[Sunnyside]

A recent question from one of our customers:

Hello

Am investigating a polycarbonate twin wall roof option.

Polycarbonate 8mm twin wall (grey) 610mm wide X 2400mm long X 14 pieces
Joiner 2400mm X 13 pieces
Outside end flashing 2400mm X 2
Inside end flashing 2400mm X 2 this butts onto a plywood wall
Ridge
I was going to provide a support under each joiner, therefore the only fasteners would run through the joiner, is that how it works?

[Sunnyside]

Our answer:

Thanks for your enquiry.

This is for the 8mm grey at 610mm wide. They are easy to trim to size with a sharp knife or hand saw. We can usually get them trimmed at factory, but unfortunately this isn’t an option for our South Island orders.

You’re correct about the joiner. If that’s sitting on a rafter, then you can put a screw through the bottom plate of the joiner, every 400mm or so. You won’t require a fastener through the Twinwall sheet itself (since it’s only spanning 610mm) as that will be held down by the joiner, once you snap the top plate into place.

I’ve also included the aluminium F channel. This can be used flange facing down on your outside edge. You can fasten the flange through the barge capping on the outside edge, to hold that edge down.

You can then use another F channel on your inside edge. You’d put this one flange facing up the plywood wall, so it would work like an apron flashing. You can also fasten the flange through the plywood, or simply glue it if you don’t want to pierce the cladding.

Lastly, I’ve put some sealer and dust tape in (sealer tape goes at the top edge, dust tape at the bottom edge). The U end cap fits over both tapes to protect it and hold it in place (including under the ridge capping).

I’ve included a 6m ridge capping, the one I think would be most suitable.

[Sunnyside]

Another recent question:

Looking at using Twinwall 610 x 4000 x 8mm sheets, joined using H snap joiners. Can you please confirm the rafter centres measurement between sheets? I’m getting 640mm to allow for thermal expansion (610 + 15 +15).

Also, can i use the off cuts from the 5.8m H snaps and combine them on another sheet (as losing 1.8m per 4.0m sheet)?

Our answer:

Thanks for your email. 640mm is correct.

So if the sheet goes flush to the edge of the first rafter, it will need to be 625mm from the outer edge of that rafter to the middle of the next rafter. Then each subsequent rafter can be 640mm from the centre of that rafter.

Depending on how square the structure is, you may want to make it 10-20mm narrower (or more). Sometimes you may need to make it slightly out of square in order to accommodate existing house/walls etc. Especially over 4m.

It’s much easier to trim the sheets down a bit (with a sharp knife or handsaw) than it is to be slightly too narrow in some places!

But if you’re confident it’ll be completely square and won’t need to trim the sheets then 640mm is right.

You can also use the H snap joiner off-cuts. If you cut them dead square then they but together fairly well. You can use a bit of sealant (suitable for polycarbonate) if you like. But otherwise, even if a very small amount of water gets in through the join it’ll just run down the inside of the joiner channel and out the end.

[Sunnyside]

An important note, our Laserlite 2000+ Twinwall has UV protection on both sides. So either side can face the sun.

[Kevin Mills]

I am looking at using Twinwall (clear) to reclad an existing timber-framed greenhouse. When installing the Twinwall, do the joins between sheets need to be located over the studs/rafters, or can the sheets be joined with joiners at any point (say midway between studs), with the sheets screwed to the studs/rafters wherever they are located. Alternatively, is it better to trim the sheets to match the existing stud/rafters spacings. Thanks

[Sunnyside]

Hi Kevin, thanks for your query.
It’s generally better to trim the sheets to join on the studs/rafters, however this sometimes means wasting a lot of the sheet. You can definitely join it midway between studs, as long as there is sufficient support for the joiner, say nogs/purlins no more than 800mm apart. If there isn’t sufficient support, you could always add some where the joins will fall. In a greenhouse situation you probably will only get the wind from the outside, pushing the sheets onto the structure anyway, so it shouldn’t be an issue.
Hope that helps! Kurt.

