Buyer's guide to windows
Chris Bates reveals the key considerations when selecting fenestration for your project
Windows perform a range of duties – from setting the tone for your home’s architectural aesthetic through to practical tasks such as letting in light and providing adequate ventilation. Here’s what you need to know when specifying this critical component of your project.
Style
Getting the position and proportion of your windows right is vital if you want to achieve a stylish result, maximise light and make the most of any views.
A self build or extension will have more design freedom when it comes to windows than if you’re working on an existing house. However, it’s important to properly consider placement in order to achieve a good-looking result – and there are some simple rules that can help. Decide early on whether you want a symmetrical look; and if so, aim to achieve something that’s balanced without being boring (the Georgians, who adopted the golden ratio concept, were great at this, for instance).
Consistency in proportion and detail is important: should the tops of the windows align, for instance, and should they be predominantly landscape or portrait? The odd unit that bucks the trend can create an interesting focal point. Modern manufacturing opens up the opportunity for creativity; consider full-height picture windows, designs with minimal framing and structurally glazed elements that can even form both the walls and the roof.
Generally, the more sky is visible through the fenestration, the brighter the space will be – hence why period properties often have larger windows for the ground floor living areas. Floor-to-ceiling fixed glazing and high-level clerestory windows are good options. Consider adding rooflights to bring light into deep corridors or loft spaces. Be careful to avoid glare and overheating; shutters, blinds and brise soleils can provide solar shading.
Efficiency
Saving energy and money are often central to a home building project, and windows have a key role to play. Thermal performance is addressed in Part L1 of the regs (approved document L1A for new builds; L1B
for renovations). A key indicator is the whole-window U-value (not the centrepane figure, which only concerns the glass pane). For self builds, the limit is 2.0 W/M2K; and for new units in renovations it’s 1.6 W/M2K (Band C on the Window Energy Rating scale).
Most modern double-glazing achieves around 1.4-1.6 W/M2K as standard, but you may well be looking to exceed that. Top-end triple glazed units can hit as low as 0.6 W/M2K; perfect if you’re building to a stringent eco standard, such as Passivhaus.
Frame materials can have an impact. Timber is a natural insulator, giving a slight edge – but the difference is marginal, and most PVCU and metal versions now come with a thermal break to address this. Remember performance is only as good as the installation: even high-spec units will score poorly if they’re badly fitted.
Security
In most burglaries, criminals get in through a door or window – so this is a crucial part of your spec. In England & Wales, Part Q of the Building Regulations sets out minimum security standards for easily-accessible glazing (basically, any window within 2m of the ground or an accessible roof). This covers aspects such as tamper-resistant multi-point locking, when panes should be laminated or toughened, etc. The easiest route to compliance is to check the windows meet British Standard PAS24:2016 (one option is to go for products with Secured by Design status). Ask your supplier for evidence of how their units meet the criteria.
Frame material can make a big difference here. Plastic (PVCU) and metal versions are practically maintenance-free. Painted timber requires more upkeep; but modern factory-applied finishes can last for 10 years before repainting is needed. Composite units blend the benefits of the natural warmth and insulation of timber with metal cladding.
It’s important to factor longevity into the equation. PVCU windows will typically last up to around 25 years, but the alternatives comfortably offer a service life of 40 years or more. Provided they’re given a regular maintenance schedule, timber units can be the most durable – as evidenced by the fact that centuries-old originals still grace many heritage properties.
Placing your order
Windows are a major investment, and will likely represent a hefty chunk of your project budget – so you should always see the products in person before ordering.
So, get down to your supplier’s showroom and ask them to give a comprehensive demonstration of the units you’re considering. Take this opportunity to find out more about the ordering and installation process (do they use in-house teams or subcontract the work, for instance?). And don’t be afraid to ask to see product certifications so you can satisfy yourself everything’s up to scratch.
When it comes to developing and placing a major order, you’ll need to work alongside your architect/ designer and window company to draw up a full window schedule.
This should detail elements such as the planned size of each opening, performance targets and the frame material you want to use (if known).
This basic document will then need to be fleshed out in full. There will be questions to answer on glazing spec, opening configurations, ironmongery styles, locking requirements, frame finishes (do you want a dual-colour design, for a different effect inside and out?), reveal depths and more.
Most window manufacturers work to a lead time of six to 12 weeks for made-to-measure products – but check in with the supplier, so you can factor their timings into your schedule. It may be possible to order some windows based on the structural drawings and technical package, but complex units will probably need to be measured on site once the builders have created the openings.