It has been known for many years that radon gas is a health hazard to occupiers of structures if concentrations of the gas accumulate within those structures. This week the Health Protection Agency has announced that a target level of 100 Becquerels should apply to dwellings  -half the current action level of 200 Becquerels. Why should radon suddenly be considered a greater risk than in the past?

Cavity Trays Ltd manufactures radon barriers and membranes, and believes it has the answer. 

‘It is important one recognises radon is everywhere rather than only in certain locations’ said a Company spokesman. ‘It is simply the extent of radon gas that varies’. 

‘The introduction of new Building Standards means structures are becoming more airtight. Windows and doors are fitting better, chimneystacks are less common, walls and floors are being insulated to higher levels of integrity and finish. Radon that infiltrates rooms can accumulate to a greater extent than in the past, because of these changes and the elimination of various previous structural exit opportunities. 

If one thinks back to when roof space insulation levels were increased, there was an accompanying need to ventilate to dissipate resultant condensation.

Now with structures becoming more airtight, there is a different accompanying requirement – to eliminate the opportunities for radon to enter.’ 

Cavity Trays Ltd maintains that any reduction in radon levels (in structures) is a positive way forward, but considers a target level as proposed by the HPA to only partially address the real problem. 

‘New properties could and should incorporate total footprint protection at ground level to prevent radon entering via the floors and walls’ is Cavity Trays recommendation. ‘Footprint protection includes an appropriate oversite membrane linked to radon cavity barriers that extend through the external cavity walls and terminate at the external face’. 

Radon that rises underneath the structure and rises via the cavity walls is arrested and prevented from continuing upwardly. Instead it is able to discharge via cavibricks located in the external masonry under the barrier level. 

Cavity Trays Ltd has for some considerable time recommended its clients incorporate total footprint protection whenever some level of radon control is required. In 2009 it commenced offering the following advice: 

The current radon action level is 200 Becquerels in dwellings and 400 Becquerels in commercial buildings. 

The UK Health Protection Agency (HPA) is aware of the recommendation of the World Health Organisation (WHO) to lower the radon action level. When the new level will be lowered in the UK is still unknown, however it is reasonable to accept change will be introduced eventually.

The following information is extracted from the Radon Handbook produced by the World Health Organisation International Radon Project chaired by Professor William Angell: 

Indoors radon is largely caused by the way homes are designed and built.

It is a long-term misconception that indoor radon is naturally occurring.   

Outdoor radon concentrations are naturally occurring, but indoors radon concentrations are profoundly influenced by the way homes are designed and built. The implications of this clarification are that it places clear responsibility for radon control on: 

•Architects and Designers

•Builders

•Building Code Officials 

Cavity Trays Ltd currently advises as follows: 

Designers may wish to consider incorporating full protection in new projects before awaiting any regulation or radon action level changes, for the following reasons: 

·        To demonstrate a duty of care by addressing a known current risk and making provision to control that risk (and thus protect the inhabitants of the building to the greatest possible extent) now and in the future when action levels lower. 

·        To preserve asset value of a structure so it is not devalued in the future because it will not protect to new levels when implemented. 

·        Maintain property appeal of occupiers / users.

 ·        If the UK follows the procedure already adopted by some countries of permitting occupation of a newly constructed property only after the property has been tested and passed a radon test, total footprint protection will become commonplace. 

Building standards are changing, as are the moves towards more airtight structures. In the absence of continuous ventilation at all times sufficient to disperse accumulating radon within a room, levels will rise. 

The view of Cavity Trays Ltd is unchanged. When constructing and radon control is required, Cavity Trays Ltd recommends clients provide total footprint protection. 

Cavity Trays Ltd is encouraged by this week’s announcement by the HPA, but considers the affects of radon are still not being sufficiently addressed within the UK. It refers to RCE-11 published last year by the HPA  in which the key points regarding the risks of lung cancer are listed. (see extract on last pages) 

Cavity Trays also draws comparison with neighbouring Ireland where every new home must incorporate protection and be tested. ‘There is no lottery regarding whether or not an area is marked on a map’ commented Cavity Trays spokesman, ‘a safer approach in our opinion’. 

Footnote: 

Two maps are currently available indicating radon areas in England and Wales.

‘Radon – Guidance on protective measures for new buildings’ (BRE 211) published by the BRE and ‘Indicative Atlas of Radon in England and Wales’ published by the Health Protection Agency. 

Designers should be aware that they are not identical, and the extent of radon area in one does not match the extent shown in the other. Hence our recommendation that full footprint protection promotes a reduction in risk. 

Reference: 

Risks of Lung Cancer from Radon.

HPA publication RCE-11

Extracted from section 3, page 21    

Key Point 3.

