Nicolas Tye’s Hertfordshire barn sports a completely glazed gable end that ensures natural light is not a problem If there is a single rule that will lead to a successful design scheme for a residential barn conversion, it is to be ‘true to the building’, in other words to ensure that the barn retains its essential character and form, and does not simply get turned into a house.

If this simple philosophy is applied to every aspect of design, from window and door treatments, to internal subdivision, the project should not go far wrong and should also be in line with the requirements of the local planning authority.

Walls

Existing exterior walls, be they in stone, brick or timber, should be repaired on a like-for-like basis.

Brick or stone walls will invariably be of solid construction (no cavity), and so the addition of insulation necessary to meet Building Regulations Part L will need to be to the internal face of the external walls.

Leaving some sections of the brick or stone fabric exposed internally can be a desirable design feature; however, because of insulation requirements, it is usually easier to achieve this with internal partition walls — although it may be possible to clad some parts of the inner face of the exterior walls with brick or stone, forming an insulated cavity wall which can be left as a feature.

New partition walls could be built in matching brick or stone and left exposed, but an alternative, and an increasingly popular design ethos, is to use contrasting materials for all new structures and to create a clear distinction between old and new.

To achieve a seamless blend between original and repairs/alterations, it may be possible to repoint the whole wall, using lime mortar to retain breathability, and ensuring that removing the original mortar is kept to a minimum.

Timber frame barns present less of a problem for converters, especially in terms of insulating the building envelope. The existing cladding – usually timber – can often be removed, and a layer of insulation added in between and over the frame, plus a breathable damp-proof membrane. Where possible, salvage and reuse as much of the original cladding, and make up balance using like-for-like materials.

Where the original sole plate and lower section of the wall studs are badly damaged by rot or infestation, it may be possible to cut back the damaged timber and introduce a new sole plate at a slightly higher level, and to raise the plinth wall.

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ABOVE: Minimal intervention – The gable wall of this barn house, designed by Andrew Shave (01449 678628) has been glazed — much better than rooflights puncturing the charming roof. The extension has been kept simple, too, in a lean-to style.

Roof

The roof is the predominant feature of a barn. In most cases it will be necessary to remove the existing roof covering to allow for roof repairs or alterations, and the addition of insulation and membrane to improve weather- and air-tightness.

Insulation can be applied between and beneath the rafters, but where the rafters are made from interesting timbers, and considered worth leaving exposed as an internal feature, it will be necessary to insulate between and over them. This will raise the height of the roof by approximately 100mm.

Part of the charm of a barn conversion can be the irregularity of the roof shape where the original timbers may have bowed, twisted and warped over time. Although evening out the roof will help the roof covering sit flush and weathertight, a completely symmetrical new roof, laid with replacement tiles, can lack character. With care, the roof can be repaired but the undulations carefully maintained.

Dormer windows are not usually appropriate other than where existing, so any new window openings in the roof will be rooflights, and in most instances metal conservation-style rooflights which sit flush with the line of the roof. Too many roof – lights usually looks wrong, and it is best to keep them on the less important elevations.

It may also be possible to introduce a larger area of glazing on minor, less prominent elevations, using a bespoke rooflight system, or by glazing a section of the roof between the existing rafters.

Roof Covering

Vernacular roofing, such as limestone or sandstone tiles, local slate, thatch or local handmade clay tiles, is often an intrinsic part of the character of a barn. It is, therefore, worth salvaging as much as possible of this material and sourcing replacements to make up for any missing material.

Conservationists prefer the use of new material for replacement, as they believe that using salvaged roof coverings encourages the market for stripping other farm buildings – not always legally – which could in turn lead to their demise.

Where new and original roof coverings are mixed together, the original material can be used on the main ‘public’ elevations and the new material on less prominent, minor roof planes, or alternatively on outbuildings. Like-for-like replacement will often be a requirement on a listed building, but for less sensitive situations planners may be more flexible, especially where the material is very expensive or unavailable.

The way the roof is detailed is also an important part of its character, so take photographs and put the roof back as it was, avoiding modern details on verges, valleys and ridge and bargeboards — a breathable roofing membrane will provide adequate ventilation without the need for modern soffit or ridge vents.

ABOVE: Extending in sympathy – Extensions to barn conversions require careful design. Here an oak frame garden room has been added to one end of a stone barn in Carmarthenshire. (Architect David Thomas, 01545 590311).

Windows, Doors and Openings

On the main elevations, window and door openings will often be restricted to those that already exist. On secondary elevations some additional window openings and doorways may be allowed.

If a new opening is to be inserted, sympathetic proportions and detailing should be used, following existing patterns on the building, or other similar farm buildings in the area. In some instances, subject to careful design, new openings could be contemporary in style, though different local planning authorities will take different views on this. For instance, replacing some sections of horizontal timber boarding with clear or translucent Perspex, or glazing part of a gable elevation, in between the timber studs.

Joinery

Windows and doors need to be simple, robust and functional in style. Setting the windows back into the walls also helps to maintain the shadow lines of the original openings and limits reflections.

Existing openings are often filled only with timber shutters or doors, or sometimes with timber slats, and are often intended to provide ventilation as much as daylight.

If there are any original windows left intact, then it is worth considering salvaging and repairing these, or at least using them as a template for replacements. If there are no surviving windows, look at local farm buildings in the vicinity for clues as to the tradition. Off-the-shelf windows are unlikely to be suitable for size or design.

Narrow ventilation slits are common in agricultural buildings in some areas, and these can be glazed with a fixed doubleglazed unit. Other openings can also be fitted with fixed glazed units, as these may read as unaltered open voids.

Many barns, especially threshing barns, have a large floor-to-eaves cart door entrance at one side, and a smaller exit on the opposite side of the barn. The treatment of this opening – invariably the single biggest opportunity to introduce light to the interior – is one of the major design considerations for such a conversion. A functional design is best, such as glazed doors and fixed sidelights, with a strong vertical emphasis and fixed-frame sections.

Frameless glazing is an option that can be used to fill even the largest opening and – when set well back into the opening – can be unobtrusive.

Barn doors are usually utilitarian, constructed from vertical planks of timber. Proportions are usually sturdy and the outer frame section wide and solid. New doors should follow this pattern with the same finish used for doors and windows. Door furniture and other ironmongery items such as hinges should also be utilitarian.

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