Double Glazing for Listed Buildings

Double glazing for listed buildings is one of those topics that gets everyone hot under the collar, and is probably the biggest single source of enquiries and hassle for Conservation Officers.  The official line goes something along these tracks:

Double glazing as a replacement for existing historic glazing is unacceptable.  For instance if you have Georgian sliding casement windows, with cylinder glass panels, there is not a snowballs chance in Hell that you will be able to change them for double glazing.  If you have 1960's timber windows, in no particular style, and they are rotten - there would be a good case for saying that you wish to replace them with something more in keeping with the building.  At this point you would be able to submit a proposal to change them for perhaps oak frames, with narrow casements in the style of the Georgian ones, but sufficiently different for them to be clearly a later addition.  These could be tastefully made with 10mm slimline glazing units, and I would pretty much guarantee your proposal would succeed.  Conservation is about managing change as well as preserving significance - every building evolves over time - we do our best to make sure it does so in a way that enhances the significance - and is sustainable too.

Secondary glazing for listed buildings is sometimes an acceptable way of preventing heat loss.  We already know that Government figures for heat loss through solid walls is being excessively overestimated.  The Green Deal is based on flawed science - embodied in RDSap - the software that does all those silly Energy diagrams on real estate brochures. It has been proven by research by English Heritage that heat loss is being over-estimated by as much as 75%.  Given this, you don't need to worry so much about walls, and can concentrate on windows. There is a new breed of secondary glazing appearing now - beautiful wooden or glass shutters, which really enhance your home, and keep heat losses to a minimum.  In theory you should have Listed Consent for secondary glazing - if it is a permanent fixture.  To date, much of the secondary glazing that we've been seeing is horrible stuff - yukky aluminium frames with sliding aluminium casements - or similar.  No wonder Conservation have kittens.  The new breed of shutters simply clip or screw onto the stop beads of sash windows for example - and are not really an invasive or permanent fixture - more like furniture - so we are in a grey area of Consent here!

Listed building windows are very much a part of the Listing.  As such they cannot be removed or replaced - they may very well be one of the most significant parts of the building, so any changes to them must be very carefully considered.  Pulling them out, and replacing with UPVc windows for example, will most likely end up with an enforcement notice being issued, and you will end up in court if you don't comply.  Having said that, if they are damaged, you are quite free to repair them in like-for-like materials.  I frequently recommend to clients that we remove sash windows from the building completely - frames, weights and all.  It's about the best way to totally strip and restore a sash window - you can remove the stop beads and parting beads, add new ones with seals incorporated, strip paint, and re-paint using a lnseed based paint system.  After re-weighting, they can go back in to live for another 100 years.  There's nothing in the Listing system that says you can't do this - you can't rebate them and put double glazing in whilst you are at it though - I've been asked enough times!

Listed building window replacement, if you really have to do it - is simple enough.  It MUST be exactly like-for-like. If I help clients, we normally try to keep the original glazing - removing historic glass is an art form - you need to soften the putty with infra red lighting, without heating the glass so it doesn't crack.   If you DO crack a pane, there is a brilliant company called Tatra Glass who supply historic glazing styles, so don't panic!

The photos on this page are from a project in Birmingham - we discovered an ancient rubble stone cottage - probably one of the earliest surviving buildings in the whole of Birmingham now.  It was encased in concrete, and Grade 2 listed.  After removing the concrete, and drying the place out, it was totally rebuilt.  The old concrete faux 'stone mullion' windows were replaced with oak, with chunky mullions, and metal casements with double glazing units.  A good example of removing and replacing with sensitively chosen designs that enhance the significance of this amazing building.

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