Along with walls and roofs, doors and windows form the elemental parts of all habitable buildings. They are so familiar that they can easily be taken for granted but, for those looking to make energy savings, these humble apertures can offer scope for significant improvements in terms of both comfort and energy savings.
Energy Saving Windows
The hard-sell tactics of replacement window companies may have brought the industry into disrepute but there is no denying that some modern windows can significantly outperform their older counterparts. There is certainly no shortage of choice but it is wise to give careful consideration to what is currently available and matching it to what is actually required.
For most people, window replacement conjures up images of double-glazed sealed units mounted in unattractive white plastic (sorry, uPVC) frames but much more is on offer. The conventional double-glazed sealed units typically offer an intermediate gap of around 16 mm which in itself provides greater levels of thermal insulation than both single-glazed or earlier double-glazed windows which tended to use a smaller gap. The modern trend is for triple glazing with further efficiencies. In many cases, simple air gaps are used but some of the most efficient units employ a heavy inert gas such as argon for improved insulation. Krypton or xenon gases can offer even better standards of insulation but at a higher cost.
The types of glass used can also have a significant effect on performance. The most energy efficient windows usually incorporate what is generally referred to as “low emissivity” or “Low-E” glass and this typically takes the form of a thin metal oxide coating on one of the internal panes. This allows the incident radiant light to enter the building but reduces the amount re-emitted greenhouse style.
Other considerations in window design include the types of spacers used between the individual glass panes. These spacers form the edge of the sealed unit and keep the glass panes at suitable distances. They also usually incorporate desiccants to reduce any chances of internal condensation but some are predominantly metal and this can reduce the unit’s thermal efficiency.
Some of the very best units employ “warm-edge” spacers to overcome this problem. Moving on to the window frames gives further options. The ubiquitous uPVC frames are readily available and their rather unattractive appearance is offset by their promise to be maintenance free. They should offer a long life but can deteriorate and become brittle with age and can be difficult to repair. At the end of their life, they can be recycled. Wood is still the first choice for those looking for a truly eco-friendly building material provided it is ethically sourced but continuing maintenance is necessary. Metal frames can maximise the glazed area but need expert design to avoid any problems of thermal bridging between the internal and external surfaces and so are seldom specified. Sometimes frames can be of composite construction or utilise different types of materials in combination such as protective metal flashings over wooden or plastic frames.
Sealed units are by no means the only options and in some situations, such as historic or listed buildings, the use of simple internal secondary glazing is often a better alternative. This may appear rather cumbersome but it gives good levels of thermal insulation and is particularly useful where noise may be a problem due to its excellent sound insulation properties. Heat loss through windows can also be reduced by other more basic methods such as the use of heavy curtains at night, well-fitting shutters or sealed blinds.
The energy saving properties of windows are therefore determined by many different factors and whereas most building components can easily be evaluated for thermal efficiency simply by considering their “U-values” (thermal transmittance), with windows this is only part of the equation. Thankfully the British Fenestration Rating Council has taken all things into account and produced a simple system of efficiency rating ranging from A++ to E in a similar manner to the energy efficiency ratings of domestic appliances. This greatly simplifies the task of choosing the best windows.
Energy Saving Doors
Just as with windows, it seems that for many years, the door’s role in heat loss has been largely overlooked. In the UK, legislation is now in force requiring the doors of newly-built properties to meet an acceptable standard of thermal insulation. In England, such doors must have a U-value of 1.8 (or less). Putting this in perspective, a traditional wooden door is likely to a U-value of around 3.0 suggesting that the wooden door is a thing of the past.
Door manufacturers have been working hard to produce suitable doors with some results being better than others. The wobbly white plastic doors beloved by budget window installers, but few others, are thankfully unlikely to comply with the modern requirements and future uPVC offerings are likely to be of a much more substantial nature. Perhaps the most exciting developments are in the field of composite doors. Each of these doors relies on the use of various different materials in order to achieve the desired levels of security, strength, thermal insulation and appearance. The materials used would typically be: wood, steel, aluminium, PVC, GRP (glass reinforced plastic) and insulating foam. Many of these doors are designed to have a traditional appearance similar to the more aesthetically pleasing wooden doors.
Of course U-values are not the only consideration and heat loss via doors often occurs as a result of a poor fit. Draught proofing is therefore the first (and cheapest!) way of overcoming such problems and this should extend not only to the door’s fit in its frame but also to any openings such as letterboxes, keyholes or cat-flaps. Another simple but often overlooked way of effectively banishing the problem of such heat loss is by the provision of an enclosed entrance porch. Two doors are definitely better than one! One of the least efficient door types, historically, were bifold doors but with modern manufacturing technology, we can now buy energy efficient exterior bifold doors that stand up to even the worst weather.
The very best energy saving doors and windows are certainly not cheap but should represent a sound long-term investment in terms of financial savings and improved comfort. As an added bonus, they should also add value to a property making this a win-win-win situation.