Membrane under Welsh slate...

[Powerjen]

We have an old cottage in Scotland which has Welsh slate and sarking boards but no membrane under the tiles. A few of the slates are tired and failing. Despite all the woodwork seeming sound underneath we have always assumed we need to reslate with membrane under. As funds are tight I am questioning if it actually needs doing and instead just tidy the slates and replace individual tiles as needed?  Thanks. 

[Russell griffiths]

Show us a pic. 

I would think doing a major renovation like you are, not doing the roof would be a mistake

how are you going to insulate your rooms in the roof ?

this may be a decisive factor in deciding if the whole roof needs to come off, to ensure adequate air flow. 

Really need to look at building regs for roof design 

[Cpd]

My existing roof is slate with no membrane and straight onto sarking, it’s over 100 years old and the timber is still serviceable. I got the house with at least 100 missing slates and no ridge..... but cash was and still is tight so I just replaced all the missing slates and checked the roof really carefully for any other damaged or misaligned slates and repaired as needed. I then put on a new tin ridge and it was back in action. Yes I need to check it and replace slates every year but that’s just life when money is tight. However when the time comes I will rip the whole roof of and start from scratch and there WILL be a high quality membrane included ! So If funds are tight do a really good survey of the roof and fix it up the best you can, but understand it’s a stop gap measure until the time / money becomes available to do a proper job. 

[Cpd]

9 minutes ago, Russell griffiths said:

I would think doing a major renovation like you are, not doing the roof would be a mistake

I was not aware of the background on this as I only read this thread..... and assumed it was just a standalone job..... assume nothing ! If it’s a major renovation then I would agree with Russell and say the roof needs to be a priority. 

[Powerjen]

@Russell griffiths thank you for the info.  The cold roof system seems to be what is currently there. As we are not planning on doing anything to the area which has no membrane I wondered if it would be fine to just replace slates as needed as @Cpd said he had done until we could afford to redo it all properly at a later date.  Thanks for the help @Cpd ?