Transforming Your Loft into a Haven: A Comprehensive Guide to Designing and Building a Loft Conversion
Fast Plans Design Team • Jan 25, 2023

Unlocking the Potential of Your Loft: A Complete Guide to Designing and Building a Functional and Stylish Conversion

Loft conversions are one of the most popular forms of extension in the UK. When ground floor space is at a premium, or when Planning Permission likely won’t permit other types of extensions, there’s another choice: extend upwards and make use of otherwise wasted loft space. 


Like any extension, loft conversions are subject to a wide range of rules and regulations concerning structural integrity and safety. However, successive UK governments have worked to alleviate the complexity of planning and building regulations. Despite this, many are still confused as to what they can and can’t do with their property. 


Today, it’s easier to build effective loft conversions than ever - if you know how.


This guide will teach you everything you need to know about loft conversions so you can get the ball rolling and unlock new living space and value for your home. 


Here’s our ultimate guide to loft conversions. 


The benefits of a loft conversion


Thinking about a loft conversion? You’ve probably pondered over the benefits for some time already. The main advantages of loft conversions are that they create new liveable space in your property without moving or extending onto the garden. 


If you need space but don’t want to move, then loft conversions really are the perfect home investment. 


If you are planning on moving relatively soon, loft conversions have the potential to vastly increase the sales price of your property, representing some of the best ROI you can achieve in today’s economic climate.


Here are 5 key benefits of loft conversions:


1: Unlocking new living space

As mentioned, adding new space to the property is the most obvious benefit of a loft conversion. 


Depending on the house, your loft might easily be big enough for a large en-suite room, or even a bedroom with a study or small sitting room. Some can even be converted into multiple rooms with partition walls. 


The average loft space for 3-bed or 4-bed semis in the UK is around 20m2 to 30m2, but some are much larger, exceeding 40m2. 


For comparison, the average living room in the UK is
around 13 to 14m2. Not all of this loft space is directly usable, as you have to account for the sloping sides. 


Even so, most 3-bed or 4-bed semis have a large loft, and even older Victorian terraces usually have space for at least one small to medium-sized room. In most houses, all that extra loft space is almost totally unused and is probably full of old and forgotten dusty boxes, and maybe a Christmas tree.


2: Room with a view

Lofts are appealing living spaces. They’re private and well-separated from the rest of the house and many have superb views. 


Dormer windows provide panoramic views which can bypass buildings at a lower level. A great view adds considerable value in itself, especially in built-up areas. The view can even be enhanced with a balcony or veranda. 


3: Save garden space

Extending into the garden isn’t always ideal and may involve obtaining Planning Permission. Contrastingly, loft conversions are more likely to fall under Permitted Development Rights, which we’ll elaborate on shortly. 


Gardens are highly sought after in today’s property market, so it’s worth preserving that space if possible. After all, once you extend into the garden, you can’t change your mind. Moreover, many houses don't even have gardens to extend onto, despite having available loft space. 


4: Adding value to your home

We’ll elaborate on this below, but loft conversions are exceptionally value-efficient and can boost a home’s value by some 20%. 


In built-up areas, loft conversions are probably one of the best investments you can make for your home. Not only are you adding another room to your home, but you’re also moving from one property bracket to another by adding another bedroom. 


5: Bright and energy-efficient 

Providing that loft conversions are well-insulated with quality and preferably A+ rated double glazed windows, they tend to be energy-efficient and don’t require much heating outside of winter. 


Natural light will help warm them up, saving on energy and electricity bills. Lofts make excellent working and living spaces in built-up areas where other rooms receive comparatively less natural light. 


Is my property suitable for a loft conversion?


Whilst the benefits of loft conversions are clear, not all properties are suitable for loft conversions. Or at least, not all properties are suitable for straightforward loft conversions. 


Here are 5 questions to ask yourself if you’re considering a loft conversion:


Q1: What are the planning constraints in your area?

Permitted Development Rights apply to every local area in England and Wales, enabling property owners to modify their house without Planning Permission. But, when Planning Permission is required, plans are open to local interpretation that varies from authority to authority. 


For example, the Planning Authority’s tolerance to loft conversions will differ for a detached period home in a village location than in a modern row of semi-detached houses in a built-up area. 


Architects, surveyors and structural engineers will explain your options regarding Permitted Development and Planning Permission. The general trend across the UK is to allow development where possible. Extending, in general, has become easier in recent years. 


