6mm solid clear polycarbonate roof

Doing a lean-to car port type structure to side of house. Timber rafters at 600mm centres. 9 degrees pitch. Using 2 sheets of 3050 x 2050 6mm solid clear side by side. Obviously need to drill for washer fixings. Diam of screw is 6.3mm so plan to drill 8mm to allow for movement. I have been advised to fix every 600mm ctrs in both directions which means 24 per sheet. Is this excessive ? Any advice for drilling as it will need to be done insitu. Do I need to place anything between the poly and top of timber rafters ? I will use glazing tape at perimeter to seal and fix angle over for weathering. Because of sheet size I will need to lie on polycarbonate to drill and fix at some locations. Any tips on how best to protect.

Hi Sam,

Just wondering if you completed this project please? Did you go with the 6mm solid? And at what rafter/purlin spacings? Much flex in the polycarb? What did you use between the polycarb and the timbers? Foam strips? A bead of silicon? And a glazing bar to join sheets? Or overlap detail?

I'm doing a pergola at the back door, which is north facing - I also don't want to use twinwall or corrugated (looks crap and less light transmission).

I had planned rafters at 1m centres and purlins also 1m centres in the other direction. It's 4m X 4m total size. I've sourced 6mm solid polycarb sheets 4000mm x 2050mm @ €367.45 per sheet, so two of those. I suspect I should reduce the purlin spacings to 500mm centre though?

Any feedback on your experience much appreciated! Thanks, Pat.

Hi Pat

Yes went with 6mm solid clear and worked out well.
Purlins are 200 x 50mm @ 600 ctrs - well over-sized but I was matching in with adjoining epdm roof which is t&g on 175 x 50.
There is flex in the sheet for sure but only when handling or fixing. When in place it looks just like glass.
For the top of the purlins you can see a grey one sided tape:
Scapa® 3507 PVC Single Sided Foam Tape 25 mm X 30 mtrs Thickness 2.5mm sourced online from Self Adhesive Supplies.
Nut sure if this is absolutely necessary but I felt it no harm to cushion the poly.
My pitch is 9 degrees so I was confident about my overlap detail as per photos.
Basically one sheet is 25mm higher that the other (2x1 batten on rafter) and overlap is circa 150mm.
Your pergola is probably close to flat to I suggest a proper glazing bar detail with gaskets and capping.
The one thing I did underestimate is the physical handling of the sheets and getting them up into place.
They are heavy and awkward, you will need a few pairs of hands and I see yours are bigger than mine !!
I had to make up a sort of a pulley / lift like this to get mine up The sheet is easy to cut using correct blade, I had to notch mine around a pier. Drilling also easy too, again with correct bit.
Don't forget to oversize holes to allow for expansion.
For the fixings I went with these from ACCU:
https://www.accu.co.uk/en/sealing-raised-pozi-wood-screws/377517-SPRKSW-4-5-70-25-A2
Used the longer ones on upper sheet to go through extra batten and the 55mm for the lower sheet.
Just preferred the lower profile as opposed to the standard hex head cladding screw.
Kneeling or walking on sheets is probably unavoidable. I just used small sheets or ply placed on a blanket to avoid scraping the sheet.
I have walked on it since and followed lines of purlins and all fine.
Use neutral curing silicone for sealing fixings.
Come back if any more queries or send a pm

Hi Sam,
Great looking job - well done. Thanks for taking the time to write such a detailed reply. Really very useful for me!

Glad to hear the 6mm poly is pretty solid when installed - judging from your photo and sheet sizes, your poly is supported on 4 sides at 600 x approx 2000? So if mine is 1000x1000 hopefully will be solid enough.

The foam tape is a good idea, will definitely do similar I think.

That lift is v clever. Would certainly be awkward so will have to think hard about how to lift them up. Not a job for the ladder anyway.

Can I ask specifically what blade you used to cut the poly? And what bits to bore?

