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Thermal insulation is a primary measure under the Green Homes Grant scheme and choosing the correct type of insulation means balancing multiple factors.

Which Green Homes Grant measures should I consider for my home?

Under the Green Homes Grant scheme announced by the UK government, eligible homeowners in England who successfully apply for a voucher must use it to install at least one ‘primary measure’. A primary measure is either the installation or upgrade of thermal insulation, or the installation of low carbon heating.

The scheme represents a significant opportunity to improve the energy efficiency of domestic buildings. Selecting an insulation measure for your home means thinking about a variety of competing factors, including the cost of the work and the value of the voucher, the level of disruption the measure will require, and any potential knock-on effects of the chosen insulation.

What insulation measures are covered by the Green Homes Grant?

Of the seven insulation measures listed on the Green Homes Grant website, one is ‘insulating a park home’. This is a very specific application which is not covered by this blog post. The remaining six measures cover the floors, walls and roofs of domestic properties.

‘Under floor insulation’ involves adding thermal insulation to either a solid or suspended floor. A solid floor has an existing concrete slab. A layer of insulation can be added over the existing slab, followed by a screed or chipboard covering and a floor finish. Alternatively, the floor can be dug out and new damp proofing, insulation and concrete installed.

A suspended timber floor sits over a ventilated air space, which can range from a few hundred millimetres deep to a full basement. Ventilation of the timber joists is essential. Installing insulation should not negatively affect the moisture content and condition of the timber in the long term and may need specialist advice.

Floor insulation work is generally costly and disruptive. However, where other building elements are already insulated, an uninsulated floor will be a significant source of heat loss. Where the floor is also subject to damp or structural issues, the opportunity to remedy that and also upgrade the thermal performance may well justify the disruption.

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Choosing external wall insulation measures

Both ‘solid wall’ and ‘cavity wall’ insulation is classed as a primary insulation measure.

Solid wall insulation can take the form of external wall insulation (EWI) or internal wall insulation (IWI). If there is sufficient space to the outside of the home, then EWI can be a relatively straightforward option. The relationship of the EWI with doors, windows, and adjoining construction elements needs careful planning and detailing, however, to avoid possible problems in these areas.

As its name suggests, IWI is fitted to the inside face of the property’s external walls. This reduces floor space and causes disruption while the work is carried out. The suitability of IWI must be carefully assessed in every individual property, depending on the age and condition of the wall construction, how exposed the walls are to rain, and the type of insulation material that is being proposed.

Walls featuring an air cavity between two masonry leafs are called cavity walls. Depending on the age of the property, the cavity may or may not feature existing insulation. New insulation can only be installed by blowing it into the cavity. A cavity wall with existing cavity insulation may also be upgraded using EWI or IWI.


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Roof insulation options covered by the Green Homes Grant scheme

‘Loft’, ‘room in a roof’ and ‘flat roof’ insulation are the three roof applications listed as primary insulation measures.

Loft insulation generally refers to an unheated roof space where the insulation is laid along the horizontal joists (i.e. the ceiling level of the uppermost storey of the house). A property may already have some loft insulation, but anything less than around 250mm is likely to be insufficient. Installing additional loft insulation is relatively straightforward and not too disruptive.

Where the space within a pitched roof is used as a habitable room, that space should be insulated along the sloping ceiling, along any horizontal ceiling in the apex of the roof, and in any dwarf walls towards the eaves of the roof space. The key is ensuring a continuous ‘thermal envelope’ around the whole of the habitable loft space.

Flat roofs can be either a ‘warm deck’ or a ‘cold deck’, depending on the age of the roof construction. Older roof constructions are likely to be cold decks with little or no insulation, and the decision must be taken whether to retain the cold deck arrangement (ensuring it continues to have sufficient ventilation), or upgrade it to a warm deck. The age and condition of the existing timber joists, and the type of waterproofing, mean flat roofing is an area of specialist expertise.

All work carried out under the Green Homes Grant Scheme must be completed by a TrustMark registered business

Which insulation measure is best for my home?

Every home is different, meaning there is never one set solution that can be applied across multiple properties. What works for one home may not be the best solution for another.

When choosing an insulation measure for your home, it’s important to think about what is practical and affordable, and where it might fit in to a longer term plan. Is there other disruptive work you want to do in the future that could be an ideal time to install a more complex insulation measure? You might consider engaging a retrofit coordinator to help evaluate which measures are most suitable.

All retrofit and refurbishment works need to be carried out with a high level of skill and care. The Green Homes Grant requires installers and tradespeople to be TrustMark registered, with the intention of achieving high quality installations that are done as part of a ‘whole building’ approach.

Saint-Gobain have a range of solutions suitable for domestic retrofit carried out under the Green Homes Grant scheme. For more information please visit our helpful FAQ page here.

Green Homes Grant Insulation


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