Theme: doors and windows
The design of windows and external doors is an increasingly complex task. Not only must the client be satisfied with the result, but there are increasing amounts of regulations to be added to the equation - and failure to meet them can be costly Specifying components such as windows and external doors is a technically complex procedure with numerous pitfalls for the unwary. Attempting to design windows and doors using any of the normal frame materials, and without the luxury of specialist advice and test facilities, places you in a risky situation. But some architects do take this risk. Whether it is in the belief that they can do better, or because they are unaware of what is available from the industry, is not clear. All too often the result is client dissatisfaction and possibly litigation.
For all types of building work, client expectation and, increasingly, Building Regulations, performance requirements in respect of windows and doors have grown hugely in recent years. The industry has spent, and continues to spend, large amounts of money developing and testing products to meet these requirements.
It is often said that there are only two ways of specifying most building components - correctly and badly. It seems to be becoming increasingly easy to do the latter, especially as the time allowed by clients before starting work on site is reduced, so that significant decisions may have to be made quickly to keep ahead of the building programme. Windows and doors should always be specified by performance, and caution should be used if a potential supplier cannot provide appropriate performance test information.
The important performance criteria for most projects are: lWeather resistance tests to BS 6375:
Performance of windows, Part 1, Classification for weathertightness and Part 2, Specification for operation and strength characteristics.
lBS 7950: Specification for enhanced security performance of casement and tilt/turn windows for domestic applications.
lProduct Assessment Specification (PAS) 23: General performance requirements for door assemblies including ease of use of hardware, weather tightness and strength.
lPAS 24: Enhanced security requirements for door assemblies.
For domestic projects there are also the requirements of Secured By Design, a police initiative to incorporate crime-prevention measures at the design stage. Many housing association and developer clients now require compliance with this as part of their initial brief.
It is also necessary to specify the U-value which the windows and doors need to achieve. Since the introduction of the new Part L Approved Document to the England and Wales Building Regulations in April 2002, all windows should meet at least an average weighted U-value of 2.2 W/m 2K for metal-framed windows and 2.0 W/m 2K for PVCu and wood-framed windows and doors. In Scotland, the revised Part J requirements of 1.8 W/m 2K come into effect this month.
The British Fenestration Research Council is promoting an alternative evaluation procedure to the basic elemental thermal performance values. The BFRC DWER (Domestic Window Energy Rating) rating is based upon a combination of thermal performance determined by calculation or hotbox testing, a solar gain (G) rating calculated in accordance with BSEN 410, and an airleakage rating determined by testing to BS 6375. The result of the assessment is given as a figure on a scale of 1 to 100 and enables different window components to be compared directly.
Although currently in its infancy in the UK, the scheme is similar to one that has been running in the US for about 10 years.
Chiltern Dynamics, which has carried out some of the first UK assessments, says the cost of extending normal weather resistance testing to encompass the full DWER assessment is modest. The advantage to clients and specifiers of having an easy performance comparison between different window and glazing specifications is obvious.
Two other aspects of external door and window performance that can cause problems relate to fire and sound resistance.
When doors or windows open on to escape routes they may be required to have 30 or even 60 minutes fire resistance to prevent an internal fire obstructing escape. Because this requirement is not particularly common, few manufacturers can produce appropriate test evidence. Where it is critical, a fire test to BS 476: Part 22 may have to be carried out specifically for the project. Otherwise, it may be possible to specify fire-rated glazing in a conventional frame using intumescent glazing materials and to have this assessed by a specialist advisor.
Timber and steel glazed doors that offer 30 and 60 minutes' fire resistance are available from a number of producers. And specialist fire-door manufacturers can supply products with longer periods of fire resistance. For example, a new range of steelframed glazed doors developed by Wright Style and incorporating 3m 2of Firelight glass can achieve up to three-and-a-half hours' fire rating when tested to BS 476:
It is worth noting that the recently issued revisions to Approved Document B of the England and Wales Building Regulations, which come into effect this spring, make reference to the new European Standard for fire-resistance testing. All fire doors should be classified in accordance with BSEN 13501-2 Fire classification of construction products and building elements; Part 2 Classification, using data from fire resistance tests. For now, this new standard will run in parallel with BS476: Part 22.
Sound resistance from noise outside the building is not included in the newly revised Approved Document E, but a specified decibel reduction is increasingly being stipulated as a planning requirement for buildings in noisy locations. Complying with these requirements can be onerous. It usually requires good-quality window seals and special glazing, allied to careful design to limit the glazed area on the affected facades.
