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This guide provides everything you need to know about loft conversion design considerations, costings, planning and building regulations. A loft conversion is an ideal way to gain more space. There may be scope for one or two extra bedrooms possibly even with a bathroom or home office.

Loft Conversion Picture

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Nationwide has estimated that an additional bedroom and bathroom could add around 20% to the value of a three-bed, one bathroom house (but do be aware of area price ceilings). This could equate to £46,000 based on an average house price of £230,292 (average house price in June 2019, Office of National Statistics).

Most loft conversions usually fall under Permitted Development, but you will need planning permission if you live in a listed building or a designated area. You will also need to adhere to the Building Regulations.

Our following guide gives you an outline of everything that must be adhered to and considered throughout an entire loft conversion.

If you are looking for ideas for your new space, check out our gallery of great loft conversions

Conversion Costs
Velux Loft Convesion
Dormer Loft Conversion
Hip To Gable Loft Conversion

How Much Does a Loft Conversion Cost?

Your loft conversion cost will depend on multiple factors including the existing roof structure and pitch, the size and the extent of remodelling work or alterations needed to accommodate the new staircase.

Here, we’ve listed the different types of loft conversion and their approximate costs:

Room in Roof or ‘Velux’ Loft Conversion

Prices start at around £45,000 for a room in the roof loft conversion, which is the cheapest and most straight forward option. Also referred to as a ‘Velux’ conversion as the roof is usually left in place and new ‘Velux’ roof windows are installed.

This will usually involve:

  • The reinforcement of the floor

  • A couple of Velux roof lights

  • Added insulation

  • A staircase to the loft

  • Electrics, lighting and heating

  • Fire safety measures to comply with Building Regulations such as fire doors and smoke alarms

Dormer Loft Conversion

This is as the above, but with the addition of dormer windows. This will increase the usable floorspace and can be used to add head height which gives you more options when it comes to placement of the stairs and bathroom facilities.

There are variations of the dormer as this could take either the form of separate smaller dormers with pitched or flat roofs (dependent on available headroom) or a much larger dormer with either a flat roof (roof has a very small pitch usually 1:40 i.e 1mm fall for every 40mm length) or catslide roof (this has a shallow pitch of usually at least 22degress and is fitted with normal roof tiles).

An average dormer loft conversion with a double bedroom and en suite will usually cost around £50,000–£65,000.

Hip to Gable Loft Conversion

This option is the most expensive as it requires the complex removal and rebuild of the existing roof. Usually the existing ridge is extended out to the Gable end and the front roof is then extended up to the new ridge. Often a new rear dormer as above is then constructed to facilitate the extra floor space needed.

Loft Conversion Pictures

Do I Need Planning Permission for a Loft Conversion?

Not always! More often than not loft conversions are constructed under the householders Permitted Development Rights but the design will need to adhere to a number of specific regulations in force from the local authority. 

What is Planning Permission?

Planning permission is the consent of your local authority on a proposed building project and is in place to deter inappropriate development. The building of a new dwelling, or extensive changes to existing buildings, usually requires planning permission. 

How Long Does it Take to Get Planning Permission?

You should find out whether your application has been approved after eight weeks, although more complex schemes can take longer.

A sign is posted outside the address relating to the proposed development and any neighbours likely to be affected are written to and invited to view the plans and to comment. This is known as the public consultation process and it takes three to eight weeks. The authority will make statutory consultations to the local Highways department, and where necessary the Environment Agency as well as others.

What is Permitted Development?

Permitted Development (PD) grants rights to enable homeowners to undertake certain types of work without the need to apply for planning permission. There are many innovative opportunities whereby PD rights can bring significant benefits to anyone who wants to undertake a project to improve or maximise their investment within the property.

Do I Have Permitted Development Rights?

Most likely yes, but there are a few things to bear in mind. Unfortunately, the slate is not wiped clean when you buy a home — any space added by past owners since 1948 counts towards your Permitted Development allocation.

If your house is located in a Designated Area, such as a National Park, Area of Outstanding Natural Beauty or Conservation Area then your Permitted Development rights may be restricted or removed under what is known as an Article 4 direction. If you have moved to a newly built property then it is also worth checking with your local authority planning department in case your permitted development rights have been removed prior to you purchasing the house. This is where rights have been removed in the interest of maintaining the character of the local area. This could also be the case if your property is listed.

