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Insulation

Increasing energy-efficiency requirements are calling for greater levels of insulation. This has implications for both new-build and retrofit projects, and each hold different complications and opportunities. This month we look at how the regulations affect what products architects are specifying.

As the government strives to meet carbon emission reduction targets, buildings are being targeted through regulation. As Building Regulations become more stringent, changes will affect all developments.

Zero-carbon homes requirements will apply to all homes from 2016, and all new buildings will be required to be ‘nearly zero energy’ by 2019. Improvements to the regulations are gearing up for these changes. Part L is the regulation most commonly associated with a building’s energy efficiency and, therefore, has the greatest influence on insulation usage. Fabric-efficiency standards have been developed in conjunction with the Zero Carbon Hub and these look set to become part of the amendments to Part L, which are due to come in later this year. All of these regulations and changes are causing insulation levels to increase.

Building Regulations’ requirements and standards refer to the average performance of the overall area of a building component. The thermal performance of a building element is measured by its U-value; Part L specifies average U-value targets for each building element to achieve and this will be greatly influenced by the amount and type of insulation included.

Part L suggests the following U-values, however it should be noted that buildings aiming for a high level of energy efficiency should exceed these:

  • Walls - 0. 30W/m2K
  • Party walls - 0.20W/m2K
  • Roofs - 0.20W/m2K
  • Floors - 0.25W/m2K

Amendments to Part L have recently been published and more are on the way. Under the new regulations, from July 2013 if a thermal element of the building is undergoing renovation, the performance of the whole element must be improved. This becomes relevant when the area to be renovated is larger than 50 per cent of the surface area of the thermal element, or when more than 25 per cent of the building is undergoing improvement.

Detailing is key to successful thermal efficiency. Insulation should be carefully planned to reduce heat losses through thermal bridges, with the insulation providing a continuous barrier. This will decrease the levels of heat loss through the building fabric and reduce the risk of any condensation build-up.

100 Princedale Road by Paul Davis + Partners

100 Princedale Road by Paul Davis + Partners

At Paul Davis + Partners’ Retrofit for the Future project, 100 Princedale Road, the architects needed to increase the thermal properties of the building enough to achieve Passivhaus standards. Being in a conservation area, insulating externally - often the most convenient way to eliminate any thermal bridges - was not an option. To combat this, 200mm of Kingspan Thermawall was used internally, giving a U-value of 0.1W/m2K, and 50mm of insulation was added to the party walls, allowing a continuous thermal seal to be created within the property.

The government’s Green Deal scheme is aimed at improving the energy efficiency of the UK’s existing buildings through a fabric-first approach, focusing on improving the building materials and structure before adding any zero-carbon technologies. With solid-wall traditional buildings numbering over 6 million and making up 23 per cent of the UK’s housing stock, this is an area ripe for thermal improvement.

Both retrofit and the Green Deal should be approached with care especially in period properties

Both retrofit and the Green Deal should be approached with care, however, especially in period properties where changing the thermal envelope could result in interstitial condensation and internal air-quality issues.
This kind of improvement calls for an indepth knowledge of building physics. Many modern methods of insulation are not well suited to period properties and the materials chosen should be considered for their appropriateness. A guide to energy efficiency and period properties published by English Heritage suggests: ‘Wall insulation alters the hygrothermal behaviour of traditional buildings, and can exacerbate existing moisture-related problems or create new ones. Any installation requires great caution and it is strongly recommended that insulation is not added to damp walls. Modern methods of upgrading thermal performance, which include vapour barriers and materials that are highly resistant to the passage of water vapour, are not normally appropriate for older buildings as they will tend to increase the risk of condensation and trap moisture, and can increase the risk of decay to the fabric - including the structural timber frame.’

With the Green Deal, it is anticipated that we will see a rise in properties receiving thermal improvements, especially through the use of additional insulation. Manufacturers are becoming wise to this, developing a range of insulation materials better suited to the retrofit market.

Foil-backed and foam insulations used in retrofit situations have been blamed for structural timber failure. Insulation materials that are breathable should be chosen to reduce these risks; hemp, wood fibre, flax, sheep’s wool and cellulose are all options. These often require the thickness of insulation to be increased over the equivalent synthetic materials in order to achieve the required U-values. The general rule is: the lower the thermal conductivity, the better the U-value. A wide range of insulation materials, however, can be specified to achieve a specific U-value; only the thickness will vary, which will affect the wall build-up.

Thermal conductivities of insulation materials 
ProductThermal conductivity (W/mK)
Synthetic materials
Mineral fibre0.032-0.044
Glass fibre0.038-0.041
Extruded polystyrene0.033-0.035
Expanded polystyrene0.037-0.038
Natural materials
Wood fibre0.038-0.050
Cellulose0.035-0.040
Hemp0.038-0.040
Wool0.038-0.040
Flax0.038-0.040

Knauf Insulation has introduced an internal wall insulation system specifically designed to upgrade the thermal efficiency of solid walls. Used by self-builder, Andrew Gill to upgrade a terraced house in Manchester, Knauf ‘s ThermoShell Internal Wall Insulation System was chosen as it could improve the airtightness alongside the thermal efficiency.

Knauf's internal wall insulation

Knauf’s internal wall insulation was used by Andrew Gill in his renovation of a terraced house in Manchester

ThermoShell comprises EcoStuds - extruded polystyrene laminated to OSB - which are fixed to the internal wall to create a frame to accept the insulation. As the system uses an insulating material rather than timber or metal to form the frame, it reduces cold bridging and allows for a thinner system to be used to deliver the thermal performance required. Earthwool EcoBatt water-repellent, glass mineral wool slabs were then friction fitted between the EcoStuds and faced with a vapour-control layer and standard plasterboard. The Earthwool EcoBatts fully fill the insulation zone and are in contact with the EcoStuds and the vapour-control layer, preventing air movement within the system.

Architype's UEA Enterprise Centre

Architype’s UEA Enterprise Centre

Increasingly, in a move away from the oil-based products that are traditionally used, some specifiers are looking towards natural materials to ensure their projects are sustainable. At Architype’s Enterprise Centre, which is planned for the University of East Anglia, the brief required the architects to not only meet Passivhaus standards, but also to achieve a BREEAM Outstanding rating while using local materials and labour that would act as a carbon sink. This has caused Architype to look at the use of natural materials for the building’s insulation. Hemp insulation will be used throughout, with calculations showing that 170 acres of hemp will need to be grown to provide this - it’s lucky the university has its own harvester. The wall construction is anticipated to provide a U-value of 0.11W/m²K at a total thickness of 473mm.

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