During earlier stages Marble will have either fitted the window frame or fitted a wooden dummy frame if there was a risk of the real thing getting damaged.

Now that the roof has been installed the risk of a new window being broken accidentally is greatly reduced. It is important to fit the new windows and doors before knocking through into the house so that the house remains weatherproof and secure.

There is an extensive range of windows and doors to choose from, but quirky designs or giant glass panels have a habit of being rejected by planning permission as they are often very energy inefficient and unsuited to the house’s original character. The basic rule is that it is best to pick a design similar to the existing style used on the property.

In terms of materials the frames range through softwood, hardwood, UPVC, Painted aluminum and galvanized steel. Most are available in or can be painted nearly any color desired. In terms of which is most economical, timber can surprisingly come out on top as if looked after can last 30 to 40 years and it is possible to repair them unlike UPVC.

The most common type of window is hinged, also know as casements, where they pivot is described in the name such as top hung, side hung or middle pivot. Windows which do not open are called fixed lights and other types of window include sliding and rotating.

The most cost effective way to go is to stick with standard factory made windows as opposed to custom windows which coust around 3 times as much. Standard window heights in millimetres are 450, 600, 750, 900, 1,050, 1,200, 1,350 and 1,500. Standard window widths in millimetres are 488, 630, 915, 1,200 and 1,770.

Mass produced timber windows come with locks as standard and can be pre-glazed or stained so they are ready to go when on sight. Any window selected needs to comply with building regulations for thermal insulation and ventilation.

Other things to take into account when choosing windows include:

• Are they fire safe? (easily unlock-able and big enough to fit through)
• Are they secure? (hinges on the inside, good quality lock)
• Are they child safe? (upper floors should have child-proof locks and safety glass)
• Will they infringe on a neighbors privacy?

Window Fitting

This is usually thought of as a small thing but can drastically change the look and usefulness of an extension. The basics are that south-facing windows are favorable and windows should be aligned by the top of the frame.

Things to check when fitted include:

• Are the sills set back from the outer underside of the front edges with a drip groove?
• Do the window sills come out far enough that dripping rainwater does not run down the building’s front?
• Is there a damp proof course or cavity closers for all wooden windows?
• If the wall is tiled or cladded, is there lead flashing under the sill to prevent water penetration?
• Are the windows completely level?
• Does the positioning of the windows match the designs completely?

Door Fitting

When installing doors it is important to consider which way the door should open, left or right? in or out? if the doors are to swing outwards it might be a safety risk for people walking past if the door is swung open.

Common door sizes are given in inches 78 by 33, 78 by 30 and 80 by 32. For UPVC exterior doors 82 by 36 or 82 by 47 for French doors.