Watermarks/Damp on sloped part of ceiling - help please!

[martintat]

Hi all,

Please advise/help if you can:

I have a damp problem on the sloped parts of my ceiling.

Can anybody provide advice on the cause and best way to solve?

The roof tiles are not backed with any felt or anything else so its just tiles in the loft so maybe water is getting through.

The roof does extend further down past the ceiling level, what the best way to solve is?

Will lining the inside of the roof with a waterproof membrane/underlay attached to the underside of the beams/struts which at the roof end runs outside to the guttering do the job, or will it cause lack of ventilation?

i have attached a photo of the damo marks on the sloped/angled part of the ceiling and have attempted to label!.



there are no damp signs on the flat part of the ceiling, however this may be solved with the loft insulation soaking it up.

any help greatly recieved!

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• martintat
• 3 Sep 2012
• 1

thankyou

 

[Burnerman]

It would be a good idea to scrutinise the slate work on the roof to start with......look for cracked, missing or slipped slates / tiles and also look to see if the ridge tiles have similar faults or missing mortar.
The felt undercloak really is there to keep dust and dirt out - its the slate that does the waterproofing but of course in extreme weather there is some possibility of rain being blown under the slate.
John

 

[foxhole]

Fix the leaking roof.

 

[martintat]

Thanks Burnerman - have checked for broken/missing tiles - were a couple broken but not directly above the area on my picture.

I have since found a white, light, fluffy mould on the bottom of the rafters in the corners/eavers - which is exactly where the plasterboard ceiling is attached to the rafters where the patches appear.

As there's no felt i think you may be correct about driving rain getting in as that part of the tiled roof is very close to this sloped ceiling, however recently it hasnt rained very much.

I wonder if this white mould is a sign of another problem - or if the mould itself is causing the patches??

I am going to vent the soffits to provide improved ventilation in the sloped eaves, and will coat rafters/corners with fungicide.

Is there anything else you could reccommend?

Many thanks for your help.

PS. contemplating buying a new roof as its old concrete tiles with now felt - but if theres an easier/cheaper fix i'd prefer that obviously.

Thanks

 

[Burnerman]

I think you're very much on the right track here - but if rain should bleach in then the dampness could occur well away from the slate issue as the water can run along joists, slaters laths etc and then drop at any convenient spot.....usually where a nail pokes through!
The white mould is likely to be some sort of efflorescence, but treating any visible timber is a good move anyway - as is providing plenty of ventilation.
John

 

[martintat]

Thanks again for responding.

I take it the efflorescence is nothing major to worry about then?

I've had a roofer round fitting a few tile vents today. He told me his son had ta similar problem and that he seems to think its condensation forming on the ceiling directly where it attaches to the rafters.

I'm just baffled by why the damp stain patches of condensation are where the rafters are and not the rest of the ceiling. All I can think is that the rafters are damp and thus colder than the rest of the ceiling making the condensation worse??

The roofer said he slotted some kingspan insulation board down the eaves of his sons roof to make the ceiling surface a bit warmer - I'm jus a bit wary as this may reduce the ventilation and trap the dampness in??

Think I'll try it and see as can't be any worse!

 

[Harbourwoodwork]

leave air gap on slate side of insulation, moisture barrier over rafters (on warm side of insulation) stop condensation getting out

 

[martintat]

Harbourwoodwork thanks for your advice but could you explain in more detail/simpleton terms as i don't fully understand..what do you mean by 'moisture barrier over rafters (on warm side of insulation) stop condensation getting out'? - a diagram would be great help.

Apologies...I'm new to this kind of thing

Thankyou

 

[Harbourwoodwork]

starting from the inside plaster board,moisture barrier (thin polythene sheet sold in screwfix) rafters with insulation between,and air gap,example if your rafters are 100mm use 75mm insulation which leaves 25mm gap on outside edge of rafters, (celotex hard foam insulation).,be certain before going down this road that all the outside repairs are done well this is not a substitute ,it just stops condensation running down the back of the plaster boards.

 

[martintat]

Thanks again Harbourwoodwork.

I understand most of that! Apart from - do you mean i use the polythene sheet over the loft floor in the eaves as such (so covering the plasterboard and joists which they attach to), or do i use it over the underside of the rafters running down the roof?


I ask as i cant see how i could get the polythene under the rafters which run down into the eaves because the rafters are attached on both edges (one side to the plasterboard ceiling, and the other side to the roof slats).

If you mean me to lay it over the joists and ceiling and then put insulaiton board over this inbetween the joists then will this not stop the joists/plasterboard (loft side) from breathing?

I will try and post another photo (later today) of inside the loft to show the eaves etc which hsould help you see my position.

Sorry to go on.

Thanks millions for your help

 

[Harbourwoodwork]

moisture barrier on rafter face some builders use foil back plaster board

 

[martintat]

heres some pics of the rafters runningdown into the eaves.

as you can see it may be difficult to lay polythene down the eaves as joists run down.

also you can see the mould growth/salts

any further advice greatfully received

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• martintat
• 18 Sep 2012
• 1

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• martintat
• 18 Sep 2012
• 1

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• martintat
• 3 Sep 2012
• 1

[/img]

 

[libby lou lou]

Scrape the siht away connecting the beams to the the ceiling.

 

[MidsTW]

Sorry to drag up an old thread.

Did you manage to fix this problem? I also have damp patches where the rafter meets the joist.