What are the costs of a double dormer?

Estimated costs double dormer

A double dormer is a spacious extension of the house in which two dormers are placed — often one at the front and one at the rear, or two next to each other across the full width of the roof.
This construction provides significantly more light, space and added value, but also involves a higher investment than a single dormer.

Average costs

The estimated costs for placing a double dormer are on average between €10,000 and €18,000, depending on material, design and construction.

The exact price depends on the construction form:

• Two dormers opposite each other (front and back) often have separate constructions and permits.
• Two dormers next to each other form one large roof structure, which requires more material and labor.

Key cost factors

1. Dimensions and construction

A double dormer often covers a large part of the roof surface.
More width means higher material costs and a heavier roof construction.
Depending on the length, this can increase the price by €1,000 to €2,000 per extra meter.

2. Material choice

• Plastic: low-maintenance and affordable; the most popular choice for double dormers.
• Wood: classic look, easy to work with, but requires regular maintenance.
• Aluminum or zinc: sleek, modern and durable, but with a higher purchase price.

3. Prefab or custom-made

A prefab double dormer is manufactured in the factory and installed in one or two days.
A custom-made construction is built on location, offers more design freedom and is better suited for complex roofs, but costs on average 15 to 30% more.

4. Permit and regulations

For double dormers, a building permit is almost always required, especially on the front of the house or when modifying the roof construction.
The costs for permit and fees are usually between €300 and €700, excluding any structural calculations.

5. Insulation and finishing

A double dormer requires extra attention to insulation, ventilation and interior finishing.
Finishes such as plasterboard, painting, lighting and window sills increase the total amount by €1,000 to €2,000.

Practical examples

Example 1 – Prefab plastic double dormer (two sides of the house, each 3 meters wide):

• Two prefab units: €9,600
• Assembly and finishing: €2,000
• Permit and additional costs: €400
  Total price: approximately €12,000 including VAT and assembly

Example 2 – Custom-made wooden double dormer (full roof width, approximately 6 meters):

• Construction and finishing: €13,500
• Interior finishing and insulation: €1,500
• Permit and drawings: €500
  Total price: approximately €15,500 including VAT and installation

Tips to reduce costs

1. Choose prefab if the roof shape is standard; this saves time and labor costs.
2. Combine work (e.g. roof renovation or insulation) to avoid double labor hours.
3. Limit customization to where it is really necessary.
4. Compare multiple contractors via an independent quotation platform such as jeofferte.nl to gain insight into price differences, materials and finishing levels.
5. Check subsidy options if the dormer is part of a larger insulation project (for example, via the ISDE scheme).

Summary

A double dormer costs on average between €10,000 and €18,000, depending on material, dimensions, construction and permit.
Prefab models are quicker and cheaper to install, while custom work offers more freedom for complex roof shapes.
A good preparation — including permit check, material selection and comparison of multiple quotes via jeofferte.nl — prevents unnecessary costs and ensures a sustainable investment with an optimal end result.

The price of a double dormer is determined by several factors:

• Material: The choice of material has a major impact on the price.
  • Wood: Offers a natural look, but requires more maintenance.
  • Plastic: Low-maintenance and durable, but may look less authentic.
  • Polyester: Lightweight and strong, but may be less environmentally friendly.
• Type of Dormer: There are two main types of dormers:
  • Prefab: Are made in the factory and installed in one go. This is often a faster and cheaper option.
  • Traditionally built: Are custom-made on site. This offers more flexibility in design and dimensions, but is generally more expensive.
• Finishing: Extra options and finishes can further increase the price:
  • Shutters: Provide extra insulation and blackout.
  • Tilt and turn windows: Provide extra ventilation and ease of use.
  • HR++ Glass or Triple Glass: Improve insulation and energy efficiency.
• Placement: The configuration of the double dormer affects the complexity of the installation:
  • Next to each other: Two dormers placed directly next to each other.
  • Above each other: Two dormers placed above each other (less common).
  • Perpendicular to each other: Two dormers placed perpendicular to each other (for example, on a corner house).
• DIY: Performing certain tasks yourself, such as the interior finishing, can save costs. Keep in mind that this requires the necessary knowledge and skills.

