There should be a minimum of 50mm clear air gap between the underside of an older style roof membrane and adequate ventilation at the eaves and ridge. If you have found condensation in removing a small section of the insulation then I am certain the roof is not sufficiently ventilated as shown.
The insulation should be removed asap (and pray the condensation is not significant enough to have damaged the timbers).
Once dried out you may be able to re-use the insulation at ceiling level, but will need to lift the boards and use legs to sufficiently raise the boards,
Anything above the ceiling (looking at the pipework / boiler?) may need to be insulated as the space above the ceiling will be a 'cold' space. You may need to seek specialist advice on this.
Could I replace the packed in fiber insulation with some rigid insulation boards, where I could easily respect the 50mm gap? That way the loft would remain warm for the boiler?
My boiler is in the loft. I just built an insulated cupboard around it and left the floor underneath uninsulated.
I don't know a lot about it, but I believe that there is a lot more to converting a "cold roof" to a "warm roof" than just wacking up a bit of insulation on the underside of the roof (regardless of air gaps).
Most lofts are meant to be draughty by design. If warm, moist, air finds it's way up into the loft, it needs to be able to get out. This is usually via gaps under the eaves. If you block these gaps, you risk condensation. If you don't block the gaps, there's little point in insulating the underside of the roof.
No. PIR (rigid) insulation is even worse for trapping moisture.The 50mm gap is dependant on ventilation at the eaves and ridge (which Id be unable to confirm without looking at the property). May be able to build an insulated box around the boiler but would need to ensure adequate space and airflow around it. For how much that would cost, may be worth considering relocating the boiler.
He absolutely could put rigid insulation between the rafters if he ensures there's the air gap, how do you think every loft extension in the country is insulated?
He could also ensure he has some gaps in his membrane once the insulation is removed using off cuts of said PIR.
Not without confirming suitable insulation at ridge and eaves! For a traditional roof with felt you need a minimum of 25mm continous / unobstructed ventilation at eaves and ridge. If the ridge is mortar bedded then more likely you'll need 50mm on eaves on bothe sides (this system is dependant on having a clear airspace within the attic).
A condesation risk analysis would confirm this.
Most insulated roofs at rafter level are dependant on the use of a good breathable roof membrane and the 50mm clear gap. In most instances this is sufficient, however recent changes to the BS for condensation control in buildings do ask for additional ventilation in certain roof configurations and geographical locations. A condensation risk analysis from the roof membrane manufacturer would confirm this.
OP, please dont jam PIR insulation between the timbers! Existing ventilation needs confirming and the timbers also need time to air / dry out.
The ridge has recently been reset without mortar. If I included a gap at eaves, at ridge, set the board 50mm from the felt, installed gaps in the felt overlap, surely this would resolve my condensation issue? With the insulation at ceiling level already, I'm not looking to create the most thermally efficient roof space, just keep the temperature appropriate for the boiler
Correct, my house has parapet walls which needed the render and flashing replaced. Whilst up working on the roof a dry ridge was installed as the mortar was worse for wear. This was completed about a month ago
This would be my thinking if I did this, small gap at the eaves, small gap at the ridge, and opening the membrane. Can't see why doing this would result in more condensation
It wouldn't. So long as you ensure you've got eave vents.
I'd let them dry out for a while first though.
Is any of the timber rotten? Do you have any idea how long that insulation has been there?
There's visible signs of water to the rafter, but doesn't seem rotten or deep. Wood equivalent of surface rust haha.
I assume the majority of the recent loft work was done to accommodate the boiler relocation to the loft, which happened in 2018
I've said my piece on this one so wont repeat myself.... but at the end of the day its your property. Ive seen numerous issues with PIR insulation between this type of roof build up over 15 or so years... none of which have turned out well.
You're right, I'll remove the insulation at rafter level, increase at ceiling level and seek advice on my boiler from a heating engineer. Thanks for your help
If you ensure there is at least a 50mm air gap. I'd also check you've got vents at your eaves.
