Annexe window styles

Glazing can make or break a annexe design. You need to consider style, cost, material and efficiency.

One of the biggest purchases in a annexe project are the doors and windows, deciding on window style is a major design factors your annexe design.

Windows and doors can cover large portions of the annexe, so it is very important to take into account the thermal performance and energy efficiency, not just how much natural light it will bring into the annexe.

The style of window you choose makes a huge impact on the overall appearance of the annexe and can influence how you interact with different rooms, research is key and you should consider the following:

  • Design: Will your windows be classic and traditional, or sleek and contemporary?
  • Style: Find out about the different types of casements
  • Material: What the different materials cost, their durability and style
  • Glazing: The thermal performance and energy efficiency of then windows
  • Costs: How does the different materials, casements and glazing affect the cost
  • Ordering: How long is the lead-in times and how will that affect your project

How to Choose a Window Style?

The positioning of windows will be informed and influenced by room layouts and the shape of the annexe itself but the shape and type of the windows themselves should be taken into serious consideration when deciding on the exterior and interior finishes.

For instance, a contemporary, annexe is improved by similarly narrow, vertical windows.

Modern window companies can replicate older styles where possible but unfortunately you cannot effectively replicate wood grain with PVCu, although there are a few manufacturers who try.

Small casement windows are associated with cottages and there are some great offerings out there, but a trickier style to replicate with double glazing is a Georgian and early Victorian era multi-pan sliding sash as achieving glazing bars which are as elegant with modern methods is tough.

Window Styles for Contemporary Annexes

As glazing became progressively cheaper and easier to work with over the centuries, the size of our windows grew. By the time of the advent of modernism in the early 20th century, simplicity became the way forward, minimising not just the amount of framing but also the frame width itself.

You could consider the more modern the build-style, the bigger and cleaner the glazing should be. Timber will soften a rendered exterior of a modern annexe, while aluminium windows are perfect for minimalist styles.

What are the different styles of Windows?

Open-out Casement Windows

A traditional British option (historically and in the 20th century), open-out casements are available in a variety of formats. Choose split casements for cottage-style designs and small glazed units to mimic ‘Georgian style’. In contemporary styles, side hung and awning formations work well as there is no mullion to interrupt the view.

  • Large casements tend to be the cheapest
  • Costs tend to be lower because they are made in modular, standard sizes
  • Great for ventilating rooms but as they can open wide, this might cause concern for those with small children or animals

Tilt and Turn Windows

Continental-style tilt and turn windows open inwards, and look best on modern designs. The ’tilt’ option provides ventilation with security.

  • They are typically made to order, increasing the cost
  • Secure
  • Great for smaller rooms where saving space is a priority

Fixed Windows

Fixed windows are just that, fixed, so they don’t open out or let in any ventilation. However, they do maximise opportunities for natural light throughout a home. As they don’t need to be made to incorporate a opening mechanism, there are endless designs and styles available.

  • Provides light in wasted spaces
  • Can create interesting designs
  • Usually the cheapest style of window

Sash Windows

Sash windows are essential when renovating or replicating Georgian and Victorian housing, still widely used on traditional-style new builds. Sizes are typically not standard but windows need to be in proport­ion to the house, so are often bespoke.

  • Timber sash windows require maintenance
  • Typically have vertical tracks so they won’t fill up with debris

Rooflights, skylights and roof lanterns

Introducing windows into the roof will bring in natural light where conventional windows can’t be installed. Fixed windows that follow the roofline are typically known as skylights, while rooflights tend to open.

Rooflights are great for one-and-a-half storey annexe, which are steadily becoming more popular options among annexes
Skylights are great at providing light deeper into the floorplan

Roof lanterns offer a greater opportunity to introduce the maximum amount of light and help to achieve the illusion of extra head-height in an annexe with a flat roof.

Clerestory window

High-level windows that are sometimes used to retain privacy but increase natural light or ventilation. In modern energy efficient annexes, clerestory windows have been used in solar gain strategy. In hotter parts of the day the elevated window position gains heat and essentially uses the structure below as a heat bank.

  • Let in extra light and ventilation
  • Great for rooms with high ceilings

Choosing the best material for Your chosen style of window

Timber Windows

Timber’s main selling point is the feel and authenticity it offers to period-style homes: there is no real replacement for the warmth of traditional timber windows.

