Sloping and uneven floors: when it is age and when it is movement

Drop a marble in a Victorian terrace and it will usually roll. That is not, by itself, a problem - it is what a hundred and thirty years of settlement, timber shrinkage and repair looks like. The question an engineer is actually being asked is a different one: is the floor sloping because the house settled long ago and stopped, or because something is still moving now?

What is normal

Older houses were built on shallow foundations, with unseasoned timber, using lime mortars that were designed to accommodate movement rather than resist it. They settled, differentially, over their first decades - and then, in the overwhelming majority of cases, stopped. Floors that are visibly out of level are the ordinary condition of the housing stock across Leeds, Bradford and every other town built in the nineteenth century.

So the existence of a slope is not evidence of a problem. Nor is the size of the slope, on its own: a large historic slope in a stable house is a better position to be in than a small progressive one.

The distinction that matters: historic or progressive

This is the whole assessment. Historic movement happened, finished, and left the building where it now sits. Progressive movement is continuing, which means the deformation you are looking at is not the final state.

The evidence engineers use to separate the two:

• Whether cracking associated with the slope has been decorated over and is dirt-filled, or is fresh with clean edges
• Whether previous owners' repairs - packed-up skirtings, levelled screeds, adjusted door frames - have themselves since moved
• Whether doors and windows that were once eased now bind again
• Whether the slope is matched by external evidence: cracking, a distorted opening, a wall out of plumb
• And, decisively where it is not otherwise resolvable, monitoring over a period long enough to cover the seasons

What actually causes it

• Historic differential settlement - one part of the building settling more than another, usually early in its life. Much the most common cause.
• Joist deflection and creep - timber sagging gradually under sustained load over decades, producing a dished floor that is lowest at mid-span
• Decay at joist ends or wall plates, letting one side of a floor drop. Often localised and often near a damp wall or an old leak.
• Removed or failed sleeper walls under a suspended ground floor
• Settlement of a solid ground floor slab, or of the hardcore beneath it - which is a floor problem rather than a foundation problem, and much less serious than it looks
• Movement of the wall the joists bear on - roof spread pushing the wall out, or bulging masonry
• An extension settling relative to the original house, which usually stabilises
• Genuine ongoing subsidence, heave or landslip - real, but a minority of cases, and it should announce itself with corroborating evidence rather than a slope alone

What is potentially serious

• A slope that has changed within living memory, or that people in the house have noticed developing
• Doors and windows that have started binding, having previously been fine, or that have been eased more than once
• New cracking, particularly diagonal or stepped cracking widening towards the top, or cracking wider than about 5mm
• External corroboration - a bulging or leaning wall, a distorted window opening, cracking on the same line outside
• A slope concentrated at one point rather than spread across a room, which points at a local failure such as a decayed joist end
• Springiness or softness underfoot along with the slope, which raises the possibility of decay
• Fractured service pipes, or a drain that has started to smell or block, which can be both a symptom and a cause

What you can check yourself this week

• Measure it rather than eyeballing it. A long spirit level, or a level with a packing block under one end, gives you a fall over a known distance. Write it down with the date - that record is the beginning of a monitoring history.
• Do it in both directions in each room, and note which way the fall runs. A consistent fall across the whole house tells a different story from a dish in one room.
• Look at the skirtings. Packing, filler and a gap under the boards tell you somebody has levelled a floor before, and when it was decorated tells you roughly when.
• Check whether internal door frames are still square and whether doors have been trimmed - a trimmed door with a fresh cut is a live clue.
• Photograph any associated cracking with something for scale, dated, and repeat in three months.
• Look outside along the walls and at the window openings, sighting from a corner, for anything out of plumb or distorted.

When to call an engineer

A threshold, not a plea. A longstanding slope in an old house, with old decorated-over cracking, doors that have been eased once decades ago and nothing changing, does not need an engineer - it needs leaving alone. Get it inspected if the slope or the cracking is changing, if doors have started binding again, if there is external corroboration, or if the movement is local and sharp rather than general and gentle.

Also get it inspected if you are buying. A surveyor who reports sloping floors will normally recommend a structural engineer, and the report either settles the question or gives you a costed basis for renegotiating.

How we would investigate it

A level survey to record what the floors are actually doing, an inspection of the structure above and below, an assessment of any associated cracking against the BRE Digest 251 damage categories, and a search for the corroborating evidence that distinguishes historic from active. Where one visit cannot settle it, monitoring across a full seasonal cycle will.

The most common outcome by a distance is a written confirmation that the movement is historic and the building is stable - which is exactly the document a buyer, a lender or a nervous owner needs. We do not carry out repairs and take no commission from anyone who does, so we have no reason to find a problem that is not there.

A structural survey and report is a fixed £580 + VAT, report inside 10 working days of the inspection, guaranteed.