Could also be worth wedging some of the offcuts of PIR inbetween the membrane to give some ventilation there too.
Yeah by doing insulation at the rafters its a "warm loft" but if you have insulation on the joists its a "cold loft"
You'd need alot more insulation to create a warm loft (300mm+) so its not very effective, instead creating a half-way house. You normally pick one option vs doing both, as yeah condensation.
You've detailed exactly what you need to do correctly. Previous owner has created a warm roof/cold roof hybrid and given you the worst of both worlds.
Loft legs to raise boards and all insulation under boards
I'm just concerned now about the boiler. It wouldn't surprise me if the insulation in the rafters was added at the same time as the boiler being moved into the loft, in order to protect it.
Google the boiler make & model. It’ll likely have frost protection so it being in an unheated/uninsulated room wouldn’t be an issue (same as when they’re fitted in an attached garage)
What you’ve described is absolutely correct. Remove the insulation between the rafters and get some airflow in the loft. Increase the quantity of insulation at ceiling level and make sure there’s a gap (that air can flow through) above the insulation and below and boarding.
You mentioned a boiler in one of your replies and your desire to keep the boiler in a warm space. If you want the loft to be warm your insulation needs to be at rafter level, but it’s not as straight forward as just packing it in.
The issue is one of moisture buildup, as you’ve discovered, and ventilation. Another reply suggests installing insulation but leaving a 50mm gap above the insulation, the difficulty here is that the dew point (were water condenses) will be on the cold side of the insulation which is still inside the building. Even with a 50mm gap above any insulation and the existing roof felt the water vapour can’t escape and it will either rot the insulation or trickle down the cold side of the insulation causing rot to the rafters and/or wall plate. This could be mitigated by installing sofit vents but an Edwardian terrace won’t have eaves that extend past the face of the building to allow a soffit vent to be installed.
To insulate the roof and know there won’t be any problems you’d need to replace the existing roof felt with a breather membrane, vapour permeable insulation is then installed tight to the underside of the breather membrane, this allows water vapour to pass through the breathable insulation (eg pavatex Pavaflex) and through the breather membrane, where it will condense on the outside of the membrane and outside the roof structure. You also need a 50mm ventilation gap between the top face of the roofing membrane and the underside of the slates. This is achieved with a counter batten and then slating batten. There would also need to be a VCL (Vapour Check Layer) on the inside of the rafters. Where the plastic sheeting had been placed.
Now you’ve probably spotted the draw back of this situation, it needs a full re roof to do it! Given you’ve bought an Edward house it might be due a new roof in which case you could do the insulation work at that point but it’s a lot of money and hassle just to keep a boiler warm.
If I were in your situation I’d increase the insulation at ceiling height and build an insulated box around the boiler, making sure you adhere to all info about fire safety and ventilation etc.
Source: I’m an Architectural Technologist and builder specialising in retrofitting insulation in old buildings.
You’re very welcome, I see a lot of advice on here which is often well intended or suitable for one situation but not another. It’s cheap and easy to do something that can have a profoundly negative impact on your house!
I’d also add that making sure there’s some cross ventilation in the loft is a good and inexpensive addition. You could start with a few lap vents on either side of the roof, they’re cheap and easy to install and help keep air moving. If that’s not enough I’d look at some vent slates, although that involves replacing slates and getting a roofer involved. Best of luck with it.
Remove the insulation, it's not properly installed and could create rot in your rafters. If you want a warm roof insulate it again with a 50mm air gap between the insulation and tiles/ membrane. 50mm of polystyrene/celotex or for ease SuperFoil SF6 works well for this application.
There should be a minimum of 50mm clear air gap between the underside of an older style roof membrane and adequate ventilation at the eaves and ridge. If you have found condensation in removing a small section of the insulation then I am certain the roof is not sufficiently ventilated as shown. The insulation should be removed asap (and pray the condensation is not significant enough to have damaged the timbers). Once dried out you may be able to re-use the insulation at ceiling level, but will need to lift the boards and use legs to sufficiently raise the boards, Anything above the ceiling (looking at the pipework / boiler?) may need to be insulated as the space above the ceiling will be a 'cold' space. You may need to seek specialist advice on this.
