Understanding Loft Conversions: Types, Benefits, and Planning Steps (Full Guide)

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Loft conversions are a fantastic way to amplify space and add value to properties. Whether you’re looking to create an extra bedroom for your home, a home office, or to maximise the rental income of your HMO, a loft conversion can provide the perfect solution. Is your property suitable for a loft conversion, and is it worth it? Let’s walk you through the essentials of loft conversions, from planning and design to construction and costs.


What Is A Loft Conversion?

How Much Value Does Loft Conversion Add? Benefits of a Loft Conversion


    Loft Conversion vs Extension

    How Long Does a Loft Conversion Take

    Types of Loft Conversion

    Do You Need Planning Permission for a Loft Conversion

    Loft Conversion Planning Process

    Can My Neighbour Stop My Loft Conversion?

    Can You Do an HMO Loft Conversion? (Feasibility)

    Should You Do an HMO Loft Conversion? (Viability)

    How Much Does a Loft Conversion Cost

    What’s the Best Time of the Year to Do a Loft Conversion


    What Is A Loft Conversion?

    Before getting into the details, let’s start from the ground up. A loft conversion involves transforming an empty loft or attic space into a habitable and functional space like an extra bedroom, gym, study, library, or home office. It’s a cost-effective way to expand your living space without needing a costly extension.

    They first became popular in the SoHo area of New York City in the 1960s and quickly spread worldwide, gaining popularity in the UK due to the smaller living spaces available. However, not all lofts are suitable for conversion. Before proceeding, we must assess factors such as head height, roof pitch, and structural integrity; we’ll return to this later.

    There are several reasons why you may decide to do a loft conversion; for HMO landlords, the most obvious one is an increased rental income.

    How Much Value Does Loft Conversion Add? Benefits of a Loft Conversion

    Depending on the area, an HMO loft conversion could be expensive, not to mention complicated. So why would a sophisticated HMO investor like yourself want to convert a loft into one or more bedrooms? As investors, we always like to think of “Return On Investment (ROI),” and here are some reasons why you should consider an HMO Loft Conversion.

    1. Increased Rental Income

    As an HMO investor, you’re looking to provide quality housing to people. But you also need to make a return on your investment. A loft conversion is an incredible way to increase your rental income. A quality loft conversion can work as a fully functional bedroom and add up to 30% more rental income to your property (depending on size). This gain is a significant way to boost monthly cash flow and get a massive return on your investment.

    Depending on the size of your loft, you could even fit more than one bedroom. What could two extra bedrooms mean for your HMO and monthly rental income?

    2. Increased Valuation (Commercial Valuation)

    For an HMO investor, getting a commercial valuation (rather than a traditional Brick-and-Mortar Valuation) is like sitting on a rocket ship. The increased valuation means you’ll get more money out of each deal. Consequently, this allows you to buy more HMOs and provide more quality housing. It’s a snowball effect from thereon.

    Commercial valuations for HMOs are based on

    • Number of bedrooms
    • Number of ensuites

    Lenders view a property as an income-generating asset and want to know its income potential. Imagine the appeal when you say you’ve added two extra rooms from a loft conversion.

    Moreover, in high-demand areas like London, the valuation for every sqm of habitable space is three times that of a brick-and-mortar space.

    3. Resource Efficiency

    Adding more people under the same roof maximises resources like the kitchen, gas, electricity, and water. As a high-quality investor who cares about improving the quality of life of your tenants —as long as you’re within the legal limit— more occupants can mean more efficient use of resources.




    HMO Loft Conversion – Ensuite Bedroom


    Loft Conversion vs Extension

    While a loft conversion isn’t the only alternative available to maximise the potential of a property, there are several reasons why property owners and landlords may consider a loft conversion instead of an extension. Loft conversions and extensions offer opportunities to expand living space, yet they differ regarding space utilisation, planning permissions, costs, construction timeframe, impact on outdoor space, and architectural considerations.