Q2: Do I have enough room?

The greatest consideration for any loft conversion is space. A conversion-worthy loft needs two things: sufficient volume and sufficient height. 


Loft converters and architects generally agree that a minimum height of 2.4m is required to make the conversion worthwhile. 


But what if the loft is massive in volume, but just a bit too low? Well, there are solutions for when the loft is ideally sized regarding its volume, but the overall height isn’t quite there. We’ll cover these shortly. 


Q3: Where will I put the stairs?

The stairs are a make or break for many loft conversions. You can’t skimp out with some form of a ladder or other thin and rickety staircases as that would never pass a building inspection. 


If space is limited, staircases are often built where cupboards are, or it might be possible to relocate the boiler and place the staircase in the airing cupboard. 


Sometimes, a redesign of the upper floor is needed to accommodate the staircase. It’s a solvable problem, even for smaller 3-bed semi-detached houses, but you’ll have to factor in the cost of reconfiguring your second floor. 


Q4: Will my loft conversion comply with Building Regulations?

Since loft conversions effectively add a third floor to your home, they’re subject to stringent rules regarding fire safety. In the event of a fire, escaping from the third floor is dangerous, which necessitates other escape routes or fire safety measures. 


Firstly, various structural materials will need to be upgraded; the walls, floors, doors, and loft stairs will all need to provide 20 or 30 minutes of fire resistance. It may also be necessary to fit fireproof materials under the stairs and in other parts of the second storey. 


Additionally, depending on your designs, you might need to construct a ‘protected escape route’. Some plans might require sprinklers or other enhanced fire safety measures. We’re going to take an in-depth look at Building Regulations shortly. 


Q5: Is my house too old?

Most homes can accommodate a reasonably straightforward loft conversion, except period homes, older listed buildings or homes built before the 1930s or so. Homes built between the 1930s and 1960s have traditional roofs, which actually make some parts of a loft conversion simpler to build. 


Homes built after the 1960s have stronger, trussed roofs, which take more work to alter, though this isn’t a major issue these days. 


Your surveyor and architect will advise if your home needs structural reinforcement to withstand the additional weight of a loft conversion. The ceiling joists normally require reinforcement.


How much head height is required for a loft conversion?


The Planning Portal states that loft conversions require a minimum height of 2.2m. Most companies prefer around 2.4m of height as a rule. 


There are two potential solutions when ceiling height is at a premium:


1: Raise the roof
: Raising the roof is sometimes not as complex as it seems. By literally extending the roof upwards slightly, it’s possible to unlock more vertical space. This can be a good option when there’s plenty of floor space, but just not quite enough height to convert. Since raising the roof affects the roof's structure, Planning Permission will usually be required. 


2: Lower the floors:
It may seem far-fetched, but it is possible to fit entirely new floor joists, lowering the floor in the process. This isn’t a simple job, but it may be appropriate in some situations. For example, if the loft conversion only covers a small portion of the top floor, lowering the floor might not be as disruptive as you might think. 


Will a loft conversion add value to my home?


Extensions have long been the best way to add value to any home, with single-room extensions displaying a return on investment of around 71% and an average profit-at-sale of around £17,000, according to Zopa. Other studies have found similar results, with loft conversions boosting home value by 15% to 25% across the UK, sometimes higher in London and other cities. 


Loft conversions specifically can boost a home’s value by some 20%, according to a Nationwide study
cited by Chancellors


The UK house price stood at £231,185 in January 2020 - 20% represents an average increase in value of around £46,000. 


The ONS has an interactive tool
to assist homeowners in estimating how much value an extension can add to their house. 


  • An average 25m2 extension in England and Wales is worth £59,075.
  • A larger 35m2 extension is worth £82,705.
  • A smaller 15m2 extension is worth £35,445.


In some parts of the country, extensions are worth considerably more:


  • For a 25m2 extension in and around the south-east and home counties: £100,000+.
  • In Kensington and Chelsea: £449,700.
  • East Dorset: £78,880.
  • Bristol: £64,400.


Types of loft conversions


There are 3 common types of loft conversion; Dormers, Mansards and Velux/roof light, and 1 less common type; the hip-to-gable. 


Most homes with a loft are convertible using one of these 4 types of loft conversions. 


1: Velux/rooflight loft conversion 

These are by far the simplest types of loft conversion, and they’re also the cheapest and quickest to build. By fitting a Velux or roof light window into a lift and converting it into a bedroom/living space, Velux conversions require minimal external work to the roof. 


