Ten Things To Look For In Good Quality Windows


Just a Quote: Expert advice without the hard sell

PVCu Replacement Windows

There are many factors to consider when choosing which PVCu replacement windows to install and we have chosen what we feel are the most important ten. One absolutely vital factor which is purposely missing from this list however is the installer. Just a Quote offers unbiased advice on this website regarding the technical aspects and characteristics windows and doors which should be taken into account. But only by visiting you, carrying out a survey and listening to your individual requirements can a surveyor guide you in terms of the correct installation company for you to use for your new PVCu replacement windows.

The customer service you receive from your installation company is paramount but as far as the product is concerned, the top ten things to look for in good quality windows which we have chosen are: –

{tab=1. Reinforced 70mm Profile}

PVCu replacement windows - cross sectionPVCu replacement windows with 70 mm frames

The 70 mm dimension refers to the width of the frame from back to front. Not only does this suggest a stronger window frame when compared to, say a 60 mm profile, but your existing wooden windows that are to be removed are also about 70 mm (actually about 3 inch thick timber, planed to just less than that). When the old windows are removed and 70 mm PVCu replacement windows are installed, the new frames will meet up with the old mastic line on the brickwork which can be then covered with new silicone sealant.

Replacing 70 mm or 75 mm wooden windows with new 60 mm frames would leave an unsightly gap between the new frame and the old mastic, which would still show. Another advantage of a 70 mm PVCu replacement windows frame is that it can take a wider insulating glass sealed unit – and generally speaking, the wider the sealed unit, the better it is at insulating your home.

Reinforced frames in PVCu replacement windows

Metal reinforcement inside PVCu replacement windows should always be included in the vertical sections of the frame, though profile extruders and window fabricators will have their own recommended specifications for reinforcement of their own products. The larger the window, the more important internal reinforcement becomes, in order to support your PVCu replacement windows and reduce any movement, although reinforcing very small PVCu replacement windows has little effect on durability and performance.

Dark coloured frames such as woodgrain effect PVCu replacement windows should always be fully reinforced as the darker material can expand and contract at up to four times the rate of white PVCu replacement windows and the internal reinforcement is designed to reduce this. Finally, we have suggested the figure of 70 mm because most of the modern, more advanced profiles for PVCu replacement windows have that dimension from back to front. We wouldn’t recommend a narrower profile than 70 mm but a slightly wider one could also be considered.
{tab=2. Fully welded frame}

PVCu replacement windows with oak effect framesFully welded PVCu frames on PVCu replacement windows

When wooden windows are manufactured they are normally glued and or screwed together and early PVCu replacement windows were manufactured in a similar way, with mechanically fixed joints. Modern PVCu replacement windows should be fully welded together for extra strength, not just at the corners but also where the transoms (horizontal bars) and mullions (vertical bars) meet the outer frame. The very best PVCu replacement windows have all four corners welded at the same time to ensure that every corner is exactly 90º. This can only be achieved by using an expensive 4 headed welder, for square or rectangular outer frames and sashes.
{tab=3. Internal glazing beads}

Internal beading can make PVCu replacement windows more secure

Traditionally, when glass was installed in wooden windows, it would be held in place with either putty or a wooden bead nailed into place on the outside of the frame. Early PVCu replacement windows also had external beads to hold the insulating glass sealed units within their frames. And because the glazing beads were on the outside of the window they were easily removable by burglars, who would simply take out the bead, lift the sealed unit out and climb through the opening.

Products such as double sided tape to hold sealed units into place are often used to improve security in externally beaded frames but ask yourself, if a sealed unit was broken and the installer returned to replace it, would he remove the unit from the outside? Yes?….then so can a burglar.

Modern PVCu replacement windows should all be internally beaded which means that the glass sealed units are installed from inside and can therefore only be removed from the inside. Burglars do not like to invite attention with the noise of breaking glass, so homes with internally glazed PVCu replacement windows are less likely to be successfully burgled than those with externally glazed PVCu replacement windows.

