How to Use the Dormer Cost Calculator
Calculating the expense of adding a dormer is essential for any homeowner looking to increase their attic space or add value to their property. This dormer cost calculator provides a detailed estimate based on industry averages for materials and labor. By adjusting the type, size, and quality of finish, you can better plan your renovation budget.
To get the most accurate result, follow these steps:
- Dormer Type
- Select the architectural style. Shed dormers are generally the most cost-effective as they feature a single flat roof slope, while Gabled and Hip dormers require more complex framing.
- Dimensions (Width & Depth)
- Enter the horizontal width and the depth (the distance it extends from the roof). Most standard dormers range from 6 to 12 feet in width.
- Finish Quality
- Choose between basic, standard, or premium finishes. This accounts for the difference between simple plywood flooring and high-end hardwood or custom windows.
How It Works: The Cost Formula
The calculator uses a weighted area-based formula to determine the estimated project total. Because roofing labor and structural reinforcement vary significantly by style, the base rate per square foot changes accordingly.
Estimated Cost = (Width × Depth) × Style Rate × Quality Factor
- Style Rate: Ranging from $120/sq.ft for shed dormers to $250/sq.ft for custom wall dormers.
- Quality Factor: A multiplier (0.9 to 1.3) based on the tier of interior finishing materials.
- Market Variance: We apply a +/- 15% range to account for regional labor costs and fluctuations in lumber prices.
Dormer Cost Calculation Example
Example Scenario: A homeowner wants to add a 12-foot wide Gabled dormer that is 10 feet deep with standard finishes.
Step-by-step solution:
- Determine Area: 12 ft × 10 ft = 120 sq. ft.
- Identify Base Rate: Gabled dormers average $160 per square foot.
- Apply Quality Factor: Standard finish uses a factor of 1.0.
- Initial Calculation: 120 × $160 × 1.0 = $19,200.
- Range Calculation: The project will likely fall between $16,320 and $22,080 depending on local contractor rates.
Common Questions
Does a dormer increase home value?
Yes, adding a dormer is one of the highest-ROI home improvements. By converting unused attic space into a functional bedroom or office, you increase the "livable square footage" of the home. On average, homeowners recoup 60-70% of the cost in immediate resale value.
How long does it take to build a dormer?
A typical dormer installation takes between 3 to 5 weeks. The first week involves structural framing and making the roof watertight. The subsequent weeks are dedicated to insulation, drywall, electrical work, and exterior siding.
Do I need a permit for a dormer?
Almost always. Since a dormer involves cutting into the existing roof rafters and changing the structural load of the house, building departments require a permit and inspections. Our dormer cost calculator includes a 5% estimate for these administrative fees.