Loft Conversion
Updated: 2022-01-12

Uncertainty in the housing market, in the wake of the so-called “credit crunch” – not to mention stamp duty – means that many homeowners are unwilling, or unable, financially, to move to a larger property, even though they may have run out of room in their current home. The extra space they need, however, may already exist within their home. A loft conversion can be an excellent method of increasing the living space in a property, without the substantial expense, and stress, of moving home. Indeed, the cost of an average loft conversion is 66% less than that of moving to a property with one extra room, and the addition of what is, effectively, an extra floor – for use as a bedroom, a bathroom, a study, or a combination – may add 20%, or more, to the value of a home. Roughly 1/3 of newly built homes have a loft space that is suitable for habitation, and the actual cost of conversion will depend on the purpose for which the space will be used, its size, and the complexity of its construction. Do bear in mind, however, that a loft conversion is a significant undertaking, and professional advice is really a necessity. A professional architect, or builder, will be able to advise you on planning permission, building regulations and structural alterations – including any major work involving electricity, gas, or water – and the costs involved.

Types of Loft Conversion


A rooflight loft conversion – also known as a “Velux” loft conversion, after the leading manufacturer of roof windows, whose products have become synonymous with the conversion, itself – is usually suitable for a smaller loft space, perhaps intended to accommodate a single bedroom, or study, for example. Rooflights, or Velux windows, are installed flush with the existing roof line, so that major alterations are not required, thereby reducing disruption, and cost. The fact that the loft is not extended beyond the original line of the roof means that planning permission is not normally required, although a cursory check with your local planning department is always advisable, before starting any work. A rooflight loft conversion does, of course, rely on there being adequate headroom in your existing loft space, but does lend itself well to Victorian style houses – where other forms of loft conversion may be inappropriate – or houses where planning approval for other forms of conversion is required.


In all but the largest houses, the typical shape of the roof does not allow enough space directly beneath it for a useful, habitable room. A dormer loft conversion offers a popular solution to this problem, and involves the extension of the roof – possibly to the rear, front or side of your property, depending on planning permission – which creates not only extra headroom, but also extra width, and floor space, for your new room, or rooms. Dormer loft conversions are usually constructed such that they occupy the full width of a property – to maximize the available headroom – but may also be set back a little from the edges, on either side to maintain the balance between upper and lower storeys. A dormer loft conversion may have a traditional, pitched roof, a flat roof, or a so-called pentroof – in other words, a roof with a single pitch, or slope – depending upon its location, and design.

A rear dormer, for example, has a flat roof, and involves the removal of the rear roof slope, and the creation of a square, box shaped extension, built on the rear wall of the house, and up on both sides. This type of loft conversion creates substantial headroom, and floor space, allowing a choice of different possibilities, in terms of use, for a loft space. A rear dormer – which often does not require planning permission – is a possibility in many terraced, or semi-detached, properties, for example, and can be finished in tiles, or slates, to suit the character of your own property and surrounding properties. A so-called “hip to gable” loft conversion, on the other hand, involves the replacement of the “hip” of the roof – the sloping edge – with a gable end. The original hip end is removed and a gable wall is built in its place, so a hip to gable conversion inevitably involves significantly more work than other forms of loft conversion. This extra work, however, in reflected in the extra space created, and the newly created gable wall can be the ideal location for a window to illuminate the staircase to the loft space. Bear in mind, however, that this type of loft conversion may only be possible in areas where planning permission is not required. Dormers on the front, and side, roof slopes – for example, if you live in a semi-detached house with a hipped roof to the side – may also be a possibility, although these are generally smaller, and need to be in keeping with the character of your neighbourhood, in order to receive planning approval.


This is a popular method of loft conversion in properties with “London”, or “butterfly” roof. This type of roof – common in Georgian, and Victorian houses, characteristically in areas of London – is constructed in a “V” shape, with a central gutter that runs parallel to a raised parapet at the front. Typically, party walls – that is, walls built between adjoining properties, and common to both – rise above the highest part of the roof, itself, so that is has no ridgeline, per se. A Mansard loft conversion involves the replacement of the original roof structure – to the front, to the rear, or both – with a steeply pitched roof, and a face set at 70°, or so. Rooflight, or small dormer, windows may be fitted to the roof. Mansard loft conversion is also applicable in situations where the pitch of an existing roof is very shallow, and is likely to be preferable, from a planning point of view, in conservation areas, or area where there is a trend towards this type of conversion.

Suitability for Conversion

Although most modern homes – those built after, say, 1975 – are suitable for loft conversion, not all are, and there are number of checks that you need to make, perhaps in association with a professional advisor, before commencing work in this respect. Legally, a loft must afford headroom of, at least, 2.3 metres, or 7’6”, at its highest point. Highest point, here, means the apex of the roof, and the measurement is taken from the floor, or ceiling, boards below to that point. Even if you can stand, upright, at this point, you may well find that a dormer window, and careful positioning of a staircase, for example, maximises headroom, and floor space.

