Roof vents, over-insulation(?) ,woodworm, condensation

[toadstooltomato]

Hi all,
a roofing question. Forgive the crappy drawings but i cannot do much better! (The one with the green line is where i suspect we have a lack of air flow)
We have curved ceilings in our bedrooms as the rafters come down through what would be corners where wall meets edge of roof.

We have recently had lots of insulation added, about 400mm now. This concerns me in that where it is stuffed down between the lath and plaster ceiling and the tiles, there cannot be much air flow. Also the membrane is an 80's type (?) looks like a swimming pool cover. Is clearly totally vapour and water proof. Thus there are beads of condensation forming on the inside and probably ending up down near the rafter ends where there is little air flow.

We also have evidence of what a BWPDA inspector calls 'historic' beetle attack.

Am considering the merits/demerits of removing all the mineral wool insulation to encourage air flow, then have loft floor sprayed with thinner layer of foam insulant?

Any thoughts?
Thanks to all.
T

Just realised; I didn't draw any battens. There are battens .... Imagine there are battens!..

 

[Mw Roofline]

Can you not get in the loft and pull the insulation away from the eaves to vent it a bit?

 

[JohnD]

tell us what ventilation the loft currently has

tell us how the rooms below are ventilated

tell us if you ever drape wet washing about the house.

 

[toadstooltomato]

tell us what ventilation the loft currently has

tell us how the rooms below are ventilated

tell us if you ever drape wet washing about the house.

I will answer, I will answer!

There are no vents that I can see at all.

We NEVER leave washing in the house- large covered area outside for this.

Rooms below are poorly ventilated. Considerable condensation on bedroom windows in the morning, common in winter.

The advice I already had- move the insulation out of the eaves- was on my mind, but then I would create very cold areas of lath and plaster, at the curves of the ceiling, if you see what I mean? Would these (relatively)cold areas of the ceiling end up loaded with condensation, as the middle part of the ceiling would still have the strip of insulation on it?

Perhaps i should remove the insul' from the eaves and then batten and t+g the bedroom ceilings (inside) with vapour barrier and insulation behind the T+G?

Have done this at a house already- can look pretty good if done well .

 

[JohnD]

start by improving ventilation of the loft. you need cross-flow of air from at least two opposite sides. it can be done by making holes in gable ends or by unblocking eaves. The objective is not to leave cold ceilings.

Then look for and rectify sources of warm wet air from the house getting into the loft. Particularly holes in ceilings where pipes or cables go through, also cracks. Also ill-fitting loft hatches.

then improve ventilation of rooms full of wet warm air, especially bathrooms but also rooms where you spend several hours breathing or doing anything hot and sweaty.

 

[darthjan]

Hi all,
a roofing question. Forgive the rubbishy drawings but i cannot do much better! (The one with the green line is where i suspect we have a lack of air flow)
We have curved ceilings in our bedrooms as the rafters come down through what would be corners where wall meets edge of roof.

We have recently had lots of insulation added, about 400mm now. This concerns me in that where it is stuffed down between the lath and plaster ceiling and the tiles, there cannot be much air flow. Also the membrane is an 80's type (?) looks like a swimming pool cover. Is clearly totally vapour and water proof. Thus there are beads of condensation forming on the inside and probably ending up down near the rafter ends where there is little air flow.

We also have evidence of what a BWPDA inspector calls 'historic' beetle attack.

Am considering the merits/demerits of removing all the mineral wool insulation to encourage air flow, then have loft floor sprayed with thinner layer of foam insulant?

Any thoughts?
Thanks to all.
T

Just realised; I didn't draw any battens. There are battens .... Imagine there are battens!..

Can you tell me if you have had any luck with any of the ideas given we have the same type roof and had no problems until we got cavity wall insulation put in we have tried alsorts.

 

[darthjan]

we have had years of problems with the condensation in our loft . had new roof felt put on, new loft insulation , that silver insultion on the roof to try and stop warm air getting to it. we have eight vents in the roof and still the same im at the end of my tether. the cavity company came out and said it was not there fault and that the eaves where clear. dont believe a word they said.HELP.

 

[chappers]

Unless your insulation is rammed in so tight that it is solid then air will pass through anyway, Have your roof vents been cut through the membrane otherwise they won't be drawing air from the loft space.
sounds like your house ingeneral has a ventilation problem do your windows have trickle vents. Can you add some vents to the gable ends if you have them.

 

[darthjan]

Unless your insulation is rammed in so tight that it is solid then air will pass through anyway, Have your roof vents been cut through the membrane otherwise they won't be drawing air from the loft space.
sounds like your house ingeneral has a ventilation problem do your windows have trickle vents. Can you add some vents to the gable ends if you have them.

the vents are cut through the membrain, sadly we dont have a gable end, the rest of the house has no problems and even with the trickle vents open we have had the trouble . we are going to try and seal the loft hatch more and get rid of the spot lights in ceiling that the previous owner put into bathroomnad a bedroom.ive just asked if someone would put in some air bricks round the eaves.