Clear improvements

Back to school for star pupil Kawneer

LOCAL AUTHORITIES FIND FRAMING SYSTEM MAKES LIGHT WORK OF LAST YEAR’S PART L
Regulations? you can always find a fancy new material to satisfy them. Problem is, though, if the whole point of your strategy is to deliver cheap buildings, cutting-edge materials can blow your maintenance costs out of the water. High-tech, argon-filled, soft-coat glazing just won’t do for the Consortium of Local Authorities Special Programme (Clasp), which has been promoting modular-build schools for nearly 50 years. State-of-the-art is more expensive to replace than bog-standard, and schools have to replace plenty of windows and doors. “Schools are aggressive environments,” says David Mackness, manager of Clasp services. “Sixteen-year-olds don’t treat windows and doors kindly, so units have to be cheaply replaceable.” Last year Clasp struck a three-year deal with Kawneer to replace worn-out doors and windows in its schools with the 451PT framing system. Because 451PT uses standard, readily available K glass, replacement is cheap. A small gasket in the glazing channel creates a polyamide thermal break that prevents cold air touching the inner pane and lets the system easily achieve the 2.2 U-value demanded by Part L. Although Part L lets you replace glass like for like, any replacement frames have to meet the new thermal insulation standard. “The impact of Part L has been dramatic,” says Mackness. “People start asking awkward questions, such as whether cavity wall ties are acting as a thermal bridge, so the detailing gets difficult.” The Clasp framing system not only had to meet the new Part L, but support 3m horizontal spans. 451PT was the only system that could do both. Because it’s dry-jointed and square-cut, 451PT is simple to assemble. David Taylor, Kawneer’s product development manager, claims its performance is equivalent to that of curtain walling but with fewer components. As the system is watertight at 600Pa and wind resistant at 2400Pa, you can use it above ground level, although the joint and expansion details don’t cater for floor movement so you can’t go above third-floor level with it. “451PT is a lot more solid and easier to build than [its predecessor] 451T,” says Andrew Stapleton, Clasp co-ordinator at Kawneer fabricator Cap Aluminium. “It’s structurally stronger, so you can span further with it.” Most Clasp refurb jobs are piecemeal replacements, but Woodham Technical College in Durham is replacing around 80% of its timber-frame windows with 451PT. After 35 years of service, the frames are rotten and many of the casement windows have seized up. Installation is straightforward, involving ripping out the wooden frame and fixing 451PT to the existing brackets. The trickiest part, says Stapleton, is making sure the client has a good idea of the sequence and vacates classrooms accordingly. 451PT is also suitable for shopfronts. It comes in a range of mullion and transom styles and offers 50mm-wide dual-colour frames – one on the internal frame and another on the external.

Enquiry number 201

The glass that can breathe...

new system proves trade-off between health and energy saving
Saving the planet is all well and good, but the single-minded pursuit of energy saving can leave you with a building that is unpleasant to live or work in. Sealing up a building as tightly as possible may help satisfy the stringent requirements of the Building Regulations but it also compromises air quality and encourages condensation and concentrations of cigarette smoke, particulates and volatile organic compounds – all factors in Sick Building Syndrome. One way to end the war between good health and energy saving is to pass the air inside a building through a heat exchanger before expelling it and applying the reclaimed heat to fresh air before circulating it within the building. Minimising heat loss while promoting good ventilation in this way sounds good. Unfortunately, in the UK the energy saved in heat reclamation is not much greater than the energy consumed by the continuously operating extraction fans. Such mechanical systems also need an awful lot of ductwork to funnel air to the heat exchanger in the roofspace. Cambridge University researcher Mike McEvoy reckons there’s a simpler and more effective solution. He’s developing a non-mechanical ventilation system that dispenses with fans and ducting altogether in favour of a ‘supply air window’ and stack vents. STACK SOLUTION
McEvoy’s system works by passing fresh air through the 30mm glazing cavity of a dual-glazed window so that solar gain and escaping heat warms up the incoming air. A pressure-controlled vent at the bottom of the outside-facing window frame draws air in. That air then travels up the gap between the external and internal panes of glass, warmed by heat from both sides, and enters the room through a trickle vent at the top of the inside-facing window frame. The system uses simple stacks or chimneys to expel the air, which creates the pull factor needed to drag fresh air in. The height of the stacks (which are fitted in kitchens and bathrooms to vent moisture too) provides enough difference in air pressure between the outside and inside to suck air out. Vanes in the sides of the stacks prevent air being pulled out too rapidly on windy days. “The design U-value of a double-glazed window is 2.1,” says Paul Baker, of BRE Scotland, which is helping to test the system. “With the same kind of glazing, the supply air window brings it down to 0.8.”

