Rolling Again, + Radon Sump

Despite the groundworks contractor telling me that he never gives any of his people time off, nothing happened on site last week, between Christmas and New year. I wasn't really surprised - I guess he was joking with me, but you never know with the building trade !

Anyway, work is back in full swing as of today. The beams are now strong enough to track the digger across so the base for the other retaining wall (the one that is un-piled where the rock is at the surface) has been prepared and laid at the back of the site. At the same time a small slab has been cast, presumably for the radon sump. This is the square in the middle of this photo, with the base for the retaining wall in the foreground :

Having decided that we need the conservatory to be underpinned too, work on that has also started :

It looks like this is going to be done in two halves. Just like under the house wall, a section has been dug out which will be blocked up at the front and back-poured with concrete, then the other half done when the first part has set.

I thought perhaps it was time I looked up this Radon Sump thing. According to a (obsolete but google cached) NRPB FAQ web-page, a radon sump is "A small void under a solid floor connected by a pipe to the outside. A small electric fan in the pipe continually sucks the radon from under the house and expels it harmlessly to the atmosphere".

From http://www.wisegeek.com comes the following : "Radon is a colorless, odorless, radioactive gas that forms when radium decays. Occurring as naturally as oxygen, radon is common, but harmful to your health and potentially deadly.
Radon is found all over the United States, but some areas have higher levels than others. Radon, like many other elements, occurs naturally, and harmlessly diffuses through outdoor air. But when radon comes into a home or building, the condensed, elevated levels can be harmful to the point of causing lung cancer.
A recent NAS (National Academy of Science) report stated that radon is one of the leading causes of lung cancer in the United States, second only to cigarette smoke. But lung cancer isn’t the only radon-related problem. Other effects of exposure to radon include: gastrointestinal problems, aching joints, mucous build up, fatigue, headaches and rashes."

Finally, there is a good article here, on the : Fedaration of Master Builders web site dating from 1999. Apparently, in Ireland a Radon Sump was already mandatory in all new houses and similar legislation was expected in the Uk. Given that this article is now over 6 years old, it might already be here.