# Joiners: design critique, please.



## MikeG. (7 Aug 2020)

I need some input on the design for my rooflight, if you wouldn't mind. There is an existing upstand, and I need to plonk some joinery on top of this. The rooflight also provides roof access, and I am proposing using cranked hinges on one of the long sides. I am not sure whether to do an internal or external glazing bead for starters, and I just need a general eye cast over the design. Rooflights are such vulnerable pieces of joinery and I want to be sure I've got it right.

Any comments welcome (oh, and what would you make it of?).


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## Mike Jordan (7 Aug 2020)

Hi Mike 
I favour type B purely on the grounds of no external beads, I like the extended top face of the glazing at the bottom rail. What type/s of glass will you be using?
What will support the glazed frame in the open position ? If you are climbing out onto the roof using a ladder it needs to be something reliable. Are you using oak or one of the oily hardwoods like Iroko? I have made roof lights ( and lots of external joinery) in Iroko, some are now over twenty five years old and still sound.


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## MikeG. (7 Aug 2020)

I was planning on just having a chain to hold the casement in the open position, say at about 120 degrees. I doubt I'd use oak because of the difficulty in finishing it. I've never used iroko, but I'm open to trying. The glazing will be 6mm toughened glass, I assume.


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## RogerS (7 Aug 2020)

MikeG.":gcs8yabu said:


> I was planning on just having a chain to hold the casement in the open position, say at about 120 degrees. I doubt I'd use oak because of the difficulty in finishing it. I've never used iroko, but I'm open to trying. The glazing will be 6mm toughened glass, I assume.



Some people are allergic to iroko. Maybe get a scrap from somewhere first.


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## Woody2Shoes (7 Aug 2020)

I'd vote for B too. Why not try Accoya? Cheers, W2S


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## Doug71 (7 Aug 2020)

B or that external bead will cause problems at the top end.

Accoya

Probably not what you are after Mike but I have seen skylights made using systems like this avoiding many of the obvious problems of having wood on top of a roof.

https://www.marchesironmongery.co.uk/ex ... ishes.html


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## Mike Jordan (7 Aug 2020)

Allergies can be a problem and Iroko is very variable in working qualities, I currently have a small quantity of 38mm that has worked as easily as softwood together a with some 63mm supplied from the same source which took the edge off the HSS planer knives after about a metre of planing. A change to TCT solved the problem but it's only great advantage is durability.
My roof lights for barges have 6.4 mm laminated glass on the bottom face to ensure that any breakages will not result in a rain of shattered bits of toughened.
Houses don't suffer from boat hooks, fenders, and other items on the roof.


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## toolsntat (7 Aug 2020)

I'd be in for Accoya as well.
Just thinking out the box here but......
Would a three sided stepped glazing unit be taking things to far? ( EDIT to say might not look right for your property )
No need for beads and the glazing silicone should be more than enough to bond to the rebate.
For the top rail how about a full width (of stepped unit) solid section with groove to receive glazing?
Cheers Andy


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## MikeG. (7 Aug 2020)

toolsntat":rdziyem1 said:


> I'd be in for Accoya as well.
> Just thinking out the box here but......
> Would a three sided stepped glazing unit be taking things to far? ( EDIT to say might not look right for your property )
> No need for beads and the glazing silicone should be more than enough to bond to the rebate.
> ...



You mean like a lantern? The opening is only about 600x800, unfortunately. If I had my time over........


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## toolsntat (7 Aug 2020)

No, just flat and sloped like you've drawn but overhanging the glass to the sides as well.
Assuming you can hinge along the top.
Andy


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## MikeG. (7 Aug 2020)

Oh, I see. That would rely just on the silicon, and I'm never going to be happy with that, especially in the middle of a howling gale.


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## toolsntat (7 Aug 2020)

I know what you're saying but it is a pig to separate.
Wonder how modern flush vehicle windows are bonded?
The same system might be applicable?
Andy


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## Droogs (7 Aug 2020)

MikeG.":1l2p4sy4 said:


> Oh, I see. That would rely just on the silicon, and I'm never going to be happy with that, especially in the middle of a howling gale.



here is the link for 3M windscreen glue spec sheet:

https://www.google.com/url?sa=t&rct=j&q ... 9mZp2e_NYy

a quick looks shows this

Performance Properties
Tensile: 1200 PSI
Elongation: 750%
Hardness (Shore A): 50-55
Cure Through: 24 Hours @ 50%RH, 75°F
Overlap Shear Strength:
(SAE J1529) (50% RH, 75°F)
6 Hours 60 PSI
72 Hours 550 PSI


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## PAC1 (7 Aug 2020)

A contrary view!
Type A because I made some windows the wrong way round glazed internally and they failed at the joint (mastic not putty) between the glass and frame. With your type B the weight of the glass is always pushing on your bead because of gravity and pulling the seal between the frame and glass apart. I think it will fail faster than on my vertical windows. I would live with replacing external beads every x years.
I would put a hydraulic ram for the stay because (depending on the size) when you go up the ladder unless you are sure you are well beyond vertical (depends on size and your arm length) the window could come back down and if a gust of wind catches it a chain is useless.
I am allergic to Iroko so I advise avoiding it. I appreciate not everyone is. But it was not a good experience and not one I would wish on anyone. It is not worth the risk when there are alternatives.


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## Fitzroy (7 Aug 2020)

I made one using the system doug71 link to, its been in a couple of years and no problems. I like the capping system as it keeps the sun off the wood so should reduce the maintenance. The capping system does extend quite a way onto the glass so could reduce the visible area. 

I also installed a stepped triple glazed skylight that is just held in the frame by the silicone. I’m confident in it because it is a fixed unit so the glass weight and silicone act together. Not sure I’d be happy on an opening casement. Especially one that will sit past vertical periodically, then the silicone would be the only thing opposing the glass weight. 

Fitz.


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## Woody2Shoes (7 Aug 2020)

Just for the record - the stuff holding the DGU together will probably be a urethane or polysulphide based compound and will only be compatible with certain other sealant gunk (not necessarily silicone-based ones) e.g. https://hodgsonsealants.com/wp-content/ ... alants.pdf

I think that failure to recognise this potential chemical incompatibility is probably a source of more DGU failures than most people realise. I also think that a drained rebate is a great idea with DGUs - moisture *will* get into the rebate at some point, it needs to get back out again asap - I realise that this is potentially quite tricky with a (near) horizontal setup. On the windows and glazed doors I've made, all rebates have drain holes/channels to the outside (apart from anything else this helps to equalise pressure on both sides of the DGU, which might otherwise tend to push moisture where it's not wanted).


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## MikeG. (7 Aug 2020)

I've a pretty simple route to vent/ drain the rebates:


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## Woody2Shoes (7 Aug 2020)

MikeG.":3b6hfo3t said:


> I've a pretty simple route to vent/ drain the rebates:



Looks good, maybe a gutter along the rebate too?


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