[GSBN] Still ventilating

Mon Apr 8 23:40:51 UTC 2013

Thanks for your detailed information, Feile.  Please tell me more about what you mean by "breathable floors" in the statement below, and why they prevent the use of a radon membrane.

If you are working with breathable floors, you will not be able to put a radon membrane underneath.

I would also like to understand the basics of where the measurements are done, in order to see if a house's radon level exceeds the threshold limits of 200 or 400 Bq/m3.  Are the levels measured in the rooms of the house, or perhaps under the floor of the house, or maybe somewhere else?  I'm curious if in your country it is standard or commonplace to test radon levels on a building site before constructions begins.  If so, what is the approach for the testing?

Radon membranes (sealing gaps) and passive vent systems (as described by John) are considered effective only up to about 400 Bq/m3.

Thank you,
Derek

On Apr 8, 2013, at 3:49 PM, Feile Butler 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).

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<mailto:feile at mudandwood.com>

W: www.mudandwood.com<http://www.mudandwood.com>

----- Original Message ----- From: "John Straube" <jfstraube at gmail.com<mailto:jfstraube at gmail.com>>
To: "Global Straw Building Network" <GSBN at sustainablesources.com<mailto: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<mailto: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<http://www.JohnStraube.com>

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Derek Roff
derek at unm.edu<mailto:derek at unm.edu>

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