DIY uPVC window installation is doable if you have building experience, a second pair of hands and stick to the order: frame on packers, mechanical fixing, insulation, sealing in three layers. Most problems start earlier, though, at the ordering stage: a wrong size, an opening side described the wrong way, a roller shutter added too late. We do not install windows ourselves, but since 1997 we have seen where these mistakes happen. Below is the whole job in order. Details depend on the system and the wall, so always check the manufacturer's instructions.
When does fitting windows yourself make sense?
- A new build or extension. Openings are straight and clean, and there are no old windows to remove.
- A sub-frame. In the Netherlands, windows are often fitted into a sub-frame (stelkozijn) already set in the wall. The configurator offers a Dutch-style frame, with or without a fin, depending on the system.
- You have help. A large triple-glazed window is heavy; you will not position it alone.
For lift and slide doors and very large glazing, consider an experienced crew. Damage caused by incorrect fitting is not covered by the warranty, and energy-efficiency grants often require installation by a company, so check the conditions with the official body first.
Before you order: three choices that shape the installation
1. Frame size, not opening size. Measure the opening in three places: top, middle and bottom, and note the smallest value. Subtract the fitting gap given in the system instructions. With a sub-frame, work from its inside size. In the configurator you enter the frame size. 2. Opening side as seen from inside. Described from outside, the sash ends up the wrong way round. 3. A top-mounted roller shutter now or not at all. Its box makes the window taller, so a decision after ordering changes the size.
These are the three things we correct most often in quotes. We check sizes, opening sides and descriptions in every quote, and once you have paid the sizes are locked. Foam, tapes, fixings and packers can be added in the configurator under "Don't forget", so they arrive with the windows.
Delivery and storage
The windows arrive on stillages. Unloading is your job, with a forklift or 2–3 people. Check the windows with the driver present, note any damage on the delivery note and take photos. Until fitting, store them upright, under cover, on level ground, away from sun and damp. Remove the protective film no later than 4 weeks after delivery, or it becomes hard to peel off.
DIY uPVC window installation in 9 steps
1. Prepare the opening. Check sizes and diagonals, remove mortar residue and dust. 2. Take the sash out on large windows. The frame alone is lighter and easier to set. 3. Stick the tapes to the frame before setting it: vapour-tight inside, vapour-open outside. 4. Set the frame on packers and wedges. Check level, plumb and diagonals. The frame must not be twisted. 5. Fix the frame mechanically with anchors or frame fixings, roughly every 70 cm and at least 2 per side. Do not overtighten, or you will bow the profile. 6. Fill the gap with expanding foam, without excess. One can covers roughly 6 m of perimeter. Foam insulates, but it does not hold the window. 7. Seal the tapes to the wall or sub-frame. That gives a three-layer installation: vapour-tight inside, insulation in the middle, vapour-open outside. 8. Rehang the sash and adjust the hardware. It should close without resistance and press evenly on the seal. 9. Finish the joints inside and out, without covering the drainage slots at the bottom of the frame.
The most common mistakes
- A window held only by foam, with no anchors or fixings.
- No tapes, so moisture from inside gets into the foam.
- Covered drainage slots, so water stays in the frame.
- A twisted or bowed frame from overtightened fixings, so the sash starts to rub.
- Foam left exposed to sunlight.
- Windows stored flat or in the sun, film removed too late.
When should you order?
Production takes 3–8 weeks from receipt of payment, depending on system, colour, roller shutters and season, so plan the fitting with some slack. In the configurator you enter frame sizes, choose system, glazing and colour, and see the price straight away. We send the quote with transport within 3 working days, and before production you get a drawing to approve. The order process is described on how it works, and the cost of windows without fitting in How much do windows cost without fitting.