[GSBN] Still ventilating

[John Straube]

If it wasn't clear form my post, I agree with Felie: any house that ends up over 200 or so when the passive vent system is installed (rare, but this sure can and does occur) has an exhaust (aka "extract") fan installed.  Installing fans when readings of over 400 are taken has been found to be unnecessary in most (can't remember but the EPA studied this and I think it was 90% or more of the houses did not need fans if the passive system was installed) IF (Big if) there is crushed stone under slab to allow air to flow and the basement walls and floors were well sealed.
In new construction it is relatively easy to get the slabs tightly sealed, and the crushed stone and dimple sheet drainage mat installed to allow for very effective sub slab ventilation. This increases the likelihood that passive stacks will work.  Of course, cold climates have more success with passive stacks than warm climates.
I am taking about slabs on grade or basement floors.  Felie may be talking about suspended floors above crawlspaces as this is common in the UK/Ireland although he discusses this as a separate solution.  Can you clarify "sub floor" Felie?

PS. High radon levels can occur in crawlspace houses if the air handler / return ductwork is in a crawlspace, as leaks in this ductwork tends to act like a vacuum sucking up any soil gases from the crawlspace.  

On 2013-04-08, at 5:49 PM, "Feile Butler" <feile at mudandwood.com> wrote:

> Hi Anthony
> 
> We deal with this issue a lot. According to the Radiological Protection Institute of Ireland, action needs to be taken where houses reach levels of radon over 200 Bq/m3. Radon membranes (sealing gaps) and passive vent systems (as described by John) are considered effective only up to about 400 Bq/m3. In areas with higher radon levels, active ventilation of the sub-floor is necessary (effective up to 2,000 Bq/m3 and higher).
> 
> Radon sumps are buried in the hardcore/drainage stone under the floor slab. If you have any footings under internal walls, it is important that there are some air-bricks/air-passages incorporated into these, so that there is no sub-floor space completely isolated from the sump. The sump is essentially a box with holes. A pipe is connected to it, which is connected to a grille in the external wall. If you are getting high radon readings, then a constantly-running extract fan must be attached to this pipe. Experiments have been carried out where the fan was switched off once the radon had dropped to an acceptable level. The readings were back up to their old level within 24 hours. The general rule of thumb is that 1 sump is adequate for a footprint of 250m2 approximately. If you need more sumps, the pipework can all be joined up and linked to the one fan.
>