Who needs a radon barrier?

The Beloved's youngest sister has done well for herself.  Through no fault of her own, she went to a different school each year for much of her teens, and so missed out on large chunks of the standard curriculum.  She covered the Young Irelanders in 1848 two or three times but missed out on Jim Larkin and the 1913 Dublin lock-out entirely.  As a teenager she went mad-about-the-nags for several years, and her marginal grades didn't matter much when she was looking for work in the riding business.  After several years of this she found that while blokes with money can do alright in the world of horses, girls with no money just shovel horse-shit.  So she jacked it in and came and stayed with us in England - and promptly got a job in the bar of the student's union to pay for her training in office and secretarial work.  She left when she was qualified, tied her few belongings up in a handkerchief, and went to London to seek her fortune.  She got a job there, made herself essential to an engineering firm, asked for a day off a week to go to college and got a diploma, then jacked in the job to go full time for year and parlay that qual into a degree in networking and systems analysis.  It took a few years (and the kind of guts, determination and ambition that I long ago left on the side of my plate as too gristly to tackle) but her degree got her a job working at the very bottom of one of the huge multinational telecoms companies.  She's now in her 40s and une tres grande fromage out East - VP AsiaPac or Mikado of Titipoo or something.  There are no OAPensions out in foreign: you have to sort that out yourself.  So she's just bought a house in Tramore, Co Waterford as a hedge against an uncertain future and a place to live when she finally gets home (assuming that yellow-jack, pirates, or the HR Department don't do for her first).  Tramore wouldn't be my idea of heaven with it's view of the disgraceful landfill along the Backstrand but that's where she wants to be in 20 years time.

She contracted an engineer to survey the house and recommend the structural, engineering and insulation issues that needed to be addressed.  This feller returned a long list of necessary and expensive alterations to bring a 1980s vintage bungalow up to modern specs.  Item 13 was something like "rip up existing concrete floor and replace with a radon barrier underneath - €8,000".

Now radon is bad news (or rather it's the polonium to which radon decays), so such advice can't be dismissed with a wave of the hand. The Radiological Protection Institute has produced a map showing the radon hazard of each 10km square for the island (thanks to Lloyd-George and Michael Collins in 1921 there is no radon hazard in the 6 counties - which is fortunate for them all in The North). A single step south into Co Louth of course and you're going to get hot, so mind yourself there.  This amazingly handy and informative map shows that Tramore is in a hot square as well as Carlingford up near the borrrder.  For those who are geographically challenged as to the location of small towns in Waterford I attach a red arrow to show where Tramore is. 

So it looks like the engineer is correct in his advice unless you're going to critically evaluate the evidence.  Radon is radioactive and itself the product of radioactive decay from Uranium-234, which as it decays over millions of years gets depleted, so the only source of Uranium that hasn't already decayed into Radon is what has come up from the earth's interior as a volcanic eruption. If the rock over which your home is built isn't of volcanic origin, you're pretty much in the clear with respect to radon.  But lets look at the detail:

This is another nice map showing the geological bed-rock for Co Waterford.  You can follow the link to get similar maps for each of the 26 counties. Here's the key: Light purple: Precambrian metamorphic rocks; Pink: Ordovician; Dark blue: Ordovician volcanic rocks; Green: Silurian sediments; Beige: Devonian sandstones and conglomerates; Light blue: Lower Carboniferous limestone.  So it's the dark blue volcanic rocks that are loaded with radioactivity including radon and its desperately dangerous descendant polonium.  So if you live a couple of miles N and W of Tramore you really do need a radon barrier, but if you're in town you don't.  You just have to deal with drunks urinating in your garden when they spill out of the Grand Hotel in the (aptly named) wee hours.