UPVC (unplasticized polyvinyl chloride) windows have become increasingly popular in recent years because of their durability, energy efficiency and low maintenance. They also offer a clean, modern appearance, making them a common choice for both residential and commercial properties. Proper installation, however, is essential to ensure long service life and optimal performance.
In this comprehensive guide to UPVC window installation, we cover everything you need to know—from the tools required to step-by-step installation tips and the key benefits of UPVC windows.
Tools required for UPVC window installation
Before you begin, gather the following tools and materials to make the installation safer and more efficient:
- Measuring tape: for accurate height, width and depth measurements.
- Spirit level: to ensure the frame is plumb and level.
- Screwdrivers / cordless drill: for fixing frame screws and hardware.
- Hammer: for minor adjustments and fixing brackets where needed.
- Silicone gun / caulking gun: to apply sealant evenly around the frame.
- Safety glasses and gloves: to protect your eyes and hands during handling and drilling.
- Appropriate sealant: a quality silicone or polyurethane sealant for weatherproofing.
- Window fixing brackets and packers/shims: to secure the frame and adjust its position.
- Foam backer rod (optional): for filling larger gaps before sealing.
For background on the material and its properties, see the UPVC entry on Wikipedia (Unplasticized polyvinyl chloride).
Steps involved in UPVC window installation
1. Measure the opening
Measure the window opening at three points for both width and height (top, middle and bottom / left, center and right). Use the smallest measurement and allow for the manufacturer’s recommended installation clearance—this ensures the frame will fit and leaves room for packers and sealant.
2. Prepare the opening
Clean the opening thoroughly and remove any loose debris, old sealant or rotten timber. Check that the sill is level and the reveal is plumb; if not, plan to correct it with packers. Ensure the area is dry before installation to prevent trapping moisture.
3. Fit window fixing brackets
Attach the recommended fixing brackets to the frame in the specified locations. Position the brackets within the opening and secure them temporarily so you can adjust the frame before permanently fixing it. Make sure brackets are level and aligned.
4. Apply primer or base seal (if required)
Some installations benefit from a thin bead of silicone or a primer on contact points to improve adhesion and prevent water ingress. Follow the window manufacturer’s guidance on whether a primer or gasket is required.
5. Insert and level the window
Carefully place the window into the opening with the help of an assistant for larger units. Use packers/shims at the hinge and lock points to position the frame. Check that the frame is square by measuring diagonals and confirm it is level and plumb with a spirit level.
6. Secure the frame
Fix the frame in place using the appropriate screws through the pre-designed fixing zones or brackets. Space fixings as recommended by the manufacturer. Tighten screws just enough to hold the frame; overtightening can distort UPVC frames and affect operation.
7. Seal the frame
Apply a continuous bead of external-grade silicone or polyurethane sealant around the outside perimeter of the frame to create a weatherproof barrier. Use a foam backer rod for larger gaps and tool the sealant smooth for a neat finish. For guidance on caulking technique, see this practical guide from This Old House (How to Caulk Windows).
8. Finish the interior
On the interior, fill any gaps with low-expansion insulation foam where specified and trim back excess once cured. Back the final joint with a neat internal bead of sealant, trim the packers flush and fit any trims or architraves.
9. Clean up and test operation
Remove protective film from the frame and glass (if present). Clean off excess sealant and debris. Open and close the window several times to confirm smooth operation and correct alignment. Check for drafts and make any final adjustments to locking points and hinges.
Installation tips and common pitfalls
- Measure three ways and use the smallest dimension to avoid fitting a too-large unit.
- Do not overtighten fixings—UPVC can bow if screws are overdriven.
- Leave a small perimeter gap for thermal expansion as per manufacturer guidance (commonly a few millimetres depending on size).
- Ensure drainage/weep holes on the frame are not blocked and that the sill slopes slightly outward for water runoff.
- Use the right type of sealant—silicone is common for external joints, while polyurethane can be used where movement is expected. Check product specifications.
Benefits of UPVC windows
Energy efficiency
UPVC frames provide good thermal insulation and, when combined with double or triple glazing, can significantly reduce heat loss and lower energy bills. For general guidance on energy-efficient windows, see the U.S. Department of Energy’s window and door resources (Energy Saver: Windows, Doors, and Skylights).
Low maintenance
UPVC requires minimal upkeep—no painting or staining. Regular cleaning with mild soap and water keeps frames looking new and prevents dirt build-up that could affect seals and hardware.
Durability
UPVC is resistant to rot, corrosion and weathering, and it maintains structural integrity for many years when installed correctly.
Conclusion
Installing UPVC windows can be a straightforward project for a competent DIYer with the right tools, careful measurements and attention to detail. However, if you are unsure about structural alterations, drainage, or compliance with local building regulations, it’s best to consult a professional window installer. Proper installation ensures your UPVC windows deliver their full benefits—energy savings, low maintenance and long-term durability.
