Can I Make My Own Timber Windows?

Can I Make My Own Timber Windows?

Yes, you can make your own timber windows. For someone with good woodworking skills, the right machinery and an understanding of window construction, it's an achievable project.

But there's an important distinction between making a timber frame that holds a piece of glass and manufacturing an external window that will operate correctly, resist British weather and meet the requirements that apply to the project.

A window has to manage rain, wind, glazing loads, drainage, timber movement, security and heat loss simultaneously. Small errors that are barely noticeable on the workshop bench can become significant once the window has been exposed to several Cornish winters.

At Wood.ED Joinery, manufacturing timber windows is part of our everyday work, while through our Academy we also teach practical woodworking and joinery skills. If you're considering making your own timber windows, understanding the complete process before buying timber is essential.

Start with the type of window

Before making anything, decide exactly what you're trying to reproduce.

Common timber window designs include:

• Fixed windows

• Side-hung casement windows

• Top-hung casements

• Traditional sliding sash windows

• Spring-balanced sash windows

• High performance Stormproof Windows

  
  

A small fixed window is considerably easier to manufacture than a traditional box sash window with weights, cords, pulleys and multiple moving components.

For a first project, a relatively simple casement window is usually a more realistic starting point.

Accurate surveying comes before woodworking

Don't start by measuring an existing window once and copying those dimensions.

Measure the structural opening at several positions.

Check:

• Width at the head, centre and cill

• Height on both sides

• Both diagonals

• Reveal depth

• External cill projection

• Whether the opening is plumb and level

  
  

Older Cornish and Devon properties can be considerably out of square.

You then need to determine the manufacturing dimensions rather than simply copying the opening dimensions. Space is required around the frame for installation, packing, sealing and movement.

Getting this calculation wrong can leave you with a beautifully manufactured window that doesn't fit the building.

Choosing timber for window making

External windows need timber capable of dealing with repeated changes in moisture and temperature.

Depending on the project, suitable choices can include durable hardwoods and modified timber such as Accoya.

Don't choose timber simply because it's inexpensive or readily available.

Consider:

• Dimensional stability

• Durability

• Moisture content

• Grain orientation

• Suitability for exterior use

• Compatibility with your chosen coating system

  
  

Timber preparation matters too. Machining poorly conditioned material and immediately assembling it into a window can create movement later.

Understanding traditional window joints

Mortise and tenon construction remains extremely useful for timber windows because it creates strong connections between stiles and rails.

The accuracy of these joints matters.

A loose tenon can allow the frame to rack. An excessively tight joint can introduce stress or cause splitting during assembly.

Before gluing anything, dry assemble the complete frame and check:

• Squareness

• Diagonal dimensions

• Joint closure

• Twist

• Overall dimensions

  
  

If the two diagonal measurements aren't equal, investigate why before reaching for the glue.

The difficult part isn't always the joinery

Someone with reasonable woodworking experience can learn to produce accurate mortise and tenon joints.

Designing the weathering details is often harder.

A window needs to control water.

That involves details such as:

• Cill falls

• Drips

• Rebates

• Weather seals

• Glazing drainage

• Ventilation around glazing units

• Junctions between opening casements and frames

Rain hitting a window in calm conditions is relatively straightforward.

Wind-driven rain is different.

On an exposed Cornish elevation, water can be pushed into surprisingly small gaps. The profiles need to encourage that water back outside rather than allowing it to travel towards the interior.

A workshop example: a few millimetres can matter

A good example of why window making requires planning came from a replacement casement project involving an older stone property.

The masonry opening was visibly irregular, but the difference became clearer when we measured it properly. The width varied by around 12mm between different points, and the stone cill wasn't level.

Simply manufacturing a perfectly rectangular frame to the smallest opening measurement would technically have allowed the window to fit, but it would have created excessive installation gaps elsewhere and inconsistent sightlines.

Instead, the opening was measured at multiple points and the manufacturing dimensions were established to balance the frame within the existing masonry.

