Tongue & groove boarded ceilings

[BarryF]

I have recently purchased a 19th century grade II listed cottage with tongue and groove boards attached to the roof joists for the bedroom celings. I have been told that using fibreglass loft insulation between the joists is likely to lead to condensation on the tongue and groove boards and eventually decay.

Does anyone have any advice - It would be much appreciated. There is currently no insulation in the loft.

Barry

 

[biffvernon]

Nonsense. Any condensation, if it were to happen at all, which it won't, would happen on the cold side of the insulation. Your t&g boards are on the warm side so quite safe. The cold side of the insulation is the air in your loft, which is why condensation won't form there either.

My bedroom ceiling is just as you describe.

Get down to B&Q today, 31/10/07, while the half price offer lasts!

 

[Ian Bond]

Hi BarryF

I'm in West Yorkshire, and am wrestling with a similar problem, although it is a lath and plaster ceiling not T&G.

There is a long, long thread here about the various merits of Thermafleece "An alternative to thermafleece". It would be worth a quick read, although it will leave you with more questions than answers!

I won't start asking loads of questions about your roof structure at this point, to save time.

Just, how are you planning to get the insulation in between the rafters? Are the tiles coming off, or the t&g boarding? Have you approached the CO for advice on this, particularly if the fabric of the building will be disturbed/altered?

It would be interesting to know what the official advice is on the subject of insulating roofs, whilst mitigating the risk of condensation...

 

[biffvernon]

Barry says he's putting it between the joists not the rafters.

 

[Ian Bond]

It was the term 'roof joists' that confused me.

I'm not sure if he means the ceiling joists, with an uninhabited attic space above, or if the bedrooms are in the attic and he meant rafters...

 

[BarryF]

Thanks for your replies. My apologies for using the wrong terminology. My question referred to insulation between the ceiling joists with an unused roof space above. So the insulation would be laid on the upper surface of the ceiling boards.

I am ecouraged by 'biffvernon's comments

The reply from local CO was not very specific :
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If insulation is put into the roof it should be a breathable type of insulation to allow air to circulate. Plastics will trap moisture and cause damp problems.

It is important that if insulation is inserted there should be ventilation gaps within the roof space to allow the area to breathe and help the area to dry out.
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Barry

 

[Lime]

Presumably the CO was thinking of a vapour barrier when he referred to plastics as the water vapour needs to be able to escape and not be trapped to be condensed somewhere in the house.
He is right about the ventilation in the roof space too.
The better the insulation the colder the loft space can become.
Then ventilation becomes more important to ensure that moist air isn't trapped in the loft during a cold weather spell.
If water vapour is not removed it can condense on any cold surface causing damp, saturated timbers and rot.

The B&Q fibreglass in silver perforated breathable plastic is easy to use and quite cheap.

 

[Ian Bond]

Sounds good to me Lime.

BarryF: How's the ventilation in the attic? Any signs of problems up there at the moment?

Has a non-breathing roofing felt been fitted, or can you see the underside of the tiles?

 

[BarryF]

York stone roof slates without roofing felt. I think ventilation is fine.

 

[Ian Bond]

Sounds like you should be OK then.

It's on my list to remove the non-breathable felt from under my stone tiles - roof's OK so far ...

There has to be some risk of condensation, given modern lifestyles and the way we seal our houses to save energy: Blocked up chimneys, draught proofed windows and doors. Non-breathing roof felt (not in your case!)

Add impervious paints and wall coatings, and there's less opportunity for moisture to get out.

Then add insulation creating a colder attic space and you have ideal conditions for condensation, as Lime explained previously.

At least you are aware of the potential problem, and will know to check the attic for signs of trouble.