Softwood Advantages:

  • Nothing can beat the tactility and detailing of a timber framed window
  • Softwood is popular among those on a limited budget as they are the cheapest option if glazed and decorated on site
  • Can be stained, but are usually painted
  • Suites both contemporary and traditional style homes

Softwood Disadvantages:

  • On-site glazing carries a risk of double-glazing failure
  • Factory glazing lowers the risk but costs more
  • Softwood requires repainting every few years

Hardwood Advantages:

  • Have a tighter grain than softwoods, making them more stable and durable
  • Can be treated to be further stabilised
  • Most popular on traditional-style homes
  • Usually stained

Hardwood Disadvantages:

  • It’s expensive — anything up to four times the cost of softwood

Aluminium Windows

One of the most popular materials for windows in contemporary homes, aluminium windows can offer slim sightlines or a frameless appearance available many colours to suit.

Plastic Windows

PVCu windows long reigned supreme as the dominant material for replacement windows and for good reason. A quick and easy option, plastic windows are low-maintenance and cheap.


  • Cheapest overall although costs var with quality
  • Low-maintenance


  • Can look cheap
  • Can reduce the value of period homes
  • Not easy to repair
  • Doors can be weak

Composite Windows

If you’re struggling with the choice of materials, there is a compromise — the so-called composite systems that mix different framing materials inside and out.


  • Best of both worlds as they usually consist of timber windows with a weather-proof capping, such as aluminium strips or plastic
  • Can withstand harsh climates (widely used in such as Canada and Sweden)
  • Great for triple-glazing
  • Complement modern designs
  • Low maintenance but offer the warmth of timber


  • Expensive
  • Unlikely to be made to standard UK sizes if ordered from the Continent

Metal/Fibreglass/Alloy Windows


  • Popular among contemporary-style homes but increasingly popular in period properties (particularly for Belgian doors)
  • GRP (fibreglass) can create a strong load-bearing frame
  • GRB can be supplied in any colour
  • Low maintenance
  • Produce finer frames


  • Not as thermally efficient as wood
  • Can be expensive

Choosing the right glazing for the style of window

On-site double glazing is the cheapest option, usually done with softwood frames which are then painted on site. Slow and time consuming, most suppliers are moving away from on-site glazing for new installations.

New methods in factory double glazing mean that many windows can be clipped into templates from inside, thus stream­lining the installation. However, it is more expensive than on-site glazing.

Low E

Low-emissivity or ‘low-E’ glass (as it is more commonly known) is a type of glazing designed specifically to prevent heat escaping through windows. Low-E double glazing meets Building Regulations in the UK (such as Part L1B in England) for replacement windows and new windows for extensions.

Benefits include:

  • Can reduce heat loss by at least as four or five times compared with single glazing
  • Solar control glass can be specified to reduce excessive solar gain in the summer for areas of the home susceptible to overheating

Triple glazing

Once only popular in low-energy homes, triple glazing is rapidly becoming a standard solution for today’s window suppliers.

Benefits include:

  • Excellent comfort levels as it evens our temperature profiles of rooms
  • Great for noise reduction for homes near busy roads etc.
  • Helps minimise overheating
  • Some suppliers offer special coatings that will allow solar gain when required (i.e. in winter)

However, the issue is really around where to put it, with most experts agreeing that it’s near-essential on north-facing elevations with lots of glazing and to be generally avoided on south-facing elevations.

I’ve chosen my windows, how and when do I order?

This very much depends on whether you’re opting for off-the-shelf windows or bespoke products, and can also differ from company to company.

A general lead time would be around 12 weeks, however, bespoke windows will inevitably carry longer lead times. It is best to not order too early on in the project in case amendments to the building design or aperture sizes occur.

How can I Increase the Amount of Natural Light in my annexe?

When you first step into a new annexe, the first thing people notice is whether it feels light and airy, or dark and dingy. This is impacted by the amount of natural light provided by window design.

Window design will obviously be near the top of your list when designing the exterior facade of a new annexe. The development of super-wide bifold and sliding doors in recent years has been something of a game changer for maximising natural light in homes. As have roof lights where rooms struggle to achieve the same levels of brightness due to the floorplan such as in a bathroom or living room.

How an light will affect the existing rooms is key in the longevity of your enjoyment in the new space so take the time to study where light will fall throughout the day and when you will utilise each room. Think about adding small side windows or clerestory windows to compensate.

For new annexes, the luxury is the floorplan is freshly designed to suit each space’s needs, but be weary of overheating in rooms with too much glazing. As anyone who has been in a conservatory tacked onto the back of a house will attest, simply incorporating a lot of glazing isn’t necessarily a recipe for a comfortable interior.