House extensions — different types of home extensions Internal Alterations Loft Conversions

House extensions - different types of home extensions Internal Alterations Loft Conversions

House extensions such asLoft conversions andconservatories. are common types of extensions known to everyone and we deal with these in detail in the sections below. In addition we also cover alternative types of house extensions including internal alterations, basements. single and multiple storey home extensions.

Internal alterations to homes

Internal alterations are not always thought of as a house extension. it is sometimes possible to alter the internal layout to provide additional accommodation. In particular, this has been made easier on the upper floor of houses by the use of prefabricated trusses on new dwellings over the last 40 years. It has meant that most of the internal walls below them are non-load bearing, however some care should still be taken in assuming which walls are load bearing. Stud walls and other lightweight forms of construction can still be load bearing and some walls may have a function in bracing the structure, if at all in doubt obtain professional advice. By relocating walls it may be possible to create additional rooms or alternatively combine rooms and give your house a more spacious layout.

A good sized three bedroomed terrace house with limited potential to extend. Re-arranging the non load bearing walls gives four bedrooms, although a little smaller than the original layout but adequate plus an en-suite.

The external elevations of the building may provide some restrictions in terms of window layouts etc. whilst sometimes necessary; dividing a window between two rooms is not always very successful. Although it may in theory be possible to change the position of the windows but care should be taken to ensure it does not unbalance the outside appearance.

Internal alterations may have implication in terms of the building regulations; in particular the means of escape from rooms should not be adversely affected. Rooms leading off other rooms (generally known as inner rooms) may not be acceptable without other measures such as windows suitable for escape purposes (generally only suitable at basement, ground and first floor levels) or a smoke alarm system or sprinklers. Open plan layouts may also not be acceptable without some additional measures such as those above and in some cases will not feasible.

Some properties with very high ceilings can lend themselves to providing additional floors. With very high ceilings (perhaps in the region of 4.5m) it may be possible to create a mezzanine type intermediate floor; in lesser situations it may be possible to obtain say 4 storeys from 3. In extreme cases this could involve the full replacement of all the floors, in practice this might involve problems in relation to existing windows etc. and so the addition of another floor over just part of the building to perhaps create bathrooms may generally be more practical.

Moving the positioning of the stairs may in some cases create more useable space although in some situations the main criteria may be to make a more spacious layout and so rooms can be sacrificed (although possibly in combination with an extension) to create this effect.

Where there is an integral garage this is often a fairly straightforward internal alteration providing an additional room provided it does not unduly restrict the parking arrangements on site. Councils will often put planning conditions to stop garage conversions happening without further approval, in practice this will often be granted providing there is adequate on site parking. It will generally be necessary to upgrade the insulation and possibly the damp proofing (particularly if only 103mm brick walls) under the building regulations.

Single storey extensions

Single storey extensions are probably the archetype house extension, often in the past, it was a simple flat roofed box usually on the rear or side of the house. This has to some extent changed over the last decade or so with an increasing preference for pitched roofs partly due to a perceived improved appearance and partly due to greater longevity. Ironically this has happened at a time when some architects have designed some ‘cutting edge’ house extensions with flat roofs and roofing technology has improved significantly such that a good flat roof should have a long life.

Tiled roof single storey extensions to houses can make access to upper windows; gutters etc. more difficult for maintenance and they should not unduly affect the use of windows to upper floors for emergency escape purposes in a fire. It can also be difficult to achieve a reasonable pitch on the roof if trying to fit below first floor window particularly where plain tiles are used which need a pitch of 35degrees or more unless some form of additional weather proofing barrier is introduced.

It may be possible to introduce a flat roof to the top of the tiled roof or take the roof higher either side of the window with a lead recess cut through the roof, although these are generally feasible it can complicate the construction of the roof. An alternative to a conventional flat roof is a green roof i.e. turf or natural vegetation which a well as being attractive helps to protect the weather proofing of the roof and has environmental advantages.

