The Building Regulations covers building over Radon areas and what to do to get round it.
Basicaly use a raft with membrain or fully vent the underfloor space and put a membrane over the site.
I have come up against house surveyors who panic when you say things like Radon. Because they don't know what they are talking about they cause many problems. When selling a house if you get a problem like this ask to see the report and see a surveyor yourself to counteract there report.

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At Alva the mineralisation includes uraninite-bearing hydrocarbon if I remember correctly so there will likely be elevated radon, though no idea how much!

Cheers - John

It's interesting, as the radon membrane hysteria extends well out of the range of granite and that of "crosscourses".

From what I gather the most serious Uranium deposits are found in N-S lodes which are in Killas (non-granite). This is most certainly true for Old Gunnislake, Kingsdown adit, East Pool, South Terras and the St Ives mines (the pitchblende ones). I think Wheal Edward (near Botallack) is also mineralised with Uranium in a crosscourse (non granite as well).

Again, in common with most features of nanny state, we have to abandon a bit of knowledge and reason and wring our hands and get all hysterical about nuclear stuff.

I remember taking a bit of S Terras into school to demonstrate the radioactivity of some Cornish Rocks and from the bullsh!t protocol nonsense involved, you'd almost think I was planning to make a dirty bomb. (it was a bit of "that radioactive building" mentioned in various texts, rather than the sealed off mine....

Nuclear = Stuff with 3 heads.....

Yet Benzene in unleaded petrol isn't even mentioned.....

Aye - we've all been zapped at some point. I was working on a fishing-boat in Cardigan Bay with Si Hughes' dad and got drenched in the same Chernobyl downpour that saw bans on lamb-meat around N Wales as a consequence, and with Simon Camm I have unearthed some hot rocks in the Wheal Edward district. I still only have three heads!

WRT Alva, Steve Moreton knows the site best. That is who I would seek to discuss that mine with. I visited it with him about 21 years back and found a cracking silver nugget :)

On the day I had a lurg so while they were underground I carried on digging and got my bit...

Cheers - John