What Will it Cost? - External Joinery

Your choice of windows and doors plays a significant role in deciding how your house will look - and how much it will cost to build.

As you build a house up and out of the ground, your concerns are really two- fold. Firstly, that the work should be of reasonable quality; secondly, that it should cost as little as possible. However, once the superstructure emerges from the ground, a world of choice opens up and there are many options available for you to select from. External joinery – doors and windows – is one of the biggest and potentially most expensive. Typically, windows and external doors will make up between 5% and 8% of the total build costs.

What do you have to consider when sourc­ing doors and windows, besides cost and quality?:

• Style
• Buildability
• Maintenance issues
• Environmental issues
• Energy efficiency
• Security (including fire escape windows)

Naturally, each of these comes with its own cost implications, but we’ll start by looking at how the windows and external doors fit into the external wall cost matrix. The Building Regulations are a useful guide here: Part L (England and Wales) suggests that the area taken up by windows and doors should be no more than 25% of the total floor area — and advises against an area of less than 20% due to the increased requirement for artificial light­ing. Our 200m2 benchmark house could, there­­fore, have around 50m2 of doors and windows without causing any problems. In fact, it has just 40m2 (20% or 1:5 ratio): this sounds mean, but in reality it looks fine. Most vernacular British house designs will easily meet the 1:4 ratio required by the Regulations.

External walling costs, minus joinery, are bet­ween £75 and £125 per m2, the variation being largely a function of the type of wall cladding chosen. In comparison, joinery costs start at £100/m2 and head up towards £400/m2 at the top of the range. So these glass-filled holes in the walls are very much more expensive than the walls themselves and, from a costing point of view, it makes good sense to stick to designs where the amount of glazing is minimised. Whilst more modern designs featuring large glazed areas may appeal to your taste, they won’t do much for your bank balance. This simple fact explains why 98% of British housing looks so conventional and why the other 2%, usually designed by architects, costs so much more.

The Cost Matrix

The relationship between external joinery and house floor area, referred to in the Building Regulations, also provides a useful yardstick to budgeting. In all but the most unconventional designs, the joinery area will be between 15% and 25% of the floor area of a house. If you have plans drawn, you can measure the area of joinery, but if you are still at the pre-plan stage, you can use 20% or a 1:5 ratio as a yardstick. Use the price of the common 1,200mm x 1,200mm (1.44m2 area) size win­dow, multiply this by your internal floor area (in m2) and divide the result by six and you have an approximation of your external joinery costs. Thus, if your floor area is 150m2, and your win­dow choice costs around £250 for a 1,200mm x 1,200mm double casement, then you can anticipate an overall cost for external joinery of around £6,250.

If you are trying to build economically, you don’t want joinery costing much more than 6% of your overall build budget. Thus if you are aiming for a build cost of around £700/m2, you want to select joinery (including glazing) that costs under £250/m2 or £350 for a 1,200mm x 1,200mm double casement. It’s easy to specify much higher specification windows but, be warned — they are budget busters.

Note that the prices referred to in joinery catalogues are all list prices. As a self-builder with some substantial spending power, you should be able to get 30%, sometimes 40%, off these prices, as would a trade buyer. Ultimately, the best way to get a price is by quotation, but sometimes you are already too far down the planning route by this stage to switch to a cheaper option.

Plastic or Timber?

In terms of cost, there’s not much in it. You can purchase basic unglazed timber windows from any builders’ merchants and fit, glaze and paint them on site. The cost of the timber joinery and the glazing combined works appears to be slightly cheaper than the basic factory-glazed PVCu window and doors. However, if you add in realistic labour costs, the PVCu option is the cheapest, at around £120/m2.

There are other issues to be considered, notably maintenance requirements (a plus for plastic), green credentials (a plus for timber) and style (a matter of taste!). Note, however, that if you want PVCu windows to look at all like timber ones, and to be finished with a woodgrain effect, the cost escalates by around 50%. There is an equivalent cost uplift in timber windows if you decide to select a hardwood rather than the standard treated softwood.

One of the preferred options for self-builders is to specify timber windows with a weather-resistant exterior covering, typically plastic or coloured aluminium. There are a number of businesses catering to this market, though they are usually sourced from over­seas. Costs tend to be relatively high, how­ever, at around the £300-£400/m2 mark, depending on the other specifications.

Off the Peg or Bespoke?

Most British house designers are well versed in the modular sizes much loved by our joinery manufacturers. By sticking to certain pre-defined heights, widths and styles, such as 1,200 x 1,200mm, joinery can be turned out in large volume with consequent economies of scale. This, by and large, keeps the prices down. Refer to a catalogue from one of the major joinery manufacturers such as JELD-WEN, Magnet or Premdor, and you can establish what the basic sizes tend to cost. As you head up the price scale, the differences become less marked and if you want anything unusual, in terms of dimensions, styling or finish, then a bespoke manufacturer may well be as cost effective as a major joinery manufacturer, and, in all likelihood, much quicker to deliver.

Styles

The basic British window style – the side opening casement – is by some way the cheapest. Fully glazed and finished costs start at around £120/m2, whether softwood or PVCu. The further you get away from this plain, unadorned style, the more the window costs. Sliding sash windows, fully finished, work out at upwards of £300/m2.

External Doors

Surprisingly, there are more choices of materials for external doors than windows. As well as timber and plastic, there are large numbers made from steel and GRP (glass fibre). Developers tend to like steel and GRP because they are pre-finished: again this is reflected in an apparently higher initial cost which is clawed back by shaving off labour fitting costs. Prices seem to be very similar, on a pro-rata basis, as windows so that an external door plus frame, at around 2m2, starts at £300 and a patio door or a set of French doors are about double this. Note that the frame is conventionally purchased and installed separately from the door, though there is a trend towards using pre-fitted doorsets.

About These Articles

This series is based on a typically constructed, 4/5 bedroom house, with an internal floor area of 200m2 (2,150 sq.ft.) plus an integral garage. Its raw build cost (that is only labour and materials) is £135,000. Professional fees, contractors’ overheads and profit, insurances and warranties would all be in addition to this. The raw build cost presumes a straightforward job finished to a fairly basic standard; the sort of finish you would expect from a professional housebuilder. In this series we will be looking at how the costs break down for all the various component parts of a house, and looking at the cost implications of choosing alternatives. This house is also featured in Mark Brinkley’s latest book, The Housebuilder's Bible (6th edition).

OTHER COST GUIDES:

• Getting out of the ground
• Insulation
• Constructing Walls
• Installing Services
• Roofing
• Internal Finishes