Your detail re the join is very tidy. As you mentioned, mine will be "flat", maybe 5 degrees just for rainwater runoff. I'll have one join between sheets so might have that run longitudinally down the slope (rather than across it like yours) and use a simple H channel to join the sheets, which hopefully should be then hidden along the top of the rafter.

Mine will also be lean-to into a pebble dashed wall - did you grind a channel for flashing? Lead?

Just on the centres of supports, you better check with supplier. My supplier suggested supports at 500/600mm ctrs so 1m might be pushing it.
I sourced specific drill bits and jigsaw blades for plastic / plexiglass.
Might be OTT but just didn't wan't to take a chance based on price of sheets and having not worked with poly before.
Here's the drill bit:
https://www.fine-tools.com/kunststoffbohrer.html
The jigsaw blades I used are Bosch T101A sourced from Toolstop.
The H section for joint should be fine with plenty of clear neutral mastic. I assume this needs to be supported so ensure you have a rafter under.
I did look at it for mine but it's not recommended for going across the roof, ok for going in the direction of the fall so good for you.
On the flashing, yes I got a friend to consaw a cut but instead of lead I got an aluminium angle flashing made up by a local cladding supplier.
Just filled to cut with mastic and pushed the flashing into place, another bead of mastic across the top.
Flashing was easier to slot into place mean less work on the poly.
Make sure you chase before fitting the poly. Flashband tape another option but I'd imagine once stuck to the wall and poly there's no going back !

Thanks again for the info Sam. Just to give a bit of feedback to you and anyone else looking to do similar job....

I finished the job - a 4 X 4m lean-to pergola, using 4" posts mounted on poured concrete footings using galvanised 100-150mm Height Adjustable Elevated Post Base Support (Size: 100 x 100mm) https://www.amazon.co.uk/dp/B085BW29NG/ref=cm_sw_r_apan_glt_fabc_R51W1YZT6BF72VHMQS71.

Wallplate/ledger, cross beam and the rafters were all 6x2's. I used larch timber as it's a bit more dense than white/red deal etc. And I had intended oiling it with osmo UV oil, but I felt it looked like a an extension waiting to be finished, so ended up painting it in the end.
I used 7 rafters, so at approx 667mm centres which I think turned out to be plenty close together for the 6mm solid polycarbonate sheets. I reckon 1m spacing might have been too far apart but not by much - they're v solid. I used two sheets each measuring approx 4 X 2 m (manufacturer cut them to exact sizes for me).

As Sam mentioned, it was v difficult to get those v large sheets up onto the 3m high roof, without marking the strong, but somewhat soft and so easily marked, polycarbonate - I made a large holder/frame from transverse 2x2" lengths and then fixed two more, long 2x2" lengths onto the end of the rafters sloping down to the ground - I then slide the frame up that ramp. Then myself and my brother, on ladders, slowly moved the sheets sideways off the holder/frame onto the rafters.
I actually ordered similar foam tape to place on top of the rafters to cushion the poly - but didn't use it in the end and I think it's grand.

To join the two sheets (joint runs down the 15 degree fall, hidden on top of the middle rafter), I just butted the sheets together with a bead of silicon between. Not perfect but the pergola is open to the sides so I don't mind if it's not 100% dry (although no drips so far after a month). Similarly, I just butted the sheets up to the wall over the wallplate. Dry enough for my purposes (there's a big eave/overhang on the house roof so that helps).
Lastly I drilled 9mm holes in the poly and used 6.3x45mm grey Tek roofing screws to fix the sheets to the rafter (Easydrive Timber Roofing Double Slash Point Screws - Screwfix). Oversizing the holes is necessary for the expansion/contraction of the sheets.

And then added some planters and made a small gate to keep our little locked fella in! Thanks again for the info Sam. Good luck to anyone embarking on similar. Pat.

Hi! I know it’s been a while but I wanted to ask how these applications are working for you guys? Anything you’d do different?

