Installing a roof window brings natural daylight into a loft space or attic room and makes it considerably more pleasant and valuable to use. The total cost of installing a roof window is €800–2,500 per window including materials and professional installation. DIY installation is technically possible but requires experience with roofing and carpentry work. This article covers everything about types of roof windows, costs, the difference between Velux and Fakro, and the step-by-step installation guide.
What Does Installing a Roof Window Cost? DIY vs. Hiring a Professional
Cost Overview
| Item | Estimated price |
|---|---|
| Standard roof window (Velux GGL, 78×98 cm) | €350–500 |
| Roof window + installation kit (for insulated roof) | €450–700 |
| Labour costs for installation (including roofer) | €400–800 |
| Internal lining (splayed reveal lining) | €150–350 |
| **Total standard installation** | **€900–1,850** |
| Electrically operated roof window | €600–1,200 |
| Large-format roof window (with dormer effect) | €1,500–3,500+ |
Worked example: Velux GGL 78×98 cm, manually operated
- Roof window: approx. €400
- Installation (roofer + carpenter): approx. €500–700
- Internal lining: approx. €200
- Total: approx. €1,100–1,300
When is DIY worth it?
Installing a roof window is a complex job requiring knowledge of roof construction, roofing and insulation. It is achievable for experienced DIYers. Mistakes with flashing or insulation can lead to leaks or damp problems. Material costs are the same — the saving is the roofer’s labour (€400–800). Be realistic about your level of experience.
Types of Roof Windows
| Type | Description | Price | Suitable for |
|---|---|---|---|
| Centre-pivot roof window | Opens outward, most common type | €300–600 | Bedroom, office |
| Electric roof window | Motor-driven, with rain sensor | €600–1,200 | Hard-to-reach locations |
| Flat roof light / rooflight | For flat roofs, fixed or opening | €200–600 | Loft, storage room |
| Fixed roof window (non-opening) | Daylight only, no ventilation | €200–400 | Stairwell, corridor |
| Solar-powered roof window (VELUX INTEGRA Solar) | Solar-powered operation | €800–1,500 | All positions |
| Roof access hatch | Access hatch to flat roof | €300–700 | Flat roof access |
Velux vs. Fakro: Which Brand to Choose?
| Aspect | Velux | Fakro |
|---|---|---|
| Market share | Approx. 50% (market leader) | Approx. 30% |
| Roof window price | €350–600 (standard) | €280–500 (standard) |
| Guarantee | 10 years on product | 10 years on product |
| Accessories | Very extensive | Good |
| Availability | Everywhere | Good at most merchants |
| DIY-friendly | Excellent (instructions + video) | Good |
Fakro is cheaper but offers comparable quality. Velux has the largest accessories range (blinds, blackout blinds, insect screens) and comprehensive installation videos — handy if you are doing it yourself.
Note: Always check that the installation depth of the roof window suits the insulation thickness in your roof. Roof windows come with installation kits calibrated to the roof build-up. Both Velux and Fakro offer extension frames for roofs with extra insulation.
What Size Roof Window Do You Need?
| Room | Recommended roof window | Glass area |
|---|---|---|
| Small bedroom | 55×78 cm (C02) | 0.33 m² |
| Standard bedroom | 78×98 cm (M04) | 0.62 m² |
| Living room / study | 78×118 cm (M06) | 0.78 m² |
| Large room | 114×118 cm (P06) | 1.16 m² |
Rule of thumb: The glass area should be a minimum of 10–15% of the floor area of the room to provide adequate daylight.
Materials List (standard installation, tiled roof)
| Material | Quantity | Estimated price |
|---|---|---|
| Roof window (e.g. Velux GGL M04) | 1 | €380–480 |
| Installation depth kit (EDW or EDP) | 1 | €80–150 |
| Flashing kit | 1 | €60–120 |
| Roofing underlay (additional) | 2–3 m² | €10–20 |
| Internal lining / splayed reveal | 1 | €150–280 |
| Trimmer / support structure (timber) | depends on opening | €30–60 |
| Sealant (silicone, exterior grade) | 1 cartridge | €8–12 |
| Screws and fixings | 1 set | €10–15 |
Step-by-Step Guide: Installing a Roof Window
Step 1 — Choose the location and check the structure
Decide on the desired position of the roof window. Make sure the window falls between two rafters, or work out whether an intermediate rafter needs to be removed (with additional support structure). Check the rafter spacing — standard roof windows are designed for 60–90 cm rafter centres.
Step 2 — Remove the roof covering
Remove the roof tiles or covering around the planned opening. When removing, always work from top to bottom; when replacing, work from bottom to top. Set the removed tiles aside (they will be reused).
Step 3 — Cut the opening and form the trimmer
Cut the opening in the roof sheathing (the timber structure). Ensure the correct dimensions (roof window size + 3 mm clearance on all sides). Install the support structure if a rafter needs to be cut: two trimmer timbers along the width of the opening. These transfer the loads from the roof window.
Step 4 — Connect the roofing underlay
Fold back the underlay (the vapour-permeable membrane already in place) and lead it around the opening. Tape the membrane to the roof window frame for a vapour-permeable seal. This prevents moisture problems.
Step 5 — Fix the roof window
Fix the roof window frame in the opening following the manufacturer’s instructions. Use the supplied fixing brackets and screws. Check with a spirit level that the frame sits level. Apply insulation around the frame (supplied or separate mineral wool).
Step 6 — Fit the flashing
Fix the flashing kit or lead flashing around the roof window on the roof structure. This provides the waterproof seal. Lead the flashing a minimum of 15 cm beneath the upper roof tiles. Follow the Velux or Fakro instructions precisely.
Step 7 — Replace the roof tiles
Replace the roof tiles around the roof window. Cut any adjacent tiles to fit if necessary. Check that every overlap is correct. Test with rain (or a hosepipe) to confirm there is no leakage.
Step 8 — Fit the internal lining
Fit the internal lining (splayed reveal lining). This is the white internal surround that covers the space between the roof window and the ceiling/wall. Fix insulation around the roof window from the inside for additional thermal insulation.
Common Mistakes
| Mistake | Consequence | Solution |
|---|---|---|
| Fitting between rafters without trimmer support | Structural damage | Always install trimmer support when cutting a rafter |
| Wrong installation depth | Roof window not flush with the roof surface | Measure insulation depth and choose the correct kit |
| Roofing underlay not properly connected | Condensation and damp damage | Always make the membrane connection vapour-permeable |
| Flashing incorrectly fitted | Leakage in rain | Follow manufacturer’s instructions exactly |
| No internal insulation | Cold bridges, condensation on glass | Always fit insulation around the roof window |
Planning Permission: Do You Need It?
In most European countries, installing a roof window is permitted without planning permission if:
- The window does not project above the roof line
- It is in the rear or side roof slope (not facing the street)
- It complies with the relevant local planning requirements
Planning permission may be required if:
- The window faces the street (front roof slope) in some areas
- The building is listed or in a conservation area
- Local planning rules require it
Check your specific situation with your local planning authority — this usually takes only a few minutes.
Conclusion
Installing a roof window brings light, ventilation and added value to a loft conversion or attic room. The total cost of €1,000–1,500 for a standard Velux window is well justified by the improvement in living quality and property value. Have the installation carried out by a qualified professional if you have no experience with roofing or construction work. Mistakes in flashing cost far more than the saving is worth.
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