Converting two or more self-contained flats back into a single family home—often called “deconversion” or “amalgamation”—has become increasingly popular in London. Whether you’re restoring a period townhouse to its original layout or consolidating a multi-flat property to create a generous family dwelling, the journey involves planning strategy, technical compliance, neighbour matters and—crucially—future mortgageability. Here’s a practical, no-nonsense guide to help you plan a smooth, compliant project.
Do you need planning permission?
Two flats to one (internal works only). If all changes are internal (removing redundant kitchens, rationalising layouts, reinstating a single staircase, etc.), this can sometimes be treated as lawful development, because you’re not materially changing the use class (C3 remains C3) and there’s no external alteration. Many clients apply for a Lawful Development Certificate (LDC) to obtain formal confirmation from the council. It’s quicker, lower-risk, and creates a robust paper trail for solicitors and lenders later.
Three (or more) flats to one. Consolidating three to one typically requires full planning permission. Expect policy concerns around the loss of housing stock; several London boroughs treat amalgamations cautiously. Islington, in particular, is known for preventing the loss of self-contained units, so a standard deconversion application may face resistance without a compelling, policy-led case. If you’re in (or near) a borough with strict policies, consider a pre-application discussion to understand the local stance before committing to full drawings and fees. If you’d like help navigating this, see our Planning Permission London page.
Constructive challenge: homeowners often assume “it’s my house, I can just merge it.” In policy terms, you’re removing homes from the local supply, which councils track closely. Build your case with evidence, not assumptions.
Planning drawings and the application pack
Before a council can determine an LDC or planning application, you’ll need clear, accurate planning drawings (existing and proposed plans/sections/elevations), plus any supporting statements the borough requests (e.g., Design & Access Statement, heritage notes). Starting with a precise measured survey—ideally a point-cloud laser scan—reduces risk and speeds up downstream stages. Here’s our approach to surveys and early design: Our Design Process. For a deeper dive into drawing standards and best practice, read How to Create Planning Drawings.
After approval: Building Regulations and SAP (energy)
Once planning or an LDC is in hand, move to Building Regulations. You’ll need technical drawings that detail structure, fire safety, thermal performance, ventilation, drainage, and so on. We prepare Building Regulation Drawings to show exactly how the works can be built compliantly and tendered with confidence.
For energy, expect a SAP calculation to verify compliance with Part L. Because deconversions can involve removing redundant services and rationalising heating/hot water, it’s smart to complete an early SAP pre-assessment to avoid late surprises. In some cases, you can argue that specific upgrades fail a 15-year payback test and therefore may not be strictly required; however, this isn’t a free pass. The availability of that route depends on the exact scope, baseline condition and assessor’s evidence. Treat the “15-year payback” as a potential optimisation, not a guaranteed exemption.
Constructive challenge: don’t bank on “we’ll argue payback later.” Get a SAP consultant engaged early and design to meet Part L; use payback arguments only as a targeted, evidence-based refinement.
Fire safety and means of escape
Even when works are “internal only,” the fire strategy changes once the building operates as one dwelling. Standard areas to resolve include protected stairways, FD30 doors where required, smoke/heat detection, compartmentation around high-risk rooms, and escape distances to a final exit. The specifics depend on layout, floor count, and whether basements or loft spaces are included. Good Building Regs drawings bring all of this together in a coordinated package. If your deconversion touches a conservation area or listed fabric, ensure fire measures balance safety with heritage constraints—more on heritage below.
Structural works and professional input
If you’re removing load-bearing walls, altering floor structures, or opening up vertical risers, you’ll need a structural engineer to design steels, pads and connections, and to provide calculations for building control. Tight urban footprints often mean steelwork seats into (or near) party walls; programme your neighbour notices early (see Party Wall below).
Party Wall, neighbours and programme
Many deconversions trigger the Party Wall etc. Act 1996—for example, where beams are inserted into shared walls, or where you excavate for new pads within 3 metres of a neighbour’s foundations. Aim to serve notices at least two months before works begin; it’s a common bottleneck that delays start on site. Our articles explain the steps plainly: Party Wall Agreements and 5 Essential Steps for Party Wall Agreements.
Practical tip: align your party wall programme with builder tendering and building control plan check to keep momentum. Don’t leave notices until the week before start.
Building control application and sign-off
You’ll submit either a Full Plans application (recommended for clarity and lender comfort) or a Building Notice (less common for complex projects). Building control will review drawings, inspect on site at key stages, and issue a Final Certificate on satisfactory completion. This certificate is often requested by solicitors and lenders, so keep it safe.
Heritage and Listed Building Consent (LBC)
If the property is listed (or within a sensitive conservation context), you may need Listed Building Consent for internal alterations—sometimes even where works are “reinstatement.” Engage this early so your planning/building control pathways stay aligned. See one of our heritage case studies here: Listed Building Consent – Southwark.
Legal checks, covenants, mortgages and warranties
Deconversions can intersect with title covenants, lease restrictions (if any residual leasehold interests exist), and lender requirements. Obtain independent legal advice to confirm you’re free to amalgamate, and to structure any title clean-up.
On finance, it’s common for lenders and future buyers to expect a conversion warranty or a Professional Consultant’s Certificate (PCC), depending on the nature/extent of works. Without recognised cover, mortgaging and resale can be difficult and may force a lower price or higher interest rate. Build warranty planning into your early cost and programme assumptions—don’t treat it as an afterthought raised by the buyer’s solicitor at exchange.
Constructive challenge: many owners proceed on “building notice + friendly builder.” That can work—but it can also limit mortgage options later. If exit value matters, procure your project in a way lenders recognise.
Utilities and services
Consolidating flats back to a single dwelling means rationalising utilities—for example, transitioning from multiple meters to one, removing redundant supplies, and re-confirming capacities for the unified layout. Engage with your utility providers early; lead times for meter alterations and service terminations can be longer than expected. Our Extension Checklist covers coordination items many clients overlook.
Typical pathway and timeline (simplified)
- Feasibility & strategy. Confirm whether your borough will accept an LDC (2→1 internal only) or whether you need planning permission (e.g., 3→1, Islington, or external works). Consider a pre-app where policy risk is high.
- Survey & concept. Commission a measured survey/scan and develop concept layouts for the single dwelling. See Our Design Process.
- Planning/LDC submission. Prepare planning drawings and any statements. See How to Create Planning Drawings.
- Technical design. Develop Building Regulations drawings, SAP and structural design; coordinate fire strategy and specifications. See Building Regulation Services.
- Approvals & neighbour matters. Party Wall notices and awards; Building Control plan check/inspections; utilities applications.
- Construction. Build in line with the approved drawings and specifications; maintain records for warranties and lender packs.
- Sign-off & documentation. Building Control Final Certificate, warranty documents/PCC, as-built records.
How we can help
We regularly guide London homeowners through feasibility, planning and building control for deconversions, coordinating structural engineers, SAP assessors, and party wall surveyors to keep your programme moving. Start a conversation on Planning Permission London, explore our Building Regulation services, or browse Our Services to see how we structure projects for lender-friendly outcomes.
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If you’d like tailored advice on your address, we can review policy risk (including borough-specific restrictions) and map out the most efficient path to approval and sign-off.
