Guide To Composite Windows in 2026

A composite window is a window whose frame is made using two different materials working together most commonly timber on the inside and aluminium on the outside. 

That hybrid approach exists for a practical reason:

• Timber inside gives a warm, natural feel where you see and touch the frame day to day.
• Aluminium outside shields the frame from weather and UV exposure, keeping the exterior looking good with far less upkeep than exposed timber. 

In other words, composite frames aim to remove the classic compromise: you shouldn’t have to choose between beautiful and hardwearing.

Most composite windows are built from a structural core (often timber or uPVC), plus a durable external layer (commonly aluminium), alongside modern glazing and sealing systems. 

A typical composite window frame includes

A practical breakdown looks like this:

• Internal face (indoors): typically timber for appearance and natural insulation. 
• External face (outdoors): commonly powder coated or anodised aluminium designed for weather resistance and low maintenance. 
• Thermal break / insulating core: a material that reduces heat transfer between outside and inside (this is where many high performance systems win or lose). 
• Glazing unit & warm edge details: many high spec composites are paired with double or triple glazing (and often warm edge spacer bars) to reduce heat loss and improve comfort. 

At Idealcombi, composite windows are commonly described as timber + aluminium + PUR (polyurethane) with Idealcombi’s idealcore™ (a thermal PUR component) designed to improve insulation and reduce issues associated with cavities, drainage routes, and moisture exposure in the frame’s “wet zone.” 

Idealcombi also explains that earlier generations of alu clad and composite designs relied on drainage holes and channels which could become blocked over time so later designs focus on solving those maintenance and durability weak points. 

uPVC is typically the budget friendly option in the UK market, and it’s widely installed.
Composite windows usually cost more up front however, composite systems are often positioned as a long term investment because they’re designed to require less external upkeep while maintaining appearance and performance. 

Durability and expected service life

Some UK pricing and buying guides cite uPVC frames as having a lifespan “around 20 or so years” in typical use, with other materials (like aluminium and well maintained timber) lasting longer.
By contrast, idealcombi composite window lifespans are in the 70 year range (or more), depending on the composite type and maintenance. 

Feel and aesthetics (the “everyday experience” part)

If you care about how a window looks and feels from the sofa, timber interiors are a major selling point. Composite frames are frequently described as combining a timber interior with a sleek, low maintenance aluminium exterior essentially “best of both worlds.” 

Energy performance: look beyond just the glass

In 2026, you’ll see more quotes mentioning U values and energy ratings. Two principles help you compare products properly:

• A lower U value generally means less heat escapes through the window.
• In the UK, the BFRC Window Energy Rating aims to show a product’s overall energy performance by factoring heat loss, solar gain, and air leakage, not just the centre pane glass performance. 

If you’re replacing windows in an existing dwelling in England, guidance summarising the 2021 edition of Approved Document L (in force since June 2022) states replacement windows should meet a maximum U value of 1.4 W/m²K or a minimum WER Band B (with transitional allowances for timber windows until June 2023). 

Well specified uPVC can meet strong energy targets, but high performance composite systems often combine advanced frames with double or triple glazing options designed to push performance further with slimmer sightlines.

People often search for composite windows and doors together because the best results come from specifying them as a system: consistent sightlines, matched colours, and a coherent performance spec across openings.

When composite makes the most practical sense

Composite systems tend to be especially attractive when your project includes:

• Large glazed openings where slim, strong framing and consistent external sightlines matter.
• Sliding doors or terrace doors where weather exposure, threshold detailing, and daily operation put more demand on materials and hardware. 
• Renovations that want a traditional look with modern performance, such as flush casement styles or “period look” solutions designed to mimic older glazing aesthetics. 

If you’re building a new dwelling in England, Approved Document Q covers standards intended to help doors and windows resist physical attack, supporting Building Regulations requirements around unauthorised access. 

That matters because doors and easily accessible windows are often where specifiers will ask about tested security standards (and ensuring your final installation matches the tested specification).

Most homeowners asking “how long do composite windows last?” are really asking two things:

1. How long will the frame stay solid and good looking?
2. How long will the glazing unit stay clear and sealed?

UK composite window guides commonly cite a lifespan of around 30 – 50 years (or more) with proper care and maintenance, depending on materials and environmental exposure. 

The most consistent cost drivers across UK guides are:

• Window size and style (bay, sash, and large openings cost more). 
• Composite type (timber aluminium, uPVC aluminium, fibreglass). 
• Glazing specification (double vs triple, acoustic, laminated/security). 
• Installation complexity (access, structural work, changing openings, lintels). 

Energy Saving Trust also notes triple glazing is typically around 20% more expensive than double glazing, which is useful when you’re comparing like for like options.