Paranoid about spontaneous failure of large skylight

[Declan52]

17 hours ago, hendriQ said:

Thinking this through a bit further, why is this the case? If I cover the inside of the glazing unit with film, the film will be stuck to the underside of the skylight. I can't see how that film is going to keep the failed glass from falling down. The film is just very thin plastic. Even a sheet that is about 2m²  is not going to weigh more than a couple of kilos. Compare that to the gravitational potential energy exerted by 140kg of glass, this film might actually make things worse. Instead of the glass falling as particles or 1cm cubes, all those pieces would be kept together by the film resulting in a heavy weight that would doubtless cause serious injury.

The skylight is about 2m above head height. So not a huge height to let it accumulate speed under the force of gravity, but enough that I would prefer it to fall as particles than as one large sheet.

Am I missing something here?

It's not going to hold the glass together whole but it would give whoever is underneath it an extra second to shift their ass out of the road. 

[PeterW]

I don’t think this has been well designed or thought out tbh, and it’s a folly that looks good but no-one has actually worked out how to deliver as I think you’re now finding out. 
 

The weight of the unit won’t be your issue, it will be the flex strength of the glass that becomes the limiting factor. I’ve installed glass roof panels on conservatories and they bend when you install them in a very unnerving manner…! Glass doesn’t have a great strength when placed under tension which is what happens when it bends, and this will bend. How you handle and lift a unit that size will be a significant challenge. 
 

I’m assuming that this is being installed perfectly flat, at which point you also need to ensure that it’s got self cleaning coating on the outer as it will very quickly become dirty. You will also have to stop anyone ever standing on it, and also think about where it could be impacted from above (roof tiles, nearby trees etc) 

 

Also I’ve assumed you’ve calculated the heat loss in for this ..? Has the insulation in the roof - and the heat loss of the room - been adequately compensated for this level of glazing in the roof itself ..?

[hendriQ]

1 hour ago, SteamyTea said:

The way I understand it is that toughened glass can take a greater impact before failure, then the laminated catches the pieces.

I agree with that. If I could afford laminated, I would go with that. But my point was that applying an aftermarket film wouldn’t achieve the same thing. It would be pretty redundant. 

[hendriQ]

11 minutes ago, PeterW said:

I’m assuming that this is being installed perfectly flat

No, it’s got a 4 degree fall to one of the sides. The other side is leaning against an adjacent wall, sort of being built into the render on that wall, then the job is being covered with lead flashing. 

 

11 minutes ago, PeterW said:

Also I’ve assumed you’ve calculated the heat loss in for this ..? Has the insulation in the roof - and the heat loss of the room - been adequately compensated for this level of glazing in the roof itself ..?

The upstand is fully insulated with PIR. There will obviously still be heat loss, but this roof light has a u value of 1.2 so not dissimilar to the rest of the glazing in the house which is between 1.0 and 1.2. I was a bit annoyed that the architect instructed the builder to use superquilt as the main insulation in this part of the roof, as reading into that I see it’s not that great. 

Edited November 20, 2021 by hendriQ

[SteamyTea]

46 minutes ago, hendriQ said:

But my point was that applying an aftermarket film wouldn’t achieve the same thing. It would be pretty redundant

It will hold the larger parts and increase the time until they fall from seconds to hours.

It is why film was fitted to the glass in Docklands after the IRA bombings.

But if you are so worried, why fit this design of skylight.

Or you could fit wired glass.

 

[hendriQ]

With wired glass, would the wires be visible, given that it will be almost 2m from head height. Because if not, that might be a great idea.

[PeterW]

2 hours ago, hendriQ said:

then the job is being covered with lead flashing.

So you have lead runoff over glazing ..? Your architect has remembered to tell you that will stain the glass then ..??

 

I would be making this into 3 standard panels, offset from the wall slightly so you can put some element of gutter behind it and redesigned with cost and safety in mind. 
 

This really is a glass of example of form over function - it’s not been thought through at design stage and you now have an expensive issue to resolve. 

[joe90]

My conservatory roof has 12 panels approx 3m x 1m each,  laminated inner and outer , guys installing them lay on them  to fix (with a sheet of insulation to stop point loading. ) The lead flashing above was treated with oil (as it should be) and I have had no staining so far ?

[hendriQ]

39 minutes ago, PeterW said:

So you have lead runoff over glazing ..? Your architect has remembered to tell you that will stain the glass then ..??

 

I would be making this into 3 standard panels, offset from the wall slightly so you can put some element of gutter behind it and redesigned with cost and safety in mind. 
 

This really is a glass of example of form over function - it’s not been thought through at design stage and you now have an expensive issue to resolve. 

Sorry, really out of my depth here. This is a drawing of what is proposed:

 

 

i now realise the angle is much more than 4 degrees.  Can somebody explain the staining? How much staining will there be and how far will it spread across the glass? If it is just a couple of cm, it shouldn’t matter because there is a a plasterboard overlap internally that will hide some concealed internal LED lighting strips as well as prevent from unseeing the edge of the roof light.

[PeterW]

Lead run off over the glass can deposit all the way across the glass - it leaves white streaks. 
 

