Hi. This is my first post, and you should know I don't really have any DIY experience. I've searched the other threads, but still am unsure as to the answer to my dilemma.

We live in a victorian semi, in a conservation area, with original sash windows, complete with drafts and rattles.

I'm not in doubt that they need refurbishing. Some of the sills are rotten, and some good draft sealing will improve the heat and sound insulation in this house significantly.

I know that some people will encourage me to have a go myself, but I haven't got the time or inclination I'm afraid. I've found a good (I hope!) local specialist joiner who has given quotes similar to ventrolla. We're going to use him.

He's also quoted, at my request, for putting double glazing in to the original sashes. I asked for this option because sound and heat insulation is important to us. The problem is that I'm now having huge problems deciding whether to go for this option.

My thoughts are:
-We do still have the original "wobbly" glass- it would be a shame to lose that.
-Our street is generally quite quiet, but occasionally things wake us- e.g. late night taxis, a neighbour's motorbike, and a church hall opposite that has late functions every month or so. We're worried that if we just go for SG, we'd then regret not having DG if noise was still an issue.
-The SG option is a few grand cheaper, but we're prepared to pay for the DG if it seems the best option.
-We're aware that secondary glazing is another option, and Storm Windows have been recommended as being particularly discreet and good, but it can't possibly look as "neat" as DG glass within the sash, can it? And, to be honest, the idea of it all getting done in one job is also appealing (i.e. rather than refurb now, and secondary glazing at a later date)
-I have some concerns about the possibiliy of DG units failing in the future- and then getting misted up.
-I know that as it's just a refurb job, rather than replacement, building regs are not an issue, but what are people's thoughts on whether DG will increase future sale value, or on whether DG will be of benefit if there will be more stringent energy efficiecy certificate requirements for house sales in future (can you tell from that last sentence that I don't really have any idea what I'm talking about??) We're not planning to sell for at least 5 years or so.
-I'm aware that DG units will require rebalancing and extra weights. This is in itself an issue. The work may be delayed if we opt for DG as the joiner can't get hold of the necessary lead due to an apparent world shortage.


In short--aarrrghhhhh! I can't decide what to do. Does anyone have any words of wisdom to help me muddle through this list of pros and cons?

Nick

Mostly just one pane per sash, except for those in the lounge bay, where the upper sashes have an additional full width panel at the top (I'm sure there's a more technical way to describe them). The joiner has told me that if goign for the DG option, I would lose this panel, or at least would need a "fake" bar stuck on to reproduce the effect.

It sounds like you should forget double glazing. So do a really good job draft sealing the sashes and frames round the outside of the windows too. This is the most economic way forward and has the best pay back in the short to middle term.

Very true, Roger. My town is an Article 4 area.

Nickrad: Heavy curtains can do a useful job because the coldest periods are winter nights. However, the inescapable truth is that windows are responsible for major heat losses and also cause uncomfortable temperature gradients in the room. Furthermore, the more you indulate elsewhere, the greater the window effect.

Single pane sashes can be replaced with purpose-made wooden DG sashes without great difficulty, but it is vital to get the technology correct.

I'll post more shortly.

Posted By: funcrusher Furthermore, the more you indulate elsewhere, the greater the window effect.

Not really. The window does not know what you've done in the attic. Heat loss through the window depends on the window's thermal resistance and the temperature difference between inside and outside. Loads of insulation elswhere in the house compensates for a leaky window.

Please do consider the value of hand made antique glass. When it's gone, it's gone. And the appearance of the townscape, even in towns where the Council doesn't care.

Thanks funcrusher, but it sounds like you're describing newly designed and built sahses. I'm keeping the original sashes, it's just whether to put in double glazed glass panes in to them.

nickrad: I am confident that fitting DG to existing sashes will be a failure. Any DG unit put into wooden sashes with the usual external rebates will require retaining beads/sealant/putty and will be very prone to failure due to water creep and destruction of the DG seal leading to misting up etc. I strongly advise against. Re-using the sashes would anyway require the rebates to be re-cut to a much greater depth to accommodate the DG. For your large pane sizes the thinnest DG would be 14mm overall (4-6-4) compared with your existing glass which is 3 or 4mm.

Since float glass was only invented in 1956, most glass of WW2 vintage will be machine drawn rolled glass - the same as what is now described as horticultural. There may be some wobbles but these will generally be parallel, across or up and down the sheet. The wobbles in cylinder glass, typical of the 18th and 19th century, are all over the place and look quite different. Crown glass has it's wobbles in concentric arcs.

