19th century buildings, 21st century tech

New materials can transform old commercial and housing stock.

So we want to bring our old, energy-guzzling buildings into the eco-conscious 21st century? Simple! We’ll just stuff several feet of insulation into our walls and lofts, replace antique appliances with A-rated equivalents, fit the windows with triple glazing, and top it off with the latest monitoring mod cons. That’ll do the trick! Or will it…?

“Imagine your tiny box room”, says Andrew Mellor of PRP Architects. “You want to fit some wall insulation, but you don’t want [that already small space] to become a cot. Even insulation on just one wall could take precious inches away.”

The trick of successful retrofitting is to make the property more efficient, without losing the things that make it work for the occupier: its space and storage, accessibility and aesthetics. The process is important too. If the work can’t be carried out with minimal disruption, it may not go ahead at all.

So which creative solutions will help us strike the right balance?

Take insulation for a start. Thanks to a NASA spin-off we have aerogel, originally developed to keep astronauts warm in space, and now the most insulating material around. As the name hints, it’s mostly air – as much as 99.8% – trapped in a loose silicon-based structure. The original material is too fragile for most uses, but commercial developers Aspen Aerogels and Thermablok have found ways to integrate a strengthening fibre. The result is a strip just 9.5mm thick that can improve the insulation of a wall by up to 42%, according to research by the US Department of Energy’s Oak Ridge National Laboratory and JM Laboratory. Moreover, Thermablok claims, it won’t age or suffer from mould or mildew, and it can be recycled. Aerogel insulation is still more expensive than traditional thermal laminate board, but demand has brought it down from twice the price a couple of years ago to a 20% premium.

New ‘intelligent’ membranes adapt to the seasons

Another promising area of research is set on sealing up leaky roofs, and protecting them against the elements. A study by the Fraunhofer Institute for Construction Physics in Stuttgart, Germany, suggests that it takes the same amount of energy to heat a house with 80m² of floor space with gaps in its insulation, as it does to heat an airtight house five times the size. Airtight membranes and sealing tapes are common enough, but when you retrofit older properties you have to be careful about moisture, particularly if damp has already penetrated deep into the structure. New ‘intelligent’ membranes offer moisture control along with protection from wind and rain. German company pro clima [sic] has developed a vapour-permeable membrane, which is both air- and water-tight, but also responds to humidity. In cold, wintry weather it is almost entirely impermeable, but in warm weather it allows moisture to escape.

Of course, even airtight buildings need some ventilation, and engineers are developing clever ways to ensure that fresh air coming into heated buildings is as warm as possible. A new dynamic insulation system, developed by Energyflo, is currently being tested in the UK. It works like this: insulation panels are fitted to the external wall. These contain a cavity where air is effectively pre-heated both by the sun and by any warmth escaping through the walls. The warm air then rises up the cavity and is channelled into the building through ventilation systems.

It would be a shame were heat then to seep out again through the windows... “You get such a serious energy loss out of glazing”, says Eric Bloom of clean technology market analysts Pike Research. “You can insulate a wall, but if the glazing does not perform well, then what is the point?”

These days, double glazing isn’t enough to meet high energy efficiency standards. While triple glazing has great thermal performance, its width means that it’s simply not an option for the slighter fittings of older properties, such as those with wooden sash windows. Vacuum glazing, which has only been on the market for a few years, is proving an excellent alternative. Instead of adding extra layers, it prevents the thermal conduction caused by the gas in the cavity between the panes. The units are extremely thin – so much so that from a distance they might be mistaken for single glazing – making them a perfect solution for listed buildings and conservation projects, as well as residential dwellings. Moreover, they are barely more expensive than standard double glazing panels.

Bloom is excited by the advent of electrochromic glass, which could be suitable for large-scale corporate retrofit projects. It works a bit like Reactolite sunglasses, and can be darkened either automatically or manually by people within the building. This kind of system helps to prevent the buildings overheating in strong sunlight, but can let more rays in during winter to make the most of the natural light and heat.

But you don’t need fancy electronics to make a difference. Even concrete is getting clever. Eco-builders tend to shun concrete, despite its impressive versatility.

“On the face of it, concrete has always appeared to present a compromise to architects and engineers”, admits Jeremy Greenwood, Managing Director – Concrete at Lafarge A&C UK. “On the one hand it is the most versatile, durable and cost-effective of all construction materials. Yet it is also one of the most maligned, both for its grey ugliness (a 40-year hangover from the 1960s) and for its sizeable carbon footprint, resulting [mostly] from the cement used to make it.”

Recognising this, Lafarge decided to rewrite the rule book on what concrete can do. It has developed a range of sustainable concrete and screed (top layer) mixes for commercial retrofit projects, with the aim of using fewer raw materials to achieve the same overall performance. Extensia, for example, is an alternative to floors containing steel mesh and fibre reinforcement. The design removes the need to use steel, but retains an excellent load-carrying capacity. It overcomes the problem of steel fibres becoming exposed under ongoing stress, and is extremely durable, cutting maintenance costs in the long term. Its compressive and flexural strength also means thinner floors can be considered, contributing to a 20% reduction in CO2 emissions.

In the future, concrete may last for ever, thanks to new research into self-healing properties [see 'Smart solutions for a material world']. Carolyn Dry, Emeritus Professor of Architecture at the University of Illinois, has developed an adhesive repair material which can be embedded in hollow fibres in the concrete. These crack when under strain, releasing the adhesive which penetrates the fissures and sets to form a new bond. It’s an automatic infusion of structural integrity, cutting repair costs and increasing safety.

Given the urgency of the retrofit challenge, it may not make sense to wait for a new generation of products to hit the mainstream. Fortunately, there are plenty of materials available today that can bring old properties up to spec. “If you are going to replace your windows or repaint or render a wall, then why not look for a product with thermal qualities?” Mellor asks. “The extra costs may be marginal, but it could really make a difference to a building’s performance.”

Edwin Colyer is a science and technology writer and founder of the copywriting and editing agency Scientia Scripta.

Photo: Extensia/Lafarge