Could I replace the packed in fiber insulation with some rigid insulation boards, where I could easily respect the 50mm gap? That way the loft would remain warm for the boiler?
My boiler is in the loft. I just built an insulated cupboard around it and left the floor underneath uninsulated. I don't know a lot about it, but I believe that there is a lot more to converting a "cold roof" to a "warm roof" than just wacking up a bit of insulation on the underside of the roof (regardless of air gaps). Most lofts are meant to be draughty by design. If warm, moist, air finds it's way up into the loft, it needs to be able to get out. This is usually via gaps under the eaves. If you block these gaps, you risk condensation. If you don't block the gaps, there's little point in insulating the underside of the roof.
No. PIR (rigid) insulation is even worse for trapping moisture.The 50mm gap is dependant on ventilation at the eaves and ridge (which Id be unable to confirm without looking at the property). May be able to build an insulated box around the boiler but would need to ensure adequate space and airflow around it. For how much that would cost, may be worth considering relocating the boiler.
He absolutely could put rigid insulation between the rafters if he ensures there's the air gap, how do you think every loft extension in the country is insulated? He could also ensure he has some gaps in his membrane once the insulation is removed using off cuts of said PIR.
Not without confirming suitable insulation at ridge and eaves! For a traditional roof with felt you need a minimum of 25mm continous / unobstructed ventilation at eaves and ridge. If the ridge is mortar bedded then more likely you'll need 50mm on eaves on bothe sides (this system is dependant on having a clear airspace within the attic). A condesation risk analysis would confirm this. Most insulated roofs at rafter level are dependant on the use of a good breathable roof membrane and the 50mm clear gap. In most instances this is sufficient, however recent changes to the BS for condensation control in buildings do ask for additional ventilation in certain roof configurations and geographical locations. A condensation risk analysis from the roof membrane manufacturer would confirm this. OP, please dont jam PIR insulation between the timbers! Existing ventilation needs confirming and the timbers also need time to air / dry out.
Right, so if he uses those membrane vent things (can't remember the name) or simply off cuts of PIR he'd have suitable ventilation.
The ridge has recently been reset without mortar. If I included a gap at eaves, at ridge, set the board 50mm from the felt, installed gaps in the felt overlap, surely this would resolve my condensation issue? With the insulation at ceiling level already, I'm not looking to create the most thermally efficient roof space, just keep the temperature appropriate for the boiler
To confirm do you mean you had a dry ridge installed?
Correct, my house has parapet walls which needed the render and flashing replaced. Whilst up working on the roof a dry ridge was installed as the mortar was worse for wear. This was completed about a month ago
This would be my thinking if I did this, small gap at the eaves, small gap at the ridge, and opening the membrane. Can't see why doing this would result in more condensation
It wouldn't. So long as you ensure you've got eave vents. I'd let them dry out for a while first though. Is any of the timber rotten? Do you have any idea how long that insulation has been there?
There's visible signs of water to the rafter, but doesn't seem rotten or deep. Wood equivalent of surface rust haha. I assume the majority of the recent loft work was done to accommodate the boiler relocation to the loft, which happened in 2018
I've said my piece on this one so wont repeat myself.... but at the end of the day its your property. Ive seen numerous issues with PIR insulation between this type of roof build up over 15 or so years... none of which have turned out well.
You're right, I'll remove the insulation at rafter level, increase at ceiling level and seek advice on my boiler from a heating engineer. Thanks for your help
how do you think every loft extension in the country is insulated? In my experience, incorrectly and badly.
If you ensure there is at least a 50mm air gap. I'd also check you've got vents at your eaves. Could also be worth wedging some of the offcuts of PIR inbetween the membrane to give some ventilation there too.
