The Complete Guide to Indoor–Outdoor Living

At its simplest, indoor-outdoor living is the removal of as much visual and physical barrier as possible between an internal room and an adjoining outdoor space, while keeping the building weathertight, secure and thermally efficient. It is achieved through four linked elements: the opening system, the threshold, the glass, and the outdoor space itself. Weakness in any one of the four undermines the whole idea — a beautiful slider onto an unusable, shaded terrace is not indoor-outdoor living, it is just a large window.

Core elements

Opening system, threshold, glass specification, outdoor space design

Common failure point

A high or poorly drained threshold that undermines an otherwise good door

Climate consideration

Cumbria's rainfall and wind exposure make shelter and drainage as important as the glazing itself

Sliding doors, bifold doors and fixed glazing with a single door each suit different patterns of use, and the choice should be based on how the space will genuinely be used rather than which looks best in a photograph.

A wide glazed opening needs to sit within a considered elevation, not just be inserted into a wall. Consider the glazing as part of a full-height composition: does it align with windows above, with a rooflight strip, with the structural beam it sits under? Extensions where the door, the fixed glazing beside it and the roof glazing were drawn together as one elevation study consistently look more resolved than those specified piece by piece.

• Draw the full internal elevation, including joinery, before finalising glazing widths and heights
• Keep a consistent frame sightline width across all glazed elements on the elevation
• Consider whether full-height glazing to the underside of the structural beam, rather than a filled-in fascia, gives a better result

This is the detail most likely to be under-designed, and the one that most affects daily use. A flush or near-flush threshold is achievable with most premium sliding and bifold systems, but it depends entirely on getting the floor build-up, external paving level and drainage right — decisions made by the groundworker and structural engineer well before the glazing is installed.

1. 01Set finished floor levels togetherInternal finished floor level, external paving level and the sill detail need to be agreed as one drawing, not decided independently by different trades.
2. 02Choose a low-threshold sill optionAsk your glazing supplier for the low-threshold or flush sill version of the system, and check it meets Part M and drainage requirements for the specific installation.
3. 03Detail the external drainageA linear channel drain set just outside the threshold, falling away from the building, prevents water sitting against the sill in heavy rain.
4. 04Consider a covered transitionAn overhang, canopy or recessed terrace immediately outside the door reduces the amount of rain blowing directly onto the threshold — genuinely useful in an exposed Cumbrian garden.

Large areas of glass change how a room performs thermally far more than an equivalent area of wall, in both directions — heat loss in winter and solar gain in summer. Getting the glass specification right is what allows a heavily glazed room to actually be comfortable to sit in through the year, rather than a space that is cold in January and uncomfortably hot in July.

• Specify a low U-value glazed unit (argon-filled, warm-edge spacer, low-e coating) as standard on any large glazed area
• Add solar control glass on south or west facing openings to manage overheating, particularly where there is limited external shading
• Consider triple glazing on very large or very exposed openings, where the extra cost is offset by a real comfort improvement
• Discuss acoustic glass if the outdoor space faces a road or other consistent noise source

Indoor-outdoor living depends as much on the quality of the outdoor space as on the glazing. A terrace with no shelter from wind or rain gets used far less than one with even modest protection. An overhang, pergola, or recessed corner of the building immediately outside the glazed opening extends the number of days and hours the space is actually usable — which, in Cumbria, is the difference between a feature used occasionally and one used most of the year.

A wide glazed opening is, from a security perspective, a large potential entry point, and it is worth specifying accordingly. Multi-point locking, laminated glass in the lower panes and PAS 24 rated hardware are all sensible on ground-floor sliding and bifold doors, particularly on more secluded elevations.

Most indoor-outdoor projects take one of two approaches: a single wide opening as the room's main feature, or a series of smaller openings distributed around a room. Neither is universally better; the right choice depends on the room's orientation, the shape of the outdoor space and how the room is used.

• A single wide slider or bifold suits a room with one clear best view or one usable terrace
• Distributed openings — a corner window plus a separate door, for example — suit irregular gardens or rooms that need cross-ventilation from two directions
• Combining a large fixed glazed wall with a smaller separate opening door often gives the best of both: an uninterrupted view and simple ventilation without opening the whole wall

“The best indoor-outdoor rooms we see are usually the ones where the door was the last decision made, not the first — proportion, threshold and orientation had already been resolved.”

Sliding and bifold doors used daily need slightly more attention than a fixed window: tracks need to stay free of debris, and running gear benefits from an annual check. Aluminium systems generally require less maintenance than timber in an exposed, wet climate, which is worth weighing against the different visual character each material offers.

• Clear tracks of leaves, grit and debris regularly, particularly after autumn
• Have running gear and seals checked annually, ideally as part of a wider home maintenance routine
• Choose a low-maintenance frame material (aluminium or a well-finished composite) for openings used most frequently