We have a similar building combo in age/roof terms, but don't have that problem. When we rewired, we found the flat roof had loft type insulation above the plasterboard, probably when that roof was last redone, which was in the last fifteen years or so according to our vendor. I'm wondering if you have no insulation at all in there?

I must say we're not happy with our roof, though at present it doesn't actually leak or get damp. It doesn't join up with the main slate roof very well and can't be made to because of differences in height- I suspect it will not be long before we have trouble with it. When our vendor last had it done he had to get the roofers back to fix it. We're even thinking of having a hipped pitch put on it when we overhaul the main roof in the next year or two, but no idea if this would cost too much, or require planning permission. I hate flat roofs, though a surveyor friend tells me modern flat roofs are better and last longer than the old ones we all love to hate.