Compliance to standards.
Technical issues involved in double glazing sash windows have a real impact on the life-expectancy, efficiency, comfort, and cost-effectiveness of your windows. It's easy to throw money down the drain, so take care to examine the options carefully:
If it's to last, double-glazing MUST be installed to Industry Standards.
What does that mean?
It means that the sealed unit glazing MUST be dry-glazed, and properly drained and vented at its bottom edge. (Preferably, the entire periphery should be surrounded by fresh air, and nothing else).
Failure to install sealed units properly will quite probably mean premature failure - possibly in weeks or months rather than years - and will certainly invalidate any guarantee offered by the manufacturer of the sealed units.
The use of bedding mastics - or, worst of all, linseed oil putty - will probably ensure failure of the edge seal in a very short time, thanks to what's known as 'plasticiser migration'. (If you wrap a piece of cheese in clingfilm, within a very short time there will be elements of cling film in the cheese, and elements of cheese in the cling film. Choose your double glazing as carefully as you choose your cling film).
If it's to perform, double-glazing MUST be installed to Industry Standards.
What does that mean?
It means that, to be most effective in terms of heat-retention and comfort, the sealed double-glazing MUST have a gas-filled cavity of between 12mm and 20mm, and ideally, the edge seal should be insulated with a low-loss (so-called warm-edge) spacer (ie NOT an aluminium spacer-bar).
The latest Building Regulations demand a U-Value of less than 1.6. This cannot be achieved by sealed units with just 4mm air-gap (even if filled with argon or krypton.)
Let's be clear, the cost of double-glazing is not something that will be recovered by savings in your heating bill in the short or medium term. To make the most of it, you want to be certain your sealed units will last and last and last.
What you WILL get - immediately - is a great improvement in room comfort and probably a reduction in noise transmission. Add these three items together - fuel economy / comfort / noise reduction and you will likely value your investment for years to come.
SupaSash replacement double-glazed sashes are simply the best in every respect:
In short, they are A COST-EFFECTIVE SOLUTION to the improvement of rising sash windows. They PERFORM, and LAST FOR DECADES, without spoiling the appearance of the building.
What more could anyone want?
the greenest option