I'm restoring a Victorian House at present and in order to retain the original Victorian facade I want to restore / upgrade the sliding sash windows. Unfortunately the windows at the rear of the house will have to be replaced with tilt-and-turn to meet the new fire exit regs.
You do not have to put tilt/turn windows in, as long as you have a 1/3 metre square opening available when the bottom sash is up, then you are okay. If you are 'renovating' what is already there, then the bureaucratic council cannot enforce any change on you. If they do try, then you should apply for a relaxation order on the grounds of destroying architectural features of the building. SPAB (Society for the protection of ancient buildings) can advise on this.
You will destroy the original sashes if you try to put double glazed sealed units in. Number one, the astragals will find it extremely hard to cope with the weight, especially if they are the original very fine Victorian sashes. Number two, the size of the astragals will have to be increased both in width and depth which will completely disfigure the windows from an aesthetic aspect. Number three, you will find it very difficult to put enough weight gain on your weights to enable them to lift the extra weight of the new sashes, this is why garbage modern reproductions have strong springs to lift the sashes instead of weights. All the same, a sash window when balanced and cared for, should lift up and down with the absolute minimal effort, as if it is floating on air as the counter-balance effect of gravity work together. You will never be able to simulate this with modern reproductions.
And be very careful of what you do, remember to get a genuine reproduction of a sash window manufactured using mortice and tenons and joggles on the meeting rail will set you back a lot more than that awful UPVC garbage.
This is one of the ludicrous situations the inept councils impose on the the populace, as they cow-tow to those face-less, name-less psychopaths in the EEC. Whilst smashing the old houses to pieces and destroying the soul and fabric of many irreplacable buildings up and down the country in the name of fuel conservation. They then allow houses to be built that are thirty times the size of older houses and take ten times more fuel to heat up and stay heated, not to mention the vast increase in the materials (especially polystyrene/plastics) that have gone up thirty fold when compared to older properties...It's sort of like pissing against the wind!
I think you will find the U-values for a mantained single glazed sash window with internal shutters and lined curtains, is better than triple glazing!
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