Timber - PVC - Aluminium - Windows, Doors & Conservatories in Hampshire
The Definitive Guide to Window Replacement (2026) | KJM Group
The Definitive Guide to Window Replacement (2026) | KJM Group
Replacing windows is a significant capital expenditure—often the third most expensive purchase a homeowner makes. This guide explains the engineering, regulations, and installation realities of replacing windows in 2025.
| Area | What You Need to Know |
|---|---|
| The Law (2025) | New windows must achieve a U-value of 1.4 W/m²K or lower. |
| Ventilation | New regs usually require Trickle Vents, even if your old windows didn’t have them. |
| Tech | “Warm Edge Spacer Bars” and “Argon Fill” are now essentials, not extras. |
Table of Contents
1. Diagnosis: Repair or Replace?
Before committing thousands of pounds, it is vital to check if replacement is actually necessary. At KJM, we often advise customers that a repair might suffice.
Failed Units: If glass is misty but frames are fine, just replace the glass unit (IGU).
Broken Hinges: If the window doesn’t close tight, it’s often just a £30 friction hinge.
Rotten Timber: Once rot sets into the core, it is compromised.
Cold Profiles: Old aluminium without a thermal break will always conduct cold.
2. The Anatomy of a Modern Window
Modern “A-Rated” windows rely on three specific technologies working in harmony.
1. The Thermal Break
In the past, frames were solid. Today, uPVC frames are “multi-chambered” (like a honeycomb) to trap heat. Aluminium windows use a polyamide thermal break.
2. Warm Edge Spacer Bars
The spacer bar is the strip separating the two panes of glass. Old windows used aluminium spacers which conduct cold. Modern units use a composite “Warm Edge” spacer which is up to 950 times less conductive.
3. Understanding Part L Regulations
Since the June 2022 Building Regulations update, the government has cracked down on “airtight” homes.
4. Material Science: uPVC vs Aluminium vs Timber
| Material | Lifespan | Expert Verdict |
|---|---|---|
| uPVC | 25 Years | The workhorse. Modern foils mimic timber almost perfectly. Best ROI. |
| Aluminium | 40+ Years | Structurally stronger. Essential for large sliding doors or thin frames. |
| Timber | 60+ Years | Unbeatable for heritage. Requires painting every 7 years. |
5. The Installation Process
A professional installation should be clinical. Here is the standard workflow:
- Removal: Frame is cut and levered away, ideally without damaging plaster.
- Fitting: New frame is fixed into masonry. The gap is sealed with expanding foam.
- Glazing: Glass is installed using “toe and heel” packing to ensure the sash sits square.
Final Advice: The “FENSA” Factor
You legally need a certificate proving compliance to sell your house. Ensure your quote includes FENSA certification.
6. Frequently Asked Questions
They will cure condensation on the glass. However, humidity might increase elsewhere in the room. This is why using trickle vents is crucial.
Yes, but only if the frames are in good condition. Putting heavy glass into old, weak hinges is often a false economy for frames older than 15 years.
For most homes in Hampshire, A-rated double glazing is sufficient to meet regulations and keep you warm. Triple glazing is best suited for north-facing rooms or areas with extreme noise issues, but the payback time on energy savings is significantly longer.
Professional installers cut the old frame fixings to minimize damage. In 95% of cases, there is no damage to tiles or wallpaper. You may occasionally need to touch up paint on the reveal (the wall directly next to the window) after the silicone sealant has cured.
Usually, no. Most modern windows are designed to be installed from the inside (internally beaded). Scaffolding is typically only required for hard-to-reach areas, such as windows directly above a conservatory roof or large fixed panes of glass.
A typical 3-bedroom house (approx 8-10 windows) usually takes 2 to 3 days. A single window can be replaced in roughly 2-3 hours.
Mark Pearce is a highly experienced specialist in the double glazing industry, having built his knowledge from the ground up through hands-on experience in installation, manufacturing, sales, and business management. Beyond his role at KJM, Mark is a keen blogger, writer, and traveller, often sharing insights on the latest innovations in the home improvement industry.
- 2026 Design Trends: The 4 Window & Door Styles Defining the Year - 19 December 2025
- The 2026 Glazing Outlook” – High-level summary of the pivot to growth. - 9 December 2025
- Industry News: The Future Homes Standard 2025 & What It Means for Your Windows - 1 December 2025
