{"id":6329,"date":"2026-06-25T09:29:51","date_gmt":"2026-06-25T09:29:51","guid":{"rendered":"https:\/\/www.buildteam.com\/blog\/?p=6329"},"modified":"2026-06-25T10:09:53","modified_gmt":"2026-06-25T10:09:53","slug":"how-to-estimate-and-plan-your-loft-conversion-costs","status":"publish","type":"post","link":"https:\/\/www.buildteam.com\/blog\/how-to-estimate-and-plan-your-loft-conversion-costs\/","title":{"rendered":"How Much Does a Loft Conversion Cost in London?"},"content":{"rendered":"
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A loft conversion in London costs roughly \u00a325,000 to \u00a3100,000+ all-in<\/strong> in 2026, set mainly by type: a Velux conversion is cheapest at about \u00a325,000 to \u00a345,000, a rear dormer runs \u00a345,000 to \u00a375,000, and a mansard is the dearest at \u00a360,000 to \u00a3100,000+. Per square metre that is about \u00a32,000 to \u00a32,800 for simpler lofts<\/strong> and \u00a33,500 to \u00a34,500 for a mansard<\/strong>. A loft is usually cheaper per square metre than a ground-floor extension, because the roof structure is partly there already and there are no new foundations.<\/p>\n<\/div>\n

A loft conversion is the most efficient way to add a bedroom in London: it uses space you already own, leaves the garden untouched, and a new double bedroom with an ensuite is one of the strongest moves for adding value. The cost is driven less by size than by which type of conversion your roof allows. This guide sets out what each loft type costs in 2026, where the money goes, what can make a loft unviable, and how it compares with extending, using current figures and our own completed projects.<\/p>\n

How much does a loft conversion cost in London?<\/h2>\n

The type of conversion is the single biggest cost factor, because it decides how much of the roof has to be rebuilt. The table below sets out the five common London types:<\/p>\n

\n\n\n\n\n\n\n\n\n\n
Loft type<\/th>\nAll-in cost (2026)<\/th>\nApprox \u00a3\/m\u00b2<\/th>\nTypical size<\/th>\nPlanning<\/th>\n<\/tr>\n<\/thead>\n
Velux \/ rooflight<\/td>\n\u00a325,000 to \u00a345,000<\/td>\n\u00a32,000 to \u00a32,800<\/td>\n18 to 28 m\u00b2<\/td>\nRarely needs permission<\/td>\n<\/tr>\n
Rear dormer<\/td>\n\u00a345,000 to \u00a375,000<\/td>\n\u00a32,000 to \u00a32,800<\/td>\n25 to 35 m\u00b2<\/td>\nUsually permitted development<\/td>\n<\/tr>\n
Hip-to-gable<\/td>\n\u00a350,000 to \u00a390,000<\/td>\n\u00a32,500 to \u00a33,000<\/td>\n30 to 40 m\u00b2<\/td>\nGable may need permission<\/td>\n<\/tr>\n
L-shaped dormer<\/td>\n\u00a355,000 to \u00a397,500<\/td>\n\u00a32,500 to \u00a33,000<\/td>\n35 to 50 m\u00b2<\/td>\nOften PD on Victorian terraces<\/td>\n<\/tr>\n
Mansard<\/td>\n\u00a360,000 to \u00a3100,000+<\/td>\n\u00a33,500 to \u00a34,500<\/td>\n35 to 55 m\u00b2<\/td>\nAlmost always needs full permission<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Figures are all-in for a one-bedroom loft with an ensuite shower room, including 20% VAT, and exclude premium finishes. In prime central postcodes a mansard can reach \u00a3120,000 to \u00a3150,000. For a wider comparison against ground-floor options, see our guide to how much an extension costs in London<\/a>.<\/p>\n

Which loft conversion is the cheapest?<\/h2>\n

The Velux, or rooflight, conversion is the cheapest because it keeps the existing roof shape: it needs floor strengthening, insulation, rooflights, a staircase and finishes, but no structural rebuild. The mansard is the most expensive because it rebuilds the entire rear roof slope to near-vertical, effectively a new storey. One point catches people out: a small loft costs more per square metre than a large one, because the fixed costs, the staircase, the steels and the fire protection, are much the same whatever the floor area, so a small loft spreads them over fewer metres.<\/p>\n

\"Flat-roof\n
A dormer almost always has a flat roof. The insulation and weatherproofing of that roof is a real part of the cost, and where a dormer adds full standing height.<\/figcaption>\n<\/figure>\n

Is a loft conversion cheaper than a ground-floor extension?<\/h2>\n

Per square metre, usually yes. A loft starts with a structure that is partly built and needs no new foundations, so simpler types run about \u00a32,000 to \u00a32,800 per m\u00b2, against roughly \u00a32,800 to \u00a34,500 per m\u00b2 for a London ground-floor extension. The exception is the mansard, which rebuilds the whole roof and sits in the same band as an extension. The choice is really about what you need: a loft adds bedrooms without touching the garden, while a side return<\/a> or kitchen extension<\/a> adds ground-floor living space. Many London families do both over time, and our guide to rear and wraparound costs<\/a> covers the ground-floor side.<\/p>\n

What does a loft conversion cost, line by line?<\/h2>\n

A loft has costs an ordinary room does not, the staircase, structural steels and fire protection chief among them. A realistic 2026 London breakdown:<\/p>\n

\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Element<\/th>\n2026 London figure<\/th>\n<\/tr>\n<\/thead>\n
Design and architect fees<\/td>\n\u00a33,500 to \u00a38,000, or a percentage of build<\/td>\n<\/tr>\n
Structural engineer (calculations)<\/td>\n\u00a3450 to \u00a31,800<\/td>\n<\/tr>\n
Planning application (if needed)<\/td>\n\u00a3548 (England householder, from April 2026); most lofts are permitted development and pay nothing<\/td>\n<\/tr>\n
Structural steels<\/td>\n\u00a31,500 to \u00a34,000 plus installation<\/td>\n<\/tr>\n
Staircase and new opening<\/td>\n\u00a31,500 to \u00a35,000, plus \u00a31,000 to \u00a33,000 for the opening and fire doors<\/td>\n<\/tr>\n
Dormer construction<\/td>\n\u00a34,000 to \u00a36,000 per dormer<\/td>\n<\/tr>\n
Rooflights \/ Velux windows<\/td>\n\u00a3600 to \u00a31,500 each fitted<\/td>\n<\/tr>\n
Ensuite or bathroom fit-out<\/td>\n\u00a38,000 to \u00a315,000<\/td>\n<\/tr>\n
Party wall surveyors (per neighbour)<\/td>\n\u00a3700 to \u00a32,000<\/td>\n<\/tr>\n
Building control<\/td>\naround \u00a3800+<\/td>\n<\/tr>\n
VAT<\/td>\n20% on the whole project<\/td>\n<\/tr>\n
Contingency<\/td>\n10 to 20% of the total<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

The staircase is the cost people most often forget: it is not just the stair itself but the opening through the floor below, fire doors at each level and interlinked alarms to meet Building Regulations. For help judging whether a quote is complete, read our guide to getting a realistic builder’s quote<\/a>.<\/p>\n

What affects the cost of a loft conversion?<\/h2>\n