Costs & Guides

Most loft conversions are considered permitted development, which means you won’t need planning permission as long as the construction meets specific requirements. So, if you’re looking for a basic conversion with roof windows, you shouldn’t be concerned (though it’s always a good idea to double-check). However, if your ideas surpass specific limits and criteria, such as extending or altering the roof area beyond its current boundaries, you will need to get planning approval.

Whether your loft conversion is under permitted development or not, you’ll have to adhere to strict building rules to ensure that the work is done safely.

When is a loft conversion permitted development?

A loft conversion is usually considered permitted development as long as it follows the guidelines laid down in Schedule 2, Part 1, Class B of The Town and Country Planning (General Permitted Development) (England) Order 2015.

It’s always a good idea to have an architect or builder check whether or not you need planning approval. A loft conversion, on the other hand, is considered authorised development and does not require planning permission as long as the following conditions are met:

• Terraced houses will have a maximum loft space of 40 cubic metres, while detached and semi-detached buildings would have a maximum loft space of 50 cubic metres. Please keep in mind that any existing loft additions must be taken into account when calculating the volume allowance.
• The loft conversion at the front of the home does not extend beyond the plane of the current roof pitch (the principal elevation).
• The loft conversion does not go any higher than the current roof’s highest point.
• There are no verandas, balconies, or raised platforms in the loft conversion.
• The loft conversion is constructed with materials that blend nicely with the rest of the house.
• Any windows with a view to the side must be obscure-glazed (to stop people from seeing in and out).

• Any side-facing windows must be at least 1.7 metres in height.
• National parks, Areas of Outstanding Natural Beauty (AONB), conservation areas, and World Heritage Sites are not within driving distance of your home.
• With the exception of hip-to-gable expansions, all roof extensions must be placed back at least 20cm from the original eaves.
• A roof addition must not extend beyond the original house’s outer wall.

Do I need planning permission for my loft conversion?

You’ll need to apply for planning approval from your local authorities if your loft conversion violates any of the limits and criteria specified above.

Please note that the above loft conversion permissible development restrictions and criteria only apply to dwellings, and you will need to apply for planning permission if you live in any of the following:

• Flats
• Maisonettes
• Converted houses
• Houses created through the permitted development right to change use
• Other non-dwelling buildings
• Homes in areas where there may be a planning condition or other restriction that limits permitted development rights

Fortunately, obtaining planning approval for a loft conversion is simple and can be done online from anywhere in the UK: England: Apply via the planning portal.

Please read the government’s technical guidelines on permitted development rights for householders for further information on permitted development.

If your loft is cramped, you may want to consider roof expansions or loft additions. Keep in mind that not all roof extensions are approved construction if you need to enlarge the space in your loft. You may need to apply for planning permission in some instances. More information on the rules for dormer, hip-to-gable, and mansard roof extensions can be found below.

Do you need planning permission for dormer loft conversions?

A dormer loft conversion is an extension of your existing roof slope vertically. In most circumstances, no planning approval is required for a dormer loft conversion. Because the structure won’t normally necessitate any major alterations to your home’s appearance, the work is usually classified as approved development. You must, however, ensure that the extension is at least 20cm away from the original eaves. In addition, the height should not surpass that of the original roof. Planning authorization will be sought if this is not the case.

Are hip-to-gable loft conversions permitted development?

A hip-to-gable extension creates a vertical wall by straightening the slanting side of your roof. This type of work is normally considered allowed development because it does not necessitate any major structural adjustments to the roof. However, if your work would violate any of the permissible development restrictions for loft conversions, you will need to apply for planning approval.

Does a mansard loft conversion need planning permission?

A mansard loft conversion includes raising the pitch of one side of your roof to almost vertical and flattening the top. A mansard loft conversion will almost always require planning clearance. This is due to the fact that it drastically alters the roof structure’s shape.

How much does planning permission cost?

If you do need to apply for planning approval for your loft conversion, you will almost certainly have to pay an application fee. The cost of obtaining a planning permit varies greatly.

Fees for alterations and extensions to a single dwelling house in England, Scotland, and Northern Ireland normally start at £202 to £206 and go up from there. Loft extension planning permit in Wales can cost about £230.

There is no application cost for certain applications, such as listed structures or those that will be demolished in a conservation area.

If you live in England, Scotland, or Wales, you may use the planning portal and ePlanning fee calculators to figure out how much planning permission for your loft conversion will cost.

How long does planning permission take and how long does it last?

Your local planning authority is required to respond to your loft expansion application as soon as feasible. A simple planning application should be decided within eight weeks, a particularly large or complex application should be decided within 13 weeks, and an Environmental Impact Assessment should be completed within 16 weeks.

The majority of planning permit notices are valid for three years from the date of issuance. You can begin work at any moment within the three-year period, but it must be completed within that time frame. If you’ve been given a longer or shorter time frame, make sure to indicate it explicitly in your letter of approval.

What are the loft conversion building regulations?

Whether or not you need planning permission for your loft conversion, you must still adhere to the appropriate building regulations listed on the Government website and obtain building control approval through the planning portal or the ePlanning website. In Northern Ireland, you’ll need to apply to your local council for building regulations approval.