On a current project, Rationel Windows has worked with Saint Gobain Solaglas to incorporate a glazing specification comprising 33.2mm-thick sealed units with a10.8mm Stadip Silence acoustic laminated glass outer leaf, a 14mm argon-filled cavity and an 8.4mm Stadip Silence acoustic laminated glass inner leaf. This combination, in a well-sealed frame, will provide a 47dB reduction compared with the 30 to 35mm dB reduction that a normal sealed-unit window would achieve. Stadip Silence laminated glass incorporates a triple-layer laminate.
An acoustic interlayer between the two sheets of glass provides improved acoustic performance as well as the safety and security performance of laminated glass.
When sound reduction of this type is required, conventional background ventilators set in the window frame cannot be used since they provide a direct sound path.
Background ventilation needs to be provided by ducting from a facade on a quieter side of the building, or by use of an acoustic ventilator. Willen Passivent produces an acoustic ventilator that fits into the window opening. This will provide about 39dB sound reduction when two ventilators providing an 8,000mm 2ventilation area are installed.
A topic that consistently causes concern to designers is the acceptable height of window sills to rooms above ground-floor level.
This is because of the different guidance given in British Standard 8213 and Approved Document K to the England and Wales Building Regulations. In the latter, the height from finished floor level to the lowest part of the window opening is shown as 800mm for all buildings. However, Part 1 of BS 8213: Windows, doors and rooflights, states that from the second floor upwards, the lowest part of the window opening should be not less than 1,100mm above finished floor level or should be protected by a safety rail at 1,100mm.
The British Standards for windows, BS 4873 for aluminium, BS 7412 for PVC-U, BS 6510 for steel and BS 644 for wood all provide useful guidance for specifiers. The proposed European Product Standard for Windows and Doors, which has been in discussion for some years, is now likely to come into use in 2004. It will, however, cover only the performance characteristics of the components and not the material characteristics, which will need to be defined elsewhere. At least until it is published, the situation with regard to Standards for external doorsets remains unacceptable, with no relevant British Standards available apart from reference to BS 6375 for exposure ratings.
Glass cleans up One of the most interesting new products introduced to the UK market in recent months is Pilkington Activ, the world's first self-cleaning glass. A special coating on the glass reacts with sunlight to break down any dirt on the glass. Rainwater then flows evenly over the surface, washing the dirt away without any streaks.
Already available in the US and Europe, it was held back in Britain until last September to allow the window industry time to come to terms with the changes introduced by Part L of the Building Regulations. Six months after its launch in Ireland, the glass was accounting for one in six of all replacement windows. In offices and other commercial buildings where window-cleaning costs are high it may be most advantageous.
Since Activ is an applied coating, it cannot be applied to the same piece of glass as other solar-control coatings, but it can be combined in double-glazed sealed units with Low E or other coatings by having the Activ coating on the external face and the Low E coating on the cavity face of the inner pane.
Perception of doors The need to comply with new thermal-performance requirements for external doors continues to generate new and improved composite doors. Sentinel's Gold Standard range of domestic doors is one such introduction. In full compliance with Part L, all the doors will be pre-tested to PAS 23 and 24 and Secured by Design. The new door is claimed to be four times harder than any other painted door skin material, to have very high UV resistance, and thermal expansion at only 10 per cent of the rate of thermoplastics presently used in the composite-door market.
Jeld-Wen is offering the Therma-Tru fibreglass door system as part of its Jeld-Wen Plus range. The fibreglass door slabs are shipped from the US and finished at Jeldwen's John Carr door factory in Lowestoft where apertures are cut, and glazing and door furniture is fitted. The doors are coated using a 10-year warrantied paint and stain system. Three ranges are available, all of which meet Part L thermal requirements.
High-security PAS23/24 doors and fire doors are also available.
Sapa Building Systems recently introduced the Dualframe high-performance entrance door. This forms part of a range of dual-coloured aluminium doors and windows which are designed to exceed the requirements of Part L. The doors also meet BS 6375: Part 1, Exposure category 2400 special and the requirements of PAS 23 and 24.
Omega Doors has consolidated and rebranded its range of specialist steel doors. The new range of doorsets includes general-purpose doors (GP), fire integrity doors (FR), fire integrity and insulation (FRI) doors and thermally insulated (TI) doors. The fire doors are certified to both the BS 476 and the new European BSEN 1634-1 test standards.
