Polycarbonate overhang and guttering

[OldKettle]

Hi,
I have built the timber frame of an attached pergola, out of 2x6 timbers, with 100x100 posts, per the design below.

The angle of the rafters is 5 degrees, and I have added two noggins between each pair of rafters.

I want to add a polycarbonate roof and a gutter to run along the cross beam. I will be running roofing battens at 400mm centres under the polycarbonate, and intend to use this stuff for the roof.

https://www.toolstation.com/corrapol-stormproof-sheet/p36591

I would just like to get some advice on how far to overhang the polycarbonate from the crossbeam and where to position the gutter relative to the edge of the polycarbonate.

I have left approx 100mm of overhang at the moment, which I can trim as needed.

Any thoughts would be much appreciated.

 

[tell80]

I'm assuming that you have falls to the rafters? 1:40 is a min.
Using a string line set your gutter clips - set them high up the rim joist.
Clip your gutter to the rim joist - the gutter must also have a fall to an outlet and down pipe.
The polycarbonate should overhang the gutter by about 30mm to 40mm

 

[OldKettle]

I'm assuming that you have falls to the rafters? 1:40 is a min.
Using a string line set your gutter clips - set them high up the rim joist.
Clip your gutter to the rim joist - the gutter must also have a fall to an outlet and down pipe.
The polycarbonate should overhang the gutter by about 30mm to 40mm

Thank you.

The fall is 350mm over 4500mm, which I believe is 4.5 degrees or 1:13.

Could you please advise on what the minimum fall for the gutter should be? I have read elsewhere that 12.5mm over 3 metres should be sufficient, which I think is 1:240. The structure is actually 8.5 metres long now, so would need a fall of 35mm on that basis. Do that sound right?

With regards to the position of the gutter and the poly, would it make sense to trim the ends of the rafters flush with the rim joist, something like this?

 

[tell80]

Whatever works so that you have the 30 to 40mm poly overhang.
Same with the gutter just so long as it falls - water test it before any final fixing.

 

[foxhole]

I always fit gutters level, rain knows where the outlet is .

 

[big-all]

corrugated will be noisy in the wind as you need cross support to stop it flapping in the wind
i have cross batons every 2 foot with a fixing each edge and central on my 2ft [i think it is ]wide sheets

 

[OldKettle]

corrugated will be noisy in the wind as you need cross support to stop it flapping in the wind
i have cross batons every 2 foot with a fixing each edge and central on my 2ft [i think it is ]wide sheets

Thanks.

I plan to run 25x50mm horizontal purlins at 400mm centres, which is what the polycarbonate manufacturer recommends.

Install guide here - https://www.clearamber.com/brochures/1584547844CORRAPOLINSTALLATIONGUIDE_WEB_V1.03.pdf

Will probably be using these

https://www.travisperkins.co.uk/roofing-batten/treated-roofing-batten-25-x-50mm-4-8m-bs5534/p/233475

Manufacturer also recommends fixings at every corrugation at the eaves and joins, and every other corrugation on intermediate purlins. I reckon that it about 65 fixings for a 4 metre sheet (minus perhaps 10, where the sheets overlap by two corrugations).

Do you think that will be sufficient to minimise noise, or should I still expect it to be noisy in the wind?

 

[foxhole]

Needs loads of fixings, has some melt in the sun and return to flat sheet, manufactures said not enough fixings.

 

[big-all]

i would say you will be fine to be honest with my set up and i have one every 4th hump its only at all noisy when the wind is playing mary poppins with fence panels so no big deal
i have a triangular moulding at the top to both shed the water off the wall and cover the gap at the top
the rain will annoy you more
and DONT overtighten the clips at it will cause all sorts problems

 

[big-all]

another point
2x1 tile batons are great and should be ok but are not structurally graded and can have many knots so will need careful selection buuuuuut------
---in this instance i think 2x2" timber would cosmetically look better as you are using substantial timbers
which way up where you thinking as flat would be least strong and upright will be hit and miss with the fixing

and another point you cant reach say 800mm away to put a screw in without something to lean or sit on

 

[noseall]

Gutter overhang = 60mm.

 

[big-all]

i mean reaching the securing screws when you slide the next sheet under the last one then screw in the row off screws at the far side off the now inserted 950mm wide sheet
https://www.toolstation.com/corrapol-stormproof-sheet/p36591

 

[tell80]

Post #5,


Without using falls try setting a gutter on three sides of a semi-detached house with one outlet available, & see what water damage, & expense might result for a householder?

Without setting a fall to outlet how will "rain know where the outlet is" when the OP's gutter is filling with debris & leaves?

What if your idea of "level" sags a few mm's and creates a pond beyond a debris dam?

What if your nonsense is contrary to the Bldg. Regs?

 

[OldKettle]

Thanks for all of the advice so far.

I have decided to go with 1x1 for the purlins. Even though I need about 90 metres of them (if I go for 400mm centres), I have found some locally which will only cost another 50 quid overall.

I have also bought a section of gutter (went with 112mm half round), that I can use to test with the first sheets (I have only ordered a couple of sheets for now).

As for reaching to fix on the overlapping edge, I think I will be OK reaching over with a bit of boarding to spread the weight.

 

[big-all]

just be aware any load will tend to flatten the humps a bit so start to distort and extend the sheet width so lay the next sheet in loose and mark on the timbers where the edge should be in at least 3 points along its length this will help you work out iff you are building up problems so you can adjust to bring back in line