The external cill detail also needed to account for the existing stonework so rainwater was thrown clear rather than tracking underneath the new frame.

This is the part of window making that's difficult to learn from a drawing alone. The woodworking might be accurate to a fraction of a millimetre while the building you're fitting it into is more than 10mm out.

Good joinery has to deal with both.

Don't overlook the glazing

Modern double-glazed units are heavy.

The frame and opening sash need to be designed to support that weight correctly.

You also need to consider:

• Glazing rebate dimensions

• Setting blocks

• Glass clearances

• Drainage

• Glazing beads

• Appropriate glazing systems

• Safety-glass requirements where applicable

Don't order the glass until the finished glazing sizes have been properly established.

A mistake of a few millimetres can make an insulated glass unit unusable.

Finishing should be part of the design

Don't manufacture the window and then start thinking about paint.

The coating system protects the timber.

Pay particular attention to:

• End grain

• Joints

• Glazing rebates

• Lower horizontal surfaces

• External cills

Where possible, components should receive the appropriate preparation and protection before final assembly in areas that will become difficult to reach afterwards.

Can I copy my existing window?

You can use an existing window as a reference, particularly when matching a period design.

Record details such as:

• Moulding profiles

• Glazing bar widths

• Frame sections

• Meeting rails

• Horn details on sash windows

• Cill profiles

Don't automatically assume every detail of the old window should be reproduced, though.

A previous replacement may itself have been incorrectly made, and some historic details may need adapting to accommodate modern glazing or weather seals.

What about Building Regulations?

This is where a DIY window project needs more consideration than an ordinary woodworking project.

Replacement windows in England can be subject to Building Regulations requirements covering areas such as thermal performance, ventilation, safety glazing and means of escape, depending on the circumstances.

Planning restrictions can also apply to listed buildings and properties in conservation areas.

Don't manufacture the window first and investigate compliance afterwards.

Establish what applies to your particular property before deciding the final design and specification.

Should a beginner make a window?

A complete beginner shouldn't start with an external double-glazed sash window.

Learn the underlying skills first.

You should be comfortable with:

• Accurate marking out

• Mortise and tenon joints

• Rebates and mouldings

• Machine setup

• Squaring frames

• Timber movement

• Safe use of woodworking machinery

A practice frame is an excellent project because mistakes become lessons rather than expensive pieces of external joinery.

This is also where woodworking courses can be useful. Making something under supervision gives you the opportunity to understand why particular profiles and joints are used rather than simply copying dimensions from a plan.

Frequently Asked Questions

Is it legal to make my own timber windows?

You can manufacture your own windows, but the finished installation may need to satisfy applicable Building Regulations and planning requirements. Listed buildings can have additional restrictions.

What is the easiest window to make?

A simple fixed timber window is considerably easier than an opening casement or traditional sliding sash. If you're learning window construction, starting simple is sensible.

What timber should I use to make windows?

The correct choice depends on design, exposure, finish and budget. Stable, durable timber suitable for external joinery is important. Accoya and appropriate hardwoods are commonly used for bespoke window manufacture.

Can I put double glazing into homemade timber windows?

Yes, provided the frame, rebates, drainage and glazing system have been designed for the insulated glass units being used. Safety and thermal requirements also need to be considered.

Can I make traditional sash windows myself?

Yes, but they're substantially more complicated. Box construction, sash proportions, glazing, pulleys, cords, counterweights, draught seals and clearances all have to work together.

Is making my own windows cheaper than buying them?

Potentially, if you already have the machinery, tools and skills. If you're starting from scratch, timber, cutters, glazing, ironmongery, coatings and mistakes can quickly remove the apparent saving.

Making your own window is an excellent woodworking challenge because it forces you to think beyond individual joints. Every component affects another. The frame has to fit the building, the sash has to fit the frame, the glass has to work with the sash, and the complete assembly has to manage water and movement for years afterwards.

If you're learning, make the first one as a workshop project rather than making your first attempt the front window of your house. You'll learn far more when you're free to make mistakes.