These studies provide powerful new evidence to help quantify the risk of residential radon exposure. The dose-response relationship appears linear, with no evidence of any threshold radon concentration below which there is no risk. There is also substantial evidence that there is a risk below 200 Bq m­з, the current Action Level in the UK. 

Key Point 5

A number of factors could not be taken into account in the recent pooled analysis of European Studies. As a result, it is likely that the true risk from radon is, if anything, somewhat higher than the central risk estimate of 16% per 100 Bq m­з. 

Key Point 6

The available evidence suggests that the same percentage increase over lung cancer risk per 100 Bq m­з increase in radon concentration applies for men and women, across all age groups and for current smokers, ex-smokers and lifelong non-smokers.  

See accompanying picture caption: 

Radon cavity barriers are available in standard and insulated versions.

Seen here incorporated in the exterior walls of a new house.

END.

L1A and L1B are very similar, with L1B being the more demanding. Anyone constructing a conservatory or porch that is attached to a dwelling must construct it in a manner that complies with the new energy efficiency provisions. October 1st 2010 is the date this comes into force.

Exemption (of the energy efficiency provisions) will only be granted where:

The conservatory or porch is at ground level only.

It has a floor area of less than 30m².

The doors and windows in the wall to which the conservatory is attached are retained, or if removed they are replaced with substitute walls, windows or doors that meet the new energy efficiency requirements.

The heating system of the dwelling must not extend into the conservatory.

If the conservatory fails to meet all four of the above conditions, it is deemed not to be exempt and must comply with the relevant energy efficiency requirements (4.8 and 4.9).

And if it is not exempt, it must be treated as a conventional extension in which case all applicable Building Regulations apply.

Under Building Regulations, the cavity wall below the roof level of the new conservatory must not suffer damp penetration. But with the outside skin above the roofline exposed to rain, dampness readily gravitates downwardly below the roofline and into the conservatory. Just flashing the intersection is not sufficient.

The remedy and compliance is achieved using preformed cavity trays that are inserted into the masonry just above the roof intersection. With versions to suit horizontal and sloping abutting roofs*, all styles of conservatories can be protected from dampness. 

‘At last there is an official line to take regarding cavity trays and conservatories’ advised a spokesman of Cavity Trays of Yeovil. ‘As a rule of thumb trays will be necessary, unless the addition is exempt. Conservatories have departed from the original dictionary definition of a glazed housing for plants and are now commonly used as extensions of the living space, so it makes sense to regularise the construction integrity’.

It is interesting to note that the NHBC advocated some years ago that trays should be fitted above conservatory roof intersections. Now its view is reinforced and from October 2010 it is thought over 90% of all conservatory proposals will be non-exempt, and thus will have to be constructed to the new Building Regulation standards.

‘Regulations are guiding this change which should result in conservatory contractors offering the same standard and compliant scope of build where the roofs attach to the original structure’

* Type E cavitrays for horizontal intersections.

* Type X cavitrays for sloping intersections.

Both manufactured by Cavity Trays of Yeovil from which a brochure dealing with the compliant interfacing of conservatories is available upon request.

This month Cavity Trays Ltd is releasing a new Product Guide – number 21.

With over 91 data changes, 145 text changes and additional products included in the guide for the first time, it is claimed to be essential reading for all disciplines involved in the design and construction field.

The A4 sized Product Guide 21 is printed in full colour and addresses compliant construction of the building envelope. Damp courses, flashings, cavity trays, weeps, thermal, acoustic and fire integrity rated products from ground to roof level are listed together with design considerations. 

Cavity Trays Ltd is the only cavity tray manufacturer awarded European Technical Approval and its approved products are accompanied with product performance liability protection for the benefit of Architect Builder and Client. 

Product Guide 21 provides the latest information and is available upon request now. At the same time the Company is accepting advance reservations for Guide 22 that is scheduled for release in January 2011 and will contain a new range of energy-efficient products that are currently undergoing appraisal and testing. 

The current list of publications from Cavity Trays Ltd is:

1.     The New Cavity Tray Product Guide 21

       Cavitrays, dampcourses, flashings, membranes etc (210)

2.     Closing Cavity Walls 

      Thermal, acoustic and fire integrity rated closers and barriers (19)

3.     Ventilation

       Products for roofs walls and floors (19/107)

4.     Gable Abutments

      Brochure focusing on stepped and staggered gable protection (21)

5.     Conservatory Construction

      The use of trays to satisfy Building Regulations (J08)

6.      The Book of Wise Decisions

Handy pocket-sized book containing concise entries of most products (2010)

Cavity Trays Ltd is the longest established in its specialised field.

