measuring for windows

Standard practice is to specify PVCu windows 10mm smaller than the opening, i.e. 5mm off each side. This seems to suggest that the window will float 5mm off the bottom of the opening. You end up with a space at the top that is rather too large for a bead of mastic. Surely it is better to specify 5mm off the vertical direction. This will still be more than enough for expansion of the plastic for most moderate sized windows. Or is there a flaw in my argument ? Only thing I can think is to bed the sill in silicone, but I've never seen anyone do this. Simon.
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In article

First use wedges to set the frame level. It's then usual to fill the 5 mm gap with expanding foam - which as well as filling the gap glues the frame in place. Remove the wedges after it's set and fill those with foam too. Trim off the excess foam round the outside and recess it by a few mm and use silicone to provide a neat weatherproof seal. Don't leave any foam exposed as it deteriorates quickly in sunlight. That's pretty well what the instructions were for the UPVC windows I bought from Screwfix - and they've been fine.
If the brick opening is a bit untidy, shutter with wood strip and run a cement fillet round it to improve the look.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) coughed up some electrons that declared:

I concur having recently fitted two windows.
The 5mm gap usually ends up compensating for irregularities in the wall anyway - and, even if using screws, filling 5-10mm with foam really firms it up (I still believe in big hairy screws - but apparently some window fitters just foam them in nowadays).
Of course, if one is absolutely sure of the opening and it is desireable to reduce the gap, no reason why not - but do allow enough gap to get some sealant in, even if not using foam.
Cheers
Tim
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Tim S wrote:

Tim S,
I must admit that I used to measure these things as part of making a living, and the teams that fitted those windows to be honest would be laughing at the method used above.
Don't get me wrong here, foam and wedged have their uses, but not in the way that has been described here - it's too slow when doing a lot of houses.

A 5mm gap all-round is about right, and very useful if the brickwork under the sill is a bit askew - plastic packers would be very useful here!

Personally, I think that any gap under 5mm is next to useless when using silicone mastic (particularly when used as a weather seal between frame and wall) as the stuff is designed to be flexible when 'set' and the thinner the bead, the less it will 'move' with the expansion and contraction of the plastic.
The only time very thin beads of mastic should be used is when they are used as a decorative finish on the edges of any cover strips.
As for using expanding foam - in my situation, this was only ever used to fill problematical gaps that would occur in stone work or No-Fine [1] constructions or when the removal of box frames were removed and difficulties occured in fixing the UPVc (but that was often overcome by using patent fittings and add-on strips) - on normal brickwork, foam was seldom used.
[1] No-Fine: A method of construction developed after WW2 where external house walls were build using cement and Chipping's only which left a large number of voids in the wall - *NO* *SAND* was used.
This method of construction causes huge problems when renewing external joinery because there is nothing really to drill because of the voids - a damned nuisance to put it mildly.
Cash
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<?.?.?.?.?.?.?.?.?.?.?.?.?.?@?.?.?.?.?.?.?.?.?.?.?.?.?.?.?.//.com.invalid > writes

The team that fitted mine must have been laughing a lot when they did them.
Gaps of 10mm or more each side of the frames, no filling, foam or otherwise, they just stuck some plastic strip on with white silicon sealant to make it look neat.
Come the first winter and a few gales the drafts were worse than ever. On close inspection I found the 10mm gaps and totally naff workmanship. Went out and bought some expanding foam. filled all the gaps. No more drafts and the windows felt a lot firmer too. Had the house re-rendered shortly afterwards and that tidied up the edges.
I do take a rather perverse delight in winding up their "sales team" whenever I meet them at the likes of Focus when they have their displays and are trying to drum up trade. I let them give me their pitch and then I tell them my sorry tale and get their sympathy about dodgy installers, until I tell them who it was. Normal reaction is "Why didn't I go back to them?" What and let them bodge it again, no thanks.
Apart from the bay window I feel now that I would rather have done it myself, next time eh?
--
Bill

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Indeed. Takes too much time to do it properly. So just cover up the rubbish.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Think most of us have seen some tremendous bodges by 'pro' window fitting teams.

Take it up with Screwfix, then, but you've got two people saying it works well for DIY. Where the idea is to do a good job - not just f. off as quickly as possible...

Most DIYers would square off a dodgy sill before attempting to fit a new window. Surely that goes without saying?