Velux loft conversions are only suitable for large loft spaces with deep, gently sloping, or boxy roofs. 


  • The cheapest type of loft conversion. 
  • Works well with large, deep loft spaces with gently sloping sides.
  • Rarely requires Planning Permission.


2: Dormer loft conversion 

Probably the most popular loft conversion in the UK, Dormer loft conversions add new windows that protrude from the existing roof, adding space in the process. Standard vertical windows tend to be larger and more practical than rooflight windows. 


Dormers can be fitted singly, for smaller lofts, or in pairs for larger lofts. It may also be possible to connect two Dormers at 90-degree angles in what's known as an L-shaped Dormer. 


Your options depend on the shape of your roof - most 3-bed or 4-bed semis usually built after around the 1960s have hip or gable roofs, whereas larger or older houses might have intersecting T-shaped roofs or less common skillion and lean-to or hip and valley roofs. 


Whilst Party Wall Agreements are not necessarily required for Dormer extensions, they may sometimes require Planning Permission for large L-shaped or double Dormers. 


  • Dormers are ideal for most homes where a Velux conversion would be confining.
  • Flexible to the size and shape of the roof, and can face forwards or backwards from the house.
  • Smaller rear-facing single Dormers rarely require Planning Permission.


3: Mansard loft conversions

Though they often look similar to Dormer loft conversions, Mansard conversions modify the external wall to slope gently back towards the house, often at a 72-degree angle. 


Whilst Dormers form a box shape that protrudes from the house, Mansards build new external walls across the edge of the new extension to unlock more space, also rounding off the boxy shape of the Dormer. Mansards are often preferable where a longer loft conversion is required across the long edge of the home and typically extend away from the rear of the property. 


Mansard conversions are complex and are usually more expensive and time-consuming than Dormers. 


  • Provide more space than Dormers.
  • Smoother external look compared to protrusive Dormers. 
  • Suitable for larger, full-length loft conversions.


4: Hip-to-gable conversion

Hip-to-gable conversions only apply to properties with a hip roof. By hip-to-gable, this loft conversion literally converts a hip roof (which slants across 4 sides), to a gable roof (which has just two slants). 


Hip-to-gable conversions build a new external wall to unlock space from an unnecessary slanted roof by converting the inward-slanting end or side of the roof. In some situations, this option avoids party wall issues too. Hip roofs are more common on larger buildings with wide ground floors. Only end terraces can have hip roofs, and they’re uncommon on modern semis too.


  • Makes use of shallow slanted lofts. 
  • Can avoid Party Wall Agreements. 
  • Good choice for end terraces as well as large houses. 


Choosing the right type of loft conversion

The best option for you depends on your spatial requirements and existing loft space. 


  • Velux conversions are quick and budget-friendly, but they may not provide enough headroom in shallow-roofed houses. Rarely a good option for hip roofs. 
  • Dormers are the most popular option and provide headroom without making major changes to the roof (in the case of single Dormers).
  • Mansards are popular for terraced houses but are usually only viable when the roof is quite long. 
  • Hip-to-gable conversions are the go-to for houses with hip roofs that are easily converted to gables in the loft conversion process.


Loft Conversion comparison table


Velux/Rooflight - Cheapest option. Dormer - Most popular option. Mansard - More expensive option. Hip-to-Gable - More expensive option.
Mid Terrace Suitable for terraced houses with large, deep lofts. Almost never requires Planning Permission. Popular choice for mid terraces. Easy way to add an extra room. Single Dormers rarely require Planning Permission. Popular choice for mid terraces. Easy way to add an extra room. Usually requires Planning Permission due to extensive roof. Not applicable to mid-terraced houses.
End Terrace Suitable for end-terraced houses with large, deep lofts. Almost never requires Planning Permission. Yes, but space at the front and rear might be more limited on the end terrace. Rarely requires Planning Permission. Yes, but space at the front and rear might be more limited on the end terrace. Usually requires Planning Permission due to extensive roof works. Excellent choice for end terraces where one side of the roof is a hip roof convertible into a gable roof. Usually requires Planning Permission due to extensive roof works.
Semi-Detached House A good budget choice for semi-d loft conversions. Probably not a great use of space compared to Dormers, though. Rarely requires Planning Permission. Probably the most popular combination of loft conversion in the UK. Rarely requires Planning Permission (size dependent). Popular choice for converting the rear-facing side of semi-ds. Usually requires Planning Permission due to extensive roof works. Great choice for semi-detached houses with hip roofs. Can be combined with Dormers or even Mansards. Usually requires Planning Permission due to extensive roof works.
Detached House A good budget choice for detached loft conversions. Probably not a great use of space compared to Dormers, though. Rarely requires Planning Permission. L-shaped or double Dormers are an excellent choice for detached houses. Often require Planning Permission due to size. Often used to create long loft conversions over the longest side of a detached roof. Usually requires Planning Permission due to extensive roof works. Great choice for detached houses with hip roofs. Can be combined with Dormers or even Mansards. Usually requires Planning Permission due to extensive roof works.

