Membrane below slates

[Kevan Marshall]

Hi,

I have a friend that mother has Alzheimer’s and needs to go into a home, due to her mother owning her home it needs to go onto the market to fund nursing cost, the sale of house went through but surveyors have picked up on the membrane below roof tiles as it is plastic and through time has started to disintegrate, the sale of house has fell through due to this, is there any way around this without removing the roof tiles which are in really good condition, I know membrane is for condensation but does it need to be there to comply with building regulations?

Any help would be greatly appreciated,

Kind regards,

Kevan.

[Crofter]

Just to clarify, is the roof slates or tiles?

Regardless of what the final covering is, there should be some form of waterproof material underneath. The exact type depends on how the roof is built.

E.g. in Scotland, a slated roof would typically have a bituminous felt on to timber sarking boards. Slates come in varying sizes and shapes so you need this continuous layer of timber to nail in to.

In England, you often will have a waterproof membrane which sags slightly between the rafters, and battens over the top to carry the tiles. You can use battens because the tiles are a uniform size.

 

But in general, yes that membrane needs to be there. The tiles or slates themselves will shed most of the water but not 100%. They can get damaged, or in strong winds rain can get forced in to the gaps. Repeated exposure of the roof structure to water will cause serious damage.

[Kevan Marshall]

25 minutes ago, Crofter said:

Just to clarify, is the roof slates or tiles?

Regardless of what the final covering is, there should be some form of waterproof material underneath. The exact type depends on how the roof is built.

E.g. in Scotland, a slated roof would typically have a bituminous felt on to timber sarking boards. Slates come in varying sizes and shapes so you need this continuous layer of timber to nail in to.

In England, you often will have a waterproof membrane which sags slightly between the rafters, and battens over the top to carry the tiles. You can use battens because the tiles are a uniform size.

 

But in general, yes that membrane needs to be there. The tiles or slates themselves will shed most of the water but not 100%. They can get damaged, or in strong winds rain can get forced in to the gaps. Repeated exposure of the roof structure to water will cause serious damage.

Thank you Crofter, unfortunately it looks like they are going to have to remove the roof tiles and place new membrane!

[Redbeard]

 

1 hour ago, Kevan Marshall said:

Thank you Crofter, unfortunately it looks like they are going to have to remove the roof tiles and place new membrane!

... or ask agent to contact the would-be buyer and offer a discount that is more than the cost of re-roofing?

 

My roof has no membrane (and, unlike your friend's mother's house, never has had). I won't say it has never leaked, but at 100+ years old it still requires very little routine maintenance. If I came to sell, however, I am sure the survey would point out the lack of sarking as an 'issue'.

[Kevan Marshall]

Thank you for the replies, much appreciated and looking like they shall have to remove the slates.

 

kind regards,

kevan

[Gus Potter]

12 minutes ago, Kevan Marshall said:

Thank you for the replies, much appreciated and looking like they shall have to remove the slates.

Hang on here before you chuck in the towel. 

 

It's quite usual to find no membrane or bituminous felt under an old slate / clay tiled roof. 

 

Can you post some photos so we can have a look at what you have from the inside and the outside. 

 

On 30/11/2025 at 10:10, Crofter said:

Regardless of what the final covering is, there should be some form of waterproof material underneath.

In a new build yes, but when we are considering old buildings and upgrading it can actually be an advantage. The old traditional roofer ( 100 years ago) did not have access to felts and membranes so they gave their slates / tiles more head lap.

 

We can use this to our advantage at times as the roof is really drafty, every cloud has a silver lining!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[dpmiller]

is this just at the bottom, draped into the gutter?