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Residents on a development in Liskeard, Cornwall, look set to benefit from the thermal performance enhancing properties of cavity closers. Here, Martin Benn, Sales Manager at Cavalok, explains why 100 per cent post-consumer recycled cavity closers were used on this development.

“There have been some fascinating changes in the new-build housing market in response to demand for better thermal performance. Cavity widths have rapidly expanded from the 75mm standard pre-2006, first to 100mm and now to sizes well above that to enable top performance U-values to be achieved. Similarly improvements have been sought to improve thermal bridging, particularly at the lintel. As a cavity closer supplier with over a decade of experience and now part of the Eurocell group, Cavalok has been quick to develop new cavity closer products to meet these needs.

The frame-forming cavity closer is ingenious in its combination of several independent features into one product. It is a wall opening former which prevents thermal bridging, simplifies bricklaying and provides a damp proof course (dpf).

The first principle of a cavity closer is that it reduces heat loss from the building. This is achieved because the closer prevents thermal bridging around the cavity through secure and full insulation across the cavity, as recommended by the Accredited Construction Details. Cold bridging allows valuable heat to escape the building and can lead to condensation around the window as well as cold draughts in the room as the relatively cooler air around the windows and doors causes ‘cold pockets’.

Cavity closers are therefore an essential element of modern building design, not least because they also simplify construction by avoiding the need to cut bricks, blocks or use special reveal blocks to suit the cavity. They help speed up installation too, by providing exact opening sizes for bricklayers. Unsurprisingly, they have become a building system preferred by contractors, building inspectors and clients.

[caption id="attachment_281" align="imgleft" width="134" caption="Improving thermal efficiency with Cavalok's Cavity closer systems"][/caption]

The benefits of using cavity closers were recently demonstrated on The Aster Group’s Extra Care scheme in Liskeard, Cornwall. The group is a collection of housing associations that own and manage over 16,000 properties across the South West. The housebuilder, ROK, carried out the work on the former Passmore Edward Hospital, which involved refurbishment of the 100-year old building as well as construction of 55 new build flats and apartments.

The designers specified Cavalok Big Blok cavity closers to create and close the openings on a variety of wall constructions on the new build properties, which had cavities ranging from 140mm to 175mm, with 90mm of insulation.

A four-sided cavity closer solution, supplied by our Cavalok approved fabricator Securiframe, was selected to accommodate a split lintel and provide a ring of continuous insulation around the opening. Subsequent SAP calculations indicated that the completed development will exceed Building Regulations thermal performance requirements by 20-30 per cent.

Traditionally, steel lintels that bridged the cavity would have meant heat flowing rapidly out of the building through highly conductive materials. However, splitting the lintel into two separate components meant a continuous insulated cavity around window and door openings was achieved to meet the thermal performance targets.

Cavalok closers were also specified on this project because of their sustainability – they are the UK’s only BBA-accredited cavity closer system made from 100 per cent post-consumer recycled PVC-U. We source post-consumer sustainable materials that had traditionally been destined for landfill sites, such as end-of-life PVC-U windows and doors that are removed from buildings when replacement products are fitted. The various materials used in the make up of a window are then separated into their individual components for recycling. The PVC-U is cleaned, reprocessed and extruded into our cavity closer frames. The cavity closer is therefore an ideal sustainable product; it improves energy usage and is manufactured from recycled material.

In addition to sealing the cavity and eliminating cold bridging around the windows and doors, the cavity closers dramatically speeded up bricklaying on the Liskeard project. This is because the pre-made cavity frame acted as a template, guaranteeing the opening size for the window suppliers. This helped avoid delays during later stages as it ensures the windows and doors can be fitted ‘right first time.’ We received excellent feedback from the contractor as the closers allowed the windows to be clipped into position within seconds, which avoided the need to store them on site where they can be vulnerable to damage.

Selecting a cavity closer depends on the cavity size to be closed. The Cavalok range varies from 50mm up to the Big Blok system, which can be produced for 300mm cavities often used in Code for Sustainable Homes (CSH) Level 6 developments. Many building designers are already specifying 125mm cavity closer systems to meet Code level 3 and demand for 150mm and above continues to grow. There is a clear movement towards the energy benefits of larger cavity sizes through regulations and best practice design.

Fire rated closers

In addition to helping sites meet the requirements of Part L and the Code for Sustainable Homes, we have developed a range of fire rated cavity closers, which again use 100 per cent post-consumer recycled material. With more construction methods and building types requiring higher fire-ratings our range provides a one-hour tested solution around windows and doors and features all the benefits of a traditional closer frame. The fire-rated closers are to be launched in Autumn 2009 to suit cavity sizes up to 150mm.

There has been a tendency for manufacturers to skimp on testing, making assumptions about what their product covers. To avoid these complications, a rigorous test was devised using multiple wall construction types and a detailed analysis of how a frame performs. The end result was a cavity closer product that actually outlasted the timber frame surrounding it, a result that will give specifiers real confidence.

Cavity closers are an essential part of helping a building achieve thermal and fire performance requirements. Choosing a system made from 100 per cent recycled post-consumer PVC-U complements these benefits and provides a means of demonstrating enhanced levels of sustainability.

As the performance requirements of buildings become more stringent we expect continued interest in these types of systems. Our aim is to provide building designers with sustainable cavity closer systems whichever level of the Code or Building Regulations they are aiming to meet.”

For more information on Cavalok’s full range of 100% post-consumer recycled PVC-u cavity closers, call 0870 120 3003 or visit: www.cavalok.com