You also need to be confident that the physical construction of your loft is suitable, and adequate, for a loft conversion to take place. The loft roof, for example, may be constructed from “purlins” – wooden supports arranged diagonally, or vertically – or roof trusses, which are more common in modern housing. Roof trusses are much more difficult to convert than purlins, and, in many cases, the only solution is to replace the entire roof. Existing ceiling joists, too – often of the 4” x 2” variety – are not designed to carry the load imposed upon them by the use of the loft as a living space. They can, however, be supplemented by 6” x 2”, or larger, joists to form a new floor that is supported by the load bearing walls below. If you are performing a loft conversion in a bungalow, however, remember that you are effectively creating a second storey where none existed previously, and was never intended to exist. Most bungalows are built with no load bearing walls, internally, and it may be necessary to underpin both internal, and external, walls to provide adequate structural support for a loft conversion.

The other important consideration, of course, is access to, and from, your loft space once it has actually been converted. You need to consider, beforehand, if you have sufficient space on the floor below your loft to accommodate a staircase, of the dimensions stipulated by building regulations. The clear width of the stair must be, at least, 2’ for access to a single room, and 2’6” for access to more than one room. This is the clear width of stair that must be available, so remember to add on an inch, or two, to your measurement at either side, for the inclusion of a handrail. Ideally, a staircase should have a pitch of no more than 42°, and headroom of, at least, 6’6”.If the existing space below your loft is too narrow to accommodate a staircase, it may be possible to position it elsewhere, perhaps utilising a portion of another room, or a cupboard, for example. Other possibilities, if space is at a premium, of course, include a spiral staircase, or a ladder.

Heating & Plumbing Issues

A loft conversion is, obviously, positioned at the highest point of a house, and, during the summer months – as heat rises from the rest of the house – can become uncomfortably hot, and stuffy, if not adequately ventilated. You do, therefore, need to give due consideration to the size, and type, of windows that you install, so that heat can be dispersed effectively. By the same token, the warm air rising from the remainder of the house serves to heat the loft space, such that little additional heating is required. Any that is required may be supplied by a radiator, or radiators, connected to the domestic central heating system, or in the form of electric radiant heat. Electric radiant heat is economical, and controllable, and so can be set to heat the whole of a loft conversion, or part of it, at various times of the day, or night. Remember, too, that a large percentage of the heat in a house is lost through its roof, so adequate insulation is required to prevent a loft conversion from becoming uncomfortably cold – and incurring large heating bills – during the winter months.

If you are intending to use a loft conversion for a full, or part, en suite bathroom, plumbing is obviously an issue. Toilets, for example, must legally be situated within 2 metres of a waste pipe. Installation of a full-sized waste pipe may be impractical, and a macerator – which reduces the size of solid waste – may be required, before pumping waste through a small bore waste pipe to the main waste pipe. Similarly, toilets with internal siphon overflows are better suited to installation in loft spaces, because they do not require an external overflow pipe. Power showers – which heat water taken from the cold mains, electronically, and deliver it at high pressure – are highly practical in loft conversions, where there may be otherwise insufficient water pressure. Power showers should be installed with their own, secure power source, direct from the central domestic fuse box, and controlled by an isolated switch. Other practical considerations, with regard to the use of water in a loft space, include the avoidance of floor tiles, and walk-in showers, and the use of shower trays in ceramic, fibreglass or plastic, to avoid any leakage problems. You may also need to examine the domestic heating, and hot water, systems. Your existing boiler, for example, may not be sufficiently powerful to heat the extra space, or provide enough hot water.

Other Considerations

Some loft conversions require planning permission, while others do not, so it is advisable to check with your local council for the current planning regulations in your neighbourhood. You may, for example, be able to carry out a loft conversion, without planning permission, provided that you do not exceed what is known as a “Permitted Development Allowance”. This is measured in cubic metres, and is typically between 40 and 70 cubic metres – or 20% of the total volume of your property – depending upon the type of property, and its location. Planning permission will be required if your loft conversion extends beyond the highest part of the existing roof, or beyond the plane of the roof at the front of your house, or if you live in a National Park, or an Area of Outstanding Natural Beauty, for example.

All loft conversion must, similarly, comply with building regulations. These are extremely complex – covering fire protection, access, and insulation, as well as standard building regulations – and you should seek advice from a professional architect, or builder. The floor of a loft conversion, for example, must be proven to withstand any load placed upon it, and the fire resistance of existing ceilings, and doors, usually needs to be upgraded. Last, but not least, whatever type of work you undertake, make sure that you inform your mortgage lender, and your buildings insurance provider. Adding an extra storey to your home may result in a higher buildings insurance premium, but failure to disclose this information may result in the invalidation of your building insurance policy, as a whole.

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