The Sash window at Ham house
The following may seem less than useful to the person in the street
However, if you own a property with sash windows fitted read on it could save you serious money ( Neil Edward England)
A Bit of building heritage history
The earliest recorded example of a vertical, sliding sash window is in a 1658 Dutch landscape painting by Vermeer. This innovation soon came to Britain, with examples at Chatsworth House in Derbyshire, Kensington Palace and, as well as a rare survivor dating from 1701 at Ham House. If you’re aware of sliding sash windows coming earlier from, say, eastern Europe, let me know!
The design was revolutionary because it allowed light to flood in, could be left wide open or with only a crack for ventilation and was less likely to rot like the casement (top and side opening window leaves), windows that preceded it – the box construction in which the
sash weights sit offer protection from damp and rain. They are also less likely to warp.
What is not readily understood is, they revolutionised, in part, the idea of building higher without concern of window issues. Being easily serviced from within, (Pop out the staff and parting beads) lower the sashes into the room, all re-roping and pulley changes/weights etc, done from within.
It is little wonder, then, that the sash became the window of choice, from cottage to palace, well into the 20th century, although there are subtle clues to figuring out their age.
Typical section.
( please note a more accurate drawing will replace this)
Generally, smaller panes and finer glazing bars indicate older windows. As glass technology improved in the Victorian era, allowing the manufacture of larger panes, glazing bars became a little thicker and horns, also known as joggles, were added to the lower corners of the upper sash and to the lower to strengthen the joint and carry this heavier weight. (this point I argue as also a fashion choice). Your choice.
The number of panes also reduced, so a typical Georgian or Regency sash might have six or eight panes in each half of the window – known as a six over six or eight over eight – while its Victorian counterpart might be four over four, two over two or even one over one.
How they were made
Box sashes get their name because they resemble boxes in their construction. The sides and top of the window form a box section made from very high-quality planks that were cut from the of slow-grown pitch or white pine. High RPI. Only the sill is solid and was usually made from knot-free English oak.
The hollow sides/boxes contain the balancing weights, which were made from either cast iron or lead and connected via a pulley mounted in a cast iron cage to the sash window with a waxed rope.
Quick naming guide. Section of a cavity wall with a sash windo
How they were installed.
This is so much more important than it seems. Ventilation is the key. The boxes were fitted, unpainted, into the brickwork that was designed to be at least 2” wider than the sash box and at least 3” taller than the box itself. It was laid against the projecting brickwork nib/reveals and held in place with wedges between the frame and the wall
This allowed six things to occur:
The joiner could align the box frame in the wall without using any nails, which might have twisted the frame and of course in time, rusted.
The gap around the frame, ensured ventilation all round the window.
It stopped the chance of wet mortar slumping against the frame.
Because the sash was installed before any external render was applied, the plasterer could work his render into the small gap between the brick and frame to create a weather-tight seal.
If water did get past the joint, the natural airflow would dry it out before rot could take hold.
The plasterer could work his render up also to the underside of the sill sealing it, ensuring the drip groove cut into the underside of the sill remained clear, maintaining good weathering characteristics.
The amazing interior panelling and shutter boxes viewable were installed afterwards.
Problems and what to do about them.
Sashes have a tough life. Glass breaks, putty leaks, mortice joints fail, locks get wrenched and meeting rails can split. They do need TLC. The good news is that a sash window that has been correctly installed and properly maintained should last for 200 years or more – even when they face the sea.
sash box 200 years old, sashes 140 years old, south facing 300 meters from the sea
In my humble opinion.
Don’t even think about UPVC replacement windows. If you live in a listed building or conservation area, you’re breaking the law if you install them. Even if you don’t, they look terrible in any period building and will only last for a maximum of 20–30 years. They could make your house more airtight than it was meant to be, causing problems with damp and rot. And if you need any more convincing, ask your local estate agent – buildings with their original sash windows are easier to sell and command a higher price, so maintenance is an investment.
This guide outlines the correct procedures to follow, so you know what should – and shouldn’t – be done but most amateurs would be daunted by the job of putting problems right and you are almost certainly better to employ a specialist than to try and do it yourself.
