Radon Barrier / DPC detail on Bison Slab

Todin

Hi there,

I'm undergoing a self build and have the bison slabs in on top of DPC on top of rising blocks. The DPC is a high grade polymer, Visqueen Zedex which can be used for Cavity Trays also, and extends across the whole of the deadblock out through the cavity to the outside. We're going to install the radon barrier across the top of the slab and down and out across the cavity which I know is the right thing to do, but it's the how that's puzzling me.

After talking with Monarflex they would advise against putting the Radon Barrier on top of the DPC (which is what I was originally going to do) because of the slip plane effect. I have read a few threads on here and on the internet that having the two laid together and blocks thereafter (DPC with one block up) that this is not necessarily an issue given the weight of the house, but I suppose it depends on who you ask.

If I can 't do the above, one option might be to cut back the DPC on the deadblocks to withing the cavity, install a radon/dpc membrane like Easi Load Radon DPC across the cavity and out to the outside and bring it up the slab and under the internal block wall and connect it to the radon membrane on the slab or just run the membrane right out across the slab and block wall. I was thinking of also taping my lovely cut DPC to the new easi load DPC to stop any rising moisture from the concrete blocks. Or do I cut the DPC right back to the side of the slab? I'm loathed to cut it at all as it'd doing a good job of stopping the rising moisture from below.

I was thinking of using Monarflex RMB 350 or 400 with their RAM system as I have a few steel beams in the cavity for a corner window to sort out too. They seem to have a good liquid for that and tight spaces.

I would appreciate some words of wisdom from seasoned Radon / building professionals on what my options are.

Thanks in advance.

Mellor

do you have a section detail of the wall/slab junction?

Todin

Hi Mellor, thanks for the quick reply. Yes, I do alright. Only thing we didn't do was the block on it's own under the slab. Architect said we didn't need it. The green is the radon barrier.

I've also attached a photo of the slab on block detail as it is now and what the radon detail would look like.

On the topic of slabs would anyone fill in the hollows at ground level?

Hope this makes sense.

Thanks

17587879713435956438150442486242.jpg

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bfclancy2

Wouldn't be overly worried about the slip plane effect the weight of the block will eliminate that, don't think there is any issue with cutting back the DPC either, the radon will perform that function, whats the purpose of the DPC as it currently stands, doesn't seem to be achieving anything as is if the intention is to install the radon as a DPM/DPC

Todin

Thank you bfclancy. I suppose I was thinking I would stop all the water vapour coming into the cavity and protecting the slab a bit more...but it's exposed to the ground below anyhow so probably doesnt do anything that the radon barrier could do.

I'll have a think some more.

Tks again

Mellor

https://www.boards.ie/discussion/comment/123848856#Comment_123848856

The details don't match the notes.

The notes say insitu slab on radon barrier on sand blinding. Details shows barrier above the slab.
Terminology flips between RB and DPM, one layer can do both, but needs to be clear. DPM label on drawign is not on the barrier. Line weight are too heavy and its hard to read, which is where confusion happens.

Also appears you are not doing an insitu slab, which is maybe why the barrier moved to above slab, no issues with that but the drawing and notes should be updated. As it stands the detail isn't right.

RB/DPM across the cavity and down at an angle is correct. But it's too low. Blocks above the RB/DPM are below ground level, meaning they'll be wet. Including the thermal aircrete block - which means there's a pathway right into the insulation/screed (and the house). The DPM should come up and over the aircrete block, under the DPC, then across the cavity.

Todin

Thanks Mellor for coming back to me.

OK I can see the confusion and many many moons ago I did ask him about his conflicting detail to which the response was basically it's a copy and paste, if I had to design every detail separately for everyone it would take an age…or something to that effect. I hear the comments already, but not going there as I've beaten myself up enough. Anyway the best he could do was the attachment on here (forgot I had that), but we did have discussion so I was clear where he was coming from and he confirmed on site too once slabs were down. So no poured slab, Prestressed slab (200mm) all the way.

So the DPM is the RB in this scenario i.e the green line.

To me, this is no more different than a poured slab where the RB goes up and over the inside block, down the exterior of the inside wall and out across the cavity. A thermal block laid on it with the DPC over it. That thermal block in this case would be the 2 blocks on the flat in the diagram. Or am I missing something altogether.

Radon Cross section.pdf

The GL will be min 150 below the DPC, probably more by the time I'm finished.

Now, for real belt and braces, I could run a separate DPC course from the top DPC down the outside of the inner wall and connect it to the RB/DPM. That would stop any water vapour entering the 1st block level. (Necoflex & Visqueen do this kind of detail) My only hesitancy on that is the insulation…how effective is it through a DPC layer than butting up tight against the block itself?

What would be your suggestion be to my initial conundrum on the Radon/DPC together?