An alternative approach with single storey home extensions to avoid encroaching on existing windows at either ground or first floor level might be to separate them from the main building with some form of link structure (totally detached buildings are dealt with separately). Whilst overcoming some problems they may take up more room which could be critical in some situations such as the amount of garden remaining and effects on adjacent properties.

Multiple Storey house Extensions

The most usual case of a multiple storey extension is a two storey house extension but occasionally more may be possible. In addition whilst the height of an extension would generally be equal or less that the original building there may be occasions, for example when the original house is lower than surrounding properties, that a greater height may be possible. As with internal alterations a greater number of storeys than the original building maybe possible even where to the same building height — provided of course there is sufficient latitude within the ceiling heights for this to be achieved.

House extensions of several storeys are perhaps one of the more contentious areas with Town Planning as they are more likely to involve loss of light or other amenities to neighbouring properties and particularly for side extensions may tend to create a terracing effect between properties where the gaps between them are significantly reduced. Front and side multiple storey extensions in particular may have to more strictly follow the style and materials of the original house than other extensions. There can sometimes be a conflict about following the level of the existing eaves, windows, etc. although often desirable it is sometimes considered preferable that the extension is subservient to the main building and as such a lower level to the extension may be preferable. This can be dictated by practical aspects where, for example, on a typical side extension the access may come off a landing which is lower than the main floor level. A dormer or roof light type of arrangement is sometimes used to the upper floor even where the original house is a more conventional design in order to keep a lower profile to the extension.

A variation to the more normal multiple storey house extension is where a further storey is added to an existing part of the building (this is partly also covered by loft conversions in particular where a totally new structure is created at roof level). A common case is where another storey is added above an existing attached garage, where this is only single skin construction, this may create some additional problems, it may be possible to use beams to carry an inner leaf, although it will depend upon the strength of the existing structure, including the foundations. An alternative might be to use a lighter form of construction such as timber frame; this could either involve basically just replacing the inner block wall or using a single wall of timber frame with a cladding type material outside (e.g. tile hanging, render, boarding etc.) This would generally be lighter than an equivalent block wall and in the case of single leaf wall would generally be narrower which might be useful where building above a fairly small existing building, a typical garage may only be about 2.5m wide and so the loss of 150mm or more with a conventional inner leaf could be critical.

Another variation of building above an existing structure is to make the new upper floor smaller or larger than the existing building below. In the former case it may be necessary to step an upper storey in to maintain a greater spacing between buildings at this level to avoid a terracing effect being created and maintaining a section of roof around the new extension at the lower level. With an upper floor that is larger than the existing structure below i.e. cantilevered beyond the existing building or in some cases constructing some form of columns in steel, brick, timber etc. outside the confines of the original building. With a cantilevered structure although it may in theory to sometimes be possible to build it in conventional brick cavity construction it will often be more practical to consider lighter weight options such as timber frame.

Loft Conversions

Loft conversions have been a popular house extension. and extension to bungalows and flats for a variety of reasons. Although primarily they make better use of what in most properties is an underutilised space storing the 15 year old television that ‘may come in useful’ and the teenager’s former baby toys. Using the loft may be a relatively cost effective way of creating extra space as the basic structure is already partly in place, it can often avoid requiring planning consent, particularly if only roof lights are used but sometimes even with dormers, gables etc. The extra volume is only measured externally in relation to the permitted development requirements and is often relatively small. (See Exemptions to Town Planning)

Creating an additional floor can avoid building in front of other rooms which can be a problem on some narrow sites. On the downside finding a suitable position for stairs can be problematic; it can fundamentally change the type of property (many bungalows are purchased by retired people because they are only on one level) and may involve additional problems. (See Building Regulations )

Some forms of roof may prove to be more difficult to convert than others. In particular the modern type of roof truss that has been popular since about the 1960’s often only relies upon the main outside walls for support making the spans for floor joist potentially too great for normal sizes of timber. Sometimes however, internal walls may still be potentially suitable for load bearing (i.e. generally brick/block onto foundations) even if they are not currently supporting the roof structure. It is often possible to provide new beams within the roof to support the floor etc. sometimes fabricating them in more manageable lengths and bolting on site but this is best left to specialist companies. A further problem with trusses is that often they were at a relatively low pitch and so the amount of headroom available can be restricted. Although there are in theory no building regulations that cover the amount of headroom required in rooms it is still necessary to have 2m of headroom over the stairs and the top and bottom landings.

