MET SURVEYORS

What Causes a Floor to Become Uneven?

 

There is no single cause.

​

The construction of the floor is important because a solid concrete floor behaves very differently from a suspended timber floor.

​

Possible causes include:

• Settlement of material beneath a concrete slab

• Poorly compacted hardcore or fill

• Shrinkage of floor screed

• Movement of foundations

• Ground movement

• Subsidence

• Heave

• Drainage problems

• Deterioration of timber joists

• Rot or moisture damage

• Movement of sleeper walls

• Inadequate structural support

• Previous alterations

• Different movement between an extension and the original house

​

Some of these issues are relatively localised. Others may indicate more significant structural movement.

​

​

Does a Sloping Floor Mean Subsidence?

 

Not necessarily.

​

Many older properties have floors that are not perfectly level.

​

A Victorian or Edwardian house may have experienced minor movement over many decades without there being an active structural problem.

​

Older timber floors can also develop slopes because joists have deflected, supports have moved or previous alterations have changed the way loads are distributed.

​

What is generally more significant is a floor that has recently changed.

​

If a floor that was previously level begins to slope, sink or separate from surrounding walls, further investigation may be appropriate.

​

​

What Are the Warning Signs?

 

Possible signs that warrant closer consideration include:

• A noticeable slope developing across a room

• One corner of the floor dropping

• A new step between adjoining rooms

• A change in level between an extension and the original house

• Cracks appearing across a solid floor

• Floor tiles repeatedly cracking

• Screed breaking up

• Gaps appearing beneath skirting boards

• Doors beginning to drag across the floor

• Furniture visibly leaning

• Cracking to walls occurring alongside floor movement

• A floor that feels hollow or unstable

• Localised sinking around walls or openings

​

The significance depends on the type of floor and whether other parts of the building are also moving.

​

​

Sinking Concrete Floors

 

Ground bearing concrete floors normally rely on properly prepared and compacted material beneath them.

​

The construction may include layers such as hardcore, insulation, a damp proof membrane, concrete and screed.

​

If the supporting material beneath the slab settles or contains voids, the floor above can move downwards.

​

This can result in:

• Cracked concrete

• Broken screed

• Cracked tiles

• Gaps beneath skirting boards

• Localised depressions

• Hollow sounding areas

• A floor separating from surrounding construction

 

Importantly, the floor slab can sometimes sink while the external walls and foundations remain relatively stable.

​

This means a dropped floor does not automatically indicate subsidence of the whole building.

​

​

Settlement Beneath a Floor Slab

 

Settlement of fill is particularly relevant in some extensions and altered properties.

​

If hardcore or other filling material beneath the floor was not properly compacted during construction, it can settle over time.

​

The floor slab may then lose support.

​

This can lead to a situation where:

• The walls remain largely stable

• The floor sinks independently

• Gaps open beneath skirting boards

• Floor finishes crack

• Internal partitions may become affected

​

This is a different defect from foundation subsidence, although the symptoms can initially appear similar.

​

​

Cracks Across Concrete Floors

 

Concrete can crack for many reasons.

​

Fine cracks may occur because of shrinkage during drying.

​

More significant investigation may be appropriate where:

• Cracks are becoming wider

• One side of the crack is higher than the other

• The floor has visibly dropped

• Several cracks form a pattern

• Tiles above the crack repeatedly fail

• Wall cracking is also present

• The floor slopes towards one part of the building

​

A crack in a slab should therefore be considered in the context of the rest of the property.

​

​

Cracked or Breaking Floor Screed

 

Sometimes the structural slab itself is not the problem.

​

The screed above it can crack, become loose or break up.

​

Possible causes include:

• Poor installation

• Inadequate thickness

• Lack of adhesion

• Movement beneath the screed

• Insufficient movement joints

• Thermal movement

• Moisture

• Underfloor heating issues

​

A breaking screed can feel alarming but does not necessarily indicate structural movement.

​

The first step is establishing which part of the floor construction has failed.

​

​

Cracked Floor Tiles

 

Repeatedly cracking floor tiles can sometimes indicate movement beneath them.

​

Possible causes include:

• Movement in the floor slab

• Poorly prepared substrate

• Inadequate tile adhesive

• Lack of movement joints

• Thermal movement

• Settlement

​

One cracked tile may simply be a local defect.

​

A line of tiles cracking repeatedly along the same route may suggest movement in the floor beneath.

​

​

Gaps Beneath Skirting Boards

 

A gap appearing between the floor and skirting board can be an important clue.

​

It may suggest that the floor has moved downwards while the wall has remained relatively stable.

​

This can occur where:

• Fill beneath the slab settles

• A suspended floor drops

• Timber supports deteriorate

• Localised ground movement occurs

​

The location and extent of the gap can help determine what part of the structure may be moving.

​

​

Suspended Timber Floors

 

Older houses frequently have suspended timber floors.

​

These normally consist of timber joists supported by external walls, internal sleeper walls or other intermediate supports.

​

An uneven timber floor may result from:

• Deflected joists

• Rot

• Fungal decay

• Insect damage

• Failed joist ends

• Movement to sleeper walls

• Poor historic repairs

• Removed internal supports

• Structural alterations

• Movement to surrounding walls

​

A timber floor that feels springy or bouncy may therefore have a very different problem from a sinking concrete slab.

​

​

When a Timber Floor Starts Sloping

 

Some timber floors have sloped for decades and may simply reflect the age of the building.

​

More concern may be justified where:

• The slope has recently become noticeable

• It is getting worse

• Doors have started catching

• Wall cracks are developing

• Skirting boards are separating

• The floor feels weak or excessively flexible

​

This can indicate deterioration or movement within the supporting structure.

​

​

Could Rot Cause a Floor to Sink?

