What are sliding doors for new openings?
A new or widened opening is structural building work that creates space in an external wall for a sliding door, either where there was only a window or wall before, or by making an existing door opening wider. Because part of the wall is carrying the floors and roof above, the load must be transferred safely to each side, usually with a steel beam sitting on padstones, sized by a structural engineer.
The work needs a Building Regulations application in England, or a building warrant in Scotland, and structural calculations to go with it. If the new steel will bear on a wall you share with a neighbour, the Party Wall etc. Act 1996 (England and Wales) may apply, which means serving notice before work starts. Planning rules differ for flats, listed buildings and Article 4 areas, so it is worth checking early. Our guide to widening an opening covers the steps in order.
We manage the job from survey to finished door. Typically that means arranging calculations, supporting the structure above with temporary props, cutting out the masonry, installing the steel and padstones, building up and making good the reveals, and passing the inspections, which usually takes 3–5 days before the door goes in. The door is then made to the measurements of the finished opening.
Who are they for?
Best suited to
- Turning a window into a door to the garden
- Widening a narrow patio door
- Opening a rear wall onto a new terrace
- Joining a kitchen to the garden with wide glass
Worth considering
- Structural work adds cost, time and disruption compared with a straight replacement in the same opening.
- There is a gap of several weeks between forming the opening and fitting the door while it is made, so a temporary closure is usually needed.
- Steel near a party wall may trigger the Party Wall etc. Act 1996 (England and Wales), which can add notice periods and surveyor fees.
Why choose sliding doors for new openings?
- Widening a standard patio opening to a larger span can transform how a room connects to the garden, giving a wall of glass rather than a doorway.
- A structural engineer sizes the steel beam and padstones for the actual loads above, so the opening is designed rather than guessed.
- Structural calculations are included in the guide price, and the Building Regulations application is handled as part of the project, so you are not left coordinating engineers and inspectors.
- Telling the engineer that a sliding door will sit beneath the beam lets them limit its deflection, which matters because a beam that sags can stop panels sliding freely.
- Temporary propping holds up the wall above while the masonry is cut out, keeping floors, ceilings and the roof safely supported throughout the work.
- Making good the reveals and head after the steel goes in leaves a square, plumb opening, which is what a precision-made sliding door needs to run smoothly.
- If the work affects a party wall, notice can be served under the Party Wall etc. Act 1996 (England and Wales) before it starts, avoiding disputes with neighbours later.
- The door is measured from the finished opening rather than from drawings, so it fits the opening as built, not as it was intended to be built.
Typical specification
| Opening guide price (inc VAT) | £3,595 for 2.4 m; £4,095 for 3.6 m; £4,495 for 4.8 m |
|---|---|
| Structural calculations | Included in the guide price |
| Support | Steel beam or lintel on padstones, as designed by a structural engineer |
| Approvals | Building Regulations application in England; building warrant in Scotland |
| Party wall | Party Wall etc. Act 1996 (England and Wales) may apply if steel bears on a shared wall |
| Building work | Typically 3–5 days before the door goes in |
| Door | Measured from the finished opening and made to suit |
Figures are typical and vary by system and size; your quote confirms the exact specification.
How much do sliding doors for new openings cost?
Forming or widening an opening to 3.6 m has a guide price of £4,095 for the steel, padstones, making good and structural calculations, on top of the door itself at £5,595–£6,895 for a three-panel aluminium slider, fitted, inc VAT at standard 2.1 m height, all fixed in a written quote after survey.
| Overall width | Typical panels | Guide price (fitted, inc VAT) |
|---|---|---|
| 1.5 m | 2 panels | £6,595–£7,295 |
| 1.8 m | 2 panels | £6,995–£7,795 |
| 2.1 m | 2 panels | £7,495–£8,295 |
| 2.4 m | 2 panels | £7,895–£8,895 |
| 3.0 m | 2 panels | £8,795–£9,895 |
| 3.6 m | 3 panels | £9,695–£10,895 |
| 4.0 m | 3 panels | £10,295–£11,595 |
| 4.8 m | 4 panels | £11,495–£12,995 |
| 6.0 m | 4 panels | £13,295–£15,095 |
Guide prices include an aluminium sliding door plus forming the opening (steel beam, padstones, making good and structural calculations), including VAT. Building Control fees are set by your council and are extra. Your price is fixed in a written quote after survey.