Cover strips? Only used on bodges.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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I'd have to admit to finding one length very useful:
http://photos.dionic.net/v/public/bungalow/2009-05-30-img_0011.jpg.html
to cover up that monster gap created by the steeply sloping sill tiles.
Couldn't think of a better way - but I did get a reasonable finish on the sides and top with foam then some frame sealant in brown - which is bloody hard to apply neatly next to those wibbly bricks :)
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Tim S wrote:

Nice job Tim S, and don't be ashamed to say that you've used the stuff, that's why they make it - you wouldn't think twice about sticking architrave around a door to hide that joint twixt wall and frame. Would you?
LOL
Cash
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Depends on whether that architrave is of a design which is correct and in proportion to the frame. Cover strips frequently are not.
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*The older you get, the better you realize you were.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

And I've seen even worse "bodges" by some of the DIY brigade Dave - but there again, bodges are practised by all trades and professions,

Not interested Dave, as far as I am concerned I merely expressed an opinion from experience (as you do when you post to various groups) - but as for your "Where the idea is to do a good job...) I have seen some almighty cock-ups when the unintelligent DIYer gets into full swing (and I don't confine that to DIY plastic window installations).
By the way, I have never used Screwfix for buying in plastic windows, during my involvement with the bloody things, each window was bespoke for its opening - and we are talking about streets of houses rather than the odd one or two here and there in a single house.

Not necessarily - if the window opening is correctly examined and measured, then that "dodgy sill" will be taken into consideration and the window made and fitted accordingly - the window opening should be cut only as a last resort with minor adjustments being 'cut' off the flanges of the window frame (for which the UPVc extrusion is actually designed for. And if you don't believe that, ring up VEKA and ask their technical people the question).

Then I would suggest that your "real" experience in general building is rather limited - especially when working in an environment where damage limitation to internal decoration is a priority.
Cash
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But you were effectively saying the Screwfix way was poor and only your 'pro' method worth considering.

Screwfix only supply certain common sizes. If you need bespoke UPC ones made it's likely they're not the right choice for the job. I absolutely hate them on Victorian etc properties. The two I've fitted are at the back of the house where I wanted much larger windows than original. I certainly wouldn't replace the front sash windows with them - and there are plenty of examples in this street which show why.

Not really interested in what one maker says. Truing up the opening before fitting makes for a far neater job. Of course not cost effective for pro fitters.

But it's not 'damage limitation'. It's covering up damage which has already been done. And often totally inappropriate to the room.
--


Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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sm_jamieson wrote:

Easy answer to this and very logical - simply just take 5mm off the height of the frame!!
Cash
In a flippant mood after spending all day painting fascias and soffits.
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wrote:

I trust you've been using high solvent paint, which always makes you feel good ! Simon.
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Simon wrote:

Nah! Just plain ordinary oil based undercoat - but the bloody rain held off long enough for me to at least give the first coat - and that's enough to make me happy today! Only three more coats to go!
Cash
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sm_jamieson coughed up some electrons that declared:

Not intending to teach granny re egg suckage - but *if* you've not done uPVC windows before, I found this most helpful - you may too:
http://www.windowsanddoors.co.uk/estimate/windowsanddoorsinstallation.html
Especially with respect to setting the glazing in correctly...
HTH
Tim
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I've only done pre-glazed ones where fixing brackets are used rather than drilling the frame. Also, the brickwork was very level. That link is interesting, mentioned cutting the sill for horns. I've noticed a lot of windows fitted where the horns are not bothered with. I guess with cavity walls, the slight extra waterproofing they give are not really worth it and it takes longer. The end caps for PVCu cover the whole end of the profile, although of course they can be cut. Don't horns originate from when the window sill was built into the brickwork ? Simon.
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In that case, make sure they give you lots of "bridge packers" (I use typically 4 per pane - methods differ, you may need more per pane for larger panes) and *loads* of glazing packers in all sizes from 1mm to as thick as possible (1mm increments).
Both of those are a bastard to buy in small quantities (often in boxes of 1000) and differ a lot from the more common "frame packers" which you can get more easily (these are of course also useful for setting the frame).

Must admit I hadn't paid much attention - I have tile sills and consequently bought windows without sills.
Cheers
Tim
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I know nothing about these different types of packers. Is there a tutorial or something somewhere ? Simon.
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Not sure, beyond that link I posted.
But basically:
Frame packers - use as you'd imagine, around or next to the screws to level the frame and allow the fixing to be pulled tight without loading the frame itself.
Bridge packers: You want the width that suits the DG panel. Length is about 5-7cm. Thickness - usually one thickness, about 6-8mm IIRC. The important thing with these is that they are a plastic strip with 2 ridges along the length. These should be used, one per packing position between the glass and the inside of the frame. The bridge packer should be against the frame with the ridges to the frame and the flat side to the glass. This allows free drainage of any water and condensation.
Glazing packers: Simple plastic shims from 1mm to many mm in 1mm increments. Shims are similar in length and width to the bridge packers and you use as many and of whatever thickness between the bridge packer and the glass to get the glass where you want it.
The glass should be wedged in firmly before you bang the beads in and consequently should not move (much) when beading.
The packers also allow the glass to add rigidity to the frame, helping to keep it square (assuming you pack the top and sides too). I didn't have this issue - my windows were small and contained *much* steel - but I suspect it would be more important on larger windows or ones of cheaper quality with less steel.
Sadly I don;t have any pictures from when I did mine...
HTH
Tim
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