Externally beaded PVCu replacement windows are cheaper to manufacture

The only valid reason for an installer supplying externally beaded windows these days is that are cheaper to manufacture. Internally glazed PVCu windows go through a manufacturing process known as reverse butt welding which is more time consuming and therefore more expensive than manufacturing externally glazed windows.
{tab=4. Ovolo shaped frame}

Sculptured PVCu replacement windows are more attractive

Flat or chamfered glazing beads and angled frames look like false imitations of wooden windows and only go to exaggerate the plastic look of PVCu replacement windows. Ovolo shaped and sculptured frames and beads can present a beautifully balanced and aesthetically pleasing appearance which more closely resembles the architecture of traditional wooden products. However, ovolo and sculptured PVCu profiles are slightly more expensive than angular ones.

Which shade of white for your PVCu replacement windows?

As regards the colour of white PVCu replacement windows, there are six recognised shades of white within the PVCu window industry. They range from brilliant white to an off-white almost cream shade of white.  It is important that where trims are used around a window or door, the same colour white is used for the frames and the PVCu architraves, D-moulds and quadrants.

The problem is multiplied when conservatories are erected with a different shade of white PVCu used for the windows and doors, compared to the roof spars, gutters and trims. Generally speaking, from our experience bright white PVCu replacement windows look better than off-white ones, which after a while can look as they have faded.
{tab=5. Multi-point locking}

PVCu replacement windows with a shoot bolt locking mechanismAdvanced multi-point locking systems on PVCu replacement windows

Locking systems on PVCu replacement windows have progressed over the years from simple cockspur handles (where a spur on the handle overlaps the inside of the frame), to espagnolette systems (where the handle operates a bar with bolts on which slide into keeps) and now to shoot bolt locking mechanisms more akin to those on doors.

The very best locking systems on PVCu replacement windows incorporate several types of lock on the same sash which operate in different ways, to effectively lock each sash to the outer frame around its full perimeter. All locking systems should also include a night vent facility which enables the sash to be locked in a slightly open position to allow for ventilation without compromising security as much as opening it fully would.

{tab=6. Insulating Glass Unit}

PVCu replacement windows - cross section of an insulating glass sealed unitDouble glazing in PVCu replacement windows

No-one would consider single glazed PVCu replacement windows and doors these days, in fact it is contrary to Building Regulations to install them in residential properties now.

The term double glazing originates from the introduction of insulating glass sealed units formed from two sheets of glass, separated by a spacer bar around the edge. The glass unit is then sealed to prevent air from getting in from outside as this would bring in water vapour which can give rise to condensation between the two sheets of glass.

The width of sealed units in PVCu replacement windows

Generally speaking, the wider the gap between the two sheets of glass, the better the insulating properties of the sealed unit are (though exceptionally wide sealed units can encourage convection within the unit, which reduces its effectiveness). Common consensus within the replacement window industry is that a 28 mm sealed unit (normally consisting of two sheets of 4 mm glass and a 20 mm spacer bar) is the most efficient combination. Sealed units which are narrower than 28 mm are only normally used by installers to save money, or because narrow PVCu or aluminium frames won’t take a 28 mm unit.

Triple glazing in PVCu replacement windows

Advancements in window technology, particularly in Scandinavia, have involved triple glazing but the benefits for use given the climate in the United Kingdom often do not justify the extra cost. Another issue with triple glazing is that the extra weight of the glass in each opening sash means that the overall size of sashes needs to be reduced, which could compromise the use of an opening window as an effective fire escape.
{tab=7. Low Emissivity Glass}

PVCu replacement windows - illustration of the effect of Pilkington k glassLow e glass keeps your home warm by reducing the amount of heat lost through radiation

Low emissivity glass, or low e glass as it is referred to, consists of a coating on the surface of the inner pane of glass facing into the cavity of the insulating glass sealed unit (IGU). Heat from your home is absorbed by ordinary glass, which then radiates (or emits) it onto the colder, outside sheet of glass, from which it is lost.