Tips for cost savings when installing a dormer window

A dormer window offers more light and space, but the investment can be significant. With careful preparation and conscious choices, it is possible to significantly reduce the total costs without compromising on quality or durability.
The tips below help to structurally save on the costs of installing a dormer window.

1. Compare multiple contractors and builders

The biggest savings start with comparing quotes.
Price differences between certified dormer specialists can be as high as 20 to 30 percent for comparable work.
When comparing, pay attention not only to the price, but also to:

• material type and insulation value;
• warranty period and quality marks;
• included interior finishing;
• installation method and transport costs.

A comparison via an independent quote platform like jeofferte.nl provides insight into realistic market prices and prevents unnecessary additional costs.

2. Opt for a prefabricated dormer window

A prefabricated dormer window is produced in the factory and installed within a day.
This limits the labor hours and reduces installation costs compared to custom-made.
The saving is on average 10 to 25 percent compared to a dormer window built on-site.
Prefabricated is particularly suitable for standard roof shapes without deviations.

3. Combine Work

When the roof is being opened anyway, it is financially advantageous to combine work, such as:

• roof insulation or roof renovation;
• installation of skylights or solar panels;
• lead or roof edge repair.

By combining multiple jobs, crane and labor costs are shared, resulting in savings of a few hundred euros.

4. Plan outside of peak season

Demand for dormer windows is highest in spring and autumn.
During the winter months or quieter periods, many contractors offer lower rates due to a lower workload.
Those who are flexible in their planning can benefit from discounts or more favorable installation dates.

5. Limit luxury interior finishing

A simple finish with plasterboard or wooden panels is functional and budget-friendly.
Luxury finishes, lighting, and painting significantly increase the price.
Those with some DIY experience can carry out the interior finishing themselves, provided the insulation and moisture barrier are correctly installed.

6. Check if a permit is required

A dormer window on the rear of the house is often permit-free, provided it is placed within standard dimensions.
In that case, the costs for the environmental permit (usually €300 to €600) are waived, and delays are prevented.
A simple check with the Online Environmental Agency or the municipality can rule out unexpected costs.

7. Choose low-maintenance materials

The choice of material not only affects the purchase price but also the long-term maintenance costs.

Those who opt for plastic or aluminum save structurally on maintenance and painting.

8. Limit customization to what is truly necessary

A fully customized dormer window is only necessary for non-standard roof shapes or specific aesthetic requirements.
A standard prefabricated model with a few adjustments is usually sufficient and considerably cheaper.
By keeping the design functional, production costs and assembly time are limited.

9. Combine dormer with insulation measures

When the dormer is installed in combination with roof insulation, the investment can be partially reduced through the ISDE subsidy or local regulations.
Conditions are:

• the insulation must cover at least 20 m²;
• the R-value must meet the standard (at least 3.5 m²K/W);
• the work must be carried out by a certified contractor.

This combination can result in savings of several hundred euros in subsidies.

10. Regular maintenance prevents replacement

Minor maintenance measures significantly extend the lifespan of the dormer window.
By annually checking and cleaning the roof edges, sealant joints, and water drainage, leaks and damage can be prevented.
Good maintenance prevents costly repairs or premature replacement.

Summary

Important tips for cost savings when installing a dormer window:

1. Compare multiple reputable contractors.
2. Choose prefab where possible.
3. Combine works to share costs.
4. Plan outside peak season.
5. Limit luxury interior finishes.
6. Check permit requirements beforehand.
7. Use low-maintenance materials.
8. Limit customization to what is necessary.
9. Combine with insulation for subsidy benefits.
10. Perform periodic maintenance.

By combining these measures, the total investment can be reduced by 10 to 30 percent.
A well-considered comparison via an independent quote platform such as jeofferte.nl provides insight into the most profitable and sustainable solution for your situation.