Leaking windows are more than a minor nuisance; they are a direct threat to your home's structural integrity and energy efficiency. In the UK’s damp climate, a ...
Professional window sealing goes beyond simply squiring silicone into a gap. It involves identifying the root cause of ingress—whether it is failed gaskets, blocked drainage channels, or degraded external pointing—and ensuring the thermal envelope of your home remains intact.
What Does the Work Involve?
- Diagnostic Inspection: Identifying the leak source using thermal imaging or water testing on frames, gaskets, and masonry.
- Surface Preparation: Mechanical removal of failed silicone, brittle glazing tape, or loose mortar.
- Cleaning: Degreasing surfaces with specialist cleaners to ensure the new sealant bonds correctly.
- Gasket and Bead Repair: Replacing shrunk rubber gaskets or damaged glazing beads that hold the glass in place.
- Sealant Application: Applying high-specification low-modulus neutral-cure silicone or polyurethane sealant to external joints.
- Drainage Clearing: Checking and clearing internal "weep holes" that allow water to exit the frame.
Typical Costs
| Item | Low £ | High £ | Notes |
|---|---|---|---|
| Call-out / Initial Assessment | £80 | £150 | Includes first hour of diagnostic work. |
| Labour (per hour) | £50 | £85 | Varies by region and specialist expertise. |
| Standard Reseal (Single Window) | £120 | £250 | Includes materials and waste disposal. |
| Timber Cill Repair/Replacement | £200 | £450 | Includes minor timber splicing and sealing. |
| Access Equipment (Scaffolding) | £350 | £800 | Required for safe access to upper floors. |
The total cost is primarily driven by accessibility and the condition of the frames. While a ground-floor uPVC reseal is straightforward, repairing rotted Victorian sash windows or working at height on a townhouse will significantly increase labour and equipment costs.
How Long Does It Take?
- Single window reseal: 1–2 hours.
- Full house external reseal: 1–2 days (depending on the number of openings).
- Timber cill or bead replacement: 3–5 hours per window.
- Drying time: Most modern sealants are "skin-over" in 30 minutes but require 24 hours to fully cure.
DIY or Professional?
Homeowners can often tackle ground-floor resealing if they use the correct materials. However, identifying the *exact* entry point of water is notoriously difficult, as leaks often travel through the wall cavity before appearing inside.
Professional tradespeople use "Low Modulus" sealants which offer better movement accommodation than standard DIY-store silicone, preventing the seal from snapping during temperature changes.
For any work above the ground floor, professional hire is essential for safety. Furthermore, if your windows are still under a FENSA or CERTASS warranty, DIY repairs may void your protection.
Choosing the Right Tradesperson
- Check Accreditations: Look for FENSA, CERTASS, or GGF (Glass and Glazing Federation) membership.
- Verify Insurance: Ensure they hold Public Liability insurance (minimum £1m-£2m) for working on your property.
- Ask about "Neutral Cure": Ask what sealant they use; neutral-cure silicone is superior for uPVC and stone as it doesn't cause discolouration.
- Warranty: A reputable pro should offer a 12-month guarantee on leak repairs.
UK Regulations
- Part L (Conservation of Fuel): Repairs must not degrade the thermal performance of the window.
- Part F (Ventilation): Sealing work must not accidentally block trickle vents or essential background ventilation.
- Working at Height: All contractors must follow HSE guidelines; ladder work is often restricted for long-duration repairs.
Common Problems
- Applying "Wet on Wet": Applying new sealant over old, damp, or dirty silicone leads to immediate failure.
- Blocked Drainage: Many "leaks" are actually caused by dust and debris blocking the drainage channels inside the uPVC frame.
- Wrong Sealant: Using "Acetoxy" silicone on natural stone or certain metals can cause chemical etching and staining.
- Ignoring the Masonry: Water often enters through cracked mortar joints (pointing) around the window rather than the window itself.
Frequently Asked Questions
Is a leaking window a sign I need new windows?
Not necessarily. Most leaks are caused by failed sealant, worn gaskets, or blocked drainage holes, all of which can be repaired for a fraction of the cost of a full replacement.
Why is there water on the inside of my window sill?
This is often caused by a "blown" seal in the double-glazing unit or a failure in the external perimeter sealant. It could also be condensation if the room lacks adequate ventilation.
Can you reseal windows in the rain?
No. Sealants require a dry surface to bond correctly. If it is raining, a professional will usually wait for a dry window or use a temporary "over-seal" and return later.
How long should window sealant last?
High-quality external sealant typically lasts 10–15 years. If your home is in a coastal area or south-facing (high UV exposure), this may reduce to 5–8 years.
What is the difference between silicone and mastic?
"Mastic" is a generic term often used for sealants. In modern trade, silicone is preferred for its flexibility, while polyurethane is used for high-movement joints or where painting over the seal is required.
This guide was written with AI assistance and is intended for general information only. Prices are estimates based on UK averages and may vary by region. Always get at least three quotes and consult a qualified professional before starting any work.