Issued by the Marketing Department,

Cavity Trays Ltd.  BA22 8HU.

May 2010

Order your copy of Product Guide 21 and at the same time reserve your copy of Guide 22 available January 2011

GreenSpec have a rigorous product evaluation and selection process so we are naturally very pleased with this acknowledgement.

The Type RC Refurbishment Cavicloser fills the gap exposed when a window or doorframe is removed from a cavity wall that has not been 'closed'. This status is regularly encountered during door and window replacement schemes.

The Type RC has a rigid faceplate to which is attached a compressible polythene sleeve containing a flexible insulating medium. This flexibility permits the sleeve to be compressed and easily introduced into an open cavity. As the compression releases the sleeve expands to take up the cavity width encountered. In addition to the thermal zoning of the reveal, there are acoustic benefites, as the insulating medium interrupts the direct sound path that previously existed where the frame meets the cavity.

For full details of the Type RC Refurbishment Closer please ask for a copy of our 2010 Pocket Guide.

Timber Frame (DPC) Profiles

Often a detail is called-for within a contract that it is difficult to reproduce on site. This has prompted Cavity Trays Ltd to release a new range of dampcourses that are ready-shaped to tackle everyday construction needs encountered when building using timber frame and SIP’s methods.

The most popular of the DPC Profiles is designed for use under sole plates. Construction standards demand dpc’s are incorporated below all timber frame sole plates of ground floor walls. Furthermore, in addressing the requirements for air tightness, Robust Details calls for the dpc to turn up and lap with a vapour control layer. Using traditional dpc to create such an arrangement can be difficult. Traditional dpc can also distort,  be damaged, or progressively sag  whilst construction is taking place.

Solution

DPC Profiles are accurately dimensioned semi-rigid shaped dpc’s that permit the installer to establish consistent dpc protection around the base of timber-framed and SIP walls.

Laid and lapped under the sole plate, the profiles rise vertically to protect the inner face of the plate. (Depicted in NHBC Standards 6.2). Profiles are also available that extend inwardly. In so doing the oversite membrane can benefit both horizontal and vertical interfacing. 

DPC Profiles will not extrude under load and functionality is unaffected by normal packing / point loading. Additional protective rise can be specified where a double soleplate is used. Internal and external angles are similarly preformed. Bespoke profiles are available in addition to the standard profiles. 

DPC Profiles can be used effectively to address Robust Details (6.11 to 6.15 inclusive) and NHBC (6.2) requirements.  

• Satisfies NHBC / Robust Details requirement
• Will not extrude or seep under load
• Close fits timber – no sagging or damage
• Consistent quality of build

The CLV lovered vent can be introduced when the wet trades have finished. It differs from most circular ventilators as it has an airflow aperture rating of 2100mm2.

The Type CLV - Circular Lovered Ventilator is available in a range of colours to suit popular masonry colours. Terracotta, Beige, Brown, White and Black.

Data:

Polypropylene.

Size 79/70 x 15mm - Requires 70mm hole.

Louvres deflect driving rain and provide insect screening.

Integral location grips.

Featured in the latest 2010 Book of Wise Decisions Pocket Guide

Cavity Trays is committed to continually reducing the environmental impact of our operations, including the manufacture and use of our products.

Introduction  

The level threshold is an everyday feature in construction that can be problematic. It is not just marrying of the external and internal levels that can prove challenging, It is doing so in a manner that protects against wetness permeating and permits a functional interfacing with the method of reveal closing / insulation and the oversite membrane.

There is now a new product manufactured specifically for this purpose. It regularises this specific area of construction. It permits internal and external floor levels to interface at an opening within a cavity wall. 

Cavity Trays of Yeovil has come up with a Level Threshold Tray (Type LTT). It provides an effective way of isolating both external and internal threshold skins to great advantage:

Phone our Helpdesk for more details or to request literature.

Complete the 'Brochure' enquiry form or telephone our Helpdesk to order your copy today.

The Type PWRB Rising Party Wall Barrier provides an alternative approach. The base of the barrier acts as a dpc and extends under both skins of the party wall. The upstand acts as a dam against water flooding from within one dwelling contaminating the adjoining dwelling. The upstand is capable of holding back a far greater volume of water than a channel.

Because the profile extends upwards instead of downwards, it can oversail and interface with commonly used perimeter gas barriers. Any water can thus be directed safely into the lower portion of the perimeter wall gas barrier, from which subsequent evacuation is via the already present barrier caviweeps. At all times the gastight integrity can be maintained.

The Party Wall Rising Barrier eliminates the problem of incompatibility, increases the capacity to prevent inter-property water contamination and satisfies the design detail requirement.