measuring up for a replacement sash window

[Robbox]

Two windows in my house are sash and I want to replace with D/G and draught-stripped units.

The company I want to use is too far way to come and measure, so I want to measure myself.

The current units fit behind a stone facade.

It's not possible to measure the old units, and anyway, the new ones are not exactly like for like.

What's the best way to get it right for the joinery shop?

 

[Deleted member 174758]

You should still measure the size of the opening on the outside of the masonry. Also measure the size of the frame on the inside. This may mean stripping out any timber cladding and/or window boards amd possibly chopping into plasterboard/plastered window reveals to find out how deep the rebates in the masonry are. As all that stuff will have to come out when the replacement windows are installed it shouldn't make any difference. I've found that what you can't do is guess, or assume that all window openings have the same size rebates. Whatever else take plenty of photographs so that the joiners can see what it is they are dealing with

 

[Robbox]

Thanks for the advice, I figured I may have to strip back the plasterwork...

If the reveal is tight or irregular, how simple would it be to make it wider?

Finally, how much of the 'outer liner' is it normal to show? The company I will use has 19mm of liner proud of the box section.

 

[Robbox]

I have had a look over the top of one of the old windows, seems that the reveal is low and the top box has been cut down quite a bit.

This may be a problem for the units I want, the box section is all enclosed, top and sides.

How would it be to hire an 8" angle grinder and cut away the extra reveal?

 

[Deleted member 174758]

If the reveal is tight or irregular, how simple would it be to make it wider?

I live in a "stone district" where almost all the reveals seen to be irregular. They can also be out of square because of subsidence (measure cormer to corner - both diagonals will be about the same if the opening is square). I wouldn't try to open out the masonry if at all possible, after all at one time it presumably held a sash window and had sufficient space for the sash weights (often cast iron). These being modern replacements I'd expect your sashes to be spring-hung, though, and casements for those don't need the large box to hold the weights.

Finally, how much of the 'outer liner' is it normal to show? The company I will use has 19mm of liner proud of the box section.

Sounds reasonable to me. The outside lining reveal is often a similar size to the staff bead on the inside of the window. Staff beads are generally something like 3/4in or 1in, although you do sometimes see 1-1/8in ones (or circa 19, 24 and 28mm these days). In the north of England and Scotland you sometimes get a "storm sash" or "Scottish sash" with larger staff beads of 1-1/4in width (32mm). A quick look around your locality will probably give you the "local" standard for the district. Any gap between the masonry and window frame is filled with mastic. Sometimes these gaps are really large and on refurbs you'll often find all sorts of (often unsuitable) things stuffed in there to pack out the gaps

I have had a look over the top of one of the old windows, seems that the reveal is low and the top box has been cut down quite a bit.

You don't have a top box on most sash windows........ On Victorian sash windows the boxes are often only at the sides (for the weights). The head of the frame is pretty much always a solid piece of timber, as is the sill. You do see boxed heads on Georgian and earlier windows, as well as on some very large windows (where the box would make for a lighter, more rigid structure), but they aren't exactly common in my area. If your top rebate is shallow then that sort of indicates the original sash was a Victorian solid head type. In which case I don't see why you'd need to grind anything away. In any case grinding anything out of a lintel will weaken the building. Not good! Remember, the lintels carry the entire weight of the walls above them!

I think that you might benefit from getting hold of a good technical book on joinery which covers the structure of sash windows......

 

[Robbox]

I have had a closer look at the head of the window. It does now look like what you say. I can just about make out (it's dark in there!) another rebate in the lintel, but close to the outer reveal.

What the joiner has done for these old replacement sashes, is to cut the front, top liner to fit under this rebate. Plus trimming the inner liner to fit under the old inner oak lintel.

These units I want to order are boxed in all round, except for the hardwood cill. I would assume they are more likely to find their way into new builds where the brickwork and lintel area can be made to accommodate the units.

