Widening an opening for sliding doors means temporarily supporting the wall, cutting out masonry and fitting a new steel beam or lintel on padstones to carry the load, to a design set out in structural calculations and checked by Building Control. The building work typically takes 3–5 days before the door goes in, and has a guide price of £3,595 inc VAT for a 2.4 m opening.
This guide walks through each stage, who does what, what the work typically costs at different widths and when your neighbour needs to be told. It covers houses in England in most detail; Scotland, Wales and Northern Ireland run their own building control systems.
Why does widening an opening need a structural engineer?
The wall above an opening carries weight: brickwork, floors and roof loads, and sometimes concentrated loads from other beams or a chimney breast. Remove more of the wall and that weight has to be carried across a wider gap, so a structural engineer works out the loads and specifies the beam, the bearings at each end and the temporary support.
Structural calculations typically start from £450 inc VAT, and our guide prices for forming an opening include them. Building Control needs them as part of the Building Regulations application, and the builders work to them on site. If you are planning a slimline or very large door, tell the engineer, as these doors need the beam above to stay especially stiff.
What does the building work involve?
- Temporary props. Adjustable steel props, with needles through the wall where needed, hold up the masonry above while the old lintel and brickwork come out.
- Cutting out. The opening is cut to the new width, and the reveals are cut back or built up square.
- Padstones. Concrete or engineering brick padstones are set at each end to spread the beam's load into the wall below.
- Steel beam or lintel. The beam the engineer specified is lifted in, levelled and packed tight to the masonry above.
- Inspection. Building Control inspects at the stages it asks for.
- Making good. Brickwork is made good outside, the beam is boxed in or plastered inside, and the reveals are finished ready for the door.
The props stay in until the new beam is fully bearing. The finished opening size is agreed at survey, and the door is made once the new opening has been formed and measured, so a temporary closure covers the opening while it is made.
Do I need Building Control approval?
Yes. In England, forming or widening an opening is structural work that needs a Building Regulations application, structural calculations and usually a steel beam or lintel. Building Control checks the plans and calculations, inspects the work and issues a completion certificate when it is satisfied. Keep that certificate, because a buyer's solicitor will ask for it when you sell.
In Scotland the same work needs a building warrant before it starts. Wales and Northern Ireland have their own building control rules, which our building regulations guide summarises. Planning is a separate question, covered in our planning permission guide.
How long does it take?
The building work typically takes 3–5 days before the door goes in, depending on the width, the wall construction and what sits above the opening. A typical sequence:
- Day 1: protect the room, set up the props and take out the old door or window and the masonry
- Day 2: set the padstones and install the steel beam or lintel
- Days 3–5: build up the reveals, make good the brickwork outside and plaster inside, with inspection at the agreed stage
- Fitting: the door goes in, typically in 1–2 days for larger doors
Plaster needs time to dry before you decorate, and all timings are typical rather than promised. The door itself typically takes 4–6 weeks to make in aluminium after survey sign-off, which runs alongside the approvals.
How much does it cost to widen an opening?
The building work is priced separately from the door. These guide prices include VAT and cover the steel beam or lintel, padstones, making good and structural calculations:
| Finished opening width | Guide price for the building work |
|---|---|
| 2.4 m | £3,595 |
| 3 m | £3,795 |
| 3.6 m | £4,095 |
| 4.8 m | £4,495 |
The door is on top: for example, a 3.6 m aluminium sliding door has a guide price of £5,595–£6,895, fitted, inc VAT, at standard 2.1 m height. Costs rise where the wall carries heavy loads, the beam needs extra support, or drains or cables have to be moved. Your written quote after a free survey itemises everything and states whether Building Control fees are included.
Who does what?
- You: check planning, serve any party wall notices and agree the finished opening size.
- Structural engineer: calculates the loads and specifies the beam, padstones and temporary support.
- Building Control: approves the application, inspects the work and issues the completion certificate.
- Builders: prop the wall, form the opening, install the steel and make good.
- Door installers: fit, glaze, adjust and seal the door, with compliance for the door arranged through a competent person scheme installer or by notifying Building Control.
We can arrange the structural calculations, the building work and the door under one quote, so one team is responsible for the opening and the door that fits it. See new opening sliding doors for how that works.
Do I need a party wall agreement?
You may. If the end of the new beam bears on a party wall, the wall you share with a neighbour in a semi-detached or terraced house, the Party Wall etc. Act 1996 applies in England and Wales. You must give your neighbour notice before the work starts. If they agree in writing, the work can go ahead; if not, a party wall surveyor is appointed to settle how it is done.
Allow time for this before booking the building work, because notice periods apply; GOV.UK sets out the process and the periods. A detached house, or a beam bearing only on your own walls, does not normally involve the Act.
Common questions
Do I need a steel beam to widen an opening for sliding doors?
Usually, yes. Widening an opening in an external wall removes support for the masonry and any loads above, so a structural engineer specifies a steel beam or lintel sized for the new width, sitting on padstones at each end. Sometimes a concrete or steel lintel is enough, but the calculations decide that, not the builder on the day.
How much does it cost to make an opening wider for sliding doors?
As a guide price inc VAT, the building work is £3,595 for a 2.4 m opening, £4,095 for 3.6 m and £4,495 for 4.8 m, covering the steel, padstones, making good and structural calculations. The door is priced separately, and the final figure is fixed in a written quote after a free survey.
Can I widen an opening without Building Control?
No. In England, forming or widening an opening is structural work that needs a Building Regulations application and structural calculations, and in Scotland it needs a building warrant. Doing it without approval can leave you unable to show the work is safe and compliant when you sell, and may mean opening it up later so it can be inspected.
Can I stay at home while the opening is widened?
Yes, most people stay at home. The work is noisy and dusty for a few days, so the room is protected and sealed off where possible, and the opening is made secure at the end of each working day. Expect that part of the house to be out of use while the props are in, and allow time for plaster to dry before decorating.