Which Doors Are the Right Choice for Your Extension?

Choosing doors for an extension sounds simple until you realise how much they affect everything: light, layout, ventilation, furniture placement, thermal comfort, and how the new space connects to the garden.

At STAAC, we design and build extensions across Sussex and Surrey with architects, structural engineers and builders under one roof. That matters because door choice isn’t just a product decision - it’s a design + structure + build-detail decision. The best-looking doors in the world won’t feel “right” if the opening size, threshold, drainage, glazing spec and installation details aren’t nailed.

This guide compares the main extension door options and helps you choose the right one for your home.

The 4 most common extension door options

Most homeowners choose between:

• Sliding doors (2–4 panels)

• Bifold doors

• French doors

• Single garden doors (often paired with fixed glazing)

The “best” option depends on how you want to use the space - not just what looks good on Instagram.

Start here: what do you want your doors to do?

Before comparing products, clarify your priorities:

• Do you want the widest possible clear opening in summer?

• Is your goal maximum uninterrupted view all year?

• Do you need doors that work well with limited patio space?

• Are you trying to keep costs controlled but still look premium?

• Is the extension open-plan (kitchen/dining/living) where ventilation matters?

Sliding doors: best for views and a clean, modern look

Why people love them

• Big glass, minimal frames = maximum daylight and view

• Great for contemporary extensions

• Panels glide rather than fold into the room

Things to consider

• You don’t get the full opening width (one panel slides behind another)

• Track and threshold detailing is crucial for a premium feel

• Larger spans can require significant structural design

Best for: homeowners who want a calm, high-end look and value the view year-round.

Bifold doors: best for opening the whole wall

Why people love them

• Creates a wide opening for entertaining

• Strong indoor–outdoor connection in summer

• Flexible configurations (e.g., traffic door)

Things to consider

• The folded stack takes up space at the side

• More frames = less uninterrupted view than sliding doors

• More moving parts means installation quality really matters

Best for: families who want the “open it all up” feeling and will use it often.

French doors: best value and timeless style

Why people love them

• Often more cost-effective than large sliders/bifolds

• Classic look that suits many property styles

• Can be paired with fixed side panels for more light

Things to consider

• Opening width is limited compared to bifolds

• Furniture layout needs to account for door swing

Best for: traditional homes, tighter budgets, or where you want a simple, elegant solution.

Single door + fixed glazing: underrated and very practical

This combo can be brilliant when:

• You want a clear route to the garden

• You don’t need a huge opening

• You want to allocate budget to other upgrades (rooflights, kitchen, finishes)

Best for: practical layouts, smaller extensions, or when you want a clean look without complexity.

The “premium feel” checklist (what most people forget)

Door choice is only half the story. The details below are what make doors feel expensive and effortless.

1) Threshold design (flush vs stepped)

A well-designed threshold:

• feels seamless

• reduces trip risk

• manages water properly

Flush thresholds can look amazing, but they must be designed with drainage and weather exposure in mind.

2) Thermal performance and comfort

Look beyond “double vs triple glazing” and consider:

• frame material and quality

• overall U-values

• draught-proofing and installation

A door wall that looks great but feels cold in winter will never be your favourite part of the extension.

3) Solar gain and overheating

Big glass can overheat a space.Consider:

• orientation (south/west facing needs more thought)

• solar control glazing

• shading strategies (overhangs, blinds)

• ventilation planning

4) Security and hardware

Premium doors should feel solid:

• multi-point locking

• quality handles

• smooth operation

5) Structure and opening size

Large door openings often require:

• steelwork

• careful load path design

• coordination with roof structure and glazing

This is where having structural engineers in-house helps keep the design realistic and buildable.

6) Planning and building regulations

Often, replacing/adding doors at the rear doesn’t require planning permission, but it depends on:

• conservation areas / listed buildings

• the scale and appearance of the extension

• permitted development limits

Building regulations will apply to glazing safety, thermal performance, and structural work.

Quick comparisons (how to choose)

• Want maximum view + modern look? Choose sliding doors.

• Want the widest opening for entertaining? Choose bifold doors.

• Want timeless + cost-effective? Choose French doors.

• Want simple + practical with great light? Choose single door + fixed glazing.

FAQ

• Are bifolds or sliders better for an extension?
  ‍Sliders usually win on view and clean lines; bifolds win on opening width. The best choice depends on how you’ll use the space.

• Do I need triple glazing for extension doors?
  ‍Not always. Good-quality double glazing with the right frame and installation can perform very well. Comfort is a system: insulation, airtightness and ventilation matter too.

• Can I have a flush threshold?
  ‍Often yes, but it needs proper detailing for drainage and exposure. It’s a design decision, not just a product add-on.

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If you’re planning an extension in Sussex or Surrey and want doors that look premium and work properly year-round, STAAC can design the opening, structure and build details as one coordinated package: architectural design, structural engineering and build under one roof.

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