To understand how sash windows are constructed, you need to fully understand what they are and how they operate. Let us explain everything you need to know about how sash windows are crafted.
In a nutshell, a sash window describes any window that does not open on a hinge. There is no outward swing. Instead, sash windows slide (either vertically or horizontally) to open.
Traditional sliding sash windows typically consist of a wooden frame attached to a building, which is made up of two sliding frames or sashes – the sashes fit into the frame, one in front of the other. Both sashes move within the frame guided by vertical channels on the window’s stiles (the two vertical edges running up both sides of a sash). The upper sash runs in the outer channel, while the lower sash operates within the inner channel.
To regulate the opening and closing of the sashes, they are counterbalanced with weights. Each sash is fitted with two weights, which are positioned on opposite sides and concealed behind the vertical stiles in the frame.
The weights are connected to the sashes with a sash cord. These cords are attached to each side of the sash and run over pulleys that are incorporated into the upper surfaces of the window’s side stiles. From there the hidden cords extend downwards to the concealed weights situated behind the styles. As a sash is lifted up, the cords on both sides pass over the pulleys causing the weights to descend behind the stiles. When the sash is lowered, the opposite occurs, and the weights travel upwards.
The size of the weight will depend on the specific sash’s dimensions and weight to ensure that the sash can move seamlessly up and down as needed and that it can be securely held in an open or closed position.
Traditionally, the sash comprises several smaller panes of glass held together with glazing bars. We can create this look by using ‘real-dividing’ bars or ‘applied’ bars. The number of panes of glass your windows have will typically depend on the era in which you home was built. Modern glazing technology means that double glazed sashes are possible. Plus, there are also energy efficient glazing options suitable for listed buildings and conservation areas that planning officers will be in favour of.
These are the general steps involved when constructing traditional sash windows:
These are the general steps involved when constructing traditional sash windows:
Frame construction
At Parsons Joinery, we make all our window frames from sustainably sourced wood, although it is possible to construct frames using materials like uPVC (unplasticised polyvinyl chloride) or aluminium too.
All our sash windows are handcrafted by our expert joiners in our UK-based workshop and we use a variety of different wood species depending on the natural characteristics of the timber. We have something to suit each customer’s personal preference. Window frames are expertly designed and crafted to support the weight of the sashes and provide structural stability to the window.
Sash construction
Each sash is a movable panel that holds the window glass. A sash consists of several components, including:
Stiles: The vertical sides of the sash that provide structural support.
Rails: The horizontal top and bottom components of the sash.
Glazing bars: Dividers within the sash that hold individual panes of glass. Traditional sash windows often have multiple smaller panes of glass separated by these bars, although modern versions might use larger panes. As professional joiners, we can achieve the look you want by using either real-dividing bars or applied bars.
Counterbalance system
As we described earlier, one of the distinctive features of sash windows is their counterbalance system, which allows the sashes to move smoothly up and down. This system typically involves weights, pulleys, and cords. Each sash has a weight hidden within the window frame that is connected to it by a cord that runs over a pulley at the top of the frame. The counterbalance system ensures that the sashes can be easily moved and will stay open or closed at any desired height without falling. The counterbalance system we install into your sashes will depend on whether you require single hung or double-hung (top and bottom opening) sash windows.
Sash cord and pulleys
Sash cords are strong ropes or cords that attach the sashes to the counterbalance weights within the window frame. The cords pass over pulleys, which are often located in pockets within the frame, keeping the cords hidden from view.
Stops and parting beads
Stops are thin strips of wood that prevent the sashes from sliding out of the window frame when fully opened. Parting beads are strips that separate the two sashes and help keep them properly aligned within the frame.
Sash locks and hardware
Sash locks or catches are used to secure the sashes in the closed position and provide some level of security. They are typically mounted near the meeting rail (the horizontal rail where the two sashes meet). Other hardware might include pulls for opening and closing the windows, as well as sash lifts for lifting the lower sash.
Finishing
The entire window, including the frame and sashes, is finished with paint, stain, or other protective coatings to enhance its appearance and protect it from the elements.
