The Complete Loft Conversion Cost Guide (2025)
Adding a loft conversion (or attic renovation) is widely considered the smartest way to add value and space to your home. Whether you need an extra bedroom, a home office, or a playroom, moving upwards is often cheaper and less disruptive than moving house. However, costs can vary wildly depending on the structural changes required.
Our Loft Conversion Cost Calculator helps homeowners in the US and UK estimate the budget needed. From simple Velux rooflight conversions to complex Mansard extensions requiring planning permission, this tool breaks down the costs of materials, labor, and professional fees.
Types of Loft Conversions Explained
1. Velux / Rooflight Conversion (Cheapest)
This involves reinforcing the floor and adding skylights (like Velux windows) without altering the roofline.
Best for: Attics with plenty of existing headroom (2.2m+).
Cost: £20k - £40k ($25k - $50k).
2. Dormer Conversion (Most Popular)
A box-like structure is added to the roof to increase headroom and floor space. "Rear Dormers" are common and often fall under Permitted Development rights in the UK.
Best for: Adding a full bedroom and en-suite.
Cost: £40k - £65k ($50k - $85k).
3. Hip-to-Gable
For semi-detached or end-terrace houses with a sloping "hipped" roof. The hip is built up vertically to form a gable wall, maximizing space.
Best for: maximizing space in 1930s semis.
Cost: £50k - £75k ($65k - $95k).
4. Mansard Conversion (Premium)
The entire roof structure is altered to have a steep 72-degree slope. This creates the most space but requires planning permission and significant construction work.
Best for: Period properties and maximizing value.
Cost: £60k - £100k+ ($80k - $130k+).
Hidden Costs to Budget For
| Expense | Estimated Cost | Notes |
|---|---|---|
| Architect Fees | $1,500 - $4,000 | Drawings for planning/permits. |
| Structural Engineer | $800 - $2,000 | Calculations for steel beams. |
| Party Wall Agreement | $1,000 per neighbor | If sharing walls (UK specifically). |
| Building Control | $1,000+ | Inspections and final sign-off. |
Does a Loft Conversion Add Value?
Yes. In the UK, a high-quality loft conversion can add 20% to the property value. In the US, the ROI (Return on Investment) is typically around 60-70% of the cost spent. The key is adding a bedroom and a bathroom.
Frequently Asked Questions (FAQ)
Do I need planning permission? ▼
In the UK, most Dormer and Velux conversions fall under Permitted Development rights, provided they don't exceed volume limits (40m³ for terrace, 50m³ for others). Mansard extensions and flats almost always need permission. In the US, you always need a building permit.
How long does the work take? ▼
A simple rooflight conversion takes 4-6 weeks. A rear dormer usually takes 6-8 weeks. Complex hip-to-gable or Mansard projects can take 10-12 weeks.
Can any attic be converted? ▼
You generally need a minimum head height of 2.2 meters at the highest point. If it's lower, you may need to lower the ceilings on the floor below, which is expensive and disruptive.
Plan your new space
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