Permitted Development Loft Conversion For HMOs (Full Guide)

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Do you have a loft in your HMO that you’re thinking of renting out as a room?

Or perhaps you’re looking to buy an HMO and squeeze one more room in there to maximise the rental income?

The permitted development loft conversion process is fairly straightforward.

A successful conversion can pay massive dividends, literally.

But how do you know if you can fit an entire room in there? If your loft is big or high enough for a tenant?

Do you need planning permission or can you use permitted development?

What measurements and drawings do you need to submit?

In this guide, I’ll talk about everything you need to know about permitted development loft conversions, planning and due diligence.

You’ll get a complete understanding of what to look for, pitfalls, can you use PD or do you need planning, and how to maximise your chance of a successful planning application.

So let’s get into it.


What Is A Loft Conversion?

Benefits Of An HMO Loft Conversion

Types Of Loft Conversions

  1. Dormer Loft Conversion
  2. Hip To Gable Loft Conversion
  3. L Shape Loft Conversion

Permitted Development Loft Conversion

Specifications — Permitted Development Loft Conversion

Change Of Class (C3 to C4) — Loft Conversion

Loft Conversion Planning Process

Can You Do A HMO Loft Conversion? (Feasibility)

Should You Do A HMO Loft Conversion? (Viability)

Can My Neighbour Stop My Loft Conversion?


What Is A Loft Conversion?

A loft conversion is a process of converting a loft or attic into a habitable and functional space.

There are several reasons why you may decide to do an HMO loft conversion but the most obvious one is an increased rental income.

I’ll touch on the benefits of a loft conversion specifically for HMOs later.

Loft conversions are used to create fully functional areas like an extra bedroom, gym, study, library or home office.

They first became popular in the SoHo area of New York City in the 1960s and quickly spread around the world.

They became very popular in the UK due to the smaller living spaces available.

Benefits Of An HMO Loft Conversion

So why would a sophisticated HMO investor like yourself want to do a loft conversion?

As investors, we always like to think of “Return On Investment (ROI)”.

Depending on the area, an HMO loft conversion could be expensive, not to mention complicated.

Here are some reasons why you should consider an HMO Loft Conversion:

HMO Loft Conversion – Ensuite Bedroom

Increased Rental Income

The reason you’re an HMO investor is that 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 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 1 bedroom.

Imagine that, what could 2 extra bedrooms mean for your HMO and monthly rental income?

Increased Valuation (Commercial Valuation)

For an HMO investor, getting a commercial valuation (rather than a traditional Brick & Mortar Valuation) is like sitting on a rocketship.

The increased valuation means you’ll get to pull more money out of each deal.

This means you can 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

Viewed as an income-generating asset, lenders want to know how much income can the property generate.

You can imagine the thought of them salivating when you say you’ve added 2 extra rooms from a loft conversion.

Also, in high demand areas like London, for every sqm of habitable space, you get 3x the Brick & Mortar valuation.

Resource Efficiency

By adding more people under the same roof you’re maximizing resources like the kitchen, gas, electricity, 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.

What’s good is the Council tax stays the same in most cases.

Although, sometimes it’s at the Council’s discretion to decide if a room is classed as “self-contained”.

Types Of Loft Conversions

Although there are several types of loft conversions depending on the property type, here are 3 main ones for HMOs.

Let’s take a look below

1. Dormer Loft Conversion

A dormer loft conversion is a popular form of permitted development loft conversion that includes a window-featured extension to the roof.

It includes 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.

They can be done with Permitted Development.

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

A Hip to Gable loft conversion can be applied 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) to extend the loft space.

Best Suited For — end-of-terraced, semi-detached properties, detached houses or bungalows. Not suitable for mid-terraced houses. 

3. L Shape Loft Conversion

The L shape loft conversion is a creative combination and connection of 2 or more dormer conversions.

One dormer conversion is done on the front roof and another on the rear roof and these are connected to resemble a distinctive L-Shape.

This type of loft conversion is very popular among HMO investors due to the possibility of an ensuite bedroom in the loft.

A well designed L-shape loft conversion also allows for 2 more bedrooms in the loft.

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

Permitted Development Loft Conversion

Now that you know a bit about the types of conversion, let’s get into the crux of this article.

Permitted development loft conversions and planning permission.

Permitted Development is the automatic grant of permission by the local authority within an area for construction or change of use.

I’ve gone into great detail on planning, permitted development and overcoming Council objections in my other article on HMO Planning Permission.

So please check that out for a deeper understanding.

Can I Build A Dormer Under Permitted Development?

Most dormer loft conversions come under permitted development (PD) and do not need planning permission.