    For instance, extensions may encroach on outdoor space, especially if they involve a rear or side extension, affecting the size of your garden or outdoor area. Loft conversions, being within the existing structure, typically don’t impact outdoor space. They often demand a shorter construction timeframe than extensions and can reach completion within weeks to a few months. Additionally, loft conversions typically require less planning permission and are more cost-effective than extensions.

    Deciding between the two depends on your budget, space requirements, planning constraints, and personal preferences.


    How Long Does a Loft Conversion Take

    The duration of a loft conversion can vary depending on several factors, and being aware of these can help you craft a better plan for the project. Here’s a breakdown of what influences the timeline.

    Timeframe Factors in a Loft Conversion

    Type and Complexity of Conversion


    The type of loft conversion you choose plays a significant role in the timeframe. A simple roof light conversion may require less time than a full dormer or mansard conversion, which involves structural changes to the roof. The complexity of the design and construction will impact the project’s duration.

    Planning and Permission

    Obtaining necessary planning permissions, when required, can add time to the process. While many loft conversions fall under permitted development rights and do not require planning permission, checking with your local authority is essential. If planning permission proves necessary, include the time needed for the application process, which can take several weeks or even months.

    Architectural Design and Structural Engineering

    Designing the layout and obtaining structural engineering calculations are crucial steps in the loft conversion process. The stage involves working with architects and engineers to ensure the conversion’s structural integrity. The time needed for design and engineering can vary depending on the complexity of the project and the responsiveness of the professionals involved.

    Building Regulations and Compliance

    Adhering to building regulations ensures safety and quality in your loft conversion. This approach includes structural stability, fire safety, insulation, and electrical wiring requirements. The project timeline must account for the time required to obtain necessary approvals and ensure compliance with regulations.

    Construction and Work

    The actual construction phase of the loft conversion can take several weeks to a few months, depending on the size and complexity of your project. Factors such as weather conditions, supply of materials, and the availability of the construction team can impact the construction timeline. Delays can occur due to unforeseen issues, such as hidden structural problems or supply chain disruptions.

    Finishing Touches and Decoration

    After completing the structural work, consider the additional time for plastering, painting, and installing fixtures and flooring; these tasks influenced, for instance, by the scope of work and the availability of tradespeople.

    Inspections and Certifications

    Following the completion, and if needed, it’s time for inspections to ensure compliance with building regulations. The phase includes inspections by building control officers and any additional certifications required for electrical or plumbing work.



    Types of Loft Conversion

    There are different alternatives for loft conversions depending on the property layout, and here are the most common types:

    The dormer loft conversion is suited for all types of houses and family homes.

    A popular form of permitted development loft conversion that includes a window-featured extension to the roof, the dormer loft conversion can take on the full width of the attic. It involves adding a horizontal ceiling with vertical walls and sits at a 90-degree angle to the floor. A dormer loft conversion is a box-like shape projecting vertically from the sloping roof. They usually have Skylights and Velux windows to provide lots of natural lighting to the room.

    Most dormer loft conversions do not need Planning Permission and fall under Permitted Development. That said, existing HMOs fall outside permitted development and require a full planning application for a loft conversion. More on this to follow.

    Best Suited For — All types of houses but Family Homes in particular.

    Permitted Development Loft Conversion


    Aerial view of a property showing the dormer conversion

    2. Hip to Gable Loft Conversion

    Best suited for end-of-terraced, semi-detached properties, detached houses, or bungalows. Not suitable for mid-terraced houses.
    You can apply a hip-to-gable loft conversion to properties with a hipped roof. A hipped roof is a sloping side roof beside the sloping front and rear roofs. This conversion replaces your sloping side roof (Hip) with a vertical wall (known as a Gable), allowing for more usable space inside the loft.

    3. L Shape Loft Conversion

    Best suited for mid-terrace, end-of-terrace, semi-detached with existing L-shaped layout.

