Sash weights

[Feltwell]

Somewhere, I've a pamphlet on renovating sash windows that tells me this, but can I find it.........

I know you make the weights for the top sash slightly heavier than the sash itself (so it pulls shut nice & tight) and the weights for the bottom sash slightly lighter for the same reason, but by how much?

I can't remember what I did for previous windows! I think it was 1/2 lb per side - i.e. 1 lb per sash - does that sound about right?

The friction from the brush seals is enough to stop them moving when they are open.

 

[88v8]

Pound under, pound over.
In total, that is.

Ivor

 

[Feltwell]

Thanks Ivor - good to know that my memory hasn't completely abandoned me, yet............................

 

[agbagb]

I've seen this advice as well but never really understood the reasoning. The sashes when closed will be held against the top rail and cill by the action of the latch (applying much more pressure than 1lb). When left open for ventilation if they aren't balanced then a little movement in a breeze can overcome the friction of the seals or cord and so the window can slowly work it's way shut.
I'm wondering if the 1lb under or over was originally just a general guide to the tolerance needed for the counterbalance. It being better for the top sash being a bit over and the bottom being a bit under so any movement does cause closing rather than opening.
I see from my stock of cast weights they come in 1/2lb increments so it will have been possible to purchase weights so they come within the tolerance of 1lb without having to faff about adding extra bit of weight during fitting. All four weights are the same size but the bottom sash normally has a thicker bottom rail so it will be heavier.

It's just a thought that "chinese whispers" down the years might have distorted the original reasoning.

 

[Penners]

I tend to agree with agbagb. A pound sounds a bit over the top. As he/she observes, the weights are there simply to counterbalance the weight of the sash, and provided this is done effectively, the sash should stay happily wherever you place it.

If your sashes are running nice and freely (as they should be) a pound sounds as though it could cause "creep".

 

[Feltwell]

I would agree with all the above, but practical experience on previous windows says that they don't suffer from creep at 1lb over/under, if my dodgy memory is right and that is indeed what I did! If done with brush seals in the staff/parting beads and new ball-bearing equipped sash pulleys then they run beautifully smoothly, the difference compared to before with no brushes, years of paint clogging them up and old badly worn pulleys is remarkable. As to if the 1lb over/under actually makes any positive difference - no idea!

Renovating sashes is a slow job if done properly though, and if they're in as bad a state as mine are. On that note, back to another coat of linseed paint.......

 

[88v8]

I tend to agree with agbagb. A pound sounds a bit over the top. As he/she observes, the weights are there simply to counterbalance the weight of the sash, and provided this is done effectively, the sash should stay happily wherever you place it.

If your sashes are running nice and freely (as they should be) a pound sounds as though it could cause "creep".

Depends on the sash. For a very small one, 'creep' perhaps. There does need to be under/overage. The catches alone will not keep them firmly shut, even Brighton fasteners. All the sashes in our previous house were hung pound over/under, ball-bearing pulleys, chains rather than cords, no brushes, they were fine.
The weighting is quite important; not only are the basic weights sold in half-pounds, one can buy additional makeweights in oz. In days of old, glass was sold by weight rather than thickness so as not to disturb the balance of sashes.

Ivor

 

[CliffordPope]

Ours were designed with weights only on the upper sashes. There are no pulleys for the lower sashes, and they don't have grooves to attach a cord to.
The lower sashes will slide, but have to be propped open if required. Great care is needed if leaning out to avoid being guillotined.

 

[Penners]

chains rather than cords

I wonder whether that's a clue to the over/under weighting. I suspect (without any empirical or expert knowledge!) that chains would offer more friction than cords.

 

[agbagb]

As he/she observes,

That was a Mr AGBAGB post, the missus shares my login just to confuse things, her post are a little pinker and with a "missus" somewhere.

Chains theoretically should have less resistance (until the oil runs dry in the chain bearings) There should be no external friction unless they rub against the stile. Cords especially new ones will not bend quite as easily to go around the pulleys. Although that is minor compared to a good design where the cord touches the stile offering draft proofing if extended to the bottom of the sash and as a runner so the timber of the sash doesn’t run against the stile. Chains being heavier will also change the counter balancing more in different window positions (more chain one side of the pulley than the other). Although it seems the general consensus is that the weight is not over critical if within a tolerance. Another thought, the tolerance would be less for small windows maybe a percentage would be better e.g. 5%.

Clifford – I think I’m right in saying the earliest sash windows had fixed (non-opening) upper sashes with only the bottom sash opening . A burly servant would lift the sash and (insert a peg?). Thomas Kinward, master joiner in the Office of the King’s Works, and Robert Hooke, fellow of the Royal Society developed the counter weight system that added to the practicality and hence popularity of the box sash window. The counterweight also makes it possible to have an opening top sash. Yours sound like a mash up, maybe to reduce costs. It would be interesting to know more ( picys ) and possible dates or indeed if this is common?

Ivor – Another reason for selling by weight, I think, was an early tax by weight on production of glass. Another one of those factors that influenced window design. Thinner glass, smaller panes, more glazing bars. Tax avoidance is nothing new.