Planning Permission 


The UK government has been trying to encourage homeowners to extend their homes for some time, relaxing the rules in the process. 


As such, Planning Permission isn’t the headache that it once was, but that does depend on where you are in the country and your plans. 


Certain extensions don’t require any form of Planning Permission - these fall under what is known as Permitted Development Rights (PDRs). 


PDRs allow homeowners to make certain modifications to their properties without seeking Planning Permission. However, you must still seek consent from the Local Authority in the form of Prior Approval. Even if your project easily falls under PDRs, the plans must be given the green light by the Local Authority and Building Control, though this is usually a quick process providing that your plans and drawings are in good order. 


Loft conversions are one such modification that are subject to PDRs, provided certain conditions are met. A loft conversion, by law, is "the enlargement of a dwellinghouse consisting of an addition or alteration to its roof". 


For your home to qualify for PDRs, it needs to fulfil the following basic criteria: 


  • Cannot be a flat contained within a building, or a building containing one or more flats. If you want to add a loft conversion to a flat, you'll generally always need Planning Permission, as well as consent from the landlord or freehold owner of the building. 
  • The home mustn’t have had an extra story added previously. 
  • If the home was converted from a non-residential building to a house, PDRs will not apply. 
  • Was not built as a ‘New Dwellinghouse’ under PDRs already


Specific conditions apply to buildings built on Article 2(3) designated land, which includes: 


  • Conservation areas.
  • Areas of outstanding natural beauty (AONBs).
  • the Broads.
  • In a National Park.
  • On World Heritage Sites.
  • There are also some designated areas specified for the protection of the countryside, which don't fall under the above categories, including some sites of specific scientific interest (SSSIs).


If your home is in any of the above areas, it doesn't necessarily mean that you'll need Planning Permission. What it does mean is that contacting the local Planning Authority is absolutely essential. Planning involves a degree of local interpretation, and your local authority will likely have specific guidance for your area. In all likelihood, most houses built on designated land will be entitled to some form of loft conversion under PDRs.


Finally, if your home is a Listed Building, you must obtain Listed Building Consent. Failing to do so before starting work is a criminal offence. 


If your home meets the above criteria…

Then you'll likely be able to build a loft conversion without Planning Permission, subject to the following limits: 


  • The conversion doesn't exceed the original height of the roof.
  • Must not extend beyond the existing front-facing plane of the roof slope, when facing the highway. 
  • Conversion can’t overhang from the front of the building. 
  • Materials used must be similar in design and appearance to the existing house.
  • The conversion doesn’t amount to an extra volume of 40 cubic metres or more for terraced houses, or 50 cubic metres otherwise. 
  • You cannot build verandas or balconies without Planning Permission.
  • Any upper-floor windows in a side elevation must be obscure-glazed and non-opening, with the exception of windows fitted more than 1.7 metres above the floor.


Visualising how these rules apply to your own property isn’t easy. The architectural and design consultation process will help establish what you can and can’t do under PDRs. 


Even if your loft conversion does need Planning Permission, the process really isn’t as tedious as it once was, so long as you provide all the necessary drawings, detail, and background for the project. 


Lawful Development Certificates

Lawful Development Certificates are obtainable from the Planning Authority for a small fee. They declare that your intended development is lawful to go ahead and is highly encouraged (or required) by many contractors. 


LDCs are also extremely useful when selling the house, as they certify that the conversion was done legally. 


Party Wall Agreements


If your project falls under PDRs, there's another piece of ‘red tape’ to cut.


