What affects the cost
Cost depends heavily on conversion type (rooflight/Velux conversion is cheapest, dormer adds more space and cost, a full mansard is the most involved), whether a new staircase needs significant space reconfiguration below, and whether the existing roof structure needs strengthening. A simple boarding-and-insulation job is a fraction of a full conversion's cost.
Common loft conversion myths, busted
"Any loft can be converted" — roof pitch, height and structure all affect feasibility; not every loft has enough headroom. "Planning permission is always needed" — often not, if within permitted development limits. "It's just adding a floor and a window" — the structural, fire safety and staircase requirements are far more involved than that.
How many quotes should you get?
Three is reasonable for a loft conversion. Make sure each quote covers the same conversion type and includes (or clearly excludes) Building Regulations fees and structural engineer costs, since these are sometimes quoted separately and can make quotes look more different than they actually are.
Red flags in a cheap loft conversion quote
A quote significantly below others is worth real scrutiny — check it includes Building Regulations coverage, proper structural floor joists (not just boarding over existing joists), and fire safety measures. Skipping any of these to hit a lower price is a serious, not cosmetic, shortcut.
Why loft floor strength matters
Standard ceiling joists aren't designed to support a habitable room's floor loading — a loft conversion needs new structural floor joists (or strengthening of existing ones), assessed by a structural engineer as part of the Building Regulations process. This is a genuine structural job, not just adding boards.
How much value does a loft conversion add?
A well-executed loft conversion commonly adds meaningful value to a property, though the exact amount varies significantly by area, property type, and how the new space compares to local expectations (an added bedroom typically adds more value than an office, for example) — worth researching comparable local sales rather than assuming a fixed percentage.
Aftercare after a loft conversion
Keep your Building Regulations completion certificate, structural engineer's calculations, and any planning permission documents together — you'll need these when you sell the property, and some insurers ask for them when insuring a property with a converted loft.
How long does a loft conversion take?
Simple boarding and insulation can be done in a day or two. A full loft conversion, including structural work, staircase, and fitting out, commonly takes 6-10 weeks depending on conversion type and complexity — dormer and mansard conversions typically take longer than a rooflight-only conversion.