 

Yes.

​

Where timber joists are exposed to prolonged moisture, their ends can decay.

​

This is particularly relevant where joists sit within external walls.

​

If the ends deteriorate, the floor can begin to drop.

​

Possible signs include:

• Localised sinking near a wall

• Springy floorboards

• Movement underfoot

• Damp smells

• Visible moisture problems

• Damaged skirting or wall finishes

​

This is a structural timber problem rather than subsidence, but the symptoms can sometimes be confused.

​

​

Could Subsidence Affect Floors?

 

Yes.

​

Where foundations and walls move because of ground movement, the floors within the property may also be affected.

​

Possible signs can include:

• Floors developing a slope towards the affected area

• Changes in level close to external walls

• Floor cracking alongside wall cracking

• Doors becoming difficult to operate

• Gaps appearing around skirtings

• Distortion across several connected rooms

​

Where floor movement occurs together with significant wall cracking, a wider structural assessment may be more appropriate than looking at the floor alone.

​

​

Settlement Versus Subsidence

 

Settlement and subsidence are different.

​

Settlement commonly relates to movement as a building or component adjusts after construction.

​

Subsidence generally refers to downward movement of the ground supporting the foundations.

​

A concrete floor can also settle independently of the foundations if the material beneath it compresses.

​

This means there may potentially be three different situations:

​

The floor has settled.

​

The building foundations have moved.

​

Both the floor and the building have moved.

​

Identifying which of these is occurring is essential before deciding on repairs.

​

​

What About Heave?

 

Floors can also move upwards.

​

This is known as heave.

​

Possible causes include changes in ground moisture, expansive clay or changes following the removal of large trees.

​

Upward movement can cause:

• Raised areas of floor

• Cracking

• Distortion

• Doors catching

• Changes in floor level

​

Heave is different from subsidence but can produce equally noticeable structural symptoms.

​

​

Sloping Floors in Extensions

 

Extensions are particularly important because the extension may have completely different foundations and floor construction from the original house.

​

You may notice:

• A step developing between old and new floors

• The extension floor sloping away from the house

• Cracking where the extension meets the original building

• Tiles breaking close to the junction

• Gaps around skirting boards

• Doors within the extension becoming difficult to close

​

This may result from settlement of the extension, movement beneath the floor slab or wider foundation movement.

​

​

A Change in Floor Level Between the House and Extension

 

A difference in level does not automatically mean that the extension is structurally failing.

​

It may have been constructed that way originally.

​

However, where a difference has developed over time, particularly alongside cracking at the junction, it should be investigated.

​

The relative movement between the two structures can provide useful evidence about what may be happening.

​

​

Floors and Hot Weather

 

Prolonged hot and dry weather can affect some clay soils.

​

Where ground beneath foundations shrinks, structural movement can occur.

​

If floor movement appears at the same time as:

• New wall cracking

• Sticking doors

• Cracks around windows

• Movement at an extension

• Other signs of distortion

​

the wider structure should be considered.

​

However, a cracked floor following hot weather does not automatically mean that subsidence is occurring.

​

​

Can Leaking Drains Cause Floor Movement?

 

Yes.

​

A leaking underground drain can affect surrounding ground conditions.

​

Where a drain passes beneath or close to a floor, leakage may wash away material or alter the ground beneath the slab.

​

Possible signs can include:

• Localised sinking

• Cracking

• Hollow areas

• Dampness

• Movement close to drainage routes

​

A CCTV drain survey may sometimes be recommended.

​

​

Floors Above Basements or Cellars

 

Where a floor spans over a basement or cellar, unevenness may result from the supporting structure rather than ground movement.

​

Possible causes include:

• Timber deterioration

• Deflection

• Altered supports

• Structural steel movement

• Historic alterations

• Excessive loading

​

The construction beneath the floor needs to be understood before diagnosing the cause.

​

​

Can Removing a Wall Cause a Floor to Move?

 

Yes.

​

Previous structural alterations can sometimes affect floor performance.

​

For example:

• Loadbearing walls may have been removed

• Supports may have been altered

• Beams may be undersized

• Joists may have been cut

• Openings may have been formed incorrectly

​

A floor problem can therefore be related to work carried out elsewhere in the building.

​

​

Should You Try to Level the Floor?

 

Not until you understand why it is uneven.

​

Simply applying levelling compound, replacing screed or installing new flooring may hide the symptom without addressing the cause.

​

If movement is continuing, the new finish may crack again.

​

The underlying issue should be understood first.

​

​

Should You Monitor a Sloping Floor?

 

Sometimes monitoring can be useful, particularly where movement is minor and there is uncertainty about whether it is continuing.

​

This can include:

• Recording floor levels

• Taking dated photographs

• Monitoring related wall cracks

• Reviewing changes over time

​

Where movement is substantial or appears progressive, however, a structural inspection should normally come first.

​

​

When Should You Be Concerned About an Uneven Floor?

 

Professional advice should be considered where:

• A floor has recently started to slope

• The slope is getting worse

• A concrete floor has visibly dropped

• Large cracks have developed

• One side of a crack is higher than the other

• Tiles repeatedly break in the same location

• Gaps have appeared beneath skirting boards

• Wall cracking is also developing

• Doors have begun dragging against the floor

• Movement affects several rooms

• The floor is unstable or springy

• There is concern about settlement or subsidence

​

​

When Is a Specific Issue Survey Appropriate?

 

Where there is one clearly defined floor problem, a Specific Issue Survey may be appropriate.

​

Examples include:

• One localised sinking area

• One cracked floor

• A slope affecting one room

• A dropped extension floor

• A gap beneath skirting in one area

• A suspected localised structural defect

​

Our Specific Issue Survey concentrates on the reported concern and provides a written assessment and recommendations.