Party Walls are shared walls that divide your home from your neighbour’s home (called Adjoining Owners). All terraces and most semi-detached houses will have at least one party wall, whereas flats will have multiple. Party Walls are controlled by a piece of legislation called the Party Wall Act


A loft conversion will likely involve the Party Wall Act if:


  • You need to cut into the party wall and install new load-bearing beams.
  • You need to install a damp course proof within the party wall.
  • You need to increase the thickness of the party wall.
  • You need to replace or remove part of the party wall. 
  • You need to cut into the wall to install insulation.
  • You want to remove or alter a chimney breast on the party wall.


In any of these situations, you'll need to serve your neighbour a (preferably professionally drafted) Party Wall Notice. Your neighbour will have 14 days to agree to your plans or object. If they object, you'll need to appoint a Party Wall Surveyor to provide an objective assessment, who will either approve your plans and provide you with a Party Wall Award, or decline them. 


If the surveyor provides you with the award, then there’s little your neighbour can do to stop you from working on the Party Wall (but bear in mind that they can appeal). 


Building Regulations and Fire Safety 


Another crucial pre-construction consideration are Building Regulations. 


Building Regulations are a legally enforceable framework for building safety. The rules differ in England, Scotland, Wales and Northern Ireland. Since a loft conversion forms a ‘liveable space’, they're subject o Building Regulations that ensure the structural safety and safe use of space for living in. 


In England, there are two main parts to Building Regulations, part A and part B, as well as 14 other groups of specifications that span everything from electrical safety to ventilation, insulation, energy efficiency and more. 


  • Part A: Part A covers the structure of the loft conversion.
  • Part B: Part B covers fire safety. Where loft conversions form a third or fourth floor, they differ if they form a second floor, as would be the case in a bungalow. 


The structure and components of the loft conversion 

Many aspects of building regs pertain to the structure and spec of the loft conversion. Here are the main considerations for an average loft conversion project: 


  • Floors and beams: Floor joists will need to be sufficiently strong to support the load of the new room and fittings. This usually requires reinforcing joists, or fitting new ones. It’s more common to fit new joists alongside the old ones. 
  • Wall construction: New walls fitted must be able to support the roof structure. Any walls fitted as part of a Mansard, Dormer or hip-to-gable must also be compliant.
  • Staircase: The staircase will be subject to rules to ensure its longevity and load-bearing properties. 
  • Soundproofing: As per Part E of Building Regulations, the loft conversion must be sufficiently sound-insulated. 
  • Thermal insulation: There are two broad ways to insulate the loft conversion; either cold or warm insulation. Cold roof insulation is laid between the ceiling joists and warm on top of the room itself. 
  • Electrics: Part P of Building Regulations specifies rules for electrical safety and load. 
  • Ventilation and Moisture Control: Rooms require sufficient opening windows and moisture control membranes to be fitted in ceilings and walls. Bathrooms and toilets have other specifications for ventilation, like vents. 


Fire Safety

Fire safety is one of the trickiest elements of building a loft conversion. Loft converters, builders and architects have an in-depth knowledge of the rules, and most modern plans and designs are built to be compliant in every respect. 


  • Windows: Windows must be large enough to form an escape route. Openings need to be 450mm x 450mm and will need to be sufficiently high from the floor, but not too high to prevent escape. 
  • Protected Escape Routes: When a loft conversion adds a third storey to your home, you'll need to build a protected stair enclosure that leads all the way down to a valid exit door. Essentially, this means that your new staircase must connect to the old one in some way, leading all the way to your ground floor hallway or another escape route. Both the stairway and any doors will need to provide 20 to 30 minutes fire protection (20 for doors, 30 for the staircase and corridor walls). 
  • It may be necessary to build a sprinkler system in open-plan houses, as the escape route will not be enclosed (required in Wales).
  • Smoke alarms: You’ll need lined mains-powered smoke alarms for each floor of the house.


How much does a loft conversion cost?


The costs of loft conversions vary depending on the size of the loft, the desired design/loft conversion type, location within the UK, the staircase and any necessary relocation of the boiler. 


Also, building a simple bedroom, sitting room or study without a toilet or bathroom is much cheaper than an en-suite. 


Here are the main cost factors: 


  • The desired style of loft conversion.
  • The age of the property and roof type (e.g. modern or traditional roof).
  • Where you are in the UK.
  • Works needed to fit a staircase.
  • Fire Safety and Building Regulations costs. 
  • Relocating the boiler.
  • Fitting an en-suite, toilet or bathroom. 
  • The spec of the insulation and windows. 
  • Planning Permission and Party Wall Agreements, where applicable.
  • Raising the roof/lowering the floor.
  • Relocating or removing chimney breasts. 


