A complete guide to loft conversion design and planning
Want to add extra space to your home? A loft conversion could be the solution you're looking for.
Transforming your unused attic into a stylish living area not only adds valuable square metres to your property but also boosts its market value.
In fact, research by Zopa shows that loft conversions can offer a remarkable return on investment (ROI) of up to 70% – the highest of any home improvement project.
This is because they provide a cost-effective way to add an additional bedroom to your property, which can push your home into a higher price bracket.
Read on as we explore the ins and outs of loft conversions, including how to plan and design them effectively.
Assessing your roof
Begin by assessing the current roof space to gauge how well-suited it is for a loft conversion.
The magic number here is 2.2 metres. To create a comfortable living space without major adjustments, you'll need at least this much height from the top of the proposed floor to the underside of the ridge beam.
To measure accurately:
Use a long spirit level to simulate the new floor's location (typically 20 cm above the existing ceiling joists).
Measure from this point to the underside of the ridge beam.
Take measurements at several points, as roof heights can vary.
Don't worry if you're a bit short on height – there are ways to gain space, such as lowering ceilings in the rooms below or raising the roof, though these options will increase costs and complexity.
Designing a loft conversion means assessing the roof. The findings guide what types and/or sizes of extensions are feasible.
Types of loft conversions: mansards, dormers, and velux/rooflights
There are three main types of loft conversions: mansards, dormers, and Velux/rooflight conversions. Here’s more information about the three main options:
1. Roof light conversion
Also known as a Velux conversion, this is the simplest and often most cost-effective option. It makes virtually no structural changes to the roof and is suitable when you have ample roof height. It involves:
Adding roof windows to the existing slope
Reinforcing the floor
Adding a staircase for access
Insulating and finishing the space
2. Dormer conversion
Dormer conversions add a box-like structure to your roof, creating additional headroom and floor space. They come in three main styles:
Single dormer: A small extension, perfect for an extra compact room
Full-width dormer: Extends across the entire roof, maximising new space for an en-suite
L-shaped dormer: Combines rear and side dormers, ideal for larger houses
Dormers offer excellent usable space and often fall under PDRs, especially for rear dormers.
3. Hip-to-gable conversion
A hip-to-gable conversion extends the sloped side to create a vertical wall for houses with a hipped roof (sloping on all sides).
This dramatically increases loft space and is often combined with a rear dormer for maximum impact. It's particularly suitable for end-of-terrace, semi-detached, and detached houses.
4. Mansard conversion
The most extensive option, a mansard conversion, alters the entire roof structure, creating a flat roof with sloping walls (typically at a 72-degree angle).
While offering the most additional space, it almost always requires planning permission and is more expensive.
Mansard conversions work well in urban areas where space is at a premium and can completely transform the look of your home.
You’ll often find these conversions topping iconic Victorian-era buildings in London, Manchester, and many other major Western European cities.
Never heard of a "Mansard" loft conversion? You've almost definitely seen them before atop of stately buildings in London and other cities.
The loft conversion planning process
Let’s start by saying that many loft conversions fall under Permitted Development Rights (PDRs), meaning you may not need full planning permission. To qualify, your conversion must:
Not exceed specified volume allowances (40m³ for terraced houses, 50m³ for detached and semi-detached)
Not extend beyond the plane of the existing roof slope at the front of the house
Use materials similar in appearance to the existing house
There are other caveats, too. You'll likely need to apply for planning permission if:
Your house is listed or in a conservation area
You want to add a balcony or veranda
You want to extend beyond the limits
The first point is key here and catches a lot of people out – PDRs don’t automatically apply if you live in a conservation area.
Now, that might give the impression of areas like the Cotswolds or Yorkshire Dales, but there are actually over 20 protected conservation areas in London.
Another key point is that, while PDRs might give you the impression you can just go ahead and build, you’ll still likely need a lawful development certificate (LDC). This certifies that the extension legally complies with PDRs.
So, there is still a planning process involved – you just won’t need to submit a formal planning application.
If PDRs don’t apply, don’t panic. It’s very common to have to obtain planning permission for loft extension plans. Working with local architects and builders who understand your loft conversion plans and the local area in question can be decisive in obtaining it quickly.
Here’s an example from a project we at Humphrey and Sons worked on:
“On a recent project we were given some very negative pre-application comments from the planning officers, and some similarly pessimistic advice from our previous architects, so we were feeling very despondent. We decided to involve Humphreys & Sons and they somehow designed a scheme to achieve more than twice what we were expecting, and through a lot of hard work they managed to gain full planning permission for it!” Kirk Hatherley — Archers Developments Ltd.
Transform your loft with Humphreys and Sons
Are you looking to unlock your loft's potential? At Humphreys and Sons, we can help you create beautiful, functional loft conversions.
We bring extensive experience with local planning laws, a keen eye for detail, and a commitment to quality to every project.
Our proven expertise in working with local planning authorities will help ensure a fluid project that gives you more flexibility to create the space you want.
What makes us unique is our comprehensive in-house expertise, including architects and party wall surveyors.
Enjoy the convenience of one dedicated contact managing your project from initial planning to final design and recommending builders to see your project through to completion.
Contact us today for a free consultation. Let's collaborate to create an exceptional loft conversion that will add value to your home.