Increase building efficiency by improving windows and insulation

Up to 75% of a building’s energy is lost through its ‘fabric’ – the walls, roof, floors, windows and doors.

Improving the insulation of these spaces is important to reducing energy costs and lowering the carbon emissions created by your building.


  1. Make a plan to upgrade building fabric
  2. Improve insulation and lower air infiltration
  3. Get finance and support

Make a plan to upgrade building fabric

Upgrading building fabric is one of the first things to consider when making a plan to retrofit your premises.

Installing new building fabric:

  • may be required to pass energy efficiency checks
  • reduces the need for heating and cooling
  • can disrupt building activities
  • is required before other upgrades, such as getting a heat pump

Use the Carbon Trust’s Building Fabric Guide for detailed guidance.

Comply with legal deadlines

The level of building efficiency required by law is increasing. In England and Wales it is set to go up in 2023, 2027 and 2030.

The quality of building fabric is a major factor in a building’s rating.

Fines between £500 and £5,000 can apply if you don’t make an EPC available to a prospective buyer or renter.

Become eligible for funding programmes

Funding programmes that help with the cost of new building systems are often dependent on the quality of building fabric and insulation.

For example – the government’s Boiler Upgrade Scheme is available to homes and small businesses until 2028, but only if they have enough insulation.

Check our finance and support page for a full list of funding opportunities.

Consult building occupants

Consult any tenants you have on plans to make major building fabric upgrades.

Major building fabric upgrades are likely to disrupt business activities.

Find out if there are upcoming occupancy changes or if tenants can change their working hours on site.

Ask your landlord about making changes

As a tenant it’s unlikely you have the authority to make major changes to building fabric.

Ask your landlord about upgrade plans and pass along feedback about building performance and comfort levels.

With landlord permission you might be able to make smaller changes such as draught proofing windows and doors.

Consider ’embodied carbon’

It is also important to consider the ’embodied carbon’ in the materials you use to make improvements.

While new products will reduce operational carbon by increasing energy efficiency, those savings can be negated by how materials are made and disposed of.

Use the Carbon Trust’s Building Fabric Guide to find out levels of embodied carbon in building fabric.

Visit our green suppliers page for more guidance on low carbon purchasing.

Improve insulation and lower air infiltration

In a typical commercial building, energy is lost through:

  • air infiltration – 35%
  • windows – 26%
  • roof – 22%
  • walls – 9%
  • floor – 8%

Preventing outside air from coming in and insulating interior spaces is therefore critical to increasing building efficiency.

Keep in mind that increasing air tightness can affect interior moisture levels. Changes to ventilation may be required to manage condensation.

Increase air tightness around doors

Doors are a major source of energy loss in non-domestic buildings.

Prevent this by increasing air tightness in commonly used areas such as entrance lobbies and goods delivery areas.

Options include fitting:

  • doors with brush strips and automatic closures
  • a revolving door or entrance lobby partition
  • PVC curtains between spaces with different temperatures
  • airtight seals around vehicular access doors

Find out more in the Carbon Trust’s Building Fabric Guide.

Improve windows

Heat and cold pass through windows more easily than other types of building fabric, so it makes sense to consider them in any improvement plan.

Compared to other fabric upgrades, replacing windows is expensive and may only be necessary:

  • as part of a major refurbishment project
  • if your existing windows are performing very poorly

Improve existing windows by installing any or all of the following:

  • draught-proofing around windows that open
  • sealing around window frames
  • curtains and blinds that control temperature and light
  • external shading such as awnings, overhangs or trees

You should also inspect your windows for cracks and moisture. It makes sense to replace sections showing excessive wear or mould.

Install roof insulation

Adding loft insulation is one of the most effective ways to lower energy cost if your business has an empty attic space.

Loft insulation can pay for itself in as little as two years and remain in place for up to 40 years under dry conditions.

It is more challenging to improve insulation in buildings without attic spaces.

Usually, these are buildings with flat roofs or ‘vaulted’ ceilings without a large empty space that can be filled with insulation.

You should not add insulation to the underside of these roofs as it increases the risk of damp within the roof system.

These roofs are easier to insulate as part of larger refurbishments where the weatherproof layer is exposed.

Install cavity wall insulation

Buildings constructed between 1920 and 1990 often have an empty space between the exterior and interior walls.

Insulation can be injected into these ‘cavity walls’ through exterior holes. It can pay for itself in 3 to 5 years.

Cavity wall insulation may not be suitable for walls that face heavy rain and winds as moisture can get through the filled injection holes.

Find out more in the Carbon Trust’s Building Fabric Guide.

Visit the Energy Saving Trust website to identify cavity walls and different options for insulating them.

Install external wall insulation

Many non-domestic buildings have ‘solid’ walls with no cavity to insulate.

In these cases, insulation panels or ‘render boards’ can be fixed on the exterior of the building.

Advantages of these systems include:

  • can be installed over different wall surfaces
  • wide variety of styles and finishes
  • improved air tightness in the building ‘envelope’

External insulation

  • must be installed on walls that do not have moisture penetration issues
  • may not be suitable for listed properties with protected exterior facades

Find out more in the Carbon Trust’s Building Fabric Guide.

Insulate floors

Floor insulation can improve comfort and increase energy savings, though major installations are often disruptive.

Sealing gaps around cracks and edges is low cost and should be done on all levels of a building.

During major refurbishments it makes sense to consider adding insulation to suspended timber floors or concrete slabs.

Check GOV.UK for detailed advice on suspended timber and solid floor installation.

Get finance and support

You might find it helpful if you have financial resources to hire a consultant to study your building fabric and make recommendations.

Check our retrofit funding page to find out what financing is available from banks, government schemes and local councils for retrofitting.

Find finance and support for your region.

Check our case studies to find SMEs that have successfully cut their costs and carbon emissions.