A mansard loft conversion rebuilds the back of the roof with a steep, almost vertical slope and a nearly flat top. It’s the type of conversion that creates the most usable space, and it’s often seen on period terraces where it fits in with the style of the street.
At ST Lofts, mansard conversions start from around £37,400 for a small loft. Most mansards are larger projects and finish well above that, so the most accurate way to see a figure for your home is our loft conversion cost calculator.
The cost calculator gives you a guide price in minutes. For an exact price, book a free survey. We’ll come out, look at your loft, talk through what you’d like and then send you a full, itemised quote.
There’s no obligation, and if you’d rather talk it through first, give us a call or send us a WhatsApp.
A mansard is a significant structural project. Our price typically includes rebuilding the rear roof, structural steelwork and new floor joists, roofing with slate or tile, windows (often set into small dormers within the slope), insulation, a new staircase, electrics, plastering and building control sign-off.
Most mansard conversions take around ten to fourteen weeks on site.
The main things that affect the cost of a mansard conversion are:
A mansard suits homes where you want the maximum possible space, and it’s especially common on Victorian and Georgian terraces. Because it changes the shape of the roof so much, it usually needs full planning permission, so it’s worth allowing extra time for that stage.
If planning is a concern, a rear dormer can often achieve a similar result with fewer restrictions. Our guide to planning permission for loft conversions in Bristol explains what’s involved.
Velux Loft Conversion Cost
From around £30,000
Dormer Loft Conversion Cost
From around £40,300
Hip to Gable Loft Conversion Cost
From around £42,000
L Shaped Loft Conversion Cost
From around £39,600
Not sure which type suits your home? Our cost calculator lets you compare all five side by side.
Our free online calculator gives you an instant price for a mansard loft conversion based on the size of your loft, with options for an en-suite, extra windows and more.
When you’re ready, we’ll arrange a free, no-obligation survey and give you a full, itemised quote.
Common questions about the cost of a mansard loft conversion.
Mansard conversions with ST Lofts start from around £37,400 for a small loft, with most finishing higher because they’re usually larger projects. Use our cost calculator for an instant price for your loft.
In most cases, yes. Because a mansard changes the shape of the roof significantly, it’s rarely covered by permitted development.
If you need the maximum amount of space, often yes. A mansard gives near-vertical walls and full head height across almost the whole room.
Most mansard conversions take around ten to fourteen weeks on site, plus time for planning permission beforehand.
