Radon Barrier, DPC, and DPM. Is this right?

[DJ_DIY]

Hi,

Could somebody please confirm my thoughts below:

Does it matter if 100mm DPC is on top of or below 600mm DPC? (I suspect not. )

Is there any Celotex under the radon barrier? (Guessing no for some reason!)

Does the DPM get sealed behind the dot and dab plasterboard up the internal wall. (I think it does).

and finally, how many weep vents? (one every 430mm?)

Thanks

DJ

p.s. This isn't DIY. Would take me a couple of years to lay all the bricks in the extension!

 

[freddiemercurystwin]

It's good practice when fitting a radon barrier to sit the edge of the slab on the inner skin, otherwise if the hardcore settles at all (and drops) the dpm can tear where it returns into the wall. You can lap it up the inside of the cavity to avoid it being exposed too. The just sit your cavity tray on top of the radon barrier eg:

Weep holes at minimum 900 centres and the ends of any cavity trays under openings. Though who's ever seen anything trickling out of them!

 

[DJ_DIY]

ah, I am currently at this stage.......

Wunda UFH is going on top at 20mm with 10mm of self levelling to finish.

 

[noseall]

ah, I am currently at this stage.......

Wunda UFH is going on top at 20mm with 10mm of self levelling to finish.
View attachment 390205

You are missing a layer of concrete under the Celotex and it should be floor screed on top of the Celotex not conc'.

 

[DJ_DIY]

You are missing a layer of concrete under the Celotex and it should be floor screed on top of the Celotex not conc'.

This is a perfectly valid way to lay a concrete floor to comply with building regs.

I was asking about the positioning of the radon and the dpm when the walls are built.

Cheers

 

[freddiemercurystwin]

Well, ignoring the whole concrete above or below the insulation debate do this then, you can just trim the black barrier that's under the concrete so it's flush with the top of the slab.

Introduce some slack into the barrier to prevent it from tearing.

 

[Charlie George]

The Radon barrier has to extend to the external brickwork, waterproof full fill insulation under the membrane, the DPM is really only protecting the floor insulation as the barrier acts as your DPM, this picture will explain it better, but i would sit tray on barrier.

 

[DJ_DIY]

@freddiemercurystwin Good spot. 20mm Celotex added to diagram between radon and DPM at concrete slab level.

@Charlie George What would a suitable full fill waterproof insulation be please?


And answers to my initial questions are:
Does it matter if 100mm DPC is on top of or below 600mm DPC?. Nope. Why I need both I dont know !

Is there any Celotex under the radon barrier? [in the cavity] Waterproof full fill insulation

Does the DPM get sealed behind the dot and dab plasterboard up the internal wall. Yes or cut off at self levelling floor level before vinyl.

and finally, how many weep vents? Weep holes at minimum 900 centres and the ends of any cavity trays under openings

Thanks all.

 

[Charlie George]

1 100mm DPC not needed, tray suffices
2 any XPS insulation will do, in the diagram i posted, it shows it under the barrier.
3 your Dpm is not really a Dpm cut off at floor level
4 900mm is fine

 

[freddiemercurystwin]

Radon barriers do not need to be continuous, you can join them wherever is necessary or to a suitable stepped dpc.

 

[DJ_DIY]

your Dpm is not really a Dpm cut off at floor level

under the plasterboard then

any XPS insulation will do

OK thanks ill check out Celotex Thermaclass Cavity Wall 21

Radon barriers do not need to be continuous

Ok thanks. WIll be a pain folding at least one of my internal corners.

I can understand the idea of a radon barrier. All good when the room has 4 external sides like a tiny house, lol. When two sides are under both sets of blocks so the gases go to the outside.... but the other two sides already have walls and the barrier can't go anywhere, where does the barrier end then?

 

[freddiemercurystwin]

Let's be clear what I was saying, the barrier needs to be continuous but the barrier can be made up of different (compatible) membranes suitable sealed together to create a continuous barrier.

Where the barrier meets an existing wall you have to use best endeavors, or just do the best you can. The rest of the house may not have a barrier at all if its old so don't overthink things too much.

 

[DJ_DIY]

thats my point in a round about way..... Radon barrier is essential for a house in a radon area, and must be through both skins or BC wont sign it off. The other sides, ah we won't worry about them. I'll seal/stick the radon barrier to the existing walls just above concrete.

Thanks

 

[endecotp]

I can understand the idea of a radon barrier. All good when the room has 4 external sides like a tiny house, lol. When two sides are under both sets of blocks so the gases go to the outside.... but the other two sides already have walls and the barrier can't go anywhere, where does the barrier end then?

If the radon barrier were sloping, the gas would percolate upwards towards the outer walls.

Of course you can’t (realistically) have a sloping barrier under a flat floor. But you can have it turn upwards at the outside walls, and turn downwards at the internal walls.

(I’m just thinking out loud. I’m not en expert!)

 

[DJ_DIY]

Is there a way i can fill in the cavity infront of the bifolds so the floor goes to the external skin?

Thanks