Enquiry number 202

Need more daylight? Take the tube

Piped daylight available for dingy dungeons everywhere
After five years without a glimpse of daylight, Peter Sanderson swore he’d never work in an office without windows again. So when his firm decided to partition off some warehouse space in the middle of its building to make anew office, the production and building manager for satellite maker Applied Satellite Technology refused to go all electric. The new office had no external walls at all. And with a false ceiling required to make the noise level tolerable for an office, the clear skylights in the roof 5m above would be of no use either. Putting glass in the ceiling wouldn’t have worked as the light coming though the skylights was diffused. As with any totally enclosed space, or where an external window would be blocked in by higher buildings close by, tubular skylights offer a way of introducing daylight. Sanderson fitted Solatubes from SolaLighting, which incorporate a new super-reflective coating called Spectralight Infinity. They weren’t cheap – it cost just under £4,000 to buy and install the three 530mm-diameter tubes needed to illuminate AST’s new, 8m by 20m office – but they are effective. “They’re like really bright torches,” says Sanderson. “I looked up one and nearly blinded myself!” COATINGS COUNT
Each tube channels daylight from its own glass dome on the roof to its own diffuser (a prismatic lens the size of a ceiling tile) in the office ceiling. The diffuser spreads the light rather than delivering it in a shaft, and the multiple images produced by the prisms give privacy for the user. Super-reflective coatings like that of Spectralight Infinity (see box) mean that tubes can be longer than previously while still giving an acceptable amount of light. “We never used to go down two floors,” says Ann Knowlson, a partner with installer Daylight Developments. “The light attenuated too much. But it’s not a problem now.” Knowlson says the tubes even get around the problem of planning permission in areas of outstanding natural beauty by allowing houses to be built underground. And, instead of using atriums, low-rise offices in heavily built-up areas could run tubes through a central shaft before branching off to the lens locations. The 610mm-long Solatubes are overlapped and taped to fit; SolaLighting’s longest tube to date travels 12m. Installation is easy, and even retro-fitting a system involves little disruption. It took a day to fit the domes and tubes at AST, and SolaLighting says installers need no special expertise.

Enquiry number 203 TUBULAR TALES
A tubular skylight is a telescopic window where the same area of glass gets three times as much light as vertical glazing. Light streams directly down the tube for only a few minutes at noon. At all other times, it bounces off the sides of the tube, losing luminosity with each bounce. The lower the angle at which the light first hits the tube, the more bounces it needs to descend the tube. As a result, even small improvements in the reflectivity of the tube lining have a big impact on the daylight that reaches a room.

Electronic locking made simple

BATTERY-powered knob offers hassle-free wireless solution
Once you’ve specified your doors, you just let your chippie get on with it and that’s that. Simple really – unless you also have to wire all or some of them up with electronic locks. It’s not a problem as such, just a bit more complicated. Now, you need an electrician as well as a carpenter, which makes the doors a two-trades operation. That’s one more thing to programme, one more thing to keep an eye on – and one more thing to go wrong. You can, however, fit electronic locks without wiring in wall-mounted pads. DOM’s new ELS wireless product takes care of all the M&E itself in the battery-powered doorknob. The same carpenter who fits the door can put in the standard Europrofile ELS lock cylinder. It’s the same size and shape as a typical mechanical cylinder, takes about two minutes more to install and can be retrofitted. To open an ELS door you have to place a transponder (a key fob, a key or a swipe card) with access rights near the lock. The system keeps an audit trail of who goes through the door, supports time zones (that is, it gives access at certain times only), and can enable and disable access rights. The client uses a handheld terminal to programme the locks. Popular applications for electronic locking are multi-occupancy offices and shared accommodation such as student flats. It’s more expensive than a simple mechanical lock – £300 as against, say, £25 – but that’s like comparing apples and pears. If your client wants the benefits of electronic access, then you need an electronic system, and £300 is competitive.