    The L-shaped loft conversion is a creative combination and connection of two or more dormer conversions. For instance, a dormer conversion on the front roof and another on the rear roof, finally connecting them to resemble a distinctive L-shape.

    This type of loft conversion is prevalent among HMO investors due to the possibility of an ensuite bedroom in the loft. A well-designed L-shape loft conversion can allow for two more bedrooms.

    Best Suited For mid-terrace, end of terrace, semi-detached with existing L-shaped layout.

    4. Mansard Conversion

    A mansard loft conversion involves altering the roof’s structure to create additional living space within the attic. This type of conversion typically features a flat roof with a raised party wall and a sloping rear roof. The main distinguishing feature of a mansard conversion is the creation of a full-height wall at the front of the property, with a shallow slope at the back.

    In a mansard conversion, builders alter the entire roof to create a flat roof with a sloping rear section. This transformation allows for maximum headroom and usable floor space within the loft. On the other hand, a dormer conversion entails extending the existing roof structure to provide extra headroom and floor space. So, typically, a mansard conversion tends to be more expensive and complex than a dormer adaptation due to the extensive structural alterations required.

    Another critical consideration is that mansard conversions often require planning permission from the local authority due to the extensive alterations to the roof structure and changes to the property’s appearance.


    Also known as a Velux conversion, this is the simplest and most cost-effective option. The roof light conversion primarily involves installing roof windows into the existing roof slope, providing ample natural light and ventilation without modifying the structure or the loft’s available space. Consequently, simple loft conversions with Velux windows can go without planning permission under the right circumstances.


    Do You Need Planning Permission for a Loft Conversion

    You don’t always need Planning Permission for loft conversions; for instance, most dormer loft conversions come under Permitted Development (PD), which is the automatic grant of permission by the local authority within an area for construction or change of use. When can you build a dormer under PD? Assuming your loft conversion follows the PD criteria, and the property doesn’t come under a conservation area, you will likely make your dormer under permitted development.

    Criteria for Permitted Development Loft Conversion

    How do you know if your designs align with the Local Authority Guidelines for Permitted Development? Although varying by Council, here’s a high-level spec:

    • The new loft space volume is less than 40 cubic metres for terraced houses and 50 cubic metres for detached and semi-detached houses. Any existing loft extension must be included in the allowance.
    • The loft conversion doesn’t extend beyond the plane of the existing roof slope at the front of the house.
    • The loft construction uses similar materials to the rest of the house.
    • The loft can’t protrude beyond the facade wall of the building.
    • A dormer extension can’t be higher than the ridge (highest part) of the roof.
    • You must keep at least 20cm of roof eaves around the perimeter of the dormer.
    • Side windows must be obscure glazed.
    • Any windows less than 1.7m from the ground must be non-opening.
    • The property isn’t located in a national park, world heritage site or conservation area.

    In HMO Planning Permission, I’ve discussed planning, permitted development, and overcoming council objections in great detail.

    While your loft conversion may not need planning permission, it’s always advisable to confirm this with the local authority. Alternatively, speak to one of our team, and we’ll be more than glad to help.

    Loft Conversion and Change of Use Class

    Is your loft conversion part of a larger project where you’ll be changing the current use of your property? In that case, you’re entering a well-known scenario for HMO developers, changing use classes. I explained the various classes relevant to HMO conversions in my post on HMO Planning Permission; these are essentially:

    • C3 — Single Family Home
    • C4 — Small HMO (up to six occupants)
    • Sui Generis — Large HMO (7+ occupants) or non-standard construction

    If you’re converting a family home (C3) into an HMO (C4), it’s best to bundle the loft changes with the rest of the conversion. As mentioned before, the leading cause is that if you’re doing a loft conversion on an existing HMO (class C4), you can’t use Permitted Development rights. Instead, you must complete a full planning application for your loft conversion.

    Planning for a loft conversion is always recommended as part of your HMO Conversion plans. Remember that before starting any work, obtaining the necessary planning permissions and adhering to building regulations is essential. Building regulations cover crucial aspects such as structural stability, fire safety, insulation, and electrical wiring.

