No insulation (and no space for it) = damp

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  • GDB2222
    GDB2222 Posts: 24,879 Forumite
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    Would it be straightforward to remove a few tiles to investigate? 
    No reliance should be placed on the above! Absolutely none, do you hear?
  • ThisIsWeird
    ThisIsWeird Posts: 5,081 Forumite
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    Since that area needs insulating in any case, wouldn't it make sense to explore this from inside?
  • stuart45
    stuart45 Posts: 4,089 Forumite
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    It looks like condensation to me, which is common on those types of ceilings.
  • MouldyOldDough
    MouldyOldDough Posts: 1,839 Forumite
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    stuart45 said:
    It looks like condensation to me, which is common on those types of ceilings.
    But its on the outside
    How does damp air get on the outer face of the ceiling board? 
  • stuart45
    stuart45 Posts: 4,089 Forumite
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    The surface of the plaster must be below the dew point temperature, so if it's an upstairs bedroom at night when the room temperature is usually low and people are putting moisture into the air condensation will form on the surface.
    Some of it will soak into the boards and some will soak into the rafters. Sometimes you get streaks of it running down the wall.
    The boards tend to dry out later as the air flow above in the loft dries them out, but they tend to stay damper where they are touching the damp rafters. This damp creates a good place for the mould spores to germinate.
  • ThisIsWeird
    ThisIsWeird Posts: 5,081 Forumite
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    edited 22 March at 11:47AM
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    stuart45 said:
    The boards tend to dry out later as the air flow above in the loft dries them out, but they tend to stay damper where they are touching the damp rafters. This damp creates a good place for the mould spores to germinate.

    That's a good alternative cause, Stuart, and I hope you're right.
    MOD, regardless of the cause - an external leak, or internal condensation - that slope needs to be insulated. This ain't a big job, but I would definitely remove the existing strip of sloping p'board first. This will allow you to inspect behind the wall and check for leaks, and also almost certainly allow for a more effective layer of insulation.
    Personally, I'd be happy with, say, 2" of Celotex-type insulation there. Yes, more is always good, but you need to counter that against loss of space and/or awkwardness of installation. For instance, if you were to fit 2" of insulated board directly on to that wall, then you'll have 2+" of extra thickness to deal with in your bedroom, and make it look good. This might well be ok, or it could be tricky. If, instead, you remove the existing p'board, you should be able to neatly cut and insert at least 1", possibly 2", of Celotex to fit in between the rafters, flush with their front edges, and leaving at least a 50mm vent gap behind where the tiles are. That means you'd only need to overboard with 1" insulated p'board, almost certainly a much easier task. And, if you do manage to fit 2" in between the rafters, then a mere 1" of insulated overboarding will give you a total of 3" - superb.
    So, if you wanted to go for a total of 3", or even 4", thickness; getting at least half of this between the rafters means that half of it won't be sticking into your room.
    2" will make a HUGE difference. Extra inches above this adds only relatively marginal additional improvements - so certainly add extra if it's easy and convenient, but don't concern yourself too much if you cannot.
    Removing that slope will also allow you to inspect the vertical wall below, possibly even slipping some insulation down there. Do you have alternative access to the vertical walls, from an eaves passage?
  • FreeBear
    FreeBear Posts: 14,855 Forumite
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    ThisIsWeird said: If, instead, you remove the existing p'board, you should be able to neatly cut and insert at least 1", possibly 2", of Celotex to fit in between the rafters, flush with their front edges, and leaving at least a 50mm vent gap behind where the tiles are. That means you'd only need to overboard with 1" insulated p'board, almost certainly a much easier task. And, if you do manage to fit 2" in between the rafters, then a mere 1" of insulated overboarding will give you a total of 3" - superb.
    So, if you wanted to go for a total of 3", or even 4", thickness; getting at least half of this between the rafters means that half of it won't be sticking into your room.
    A minimum of 25mm (1") air gap between insulation and the membrane under the tiles is all that is required. So depending on the size of the roof timbers, 50-75mm (2"-3") can be fitted. Aim for 150mm (6") of Celotex/Kingspan to hit B.R. recommendations. If this is not practical, put in as much as possible. Don't forget to stagger any joints between the lengths of insulation, and use expanding foam to fill any gaps. Aluminium foil over the top will aid the vapour barrier effect of the foil facing on the sheets of insulation.

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  • MouldyOldDough
    MouldyOldDough Posts: 1,839 Forumite
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    We have a roofer coming to  have a look early next week
    hopefully they will be able to help
    unfortunately - I am disabled and unable to do "anything"
  • stuart45
    stuart45 Posts: 4,089 Forumite
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    You might be better off with a handyman to fit some insulation into the rafters.
    If you know and trust the roofer it's OK, but one you don't know might charge you for some unnecessary work.
  • MouldyOldDough
    MouldyOldDough Posts: 1,839 Forumite
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    stuart45 said:
    You might be better off with a handyman to fit some insulation into the rafters.
    If you know and trust the roofer it's OK, but one you don't know might charge you for some unnecessary work.

    No "handyman" will venture INTO the loft - we tried to get our regular chap to - but he told us that if he put his foot through the floor - he wouldn't be covered by insurance
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