Enquiry number 204

Building the sustainable school

Timber-framed windows and doors proved the eco answer
BRENZETT SCHOOL IS made ENTIRELY OUT OF sustainable materials. It’s a building that harvests rainwater to flush the toilets, filters its waste through reedbeds, and keeps itself warm with recycled newspaper and eco-friendly, super-efficient windows and doors. So when it came to the doors and windows, timber frames were in and aluminium (the norm on a school because it requires so little maintenance), steel and PVC were out – the manufacture of timber frames consumes far less energy than the alternatives. Budget was also a key issue, with architect Philip Payne looking for ways to cut costs so he could remain inside the £1.2m limit. Downspecifying windows and doors usually means PVC frames, but although low maintenance, efficient and cheap, PVC is an environmentally hostile material - and not right for this job. Instead, Payne specified Ecoplus timber-framed windows and doors. Although around 10% more expensive than PVC would have been, Ecoplus is cheaper than aluminium, and allowed Payne to cut costs. Maintenance is an issue, as with any applied finish, but the Ecoplus coating (mineral pigments and oils derived from thistles and soya rather than biocide-treated polymers) requires much less maintenance than gloss-painted timber; Payne anticipates a five-year redecoration cycle. And because the Ecoplus windows incorporate Iplus argon-filled double-glazed units from Interpane Glass, they are super-efficient thermally. Main competitor Pilkington’s K glass costs about £40 per sq m compared with £55 for Iplus, and Pilkington K’s 1.65 U-value comfortably undershoots the 2.0 U-value for timber and PVC frames imposed by last year’s Part L. However, with a U-value of 1.1, Iplus offers overall better insulation than K. And because Iplus has a soft coating rather than a hard one, it is almost as transparent as ordinary glass; the S version of Iplus, which appeared last year, increases light transmission by 7%. Hard coatings such as K typically impart a colour cast to glazing and have poorer optical clarity. Payne says K glass would make classrooms look dull. Brenzett School was completed last May. Sustainability has left the school thrilled, Payne proud and purseholder Kent County Council keen to take some of the credit.

Enquiry number 205

Glass through the past

PETER KERNAN LOOKS AT the history of glazing
Now the most commonplace of materials in the built environment, glazing was a rare sight in buildings before the 18th century. Until then, most windows were just holes in the wall, with shutters or horn for weather protection. Manufactured glass first appeared around 4500BC in Mesopotomia for jewellery and storage vessels, but it wasn’t until the invention of glass-blowing in Syria around 2,000 years ago that glass windows were made. Roman windows were not very transparent (although opaque was preferred in the Mediterranean area anyway to give protection from the sun), and because the surfaces were not flat or parallel, optical distortions were common. A luxury item, windows appeared only in villas and palaces – examples still survive from Pompeii. After the fall of Rome, glazing production declined and went mainly into ecclesiastical buildings and palaces, where small pieces of coloured glass were leaded together, only slowly spreading into the houses of rich merchants. COMMERCIAL USE
In 1600, glazing in England was still so precious it was bequeathed in wills, with legatees ripping it out of the deceased’s house and installing it in their own. By 1800, most houses had windows, typically made up of smallish panes of thin, optically imperfect glass. Cheap mass glazing took off in the middle of the 19th century, driven by free-trade Britain’s abolition of glass and window taxes, and the construction of the Crystal Palace in 1851. Built by conservatory maker Joseph Paxman as an advert for his industry (and the conservatory was the sweet-scented party venue of choice for Regency Britain’s hygiene-challenged beau monde), the Crystal Palace was a glazing phenomenon, boasting millions of square feet of cheap, large and thin panes. Modern glass dates from Pilkington’s discovery in the 1950s that floating molten glass on top of molten tin gives a brilliant finish and perfect performance. Cheap float glass rapidly replaced sheet glass and plate glass and now constitutes about 90% of glass production. Float glass manufacture allows coatings to be easily applied. With the appropriate coating, windows can now clean themselves, act as heaters, get darker in bright sunlight and screen TV programmes.