If you plan on extending beyond the limits and conditions of PD, or your property is listed or located in a conversation area, then you will need to apply for planning permission. You will also need planning permission if you are altering the roof height or shape (which may be the case if you have to raise it for headroom).

Rooflights and dormers can be installed under PD, but they must not sit forward of the roof plane on the principal elevation, nor must they be higher than the highest part of the existing roof.

"Always check with your local planning office before you start any work!"

Types of Permitted Development Rights

Householder PD rights fall into different categories depending on the work being planned. These are:

Class AExtensions (enlargement, improvement or alteration)

This allows a householder to build a single-storey side extension up to half the width of the existing dwelling; a single-storey rear extension up to 4m in length for a detached dwelling and 3m long for a semi or a terrace house; and, in certain circumstances, 3m two-storey rear extensions. 

The changes that took effect on 30 May 2019 now make permanent the decision that larger single-storey rear extensions of up to 8m (6m for semi or terrace) are permissible under Class A — but do require prior notification (‘Lawful Development Certificate’).

Class B Additions to the roof

This allows for rear dormers and hip-to-gable extensions as long as the additional volume created does not exceed 50m3 (40m3 for semis and terraced homes).

Class COther alterations to the roof

Class DPorches

Class E Buildings etc. (outbuildings)

This allows for an outbuilding to be erected within a residential curtilage as long as it is sited behind the principal (often the front) elevation, does not cover more than 50% of the curtilage and is not more than 3m in height (4m for a dual-pitched roof; 2.5m where within 2m of a boundary).

Certificate of lawful development

It is extremely advisable to apply for a Lawful Development Certificate (LDC), to ensure that your proposal complies with the regulations and that you will not be faced with difficulties post construction.

If, once an extension or outbuilding etc. is constructed, the Local Planning Authority determines that the proposal does not comply with PD regulations then you may be faced with enforcement action, which would normally result in a request for a retrospective application. Should permission be refused there is a real likelihood that any extensions or associated works would be required to be demolished. As such, confirmation in the form of the LDC is highly recommended.

Could I Both Extend My Home and Convert My Loft Under Permitted Development?

In the past, volume limitations were applied to the entire house — so if you extended, you were unlikely to be able to convert your loft under Permitted Development rights as well. The good news is that the latter has now been separated out, allowing you to undertake both without one restricting the other.

So, you can also convert your loft into a bedroom or extra living space by up to 50m³ in a detached house, or by 40m³ within any other home. Flush rooflights or those which do not project further than 150mm are permitted, but you will need permission to add a dormer window on any roof elevation which faces the highway.

However, you cannot cover more than 50% of the land around your house with extensions (including extensions by previous owners), and you have to include any outbuildings when calculating this coverage. Sheds and other outbuildings count in this calculation.


Planning Permission
Loft Conversion Pictures

What are Building Regulations?

When converting a loft, you will need Building Regulations approval. This is initially achieved by submitting the proposed drawings and sets of calculations in regards to all supporting structures and provisions of complying with all other associated regulations.

A local Authority building control surveyor will also inspect your conversion at various stages and will be responsible for issuing a completion certificate upon final inspection.

If your home is semi-detached or terraced, then you will need to notify your neighbours of your planned work if it falls under the requirements of the Party Wall Act.

When it comes to a loft conversion, you are most likely to be concerned with Parts L, K, B and P of the Building Regulations.

Part L of the Building Regulations requires U-value targets for thermal efficiency to be met when you convert your loft into habitable space.

Part K concerns preventative measures from falling, collisions and impact, and requires a minimum headroom of 2m for all escape routes, including the stairs (although the rules are relaxed a little for staircases providing access to a loft conversion).

Parts B and P are concerned with fire and electrical safety respectively. Complying with Building Regs’ requirements on fire safety can be complex. In two or more storey homes, where an escape window would be more than 4.5m from the ground level, a ‘protected’ staircase needs to lead down to an exterior door — which can cause some issues if your staircase rises from a room, rather than the hallway on the ground floor, or your ground floor is open plan. There are typically solutions in both instances, but this area needs consideration with your design and/or build team.

