Attic Conversion Cost Calculator
Get a detailed estimate for your attic conversion in under 60 seconds. From basic room conversions to full dormer attic conversions — free, instant, no sign-up.
What is your attic floor area?
Measure the usable floor space where you can stand upright (ceiling height ≥ 7 ft / 2.1 m recommended).
💡 Typical attic conversions range from 150–500 sq ft (14–46 m²). Not sure? Measure the main bedroom below as an estimate.
Cost Breakdown
Cost Split
Full Breakdown
| Item | Low | Mid | High |
|---|
Average Attic Conversion Cost by Type
Attic conversion cost ranges vary significantly depending on the type of conversion, the size of your attic, and local labour rates. The figures below are general mid-market estimates — your actual attic conversion cost will depend on your specific project and contractor quotes in your area.
| Conversion Type | Typical Low | Typical Mid | Typical High | Notes |
|---|---|---|---|---|
| Basic Loft Room | $12,000 | $22,000 | $35,000 | Rooflights only, no structural alterations |
| Attic Bedroom Conversion | $18,000 | $32,000 | $55,000 | Includes floor joists, insulation, plastering, electrics |
| Dormer Attic Conversion | $28,000 | $50,000 | $85,000 | Structural dormer extension for headroom; higher cost |
| Attic Office Conversion | $14,000 | $25,000 | $42,000 | Similar to bedroom; may require added data/power points |
| Attic Storage Conversion | $4,000 | $9,000 | $18,000 | Boarding, hatch, lighting — minimal structural work |
| Attic + Ensuite | $30,000 | $55,000 | $95,000 | Full attic to bedroom conversion cost with en-suite WC/shower |
A dormer attic conversion commands a premium because it involves cutting into the roof structure, extending the roofline, and weatherproofing new exterior walls — all of which require skilled tradespeople. By contrast, a simple attic storage conversion involves minimal structural work and can often be completed in a few days.
For a more precise figure, use our House Build Cost Calculator to benchmark your full project costs alongside the attic estimate above.
Attic Conversion Cost Per Square Foot
Understanding attic conversion cost per square foot helps you benchmark contractor quotes and identify where your budget is going. Rates vary by conversion type and finish level.
| Conversion Type | Basic ($/sq ft) | Standard ($/sq ft) | Premium ($/sq ft) |
|---|---|---|---|
| Attic Storage | $18–$25 | $25–$35 | $35–$55 |
| Loft Room | $37–$52 | $52–$80 | $80–$110 |
| Attic Bedroom Conversion | $45–$65 | $65–$105 | $105–$140 |
| Attic Office Conversion | $43–$62 | $62–$98 | $98–$130 |
| Dormer Attic Conversion | $66–$95 | $95–$150 | $150–$195 |
How Attic Loft Conversion Costs Are Calculated
Understanding how attic loft conversion costs are broken down helps you evaluate contractor quotes and spot where your budget is going.
The core formula used by most estimators is based on the usable attic conversion cost per square foot (or per m²) of floor area, multiplied by a type and finish factor:
The base rate per square foot covers labour (structural work, carpentry, plastering, electrics, and decoration) and materials (floor joists, boarding, insulation, plasterboard). Typical base rates range from $50–$120 per sq ft ($540–$1,290 per m²) in most markets, with costs higher in major cities and lower in rural areas.
The type factor reflects how much extra structural work is involved. A simple rooflight conversion (no structural changes) has a factor near 1.0, while a dormer attic conversion that extends the roof structure carries a factor of 1.4–1.7. The finish multiplier accounts for materials and specification — basic finishes sit around 0.82× while premium finishes run 1.30–1.45× the base rate.
Add-ons like a new staircase ($2,500–$8,000), ensuite bathroom ($5,500–$18,000), fitted wardrobes attic conversion eaves storage ($1,500–$6,000), and a structural engineer for attic conversion drawings ($500–$2,500) are then added on top.
Use our Raw Material Cost Calculator to separately estimate your materials budget before getting contractor quotes.
Factors That Affect Attic Conversion Cost
These seven variables have the biggest influence on your final attic conversion cost. Understanding them helps you make informed choices when reviewing quotes from attic conversion contractors.
Attic Conversion Prices by Attic Size
The table below shows typical attic conversion prices across different floor areas for a standard bedroom conversion at mid-range finish. Use these as a sanity check against contractor quotes in your area.
| Project Size | Floor Area (sq ft) | Floor Area (m²) | Room Conversion Cost (Mid) | Dormer Conversion Cost (Mid) |
|---|---|---|---|---|
| Small attic conversion | 150–200 | 14–19 | $18,000–$28,000 | $28,000–$42,000 |
| Medium conversion | 200–300 | 19–28 | $26,000–$38,000 | $38,000–$58,000 |
| Large conversion | 300–400 | 28–37 | $35,000–$52,000 | $52,000–$78,000 |
| 2-bedroom attic conversion | 400–600 | 37–56 | $48,000–$75,000 | $70,000–$110,000 |
Note: These figures represent general market ranges and assume standard-height ceilings, existing staircase reuse, no ensuite, and standard insulation. Add 25–40% for premium specification or complex roof structures. All costs vary by region — consult local attic conversion contractors near you for accurate pricing.
Attic Conversion Types Explained
Choosing the right conversion type is the most important decision in your project. Here's what each type involves, who it's best for, and a realistic cost range.
Attic Conversion Stairs, Permits & Building Regulations
Regulations vary by country and municipality, but most jurisdictions require a building permit and fixed staircase for any attic conversion creating a habitable room.
