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Warm mongers
Winter 2007
Published:  23 February, 2008

Steico Canaflex boasts high thermal and acoustic properties

Timber construction is renowned for its energy performance, but it makes special demands of insulation products. David Castle reports

The basic requirements of timber-based construction systems for insulation are the same as other construction methods – to meet U-value requirements for that type of building.
However, timber frame buildings move and breathe, partly as a result of moisture loss over time, so the insulation must be capable of flexing with the building; rigid insulation will leave gaps between the timbers, eroding the U-value performance of the envelope.
“Insulation must also be compatible with the different techniques of construction used, whether fitting between joists, studding or rafters, wall panels or as insulating slabs below ground floor slabs or intermediate floors,” said Rockwool timber frame specialist Huw Evans. “While timber framing has high acoustic performance, the insulation must also be compatible with designs to eliminate flanking sound transmission noise.”
Given that timber ticks all the right boxes when it comes to sustainability, are timber frame manufacturers and housebuilders looking for insulation products that are equally green?
Evans thinks so: “One of the prime movers in designing in timber is the desire to construct more sustainably, including sourcing sustainable materials.”
Rockwool also makes the green connection with timber building. Made from abundant natural igneous rock, the stone wool insulation is billed as saving hundreds of times the greenhouse gases generated in production over its life.
The Code for Sustainable Homes (CSH) has been another major factor prompting increasing numbers of specifiers to opt for the insulation solution highlighting its green
“Over the last six months attitudes towards sustainability have change considerably and, as a supplier of ecologically-sound building products and systems, we are now speaking to large-scale housebuilders and contractors,” said Neil May, managing director of NBT, one of the UK’s suppliers of ecological building systems.
According to Second Nature UK, its Thermafleece product, made from sheep’s wool, is growing in popularity, particularly in timber frame applications. “Thermafleece is ideal for timber frame as it offers an alternative environmental and  technical specification and can be used in a wide variety of roof, wall and floor constructions,” said production and customer sales executive Will Brimmer.

Thermafleece can be used for a wide variety of roof, floor and wall constructions 

Thermafleece, he added, was used in one of the first sustainable housing projects conducted by a local authority in the UK. The scheme in Hadston, Northumberland, for 15 bungalows, constructed from slow-growing Nordic spruce, was a sustainability showpiece and used Thermafleece in the walls. More recently, it was used to insulate a timber frame structure for the Creekside Education Trust in Deptford, London. “We liked the fact that it has low embodied energy and won't cause future landfill problem, being biodegradable and recyclable,” said Chris Gittner, head of the new Creekside Education Centre.
But a note of caution on the rush to natural-material based green solutions was sounded by Ieuan Compton, marketing head at Kingspan Off-Site, the UK’s biggest manufacturer of MMC building systems. Insulaton billed as ‘natural’, he maintained, may not be the best option for timber frame on every occasion. “Before insulation is specified, a number of factors need to be considered – desired levels of thermal performance, size of build and type of timber frame,” he said.
He added that natural insulation products may have a slight environmental edge to start with, but this can be “overwhelmed” in the long term when in-use performance is taken into account. “As little as half the amount of man-made insulation may be required compared with the natural alternative to achieve the same thermal efficiency,” he said. The true environmental impact, he contended, should be calculated on the ability of insulation to cut heating demand and CO2 emissions.
According to May from NBT, a potential risk in the drive to sustainable building is that some specifiers incorporate timber frame into a build assuming this alone will ‘tick the environmental box’ and don’t think further in terms of ecological products.
“This can lead to the incorporation of some incompatible insulation materials that don’t work with the timber structure and might not offer adequate levels of sound or thermal performance,” he said. “They may even have a detrimental effect on the structure.” 
There are also possible risks with highly-insulated airtight timber frame buildings, the foremost being overheating and trapped moisture problems. Woodfibre insulation systems, said May, address both issues, whereas many conventional products and system designs unfortunately make the problem worse. The CSH also gives a lot of points for the material qualities of the insulation system and, here again, natural insulation materials can make a lot of difference, enabling specifiers to meet their code targets more easily.
“For these reasons,” said May, “many conventional insulation suppliers to the timber frame sector will have to up the ‘technical ante’ to achieve the desired points level and provide robust long-term performance.”

Sound solutions

Contrary to popular belief, timber does have credible sound insulation properties, but the key to maximising these is planning developments with acoustics in mind and knowing which acoustic products are most compatible with timber.
David Holder, director of CMS Acoustic Solutions, said that, providing the development has been planned effectively, timber frame party walls offer a natural sound barrier, as their design creates a large void.
Where there is sufficient isolation between the two stud leaves, a reduction in noise transmission through timber party walls is generally achieved by applying an additional mass with plasterboard. To maximise performance, different thicknesses of board should be fixed either side.

The SoundBar system has been used by Bellway Homes 

For timber floors there are a number of products designed to improve acoustic performance. These include acoustic underlays, overlays and cradle and batten type systems.  
As timber is less dense than concrete, timber floors will generally require greater acoustic insulation to prevent impact sound from becoming airborne as well. Products like the SoundBar System, developed by Finnforest and Lafarge Gyvlon, and the Screedflo dB acoustic floor system, combine both timber and screed for optimal airborne and impact sound reduction.
The SoundBar System has been used by Bellway Homes in Purfleet to deliver time and cost savings. The system has also recently been specified for all Bloor Homes’ timber frame flatted developments.
Comprising the Finnjoist engineered timber I-joist with a SoundBar board and anhydrite screed from Lafarge Gyvlon, Finnforest says the system enables builders to construct a shallower compartment floor than the current E-FT-1 Robust Detail 4 layer systems. This can “unlock savings in the floor make-up and a reduction of brick coursework”.
Meanwhile, Screedflo is discussing its system with four of the top five house builders. Managing director Mark Baillie said the product was developed to provide a “better quality party floor in timber frame acoustically and in feel”.
“A problem with a batten floor is that you have to design each individual floor to make sure they’re in the right way,” said Mr Baillie. “Our system is uniform across the floor and simple to install.”
There are three main elements in Screedflo dB: a rapid-drying 40mm Screedflo Anhydrite screed; a two-part acoustic layer, consisting of Screedflo dBoard, a high-density, moisture-proof fibreboard, and dBfoam, a compression-resistant foam; plus an edge isolation system.
“The floor is much shallower and less quality critical to install,” said Baillie. “It’s also faster to install than a traditional batten system and feels like you’re walking on concrete: there’s no movement or vibration.”

Keywords: SoundBar Screedflo Thermafleece Steico Warmcel Rockwool