    We’ve covered the HMO regulatory ecosystem in depth, exploring everything from planning permission and fire doors to licensing, space requirements, and council taxes.


    Loft Conversion Planning Process

    Let’s say you’re doing a more complex loft conversion, and it doesn’t come under Permitted Development rights (as it would be the case for operating HMOs).

    • How do you go about the planning process?
    • What drawings or documents should you submit for planning?
    • What is the duration and cost involved?

    Documents/Drawings to Submit

    It’s highly advisable to appoint an architect to help you with this as the level of detail required in the drawings varies from Council to Council.

    Here’s a non-exhaustive list of documents and drawings you need to submit for your loft conversion planning:

    • Concept drawings.
    • You also need to show the section, side elevation, roof plan, front and rear elevations, dormer plans
    • The Council needs to know the volume, height, materials (to cover the dormer) and other specific materials, as well as the street appearance of the dormer (e.g. cladding).
    • They don’t care about insulation/structure at this stage.
    • Ordnance Survey Map (showing the location of the building on a scale of 1250)
    • Complete the form on the planning portal.

    As you can see, the process is relatively straightforward and not overly complex.

    However, if the details submitted are insufficient or incorrect, the Council will refuse the application only if the design doesn’t meet the permitted development rights requirements. The Council may also request more information or to rectify the application with drawings more pertinent to the PD application.

    This is all part of the validation process.

    Application Process

    The planning process for a loft conversion is much like that of a Change of use class (C3 to C4).

    • Step 1 — Create a new application on the planning portal.
    • Step 2 — Upload the relevant documentation and drawings.
    • Step 3 — Fill out the form.
    • Step 4 — Submit the application and pay the fee.


    How long does the Permitted Development Loft Conversion application take, and what if you need to go through planning? Well, the timelines are comparable. It takes approximately two weeks for the Council to acknowledge your application and six weeks for a decision notice.

    For unusual designs/constructions or unforeseen circumstances, this may take longer, depending on the Council.

    Also see: What is Article 4, and how does it affect your HMO’s loft conversion plans?


    Can My Neighbour Stop My Loft Conversion?

    The short answer is NO if you’re going through a Permitted Development Loft Conversion. A PD application doesn’t go through a consultation period and doesn’t include the scope for neighbours to raise objections.

    But, if you need to go through a full planing application, there’s a chance you may receive objections from neighbours. As I always recommend, informing your neighbours about your plans well in advance is best. This strategy can reduce the likelihood of objections and foster a friendly relationship.

    Will You Need a Party Wall Agreement?

    In certain cases, if you share a common wall or boundary with your neighbour, you may need a legal agreement upfront. This process, commonly known as a party wall agreement, is necessary when a loft conversion involves work on a shared or adjoining wall between properties, particularly work that may affect the stability, structure, or integrity of the wall.

    A party wall agreement, typically obtained before initiating any work, outlines the proposed work, access arrangements, responsibilities, and dispute resolution procedures. The property owner undertaking the loft conversion initiates the agreement, usually through a qualified party wall surveyor or building professional. They can offer guidance on whether a party wall agreement is necessary, the process involved, and how to comply with relevant legal requirements.


    Can You Do an HMO Loft Conversion? (Feasibility)

    How can you tell whether an HMO loft conversion is possible before purchasing the property? After all, you want to know exactly what outcome to expect before signing the dotted line. One of the worst things for you as a property investor is to buy a property with the hope of getting X number of occupants in, only to discover you can’t make it happen.

