Entry 27 · Doors
Step-free thresholds at doors and patio doors
How to achieve level access at an existing door in England: thresholds, Part M, Part K, drainage, and what to record before work starts.
Level access at an existing door means the finished floor inside and the ground outside sit close enough, and flat enough, for a wheelchair, a walking frame or a pram to cross without a step. In practice that usually means a threshold no higher than 15 mm, a level landing of at least 900 mm by 1200 mm on both sides, and a door that can be opened and closed from a seated position. Anything more than a shallow lip needs a designed solution, not a rubber ramp laid over the existing cill.
The starting point is measurement, not product choice. Record the exact difference between the internal finished floor level and the external surface, the door width in the clear, the direction of swing, and whether the door sits under a canopy or is fully exposed. The same discipline applies when adapting existing housing rather than building new, because the constraints are already fixed by the structure. Take those four numbers to any supplier or builder and the conversation changes from opinion to arithmetic.
01 What does Approved Document M actually require at a door?
Approved Document M, Volume 1, covers dwellings and is the document most often cited when a level threshold is discussed. It sets out that the principal entrance should have a level approach, or a gently sloped one, and that the threshold should not exceed 15 mm where the approach is level. Where a step is unavoidable, the document expects it to be treated as a design decision with a ramped or gently graded alternative, not left as a single upstand.
For a new dwelling the requirement is straightforward. For an existing one, the document is applied through Building Regulations approval only when the work is controlled, for example a change of use, an extension, or a conversion. A like-for-like replacement door is normally outside that scope, which is why so many existing thresholds stay as they are. That does not make them compliant with anything; it simply means nobody has had to sign them off.
Approved Document K sits alongside it and deals with protection from falling, collision and impact. It matters at a threshold because a raised external landing with no guarding, or a door that opens directly onto a drop, can raise a question under K even when M has been satisfied.
02 Can a level threshold be fitted without removing the door?
Sometimes, but the honest answer depends on the depth of the frame and the height of the existing cill. A surface-mounted ramp or a threshold strip can bridge a lip of perhaps 20 mm to 40 mm, and products of that kind are widely sold. They work best where the door opens inward and the external surface is already well drained.
Where the step is larger, the usual approach is to lower the external ground, raise the internal floor, or replace the frame with one that has a rebated or low-profile threshold. Lowering external ground is often the cheapest option, but it changes how water behaves. A paving level that once shed water away from the door may now sit below the damp proof course, and that is a problem the ramp catalogue will not mention.
Replacing the frame is the most disruptive and the most reliable. It allows a threshold with an integral drainage channel and a thermal break, which is the arrangement used on most new-build level access doors. It also allows the door leaf to be widened, which matters because a level threshold is of limited use if the clear opening is only 700 mm.
03 What about drainage and the damp proof course?
The damp proof course is the horizontal barrier in the wall that stops rising moisture. External ground level should normally sit at least 150 mm below it, and that figure appears in guidance from lenders and surveyors as well as in the regulations. A level threshold inevitably reduces that margin, so the design has to manage water in another way.
Typical measures include a linear channel drain across the full width of the opening, a slight fall on the external paving away from the door, and a canopy or recessed reveal to keep wind-driven rain off the threshold. Where the door faces the prevailing wind, a threshold with a raised upstand behind the drainage channel is often the practical compromise: it is not strictly level, but it is crossable and it keeps the floor dry.
This is the point at which a surveyor or an experienced installer earns their fee. Water that reaches the internal floor at a level threshold does not announce itself immediately; it shows up as a lifted floor finish or a damp patch months later.
04 Does a level threshold affect thermal performance?
Yes, and this is often overlooked. A conventional threshold contains a thermal break between the frame and the external cill. When the threshold is lowered, that break can be compressed or bypassed, creating a cold bridge along the base of the door. The result is condensation on the internal floor in cold weather and a measurable loss of performance.
Approved Document L sets the energy efficiency standards for windows and doors, and replacement doors are expected to meet a stated U-value. A door that meets the U-value in the test report may not meet it once the threshold has been modified on site. Where the threshold is altered, it is worth asking for the manufacturer's detail drawing for that specific threshold, not the generic one for the door range.
05 What should be recorded before work starts?
A short written record prevents most disputes. It should include the measured step height, the clear opening width, the door swing, the position of the damp proof course relative to external ground, the fall of the external paving, and the location of any drain or gully. Photographs with a tape measure in frame are enough.
If the property is rented, or if the work is funded through a local authority adaptation grant, the record also needs the specification that was agreed and the name of whoever approved it. In England, grant-funded adaptations are usually handled through the local authority housing or social care team, and they will expect the threshold detail to be shown on a drawing.
Finally, keep the FENSA or equivalent certificate for any replacement door, along with the Building Regulations completion certificate if the work was controlled. These documents are what a future buyer's solicitor will ask for, and they are difficult to reconstruct afterwards.
06 Are there alternatives if a level threshold is not achievable?
Where the structure genuinely will not allow a level threshold, the options are a gently sloped approach, a short internal ramp, or a platform lift at the entrance. A slope of 1 in 12 is the usual maximum for independent wheelchair use, and 1 in 20 is comfortable for most people. A ramp inside the door line is easier to protect from rain but eats floor space.
A portable threshold ramp is a reasonable interim measure. It should be wide enough to cover the full clear opening, fixed so it cannot slide, and checked for a lip at its leading edge. It is not a permanent solution and should not be presented as one.
The wider principle is that a threshold is one component in a chain. A level door with a 750 mm clear opening, a heavy leaf and a latch that needs two hands is not accessible, whatever the step height. Measure the whole route, not just the sill.