Loft Conversion Cost Calculator

What Does a Loft Conversion Cost?

Loft conversion costs in the US typically range from $150 to $300 per square foot, depending on complexity, finishes, and location. A basic rooflight conversion can start around $25,000–$40,000, while a full dormer or mansard conversion with bathroom can exceed $80,000–$120,000.

Conversion Types Explained

• Rooflight / Velux ($120–180/sq ft): Basic conversion using existing roof structure with added windows. Minimal structural work.
• Dormer ($150–220/sq ft): Adds a box-shaped extension to create headroom and floor space. Most popular option.
• Hip to Gable ($180–260/sq ft): Extends the roof slope to create more internal volume. Ideal for detached homes.
• Mansard ($200–300/sq ft): Full roof restructuring that maximizes space. Highest cost but maximum usable area.

Key Cost Factors

• 🏠 Property Type: Bungalows typically cost less than multi-story homes due to simpler access
• 📐 Size: Larger areas cost more overall but have lower per-square-foot rates
• 🪟 Windows & Doors: Velux windows ($800–1,500 each), French doors ($2,500–5,000), bi-folding ($4,000–8,000)
• 🛁 Bathroom Addition: Adds $10,000–$25,000 depending on fixtures and plumbing complexity
• 📍 Location: West Coast and Northeast are 15–25% more expensive than South and Midwest

Structural Considerations

• Headroom: Minimum 7 feet for code compliance in most US jurisdictions
• Floor Joists: May require reinforcement to meet load requirements (adds $2,000–$6,000)
• Roof Structure: Hip roofs cost more to convert than gable ends
• Staircase: Spiral stairs ($2,500–5,000) vs. standard pull-down ($500–1,500) vs. permanent stairs ($3,000–8,000)

Permits & Professional Fees

Building permits typically cost $1,000–$3,000. Structural engineering fees add $1,500–$4,000. Always check local requirements — many jurisdictions require licensed contractors and stamped plans.

Return on Investment (ROI)

A loft conversion typically adds 10–20% to your home's value. For a $60,000 conversion, you can expect $50,000–$80,000 in added home value, making it one of the highest ROI home improvements.

Frequently Asked Questions

• Do I need planning permission? — Many loft conversions fall under permitted development, but always check local regulations.
• How long does a loft conversion take? — Typically 8–12 weeks for a standard dormer conversion.
• What's the minimum ceiling height? — Most building codes require at least 7 feet of headroom in habitable spaces.
• Can I DIY a loft conversion? — Structural work and electrical/plumbing must be done by licensed professionals in most areas.
• Will a loft conversion add value to my home? — Yes, typically adding a bedroom and bathroom provides the highest ROI.