[GSBN] Still ventilating

Mon Apr 8 21:49:03 UTC 2013

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).

All houses in Ireland built since 1998 must be fitted with radon sumps. They 
don't actually do anything unless you fit a passive vent system or an 
extract fan to them. This decision will depend on the radon readings you get 
for the house.

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.

Improving the ventilation within the building itself will help somewhat 
too - but again only up to about 400 Bq/m3.

In Ireland in high radon areas, it is mandatory to have radon membranes as 
well as sumps - a 2-pronged solution. The radon membrane must lap up and 
meet with a radon course crossing the wall 150 - 200mm above ground level. 
Any overlaps should be minimum 100mm and sealed with a proprietry tape.

The issue of a good seal is really important - and unless the builder has 
been educated in this, it can be difficult to achieve. The biggest problem 
is where there are multiple services passing through the floor slab. For 
larger pipes, top hats can be used. However, lots of smaller pipes and 
cables bunched together are an issue. It is important to think of these when 
designing and if possible, have them coming through the slab in a neat row, 
with at least a finger width or two between them. Easy-pour liquid radon 
sealants are available, which are used with flexible moulds (about 30mm 
high). But in order for the liquid sealant to effectively seal around each 
of the services, there needs to be a small bit of surrounding space (hence 
the finger width).

If you are working with breathable floors, you will not be able to put a 
radon membrane underneath. In this situation in a high radon area, it may be 
possible to compensate by putting in additional sumps. Even in small 
traditional cottages, we have specified one sump per (small) room. However - 
you are relying completely on constant mechanical ventilation (which may go 
against your desire for passive survivability - which I understand, but 
don't want to get into that debate again).

I am not sure if you combine a number of passive solutions - radon 
membranes, passively vented sumps and improved naturally ventilated rooms - 
will this get you results with radon levels over 400 Bq/m3.

The other option is to build up off the ground completely - with a suspended 
ground floor. Then radon penetration will not be a problem at all.

Cheers

Feile

Féile Butler

MRIAI B.Arch Dip. Arch Conservation Grade III

Mud and Wood

Grange Beg, Skreen, Co. Sligo, Ireland

T:  +353 (0) 71 930 0488

M: +353 (0) 86 806 8382

E : feile at mudandwood.com

W: www.mudandwood.com

----- Original Message ----- 
From: "John Straube" <jfstraube at gmail.com>
To: "Global Straw Building Network" <GSBN at sustainablesources.com>
Sent: Monday, April 08, 2013 8:35 PM
Subject: Re: [GSBN] Still ventilating

> Hi there,

> Use best practise Radon control: a very airtight enclosure that interfaces 
> with the soil, an air permeable gravel bed / drainage mat around the 
> horizontal and vertical elements respectively, and then connect this layer 
> to a passive stack pipe that runs vertically with no elbows through the 
> living space and projects about the roof ridge and above snow pile depth.
> If the radon levels remain high in your spot checks, add a radon fan.
>
> On 2013-04-08, at 2:53 PM, Anthony Novelli <anthony.novelli at gmail.com> 
> wrote:
>
>> We at DCAT along with Laura at GreenWeaver are doing some technical 
>> support for tribes right now, and one in particular is facing a lot of 
>> radon problems. I'm not up on the best approaches to dealing with this, 
>> and wonder, in the context of passive survivability and tight buildings, 
>> what should we be keeping in mind as best practice?
>
> John Straube
> www.JohnStraube.com
>
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