And also from Tatra Glass of Loughborough, made in Poland. About £80 per square metre last time I bought it.

True, in principle, bayouboy, but there's a lot more to it than that. Only works to its best on SE/SW facades, where solar gain between the panes can add its effect. Also, effect will be unpredictable unless part of a whole-house airtightness plus extract stack ventilation scheme. Given that, secondary glazing inside extg single glass does look like option that's fuller of potential than previously thought, for old houses.

funcrusher, I'd love to see your sash details, if you'd have another go - open a Photobucket account, do it that way?

Here's my solution: http://i30.photobucket.com/albums/c301/fostertom/Waterheadwindows002.jpg http://i30.photobucket.com/albums/c301/fostertom/Waterheadwindows.jpg . These are for new windows but the same principle applies to new sashes in extg sash boxes; the extra sash depth, above standard (usually 44mm), is provided inboard, a loose between the staff beads; and outboard similarly a loose fit between the outer fence, whatever that's called. Similar in principle to the stepped casement window version (and could similarly encroach a little into the parting bead zone). While at it, nowadays I'd increase the sash depth even more, to not 56mm but say 63mm, whatever necessary to fit in full-16mm cavity 2G units, or at least 12mm cavity. Not quite authentic, but unnoticeable in practice - important to keep some depth in the moulded part, not be tempted to make it shallow.

Note - no question of fat glazing bars - the stick-on inner and outer half-bars look just fine, to me, tho' others insist on squinting sideways to notice that there's nothing in between. If really fussy, a between-pane spacer bar - but hard to locate that sufficiently accurately. No problem with sticky tape durability - if it's good enough for rubbing strips on side of a car.......

As far as sash weights, 40x40 or possibly 45x45 square section steel weights are normal now, not lead. The large square, not smaller round section adds weight, but the weights may still need to be extra-long, possibly slightly restricting travel. You'll need ball-bearing pulleys.

funcrusher - technology - does that mean lack of broadband, or scanner? Anyway, I'd love to have sight of your son's design, and I'd be glad to post you a paper copy of mine in exchange for ditto yours. email me privately if nec.

NB my drawings that you've seen are for new frames, but I'm saying cd be adapted to new sashes in extg frames. Mine are large single panes, with glazing bars (astragals) glued on as nec. Why wd your son wish to use structural astragals - difficult, expensive, thermally inefficient and visually unnecessary - ways to make the stick-on ones look even more like real ones, if that's desired.

I found this on a window renovators web page, is it true?

"Energy performance of a window is measured in two ways:

Thermal efficiency of the window (U-Value), which provides only 20-30% of a window’s efficiency.
Air permeability (air-leakage rate or air change rates) that makes up 70-80% of a window’s efficiency."

I restored sashes with (4mm glass-8mmgap-4mm glass) double glazing. This was the thickest i could do, and left me with skinny 8mm beads, and extra weights,( 2and a half sash weights each side) the fit is nice and tight when closede and nice and loose when open. with no edge brushes needed. the heat and sound insulation is superb, much better than old wobbly single glazed.
AS i got my Polish joiner to do it I know that it has been done well. We super insulted the weight boxes with 18mm of super quilt insulation, as these are the thermal weak link.
It is better than Ventrolla and cheaper. The double glazing is harder to see thru from the outside so u privacy advantages as well.
The windows look really good with silver spacers and stained wood. I wouldn't want to cover them up with ugly secondary glazing. I have 100 year old windows restred with Double Glazing, draughtproof and rattle free.Once chunky curtains are fitted it will be super insulted.
one problem is the condensation. on inside. cos the house is unheated at moment in the morning there is much moisture which i wipe upwith cloth.
DOUBLE GLAZE RESTORE OF SASH IS RECCOMENDED

There's another issue here as well, safety. we've all seen badly maintained sliding sashes where the glass looks like it could fall out at any moment. that is more of an issue with double glazed units, and particularly with skinny glazing bars. I've built windows where the glass was so heavy that I felt I had to strengthen the window with steel angle iron- set into the rebate. a window that is easily strong enough when it is made can be anything but after a few years too long without a paint job-or if the cord breaks and it slams down. and from the 1st or 2nd floor, a DGU on your head would be likely to kill or maim. seriously.