Repair rotten Pergola beams

[elmag28]

Hi,
I will be grateful for some advice regarding repair/ replace parts of pergola roof beams which have gone rotten in areas towards the ends.
Can I just do a step or angle cut & replace the rotten part only or should whole beam be replaced.
Secondly, I want to put a polycarbonate roof later this summer.
Which thickness is reasonable- 10, 16 or 25 mm. The joists are at 50 cm centres & I was planning to use 1m wide sheets with glazing bars.
Any recommendations for polycarbonate & glazing bar value for money brands/ suppliers.
Thanks

 

[Deleted member 323070]

As the timber will be visible below the polycarbonate, it makes sense to replace the complete beam.

The different thicknesses of the polycarbonate offer varying degrees of insulation, sound transmission, etc.
As the sides are open to the atmosphere, there's no point in using thicker sheets of polycarbonate.
10mm will suffice.
But 16mm is stronger and allows for fewer supports.
25mm would be used for conservatories due to its enhanced insulation qualities.

 

[foxhole]

https://www.nationalplastics.co.uk/clras10c30-axiome-clear-polycarbonate-sheet-10-1400-x-3000.html

I used 1400mm x 3000mm sheets as it suited my dimensions [3mx7m].With a simple "H" push fit joint strip.