Some average costs for different types of loft conversions in the UK are below. These prices are just a guideline of what an average project will cost. The price will generally be lower in Wales and the north of the UK, and higher in the south and London. 


As you'll see, Velux loft conversions are by far the cheapest option as they don’t require any external roofing works and few structural modifications, except fitting the window and possibly moving or removing some beams. 


Dormers are usually cheaper than Mansard and hip-to-gable conversions since they require fewer works to the roof and structure.


Average Loft Conversion Prices Velux Dormer Mansard Hip-to-Gable
Terraced/Semi-d: 20m2 floor space or 1 room £10,000 to £22,000 (with one window) £25,000 - £42,000 (with one Dormer) £28,000 - £48,000 (with one window) £28,000 - £48,000 (with one window)
Semi-d: 30m2 floor space or 1 room £20,000 - £26,000 (with one window) £30,000 - £50,000 (with one Dormer) £35,000 - £55,000 (with one window) £35,000 - £58,000 (with one window)
Large Semi/Detached: 48m2 or 1 to 2 rooms £24,000 - £38,000 (with two windows) £40,000 - £65,000 (with two Dormers) £45,000 - £68,000 (with two windows) £40,000 - £70,000 (with two windows)
Detached: 64m2, or 2 rooms £30,000 - £60,000 (with 2+ windows) £45,000 - £90,000 (with two Dormers) £50,000 - £95,000 (with two windows) £50,000 - £95,000 (with two windows)

Cost breakdown


Project Planning
Architectural fees, survey, consultation and project management £1500 to £3000
Lawful Development Certificate £100 to £250, depending on the council
Planning Permission Currently £206
Building Inspections and Approval £500 to £1000
Building Works
Scaffolding £3000 to £5000
Internal preparation to the walls and floors £2000 to £3500
Installing a Dormer, Mansard or hip-to-gable £5,000 to £10,000
Installing a Velux or roof light window £1,000 to £3,000
Joinery, walls and staircase £6000 to £8000
Strengthening the floor and steelwork to reinforce structure £5000 to £8000
Plastering £3000 to £5000
Electrics £1,000 to £1,500
Plumbing £2,000 to £3,000
Decoration and interior design £2,000 to £5,000
VAT (20%) Around £8,000
Total £45,000 to £60,000+ (for an average project)
Extra Costs
En-suite £3000 to £6000
Moving boiler £1,000 to £5,000
Underfloor heating £800 to £2,000
Bat Survey (if applicable) Around £300

The loft conversion process


The average construction time for most loft conversions is approximately 4 to 8 weeks. You should factor in an additional 4 to 12 weeks for architectural drawings, surveys, consultations and project planning, as well as Planning Permission, surveys and Party Wall Agreements.


1: Planning stage - 4 to 12 weeks

Planning your loft conversion requires conducting surveys, which Fast Plans provides as part of our drawings service. This will help you work out what you can and can’t do with your space and whether you’ll need Planning Permission, a Party Wall Agreement or other surveys, like a Bat Survey. 


Then, your chosen architect or drawings service will draw up initial plans for your loft conversion. This might take 1 to 2 weeks. Once you give your plans the green light, you’ll need to submit them to the Local Authority and Building Control for approval. 


Lawful Development Certificates are then obtained. If you require Planning Permission, submitting full plans and detailed drawings will expedite the process. Fast Plans will submit your plans to local authorities on your behalf. 


Your drawings and plans will also guide your search for contractors. Fast Plans provides full specifications and projected costings, which will help you gain an accurate and competitive quote. 


2: Scaffolding and site prep - 1 to 2 weeks 

The loft is cleared, and any cold water tanks are removed. Scaffolding will secure the exterior of the building and prepare the site for construction works. Electrical wiring and any existing plumbing will be assessed to ensure that construction works don't cause any damage. 


3: Construction stage - 2 to 8 weeks

The construction phase varies depending on the size and scope of the project, as well as access and any extra procedures required, such as installing a bathroom, partition walls, moving or reinstalling the boiler, etc. 