At Parsons Joinery, we use Teknos for all paint and treatments for our timber products. Teknos is an extremely high-quality manufacturer of low VOC paints that values sustainability at their core. Prior to painting our windows and doors, we use a Teknos End Grain Sealer which seals the wood on the face/end grain and prevents it from starting to dry. This evens out the drying on the piece of timber. We then apply two coats of Teknos Water-Based Primer followed by two coats of Teknos Water-Based Topcoat.
All the paints we use are spray paints as they give a perfect, smooth finish and you do not get the brush strokes or paint runs that you can get with hand applied paints. Brands such as Farrow & Ball, Dulux, Little Green, and Fired Earth all offer paint that contains virtually zero VOCs too. It is also worth noting that if you cannot find a Teknos colour that you like for your joinery, we are able to colour match any other paint brand.
The wooden window construction process at Parsons Joinery
Our Workshop Manager, Craig McCombie, takes us through the steps his team typically follow when constructing completely new windows at Parsons Joinery:
Sliding sash windows
- Check the joinery sheet for job specifications which includes which type of timber and style of item is to be made.
- Use cutting sheet and cross-cut the timber to the correct lengths, seeing how to best minimise wastage in the thicknesses, width, and lengths.
- Rip the timber to the required widths, leaving enough on to straighten for planing of the timber.
- Plane all 4 edges of the timber, ensuring all edges are square to the correct section sizes.
- Machine the cills.
- Trench cut the heads and cills to take the jamb linings.
- Machine the parting bead groove into the frame jamb and heads.
- Machine edges to take internal and external face fascia linings.
- Machine the sash pully and access pockets.
- Assemble the frames.
- Machine internal and external fascias and fit.
- Machine the rails and stiles for the casements and assemble.
- Sand frames and casement faces.
- Machine casement sash cords and draft seals.
- Machine glazing beading, cut to size, and fix together.
- If the job requires glazing bars, machine them by scribing over the beading and moulding. Machine any half lap joints required if there are multiple panes.
- Finish by sanding the job.
- If working with softwood timber, treat all the items with preservative.
- Seal the ends of all exposed joints with sealant.
- In the spray shop, spray two coats of primer and two coats of topcoat to the customers’ requirements, removing any imperfections between coats.
- Fit seals, attach glazing tape, and fit casements into frames.
- Fit ironmongery.
- Glaze the items ready for installation.
Flush/stormproof casement windows
- Check joinery sheet for job specifications – includes which type of timber and style of item is to be made.
- Use cutting sheet and cross-cut the timber to the correct lengths, seeing how best to minimise wastage in the thicknesses, width, and lengths.
- Rip the timber to the required widths, leaving enough on to straighten for planing of the timber.
- Plane all 4 edges of the timber, ensuring all edges are square to the correct section sizes.
- Tenon and scribe the mould detail on the ends of the jambs/mullions and transoms to the correct lengths.
- Mortice the heads and cills to take the jambs and mullion tenons.
- Machine the rebates into the frames, machine the moulding, and draft seal grooves.
- Assemble the frames.
- Repeat the machining of the rail and stiles for opening or fixed casements and assemble.
- Sand frames and casement faces.
- Machine casements to take any locks and hinges to the spec on the paperwork for each item.
- Hang casements/fit locks and fit keeps into frames.
- Machine any fixed casements to fit into frames
- Machine cill projections if required for the frames and fit.
- Machine glazing, cut beading to size and fix together.
- If job requires glazing bars, machine them by scribing over the beading and moulding. Machine any half lap joints required if there are multiple panes.
- Finish by sanding the job.
- Seal the ends of all tenons/joints with end grain sealant.
- In the spray shop, spray two coats of primer and two coats of topcoat to the customers’ requirements, removing any imperfections between coats.
- Fit seals, attach glazing tape, and fit ironmongery.
- Glaze the items ready for installation.
For more information on how we restore sash windows and our process of replacing sash windows, check out our blog.