Building Regulations
Loft Conversion Pictures

Can all Lofts be Converted?

Assessing your loft space’s suitability for conversion involves considering numerous factors, including:

  • available existing roof height

  • roof pitch

  • roof structure

  • obstacles such as water tanks or chimney stacks


Roof Height

While the Building Regs impose no minimum ceiling height for habitable rooms, you will need to factor in the 2m headroom required for stairs (although you could relax this to 1.8m on the edge of the stair if needs be). 2m is the minimum requirement that must be achieved when installing the new staircase. You must have 2m minimum below your new staircase – be aware of crossing over landings or existing staircases. The new staircase must also have at least 2m clearance above its ‘pitch line’ (the line drawn from nose to nose joining each step along the centre of the staircase). To this end you will need to achieve 2m head clearance on the top step at its centre point


Measuring Head Height for a Loft Conversion

When you measure from the bottom of the ridge timber to the top of the ceiling joist, you need to have at least 2.3m of usable space for a conversion to be suitable. 

If the initial roof space inspection reveals a head height of less than 2.3m, there are two available – but costly – solutions that will require professional input.

Solution 1: Raise the Roof

This is structurally feasible, but the major problems are the high cost and getting planning permission approval. If the whole roof area needs removing, a covered scaffold structure, to protect the house from the weather during the works, would also be required.

Solution 2: Lower the Ceilings on the floor below

This will require all the existing ceilings in question to be removed, causing much mess. With this method a plate will need to be bolted to the wall using shield anchors or rawlbolts, for the new floor joists to hang from. There is also a need for a suitable tie between the roof structure and the dwarf wall formed, to prevent the roof spreading.

You will also have to assess whether the space you are gaining in the loft makes up for the space you are losing in the rooms below.

Another consideration is that you also lose space above your first floor windows which can then be a potential problem for hanging curtains.



Is My Roof Pitch Right for a Loft Conversion?

The higher the angle of the roof pitch, the higher the central head height is likely to be, and if dormers are used or the roof is redesigned, the floor area, and potential for comfortable headroom, can be increased.


The two most common types of roof structure in the UK 

1.    Trussed Rafters 

Most roofs built from the late 1960s onwards are of prefabricated trussed rafter construction, with distinctive W-shaped webbing. Although once regarded as ‘hard to convert’ on account of their relatively slender roof timbers (typically only about 30 x 70mm), many lofts of this type can be successfully converted.

The key is to ‘preserve the triangulation’ ensuring that the opposing roof slopes are fully supported and tied together at the base (e.g. with new floor joists) and near the apex with new collars. Also, it’s essential that the new structure is fully in place before cutting any of the trusses. The rafters may also need to be strengthened by doubling them up with new ones fixed alongside, or with sheets of orientated strand board (OSB) for windbracing.

Trussed roofs require greater structural input, normally involving the insertion of steel beams between loadbearing walls for the new floor joists to hang on and the rafter section to be supported on — together with a steel beam at the ridge.


2.    Purlin supported roof

Traditional frame type roof structures are often the most suitable type for loft conversions, allowing the space to be opened up relatively easily and inexpensively. The rafters may need to be strengthened or additional supports added (your structural engineer will advise on what is required).

Loft Conversion Pictures

Do I Need a Designer for my Loft Conversion?

Whilst you can design a loft conversion yourself, employing the services of an architect or designer is advisable. Another alternative is a design and build company like elite lofts ltd

You have two main options (both will deal with planning permission, if required, and Building Regulations approval):

Option 1: Design and Build Company

For an all-inclusive service, elite lofts is a great option. Design solutions and details are flexible and can be tailored to your exact needs from the initial survey through to the production of the quotation with 3D visual images so that you can see the exact possibilities that are available with your space. The Drawings, structural fees and council fees are also included in the cost of the deposit.


Option 2: Architect or Designer

Taking this route means that you can steer the design to your exact, bespoke specifications, but remember that, as this is likely to be a relatively small project, the design fees are likely to be a high percentage of the overall costs. 

