DESIGN

Choosing windows and doors

Picking you windows and doors is often a matter of personal taste or style, however, as they are one of the biggest single items of expenditure it is important to spend time looking at the options available. The three main factors to consider are cost, design and energy performance. The shape and size will have a knock on effect on how you dress the windows, e.g. curtains, blinds, may become expensive or tricky to install. Your architectural designer will guide you on the choice of double versus triple glazing with the latter having come down in price and become the norm on most new builds. 

Very generally, uPVC tends to be the cheapest with solid aluminium and hardwood at the more expensive end of the spectrum. The type of glass such as single (for existing homes only), double or triple glazing and any coatings will also have a significant impact, as will any tech additions. From a design point of view the choice of material is critical given the effect this has on other aspects and the longevity of the productSolid timber windows, once the standard for homes has dropped in popularity as uPVC and aluminium options have become widely available. Our wet climate and the subsequent requirement for wooden windows to receive regular painting and maintenance has led to selfbuilders increasingly choosing uPVC with the possibility of realistic wood effect. Most popular is aluclada uPVC or wood frame externally clad in aluminium 

The energy performance of the windows and doors will form a significant part of the house’s overall thermal performancalongside the walls roof and floor and must therefore be taken into consideration when doing energy loss calculations. 

Bear in mind that solar gain must also be considered as its not always a good thing with homes now more insulated – too much and you will make the house uncomfortably hot. Whilst the performance of the glazing is, of course, important it is unlikely to vary significantly between suppliers. However, the frame from both a thermal performance and airtightness aspectcan vary considerably from one supplier to another. This is an area where you need to pay close attention.

Some manufactures of high performance windows and doors have them certified to PassivHaus standard but most aren’t – making it difficult to know how well they perform in the real world. As usual, the old adage of you get what you pay for, will be true here so be wary of seemingly cheap products claiming high performance. 

A checklist of what to look for includes: 

  • Soft low-E coating on the glass  
  • Air leakage Class 4 or better 
  • Insulated spacer bars 
  • Where relevant install security windows certified to BS PAS 24; existing glazing may be protected from being smashed with the addition of accredited adhesive window film 
  • Aim for an ‘A’ window energy rating / window energy performance cert

Just as important as anything else, is the likely lifespan of the product and you will get a good idea of that by examining samples or visiting the showroom to assess the quality of seals, locks, mechanisms and opening sashes.

Find out for example, how the hinges are supported inside PVCu sashes and door stiles and check what guarantees are in place if any window or door furniture becomes loose or otherwise defective. Doors get a lot of abuse, so make sure they are sturdy and will remain dimensionally stable and rigid over their expected lifetime.

Windows will also form part of your ventilation strategy, even if you have mechanical ventilation. You need to allow for good cross ventilation in the event of a burst pipe, for example. Also consider that all windows allow UV light in which means that soft furnishings and other textiles will fade over time if directly exposed. For the same reason consider doors for the wardrobe. 

You will need to determine the exact size and location of your roof lights and whether they should open. This is essential in the case of truss roofs as the roof structure will have to be partially designed around the openingsBuilding regulations will dictate most of the requirements, such as minimum heights off the ground for vertical windows on the upper storey, and safely using windows as fire escape routes. 

If you are looking to build to a high thermal performance level then you will want to check that the manufacturer can supply frame extension pieces to allow you to overlap insulation onto the frame by approximately 50mm to address any thermal bridging possibilities. Finally, don’t forget to check out the warranty. 

Doors will all need to meet minimum standards as per the building regulations in terms of locking mechanisms to prevent break-insthere are some certification systems you can check for to get additional peace of mind. Windows also need to be secured for this purpose. Most doors nowadays are engineered and insulated to meet building regulations requirements.

Solid wooden doors are a thing of the past although Accoya is still a possibility. If you want to incorporate glazing, the minimum is likely to be double glazed, which tends to rule out steel frames. That said poor thermal performance in one element such as a door can be made up in other areas, but it will still need to be up to a minimum standard as insulation and airtightness are only as good as the weakest link.