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Turn a Window Into Bi-Fold Doors — From £2,995 Fitted

Most rear elevations in Warrington have the same problem: a decent-sized kitchen or dining room with a single window looking onto a garden nobody uses, and a back door tucked round the side. Knock the window through to full-height bi-fold doors and the room changes completely — and it costs a fraction of an extension.

We do the whole job. Structural calculations, the steelwork, the opening, the doors, the making good and the Building Regulations certification. From £2,995, fully fitted.

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What’s involved

This is structural work, not a glazing swap, and it’s worth understanding what you’re buying.

1. Survey and structural calculations

We measure the existing opening, check what’s above it, and establish what the wall is carrying. A structural engineer produces calculations for the beam that will span the new, wider opening. This is not optional and it’s not something to skip — the wall above the window is holding up floor joists, a roof, or both.

2. Propping and beam installation

The load above the opening is taken on temporary props while the existing lintel comes out and the new steel goes in. The beam is sized from the engineer’s calculations, seated on padstones at each end to spread the load into the masonry, and fire-protected. This is the day that makes noise and dust. It’s usually one day.

3. Forming the opening

The masonry below the window — the spandrel panel — comes out down to the finished floor level, and the reveals are squared up and rebuilt. The threshold is prepared, including a drainage detail so water runs away from the door rather than sitting against it.

4. Doors in

The bi-fold is fitted, levelled and adjusted, the frame is sealed and insulated around the perimeter, and the gear is set so every leaf folds and locks properly.

5. Making good

Reveals plastered, external brickwork made good and pointed, internal floor finish brought up to the threshold, silicone lines cut in. This is the stage that separates a conversion that looks original from one that looks like a conversion.

6. Certification

We’re CERTASS registered, so the glazing installation is self-certified and registered. The structural work is signed off with the engineer’s calculations and, where required, a Building Control completion certificate.

What £2,995 covers

£2,995 is our starting price for a straightforward conversion — a standard rear window opening, converted to a bi-fold door in a standard colour, fully fitted.

Because every opening is different, we confirm exactly what’s included for your job at survey and give you a fixed price in writing before you commit to anything. What we won’t do is quote a headline number and then discover extras on day two.

What moves the price:

  • A wider opening than the existing window — more span means a bigger beam and more structural work
  • Two storeys above the opening rather than one
  • A cavity wall requiring separate inner and outer beams
  • Non-standard or dual colours, integrated blinds, or laminated glazing
  • Difficult access — narrow side passage, no vehicle access, a raised patio
  • A drain, soil pipe or manhole in the wrong place, which is more common than you’d think
  • Levelling work where the outside is significantly higher or lower than the inside floor

There are no unit rates and no “subject to” clauses beyond genuine unknowns we’ll have flagged to you on the day of the survey.

Do I need planning permission?

Usually not. Converting a window to a door on a rear elevation is normally permitted development, because you’re not extending the property or altering its footprint.

You will need planning permission or additional consent if the property is listed; if it’s in a conservation area and the work affects a visible elevation; if you’re in a flat or maisonette; if permitted development rights have been removed by an Article 4 direction or by a planning condition on a newer estate; or if the opening is on a front elevation facing a highway.

We’ll flag any of these at survey. If it needs an application, we’ll tell you before you commit to anything.

Building Regulations are separate and always apply. Structural work and new glazing are both notifiable. We handle both.

Window to bi-fold conversions we have completed

House with new openings formed in the brickwork during building workGrey glazed doors fitted in a hallwayGrey aluminium bi-fold doors opening onto a garden patioAnthracite grey bi-fold doors fitted to a rear extensionAluminium bi-fold doors seen from inside a living room

Why it’s worth doing

It’s the cheapest way to transform a room. A rear extension is a five-figure project before you’ve bought a light fitting. A bi-fold conversion starts at £2,995 and changes how the same room feels almost as much — because what actually makes a room feel bigger is light and a view through to outside, not floor area.

It fixes the dead garden problem. A garden you can only reach by going round through a side door is a garden you use twice a year. A garden you can walk straight into from the kitchen is one you use daily.

It improves the thermal performance. Counter-intuitively — an old single-glazed window plus an uninsulated spandrel panel below it usually performs worse than a modern thermally broken bi-fold with low-E glazing.

It adds value. Estate agents in the North West consistently list bi-fold doors among the improvements that get houses viewed, and a rear elevation with full-height glazing photographs considerably better than one with a window.

Conversions we do

  • Kitchen window to bi-fold — the most common by a long way
  • Dining room window to bi-fold — usually the best-looking result, because the room already faces the garden
  • Lounge window to bi-fold on a rear elevation
  • Existing patio door to bi-fold — no structural work needed if the opening stays the same width, so this is the cheapest version of the job
  • Conservatory rear wall to bi-fold
  • Garage conversion — new opening in a garage rear or side wall
  • Window to sliding patio doors — same structural work, different door

Fitted across Warrington and Cheshire

We work out of JL Enterprise Park in Rixton, and we do this work throughout Warrington, Cheshire and the surrounding areas — Widnes, Lymm, Culcheth, Leigh, Golborne, Chester, Northwich, Knutsford, Wilmslow, Altrincham, Sale and Hale. Have a look at our recent work for before-and-after examples, and at aluminium bi-fold doors for the door specification itself.

Frequently asked questions

Three to five days on site for a typical conversion. Day one is props and steel, day two is forming the opening, day three is the doors, and the remainder is making good. Doors are made beforehand, so the house is never open overnight.

No. The opening is formed and the doors are fitted the same day, or the aperture is boarded and sealed overnight. We plan the sequence around this.

Yes, and we arrange it. The calculations are part of the job, not an extra you organise yourself.

Yes. Two storeys above the opening means a heavier beam and more propping, so the price is higher, but structurally it’s routine work.

It happens. Sometimes it can be re-routed, sometimes the opening shifts a few hundred millimetres, and occasionally it changes the design. We check for it at survey rather than discovering it on day two.

Yes — the structural work is identical. Some openings suit a sliding patio door better, particularly where there’s nowhere sensible for bi-fold leaves to stack.

Yes — it’s quoted as a fully fitted price for a standard opening, not a doors-only figure. We’ll confirm exactly what’s covered for your opening at survey and put it in writing.

That’s the aim, and it comes down to the making good. Matching brick where the reveals are rebuilt, proper plastering, and a threshold detail that sits right with the floor finish. It’s the part of the job we spend the most time on and the part cheap quotes skip.

Why buy from Exclusive Bifolds

  • 10-year guarantee on every installation
  • CERTASS registered — we self-certify and register your installation, so there’s no Building Control fee
  • We’ll beat any genuine like-for-like quote dated within the last 14 days
  • £100 locks your price against sector price rises
  • Our own installers — no subcontractors, no franchise
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