Your architect or designer will produce drawings which you then put out to tender, and you may find that you need to also hire a structural engineer.This route often turns out to be the most expensive due to the high Architectural and structural engineers fess

Loft Conversion Pictures

Adding a Staircase to a Loft Conversion

The ideal location for a staircase to land within the area of the ridge as this will make best use of the available height above the staircase.

The minimum height requirement above the pitch line is 2m, although this could be reduced to 1.9m in the centre, and 1.8m to the side of a stair.

In practice, the actual position will depend upon the layout of the floor below, and where necessary the available height can be achieved using a dormer or adding a rooflight above the staircase or, if appropriate, converting a hip roof end to a gable.

The following points must also be complied with:

  • Maximum number of steps: the maximum number of steps in a straight line is 16 (typical installation usually only requires 13 steps.

  • Step size: the maximum step rise (height) is 220mm, whereas the step depth or ‘going’ is a minimum of 220mm; these measurements are taken from the pitch point. The step normally has a nose that projects 16-20mm in front of the pitch line. However, the ratio of size must not exceed the maximum angle of pitch requirement of 42°. Any winders (turning steps) must have a minimum of 50mm at the narrowest point. The width of steps is unregulated, but in practice the winders are likely to limit the reduction in width.

  • Balustrading: The height minimum is 900mm above the pitch line, and any spindles must have a separation distance that a 100mm sphere cannot pass through.

Loft Conversion Pictures

Do I Need to Replace the Ceiling Joists When

Converting a Loft?

In most cases, additional new joists will be required to comply with the Building Regulations as existing ceiling joists are unlikely to be able to take a conversion floor.

Your structural engineer will specify the size and grade required.

The new joists span between load-bearing walls, and are normally raised slightly above the existing ceiling plasterwork by using spacers below the joist ends. This spacing must be sufficient to prevent any new floor joist deflection from touching the ceiling plaster below.

The new joists run alongside the existing joists. Above window and door openings, thicker timbers are used to bridge the opening, so that pressure is not put on the existing opening lintel.

Rolled steel joists (known as RSJs) are also specified to distribute the load, and in some installations are used to carry the ends of the new joists. If head height is limited, then thicker joists, more closely spaced, can be specified.

Ceiling Joists
Loft Conversion Pictures

Bringing Natural Light into a Loft Conversion

You have two feasible options when it comes to bringing in natural light — rooflights or dormers.


The most straightforward method is to use rooflights that follow the pitch line of the roof. This type is fitted by removing the tiles and battens where the rooflight will be fitted. The rafters are cut to make way for the rooflight after suitably reinforcing the remaining rafters.

The rooflight frame is then fitted and flashings added before making good the surrounding tiling.

This type of window is the most economic, and more likely to be allowed without planning permission.


Dormer Windows

Dormers not only give natural light but can add space to a loft conversion. They are particularly effective where the pitch angle is high, as the useful floor area can be increased.

Dormers and other similar conversions are normally installed by opening up the roof, and cutting the required specified timbers to size on site.

Adding Artificial Lighting in a Loft Conversion

As in any successful interior scheme, different light sources should be combined, including ambient (substituting for daylight), task (reading, working) and accent (to add atmosphere) lighting.

Lighting options on sloping ceilings include downlights and track lighting. A section of flat ceiling beneath the ridge or within a dormer window is the ideal surface for downlights. Where the ridge is higher, it may be possible to suspend pendants or a track lighting system.

Ambient lighting can also be provided using floor and table lamps, providing they are on a switched lighting circuit so that they can be controlled, and ideally dimmed from the main wall switches.

Loft Conversion Pictures

Plumbing & Heating requirements

Any Extensions normally increase the heat load requirement of the house and so the boiler sometimes has to be upgraded, but a loft conversion may require little extra capacity as the space will be well insulated and can improve the overall energy efficiency of the house.

Options for heat emitters in attic rooms include radiators, underfloor heating, or a combination of both, perhaps with electric underfloor heating mats in bathrooms.However, if a bathroom is added, a boiler upgrade may be necessary. It is a good idea to switch to an unvented system that does not require header tanks but relies on mains pressure (as long as it’s at least 1.5bar).


Will I Need to Move the Water Tank When Converting my Loft?


Ideally any water tanks should be removed to gain maximum space within the loft unless there is plenty of room and height to place them. The problem you have with keeping the tanks in the loft is that you may require a new shower in the conversion and it is likely that the new shower head will be higher than the water level in the tanks and will therefore not work. 

