I'm thinking to remake 5 sash windows, so 10 sashes, each sash divided vertically by one slender bar. Thought I'd use oak for longevity and strength to take the DG units whilst allowing some dainty profile on inner edges (originals have lamb's tongue)....
How far can you go re: overall thickness of DG unit? current sash thickness is 42mm...
How best to install DG units in sashes? I'm a fan of drained and vented usually but can't immediately see how I can apply this here..
Any tips for dealing with sash weights to cope with extra weight involved ?
That's the problem. A lot of boxes haven't got space for extra width of weights, and extra length can restrict travel of the sashes. I think that's why spiral balances are used, but IME they're a PITA
We had DG sashes 35mm thick made up to fit into existing boxes - with
42mm you shouldn't have a problem. Sashes twice as heavy as existing so you'll need to use lead weights instead of cast iron.
You mention a glazing bar with a dainty lambs tongue profile and this is where your problems really start. The aluminium spacer bar used to make conventional DG units is simply to high to fit into the glazing rebate without showing from inside. So your rebate needs to be deeper, and the dainty glazing bar turns into a big fat ugly thing. The work around is to use stuck on glazing bars, or some DG units made with a low profile foam spacer which will fit into a traditional sized rebate. Google for 'Slimlite'.
I replaced the original cylindrical cast-iron weights with square lead ones. Even with the double glazing I was able to use a slightly smaller square section than the old cast-iron ones, and got rid of my 'clashing' problems at the same time.
Why bother - sliding sashes always leak air so what''s the point of DG. And anyway the heat loss through windows is always small in comparison to the losses elsewhere so put your money and effort into insulation where it will make a difference.
air leaks can AIUI be addressed as part of the rebuild with brush strips, neoprene etc as per any opening window...
why bother? well all this for starters:-
"A single glazed window is sometimes referred to as a =93Thermal Hole=94. It is considered that single glazed windows lose around one third or
33% of its heat in the average house. Payback time currently for high insulation double glazed units is estimated at around 5 years depending on cost of units and cost of energy. Future energy costs are a major concern and insulation today is one of the most important factors.
A recent commissioned report claims that since de-regulation of prices in 2002 and from 2002 to 2005 average energy prices have risen by about 60% more than inflation.
Convection is one of the major heat loses relative to a window which is single glazed when it is cold outside and reasonable warm inside.The warm internal air contacting the cold glass becomes heavier, and drops downwards at a speed of around two metres per second depending on relative temperatures, causing a perpetual expensive heat loss and generally felt as a draught around the legs and feet. It is considered that a one degree increase in temperature in a room at comfort level will increase energy costs by 2%.
Radiant transfer in respect of glass occurs when the warm internal air contacts the cold single glass in a window and radiates or transfers heat outwards through the glass at a constant rate.
Low emissivity glass used in the construction of a double glazed unit reflects the long wave radiation or heat back into the room and therefore reduces the radiant heat going out through the glass.
A window construction should use low conductive material and particularly a double glazed unit which forms the largest area normally in a window. All the material in a window will conduct heat or cold depending on the conductivity of each material and a double glazed unit has a major contribution to the insulation factor."
diameter steel ones instead. I replaced the 40mm dia cast iron originals for 50mm steel ones cut from scrap which are 50% heavier (just from the greater volume).
I found long lengths of 50mm round bar in a scrap yard (after much searching) and cut it to appropriate lengths after weighing the glazed sashes.
My original glass was 6mm (1/4" rather) but 4 + 4 was fine for the DG units which made them only 50% heavier than the originals.
Top marks to the o/p for sticking with sashes, they're great once draught-proofed and can be made more secure than other types IMO.
CAn you use two weights, one tied under the other? You'd have a smaller sash movement but you'd still be able to extract the weights out of the pocket.
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