Builders Advice Please

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BryanDC

Well-Known Member
Is your ventilation system venting outside or back into the loft?
If it is discharging into the loft you will always have a condensation problem in winter because of the water content from your houshold activities; bath, shower, cooking and breathing. I just had to clear up a small water leak in the loft as the drain from my ventilation had become blocked. Then the drip tray overfilled.
 

downwind

Well-Known Member
Has this problem been since insulation was fitted and has it been more noticeable in the recent still and cold conditions we have had lately.
It was already a problem, I increased the depth of insulation in the hope of reducing the condensation. This was on advise of a roofer who also wanted to remove the complete roof (tiles and felt) and replace the felt at great expense.
 

downwind

Well-Known Member
Is your ventilation system venting outside or back into the loft?
If it is discharging into the loft you will always have a condensation problem in winter because of the water content from your houshold activities; bath, shower, cooking and breathing. I just had to clear up a small water leak in the loft as the drain from my ventilation had become blocked. Then the drip tray overfilled.
The ventilation system draws air from the loft, filters it and discharges to the livings areas. We did have problems with condensation on all the PVC double glazed windows. The Nuaire system cured that overnight.
 

Norfolk Horn

Well-Known Member
It was already a problem, I increased the depth of insulation in the hope of reducing the condensation. This was on advise of a roofer who also wanted to remove the complete roof (tiles and felt) and replace the felt at great expense.
If you want to message me your number I will ring you if you want.
It would be better to talk through this.
 

BryanDC

Well-Known Member
The ventilation system draws air from the loft, filters it and discharges to the livings areas. We did have problems with condensation on all the PVC double glazed windows. The Nuaire system cured that overnight.
So it is supply only? Where does the excess air go out af the house?
 

downwind

Well-Known Member
So it is supply only? Where does the excess air go out af the house?
That's a good question, with the PVC double glazed units the only real route out for the excess air would be up the chimney which is in effect sealed by the log burner. I may have to look into the possibility of fitting trickle vents to some of the window units.
Thanks to all for the helpful suggestions, more roof ventilation looks to be the way forward.
Cheers, Pete. :tiphat:
 

shakey jake

Well-Known Member
That's a good question, with the PVC double glazed units the only real route out for the excess air would be up the chimney which is in effect sealed by the log burner. I may have to look into the possibility of fitting trickle vents to some of the window units.
Thanks to all for the helpful suggestions, more roof ventilation looks to be the way forward.
Cheers, Pete. :tiphat:
my understanding of the nuaire system is the air pushed into the building keeps the air moving and encourages air change when you open the external doors and windows, ive seen loads fitted to old houses especially ex council houses, trickle vents my help with this aswell
 

downwind

Well-Known Member
my understanding of the nuaire system is the air pushed into the building keeps the air moving and encourages air change when you open the external doors and windows, ive seen loads fitted to old houses especially ex council houses, trickle vents my help with this aswell
Nuaire describe the PIV system as "creating a positive pressure within the home forcing air pollutants out through the natural leakage gaps found in every home" which makes sense but I suspect a couple of trickle vents may help.
 

Finch

Well-Known Member
It's because you've got a "cold roof", ie. your insulation is on top of the ceiling joists not between the rafters, and your bituminous felt is non-breathable.

Warm moist air rises through the ceiling insulation in your loft (insulation only slows down heat loss, it doesn't stop it), hits the icy cold and completely impermeable bitumin felt, condenses into water droplets and runs down the felt, often dripping off onto the mineral wool which becomes damp and causes mildew on the underside of the ceiling below, or it runs all the way down the felt, and if your lucky, drops onto the soffit where the felt meets the fascia board and is vented away - if you have sufficient venting in your soffit.
this is why it is vital when fitting above ceiling mineral wool insulation that you leave a small gap at the eaves so the wool cannot come into contact with the underside of the felt. If it does the wool will become damp from condensation running down the felt and you end up with terrible mildew in the room below at the junction of wall and ceiling.

Ideally, all roofs should use breathable membrane under the battens rather than felt, and they should be insulated between the rafters with PIR (Selotex etc) foam board - a "warm roof" - rather than just mineral wool between on top of the ceiling joists. That way, there is no cold surface on the roof slope for the moist air to condense on.
If this is done with breathable membrane and counter battening and a small gap is left in the insulation at ridge and eaves, you can use tile/slate vents and all moisture will vent through the roof.

In an ideal world you'd re-roof your house using breathable sarking membrane and fit insualtion between the rafters while the roof is open. That way your loft will have the same climate as the rest of the house with no cold surfaces and the moisture can escape without condensing.
As it is, your best bet is to push PIR insulation board between your rafters and make sure you have plenty of airflow with a couple of 9" air bricks in the gable ends and well vented soffits. There is no point using vent tiles/slates with impermeable bitumen felt or plastic. It won't be as good as a re0roof with breathable membrane but it should cure your damp problems.
 

downwind

Well-Known Member
It's because you've got a "cold roof", ie. your insulation is on top of the ceiling joists not between the rafters, and your bituminous felt is non-breathable.

Warm moist air rises through the ceiling insulation in your loft (insulation only slows down heat loss, it doesn't stop it), hits the icy cold and completely impermeable bitumin felt, condenses into water droplets and runs down the felt, often dripping off onto the mineral wool which becomes damp and causes mildew on the underside of the ceiling below, or it runs all the way down the felt, and if your lucky, drops onto the soffit where the felt meets the fascia board and is vented away - if you have sufficient venting in your soffit.
this is why it is vital when fitting above ceiling mineral wool insulation that you leave a small gap at the eaves so the wool cannot come into contact with the underside of the felt. If it does the wool will become damp from condensation running down the felt and you end up with terrible mildew in the room below at the junction of wall and ceiling.

Ideally, all roofs should use breathable membrane under the battens rather than felt, and they should be insulated between the rafters with PIR (Selotex etc) foam board - a "warm roof" - rather than just mineral wool between on top of the ceiling joists. That way, there is no cold surface on the roof slope for the moist air to condense on.
If this is done with breathable membrane and counter battening and a small gap is left in the insulation at ridge and eaves, you can use tile/slate vents and all moisture will vent through the roof.

In an ideal world you'd re-roof your house using breathable sarking membrane and fit insualtion between the rafters while the roof is open. That way your loft will have the same climate as the rest of the house with no cold surfaces and the moisture can escape without condensing.
As it is, your best bet is to push PIR insulation board between your rafters and make sure you have plenty of airflow with a couple of 9" air bricks in the gable ends and well vented soffits. There is no point using vent tiles/slates with impermeable bitumen felt or plastic. It won't be as good as a re0roof with breathable membrane but it should cure your damp problems.
Thanks for your reply Finch. As you say, in an ideal world a full re-roof would be a belt and braces approach but the cost would be prohibitive.
I've had some useful suggestions which I will follow up as my first options and see if that helps.
Thanks again to all who have replied to my post.
 

Cyres

Well-Known Member
I had a similar problem and it was a simlpe fix. Basically you need to increase the ventilation and can be achieved by allowing air to move through the felt overlap. I did this by buying some oval plastic pipe which is used for running electric cable through. You need to cut lengths just a little longer than the overlap and slide them in down through the overlap joint. I held them in place by a bit of bent copper wire. This has two effects creates an air gap as it slightly seperates the felt on the overlap and air can move through the pipe. My knowledgable builder was impressed, previuosly he had seen wooden clothes pegs clipped to the under piece of felt to create a gap. In my case this was part of a roof which used a plastic type underfelt. Other side was breatherable type.

Anyway will cost next to nothing wont damage the roof or felt and easy to install or remove.

D
 
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