    Understanding feasibility pre-purchase is vital to your job as a professional property investor. Here are four no-sweat tricks I’ve picked up over the last 15 years of investing in HMOs to speed up your assessment:

    • Stand outside the property — look at the neighbouring properties and check for dormer conversions; this tells you the loft has enough height for conversion, and there might not be a lot of restrictions.
    • Measure the loft height by measuring the ridge (highest point of the roof) to the loft floor. The height should be at least 2.5m; this will ensure that you have sufficient height to meet the minimum 2m headroom requirement for your loft to be signed off as a bedroom.
    • Measure the thickness of the loft floor. In most cases, it is 11–13 cm. In general, the thicker the floor, the better.
    • Measure the height of the first floor. The recommended height is 2.5–2.7m for a comfortable loft conversion.

    Armed with these tips, you’ll soon be able to tell within minutes if you can fit a loft into the property and convert it into a bedroom; this will help with your numbers and negotiation. So, make sure to check this on each HMO viewing.


    Should You Do an HMO Loft Conversion? (Viability)

    In the previous section, we discussed feasibility, which involves determining whether a loft conversion is possible by inspecting the property and starting with three key measurements. But just because you can do it doesn’t mean you should; this is where the viability study comes in.

    Budgeting and costs are essential considerations when planning a loft conversion. Here’s an example of the most relevant aspects to assess:

    1. Initial Budgeting: The first step in a loft conversion is determining your initial budget. What is the estimated amount of money you plan to allocate for your loft conversion? In your budget, you should weigh factors such as the size and complexity of the conversion, the type of conversion (e.g., roof light, dormer, mansard), and any additional features or modifications you want to include.
    2. Cost Breakdown: A typical loft conversion involves various costs, such as:
    • Construction costs: Labor, materials, equipment rental, and subcontractor fees.
    • Architect and structural engineer fees: For design, planning, and structural calculations.
    • Building regulations and planning permission fees: Application and inspection costs.
    • Fixtures and fittings: Flooring, windows, doors, insulation, heating, and lighting.
    • Contingency fund: To cover unexpected expenses or changes during construction.
    1. Financing Options: Depending on the project and individual circumstances, here are different financing options available for backing a loft conversion:
    • Personal savings: Using savings or investments to cover the conversion cost.
    • Remortgaging: Increasing your mortgage or taking out a new loan secured against your property.
    • Home improvement loans: Unsecured loans specifically for home improvement projects.
    • Equity release: Releasing equity from your property to fund the conversion, either through a lump sum or regular payments.

    Interested in HMO mortgages? Check our guide to HMO project financing

    1. Potential ROI: A loft conversion can add significant value to your property, potentially offering a favourable return on investment. The exact ROI will depend on factors such as the quality of the conversion, the local property market, and the overall desirability of your property or HMO. In general, loft conversions can be a sound investment, with studies suggesting they can increase property value by up to 20%and, as mentioned before, rental income by up to 30%.
    2. Considerations for ROI: To maximise the potential ROI of your loft conversion, consider the following:
    • Quality of the conversion: A well-designed and professionally executed loft conversion will likely command higher resale and rental values.
    • Market demand: Research local property trends and buyer/tenant preferences to ensure your conversion meets market demand.
    • Added functionality: Think about the intended use for the loft space and whether it adds significant functionality and appeal to your property.
    • Energy efficiency: Investing in high-quality insulation, windows, and heating systems can enhance energy efficiency and appeal to buyers and tenants.
    1. Cost-Saving Measures: To manage costs effectively, consider tactics such as:
    • Obtaining multiple quotes from reputable contractors and suppliers to ensure competitive pricing.
    • Planning the conversion exhaustively to minimise changes and avoid costly delays or rework.
    • Opting for cost-effective materials and finishes without compromising on quality or durability.
    • Can you do a loft conversion yourself? Some homeowners consider DIY or semi-DIY options for specific tasks. Providing you have the necessary skills and experience required to keep your project compliant, this alternative could help you lower costs. However, you also need to factor in the time to invest and resulting risks (e.g., no guarantees on works, no compliance with fire regulations).

