Is a roof membrane compulsory? (Ed.) Loft Conversion with 1930s boarded roof

[FlatWhite]

Hi all, We want a Velux loft to a 1930s semi in north London. Our roof was closed-boarded in the original 1930s without any membrane. A not so great photo below.

There has been a debate on whether the roof must be "membraned" to meet building regulations for loft conversion. One builder told us we need to lift all the tiles to put in a membrane, while others say you can probably get away with not doing it.

I wonder if anyone has any idea if the membrane is a "must" or just "good practice"? Is there any way around this? Basically, for where the house is, lifting the roof up will add a significant cost to the project.

Thanks in advance!

 

[wessex101]

No requirement to add a sarking felt membrane but you will need to add insulation below the rafters and create cross ventilation above the insulation.
Obviously if the roof tiles are getting towards the end of their life it would make sense to strip the roof and add a vapour permeable sarking felt to remove the need for cross ventilation.

 

[freddiemercurystwin]

Whilst there's no requirement IME Mr Building Control will want to have a look see beforehand to be satisfied the roof isn't gonna leak like a sieve.

BTW what's that brown stuff?

 

[FlatWhite]

Thank you both for the reply! I think the brown staff are just some sort of sheets that have been stuck on at some point. They are only on a small part of the roof, though.

So, is it fair to say that adding membrane is just a "good practice," not a "must," but not doing so may be counterproductive as it runs the risk of leaks later. Basically, my understanding is that due to our loft only being a Velux, not touching the roof will save a fair bit (both the scaffolding cost and the labour/material resurfacing cost).

 

[freddiemercurystwin]

Seems like you have the gist of things, if your loft can be converted sensibly without a dormer then yes some savings to be had there, they should be able to do the rooflights from the inside.

 

[FlatWhite]

yeah, that's what we initially thought (just doing the Velux from the inside). With the reroofing added to the equation, we are looking at an additional 20-30k of cost out of nowhere. While I may sound like i got the trade-off, I have no real sense of how risky that is though.. Would it be a risk most peopel happy to run?

 

[freddiemercurystwin]

Well only you can know the answer to that, condition of the existing roof, how long before it needs replacing, will you be there for five years or fifty etc.

 

[FlatWhite]

yeah fair - thank you!

 

[FlatWhite]

My builders insist on lifting the tiles to add felt. Is it a definitive way to get an answer from building control? (happy to pay a small fee if needed)

 

[freddiemercurystwin]

You may need to appoint them first, give them a ring, see if you can speak with the BCO who does your area, not that long ago our local Building Control officers would have popped their head up the loft when they were next in the area, they're generally not so amiable these days. why are your builders insisting? Change your builders.

 

[wessex101]

My builders insist on lifting the tiles to add felt. Is it a definitive way to get an answer from building control? (happy to pay a small fee if needed)

What stage are you at with Building Control? Has work already started or are you just getting quotes from builders?
How do you intend to deal with Building Control - Building Notice or Full Plans Application?

You can try to ask Building Control but until you have an application they probably will not be very helpful. If you do the work on a Building Notice you can ask the inspector. If you do it on a Full Plans Application then Building Control will tell you if they want sarking felt added.

You could ask the builder to provide a quote with the re-roofing as a separate provisional item to give you the option to add or delete it depending on the reply you get from Building Control.

EDIT: crossed post with Freddie.

 

[FlatWhite]

Thanks, both, I will try to answer both in the same post:

We are at the tender stage. This is a renovation project, with the only structural changes being the Velux loft. The builders want to retrofit a membrane into the roof, which involves removing the tiles. They did offer to recycle tiles to save money, but the scarffolding and labour will still add up to 20k extra.

We do have an architect who holds the pen on the project (and the project's liability, too, I presume). He has just been cautious on the subject (and throughout the project) and primarily sided with the builder. He's not interested in "taking the risk". Though all I wanted to know is if it is actually a risk we are taking.

 

[freddiemercurystwin]

So will you be submitting plans for approval before the work commences? If you are then do as Wessex said, then once Building Control are appointed they can be take a view on it and it can be added or subtracted form the contract. Is it a big roof? £20K sounds a lot, do your architect and builder often work together?

 

[FlatWhite]

I have yet to ask them how we plan to do the building control. As Wessex said, it will probably have to involve building control now.

A semi-detached house, so it is slightly bigger than a terrace house. Yeah, the architect recommended the builder when we went out to tender.

 

[wessex101]

You could ask the builder/architect to explain WHY they think sarking felt needs to be added to the existing roof to comply with Building Regulations for a loft conversion?
Apart from anything else I would be interested to hear their reasoning because I certainly have never heard of it.