Environmental Information Exchange


Insulation is part of a building that reduces the tendency for internal and external temperatures to equalise.  Insulation reduces the need for heating in cold weather by keeping heat air inside and keeping out cold air. In the summer insulation reduces the heating effect of the sun on the interior.

New buildings must be built to have minimum levels of insulation.  There are other standards that define higher levels of insulation to help improve energy efficiency.  However, insulation often needs to be added to existing buildings, particularly because standards in the past did not require particularly high levels of insulation.

How much can be saved by adding insulation?

The exact amount varies from building to building because of insulation levels, energy consumed for heating and cooling, and the total area each aspect (roof, walls, windows, etc.).  Generally adding insulation to walls and roofs is the most beneficial, with windows, doors, and floors being more costly projects.  However, simple draught proofing measures can be simple to implement and potentially very beneficial.

Insulation options

The following table describes the possible addition of insulation for many aspects of a building.  For each aspect below, generally, the greater the thickness of insulation, the greater the benefits to energy efficiency.


Possible improvements to insulation

Pitched roof (unheated loft)

A pitched roof may have an unheated loft where insulation is placed above the ceiling of the floor below.  Traditionally loft insulation made of synthetic or natural materials is used.  Current standards require a minimum of 270mm, but up to 400mm of insulation has increased benefits.  Loft insulation functions only when it is not compressed.  Further, lofts need to be vented to keep moisture levels as low as possible.

Pitched roof (heated loft)

When the area below a pitched roof is heated (such as a loft or room), insulation can be added to the inside of the roof.  Traditionally rigid foam boards are used, though other insulation options exist.  As with loft insulation, the thickness indicates the level of benefit.  Foam boards are usually installed by contractors.

Roof (flat)

Insulation can be added to flat roof areas either via the exterior or interior.  There are a range of products available, usually installed by contractors.  Adding insulation adds a thickness of at least 1 foot, so some areas many be suitable for adding to the interior.  Exterior additions of insulation are often easier when replacing the roof.

Walls (cavity)

If an external wall has an un-insulated cavity, insulation can be added.  Again a range of materials are possible and installation is usually carried out by contractors.

Walls (no cavity)

Like a flat roof Insulation can be added either to the interior or exterior of external walls.  Exterior options are generally more expensive, particularly if there are particular cosmetic finished required.  Interior insulation reduces the size of rooms by at least 1 foot on all exterior walls.  By improvements are usually installed by a qualified contractor.


It can be difficult to determine if a floor has insulation. Older buildings may have suspended timber floors and insulating material can be added between joists. More modern buildings with concrete floors can have rigid insulation laid between the floor and the eventual finish. Installation is usually carried out by contractors and may be subject to Building Regulations.


The insulation value of windows can be improved by replacing single-glazing with double or triple glazed units.  There are a number of products to consider, including the materials of the window frame. In some cases a single glazed window can have secondary glazing added to the building’s interior to add an insulating effect.  There are also various plastic products that are cheaper alternatives to secondary glazing.


Exterior doors can be improved by replacing them with a more insulate and better fitting unit.  This can be expensive and often a door can be best improved by blocking draughts.


Draughts are caused by exterior air getting directly into a building.  This is usually around doors and windows.  Other draughts may be caused by holes where pipes or wires enter and exit buildings or through vents for fans, etc.  Draught proofing measures for doors, windows, and other holes are widely available.