Perspex screw type and upper or lower part to fix

2012paddy2012

This is a job done. I don’t think he should have put the screws he used in the lower part of the Perspex sheet , I thought it should be through the higher part and put just tight enough to allow a little expansion.

Question:
Which part of the Perspex should be fixed to the bridges?
Is the screws he used long enough.


Reason: I’ve just completed side entrance to cover over. I’m getting Perspex Monday , so I’m preparing for that I want to get correct length of fittings and know where the fittings should be affixed to on the sheets.

Thks

Lumen

This is interesting.

Note the fixing through the valleys and the use of foam support, but the seals on these screws look much more flexible than the usual rubber-washered tek screws.

edit: it looks like the preview pic shows fixing through the peaks, but the video shows fixing through the valleys. Valleys seems madness, though I do like the look of these screws.

https://www.youtube.com/watch?v=sk2__zxXRRc

GreeBo

Surprisingly you are always supposed to screw through the troughs!
It gives a firm fixing and the rubber washers on the screws can be compressed and be watertight.
If you go through the peaks you cant get a good fixing (unless you have a solid support) and so the roof will flex and you are actually more likely to get a leak.

Padre_Pio

GreeBo wrote: »

Surprisingly you are always supposed to screw through the troughs!
It gives a firm fixing and the rubber washers on the screws can be compressed and be watertight.
If you go through the peaks you cant get a good fixing (unless you have a solid support) and so the roof will flex and you are actually more likely to get a leak.

I always thought it was through the top, it never have runs of water and always dries first. Never bothered leaving space for expansion.

My thinking was that a screw in a trough was likely to leak, then soak the wood, then rust through the sheet from the inside. Are the rules different for galvanise and PVC?

stoneill

He says in the video the fixings can be used on hills and valleys.

2012paddy2012

stoneill wrote: »

He says in the video the fixings can be used on hills and valleys.

I think that the thinking is to screw them on the hills as the water runs off along the valleys. But really does it make much difference to the life of the screw if the water runs off around it in the valleys or the screw is soaked in the hills.
I don’t know the answer but I wouldn’t have thought that it would make that much difference.

I think it’s handier to fit them in the valleys , just bearing in mind the expansion that will naturally occur with plastic. Otherwise after a while the Perspex will just break round the screw