Life in the Middle of the Supply Chain…
Firstly, can I just say a big thank you to all of you who read my post last week. The viewing numbers were really good, much better than I had expected to be honest, and even better than that was the number of you who took the time out of your busy schedules to comment and give feedback, I really appreciate it. The Twitter community also did your bit sharing and #RT’ing where ever you could.
This week we are going to go through the finer points of Energy Ratings and Glazing.
But first, one of my pet peeves…there is no such thing as A rated glass. WER ratings are calculated using a standard window specification and a specific glazing unit, with different combinations of either giving a different energy rating. Apologies if I am sounding like I’m trying to teach you all to suck eggs, but you cannot imagine the number of enquiries I get for windows and doors to come with A rated glass. If I supply you an E or an F rated window and put the best specification glass I can find you may achieve an A rating, but the likelihood is you wont.
The same can be said for DER ratings, my knowledge of the door industry is large but I do not claim to be an expert, but as far as I have seen the only A rated doors on the market at current are Composite doors, feel free to correct me if you have seen otherwise. I get numerous enquiries from installers nationwide who have seen companies advertising A rated bi-folding, patio, or residential doors. Upon closer inspection these companies are supplying standard specification doors, with glazing units which they would supply with their A rated windows, something similar to a Low E/ Low Iron combination unit with a ceramic spacer bar. It is NOT an energy rated product if it has not been professionally and independently tested by a competent person/scheme/company. I think there should be some more policing of the way companies advertise their energy rated products, as it is the installers and end users who are being supplied with products which are not what they think they are.
The modern aluminium market has numerous products which allow for the ever improving building regulations. The introduction of first resin thermal breaks and now more modern nylon or polyamide, allows very low U-values to be achieved. The Smart Alitherm300 slimline casement can achieve an overall A rating with a u-value for comparison of 1.6W/m2K with a standard double glazed unit, and a u-value of 1.2W/m2K when glazed with a standard Low E triple glazed unit. These are also comparable window systems on the market supplied by Comar, Sheuco, Sapa and Beaufort. We would also always recommend using a ceramic spacer bar with all aluminium products to guarantee prevention of cold bridging and thus condensation.
There are draw backs to these highly energy efficient windows. To achieve such low values the overall percentage of aluminium in the actual window must be reduced, and therefore all of the profiles are very slim. The alitherm300 slimline outer frame is only 53mm deep and has a face dimension of just 33mm. This application is great for steel window replacement and for new build/face brick installations, but the major draw back is that the inherent strength of the window is greatly reduced. We wouldn’t recommend manufacturing these windows any larger than 600mm x 1200mm, to avoid any issues with twisting and warping around corner cleats. On the flip side, when I get enquiries for larger windows which are still required to meet low u-values have to use much improved glazing units, possibly even triple glazing which obviously increase the price of the product.
What I think I’m trying to get across is that unlike the uPVC market the increase to an A Rated window from a standard C rating is vast, and the slimmer profiles which have to be used can decrease the structural performance of the window, as I have said before, the best policy is to speak to your fabricator prior to estimation or ordering to get the best advise you can.