Building regulations are vital since they ensure that any loft conversion is physically sound and stable, that stairs are properly placed, and that it is safe to escape in the event of a fire. Depending on the type of expansion you’re considering, you’ll need to be aware of the following loft conversion regulations:

• Converting your loft into a storage space: You may need to seek building regulation approval if you wish to convert your loft into a storage room. The timber joists that serve as the “floor” of your loft (and the ceilings of the rooms below) aren’t usually meant to hold a lot of weight. If you place too much weight on these joists, they will be loaded above their intended capacity, and you will need building code approval to assure their safety.
• Creating a livable space: If you want to turn your loft into a livable area and use it as part of your home, you’ll need to get building code permission. Full loft conversions often necessitate a wide range of adjustments, some of which may compromise the building’s original structural integrity. Any renovation that does not adhere to building codes may endanger both the structure and its residents.
• Here’s a rundown of some of the loft conversion rules you’ll need to follow. Please keep in mind that this is just a starting point, and you should always consult a builder or your local government before starting any work.

Boarding

If you want to use your loft space for storage, you can board out the floor without needing to get Building Regulation approval. However, this is only true if you simply intend to store light objects. The majority of loft floors are designed to withstand a load of no more than 25 kilogrammes per square metre. If you plan to store anything heavier than this or convert your loft extension into a habitable room, you’ll need to apply for Building Regulations permission and build additional support.

Floor Joists and Beams

If you plan to convert your loft into a usable space, such as an extra bedroom, your existing ceiling joists would most likely be unable to withstand the weight of a loft conversion. To take the extra weight, new floor joists will likely need to be built alongside your current ones. To establish how far apart the floor joists must be to sustain the weight, a structural engineer will need to add the area.

Load-bearing walls

You’ll need to consider how new loads will be supported by your current internal and external walls because you’ll be adding extra weight to your loft. If new floor joists are required, they must be supported by a wall that runs the length of the home, all the way to the foundation.

Removing rafters

If you want to add light to your loft, you’ll probably need to cut a hole in the existing rafters and install roof windows. Because this will eliminate part of the roof’s support system as well as add weight, the roof will need to be reinforced by adding new timbers to handle the extra load.

Loft insulation

If you’re going to convert your loft into a living space, you’ll need to make sure it’s adequately insulated.

The U-value of an insulating material is measured in Watts per square metre per degree Kelvin (W/m2K), and it is expressed in Watts per square metre per degree Kelvin (W/m2K). The lower the U-value, the better at insulating heat the material is. Building requirements call for an insulation material with a thermal conductivity of 0.18W/m2K or less and a depth of at least 270mm for mineral or glass wool insulation in a loft conversion.

Sound insulation

Between usable rooms, sound insulation is essential, and in terraced and semi-detached houses, sound insulation between your loft and your neighbours’ lofts may be required. If this is required, the current party wall must be upgraded with soundproofing material.

Fire safety

According to loft conversion fire rules, extra fire protection with a minimum of REI 30 fire resistance must be installed in the floor between the loft and the rooms below. Each level of the stairwell should have smoke alarms installed, as well as an escape window that is at least 45cm wide. To safeguard the stairwell and create a safe escape route in all corridors, you may need to install new fire-resistant doors or partitions (FD 20 or 30).

Staircases

If you want your loft conversion to be habitable, you’ll need a permanent staircase that can also serve as a fire escape. The centre of your staircase should have 2 metres of headroom (1.9 metres for pitched roofs) and a pitch of no more than 42 degrees.

If there isn’t enough room, a smaller, space-saving staircase may be installed, however retractable ladders aren’t usually allowed. Loft ladders should only be used to get access to the roof for the purpose of storing items or doing repairs.

Because they’re a little steeper than standard stairs, most space-saving staircases have a smaller footprint, but each step must be no more than 220mm tall to comply with building regulations.

Another alternative for reducing space is to create a spiral staircase, which has its own set of restrictions and regulations. The ‘100mm sphere rule,’ which states that no gaps should exceed 99mm, should be followed by all spiral stairs. This applies to the space between the treads as well as the balustrade. Depending on how many rooms your loft conversion will have, you’ll also need to stick to certain measurements.

For loft conversions with only one room, your spiral staircase should have:

• A width of 600mm
• A maximum riser height (the height from the top of one tread to the next) of 220mm
• A maximum centre going (the measurement from the nose of one tread to the next) of 145mm

For loft conversions with two rooms or more, your spiral staircase should have:

• A width of 800mm (900mm in Scotland)
• A maximum rise of 220mm
• A maximum centre going of 190mm

Is it against the law to convert a loft without following building regulations?

If you don’t follow the laws for construction regulations and obtaining planning approval, you’ll have to undo the work you’ve done and face a big punishment. It’s usually a good idea to seek out all required planning approval because it can be time consuming and costly.

What is the four-year rule?

The four-year guideline applies to construction projects in England, Scotland, Wales, and Northern Ireland. Once all works have been completed, this is the time period during which enforcement action against an unlawful development can be conducted. Even if you don’t have planning approval, your loft conversion will be regarded ‘lawful’ after the four years have elapsed, and enforcement action will not be brought against you.

You will also be able to file for a Certificate of Lawfulness after this time, which is necessary if you want to sell your home. If you can show that the work was finished more than four years ago and has been in use during that time, you can apply for a Certificate of Lawfulness.

Please note that if the illegal work was disguised for four years, a Certificate of Lawfulness will not be issued. It’s far preferable to get the necessary permissions before commencing work than to risk it by not getting planning permission or building rules approval.

Your loft conversion may require planning approval, depending on the work you’re having done, and the tips above should help you figure out exactly what you need to do. Remember, if you’re ever in question, we recommend consulting an architect or builder, who will be in a better position to analyse your specific scenario.

You’ll probably want to bring in as much natural light as possible if you’re planning to convert your loft. Buildify specialises in loft conversions, house extensions, and property refurbishments, as well as a variety of flashings and coverings to meet your specific requirements. Not only can we assist you in finding the ideal goods for your conversion, but our guide to obtaining planning permission for skylights and roof windows will ensure that you meet all of the necessary requirements.