Radon - do I need edge bearing slabs?

[DevonKim]

Good afternoon, 

 

I am after some advice on radon protection.  The current proposal for my radon barrier is that I should have an edge bearing slab, as shown in the snip below. 

 

I would prefer a floating slab (easier and cheaper to construct).  My BC seem to prefer an edge bearing slab too.  Has anyone got a foundation detail for a radon barrier floating slab foundation? My house is going to be timber frame, so it is lightweight.  The ground is reasonably firm clay, so there should be no problem with narrow trench foundations.

 

Any advice would be gratefully received.

 

Kim 

 

 

 

  

[JohnMo]

Sorry cannot answer your radon question, but your insulation looks rubbish, does even meet building regs?

 

Not sure my choice would be Actis Hybris, you would be better using something like Frametherm 32. You also need an insulation layer inside the studs to get rid of the repeat thermal bridge, so a layer of 25mm or better 50-75mm PIR insulation or insulated plasterboard.

 

Sorry not really the answer you were looking for.  Pay once for insulation or every year on heating bills.

[Jenki]

What's the reason for edge bearing slab, have you had to make up the ground?  Engineers love to over engineer, of the ground is fairly level, and make up is less than 500mm insist that you want a ground bearing slab.

as with @JohnMo, this can't meet building regulations, I think the actis stuff is 0.33. 

The detail here has too many cold bridges, footing / slab / wall etc. 

 

My advice get the slab sorted, minimum 150mm PIR or 300mm EPS . then the radon barrier can be lapped up over the edge. this does depend on what radon protection you need. have you paid for the cheap desktop survey, that gives you an idea of the radon risk on your site?

[saveasteading]

28 minutes ago, Jenki said:

Engineers love to over engineer

This one doesn't.

 

I don't like this at all.

Edge bearing with a skinny slab is new to me and I can only see problems. If there is any differential movement the slab will become suspended, and crack.

 

Cold bridges too.

 

And a dolly course, whatever that is. Seems a right mess to me, overcomplicating everything. Apologies if it is your own drawing.

 

Radon barrier is no different to dpm in principle.. you can use laps and seal them. So it can be dressed up the edge block and over it, and at the corners fold like wrapping paper, or cut and seal.

 

[ETC]

[DevonKim]

Thank you folks, 

 

That is really helpful, as it looks as though the consensus is that it is not a great detail.  

 

@saveasteading no, not my own detail, which is why I am querying it! 

 

@ETC really helpful, thank you.  

 

 

[saveasteading]

The @ETC detail perhaps doesn't work for your construction, but the principle  is correct. This has been done before but the detail you showed us suggests that it is idea no 1 for a new invention called a house.

 

[DevonKim]

Yes @saveasteading and @ETC, thank you for your comments.  It isn't quite correct for my timber frame, but I have not got enough info to sketch up a detail myself which will give me something that I can use to discuss with Building Control.  

 

@Jenki I'm right on the edge of Dartmoor, so I will definitely need the radon protection sadly.  

[saveasteading]

Have you tried googling radon barrier then images. Loads of examples on there.

 

More to the point, your designer could do that.

Edited June 1, 2023 by saveasteading

[ETC]

5 hours ago, DevonKim said:

Yes @saveasteading and @ETC, thank you for your comments.  It isn't quite correct for my timber frame, but I have not got enough info to sketch up a detail myself which will give me something that I can use to discuss with Building Control.  

 

@Jenki I'm right on the edge of Dartmoor, so I will definitely need the radon protection sadly.  

Speak to Visqueen first. BC will only give you a general idea of what is required.