As long as it follows the PD criteria and the property doesn’t come under a conservation area, you can build a dormer under permitted development.

Although, it’s always advisable to confirm this with the Local Authority before you begin any construction.

Alternately speak to one of our team and we’ll be more than glad to help.

Specifications — Permitted Development Loft Conversion

So what are the specs for a permitted development loft conversion?

How do you know if your designs are in line with the Local Authority Guidelines for Permitted Development?

Although varying by Council, here’s a high-level spec.

  • The new loft space is less than 40 cubic metres for terraced houses and 50 cubic metres for detached and semi-detached houses. Any existing loft extensions 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 have to keep at least 20 cms 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.
  • Property is not located in a national park, world heritage site or conservation area.

As I mentioned above, if your property comes under a conservation area, it’s likely your loft conversion plans will need to go through planning permission.

Loft Conversion on an HMO in Liverpool
Loft Conversion on an HMO in Liverpool

Change Of Class (C3 to C4) — Loft Conversion

I explained the various classes in my post on HMO Planning Permission where essentially

  • C3 — Single Family Home
  • C4 — Small HMO (up to 6 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.

But, if you’re doing a loft conversion on an existing HMO (class C4) you cannot use Permitted Development rights.

You’ll need to go through a full planning application for your loft conversion.

It’s always recommended to plan for a loft conversion as part of your HMO Conversion plans.

Loft Conversion Planning Process

Let’s say you’re doing a more complex loft conversion and it doesn’t come under Permitted Development rights.

How do you go about the planning process?

What is Article 4 and how does it affect your loft conversion plans?

What drawings or documents should you submit for planning? How long does it take and how much does it cost?

Lets’s take a look.

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

As you can see the process is fairly simple and not complicated.

But 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. 

If the details submitted are insufficient or incorrect, the council will ask for more information or to rectify the application with drawings more pertinent to the PD application. 

This is part of the validation process.

HMO - Cut Out Side View
Side Section View Of An HMO (CGI)

Application Process

The process to get planning for a loft conversion is pretty 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 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 pretty much similar, approximately 2 weeks for the Council to acknowledge your application and 6 weeks for a decision notice.

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

10 Bed HMO - 2
Concept HMO Showing Dormer Conversion

Can You Do A 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 the outcome is going to be before you sign on 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.

Understanding feasibility pre-purchase is a key part of your job as a professional property investor.

Here are some tips and tricks I’ve picked up over the last 15 years of investing in HMOs and glad to share them with you.

  1. 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.
  2. Measure the height of the loft by measuring the ridge (highest point of the roof) to the loft floor. This should be at least 2.5m.
  3. Measure the thickness of the loft floor. In most cases is 11–13 cms. In general, the thicker is the floor the better.
  4. Measure the height of the 1st floor. Recommended height is 2.5–2.7m for a comfortable loft conversion.

Armed with these tips, over time you’ll be able to tell within minutes if you can fit a loft in 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 A HMO Loft Conversion? (Viability)

In the previous section, we discussed feasibility.

How to know whether you can do a loft conversion by looking at the property and taking a few measurements.

But, just because you can do it, doesn’t mean you should.

This is where the viability study comes in.

How Much Does It Cost To Convert Loft Into Bedroom?

A loft to bedroom conversion can cost anywhere from £15-£20k in Liverpool to up to £50k in more expensive cities like London.

It depends on several factors like

  • Size of the loft
  • Floor area
  • Construction and interior furnish material
  • Type of loft
  • Whether ensuite or not

As you can see, a loft conversion can be expensive.

The easiest way to decide if you should invest in a permitted development loft conversion is to consider the financial implications.

The subsequent rental income and valuation should generate a positive return.

This is more a business decision than anything, and it’s one we’re heavily experienced in helping investors make the best decision.

Can My Neighbour Stop My Loft Conversion?

If you’re going through a Permitted Development Loft Conversion, the short answer is NO.

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 planning application, there’s a chance you may receive objections from neighbours.

As I always recommend, it’s best to inform your neighbours about your plans well in advance.

This can reduce any possible objections and foster a friendly relationship.


I hope this permitted development loft conversion article gave you insight on how to plan for a loft conversion.

We looked at the loft conversion benefits, types of conversions, permitted development specs and the planning process.

I also shared some quick tips you can apply today on your HMO viewings to check the feasibility of a permitted development loft conversion within minutes.

Lastly, we went through why a viability study is important from an investor’s point of view.

If you’d like to talk to an architect, we’ve advised and helped many HMO landlords with some impressive permitted development loft conversions to maximize their rental returns.

So please get in touch. We’d love to help you.


10 Step Checklist To Prepare Your HMO For Tenancy & Maximise Cash Flow

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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