Twenty years ago, virtually everyone building a new home or an extension used timber windows. They arrived on site as bare frames, with just a base coat of stain applied to them. These frames were then fixed into the walls as the building went up, and the glazing was carried out weeks later, usually just before the scaffolding was taken down. Sometimes it got overlooked and ended up being done off a ladder a week or two later. Back then, the glazing was just a single pane: anyone fitting double glazing would have had to be building an eco-house. After the glass was fitted, the sole question was whether to paint or stain the frames.
Meanwhile, over in suburbia, things could not have been more different. There a replacement window boom was in full swing. Replacement windows were almost always plastic — technically uPVC. These windows sold themselves on adding value, comfort, efficiency (by virtue of being double glazed) and offering a maintenance-free product.
Unlike the new build market, where designers and builders were all used to working with standard openings into which manufactured frames could be easily fitted, the replacement window manufacturers were all producing made-to-measure products, which made them rather more expensive on a like-for-like basis, and thus effectively kept them out of the new build market. So the two markets, new build and replacement, remained more or less separate.
Changes To Building Regulations
However, a change in the Building Regulations in 1990 at last made double glazing mandatory in new builds and extensions and much of the cost advantage enjoyed by the timber window suppliers vanished overnight. For the timber window manufacturers, it got worse still. It turned out that fitting double-glazed sealed units into bare frames on site was a distinctly hit or miss affair and soon the NHBC, the housebuilders’ main warranty provider, was swamped with complaints from angry new homebuyers about their windows misting up, only to find out that the NHBC warranty didn’t even cover glazing defects. Ouch.
Not surprisingly, the major housebuilders abandoned timber and switched en masse to pre-glazed plastic windows. It was a move many of their customers approved of in any event, as they liked the idea of maintenance-free windows. Manufacturers such as Speedframe then set up shop to cater for this new market and started to make plastic windows in long production runs, designed to slot into the standard opening sizes beloved of the UK housebuilding industry.
NHBC To The Rescue
But all was not lost for timber windows. In 1998, the NHBC at last brought glazing failures within their warranty scheme, but with some very strict conditions. No longer would they tolerate sloppy glazing-off-a-ladder-with some- putty stuff, but insisted that glazing should be housed correctly in the frame and that the bottom rail should be drained and vented, to avoid moisture build-up. By far the easiest way to do this was to glaze in the factory, not on site, and this was the catalyst to change the way timber windows were supplied.
You can still build timber window frames in the old manner, but it’s not to be recommended. As Andrius Valatka, Director of Privett Timber Windows says, “90% of the problems we have with glazing units stem from the 10% of our market that still uses on-site glaziers. Misting up on factory-glazed windows it’s virtually a thing of the past.” So rather than having two different window industries, as we did in the 1980s, we now tend to have all windows supplied the same way.
However, factory glazing is still not without its issues. The product is essentially pre-finished before it arrives on site and so is liable to damage in transit, as well as during and after fitting. It makes sense, therefore, to fit the windows in as late as possible in the build programme, ideally after the external cladding is complete. This has led to the use of various sub-frames which are built into the wall and act as housing for the windows, often allowing them to be fitted from the inside.
So bear in mind that there is a lot more to it than choice of material. Ask questions about how the windows are fitted into your walling system, and at what stage they are best fitted. Do they use proprietary sub-frames and if so are they compatible with your build methods? Generally made-to-measure windows are between 20-30% more expensive than ones made for standard British openings.
Spot the Difference
A keen observer will spot that the left-hand casement window (in both pictures) is the timber version (from Privett Timber Windows) and the right is of PVCu. The finer glazing bars, equal site-lines and slim sections are the biggest giveaway.