Sash Windows - Weights, Spiral Balances, and.....

[Fitzroy]

I'm rebuilding a sash dormer window and then original design/construction is 'interesting'. The widow has a 1000mm wide center window and two 500mm wide side windows at 45° to the centre one. The centre sash has weights and the side windows do not, the weight pocket for the centre window is the triangular space between the pulley stiles of the two windows. The two small widows have a 18mm thick pulley style next to the centre window and a 34mm pully stile on the outside edge.

I'm rebuilding the window as I currently have access due to removing all the room lath and plaster to insulate, and additionally the cill has pretty much rotted out. The focus of the room renovation is insulating it, so I don't really like the idea of a weight pocket with the only insulation being the inner and outer linings at 18mm thick. Additionally I would like to be able to open the side windows without needing to have something to prop them open.

From my research my only options for sash window balance are weights or spiral balances. Long story short are there any other options apart from these two? I see lots of negative press on spiral balances, so if there are idea of how to insulate the weigh pocket or facilitate the operation of the side windows without these I'd welcome those thoughts also.

Fita.

 

[deema]

A bit off the wall, but I’d look at gas struts. Constant force over the entire travel. You can use pulleys to double (which would be my plan), triple etc the struts travel and it’s easy to get struts of almost any force. I intend to try using them the next time I make a sliding sash.

 

[ChaiLatte]

The weights have two effects: they lighten/balance the load when you are opening or closing and they retain the position of the window when you let go.

As you have used them for a long time without weights, would it be correct to say that the weight is managable and therefore we only need a solution that replaces your hi-tech propping stick?

Could you put some spring loaded arms in the sides, which will stop the window dropping, and then have a lever to withdraw/disengage the arms whe you want to lower it again?

There are many one-way mechanisms in common objects; we just need to think of one which would have best suitability to a window.

 

[Jacob]

I'd stick with the existing arrangement. Weights much more convenient and relatively maintenance free - a bit of attention every 30 years or so or longer.
To be realistic there is unlikely to be a strong reason for open the little side sashes but if you wanted to it is possible to string both sides to one weight in the empty side.
Or just have a fixed stop to lower the top ones to, or a little prop, or tower bolt for the bottom one.
I wouldn't bother about insulating the boxes - a tiny contribution to the overall insulation and you might have a future prob with lack of ventilation in the voids.

 

[johnnyb]

How are you glazing as that will determine how lossy they will be imho.

 

[Doug71]

I've used the spring balances a few times and found them okay, not as nice as weights and cords but useful in some situations like your side sashes.

Funnily enough a customer of mine has just had a few sash windows fitted and was commenting on the draught coming through the pulleys. He had some similar windows fitted by a different firm a couple of years ago and there isn't any draught through them, the none draughty ones were more expensive and look better quality.

I'm guessing the better quality firm probably used the draught proof pulley covers.

https://www.mightonproducts.com/shop/sash-window-hardware/sash-pulleys/2-draught-proof-pulley-cover/

 

[Fitzroy]

How are you glazing as that will determine how lossy they will be imho.

22 or 24mm Argon filled DGUs. I was thinking of vacuum glazing but the cost is hideous. £1200 cf. £400 for DGUs. Will be largely copying the mumfordwood designs.

Room is being given 120mm PIR throughout. The current issue with the window is condensation on the single glazing. What I don’t want is condensation on the internal frame.

 

[Ollie78]

As a person who has restored thousands of sash windows I have come to the conclusion that spiral balances are the devils work and should be avoided at all costs.
They are primarily used so you don`t need to accomodate a box frame in the brickwork and joinery shops can bash them out quicker, there is no advantage for the end user over weights and cords, and several disadvantages.
The insulation of air is actually not bad, if the box frame is sealed well on the oustide then it is just a box of still, dry air.

 

[woodieallen]

I agree 100% with Ollie. You are worrying unnecessarily about the minimal heat loss.

 

[Jacob]

22 or 24mm Argon filled DGUs. I was thinking of vacuum glazing but the cost is hideous. £1200 cf. £400 for DGUs. Will be largely copying the mumfordwood designs.

Room is being given 120mm PIR throughout. The current issue with the window is condensation on the single glazing. What I don’t want is condensation on the internal frame.

It would be on the glass i.e. the coldest surface, not on the woodwork .
If condensation is an issue then the best place for it is on a sash window. The gaps between meeting rails and at the bottom between bottom rail and staff bead, allow it to drain out. Sashes work very well as passive dehumidifiers.
Whatever you do don't seal these gaps.

 

[Fitzroy]

Thanks everyone for all the great info, especially around the heat loss. Time to make my choice on design and let future history judge me.