How to maintain remove and repair. - Very short version.
First, ease out the stop bead –, the square rebated strip of wood – that runs around the internal face of the edge of the frame – and the parting bed (the timber rail in the middle of the internal face). Then an access plate or pocket cut into the side of the box frame can be removed and the weight lifted out. Advice, don’t drop it on your toe, potentially damaging this precious window.
Release the ropes carefully as they will still have the weights attached, lower down into box bottom then remove/unscrew the pulleys, inspect the axles if a little worn grease and return, if they worn the wheel touches the chassis look to replace. Be careful when purchasing new pulleys tere is a lot of rubbish on the market. Repair. refit. or appoint a recommended joiner/carpenter to the tasks.
Rotting sills/boxes
The main areas at risk are usually where the box stiles are cut into the sill or the underside of the sill if moisture has been trapped.
If there is not too much rotten wood, dig out the pulp, expose the remaining wood so it can dry, then cut in new wood or for small areas use two-pack resin filler, sanding down to give a smooth surface before you repaint.
If the old sill will come out in one, the new one will go in the same way, but point taken so try this
If a significant proportion of the sill has rotted, cut it out by removing the mortar from under and around the ends, tap it down into the void created and take it out If the bottom of the sash box stile has rotted, only cut out the bad wood. Track down some reclaimed pine (try architectural salvage yards) and scarf then glue it in.
Rattling and draughts
Curing this means taking the sashes out of their frames.
Drive a pin/nail through the exposed rope near the pulley to the jamb face this will allow you to lift out the sash as the weight is now trapped, hung on the nail , then remove the stop beads, lift out the inner sash and using, pinchers or pliers remove the rope from the sash then the parting beads, remove the outer sash. The pockets, will now come out, ease out the counterweights
Badly weighted sashes
When smaller, lighter panes, are substituted for larger, heavier panes of glass the sash needs heavier weights on the pulley if it was to move only when pushed /pulled and not drop on its own - imbalanced
The 19th century answer was to add a lump of lead to the top of the original, round weight. This did the trick but reduced the travel of weight in the box and thus the sash. Today, you can buy square section lead weights that return travel to the sash, (more mass in a shorter length.)
Re-weigh by first weighing the sash then the two weights and adjust the difference before replacing the rope, parting and stop beads. Ensure that the meeting rails are face tight when the catch is engaged. When re-installed rub a candle up the sliding faces so they move smoothly, this is a very demanding job for an amateur. You are almost certainly better off hiring a specialist.
Pulley failure
Whenever your window is overhauled, you should take the pulleys out, even if they are resistant. Check for axle wear, rusting and cracking; make sure that the wheels still spin properly; and look for warping of the face plate (this is the strip of metal the screws go through to locate and hold it in place.)
Only replace the pulleys as a very last resort! Modern versions will not work as well or last as long. Again, architectural salvage is the answer.
Now were rolling!
Do
• Ask around for a specialist in maintaining and draught-proofing sash windows – word of mouth is always the best recommendation.
• Interview and get quotes from several potential suppliers.
• Be suspicious if quotes seem on the low side, as the contractor may intend to skimp on materials or bodge the job, which will only lead to future problems.
• Turn to architectural salvage if you need new pulleys and wheels – There are a huge collection of salvaged fittings and fixtures from old buildings, look online to help you to identify exactly what you need.
Don’t
• Replace a sill with green (new) oak or pine.
• Glue joints with an internal grade PVA glue – use a marine glue instead, as it will withstand the weather better.
• Use engine/lubricating oil ease the sashes
• Use large nails to fit backstop rails or any nails at all on the parting rails
• Use any other type of rope than waxed cord
• Don’t fit modern pulleys, which are usually made of tin plate and are brass plated and not cast – as a result they rot or break quickly.
• Even think about UPVC replacement windows.
Disclaimer
This fact sheet is not intended as a substitute for advice from a qualified surveyor or professional builder. Anyone wishing to repair, decorate or renovate a building should consult a qualified person The information provided in this fact sheet is believed to be accurate at the time of writing. The author asserts his copyright.
