Conservation of Fuel & Power

At the time of writing Approved Document L of the Building Regulations for England came into force in 6th April 2014. Further revisions are planned for 2016 and 2019 implementing increasing percentage reductions in energy use through improved insulation values, renewable energy sources and more efficient heating, lighting and ventilation services, culminating in all new buildings being “Zero Carbon” by 2019. The Government’s aim is to similarly reduce energy use in existing buildings through the Building Regulations (Consequential Improvements) and initiatives such as “The Green Deal” for residential buildings.

 

For Wales and Scotland, similar requirements are contained in the local Regulations & Approved Guidance for the individual country. Building Regulations (Wales) and Section 6 (Energy) of the Scottish Building Standards Agency’s Technical Handbooks.

 

The latest edition of the relevant local Building Regulations should always be referred to.

 

Approved Document L (England & Wales) is divided into four separate parts dealing with the following:

 

  • Part L1A – New Dwellings, Part L2A – New Buildings other than Dwellings. Parts 1A and 2A require CO2 emission targets to be met and there are also limiting ‘U’ value standards for various thermal elements of a building such as roofs, rooflights, ventilators, etc.
  • Part L1B – Existing Dwellings. Part L2B – Existing Buildings other than Dwellings. Parts 1B and 2B require specific ‘U’ values and minimum services performance to be achieved.

New Buildings

The regulations require that all aspects of the construction are to be taken into account in the design process in assessing the potential overall carbon emissions of the building. Apart from the construction materials themselves it includes the design of the details, choice of heating system and its controls, type of lighting, etc. When constructing the building envelope, the major factors in meeting the requirements to limit energy losses will be the incorporation of insulation and the achievement of a level of air tightness.

Existing Buildings

For existing buildings, the regulations require that if any refurbishment works are being instigated the need to upgrade the thermal performance of the existing construction must be considered. Generally, if renovating a ‘thermal element’, a roof or wall for instance, there are certain specific ‘U’ values that need to be met, usually by the provision of extra insulation.

 

The requirements are limited by a cost effectiveness factor, which would normally expect ‘pay back’ from the works within 15 years. They can also be limited by factors of technical feasibility. There are exemptions, for example some specific types of building uses are exempt, listed buildings may not need to meet the full requirements under certain circumstances. However ultimately this should be confirmed with the local building control body.

 

These are a complex set of regulations and reference to the actual documents is recommended for each individual project as is the advice of a ‘competent person’ as outlined within the regulations themselves.

Insulation

In all roofs heat will flow from the warm side to the cold side. In most cases the Building Regulations will require a certain level of resistance to this flow in order to conserve energy, limit heat loss and reduce carbon emissions. This resistance is known as the ‘U value’ of a particular thermal element and is established by the calculation methodology contained within the regulations and is expressed as
W/m2K.

 

There are certain factors in the regulations that need to be considered in the design process of any roof build up. The use of all metal fasteners in a mechanically fixed membrane roof is deemed to cause thermal bridging and requires a correction factor to be used, this is governed by the number of fasteners per square metre, the material they are made from and their cross sectional area. Normally this can entail an increase in insulation thickness of around 10%, this extra cost can be avoided by utilising ‘thermally broken’ fasteners and are therefore recommended. Correction factors also need to be applied to cold deck timber roofs where the insulation is laid between the rafters. Finally, inverted roofs have a factor that compensates for the cooling effect of rain water percolating down through the insulation boards and impinging on the membrane.

 

Most structures, unless constructed of naturally insulating materials, will need the addition of manufactured insulation products to achieve the required ‘U’ values.

 

There are many different types of insulation available with widely varying characteristics and properties. Selection of the appropriate type for a particular roof will depend on many different criteria, some points that should be considered follow:

  • Compatibility with other components in the roof build-up - this is to avoid the risk of reaction with the membrane and other components or corrosion of any metal items.
  • Compressive strength - especially related to the amount of traffic the roof will receive both during construction and in use.
  • The long term thermal conductivity performance, W/mK, which takes into account the effects of ageing of the board, can vary according to type or even the facings used, a better aged performance can mean a thinner board being selected at the time of specification.
  • Fire resistance related to the application.
  • Thermal conductivity can vary between different types of board; this can affect the thickness required to meet the required U value for the roof.
  • Cost of purchase
  • Cost of installation - some products involve more effort than others to lay and this is reflected in the overall costs.
  • Moisture resistance - products should be capable of accepting a degree of wetting during the laying process without deterioration.

Physical Properties

The main physical property required from any insulation that may be used under Sika-Trocal is sufficient compressive strength to provide adequate support for the Sika-Trocal membrane and its fasteners. The minimum compressive resistance for plastic foam insulation boards is 150 kPa at 10% compression. It should be noted that some extruded polystyrene boards can typically provide a resistance of 220 kPa and upward. This can make them the preferred choice for paved roofs with support pads. The minimum overall compressive resistance for ‘dual density’ mineral wool (MW) insulation boards is 60 kPa at 10% compression. It should be noted that these products are also available with a higher resistance of 75 kPa. Single density mineral fibre insulation boards are not recommended.

Compatibility

Generally, the insulation materials commonly used in flat roof construction are not compatible with the Sika-Trocal if the two are in direct contact, that is un-faced, as there will be a reaction that adversely affects both products. A suitable separation layer will therefore be required. Fortunately, in virtually all cases, insulation manufacturers can supply their products with suitable factory applied facings so that compatibility is assured. All rigid plastic foam boards must be supplied either with aluminium foil or glass tissue facings to the upper surface applied either during or post production. The commonly used products are rigid polyisocynanurate foam (PIR); extruded polystyrene (XPS); expanded polystyrene (EPS); and mineral wool (MW).

 

For mechanically fixed and ballasted applications, utilising the Type S, Type SG and Type SGmA membranes, where they would be in direct contact with the rigid plastic foam insulation boards, the aluminium foil faced types should be used. For adhered membrane systems using Sika-Trocal Type SGK, mineral filled glass tissue faced insulation boards must be used. Note that the insulation boards utilised for the specialised adhered application must be agreed with Sika-Trocal prior to installation.

 

Note that the use of glass tissue faced boards will generally require a greater thickness to achieve the required ‘U’ value and the installation of a vapour control layer is mandatory. Mineral fibre resin bound insulation boards must be supplied with a glass fibre tissue facing, factory applied to the upper surface of the board, note there is a specific facing for use with adhered applications. In the event of wanting to specify an insulation type or product for use with Sika-Trocal membrane that is not listed here please contact us.