Options and extras
- Window to door conversion. Cutting down below an existing window to form a door opening to the garden.
- Widening an existing door. Removing masonry each side of an old patio door to take a wider slider.
- Steel beam with padstones. A beam sized by the engineer to carry the wall, floors and roof above.
- Concealed steel. Setting the beam so it sits above the ceiling line, giving a cleaner head detail inside.
- Temporary door or boarding. A secure, weathertight closure while the made-to-measure door is being manufactured.
- Low threshold detail. Adjusting floor and outside levels during the building work to allow a lower sill.
Lead times and fitting
Lead time: Typically 4–6 weeks for the door after the opening is measured; building work scheduled around approvals.
Fitting: Typically 3–5 days of building work, then 1–2 days to fit the door.
Nothing is ordered until you confirm the surveyed specification in writing. See how it works.
Rules and approvals
England
In England, forming or widening an opening is structural work that needs a Building Regulations application, structural calculations and usually a steel beam on padstones. The new door is also a controlled fitting (U-value 1.4 W/m²K or better if more than 60% glazed). If steelwork bears on a party wall, the Party Wall etc. Act 1996 may apply.
Wales
In Wales, structural work to form or widen an opening needs Building Regulations approval and structural calculations, and the new door must meet the Welsh energy and safety glazing requirements. The Party Wall etc. Act 1996 may apply where steelwork bears on a party wall.
Scotland
In Scotland, forming or widening an opening needs a building warrant before work starts, with structural details for the new beam. The door must meet the Scottish building standards for energy and safety glazing.
Northern Ireland
In Northern Ireland, structural alterations need approval from your district council's building control service before work starts. New openings in Northern Ireland are by arrangement.
Sliding doors for new openings: common questions
How much does it cost to widen an opening for sliding doors?
Our guide price for forming or widening an opening is £3,595 for 2.4 m and £4,495 for 4.8 m, covering steel, padstones, making good and structural calculations. The door is priced separately, and Building Control fees are set by your council. All figures are guide prices inc VAT, fixed in a written quote after we survey the wall and see what is above it.
Do I need building regulations to widen a door opening?
Yes, forming or widening an opening is structural work and needs a Building Regulations application in England, supported by structural calculations. Building Control inspects the work, typically including the steel and its bearings. In Scotland a building warrant is needed. Wales and Northern Ireland follow their own building regulations through local authority or district council building control.
Do I need a steel beam for sliding doors?
A widened or new opening usually needs a steel beam or a suitable lintel to carry the wall and anything above it, and for wider openings a steel beam is the usual answer. A structural engineer chooses the size and bearing details based on the loads. The beam is placed on padstones at each end to spread its load into the masonry.
Does the Party Wall Act apply to my new opening?
The Party Wall etc. Act 1996 (England and Wales) may apply if the new steel beam bears on, or is cut into, a wall you share with a neighbour, as is common in semi-detached and terraced houses. If it applies, you must serve notice on the neighbour before the work starts. A rear wall entirely on your own property is less likely to be affected.
How long does it take to form a new opening?
Forming or widening an opening typically involves 3–5 days of building work, including propping, cutting out, installing the steel and padstones, and making good. The sliding door is then made to the finished opening, which typically takes 4–6 weeks for aluminium, so a secure temporary closure is fitted in between. The door itself typically goes in within one to two days.
Can you turn a window into a sliding door?
Yes, a window opening can usually be extended down to the floor and often widened to take a sliding door. The work involves removing the masonry below the window, forming a new threshold, and fitting a steel beam or lintel if the opening is widened. Drains, air bricks and floor levels outside need checking, and the work needs a Building Regulations application.
Why does beam deflection matter for sliding doors?
Beam deflection matters because a sliding door needs a straight, level head to run properly. Every beam bends slightly under load, and if it bends too much the frame can be squeezed, making panels stiff or causing them to bind. Telling the structural engineer that a large sliding door will go underneath allows them to design a stiffer beam.
Do I need planning permission for a new opening?
Planning rules for altering an elevation depend on the property and where you are, so it is worth checking with your council before you commit. Flats, listed buildings and properties covered by an Article 4 direction are the most likely to need consent. Wales and Scotland have their own planning rules. Our planning guide sets out the questions to ask.