On Feb 10, 9:32 pm, "Newshound" wrote:
I'm planning to replace 50's steel framed windows on an 18th C cottage with
timber casements. On the rear elevation these are 2300 wide and 1200 high so
I have some choice over numbers of casements and glazing bars. Does anyone
know of any design software that would help sketch out the options quickly?

Second question, I know there is a rule requiring toughened glass for
windows with cills below 800 mm. Does that apply both sides? My outside cill
is only 300 mm from ground level. (Can't easily dig it out, although I would
like to, because I would have to re-lay all the drains).

The toughened glass law came out in the '80's to replace 3mm glass
with 4 mm float. Most modern galss is of the required standard so
don't worry about that.

An immediate fix for the most likely problem you have with that sort
of window is to clean the rebates on the opening casements and stuff
and coat one edge with a thin lick of engine grease, brush with a pva
and meths mixture, or thick washing up liquid and immediately apply a
thickish line of silicon mastic to the other meeting faces.

Don't forget to silicon all around the outer edges of the window too.
All being well this should last you well into the summer. Take
measurements to replace the whole lot from the outside after knocking
back a little of any plaster on the reveals to get the true opening
size.

If you order ready made units, check they have given you half an inch
overall on the height and the width before you accept delivery. And
make sure that is in the contract that they will accept immediate
return of the windows if US.

When closed, the silicon will fill any draughty gaps and might squeeze
out past the rebates. Scrape the excess off and leave closed until the
silicon has grown hard. Use an high modulus.

These casements were fitted with a very hard bedding compound. Getting
them out might be a PITA. Go easy if you wish to save the timber
subframe.

If you can save that, you can get ally frames to fit it. They will
look a lot better than plastic windows in an old building.

Score down the reveals if they are plastered; to stop the plaster
breaking past the edges of the windows and making a patch necessary
and time consuming. (And almost always impossible to match.)

If you can afford it get double glazed oak windows made and pressure
treated.

Finally, replace the plaster on the reveal with a sand and cement mix.
Screw or wedge a lath onto the edge, so it sticks past the reveal
about an inch depending on how much cover you need. (Never less than
an half inch.)

Slap the mix in with a gauging trowel and brush the exces off the
window straight away. If you are using aluminium, protect that with
masking tape or you will regret it.

Scape the finish level and brush the finish with a soft bristled
brush. You can knock the lath off straight away if you are half
competent. Then brush excess from behind that.

It could be left a day or so if you are a newbie and a trowel or wire
brush used to scrape off any excess from under the lath.