So … given this is 4m by 1m, how was the architect planning the roofer insert that flashing too ..?? You need to be able to kneel in front of the wall to do it - as it stands you’ll need to stand on the glass to install it. 
 

Also, how will the rendering company render down to that flashing ..?  It is incorrectly designed as the flashing just needs to cut into the blockwork by 30mm and then the render goes over the top with a bell cast or stop bead. 
 

None of that has been thought about and it really should have been from the outset. 
 

 

 

 

[Iceverge]

I'm not convinced that you'll have much success with the single glazing unit so close to the wall. It looks very tricky to install and difficult to detail.

 

  Running a 3.9m roof window parallel to the existing house will no doubt create some issues with differential movement of the structures as they won't be tied together very well. 

 

This could well lead to leaks and drafts not to mention the nearer it is to the existing wall the more difficult it will be to keep clean with rain splashbacks etc. 

 

I would scrap the idea of a bespoke unit altogether. Detail the flat roof to wall junction as per a normal flat roof setup and opt for 3 900*1200 velux flat roof units placed at least 200mm away from the wall ensuring that there's plenty of clear area all around them for rainwater drainage. 

 

I haven't checked but I assume Velux (other brands available) have taken care of all the issues with breaking glass etc. 

 

[hendriQ]

Ok, so maybe it’s not as bad as I thought. The builder had thought about this and actually already installed the flashing into the wall, with the bottom hanging off the wall so that the skylight can be slid underneath it. The company supplying the skylight are also installing, together with some labourers from the builder’s team. There will be 6 men carrying it, so about 27kg each. A couple of the men are real hunks, like Brad Pitt as Achilles, so I’m not too worried about that. If they need to reach over the skylight to finish manipulating the flashing, they can build a small platform over it with scaffolding. Plenty of that on site, but it may not be necessary as I completely forgot that only part of the skylight goes up against a wall. Maybe about 1.5m of it. The rest is fully exposed on three sides (both long sides and one short side). 

 It is a shame I didn’t know about this streaking before, as there appear to be lots of cheaper non-lead alternatives in the market. 
@joe90 you mentioned your lead had been oiled to prevent staining. Which product did you use for that? Maybe that’s the solution here. Is it something like this: 
https://www.trulypvc.com/roofing/flashing/lead-roll/patination-oil-500ml?gclid=CjwKCAiA1uKMBhAGEiwAxzvX92OO5zHc1bteNM-FPCuQWsY3_s0sxFT1HtHTv7tkRrBDBFr_vyQCDhoC47cQAvD_BwE

 

Edited November 20, 2021 by hendriQ

[dpmiller]

you've obviously already decided what you're doing then- what are you asking us for?

[hendriQ]

15 minutes ago, dpmiller said:

you've obviously already decided what you're doing then- what are you asking us for?

I'm just trying to understand what the least worst option is. The options being suggested here are that I should effectively change my opening and move it away from the wall so that I can fit an off the shelf skylight or modular system that doesn't touch the wall and therefore doesn't require flashing. I cannot really do that at this late stage because my roof has already been built, including a very expensive rubberised coating that has been applied, and the wall has already been built.

So if anybody can advise on whether patination oil does what it says on the tin, then I think the solution is to apply two coats of that and then reapply every couple of years.

[PeterW]

Patination oil does work but make sure they also put some on the underside of the lead. 
 

TBH there is nothing stopping you changing the design now to a framed design with 3 or 4 panels and a back gutter - if you’ve not ordered the glazing, it could all be modified. 
 

Patination oil doesn’t fix your original issue here which is one of the unit design and the glazing type, both of which do need to be addressed before you finalize the order for the glass. 
 

I’m  assuming that there is a timber fillet/bearer against the wall that is shaped for the glass to sit on ..? How has that been sealed against the wall ..?

[hendriQ]

13 minutes ago, PeterW said:

Patination oil does work but make sure they also put some on the underside of the lead. 
 

TBH there is nothing stopping you changing the design now to a framed design with 3 or 4 panels and a back gutter - if you’ve not ordered the glazing, it could all be modified. 
 

Patination oil doesn’t fix your original issue here which is one of the unit design and the glazing type, both of which do need to be addressed before you finalize the order for the glass. 
 

I’m  assuming that there is a timber fillet/bearer against the wall that is shaped for the glass to sit on ..? How has that been sealed against the wall ..?

I haven't ordered the glass, so in theory you are right that everything is still possible. In practice changing things up at this stage is going to be prohibitively expensive. here are some pictures. Keep in mind the pitched roofs on either side AND the wooden upstand on the left and the top frame of the opening all the way around is ALL covered in a rubberised coating that also covers the pitched roofs. That coating insn't straightforward to re-do so moving the hole is not going to be cheap. Structurally, there are a couple of steel beams under either side of the opening. One of those beams supports both the first floor extension wall and will also support that side of the rooflight, whereas the other beam supports the rafters and the other side of the roof light.

pictures:

[PeterW]

Here you go - Velux modular long lights. Will do what you want, out of the box design and can also be opened. 
 

https://velcdn.azureedge.net/-/media/marketing/master/velux modular skylights professional/pdfs/50405501v11953048010technicalhandbook31.pdf

[joe90]

2 hours ago, hendriQ said:

you mentioned your lead had been oiled to prevent staining.

