Floors

The ground floor of your home is unheated below. Depending on the floor’s construction it could be allowing cold draughts into the house and wasting £100s of heat.

Suspended floors

These have a ventilated space underneath. The telltale sign of a suspended floor is the presence of air vents through the outer brick wall. You will typically see some kind of special terracotta or cast iron grilles toward the bottom of the outside face of the wall.

In older houses suspended floors usually comprise timber joists supported on brick sleeper walls with timber floorboards on top. Because the void underneath is open to the outside it will be close to ambient temperature and very cold in winter. If the floor finishes are not airtight cold draughts can pass between the floorboards. This cold air will rise through the house and can be a source of significant heat loss. Carpets provide some insulating and airtightness benefits but the recent trend for exposed floorboards has made many houses very cold and draughty!

Diagram of a building foundation with labeled components including solid brick main wall, timber floorboard, sleeper wall, timber joist, and air vent.

Typical Victorian suspended timber floor. The space underneath is vented to outside meaning it will be cold. If there are any gaps between the floorboards (there usually are!) you will get cold draughts passing through.

Terracotta air vent - a sign that you probably have suspended floors

Example of a terracotta air brick. If you see these in the outside face of your wall you probably have a suspended floor.

Insulating Suspended Timber Floors

Suspended timber floors can be insulated by removing the floorboards and placing wool insulation between the joists. This is a relatively simple job and will prevent draughts as well as keeping your floors warm under-foot. This can have a dramatic effect on the warmth of the whole house. The process is explained in our section on Floor Insulation.

Digital illustration of a brick fireplace under construction with wooden and metal framing for the hearth.

Floor insulation installed between the joists. A relatively simple project that can have a dramatic effect on the whole home.

Solid floors

In contrast to suspended floors, these are laid directly on the ground. If you have a solid floor you usually won’t see air vents on the outside face of the wall.

Basic ground-bearing concrete floors took over from suspended timber floors as the industry standard around 1950 due to a scarcity of timber after the Second World War. These have developed into today’s high-performance floors with concrete slabs, damp-proof membranes, insulation and underfloor heating. Very old houses may also have primitive solid floors with flagstones directly on compacted earth or ash.

If you have a solid floor constructed before the 1990s its unlikely to have any meaningful insulation and will lose heat to the ground below. However, it won’t suffer from the draughtiness of a suspended floor.

Modern solid ground floor

Image credit - https://www.selfbuildanddesign.com

Insulating solid floors

The most common way to insulate a solid floor is to add insulation on top (often extruded polystyrene “XPS” - see Materials) however this will raise the floor level by about 150mm. You will need to consider the implications of this - for example it will reduce the headroom at door openings. Electrical sockets and other fixtures may also need to be raised.

If you don’t want to raise the floor level then you will need to break out the existing floor first, which becomes a messy, noisy and expensive job. If you fall into this category you will probably find loft and wall insulation to be more cost-effective alternatives so these should be considered first.

Cross-section diagram of building foundation walls and floor, showing different layers of insulation and materials.

Solid floor insulation on top of a concrete slab.

Image credit - Kingspan

Planning floor insulation projects

Bear in mind that different parts of your house may have different floor types. For example, any recent extensions may be solid floor construction even if the rest of the house is suspended. Victorian housing also often had entrances, hallways and sculleries (store rooms) on solid floors while the main rooms were on suspended timber.

For more information and step-by-step instructions, see our page on floor insulation.