The Approved documents regarding the Part L changes coming into force in October make truly depressing reading for anyone with a non-listed period property. My read is that if you are Listed than, provided your local Conservation Officer is strong-willed enough, then it is very much business as usual. If, like me, you live in a period property that is non-listed then getting your windows replaced with bespoke timber-framed units is going to be very expensive - that is if there are any small joinery firms left who will be available to do the work.

To precis....any replacement window (ie replacing the complete unit including the frame) will require either :

     a window with a WER (windows energy rating) certificate of C or better OR

     have an overall u-value of 1.6 OR

     a central-pane u-value of 1.2 or better.


Getting a WER certificate for a small joinery company is financially out of the question. So let's look at option 2.

For a kick-off, we don't have a level playing field. New builds need only have an overall u-value of 2. So why are existing property owners penalised by having this draconian value of 1.6 thrust on them? I would dearly love for someone to force a judicial review on this.

OK - an overall value of 1.6. You can't meet this with normal double-glazed units. Nor any filled with argon unless you go for very expensive specialist coatings as you need to have a glazing unit with a u-value of around 1.2. You could go krypton fill. I have no idea as to cost on this. Expensive I think. Specialist coatings? Also expensive. I got a quote for £540 + VAT for the specialist dgu's for a 6x6 sash window. That is before the cost of the wood or labour to make it or cost to install it.

You can reduce the cost by going for a single dgu and then putting in ghastly duplex bars or stick-on faux glazing bars. Lovely. Really fits in with the period property ethos.

Or you could triple glaze. That will make your windows about 66mm thick. Now factor in the extra width you'll need in the glazing bars to carry the extra weight...but hang on, the heat loss via the timber is greater than that through the triple glazing units.....

Oh, I forgot. How are you going to convince the Building Control Officer that your windows are 1.6 u-value overall?

Ah..I hear you say...the double-glazing people will have the same problem. Not so. Nor will people like Magnet because they are large enough to pay for their windows to be WER certified.

But...you say..they still will have the problem re expensive double glazing units, won't they. No, they won't. I played around with the WER formula. Take a window with a frame that is 10% of the overall window area. Take a total solar gain of around 0.65 ...a not out-of-the-norm value. Add in a very leaky air leakage of 1 and what overall u-value do you need to achieve to get your C-rating? Why....2.0...which is fairly easily achievable with standard dgu's.

So the uPVC boys are going to have a field day and small joinery companies will go out of business.

and exactly HOW prey tell are they going to police it!!

as the incompetants still can not police any of the existing PART docs....

and forget P or L.... the one creeping in to totally screw everyone, as its been back door jobbed when no one was looking was the SUSTAINABLES ... mainly water (PART G and H) using a MAXIMUM of 125 litres per person per day, and having to install grey water facilities.. etc etc etc............