    How Much Does a Loft Conversion Cost

    On average, a bare roof light conversion can cost between £15k and £25k, while a complete dormer attic conversion with ensuite can range from £30k to £50k and more. The location also plays a critical role; a loft-to-bedroom conversion can cost anywhere from £20-£25k in Liverpool and easily exceed the £50k mark in more expensive cities like London. The final cost for a loft conversion depends then on several factors, including:

    • Type, complexity and size of loft
    • Location of property
    • Floor area
    • Construction and interior furnishing material
    • Whether ensuite or not

    As you can see, a loft conversion can be expensive. Setting a realistic budget, factoring in any additional expenses for fixtures and fittings, and some flexibility for unforeseen issues arising during construction is essential. Before deciding if you should invest in a Permitted Development Loft Conversion, consider the financial implications and desired outcome, including the subsequent rental income and valuation of your property, which should generate a positive return.

    This is more of a business strategy than anything, and we’re experienced in helping investors make the best decisions.


    What’s the Best Time of the Year to Do a Loft Conversion

    A common concern among homeowners and landlords is finding the best time of year to carry out a loft conversion. In short, the right time will depend on your specific situation and other contributing factors, including scope of work, location, weather, contractor availability, and potential disruptions to your daily life. While you can’t anticipate all variables, you can weigh these factors and plan accordingly.


    One advantage is the typically mild weather and the extended daylight hours, which could potentially allow for more time to get work done and speed up the construction process indoors (or not delay it).

    On the flipside, spring is a popular time for home improvement projects, meaning contractors and tradespeople may be in high demand, potentially leading to longer waiting times and higher costs.



    The warmest months of the year also offer long daylight hours and (generally) favourable weather conditions, which are optimal working conditions for outdoor construction if necessary. With broad daylight and fewer weather-related disruptions, construction work may progress faster.

    However, summer is a peak season for construction projects, increasing competition for securing contractors and potential costs.



    As autumn progresses, the reduced daylight hours may limit the amount of work completed in a day. While autumn weather is usually mild, occasional rain showers or storms can still cause delays in outdoor construction work.

    Autumn often offers suitable temperatures and stable weather conditions, making it conducive to outdoor construction work. Moreover, with the peak summer season over, contractors may be more readily available and willing to take on projects, potentially leading to shorter wait times and lower costs.



    Winter weather can be unpredictable, with low temperatures and the potential for snow, and ice, which may impact outdoor construction work and, in extreme conditions, the transportation of materials. Also, shorter winter days limit the amount of daylight available for work, which could extend the overall duration of the project. If your loft conversion involves opening the roof, you may face increased heating costs as heat escapes through the exposed area.

    On the plus side, winter is typically a slower season for construction projects, so contractors may have more availability and be willing to offer discounts or incentives. Providing much of the construction work remains indoors, you could avert some potential weather-related delays.


    This guide for permitted development loft conversion provides valuable insights into planning for a loft conversion.

    We covered the benefits of loft conversions, distinct types available, permitted development specifications, timelines, and the planning process. I also shared clear-cut tips for assessing the feasibility of a permitted development loft conversion within minutes during your HMO viewings. Lastly, we discussed the significance of conducting a viability study from an investor’s perspective.

    If you’re interested in further guidance or assistance, talk to us. Our team of architects has supported numerous (dozens?) HMO landlords with successful loft conversions under permitted development to maximise their rental returns.

    Get in touch with a free discovery call. We’d love to help you.

    Picture of Giovanni Patania

    Giovanni Patania

    (Architect Director, Co-Founder)

    Giovanni Patania is the Lead Architect and Co-Founder at HMO Architect and Windsor Patania Architects.

    Originally from Siena, Italy, Giovanni worked as a Project Lead Architect at Foster+ Partners, designing Apple stores across the world,

    An HMO Investor himself, Giovanni understands property thoroughly, both from an investor's perspective and technically, as an Architect.

    With over 15 years of HMO development experience, working on over 150+ HMOs and a 95% Planning and Building Regulation success rate, Giovanni has the expertise and credentials to help you on your HMO journey."



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