Also with regards to the existing hot water cylinder – is this currently in the way of the proposed staircase? In which case this must also be moved or converted.


There are a couple of options suited to different scenarios:

Option 1 – Unvented system

An unvented system does not require any water tanks. This also means that providing your boiler is not too old you can still use it. The system replaces the job of your existing hot water cylinder and can physically be placed on any level of the house as the water is now under mains pressure. The existing hot water cylinder and water tanks are then made redundant.


  • Unvented hot water cylinders make a better choice than replacing the boiler with a combi boiler

  • You will always have a cylinder of hot water

  • Your showers will now be at mains pressure

  • You can often keep your existing boiler

  • Saves on space in terms of not having water tanks in the loft

  • If the power goes off – you will still have a tank of hot water

  • If the boiler breaks down – you can still have an electric immersion heater for hot water


  • They do take up a cupboard-sized room, which you will have to find space for

  • There may not be enough pressure coming into the property for this to work properly

  • You may have to replace existing low pressure showers in the house


These are a great system but as mentioned you may not have enough pressure – so you may either have to contact the local water board who may suggest running in a new larger water supply OR you could install an ‘Accumulator tank’ – which is another large cylinder which can improve the flow rate of the system and will also have to be installed if you do not have enough pressure.

A plumber can check your existing pressure and flow rate to recommend if this is system is possible and if you would need an accumulator tank.

Option 2 – Combination Boiler

A combination boiler is a viable option on a smaller property. This type of system is literally a stand alone boiler with no need for any tanks or water cylinders as this heats both the water and radiators as required.


  • This is often a little cheaper than the unvented system option

  • You will only heat the water that is used

  • You will save lots of space once the hot water cylinder and water tanks are removed



  • They have a limited flow rate of hot water i.e the water may go cold if a second shower or any other taps are turned on whilst your in the shower

  • You may have to replace existing low pressure showers in the house

  • They can struggle when supplying multiple showers at the same time

  • If the power goes off you do not have any hot water


These are ideal on a smaller property but if you're adding an extra bathroom or you have a growing family where it is likely that multiple showers are going to be required then consider investing in the unvented system option 1.

Option 3 - Pump

By using a pump to supply the loft you would keep all the existing system in place – although be aware you may have to move the hot water cylinder if that’s the new staircase position and you may also have to relocate the water tanks. The type of pump needed would be a ‘negative head’ type pump which senses the drop in pressure when a tap is turned on and then activates the pump


  • This is by far the cheapest method

  • You will have a great pressure shower in the loft

  • Require minimal space to install


  • They have a limited life

  • They can often be very noisy on the floor that they are installed

  • They located usually next to the hot water cylinder

  • They turn on every time the shower OR sink is used in the loft 

  • The Hot water cylinder may still need to be relocated if the stairs are to be located in the same position 

  • They can be quite expensive – around £600 each time it is installed or replaced


Although this is by far the cheapest option the motors are obviously a moving mechanical item and will only have a limited life and can be very annoying due to the noise generated from them to other occupants of the house

Adding a Bathroom in a Loft Conversion

If you are adding a bathroom you’ll need to think about the location of existing services.


Adding hot and cold water supplies is straightforward, branched off the existing plumbing system either at the boiler or from the floor below. Flexible plastic plumbing is easy to thread through the joists.Existing soil pipes are likely to be vented above roof level and it may be possible to boss a connection into this, or into another soil pipe on the floor below.


Where there is no existing soil stack you may be able to add one.

If you are going to put a bedroom in the attic then it makes sense to try and fit in a bathroom,

but do follow these tips:

  • Place a shower where there is full headroom

  • A bath can be tucked under the eaves

  • A WC ideally needs full headroom, as does a washbasin

  • wetroom can be a space-efficient option, but needs full tanking

  • Use the voids in stud walls for concealed shower and tap mixers

  • Concealed cisterns in metal frames for building into studwork are ideal

  • Good lighting and large wall-to-wall mirrors create the illusion of space

  • Wall-mounted sanitaryware helps make a small bathroom appear more spacious

Plumbing and Heating
Loft Conversion Pictures

Insulating a Loft Conversion

The roof structure can be insulated in one of two main ways:

Cold Roof Loft Insulation

The most straightforward is to use a ‘cold roof’ method.

