Window deflection query

[PlasmaParticipant @plasma]

[PlasmaParticipant @plasma]

Not a topic within my knowledge base and bit of a shot in the dark to pose it, but there are so many knowledgable folk on here someone may be able to shine a light on my question.

I have a 4m x 2m upvc double glazed front window. It's not one big pane but five separated units within one large reveal. It faces west and has a very open aspect towards the foot of the pennines. So its windy, very windy.

It moves back and forth quite a bit and I'm assured by the firm who replaced our windows 2 years ago that it was well up to the job.

I measured the deflection inwards last night as freya did her best, it moved half an inch inwards, but also moves outward too due to lower pressure I guess. I think this is quite a lot of movement and it can be quite alarming watching the glass breathe like this.

Is there any opinion as to whether this is normal or acceptable. Am I being a bit over worried? Is there an industry standard I can refer to if I want to get the window changed.

The previous window we replaced on moving in was a huge expanse of glass, not smaller bays and that survived for years, but I suspect it was better quality than that we replaced it with.

Best regards

[Mike PooleParticipant @mikepoole82104]

It is most likely toughened glass if that is a floor to ceiling window and that will take a lot of breaking. I suppose the manufactures are going to be reluctant to say it’s too much movement as it is then their problem but they are probably right, as to engineer it for zero movement is going to make it very thick and heavy.

Mike

[HopperParticipant @hopper]

Having stood inside a room with floor-to-ceiling windows and sliding glass doors during a Category 5 cyclone, I can tell you that glass panels can and will bow by WAY more than half an inch. Several inches more like it. Quite amazing to see – and scary. Mind you, I was not standing in the line of fire, should they have let go! And our windows here in the tropics are toughened glass. So I would not be at all worried about half an inch of movement. Normal breezy day, that.

[Martin KyteParticipant @martinkyte99762]

We have a 'glass wall' of 2m hight architectural glass panels around our rooftop restaraunt at work which are cantelever supported at the bottom edge. They move a good 2-3 inches at the top in a strong wind. I suspect most of the 'worry' is because we intuitlively think of glass as rigid.

regards Martin

[Frances IoMParticipant @francesiom58905]

can’t match a cat 5 cyclone but my flat on IoM above Peel harbour faces SW with 3ft x 5ft single pane double glazed window – that bowed by about 0.5inch in the storm force 11 we had some years ago – must admit it was sheer fascination as to what would happen that kept me in the same room

[JohnFParticipant @johnf59703]

Look at FENSA site and google British standards for windows but I agree everything has to bend or give or it will break !

John

[John Paton 1Participant @johnpaton1]

A lot of work was done on this in the late 1970s looking both at breakage due to human body impact 'safety glass' and also to withstand wind load. I no longer have access to the old British Standards and Codes of practice (that cover glass sizes and fixing methods) but you should be able to find these through the Glass and Glazing Federation.

Having seen the effect of glass breakage due to wind pressure – a glass shard impaled in the opposite wall of the room about 8 m away following a freak wind gust, I would always check the thickness of glass in exposed locations when the minimum span of the glass exceeds 1.2 m (for old glass) or 1.8m for more recent installations where toughened or laminated glass should have been used. I should remark that the freak wind gust also stripped the flat roof covering from the adjacent building so was clearly abnormal.

A simple test for toughened glass is to look at it with polarised sunglasses when the stress patterns from the toughening process can be seen (often you can se little dots on one edge where the glass was suspended by tongs while being heat treated).

Thickness of glass is also simply checked using a plastic gauge with a bevelled edge with graduated lines which show thickness when diffraction of reflected image of the graduations lines the markings up against a particular pair of marked lines.

I have found cases where glass has been installed that was too large for its dimensions and wind load exposure, but that is a rare occasion and glazing companies and window manufacturers are pretty careful to meet the glazing code.

John

[BazyleParticipant @bazyle]

Very confusing to say 4mx2m divided into 5. Which is the horizontal? I assume each pane is 2ft6 wide x 6ft6 high about the size of a door. Is it the middle of the pane moving, the sub frame, or the whole frame? If the whole lot was just stuck in with some expanding foam around the edges and no screws it might all be heading out – or in.

[SillyOldDufferModerator @sillyoldduffer]

Watched a tv programme a few years ago where a house was set on fire and a chap tried to escape from an upstairs bedroom.

Two things struck me: one was how fast an ordinary house goes from 'Is that smoke?' to 'Towering Inferno'. Only a few minutes before the fire went blast furnace and the Fire Brigade stopped the experiment by flooding the house. The other was the chap's total failure to escape by breaking the double glazing – even whacking the glass as hard as possible with a chair had no effect.

Recommendations: leave window unlocked, or make sure the key is handy, or keep one of those pointy emergency hammers.

