Cladding: what’s new

Every few years Part L mutates and makes fresh demands on a building’s energy performance, resulting in deeper cladding systems being specified and an increased focus on improving airtightness.

The Steel Construction Institute (SCI) has now reviewed how the legislation is changing the way we build. Its findings have been published in a guide, which tackles the specification and installation of building envelopes and the supporting secondary steelwork.

The guide is for architects, specifiers, designers and site erectors. It covers relevant aspects of modern steel cladding design and installation, and aims to improve building envelope performance, health and safety, and efficiency.

Many industrial developers are already producing metal-clad buildings that exceed the requirements of the latest Building Regulations in terms of air leakage and energy performance, but SCI says there are instances where problems have arisen due to poor practices in the design office

or on site. “The reasons for these problems are varied, but a common theme is the lack of

appreciation of the mutual dependence between the various components and, consequently, the need for greater co-operation between the members of the project team,” said Dr Martin Heywood, manager of construction technology at SCI. He added: “This is particularly relevant in the light of recent regulatory changes.”

The publication covers many aspects of cladding specification but will be particularly relevant for those working on large-span single-storey buildings such as distribution centres, retail outlets, sports and leisure facilities, and manufacturing premises. Sections on various systems, their performance and on cladding and purlin installation are covered in detail.

“We want to promote a greater understanding of the issues faced by the construction team so that it leads to better co-operation on site and in the design office,” said Heywood.

www.steel-sci.org

Now you see it... now you don’t

Even David Blaine hasn’t attempted this. Starving himself in a glass box near Tower Bridge yes, making a building disappear, no.

In October last year, British-American research teams unveiled a “cloaking device”, which takes the notion of invisible buildings a step closer to reality. It could mean the end of the great “taste” debate that accompanies the completion of any new project. Who cares what it looks like if you can make it disappear?

The teams, based at the Imperial College London and Duke University, North Carolina, have constructed a prototype cloak from metamaterials – engineered mixtures of ceramic and fibre composite materials. These metamaterials can literally bend electromagnetic waves around an an object – in this case a small copper cylinder – so that they regroup on the other side and carry on as if they’ve passed through empty space. It works in the same way that water flows around a rock in a stream.

Project leader Professor David Smith of Duke University told technology bible Wired that looking at a cloaked item, the viewer would see whatever was behind the cloak.

The scientific know-how is not quite there, however. The cloak currently only redirects microwaves, rather than waves of visible light. Nevertheless, co-author of the research from Imperial College, Sir John Pendry, says that in principle, the same theoretical blueprint could be used to cloak objects from visible light.

SCI says there are instances where problems have arisen due to poor practices on site

Unsurprisingly, uses for the technology have already been postulated by the military.

But Smith and his team have suggested using cloaks to keep ugly buildings, such as factories or refineries, from spoiling the view.

The technology is still in its infancy and a real working invisibility cloak may be some years away, but at least we’ve got David Blaine and his whacky stunts to keep us amused in the mean time.

Watch the scientists report on their research: www.youtube.

com/watch?v=Ja_fuZyHDuk

Panels provide cold comfort

When designers were tasked with cladding the British Antarctic Survey’s new research station, Halley VI (see project report, p24) they knew it would have to withstand temperatures as low as -56oC and deal with extreme winds. But rather than start from scratch, they looked to the skies for inspiration.

Drawing upon aviation industry technology, engineer Faber Maunsell and Hugh Broughton Architects have created panels constructed as a sandwich of closed cell polyisocyanurate insulation foam between skins of glass reinforced fibre. Due to the reduced levels of ozone in the atmosphere, the external paint finish has integral UV protection. Thermal performance is also important: panels will achieve 0.113w/m2 oC.

Short of being placed in the heart of an active volcano, the cladding system will have to operate in what must surely be one of the world’s harshest environments: wind driven snow for 180 days each year that smothers buildings, year-round gales and a pitch black winter that lasts for 105 days.

“It’s why we looked at aircraft technology,” says Broughton. “We wanted to apply tried and tested technology but had to look outside our own industry to find it.”

The panels are 230mm thick, mechanically jointed and sealed using a specially designed gasket. Broughton explains: “The cladding envelope needs to be robust and weathertight to ensure the ubiquitous spin-drift – very small particles of ice and snow that range in size from 10 to 700 metres in diameter – does not enter the modules. At the same time, they must be flexible enough to accommodate movement and deflections.”

The team is now busy with an Antarctic research centre for the Indian government and will use similar technology, although this scheme is much smaller. “We’re looking to make improvements to the design, perhaps making the skin structural,” muses Broughton.

www.hbarchitects.co.uk

www.fabermaunsell.com