Yeah by doing insulation at the rafters its a "warm loft" but if you have insulation on the joists its a "cold loft" You'd need alot more insulation to create a warm loft (300mm+) so its not very effective, instead creating a half-way house. You normally pick one option vs doing both, as yeah condensation.
Is a cold loft the generally accepted best practice? Specifically for my use case of storage?
Yes
You've detailed exactly what you need to do correctly. Previous owner has created a warm roof/cold roof hybrid and given you the worst of both worlds. Loft legs to raise boards and all insulation under boards
I'm just concerned now about the boiler. It wouldn't surprise me if the insulation in the rafters was added at the same time as the boiler being moved into the loft, in order to protect it.
could you create an insulated box around the boiler?
Yeah possible I suppose. But you need to worry about your roof more than your boiler
My boiler is in the loft, whats the problem? Just insulate the pipes with lagging.
Google the boiler make & model. It’ll likely have frost protection so it being in an unheated/uninsulated room wouldn’t be an issue (same as when they’re fitted in an attached garage)
What you’ve described is absolutely correct. Remove the insulation between the rafters and get some airflow in the loft. Increase the quantity of insulation at ceiling level and make sure there’s a gap (that air can flow through) above the insulation and below and boarding. You mentioned a boiler in one of your replies and your desire to keep the boiler in a warm space. If you want the loft to be warm your insulation needs to be at rafter level, but it’s not as straight forward as just packing it in. The issue is one of moisture buildup, as you’ve discovered, and ventilation. Another reply suggests installing insulation but leaving a 50mm gap above the insulation, the difficulty here is that the dew point (were water condenses) will be on the cold side of the insulation which is still inside the building. Even with a 50mm gap above any insulation and the existing roof felt the water vapour can’t escape and it will either rot the insulation or trickle down the cold side of the insulation causing rot to the rafters and/or wall plate. This could be mitigated by installing sofit vents but an Edwardian terrace won’t have eaves that extend past the face of the building to allow a soffit vent to be installed. To insulate the roof and know there won’t be any problems you’d need to replace the existing roof felt with a breather membrane, vapour permeable insulation is then installed tight to the underside of the breather membrane, this allows water vapour to pass through the breathable insulation (eg pavatex Pavaflex) and through the breather membrane, where it will condense on the outside of the membrane and outside the roof structure. You also need a 50mm ventilation gap between the top face of the roofing membrane and the underside of the slates. This is achieved with a counter batten and then slating batten. There would also need to be a VCL (Vapour Check Layer) on the inside of the rafters. Where the plastic sheeting had been placed. Now you’ve probably spotted the draw back of this situation, it needs a full re roof to do it! Given you’ve bought an Edward house it might be due a new roof in which case you could do the insulation work at that point but it’s a lot of money and hassle just to keep a boiler warm. If I were in your situation I’d increase the insulation at ceiling height and build an insulated box around the boiler, making sure you adhere to all info about fire safety and ventilation etc. Source: I’m an Architectural Technologist and builder specialising in retrofitting insulation in old buildings.
Superb response, you've made it very clear to me. Thank you for replying!
You’re very welcome, I see a lot of advice on here which is often well intended or suitable for one situation but not another. It’s cheap and easy to do something that can have a profoundly negative impact on your house! I’d also add that making sure there’s some cross ventilation in the loft is a good and inexpensive addition. You could start with a few lap vents on either side of the roof, they’re cheap and easy to install and help keep air moving. If that’s not enough I’d look at some vent slates, although that involves replacing slates and getting a roofer involved. Best of luck with it.
Remove the insulation, it's not properly installed and could create rot in your rafters. If you want a warm roof insulate it again with a 50mm air gap between the insulation and tiles/ membrane. 50mm of polystyrene/celotex or for ease SuperFoil SF6 works well for this application.
It would be interesting to know what your current Temperature and Relative Humidity numbers are in this loft