advice on roof rafters and underfelt

[nottsrob184]

Hi all.
I am not experienced with roofs just a diy'er looking for some advice.
I am building a single storey rear extension 7.6Mtr x 4Mtr.
I have just ordered the 7x2 roof rafters and ceiling joists. These have come untreated and builders merchants says thats standard.
Do i have to treat them? and if so what with?
Next question is...i am using breathable roof felt (advice from building control inspector,....Do i have to use a polythene sheet under it, or can i fix the felt direct to rafters then batten and tile?
I am using Marley Melbourn tiles...so any advice on them would be appreciated especially regarding how to finish the sides (verges) and what flashing to use.
Thanks so much.

 

[SASroofer]

Cuprinol the joists, make sure the battens you buy ARE already tanalised though.

Fix the felt straight to the rafters, dont allow to sag between them, and batten over.

This site has all the info you need. Good luck.

http://www.marleyeternit.co.uk/Roofing/Slates/Melbourn-Interlocking-Slate.aspx

 

[^woody^]

Generally roof timbers do not have to be treated unless the work is in the areas of the UK susceptible to Longhorn Beetle infestation (Home Counties or thereabouts) but its good practice to use pressure treated timber in any case

You don't need to bother treating the timbers now, but you should treat the cut ends - specifically at the eaves. Use any suitable preservative or specific endgrain product

No polythene required

Don't forget your plastic eaves tray and corrugated vent to keep the insulation down at the eaves