This involves filling the space between the rafters usually with 100mm-thick PIR insulation boards such as ‘Celotex’, ensuring that there is 50mm spacing between the roofing felt and the insulation (for ventilation via the roof and soffit vents).


In addition, 50mm-thick PIR insulation boards are attached to the inside of the rafters, giving a total of 150mm of insulation. If the rafter thickness is less than 150mm, a batten may be required along each rafter to allow the 50mm spacing and the 100mm insulation. This method is used both on sloping roofs and also flat roofs.

Warm Roof Loft Insulation

This method uses 100mm Celotex insulation or similar over the rafters, and a covering capping, followed by the tile battens and tiles. This is not really a practical option unless the roof coverings have been stripped off. It could be used with a dormer, especially if it has a flat roof.

Continuity of insulation between walls and roof is required to avoid any cold bridging. The dormer walls can be insulated with 100mm Celotex between the studwork.

The internal partition walls use a 100mm quilt that will provide sound insulation. Plasterboard is attached to one side of the wall then the quilt inserted, followed by plasterboard on the other side.

Insulation is also placed between floor joists, and this is typically 100mm-thick Rockwool fibre or similar — mainly for its sound-reduction properties and your Building Control inspector will specify exactly what you require.

Insulating Party Walls

It is often necessary to insulate party walls — both against heat loss and noise. Introducing timber studwork with mineral fibre insulation will allow you to achieve both and it can be covered with sound-rated plasterboard.

Loft Conversion Pictures

Getting Ventilation Right in a Loft Conversion

To maximise energy efficiency, the roof space should be made as airtight as possible, and to counter this it is essential to introduce controlled ventilation to prevent the risk of condensation and maintain good air quality.

This means including background ventilation (airbricks and trickle vents) and rapid ventilation (via windows), plus extract ventilation in wet areas, such as bathrooms or a kitchen.

Loft bathrooms are not required to have a window providing the extract fan can provide rapid ventilation.

Loft Conversion Pictures

Loft Conversion Fire Safety

Single storey

Ensure that the new windows are large enough and low enough to escape from:

  • Egress window openings are needed to serve all first floor habitable rooms, but not bathrooms

  • Openings should be at least 450mm x 450mm and at least 0.33m2 in area

  • Rooflights are usually top opening — you must ensure the bottom of the opening is between 800mm and 1,100mm from the floor

Two storey

Things become more complicated if your loft conversion transforms a two-storey house into a three-storey home:

Escape windows that are over 4.5m from ground level are not viable. Instead, the Building Regs require a protected stair enclosure that leads right down to the final exterior door.

If your staircase rises from a room, rather than a hall, you have two choices:

  1. It can be entirely enclosed within a hallway to an external door

  2. The staircase can be enclosed in a lobby at the base of the stairs. The lobby will have two separate doors, to offer a choice of either a front or back route of escape. These doors and the lobby walls will need to be fire-resistant and most likely open outwards into the rooms to avoid fouling the bottom of the stairs. If the doors do not open outwards into the rooms, they will be acceptable as long as they create viable options for escape in the event of a ground floor fire

For open plan homes, where the staircase lands in an open plan space, a sprinkler system may be the only option.

Floor Joists

The new floor joists of your loft conversion will need to offer at least 30 minutes’ worth of fire protection, which could mean replastering the ceilings in those first floor rooms below. 


The loft room will also have to be separated by a fire door, either at the top or bottom of the new stairs.

The existing doors on the stairway to both ground and first floor should be able to provide 20 minutes of fire resistance or be replaced. They can’t be glazed either (unless with fire-rated glass), so you may want to consider windows or rooflights to bring daylight to the stairwell.

Smoke alarms

Mains-powered smoke alarms should be installed on each floor of your home and interlinked so that they all sound off when one is activated. Most have a rechargeable battery as a back-up that allows the supply to be extended from a lighting circuit if necessary. 

Wireless, radio-linked alarms can be fitted if you can’t hardwire to the ground floor ceiling.

Fire Safety
Loft Conversion Pictures
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