In assessing whether a roof is likely to be suitable for a loft conversion room allowance needs to be made for the additional thickness of the new floor joists and the rafters will need to be insulated and lined. Typically this might rise above the existing ceiling joist level by about 150mm and lower below the rafters by 80mm but it depends upon the exact nature of the existing roof and the specification of the proposed work. In general the lower walls around a loft conversion (sometimes known as ashlaring) are in the order of 1m high, much below this would be too low to be particularly useable and could be more problematic in supporting the existing roof, usually most of the existing inner structure of a roof such as purlins, struts etc. can be assumed to be removed provided some new support such as in the form of ashlaring is provided. Another type of roof that can be more difficult is where there is some sloping rafter within the rooms below (in an extreme case it might be like two storeys within the roof space). This makes it more difficult to support the new floor joists on the main walls, this may again be solved by the provision of large beams to support the new floor.

Where a roof is large enough to provide adequate headroom in a loft conversion usually the most cost effective approach and simplest in that it may avoid town planning consent (See ) is to use roof windows. these come in numerous sizes and can be doubled (one above the other and side by side) if required and there are some special types such as those that form into a balcony.

To provide more headroom in a loft conversion the traditional answer has generally been to build a dormer. Whilst a modest dormer can look attractive and sometimes enhance the appearance of a roof rather too often the temptation is to make it as large as possible which can end up looking like a large box put on the roof. Although in theory many planning authorities would in general prefer pitched dormers, where the existing roof is not particularly high this may not be practical and for some types of property a modest sized flat roofed dormer (often traditionally a lead roof) may be less dominant on the roof.

Two or more dormers will often look better than one and should not lose the basic shape of the roof

For hipped roofed properties a useful way to extend in some cases is to convert the hips to gable ends. This can often be a more cost effective way of providing extra space in a loft conversion than dormers and by effectively lengthening a roof it may make it easier to perhaps provide two rooms instead of one. Where it requires planning consent (always when on the front) some local authorities may not like to see one gable amongst what may be primarily hipped roofs. In addition where perhaps it is only done to one side of a building it should not end up looking lop-sided.

One form of roof alteration which is not strictly a ‘loft conversion’ but many of the same principles apply is the total replacement of a roof generally with a higher roof. This is mostly done where the existing roof is too low to provide a usable amount of space although there may be situations such as roofs in a generally poor state of repair where total replacement is a viable option. There may sometimes be town planning objections where one roof ends up significantly higher than others in the vicinity. It can also provide more problems in keeping the building weather tight during construction than more limited alterations with the possible additional costs of providing a temporary roof over the whole building. If it enables another floor to be created that would not be possible otherwise and other forms of extension are not viable it may be an approach worth considering.

Basement conversions

Many properties particularly during the Victorian era were built with basements which if not already in use may be suitable for conversion. With 20 th century mass housing such as the ubiquitous inter-war semi the construction of basements dwindled except perhaps on sloping sites, as in general they are a fairly costly way of providing space and in an era of fairly plentiful land as towns were expanded into the countryside it fell out of fashion.

With an existing basement. provided it does not require extensive works such as making it deeper it may be worthwhile considering as a form of house extension. Windows are generally provided by means of shafts cut in front of them, in some cases it may be worth considering lowering the ground more extensively outside to allow access in and out to a lowered patio level.

