Loft Conversion and House Extensions FAQs: Everything You Need to Know

Most lofts in London can be converted, but suitability depends on your roof structure, the available head height and your property's planning situation. As a general guide, you need at least 2.2 metres of head height at the highest point for a practical conversion. The best way to find out is a free site visit — we'll assess your loft and tell you exactly what's possible.

You need a minimum of 2.2 metres from the floor joists to the ridge beam for a practical loft conversion. If your head height is just below this, certain conversion types such as a mansard or dormer can increase it significantly. We'll measure during the free site visit and advise on your options.

We build all main types of loft conversion across London, including Velux, dormer, L-shaped dormer, mansard, hip to gable and bespoke conversions for more complex properties. During your site visit we'll advise on which type is best suited to your home, budget and planning situation.

Costs vary depending on the type of conversion and the specification of the project. As a guide: - Velux / rooflight conversion: £30,000 – £40,000 - Dormer loft conversion: £45,000 – £65,000 - Hip to gable conversion: £50,000 – £75,000 - L-shaped dormer: £65,000 – £95,000 - Mansard loft conversion: £70,000 – £95,000 All costs are approximate and subject to a site survey.

Many loft conversions fall under permitted development rights, meaning no full planning application is required. However, mansard conversions and any work on a property in a conservation area almost always require full planning permission. LLAC handles all planning submissions as part of our service — we'll confirm exactly what's needed for your property from the outset.

Permitted development (PD) allows certain building works to go ahead without a full planning application. For loft conversions, PD typically allows rear dormers up to a set volume limit, as long as the conversion doesn't exceed the ridge height of the original roof. PD rights have been removed in many London conservation areas, so it's always worth checking your specific situation before assuming your project qualifies.

Yes — all loft conversions require building regulations approval regardless of whether planning permission is needed. Building regulations cover structural integrity, fire safety, insulation and means of escape. LLAC manages the building control process as part of every project, and sign-off from an independent inspector is required before the project is considered complete.

Most loft conversions take between 8 and 14 weeks on site. A Velux conversion is typically 6 to 8 weeks; a dormer 10 to 12 weeks; a mansard 12 to 16 weeks. Including design and planning, allow 4 to 6 months end to end for a permitted development project, or longer if full planning permission is required.

Less disruptive than most people expect. The noisiest phase is the structural work — typically the first 2 to 3 weeks when the roof is opened and steels are installed. After that the build becomes progressively less disruptive. We seal off the loft opening, keep the site clean throughout and plan noisy works around your household where possible.

Yes. Adding an extra bedroom with an en-suite is the most popular use of a loft conversion in London and one of the most effective ways to add value. Many of our projects also include built-in storage to make the most of the sloping walls.

Yes, and it is often cost-effective to do both together. Combining a loft conversion with a rear or wraparound extension means one planning application, one build phase and one period of disruption rather than two. LLAC regularly manages combined projects and can design them together to maximise the overall space and value added.

For most homeowners, yes. A well-executed loft conversion in East or North London typically adds more value to the property than it costs to build, particularly when a proper bedroom and bathroom are created. It also avoids the stamp duty, legal fees, and disruption of moving to a larger home, which in London can easily cost more than the conversion itself. The strongest returns tend to come in high-demand areas like Hackney, Walthamstow, Islington, and Haringey, where an extra bedroom makes a meaningful difference to what a property is worth and how quickly it sells

Beyond the conversion type, several factors move the final figure. Structural condition is a key one. Access and logistics matter on tighter London streets, where scaffolding and waste removal require more planning. Your choices for the staircase, windows, insulation, and finishes have a significant impact, particularly if you are adding an en-suite bathroom. Planning permission may be needed depending on the conversion type and whether your property sits in a conservation area. A party wall agreement is usually required if you share walls with neighbours, which adds time to the programme and some professional fees.