Attic Conversion Stairs Cost
A new fixed staircase for an attic conversion typically costs $2,500–$8,000, depending on the run length, materials, and whether a handrail enclosure is required. Straight staircases are cheapest; space-saving alternating tread or spiral stairs cost more. Building regulations in most regions require:
- Minimum headroom of 2.0 m (6 ft 6 in) on the stair pitch line
- Maximum rise per step of 220 mm (8.6 in)
- Handrails on one or both sides
- Fire-rated doors or escape windows if the attic is a habitable room
Attic Conversion Permit Cost
In the US, a building permit for an attic conversion typically costs $400–$2,000 depending on the municipality and project value. In the UK, building regulations approval fees run £200–£900. Always factor permit costs into your budget — unpermitted attic conversions can cause issues when selling.
You can model permit and staircase costs in our attic conversion cost calculator above using the advanced options toggle.
Structural Engineer for Attic Conversion — Do You Need One?
A structural engineer for attic conversion projects is typically required whenever you alter the roof structure, replace ceiling joists, or add a dormer.
Structural engineer costs for attic conversions range from $500 to $2,500 in the US, and £500–£2,000 in the UK. They provide stamped structural drawings showing:
- New floor joist sizing and spacing (to carry live loads of 40 lbs/sq ft or more)
- Roof truss alterations or replacement details (for trussed roofs)
- Dormer frame and connections to existing roof structure
- Load path from attic floor to foundations
- Specification for any steel beams (RSJs) required
When you always need a structural engineer:
- Adding a dormer of any size
- Converting a trussed roof (modern homes built after ~1960)
- Installing a steel beam (RSJ) to open up the attic
- Required by local building regulations or permit conditions
You can include a structural engineer allowance in our attic conversion cost calculator by enabling the "Structural Engineer" toggle in the advanced options. For related structural costs, also see our House Build Cost Calculator.
Attic Conversion Ideas & Added Home Value
The best attic conversion ideas balance upfront cost against long-term value, livability, and return on investment. Here are the most popular options and what each adds to your home.
Frequently Asked Questions — Attic Conversion Cost
Attic conversion costs vary widely based on size, conversion type, and finish quality. A basic attic-to-room conversion typically ranges from $15,000 to $35,000, while a full dormer attic conversion with bedroom and ensuite can reach $50,000–$90,000 or more. Always get at least three quotes from local attic conversion contractors to compare prices in your area.
An attic bedroom conversion generally costs between $20,000 and $55,000 depending on attic size, whether a dormer is added, and the quality of finishes. Adding an ensuite bathroom or fitted wardrobes will increase the total. Labour and material costs vary significantly by location, so the attic to bedroom conversion cost in your area may differ substantially from these ranges.
A dormer attic conversion cost ranges from $28,000 to $85,000 for most projects. The dormer structure itself — cutting the roof, building out the dormer box, waterproofing, and finishing — typically adds $15,000–$35,000 over a simple rooflight conversion of the same floor area. Dormer conversions almost always require a structural engineer and building regulations approval.
Attic conversion cost per square foot ranges from $18–$55/sq ft for a basic storage conversion, $45–$110/sq ft for a standard loft room, $55–$140/sq ft for a bedroom conversion, and $80–$195/sq ft for a premium dormer attic conversion. Use our attic conversion cost calculator above for a personalised per-sq-ft estimate.
Attic loft conversion costs depend heavily on the conversion type. A rooflight or Velux-style conversion is the most affordable option (typically $15,000–$25,000), while a hip-to-gable or full dormer conversion costs significantly more ($35,000–$80,000+). The attic loft conversion cost per square foot typically ranges from $80–$200 depending on your region and specifications.
A structural engineer for attic conversion projects is usually required when you are converting a trussed roof (the most common type in newer homes), adding a dormer, or significantly altering the roof structure. Structural calculations are typically needed to comply with building regulations covering attic conversion framing and floor joist sizing. Engineer fees generally range from $500 to $2,500 depending on project complexity.
In most regions, attic conversions that create a new habitable room require building regulations approval (or a permit), regardless of whether planning permission is separately needed. Regulations typically cover structural attic conversion floor joists, fire safety, insulation standards, means of escape, and staircase dimensions. Check with your local building authority before starting any attic conversion work, as non-compliant conversions can cause serious issues when selling your home.
To find reputable attic conversion contractors, ask for referrals from neighbours or friends who have had similar work done, search trade directories, and request at least 3 written quotes. Always verify that contractors are licensed and insured in your area, and ask to see examples of previous attic conversion projects before committing. Avoid contractors who cannot provide a fixed-price written quote.
The best attic conversion ideas for adding value include: converting to a bedroom with ensuite (highest ROI at 10–20% value increase), adding a dormer to maximise headroom and floor area, creating a dedicated home office, and installing fitted wardrobes attic conversion eaves storage. A well-executed attic room conversion typically adds 10–15% to a home's value.
Yes, a small attic conversion is possible if you have at least 7 feet of head height at the ridge. Small attic conversions under 150 sq ft are typically used for offices, hobby rooms, or storage. The minimum recommended floor area for a comfortable bedroom is around 70 sq ft, though regulations vary. A small attic conversion typically costs $12,000–$28,000 depending on finish level.
A typical attic conversion takes 4–10 weeks from start to finish. A simple rooflight loft room conversion can be completed in 3–4 weeks, while a full dormer attic conversion with ensuite may take 8–12 weeks. Factor in 2–6 weeks for structural engineer drawings and building regulations approval before work begins — so total project timeline including planning is typically 3–5 months.
Attic conversion cost UK ranges vary widely. A basic rooflight loft conversion costs around £15,000–£30,000, a dormer loft conversion £30,000–£60,000, and a mansard conversion £45,000–£80,000+. Costs in London and the South East are typically 30–50% higher than in the North of England or Scotland. Always get 3 local attic loft conversion quotes for your specific area.