  1. Most contractors will secure the floor first, reinforcing joists and adding new ones where needed. Floor insulation and flooring is laid. 
  2. The rafters will be partly or wholly removed where a Mansard, Dormer or hip-to-gable is being constructed. Reinforcements or new rafters may be required. Walls reinforced and chimney breast removed, if applicable. 
  3. Mansards, Dormers or hip-to-gable conversions are constructed after the structure is secured. Rooflights or Velux windows will be fitted in the ceiling around now. 
  4. Insulation and exterior roofing works will be carried out, and windows installed.
  5. Any new partition walls are likely to be installed once the conversion itself has been built. 
  6. Electrical, plumbing and insulation work usually begins around now, once wall plates have been inserted and insulation fitted in partition walls.
  7. The new bathroom or toilet is fitted, if applicable, and the boiler re-routed or moved.
  8. Often, the staircase is fitted after the main construction is finished but before plastering and interior design. This varies from project to project.
  9. Once fitted out and decorated, the loft space is cleaned up ready for inspection.
  10. Contact Building Control for inspection (they may also inspect the building at various stages throughout construction). A Completion Certificate is issued. 


From start to finish, it’s wise to budget around 6 months from the minute you get the ball rolling to the minute a Completion Certificate is issued, and this is sparing any setbacks or delays. 


In addition to obtaining permission from authorities obtaining a Party Wall Award from a troublesome neighbour is one of the most significant delays. The larger and more complex the project is, the longer it'll take, especially when Listed Building consent or a full structural survey is required. 


Do I need an architect to design my loft conversion?


To carry out a loft conversion, you'll need to obtain certain compliant drawings to submit to both local authorities and contractors. These will need to be of an accurate and professional standard - if they're incomplete, inaccurate or of otherwise poor quality, you'll not be able to get your project off the ground. 


It’s imperative to obtain plans from an architect, structural engineer or professional drawings service. Fast Plans offers a streamlined loft conversion planning and drawings service that provides you with:


  • A full measured survey and consultation. 
  • Professional design and drawing service with unlimited revisions. 
  • Submission of plans to local authorities, fully managed by us.
  • Complete engineer's drawings and calculations, ready for submission to Building Control (which we’ll also manage for you).


Plan your perfect loft conversion with Fast Plans


Loft conversions can add significant value to your home and rate as one of the most popular extension types in the UK. By converting your disused loft into a liveable space, you’re adding an extra room to your house without the need to move or extend outwards onto the garden. 


Fast Plans is a loft conversion and home extension planning, design and drawings service that will help you get your ideas off the ground. We provide a streamlined, professional service that doesn’t sacrifice attention to detail. 


If submitting plans to local authorities for Building Regulation approval seems like a major hassle, then don’t worry, we’ll handle it for you.


Our team of professional engineers, architects and design and construction professionals work together to produce the accurate, compliant and effective drawings you need to make your loft conversion dreams a reality. 


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Loft conversion design consideration FAQ


Here’s an FAQ of common questions regarding the design process and options of loft conversions: 


  • Do I need to soundproof my loft conversion?

    Some level of soundproofing is necessary for Building Regulations if you have neighbours that share Party Walls. Mineral fibre quilts are often laid in the floor for insulation and soundproofing purposes.

  • What ventilation will my loft conversion need?

    Proper ventilation is necessary for Building Regulations. Rooms will need sufficient opening windows. There are separate, more intensive rules for toilets and bathrooms. 



  • How to heat a loft conversion?

    Most people choose to install new radiators in the loft conversion, but the existing central heating system may need to be upgraded or even replaced in the case of conventional gravity fed systems. Electric radiators are a popular option, as is underfloor heating. Underfloor heating is an inexpensive and efficient way to heat a loft conversion that avoids placing extra strain on the central heating system (in the case of electric systems). 

  • Choosing windows for a loft conversion

    Windows vary hugely in price, with cutting-edge A++ rated double glazed or triple-glazed windows costing well into the thousands. Installing good-quality, well-insulated A+ rated double glazed windows is highly advisable. 



  • How should I insulate my loft conversion?

    Sufficient insulation is required for Building Regulations. Wool-type insulation is the cheapest but also the thickest. Polyfoams are a newer option that's suitable for thinner insulation cavities.



  • Can I add a bathroom in a loft conversion?

    Yes, but this will incur additional costs. Installing a bathroom also increases cold and hot water demands, leading to additional strain on the home’s central heating system. It may need upgrading if the room is going to be used often. 



  • Do I need to change the ceiling joists?

    It’s highly likely that the joists will need to be reinforced or replaced entirely. This depends on the house's design, but it’s standard practice to make structural changes to the weight-bearing ceiling joists. 



  • How to add a staircase to a loft conversion

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