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  • Writer's pictureKelvin Mureithi

Types of Window Frames

Updated: Jan 19


When designing and constructing buildings, one of the key decisions is which window frame material to use. The frames impact energy efficiency, noise reduction, security, lifespan and aesthetics.

Here are the most common options architects, developers and homeowners choose from:

  1. Timber frames

  2. Aluminium frames

  3. Vinyl or uPVC (unplasticized polyvinyl chloride) frames

  4. Steel frames

  5. Composite frames

  6. Fiberglass frames

Let's explore the 6 common types of window frames, one by one...

Double glazed window system, energy efficient windows, common types of window frames
Modern window frame profile

Each has their own advantages and limitations.

Timber Frames

Timber window frames are fabricated from various wood types like pine, oak and meranti. The natural material provides a timeless, classic look suitable for traditional architectural styles. Timber is renewable and sustainable. It also acts as an effective insulator, with a low thermal conductivity that reduces heat transfer through the frame. However, timber frames are prone to swelling and warping if exposed to moisture, requiring more maintenance and sealing than other materials.

Vinyl or uPVC Frames

Unplasticized polyvinyl chloride (uPVC) frames are a popular low-cost option made from weather-resistant plastic with added strengtheners. uPVC prevents heat loss well due to its low thermal conductivity. Insulated chambers within the frame further improve energy efficiency. UPVC resists humidity, rotting and corrosion, making it ideal for coastal areas and tropical climates. Limitations include a less aesthetically pleasing look than wood or metal and reduced strength.

Aluminium Frames

Aluminium window frames are lightweight, durable and long-lasting. Fabricated from aluminium alloy extrusions, they resist corrosion in seaside and industrial environments. Aluminium provides a slim, modern aesthetic appreciated by architects and developers. However, aluminium is prone to heat transfer and energy loss due to its high thermal conductivity. Thermal breaks made of polyamide help limit this effect. High-performance glazing also improves overall energy efficiency.

Catch up quick: What is a thermal break? Here is a short clip from Oknalux Windows that explains it simply —

Steel Frames

Steel window frames are extremely strong, durable and resistant to wind, rain and rotting. However, unprotected steel can corrode. Frames are galvanised or given a baked enamel finish to prevent corrosion. Steel frames provide security but similar to their aluminium cousins, they have high thermal conductivity, leading to heat transfer issues. Which means indoor spaces will be hotter in warmer months and chilly in colder months. Thermal breaks within the frame are, therefore, important for energy efficiency.

Composite Frames

Composite frames combine materials like aluminium or UPVC on the exterior with an inner wood layer for insulation. This improves thermal performance and allows custom exterior finishes and colours. Composite frames have a long lifespan and low maintenance needs. They are also resistant to rotting, swelling and corrosion. Higher cost is the main limitation — but this is highly dependent on the supplier.

Let's look at an example of a composite product from window manufacturer Miglas:

Fiberglass Frames

Fiberglass window frames are highly energy efficient and durable. The glass fibres set in a polymer resin create a strong, weather-resistant material that insulates against heat transfer. Fiberglass frames won't corrode and require minimal maintenance. Drawbacks include higher cost and a lack of aesthetic appeal for some architectural styles.

When choosing window frames —

Architects, specifiers, building owners must weigh factors like energy efficiency, acoustic insulation, security, lifespan, aesthetics, and cost. However, we often see an overemphasis placed on two consideration: upfront cost and aesthetics. And little consideration for energy efficiency, durability, and other performance factors.

Advances in materials and technology continue to improve thermal performance and durability. Selecting the right window frames is crucial during design stages to balance functionality, design and long-term value. Focusing on high quality materials and proper installation will result in attractive, efficient and long-lasting window systems.

Yes, but: Some argue that window frames receive too much attention and that other components like glazing and shading ultimately have a bigger impact on performance.

  • They suggest that as long as basic structural integrity and weatherproofing are achieved, obsessing over minute thermal advantages between frame options is unnecessary.

  • Others contend that with regular maintenance and re-sealing, even basic aluminium or timber frames can deliver adequate insulation and longevity.

  • And that from this perspective, architects and design teams should prioritise holistic building performance analysis over fixating on individual frame materials.

  • While the merits of these contrarian views can be debated, we are in favour of promoting maximum indoor thermal comfort and energy efficiency.

Therefore, we recommend the most thermally advanced options like timber, uPVC, composite, fiberglass, and thermally broken aluminium or steel frames, in that order.

Most experts maintain that informed window frame selection remains an important factor in building design. Carefully weighing the strengths and weaknesses of each material against project requirements will lead to choices that balance functionality, comfort and aesthetics.


Building your dream home? Or a sustainable, comfortable building? Our team and analysis ensures it performs as envisioned, for savings and comfort over the long haul.


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