New roof / Major condensation.

[Sparky321]

Hi all, 
I'm really hoping someone can give me some advice. We had a new roof installed around 3 months ago and we have massive condensation issues. Our loft room has been converted by previous owners so it's a big open space with cupboards that go in to the eves which are all open. 
The new roof had all new non breathable felt used (roofer saying this is current building regs for man made slate, using GuardeShield) It's had 3 roof vents on the back (an additional 2 installed recently because of the issue) and I believe 3-4 on the front. We decided to keep all the old ridges as it fits the style of the houses around here and looks better so these have been cemented back on. The tenement on the back of the house is using a dry ridge system. 
I decided to check in the eves one evening when we had the last big storm and was amazed to see the amount of condensation in the back of the eves. Timbers soaking wet. Pictures for reference. It looks like the condensation runs all the way up the roof ridge line. 
It turns out there is a plastic vapour barrier there from when the last roof was put on, no idea how long ago that was. Roofer saying this could potentially be the issue or the fact the old ridges have been cemented back on. I'm a little unsure on that simply as every single house you see has cemented ridges but hey, I'm no roofer. 
Any advice would be greatly appreciated as I'm kind of at a loss as to what to do at the moment. 
Thanks

[JohnMo]

Couple of things come to mind

 

How is the space ventilated? There seems a load of old insulation blocking any ventilation from coming up in to the loft space from below. Plus how is the damp air getting back out again? You need a clear ventilation route.

[MikeGrahamT21]

No evidence on the photos that those vent tiles have been properly installed, at present they'll be venting the bit between the tiles and the felt, not much use if its non-breathable.

 

See here, this is for connection to a vent in the house, but you should be venting into the loft space: https://www.roofgiant.com/resources/files/srv10u_srv10-20_updated_feb19.pdf/?gad_source=1&gclid=CjwKCAiAp4O8BhAkEiwAqv2UqB9fneUWJcPJHrCEtULX3YEKj8pgurFjbm9ZRjvhn452GNYmdHg2ThoCuFUQAvD_BwE

 

I guess you may have already done this, just not shown on the photos

[Sparky321]

On 10/01/2025 at 13:50, JohnMo said:

Couple of things come to mind

 

How is the space ventilated? There seems a load of old insulation blocking any ventilation from coming up in to the loft space from below. Plus how is the damp air getting back out again? You need a clear ventilation route.

Hey John, 

 

Thanks for the reply. That's actually a job for me to do, get all the old insulation out and put all new in. There should be a gap towards the end of the eves for the air to flow up from outside right? I assume the damp air should be going out through the roof 

vents installed, they cut holes in the felt so they're open?

Edited January 11 by Sparky321

[Sparky321]

On 10/01/2025 at 13:55, MikeGrahamT21 said:

No evidence on the photos that those vent tiles have been properly installed, at present they'll be venting the bit between the tiles and the felt, not much use if its non-breathable.

 

See here, this is for connection to a vent in the house, but you should be venting into the loft space: https://www.roofgiant.com/resources/files/srv10u_srv10-20_updated_feb19.pdf/?gad_source=1&gclid=CjwKCAiAp4O8BhAkEiwAqv2UqB9fneUWJcPJHrCEtULX3YEKj8pgurFjbm9ZRjvhn452GNYmdHg2ThoCuFUQAvD_BwE

 

I guess you may have already done this, just not shown on the photos

Hey Mike, 

 

Thanks for your reply. So the vents have been installed and the felt has been cut out so they're exposed in to the eves. Looking at that link you've sent, me not knowing of course, but how does that vent the eves if the pipe is running in to a room below and then straight out through the roof. 

 

Just as a side note, I should add that it's an open loft space that has been converted. So stairs up in to the loft so it's always open. No loft hatch. 

[ETC]

Vent tiles are no good for a roof where the insulation is placed between the rafters - the tile vent will only vent the space that it has been installed in. You should have had a continuous eaves ventilator installed. You really should have ventilated the ridge as well.

Edited January 11 by ETC

[Sparky321]

7 minutes ago, ETC said:

Vent tiles are no good for a roof where the insulation is placed between the rafters - the tile vent will only vent the space that it has been installed in. You should have had a continuous eaves ventilator installed. You really should have ventilated the ridge as well.

Hi ETC, 

 

Thanks for the reply. Could you tell me what continuous eaves ventilation is? 

[MikeGrahamT21]

33 minutes ago, Sparky321 said:

Hey Mike, 

 

Thanks for your reply. So the vents have been installed and the felt has been cut out so they're exposed in to the eves. Looking at that link you've sent, me not knowing of course, but how does that vent the eves if the pipe is running in to a room below and then straight out through the roof. 

 

Just as a side note, I should add that it's an open loft space that has been converted. So stairs up in to the loft so it's always open. No loft hatch. 

Yeah I know that’s what the guide shows but was meaning without the pipe, sounds like they’ve been installed correct anyway.

 

Cross ventilation will be the key here, as ETC says, get some air flowing through the eaves, many different ways of achieving that

[ETC]

1 hour ago, Sparky321 said:

Hi ETC, 

 

Thanks for the reply. Could you tell me what continuous eaves ventilation is? 

 

[ETC]

https://glidevaleprotect.com/app/uploads/2023/03/BS5250-white-paper_FINALAPPROVED_March-2023.pdf