Timbmet Doors has merged with M&V Woodcraft to create Timbmet Door Solutions to offer a complete internal doorset package and provide a 'one-stop shop' approach to the sourcing of high-performance bespoke doorsets including all required hardware. TDS specialises in the supply of high-performance doorsets to the commercial, education, health and leisure sectors. Its product range includes flush wood-veneered, plastic-laminated, x-ray, solid timber-panelled and painted door options, with up to FD120 fire ratings and 44dB acoustic levels.
Two interesting products related to door safety were introduced at the end of last year.
Lorient Polyproducts has produced a twoseal finger-guard system for fitting on both sides of the door at the hinge stile to prevent fingers becoming trapped and crushed as the door closes. Children are particularly at risk from this type of accident and many organisations are requiring protective measures to limit such hazards.
The Lorient seals comprise a gasket seal on the hinge face of the door and a larger concertina seal on the opposite face of the door.
This expands across the gap between the edge of the door leaf and the frame when the door is opened. The concertina seal also incorporates twin elastomeric blades to help reduce noise transmission. It can be used in combination with other Lorient seals to provide smoke, draught and acoustic containment.
The Dorgard, which has been developed by Fireco, is a retrofitted electronic fire-door release device, intended to replace the wedges, waste bins and fire extinguishers that are regularly and illegally used to wedge open fire doors in offices and buildings such as residential homes. Dorgard is a batteryoperated, acoustically activated electronic fire-door release that is screw-fixed to the bottom of the door and does not interfere with the door's integrity. It is designed to release the door when a fire alarm sounds and can be adjusted to set its acoustic sensitivity with a fail-safe mechanism for when the battery needs replacement.
Windows of opportunity Technal's recently introduced Fxi65 window range incorporates a 19mm flush polyamide thermal break and innovative gasket detailing to improve performance. The 65mm module system accommodates doubleglazed units from 17mm up to 48mm and allows more economical glass specifications to be used while still meeting the required Uvalue of 2.2 W/m 2K. When tested to the new BSEN Standard, the Fxi65 met, and in some cases exceeded, the requirements. It can be supplied as fixed lights, projecting top-hung and side-hung casements, bottom-hung casements and tilt/turn casements.
Rationel Windows has also introduced a new tilt/turn range of windows to its Domus pre-finished timber and Aldus aluminium/ timber composite window lines. Unusually for a timber window, the tilt/turn frame profiles are the same size as the side - and tophung casement and fixed-light windows enable different types to be linked in the same opening when required.
A member company of the Steel Window Association has developed a thermally broken stainless-steel window system which is now available from all SWA members.
Klockner RP Profiles' Garant system stainless-steel sections can accept insulating glass units up to 36mm thick and can attain a Uvalue of 1.3 W/m 2K where required.
The frames are jointed mechanically at the corners. Widths of up to 1,350mm and heights of 2,100mm can be produced for windows with side-hung, top-hung or tilt/turn openings. Matching doorsets may be up to 2,500mm wide. The stainless steel frames can be supplied with either a brushed or polished finish or can be polyester-coated in any RAL colour.
LB Plastics' new Thermalock is a thermally enhanced reinforcing profile which will enable its PVCu windows to meet the 1.8 W/m 2K U-value rating required in Scotland from March 2003 without the need for costly soft-coat glazing. Used with Sheerframe four-chamber profiles, Thermalock will enable even the most complex fully reinforced profiles to meet the required thermal performance and have greater pull-out strength for hinge and handle fixings.
The Monodraught Sunpipe is a useful way of getting daylight into internal spaces where conventional windows are not possible, Monodraught has recently joined forces with The Metal Window Company to produce the Conservation Sunpipe, which has the appearance of a traditional cast-iron rooflight with no projection above the roof plane. It is claimed to capture about three times the light of a conventional Sunpipe and to be condensation-free due to a patented Thermoliner.
The company says that, although designed to suit its standard 300mm and 450mm diameter Sunpipes, there is virtually no limit to the size or length of Conservation Sunpipe that can be provided.
READER ENQUIRIES Alfas Industries 1400 Baydale 1401 Deceuninck 1402 Efaflex 1403 Fireco 1404 HW Systems 1405 Jeld-Wen 1406 Klockner RP Profiles 1407 LB Plastics 1408 Lorient 1409 Monodraught 1410 Omega Doors 1411 Parkside Group 1412 Pilkington 1413 PPG Industries 1414 Rationel 1415 Saint Gobain Solaglas 1416 Sapa Building Systems 1417 Sentinel 1418 Technal 1419 The Metal Window Company 1420 Therma Tru 1421 Timbmet Door Solutions 1422 Veka 1423 Willen Passivent 1424 WHS Halo 1425 Wright Style 1425 Enquire at www. ajplus. co. uk/ajdirect