Windows are the eyes of your building. They determine your homes two most important features: its aesthetic appeal and its energy efficiency. Whether you’re building, renovating or extending, there are a variety of window options out there to meet your preferences, and it can be challenging to navigate them all as a self-builder.
As self-build specialists we know a thing or two about good window design, and we know that getting your windows right is vital. With the help of our design team, we’ve put together this detailed guide to make sure you’re making the right choices on your windows and integrating them effectively into your design.
This is Part 1 of a 2 part series.
THE IMPORTANCE OF GOOD WINDOW DESIGN
Every window must be tailored to fit the specific needs of your project, which means every window is unique. Different window manufacturers have different tolerances, manufacturing constraints, thicknesses, and energy performance. Your windows may be unique to your project, but there are some fundamental steps to good window design that apply to all builds. A few examples include:
- Placing windows to maximise the use of natural light and energy efficiency, South-facing windows in the UK, for example, can capture the most sunlight.
- Maintain appropriate proportions and scale in relation to the overall structure. Avoid windows that are too small or too large for the wall space.
- Strive for consistency in window design throughout the building to create a cohesive look.
- Maximise views and take in key features of the surrounding landscape
- Minimise sight lines to maximise glazed area and increase aesthetics
- Maintain safety and compliance
The role of your design team in the window process is to turn your requirements into reality. Your architect will ensure your windows are placed to suit the Architectural Style and brief, while considering the optimal amount of sunlight to maximise daylight and minimise overheating. Additionally, the services of an architectural technologist will assist in choosing key technical aspects, like window materials, thermal performance, operation and ventilation, that all have a key role to effectively integrate with your chosen method of construction.
With consideration to your energy-efficiency requirements, you’ll want to get the thermal efficiency (u-value) of your windows as low as possible. A u-value is the rate at which heat will transfer through a specific material, measured in W/m²K. The lower your u-value, the less heat you lose through your building fabric. The percentage of frame to glass (frame factor) is also a key consideration in heat loss, this is reviewed for SAP & EPC and is one of the key factors for Passive House and PHPP.
Another important aspect is window ventilation. Trickle vents are small openings in the window that allow constant airflow into your building and rely on prevailing wind direction and a collective free area per habitable room. Opening windows allow for purge ventilation to remove unwanted warm stale air. Both factors require careful design consideration and placing them incorrectly can have an impact on overall ventilation of the building. Building an airtight energy-efficient home using the 'Fabric First' approach removes the need for trickle ventilation altogether as it’s provided by other means and liaising with your architect is your best course of action for all ventilation aspects to consider.
CHOICES OF MATERIALS FOR WINDOWS
One of the first key decisions you’ll be making is the material of your windows. Your choice of materials affects both the look and performance of your windows, so take time to research each one carefully. These are three of the most-common choices for self-builders:
Timber Aluminium Clad is the most popular choice amongst our self-build clients. This is due to its natural timber look and the variety of finishes it comes in coupled with the low maintenance requirements. These windows are made up of a solid timber frame fitted with external aluminium casing. These windows require very minimal maintenance and generally have a longer lifespan than traditional timber due to their superior cladding.
The aluminium cladding can be fixed in different methods across suppliers. Some include a ventilation gap and others can be bonded to the frame with insulation, adding to the overall thermal efficiency of the window.
Full Aluminium is another option for your windows. These windows may not have the variety of traditional timber finishes you get with the previous option, but they do provide a unique look and architectural style to your self-build that you won’t find with another window material. These windows generally feature a strip of high-performance insulation and small pockets of air inside its aluminium casing, which works to give them a performance value that will benefit your energy-efficiency requirements.
One advantage of full aluminium windows is the frame can span a much further distance than other options. This is something aluminium timber clad windows will struggle to achieve as the wood can only span so far before bending. The strength of the aluminium makes it the best choice for any large feature windows or wide doors with large openings.
uPVC windows are an option for those looking to keep their costs down. These windows don’t offer the natural aesthetic appeal of the other options but can still provide a durable frame that’s low maintenance. Some manufacturers now offer a range of internal finishes to suit your needs and can even be aluminium clad on the outside to add architectural style. They may not have the flexibility in sizes compared to timber aluminium clad or full aluminium, but if cutting costs is your top priority, then these are your best option.
DOUBLE OR TRIPLE GLAZING?
We’ve talked about the framing, now let’s touch on the glass itself. Window technology has taken significant strides in the past few years and is now a major player in building an energy-efficient home. As with most modern homes, you’ll have to choose between double and triple glazing.
Modern double glazing is the most cost-effective option. These windows comprise of two panes of glass tightly packed with a layer of gas in between. Double glazed windows can improve your home’s heat loss and make your home more energy-efficient by holding in heat during the winter months. In our experience, we’ve seen lot of window companies phase out double glazing as an option, but that doesn’t mean it can’t help to improve the thermal efficiency of your home.
With the changes in regulations on energy performance, you need to be careful of the percentage of glass to floor area if you are looking to use double glazing, they will lose more heat and can affect you overall SAP & EPC rating if not used correctly. Losing more heat in the winter also means they gain more heat in the summer, which can affect any overheating calculations you need to comply.
The popularity of triple glazing continues to rise and are almost the default for most window quotes as they meet the more demanding thermal efficiency requirements. These windows are made up of three panes of glass and two layers of gas in between them. Triple glazed windows offer superior thermal efficiency and are the best for retaining heat. The increased thickness also improves the soundproofing of your windows and can improve any overheating calculations by fractionally reducing solar gain.
Triple glazing options are certainly more desirable in our colder British climates. They help retain the heat in the dwelling (where you want it to be) improving the fabric of the dwelling to meet Fabric First Principles. In some dwellings, it can be beneficial to use a mix of triple and double-glazed windows, keeping double glazing to the south and west facing elevations to maximise solar gain. This requires careful consideration to minimise over heating risk and should be explored in more detail using PHPP software to generate detailed reporting you can explore with your architect.
Want to find out more about what glazing to choose? View our article here!
HOW DO I ENSURE MY WINDOWS ARE SECURE?
Your design team will advise you of the requirements to ensure your windows meet safety & security compliance. This is a mandatory requirement of Building Regulations and gives you peace of mind your windows will meet required security ratings. The two regulatory listed methods to meet this requirement are the Publicly Available Specification (PAS) 24 standard and Secure by Design. Your manufacturer should be able to list which safety scheme their units are registered with, this ensures your windows are of a certain quality and offer the right level of security.
If they don’t list either of these methods be sure to ask them about their security rating. They may have a European equivalent standard that can be recognised and approved. It will be down to the discretion of the building control body if alternative methods can be accepted, so ensure you start discussions with them before signing any orders. Your architect can help navigate the compliance and specification requirements with the manufacturer before you formally place any deposits to secure your place.
Want to know more? Keep an eye out for Part 2 of this article, where we'll go through costs, finding a supplier and the final considerations before you make your purchase!
