Damp chimney breasts and lof condensation

[rickb72]

hi,

I have recently bought a 1930s detached house which I am renovating. When we stripped back all the wall paper the tops of the upstairs chimney breasts, they both had signs of damp. The house has has loose rockwool insulation retro fitted to the cavities and also has about 300 mm deep rockwool in the loft.

The damp got worse as we got closer to winter and is now about 1.5m down from the top of both the chimney breasts. Also during the really cold spell we had a lot of condensation in the loft space.

I had the roofer check the chimneys and he is happy the chimneys and flashings are both ok.

I was thinking of fitting some slate tile vents and an air brick at the top of the gable end to ventilate the roof space.

Any advise on the cause and remedy for this would be much appreciated!!

 

[foxhole]

Is the chimney capped, ventilated? It should be .

 

[rickb72]

Yes both chinmeys are vented.

One other thing is that as the damp has got worse it is coming further down the wall, which makes me assume it is coming from the rook space ??

 

[foxhole]

Where are the vents ? on chimney breast? at ground and first floor level?

 

[rickb72]

both chimneys are open on the ground fllor and have vents fitted about 300 mm above floof level upstairs, all have pots/cowls on the tops

 

[foxhole]

Must have problems at roof level, get another opinion on chimney, must be a leak there.

 

[deniance]

If yor chimney and flashing is ok, and you can see water droplets all. Over your roof , in a uniform condensation type of pattern then its condensation, your attic doesn't produce condensation, you do, breathing showering, cooking drying clothes indoors etc, warm air rises to your ceiling carrying the moisture, its kept there because your rockwool is keeping it warm, then the rest of the room fills with warm moist air during the days with heating on, it will then start to find its way up through any cracks or holes and get into your attic, the hole for a light in every room a hole for light switch cable in every room, attic hatch not giving good seal, downlights, leaking or loose fitting shower vent ducting etc, seal them up and moisture cannot get up into attic, these are vital points that I cannot believe are not mentioned on leaflets and instructions for loft insulation,

I know this sounds like rubbish, but I spent ages looking for leaks, in my roof when all along it was condensation buildijng up on my felt in attic, dripping and running off onto various parts of ceiling, warm air was going through my loose fitting attic hatch touching the chimney breast, which is obviously freezing cold, condensing, building up to droplets then running down chimney into bedroom leaving a big damp cloud that looks like and makes you think you have a leak, I sealed my attic hatch, sealed downlights, airtighted the shower vent ducting, and the natural ventilation of the attic has died the condensation away, the damp patches on my room walls, took months to finally dry, nearly a year now and hasn't returned,

My advice to you is get up in attic and have a look, before your beams start to rot, fill all holes with caulk or expanding foam from screwfix, cheap, let us know how it goes

 

[deniance]

I would like to add, in case anyone reads this after searching for an answer, my sister has damp on chimney breast upstairs in bedroom, i found chimney was vented at bottom with small plastic grill, and a pepperpot cowl outside, i poked drain rods up and could see the pepperpot moving so flue was clear and vented, but still damp, the root cause was the loft insulation , it was not at fault just doing what it is meant to do, keep below warm resulting in a freezing attic, this meant that the moist warm house air being vented through the flue was passing from a warm flue to a really cold flue at the insulation level, this was then condensing and running down inside the flue, until the damp appeared. We proved our theory by removing a red chimney brick in the loft, inside we could watch the drips run down the flue, and it wasnt raining!, to solve the problem we pushed a black bag stuffed with vermiculite, into the flue, this had a rope attached to it, rope down first, then bag, pushed this down about a metre below the loft insulation level then poured the rest of the vermiculite on top and brought it level to the loft insulation. The rope has dropped down to the fireplace and will hopefully pull it out if flue needs to be used. We then put the cemented the brick back in sideways so the top of stack is still vented from attic to roof.we went into the attic the following day and all the red chimney bricks that were really wet had started drying already, ive told her to paint her bedroom because i have every confidence that its the end of the matter. Hope this helps someone, my sister had a roofer out, all fine, then a damp speacialist, who said that it was some sort of salt and wanted to strip and replaster whole wall in speacial render!!! Never under estimate condensation

 

[deniance]

Oh and we blocked the lower vent at fireplace to stip any moist house air getting in to the flue, the rooms ventilation which was supplied by the old fireplace has now gone, ive made her aware of this, and told her to make sure she gets better ventilation in the bedroom as it is suffering from waterfall condensation on the windows in the mornings, she was bidding on a through the wall mvhr unit but no joy.......