I guess two things concern me, one is that when the units are fitted, the rough stonework behind outer stone surrounds will interfere with the easy fitting of the new windows (I suppose any projecting stones could be trimmed back with an angle-grinder and stone blade)

The other concern is that from the outside the windows will have too much of the side piece showing and start to look out of proportions.

have a look at this pic of the lower window...
View media item 43738 View media item 43740
Certainly the stonework is not absolutely true, the sides are out by a small amount, the lintel is even more out. Plus I think the joiner didn't manage to put in the sash unit square.

The oak lintel on the inside is too low and the old sash was cut down to fit inside.

I guess it's all so wonky, that my second concern is just not really justified....

Finally, I was going to get the fitter to fill the sides and top with foam. Since the sides and top are all boxed in, it would prevent wall debris falling out and secure the unit.

 

[Billb47]

there is another way of doing this, if the timber suround is sound, you could take out the sashes and fit a upvc window in between and leave the sash boxes inplace.Then you can either plater board them or cover with trim. I know from past experiance, taking out a sash window is a messy job.

 

[Deleted member 174758]

I guess two things concern me, one is that when the units are fitted, the rough stonework behind outer stone surrounds will interfere with the easy fitting of the new windows (I suppose any projecting stones could be trimmed back with an angle-grinder and stone blade)

Once again I think you are fretting unneccessarily. The opening originally had sash windows, so the masonry isn't likely to be that far out. Even if it is (and it's likely to be the other way, hollows in the masonry against the window frame rather than projections) then the way to cover this it to fill these hollows with trowelling mastic.

The other concern is that from the outside the windows will have too much of the side piece showing and start to look out of proportions.

The last lot I refurbed were about 5ft high x 3 ft wide and had around 1-1/2in visible before the mastic went in. The mastic was built to a heavyish bevelled bed and it all looked fine to my eye

Certainly the stonework is not absolutely true, the sides are out by a small amount, the lintel is even more out. Plus I think the joiner didn't manage to put in the sash unit square.

This is a common enough problem with old buildings where getting it to look right is often more important than it being techically correct (plumb. level, etc - ever seen a sign box installed dead level when the masonry runs out a few degrees?). When installing stuff like this it is often better to hold in place with folding wedges then stand back and eyeball the window opening before making the final fix

Finally, I was going to get the fitter to fill the sides and top with foam. Since the sides and top are all boxed in, it would prevent wall debris falling out and secure the unit.

If a fitter working with/for me pulled out a foam gun to secure a sash window I'd sack him (assuming it were in my power) for his incompetence. Sash windows aren't PVCu units with sealed units. If you spray expanding foam in behind the box it will put the sides of the window frame under pressure and potentially cause the sashes to run jerkiily or even stick because the frames have been pin-cushioned by the pressure of the foam. Once you put too much pressure on those boxes it is all but impossible to ever sort the windows out. I feel that the correct way is to fix through the head lining (if solid) and sill and to use metal straps fixed into wedges in the mortar joints for the boxed sides (and likewise for the head if it's the boxed type). These straps are going to be plastered over so appearance is not important and you don't need that many. Once the window is secure the sides and top are sealed with trowelling mastic. On traditional windows fixing through the sill wasn't necessary as the masons generally left you a metal weatherstrip embedded into the masonry sill and the groove on the underside of the wooden sill would align with this. Obviously on replacement units you may well not have this option.

If you need to weatherproof and draught-proof the window the way to do it is to gently pack mineral wool around the outside of the frames (in the gaps) and trowel mastic the outside of the frame. Properly sized frames won't have a huge gap around them and in any case the plasterwork will cover gaps on the inside

 

[Robbox]

Thanks, for your advice.

One thing I see around this village is that most of the older sash windows have no wooden cill and the lower sash sits on the sloping stone cill. There is a small upstand at the back of the stone cill. But I don't imagine that is very draughtproof.

I have measured and made an average of the stone openings, then added on the width of the two side boxes, The total comes to a figure very close to the original units in total width. So I am now feeling a lot more confident.

I do have an experienced joiner to fit and when I mentioned foam....he didn't explode, but kindly suggested that he would use metal straps! Thanks for the tip on foam, I have wondered about the pressure it may exert.

I guess I feel good to go now.

Cheers