Yes patination oil….

[PeterW]

Ok so that needs doing in 2 sections. The “architect” has drawn something that is only suitable for the enclosed end, the open end will need a full aluminum flashing as there is nothing for the glass to mount onto. You can’t just stick some structural glass compound on top of that rubber coating and hope the glass sticks to it. 
 

Have you taken a straight edge to any of that ..? More than 3-4mm out of plane and it will need packing etc. 

 

Have you spoken to a specialist and got them to properly survey this as that is not a quick or simple job - a picture speaks a thousand words. 
 

Also - where is the insulation in that kerb, and how are you insulating that flanking wall as it’s a big cold bridge. 

[hendriQ]

5 minutes ago, PeterW said:

Ok so that needs doing in 2 sections. The “architect” has drawn something that is only suitable for the enclosed end, the open end will need a full aluminum flashing as there is nothing for the glass to mount onto. You can’t just stick some structural glass compound on top of that rubber coating and hope the glass sticks to it. 
 

Have you taken a straight edge to any of that ..? More than 3-4mm out of plane and it will need packing etc. 

 

Have you spoken to a specialist and got them to properly survey this as that is not a quick or simple job - a picture speaks a thousand words. 
 

Also - where is the insulation in that kerb, and how are you insulating that flanking wall as it’s a big cold bridge. 

Yes, there are two sections to the design drawings. I have only shown one, which is where the wall is. The other one also has a  flashing, but it will take water away from the glass down a fall in the opposite direction, so there shouldn't be any movement of rainwater from that flashing onto the glass. The wall you are seeing is a cavity wall, with insulation in the middle. The three sides of the upstand that abut that wall (the wall being the fourth side of the rectangle) are a timber frame constructions with PIR on all sides.

 

Looking at the cross sectional design of the Velux product you've suggested, it also has a flashing (marked "Top flashing (EWC)"). See below.

So I query what the difference is. I think it's that Velux flashings are made of aluminium and then painted grey. What's to stop me painting my flashing with an appropriate grey paint?

 

 

[PeterW]

The EWC flashings are correctly designed for this sort of installation - you can see how they are cut into the wall with the lip to stop the flashing pulling free. 
 

7 minutes ago, hendriQ said:

What's to stop me painting my flashing with an appropriate grey paint?

You can’t paint lead very successfully ..!

 

7 minutes ago, hendriQ said:

The other one also has a  flashing, but it will take water away from the glass down a fall in the opposite direction,

So how is that detailed at the change of direction ..? I can’t see any flashing return round the corner which you need to seal the top of this detail. There is a lot of things that can go wrong here and leak - it needs to be right first time. 
 

I would be treating this as two separate panels - the first up to the end of the wall, then a second unit covering the end that is open. Both need different fixing and watertight detailing. Due to the thickness of the upstand you’ve got room to play with a frame system too - that allows you to detail all the fixings, sealing and flashing and then fit the glass. 

[PeterW]

10 minutes ago, hendriQ said:

The wall you are seeing is a cavity wall, with insulation in the middle.

Think you miss the point - that outside rendered wall becomes the inside when it drops below the glazing so it’s a huge thermal bridge. Needs some element of insulation. 

[hendriQ]

25 minutes ago, PeterW said:

Think you miss the point - that outside rendered wall becomes the inside when it drops below the glazing so it’s a huge thermal bridge. Needs some element of insulation. 

Yes, you’re right. Not sure how to solve that. Is it too late to solve it by applying insulated plasterboard to the inside?

 It’s not a passive house, but agree that thermal bridging is not ideal. At least it’s a breeze block construction, si not the best conductor of heat. 

Edited November 20, 2021 by hendriQ

[PeterW]

52 minutes ago, hendriQ said:

Yes, you’re right. Not sure how to solve that. Is it too late to solve it by applying insulated plasterboard to the inside?

 It’s not a passive house, but agree that thermal bridging is not ideal. At least it’s a breeze block construction, si not the best conductor of heat. 

You’ve got space for insulated plasterboard. Need to get the detailing right on that corner though, especially with steel, timber and blockwork involved. 

[hendriQ]

Update: builder already had some patination oil on site and has been meaning to do the flashings (which I hadn't realised had already been installed a couple of weeks ago). So we agreed he is going to clean them up with wire wool to remove the little carbonate that has probably formed in the last couple of weeks and then once it's dry apply the patination oil on both sides;

 

After the rooflight goes in we are laying seedum trays on the roof, so now need to consider how to access the lead flashings to service them in future years. How often does one tend to need to reapply patination oil? If it is only every 24 months, do people think it's okay to walk across the seedum trays? Alternatively, I could leave a small gap along the roof just under an openable window on the first floor and fill that with gravel instead of seedum trays. This would then allow me to walk up to the ~1.6m strip of flashing that is angled towards the glass (the rest of the flashing is angled away from it) and apply patination oil.