The low emissivity coating is a poor radiator of heat, so the heat absorbed by the coated glass does not travel across the air gap to the outer, cold pane. Instead the coating reflects some of the heat back into the room, so that it isn’t lost. In this way, low e glass reduces the amount of heat lost from your home by way of radiation.

Illustration showing how low emissivity glass works – courtesy of Pilkington™, manufacturer of Pilkington K™ glass
{tab=8. Argon-filled Units}

PVCu replacement windows - showing where a sealed unit is filled with argon gasArgon-filled sealed units keep your home warm by reducing the amount of heat lost through conduction

Although air is a good insulator (as the use of Thermos™ flasks illustrates), the density of argon is greater than that of air and so filling the gap between the glass panes of an insulating glass sealed unit (IGU) with argon improves the window performance. It does this by reducing the amount of heat lost through the glass by way of conduction and also reduces the effect of convection within the IGU.

Argon is present in the air that we breathe

After nitrogen and oxygen, argon is the third most common gas in the Earth’s atmosphere, making it more common than carbon dioxide. Argon is an inert gas which means that it does not react with anything else, in fact the word argon is derived from the Greek word ‘apyov’ meaning lazy or inactive. Argon is also colourless, odourless and non-flammable. Another advantage of using argon in an IGU is that the inner sheet of glass remains warmer and so should not result in as much condensation as there would be if the sealed unit was filled with air.

An insulating glass sealed unit showing the entry point for the introduction of argon gas
{tab=9. Warm Edge Spacer Bar}

PVCu replacement windows - warm edge spacerWarm edge spacer bars in a sealed unit can reduce heat loss and condensation

The term double glazing originates from the use of insulating glass sealed units (IGU) formed from two sheets of glass, separated by a spacer bar and then sealed. The spacer bar is traditionally extruded aluminium with a silicone desiccant inside (to absorb any water vapour which happens to be in the air inside the factory at the time of manufacture). Aluminium though, is a good conductor of heat – and cold – and is therefore inefficient at preventing heat loss around the edge of the IGU.

A warm edge, or thermal break spacer reduces the heat lost around the perimeter of an IGU and some types can provide almost 1,000 times more thermal insulation than aluminium spacer bars, thus improving energy efficiency. With an aluminium spacer bar, the edge of the inner pane of glass within an IGU can be quite cold, which can result in condensation around its perimeter; this is vastly reduced by using a warm edge spacer bar.

Showing how a warm edge spacer bar in an insulating glass sealed unit reduces heat loss when compared with an aluminium spacer bar – courtesy of Edgetech™
{tab=10. ‘A’ Rated Windows}

PVCu replacement windows are rated for energy efficiency in a similar way to household appliances

Over 25% of the heat in your home escapes through windows and doors, so energy efficient PVCu replacement windows not only keep your home warm, they are also good for the environment. The Government’s commitment to reducing energy emissions combined with the potentially harmful effects of global warming are central to new legislation requiring that PVCu replacement windows meet minimum standards of energy efficiency.

Window Energy Ratings are based on a scale of A to G in exactly the same way that household appliances such as refrigerators are rated – A being the most efficient, G being the least efficient.  PVCu replacement windows in domestic properties must now achieve a minimum of a C rating to satisfy current Building Regulations. An ‘A’ rating can only generally be achieved for a window when it includes an insulating glass sealed unit (IGU) which includes low e glass, argon and a warm edge spacer.

Window Energy Ratings take into account the following factors: –

• The effectiveness of PVCu replacement windows in preventing heat loss from your home.

• The amount of light and heat a window allows in from the sun, known as solar heat transmission or solar heat gain.

• Air leakage through the seals of a window.

• The proportion of the total window taken up by the frame.

Typical Window Energy Rating (WER) certificate for a PVCu casement window. This shows an ‘A’ rated window certificate with an Energy Index of zero, courtesy of Dempsey Dyer