Good news – wind is unlikely to break a window. Bad news – you're doomed if the house catches fire…

Dave

[Nick WheelerParticipant @nickwheeler]

Posted by SillyOldDuffer on 04/03/2019 20:44:10:

Watched a tv programme a few years ago where a house was set on fire and a chap tried to escape from an upstairs bedroom.

Two things struck me: one was how fast an ordinary house goes from 'Is that smoke?' to 'Towering Inferno'. Only a few minutes before the fire went blast furnace and the Fire Brigade stopped the experiment by flooding the house. The other was the chap's total failure to escape by breaking the double glazing – even whacking the glass as hard as possible with a chair had no effect.

Recommendations: leave window unlocked, or make sure the key is handy, or keep one of those pointy emergency hammers.

Good news – wind is unlikely to break a window. Bad news – you're doomed if the house catches fire…

Dave

People think that you break windows by hitting them in the middle of the glass. As this thread has shown, that rarely works because sheet glass is surprisingly flexible. What is needed is a sharp blow with something hard in the corner of the glass.

[Mike PooleParticipant @mikepoole82104]

An automatic centre punch used in a corner is a useful tool to break toughened glass but pointy hammer is probably cheaper. After I locked my keys in the car on holiday it was very difficult to break a window even with a bicycle u lock which was the only useful thing to hand. Difficult to aim useful blow as a miss tends to mean a body repair as well as a window.

Mike

[JonParticipant @jon]

Thats a large pane of glass.

To give you some idea bog standard presume 4mm glass 3ft x3.5ft you wouldnt believe how much it will bellow, well over 2" in the centre.

[PlasmaParticipant @plasma]

Lots of information as I anticipated .thank you all.

Bazyle, I know my description was not too detailed but it is a complicated window. It's not evenly divided and has transome windows and larger panels of different sizes.

The whole frame is flexing, not just the glass deforming under wind pressure.

I imagine the upvc will fail long before the glass will. It is bonded and screwed in to the brickwork. So I hope it won't go anywhere.

I'm considering taking it out and having brick mullions put in to reduce the overall size of the window. Less of a view but more secure.

Best regards

[phil gardinerParticipant @philgardiner73127]

What's even more confusing to me is why do we still mix imperial with metric measurements here in Australia we went metric in 1966 especially in the building industry.

[HopperParticipant @hopper]

Posted by phil gardiner on 05/03/2019 02:10:41:

What's even more confusing to me is why do we still mix imperial with metric measurements here in Australia we went metric in 1966 especially in the building industry.

We did? Go down to Bunnings and see what size nuts and bolts and threaded rod they are selling for building work. Imperial. And sheets of everything from plywood to glass in nice round metric nominal sizes like 1.2m x 2.4mm, actual sizes more like 1220mm x 2440mm, which just happens to be dead on exactly 4 foot by 8 foot. And standard wall stud spacing is a nice, round metric 450mm, which is divisible into exactly no round meters, but just happens to be smack on 18". If we had converted to metric, sheets of material would be 2m x 1m like in Japan and standard lengths of timber and steel bar etc would be 2m and 3m, not 2.4m and 3.1m (aka 10 foot).

Whenever I go to the local steel supply yard, all sizes are in imperial. But they only sell it by the meter. Hence:

"I need some 25mm round bar."

"We only have one-inch bar."

"OK. Give me six feet of that then".

"We only sell it by the metre."

Absolutely true story, to the word.

[Howard LewisParticipant @howardlewis46836]

When we lived on Shoreham Beach, in a split level house, our lounge had windows over almost all of one wall, so about 8 high x 12 long. When a gale blew (frequently ), the single glazed window glass could be seen flexing. We were not the first owners, and in the three years that we were there, the glass never cracked, let alone broke.

A double glazed unit is going to be MUCH stronger (bd^3 / 12) than single glazed, so I would not worry too much.

Howard.

[JonParticipant @jon]

Posted by Plasma on 04/03/2019 23:44:06:

The whole frame is flexing, not just the glass deforming under wind pressure.

Put money on it the installer has only screwed towards the top and bottom only.

Must admit i have a little laugh when a customer says something like 113mm diameter and probably reply with 4 1/2". Hell i even mix imperial and metric up on same paragraph.

I was taught imperial at school, some years later what a godsend worked at an engineerring co using millimeters to indefinate. So could have a dimension 7500 which is 7.5m or in the case of spec conformity on steels 25.4 x 4.76 (which is 1" x 3/16&quot

Last employed place when i started in 99 i thought i took a step back in time to the 30 and 40's in every way. They worked in thous and general imperial, problem was deciphering US sketches for high value high quality parts to which i always converted to metric.

What surprises me considering metrics been the industry standard for more than 35 years is when you buy aluminium, its 95% still imperial. Unless of course yo have your own rolling mill.

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