French Doors near you

For most houses, turning a rear window into French doors is permitted development. The Planning Portal's guidance on doors and windows treats the insertion of new windows and doors that are of a similar appearance to those used in the construction of the house as not requiring permission. That wording is about appearance, so French doors in a style and material consistent with the rest of the house on a rear elevation are the straightforward case.

The exceptions are specific. The Planning Portal states that where new windows are in an upper-floor side elevation they must be obscure-glazed and either non-opening or more than 1.7 metres above the floor level, which rules out most upper-floor French doors on a side elevation without permission. It notes that a new bay window will be treated as an extension and may require permission. In a listed building you will need listed building consent for any significant works, internal or external. And in a conservation area, national park or area of outstanding natural beauty there may be additional restrictions, with councils able to make an Article 4 Direction withdrawing permitted development rights.

Flats and maisonettes do not carry the same permitted development rights as houses, and a leaseholder altering an external wall will almost always need the freeholder's consent as well as any planning consent. Front elevations are also more sensitive than rear ones almost everywhere. A ten-minute call to the council's planning duty line, before ordering doors made to measure, is the cheapest insurance available on this job.

Forming a new opening or enlarging an existing one is structural work, and the support over the doors has to be sized for what it carries rather than copied from the neighbours. That is separate from, and additional to, anything the doors themselves must achieve, and it is the part of the job that needs designing and inspecting properly. Work with an installer who treats the lintel as an engineering question rather than an item on a price list.

The rule that surprises people sits in Approved Document L paragraph 10.5. If a window is enlarged or a new one is created, either the area of windows, roof windows, rooflights and doors should not exceed 25 per cent of the total floor area of the dwelling, or, where it does exceed 25 per cent, compensating measures should be taken to improve the energy efficiency of the dwelling. French doors replacing a modest window add a good deal of glazed area, and on a house that has already gained a large rooflight or a glazed extension the cumulative figure can pass the threshold.

The doors themselves are controlled fittings, and Table 4.2 splits doors by how much glass they carry. A door with more than 60 per cent of its internal face glazed must meet a maximum U-value of 1.4 W/(m²·K) or a Doorset Energy Rating of Band C minimum; other doors must meet 1.4 W/(m²·K) or Doorset Energy Rating Band B minimum. A pair of French doors is comfortably in the first category, so it is the Band C line that applies if the energy rating route is being used.

In a great many British houses a habitable room's window doubles as its emergency escape route, and replacing that window changes something the fire strategy depended on. Approved Document B Volume 1 sets out what such an opening must do. Windows providing emergency escape should have an unobstructed openable area with a minimum area of 0.33m², a minimum height of 450mm and a minimum width of 450mm, where the route through the window may be at an angle rather than straight through, and with the bottom of the openable area a maximum of 1100mm above the floor.

It adds two practical provisions that matter here. Locks, with or without removable keys, and opening stays with child-resistant release catches may be fitted to escape windows; and windows should be capable of remaining open without being held. People escaping should also be able to reach a place free from danger from fire, which is why an escape opening onto an enclosed courtyard or an inaccessible back garden is treated separately.

The good news is that a pair of French doors onto a garden generally makes escape from that room better rather than worse, because a full-height external door is a more generous exit than a window ever was. The trap is the reverse case: replacing an escape window with French doors that open onto an enclosed courtyard from which there is no way out, or doing the work on an upper floor onto a Juliet balcony where the opening is guarded. Raise the escape question with your building control body rather than assuming a bigger hole is automatically a better one.

Approved Document K identifies critical locations in internal and external walls and doors where glazing must be dealt with because of the risk of human impact, and a French door is glazed from close to floor level upwards, so essentially the whole of each leaf sits inside them. Requirement K4 is met in one of four ways: glazing that breaks safely, glazing that is robust, glazing in small panes, or glazing permanently protected by a screen.

For a French door in practice, the first route is the one taken, and the classification depends on the pane width. A glazing material is suitable for a critical location if it satisfies Class 3 of BS EN 12600 or Class C of BS 6206, or, where installed in a door or door side panel with a pane width exceeding 900mm, Class 2 of BS EN 12600 or Class B of BS 6206. Side panels flanking French doors are caught by the same rule, and are the element most often overlooked because they are not the door.

Approved Document K's fourth route is worth understanding so it is not misapplied. Glazing protected by a permanent screen does not itself need to comply with K4, but the screen must prevent a sphere of 75mm coming into contact with the glazing, be robust, and, where it protects glazing installed to help prevent people falling, be difficult to climb, with no horizontal rails. That is a genuine guarding element, not a blind, a grille or a piece of furniture placed in front of the door.