50 INSULATION
wall insulation such as styrene beads or mineral wool.
These forms of insulation work well, but they do not significantly address the crucial factor of preventing convective heat loss. In the UK, U-values are the measure of insulation’s ability to limit conductive heat flow – the lower the U-value the better the resistance to heat loss. However, it should be noted that up to 40 per cent of a building’s heat loss can be attributed to air leakage.
Moisture vapour in the air within a build- ing carries heat and moist, humid air can support up to 4,000 times more heat energy than dry air. As air leaks out of a building, it carries with it this moisture vapour, and with it, heat. Therefore, the best way to increase the
energy efficiency of a building is not merely to reduce U-values as required by Building Regs, but rather to combine U-value reduction with an air barrier – creating a ‘sealed box’ effect to reduce air (and heat) leakage to a minimum.
SPRAY APPLIED INSULATION Traditional forms of insulation are relatively inefficient in ‘sealing the box’, in that they cannot completely fill all voids or seal the interface between the insulation and the building structure. Nor can they cope
with small structural movements which will often lead to air gaps, particularly in difficult-to-treat situations where access is poor and/or when voids are of complex geometry. This can lead to cold bridging and thermal bypass, with the consequent risk of localised condensation and inevitable dampness.
Air leakage can be eliminated by the introduction of an air barrier. These can take many forms, but must be installed with great care if they are to perform as desired. Real world experience also shows that the more difficult a component is to install, the less likely it is to be installed correctly! A more modern alternative is spray foam insulation, which is applied using a pressurised gun system. Here, foams are applied as a two-component mixture that come together at the tip of a gun forming a foam that expands 100-fold within seconds of application, sealing all gaps, service holes and hard to reach spaces, virtually eliminat- ing cold bridging and air leakage. When selecting spray applied insulation it is important to understand a number of factors. Unlike the urethane foams of 20 years ago, modern spray foams use water as the blowing agent. This means that the reaction between the two compo-
nents produces CO2 which causes the foam to expand. Also, because the CO2 in
SPRAY FOAM IS A COST-EFFECTIVE ALTERNATIVE TO RIGID BOARD TYPE INSULATION
modern spray foams is replaced by air as the foam cells burst, products have much better environmental performance. Spray applied insulation tends to be more expensive than conventional fibre- based and rigid board type insulation materials, and is usually applied by special- ist contractors using bespoke equipment. However, its speed of installation, minimal waste, its ability to perform in difficult-to- treat applications, and the fact that it can be injected into voids that would otherwise require invasive tear-out of surfaces, means spray foam is a cost-effective alternative to rigid board type insulation for both refur- bishment and new build projects. The fact that spray foam insulation can create airtight envelopes has also made it the insulation material of choice in new build homes built to Passivhaus- type standards.
Paddy Leighton is UK director for Icynene
Schöck meets curved balcony challenge in Docklands
W
ith its striking series of curved forms, Gateway Tower, just a few hundred yards west of the ExCeL Exhibition
Centre at Royal Victoria Dock, is an intriguing example of modern urban design. The 73 metre high, 24-storey mixed-use scheme provides 161 spaciously designed apartments and penthouses, with office and retail space at ground level. Each apartment features a terrace or a balcony. The design specifications on the project were demanding and the avoidance of thermal bridging at any of the critical connectiv- ity points was key. To counter such problems, the Schöck Isokorb structural thermal break for concrete-to-concrete applications was incorpo- rated – but there was an installation challenge or two.
CURVED FACADE MEANT A TIGHT RADIUS The first being that there was a tight radius in which to position the thermal breaks, due to the unusual curved styling. The Isokorbs were supplied with alternating depths of rebar and concrete cover to the tension bars. This allowed the rebar in the Isokorb to sit underneath the internal slab reinforcement and not clash with the bars from the Isokorbs on either side of each unit. Schöck also had to create a bespoke unit for one of the balcony types, where a beam was introduced to the balcony to reduce the deflection of the slab.
TOTALLY VERIFIABLE PERFORMANCE In addition to concrete-to-concrete, the comprehensive Isokorb range from Schöck also offers concrete-to-steel solutions, a modular product for steel-to-steel applications – and even a maintenance free alternative to wrapped parapets. When any Isokorb product type is incorporated into residential buildings, the required fRsi value is always comfortably met and the range also complies with the Government Standard Assessment Procedure, SAP 2012. Products meet full compliance with the relevant UK building regulations, have NHBC
WWW.HBDONLINE.CO.UK
approval and offer LABC Registration. There is also the security of independent BBA Certification. Visit the Schöck website or call (see below) for
a free copy of the Schöck Thermal Bridging Guide; the Schöck Specifiers Guide and to view the full range of downloadable software.
01865 290 890
www.schoeck.co.uk
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