Where there is no existing basement or it is too low to be usable it may still be possible to construct a totally new basement but it is not without its problems. It will generally be a fairly expensive way to extend your property, particularly in relation to an existing property where large amounts of soil have to be dug out and removed. This will often only make viable in places of high property values and where other, possibly cheaper house extension options are not possible or have been exhausted. Where one is likely to be extending below other properties in the vicinity it is likely that the Party Wall Act will apply. In fairly crowded urban layouts this may mean several other properties are involved and will potentially add to the overall costs in terms of Party Wall surveyor’s fees alone and possibly in agreeing the way the works are carried out.

Perhaps the biggest problem with basements both existing and new is keeping the water out; although there are in theory plenty of acceptable materials around it does require the work to be carried out well as basements are not very tolerant of imperfections. The main approaches are either a water proofing material inside or outside the main walls, the latter is preferable in certain respects as water behind is not trying to push it off the wall as occurs internally but it can be more difficult to apply particularly to existing basements. An alternative approach is a waterproof membrane internally which contains a drainage cavity behind which can be drained away. This accepts the almost inevitable fact that the wall might allow water through (but is then drained away) however, it has the slight disadvantage that it may require active pumping to maintain it dry.

There are some specialist products that fall within the general category of basements and could be termed ‘mini cellars’. They are much smaller than usual basements and often used for more specialist applications such as storing wine or as a larder ( ) where they can benefit from the more stable temperature below ground which in England is usually cool rather than frozen or hot. They usually come in a partly prefabricated form and may incorporate stairs as an integral part of it.


Conservatories were popular during the Victorian period when they were often attached to larger houses and used for growing tender plants. During much of the 20 th century they fell out of favour although the advent of corrugated plastic sheets gave a safe and economical alternative to glass but with a finite life. It was not until the 1980’s with a combination of a growing upvc window industry, the exemption of conservatories under the building regulations and the widespread availability of polycarbonate roof sheets that their popularity as a home extension took off.

The most common type of conservatory now consists of a dwarf wall in a material matching the property, upvc window frames and a polycarbonate roof. More elaborate conservatories may be in timber (sometimes hardwood) or aluminium and with a glass roof.

Typical Conservatories

The usual definition of a conservatory is that it has a translucent roof (see Building Regulations — exemptions to the regulations) but there are extensions which do not fully comply with this but have some aspects in common with conservatories these include:

  • Orangeries — with a central glazed area to the roof but solid area around it.
  • Sun lounges or garden rooms — usually with extensive windows but with a solid roof, often tiled.

With these clarification should be sought as to whether they can still be considered exempt from the building regulations, they should generally have at least three quarters of the roof and half the walls of translucent material. With sun lounge type extensions consent will generally still be required. Where this or any other type of conservatory is required as an integral part of the main house it may be possible to justify with thermal calculations (see Plans and who draws them ) but his may entail increasing the insulation elsewhere.

Windows and translucent type roofs do not provide anything like the insulation values required of solid walls and roofs under the current regulations so potentially conservatories will be much more difficult to heat. Whilst they gain to some extent from the heat of the sun, during the summer this can prove too much and some form of shading may be needed to the roof or windows or even air conditioning. The best orientation for a conservatory is generally east or west (although this may not be practical) to gain to some extent from direct sunlight whilst avoiding it being excessive.

Although there are obviously significant attractions to having a conservatory, particularly during the spring and autumn, they should generally be considered as additional accommodation used when at their best, rather than an extension that would be needed most of the time.

Detached Buildings

Although arguably not an extension to the house there may be situations where a detached building in the garden may be a good method of giving additional accommodation. In certain circumstances it might be preferable to be separated from the main building, for example as an office for someone working from home, or a music room. With modern communication equipment such as closed circuit television contact could be maintained with the building in the garden.

Other possible advantages of a detached building are that it may in some cases be exempt from Town Planning and sometimes Building Regulations control it may also at times avoid other requirements such as the Party Wall Act or when building near sewers .

One problem with a detached building is its physical separation where it is required as a more integral part of the house. In some situations a partly or fully enclosed covered way might be a method of providing linkage.

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