Feltwell – All the best with the painting, I’m hoping Friday will be fine for mine.

 

[agbagb]

Ivor- I Missed the bit about the fastners, yes brighton fastners dont give much up and down force but are excellent at clamping the meeting rails together. Fitch fastners do more up and down than clamping.
If the meeting rail is detailed with angled faces, the hooking over and clamping together should also push the sashes apart height wise. Brighton fastners don't work in this way on flat faced meeting rails.

 

[CliffordPope]

Clifford – I think I’m right in saying the earliest sash windows had fixed (non-opening) upper sashes with only the bottom sash opening . A burly servant would lift the sash and (insert a peg?). Thomas Kinward, master joiner in the Office of the King’s Works, and Robert Hooke, fellow of the Royal Society developed the counter weight system that added to the practicality and hence popularity of the box sash window. The counterweight also makes it possible to have an opening top sash. Yours sound like a mash up, maybe to reduce costs. It would be interesting to know more ( picys ) and possible dates or indeed if this is common?

Pembrokeshire farmhouse, about 1875.
They look just like ordinary double sashes, and both sashes slide. The apertures for the weights are there, but there is nothing in them, no pulleys, and no access panels.
As you say, it was probably for economy, but it can't really have saved much in the overall construction costs.
I did once convert one to counterweights, just out of interest really. There's little practical value in opening the lower sash, it just leaves ornaments and plants liable to be swept off by the curtains in a gust of wind.
The main use I find in opening the lower sash is to sit on the cill to paint the outside.

 

[Penners]

Clifford - while I would be proud to be able to demonstrate such knowledge of sash windows and their history, I'm afraid I must confess that the above quote attributed to me should, if fact, be credited to someone far more knowledgeable than I am.

 

[JanJonWestWales]

here's what i used and it worked a treat....

1, Find the total finished weight of your top and bottom sashes including glass.
2, For the top sash, add 2 lb to the total, the weights must be heavier than the top sash to ensure the sash stays in place.
3, For the bottom sash, subtract 2lb from the total, the weights must be lighter than the bottom sash to prevent the sash rising.
4, Divide the totals by 2 to find the sash weights required, 2 sashes = 4 sash weights.
Example,
44lb top sash
+2lb balance adjustment
46lb total

 

[agbagb]

here's what i used and it worked a treat....

44lb top sash
+2lb balance adjustment
46lb total

That'll be a double glazed sash or a very large window? The 2lb on that weight falls perfectly in the 5%. This strengthens the theory that under/ over weighting recomendation should be related to the size/ weight of the sash not just a single figure that will be right for all windows.

Having said the ones I've made don't have under/over weighting and they work a treat as well. I'll experiment on the next ones to see if I can measure / assess any practical advantages one way or the other.

Penners, I did a bit of study in to the influence of available technology on the design of windows over time as background to try and workout a design for a high performance modern timber sliding sash window (blue blob links to more). It's mostly conjecture on my part and shouldn't classed as academic certainty as such it's open for debate. But thanks anyway.

Clifford - It's sound like they where just saving a shilling.. However there is an advantage to beeing able to open both during hot weather, if both are open equally just a few inches a convection current of air is created. This makes a big increase in the number of air changes per hour compared to just one or other sash being open, it's actually one of the great advantages of sliding sash windows. If you have security stops limiting the movement you can have really good ventilation all summer without worrying about unwanted entrances.

 

[CliffordPope]

However there is an advantage to beeing able to open both during hot weather, if both are open equally just a few inches a convection current of air is created. This makes a big increase in the number of air changes per hour compared to just one or other sash being open, it's actually one of the great advantages of sliding sash windows.

That's an interesting point I'd never thought of.
I'd only ever thought in terms of ventilation being a horizontal flow through a room, on to an outlet somewhere else.
But you are right - a vertical convention current at a window will induce a circulation within a room, taking out hot air at the upper sash, letting in cooler at the bottom.

So I need a small moveable block available at each window to raise the lower sash too.

 

[Penners]

The only thing I know about sash windows is that they have long weights.

When I started my engineering training at Ransomes Sims & Jefferies in Ipswich, one of the first things that my trainer got me to do was... "just pop down to the maintenance stores, boy, and tell them that Arthur sent you for a long weight." In my innocence I went to the maintenance stores and did just that. They told me it would take a few minutes. Ten minutes later the storeman came back to the counter and said "right, son I think that wait's long enough, don't you?"

Red face, embarrassed grin...

Still, at least I didn't fall for it when Arthur sent me down for a bucketful of compressed air.

 

[DJH]

or a new bubble for the spirit level...

 

[Penners]

Or a glass hammer for fine work.

 

[Feltwell]

Or a long stand - a variation on a long weight.

Or a bag of sparks for the grinder.

Anyhow, my newly refurbished window is working very nicely at a pound over & under - with sashes that are around 15 lbs each. The sashes didn't move at all, even when the sash was hanging loose before the beading went in - the friction of bending the cords round the pulleys was enough to make them stay put. The brush seals in the beads are now of course adding more friction to hold them in place.