Floor insulation: how to make your home warmer by insulating old floors

Floor insulation is the best solution when boards or tiles are draughty, damp or cold to the touch. Find out how to make them warmer without damaging their integrity

Floor insulation. Dog lying on original floor in front of fire
(Image credit: Brent Darby)

In the quest to make our homes warmer and more efficient, floor insulation is often overlooked. Unfortunately, in old homes this is a common place for heat to escape, so it’s worth thinking about how insulation can make them more thermally efficient, hold heat for longer and protect your home from damp.

Original floors represent a precious link with the past – their wonderful undulations and patina of age telling of the passage of generations of feet and the knocks and spills of everyday life. So the challenge is to add insulation without destroying the character of the original flooring.

It's also important that insulating floors doesn't cause dampness within the structure, which may result in decay and damage over time.

Original tiled floor

Lifting original tiles to add floor insulation can be detrimental to their character and needs to be tackled with the utmost care. Number them to ensure they are relaid in the same positions

(Image credit: Roger Hunt)

Which type of floor?

Floors are constructed in two ways, either suspended or solid. Suspended timber floors consist of floorboards nailed to joists, often carried on ‘sleeper’ walls of brick. It is important that the underside of a suspended floor is ventilated to avoid the build up of moisture.

To achieve this, grilles are incorporated at the base of the walls to allow a cross draught. This often has the downside of resulting in draughts within the room. 

Solid floors of brick, tile or stone were frequently laid directly on to soil, sometimes with a bed of lime mortar or sand. Consequently, they can be cold to the touch and are difficult to thermally insulate.

Original suspended wood floor

In historic and listed homes, insulating under floorboards requires the utmost sensitivity and care, and may be best avoided

(Image credit: Brent Darby)

How to insulate a suspended timber floor

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There are two priorities with suspended floors: improving the thermal insulation and draughtproofing. If there’s access from below, for example a crawl space or cellar, installing insulation is fairly straightforward. 

The easiest method is to push quilt-type insulation into the spaces between the joists from below. This is supported with plastic garden netting tacked into place. To provide additional insulation, tongue-and-groove wood-fibre board can be fixed to the undersides of the joists.

Insulating from above is more complex and will mean lifting floorboards. This has to be done carefully and, even then, is likely to result in damage, so isn’t an option if the floor is valuable aesthetically or historically. 

Taking up floorboards to insulate suspended timber floor

Where possible, it's best to avoid taking up original floorboards to insulate a suspended timber floor. However, if you do go down that route, remove only a few at a time, and number and map them to ensure they can be correctly refitted

(Image credit: Historic Scotland)

Unless major renovation work is being undertaken, it’s best to lift only a small number of boards at any one time, otherwise you’re likely to destabilise the joists and sleeper walls below.

By laying garden netting over the joists so it forms troughs, quilt insulation can be laid to fill the spaces between the joists. Another option is to use a breathable membrane and then to fill the troughs with cellulose (recycled newspaper) insulation.

Alternatively, foil-faced foam or woodfibre insulation boards can be fitted between the joists, supported on timber battens. This can sometimes be achieved by lifting occasional floorboards and sliding the insulation into place. 

Insulating a suspended timber floor from either below or above

From above or below? It’s easier to insulate if there’s access to the floor from below, and you won’t have to disrupt the floorboards – here (left), quilt insulation is pushed between the joists. When insulating from above (right), a loose-fill insulation such as cellulose is breathable and will fit into every nook and cranny

(Image credit: Roger Hunt)

Draughtproofing a timber floor

It is worth remembering that insulation on its own does not necessarily stop draughts so you will need to ensure all gaps are filled, otherwise you’ll still feel the chill and energy will be wasted because heat is being lost.

There are many draught strips designed to go between wooden floorboards and you can find them in most DIY stores. These can easily be slotted in the gaps (and they expand with movement) to decrease draughts and heat loss.

Draught-proofing suspended timber floors is relatively easy using proprietary draught strip systems

Draught-proofing suspended timber floors is relatively easy using proprietary draught strip systems such as DraughtEx or StopGap

(Image credit: Roger Hunt)

How to insulate a solid floor

By their very nature, traditional solid floors may be slightly damp as the tiles, bricks or flags that form their surface are in direct contact with the ground below. For this reason the floor must be able to ‘breathe’, otherwise moisture will be trapped, potentially resulting in damp problems within your home.

It is no surprise that excessive dampness will make a floor colder. Where damp is evident, ensure external ground levels are lower than the floor, and drains and gullies are not blocked; also check that water pipes are not leaking.

Without lifting solid floors, it’s difficult to introduce any permanent thermal insulation, but coir or other breathable floor coverings can help. Avoid covering the floor with impermeable insulation materials or rubber-backed carpets, as they’ll trap moisture.

Where concrete floor slabs have replaced earlier floors, they may include a damp-proof membrane (DPM) but, unless laid comparatively recently, they might not be well insulated. 

Where floors do include a DPM and show no evidence of moisture, laying a floating wooden floor or thermal underlay with a carpet on top is often the easiest means of improving their thermal performance.

Fitting floor insulation in old house

A traditional solid tiled floor is usually in direct contact with the ground below. If it isn’t able to breathe it could result in damp, due to trapped moisture

(Image credit: Douglas Gibb)

Top tips for insulating a floor

  • Remember to seal all the gaps between the skirting board and the floor to prevent draughts. This needs to be done before a fitted carpet is laid, as it will not be possible afterwards.
  • Ensure you insulate thoroughly but avoid squashing insulation material, as this will seriously compromise its effectiveness.
  • Consider underfloor heating if replacing a floor as this can provide a comfortable and energy efficient means of heating, especially when used in conjunction with solid floors.
  • Refrain from lifting an old floor without good reason, as it will never look the same when relaid and you may upset the equilibrium of the building.
  • Always number floorboards, flagstones, bricks or tiles with chalk if they are being lifted temporarily.
  • Don’t inhibit the ability of a solid floor to ‘breathe’ by topping with impermeable layers.
  • Don’t obstruct external air vents under suspended timber floors, as air movement is essential to prevent damp and decay to the timber.

Original tiled floor with undulating surface

This original floor is undulating after centuries of wear

(Image credit: Paul Dixon)

Replacing a concrete floor

If a concrete floor is being replaced because it is causing damp or other problems, limecrete offers an alternative. 

This material is similar to concrete but doesn’t contain cement, consisting instead of lime and aggregate, and so provides a floor slab that is vapour permeable. 

Limecrete floors are increasing widely available from suppliers such as Mike Wye & Associates and Ty-Mawr Lime; they can be insulated efficiently and can successfully incorporate underfloor heating.

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Roger Hunt

Roger Hunt is an award-winning writer specialising in old houses and sustainability. He works closely with the Society for the Protection of Ancient Buildings and Period Living, educating owners of historic homes on how to properly maintain their property.