Radon gas membrane

[Sun200]

Hi,

New to this forum and I'm in the process in building an orangery.
BCO have stated that I need to lay a Gas membrane. I've seen other comments on this site which are extremely useful.

The attached image shows what I think should I need to do however I just wanted to know any thoughts people may have on any foreseeable issues with this layout of the membrane.

The drawing shows the gas membrane overlapping the inner leaf on top of the dpc and then dropping down to the outer leaf by 150mm to ground level.

A weep vent is added.

Would I need a cavity tray that sits above dpc as well?

Is the other solution to lap the inner and outer leaf at dpc level and then add a cavity tray plus weep vent above dpc level?

The diagram is something similar I saw on this forum but don't have the link.

My next stage in the build is to add the sub base mot Type 1 then a 50mm blinding layer before the membrane goes down.

Any help is much appreciated!

 

[freddiemercurystwin]

First question, why is it a suspended floor and not concrete?

 

[freddiemercurystwin]

Second question, as the void would be vented why would you need a radon barrier anyway? Unless the rest of the house is newish it won't have any protection anyway, I would check my copy of BR211 but not sure if I have a copy about I can refer to.

 

[Sun200]

Hi freddiemercurystwin,

I've been going around in circles regarding the type of floor to construct and I've asked few general builders which is better suspended or concrete.

I've decided to go with suspended as the current property has floor joists.

I will also be adding insulation between the joist, just not gone into that detail.

The build has a 32 sqm footprint.

Thanks

 

[freddiemercurystwin]

Where the existing floor is suspended and there are existing airbricks they can just be ducted under the slab it's a pretty common detail https://www.diynot.com/diy/threads/garage-floor-building-control.171482/

 

[Sun200]

Hi,

Please do send me link to BR211.

When BCO came to check the depth of my footings he mentioned the membrane and even the colour (yellow or red), BCO also stated that I required it but not my neighbour below me. I'm right on the boundary as it's a requirement for the homes above me.

I've just had the brickies in today and added several air vents.

 

[freddiemercurystwin]

OK you're doing this on a Notice then? Bit of a weird set up you've got going on with the top of the foundation being at ground level, if that really is what's happening, BR211 is not free to look at on the web these days but I guess something like this would be OK, the different colour of membranes refers to the grade and I'm not sure its all that relevant TBH I think the coloured membranes are exclusive to Visqueen (though maybe wrong) https://www.visqueen.com/products/gas-membranes/radon-membrane
Check to see if he's expecting a sump.

 

[Sun200]

Yes it's on a Notice. And will check if I require a sump.

I should have got the membrane installed at that point as you have drawn however I now have two courses of brick up on the inner leaf as shown in the drawing attached. Is my only option to go along with the first image I started with?

The following link is a list of Q&A's regarding radon barriers in new build/extensions and conservatories:
https://www.bre.co.uk/page.jsp?id=3150#protecting

 

[^woody^]

I thought a membrane was required across the floor and the cavity walls too.

 

[freddiemercurystwin]

I thought a membrane was required across the floor and the cavity walls too.

Correct. Or continuous across the floor so that its edges meet the outer face of the outer wall.

 

[freddiemercurystwin]

Yes it's on a Notice. And will check if I require a sump.

I should have got the membrane installed at that point as you have drawn however I now have two courses of brick up on the inner leaf as shown in the drawing attached. Is my only option to go along with the first image I started with?

The following link is a list of Q&A's regarding radon barriers in new build/extensions and conservatories:
https://www.bre.co.uk/page.jsp?id=3150#protecting

Your first drawing showed the top of the foundation flush with ground level, your second drawing does not match? There seems to be some ground, three blocks and then two bricks, where is the foundation in the second drawing?

 

[freddiemercurystwin]

Well I had a quick scan through BR211 which is the industry wide guidance document dealing with radon protection and what BC will accept/use themselves. I can’t share the document, it has my company’s name plastered all over it, I can share the pages on suspended floors though, which details what would normally be built, which is pretty much what I showed in my crappy detail. But it shows the principal. So I guess your first drawing should be acceptable, there is little else you can do now anyway though you will need to get vents through above your membrane. If I was being pedantic I think the official Radon detail (and the one I drew) is a bit crap because if the slab drops over time with a bit of settlement the membrane could tear so I would allow for that by making sure there is a little bit of slack membrane where the horizontal membrane turns up against your inner skin. But then if the rest of you house has no radon protection you’re really just going through the motions anyway!

Down this neck of the woods where we have a blanket stipulation that radon protection is installed (ignoring any maps as they are not conclusive) some BCO’s ask that ground bearing slabs are actually sat on the inner skin to avoid this issue but then the slab needs a bit of reinforcement in the bottom of the slab but anyway I digress.

 

[Sun200]

The attached drawing depicts what has currently been built.

I will have a good read through you notes, really appreciate your expertise on this matter

 

[jacko555]

Lots of us do

UKradon - UK maps of radon

www.ukradon.org

 

[^woody^]

Nuffink rong with Cornwall (or people from parts of Devon). Nope.