[Kevin Mills]

Thanks for reply. Another question – the greenhouse has now become a greenhouse/potting shed that will have a roof of half Twinwall and half corrugated iron. Can you suggest a detail for where the two meet. Thanks.

[Sunnyside]

No worries. Will the iron be running onto the Twinwall, or the other way around? If the iron is running onto the Twinwall, you can just overlap it say 300mm, and you could put some corrugated foam infill in-between to seal it. If the Twinwall is running onto the iron, you could do a similar thing. Or have an apron type flashing with a soft edge, so the Twinwall runs onto that, and the flashing then runs onto the iron with the soft edge forming to the corrugations.
Thanks,
Kurt

[Kevin Mills]

Thought I had better clarify my last question. Roof is one plane surface at 10 degrees. Structure is approx. 5m long x 2m wide. Roof slopes over the 2m width. So, half of the length will be Twinwall and half corrugated iron, with the longitudinal direction of the iron and Twinwall running over the 2m width. The junction between Twinwall and iron is parallel with Twinwall cells and the iron corrugations. Hope that is clear, as I think your suggested solution assumes then join to be running the other way.

[Sunnyside]

No worries, thanks for clarifying. I had assumed it the other way. In this case, some sort of capping might work, depending on how watertight you want it. Otherwise an easy way would be to lap the iron over the Twinwall, with some closed cell foam (similar to thermal/camping mat material) in-between the edge of the iron where it sits on the Twinwall. This would protect the sheet, as well as seal the gap pretty well.

[bob kerr]

Thinking about a curved roof structure. Will the Twinwall bend, if so how much? (5m sheet).
Thanks.

[Sunnyside]

Hi Bob, it can handle a fair amount of curve. See page 5 and 6 of this brochure for details:

https://sunnyside.co.nz/wp-content/uploads/2018/03/Laserlite-Twinwall-Brochure-web.pdf

Thanks,

Kurt

[Kevin Mills]

Just starting to install Twinwall on the walls of the greenhouse and have a couple of queries. Firstly, the installation brochure on the website talks about screwing the H-joiner to the studs with self-tapping screws and elsewhere to use screws with neo washers – which is correct? If screws with neo washers is correct, do I just use normal roofing screws. Secondly, when screwing the Twinwall to the studs, the installation brochure says to provide a larger screw hole to allow for expansion/contraction. Do I just drill a larger hole before final screwing, or can I use something similar to the screws used for the corrugated polycarbonate roofing, i.e. the screws that have their own cutters to provide the oversized holes. Thanks again.

[Sunnyside]

No worries. You can use any screw suitable for outdoor applications to screw the H-joiner to the rafters/studs. It doesn’t need to have a neo washer. Usually a pan head or button head works best as they have a nice flat head on them. Normal roofing screws for the joiner would be fine too, as long as the head fits inside the middle channel of the joiner.

For screwing the Twinwall on, just drill a larger hole (10-12mm) before putting the specific Twinwall screws in (these ones have the neo washer). The screws used for polycarbonate don’t work on Twinwall. The cutters tend to get jammed up in the double wall, and the washers are too flexible for a flat surface.

Thanks,
Kurt

[Michel de Boulay]

Hi Sunnyside team, just about to install twinwall on a new greenhouse and was wondering if I can use roofing screws you would normally use for colour steel roofing applications. I seem to have heaps of them in my shed.

Cheers
Michel

[Sunnyside]

Hi Michel, no worries. We have special Twinwall screws with an aluminium washer and a neoprene washer underneath. They’re usually slightly bigger than standard roofing screws. However, since it’s for a greenhouse and I guess it wouldn’t matter too much if a bit of water got through, you could use normal roofing screws. Just make sure you drill an expansion hole (as large as you can, it won’t be too large since the washers are smaller).

Cheers,
Kurt