I currently have corrugated clear panels and want to replace with solid PolyCarb. Trying to figure out what thickness, size sheets I need and what modifications to my current set up I will need.

I was hoping to have at least 36in width opening (yes, I’m the US. Had to do some converting on these numbers, A little less than a meter) but, after reading your posts, I’m afraid it would sag.

36 inches = 3 feet = 914.4mm. That is wide. Is this an existing structure with timbers at those 3 foot centres ?
Is flat multiwall sheeting an option for you - those spans might be ok with a thick multiwall.
Your supplier should be able to advise.
If you are set on clear poly then I suggest you consider providing additional rafters in between existing to make span a foot and a half.
I am happy with my installation but it does go green with algae etc but nothing a power wash a couple of times a year wont sort.
Here are the 2 main suppliers in Ireland which have some good technical info and videos:

https://www.plasticsolutions.ie/

https://365plastics.ie/

Its easy to think you are over fixing things - say at 600 centres when you are doing the job on a nice warm sunny day but its a good idea to remember how bad the wind can get and you will be glad for that few extra screws.

Hi, Guys
I appreciate the responses. Currently I have the corrugated sheets that are very thin and lightweight, so my minimalist pergola has worked out pretty decently. I have had wind issues! ...... but only because the 2x2"(50mmx50mm) purlins were nailed in, not screwed, and only driven in an inch (25mm). Might as well have velcroed it on. The panels themselves have held on surprisingly well.

I prefer to have as few bulky Rafters as possible, so thought if I had 36in (914mm) spaced rafters, I could have smaller profile cross supports every 2-3ft. (609-914mm).

The multi-wall has been suggested. I am considering it as it is a significant price difference and would actually provide some thermal insulation, which would be nice, as our summers here can get into the mid 40's C.

Honestly70 said:

Hi, Guys
I appreciate the responses. Currently I have the corrugated sheets that are very thin and lightweight, so my minimalist pergola has worked out pretty decently. I have had wind issues! ...... but only because the 2x2"(50mmx50mm) purlins were nailed in, not screwed, and only driven in an inch (25mm). Might as well have velcroed it on. The panels themselves have held on surprisingly well.

I prefer to have as few bulky Rafters as possible, so thought if I had 36in (914mm) spaced rafters, I could have smaller profile cross supports every 2-3ft. (609-914mm).

The multi-wall has been suggested. I am considering it as it is a significant price difference and would actually provide some thermal insulation, which would be nice, as our summers here can get into the mid 40's C.

Click to expand...

I think the multi wall thermal benefit is for the other end of the "C" scale to help keep the heat in the winter but makes no difference with 4 open sides.

What I understood was that it helped with the heat transfer to what is below, like when you are under the shade vs direct sunlight, not with actual atmospheric temps. lol.

Honestly70 said:

What I understood was that it helped with the heat transfer to what is below, like when you are under the shade vs direct sunlight, not with actual atmospheric temps. lol.

Click to expand...

I see but with regular 40C in your summer months I think you are the expert, 40c in the Uk and the country literally starts to melt

We ARE melting. The last few years have gotten pretty bad. Summers we get to 112F and we are by the gulf coast so it’s also With humidity. Imagine a wet sauna…. That’s what some of our days feel like. If you were ever inclined to, don’t visit texas between late July-mid Sept.

Doubt you'll get an thermal properties with polycarb or multi-wall panels, especially if the structure is open on the side.

Last year in the UK we did hit 40°c (a rarity I know) and my canopy (16mm twin-wall) faired well, it does cut down the sun's intensity, but it was still hot. My centres for my panels are 690mm, the panels came in this size.

I've just removed a friends canopy that was bodged by a contractor these were 800mm centres, everything was saggy.. as it was all under spec, the wood too thin and far apart, the glazing 6mm twin wall, no proper glazing bars, blah blah blah.

I've been using products from here, not the cheapest, but a good range of items.

Clear Amber