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I'm building a shed this summer. The plan is to use a stud frame construction. Cover it in 12mm OSB3 and a breather membrane to keep the interior dry and use feather edge as the cladding. The thing I am wondering is should I put the feather edge on rails or directly to the OSB3 through the breather membrane? I've seen it done it both ways online

It's pressure treated pine. I've planned a 20cm roof overhang so I am not planning for it to get soaked on a daily basis but I want to be on the careful side.

Using rails should mean there is a 40mm air gap between the backside of the feather edge and the breather membrane so if moisture accumulates on the backside of the feather edge there is some air movement to let it dry. This has the added advantage of meaning less holes through the breather membrane.

Without using rails mean less material will be required and I can use fence posts for the edge similar to this video on Youtube by Colin Furze. Seems like he knows what he's doing and lives in the same climate as me (UK - so moisture is gonna be a bit of an issue).

https://youtu.be/LP67MAoihZk?t=110

If anyone has got any experience doing it one way or another then advice would be greatly appreciated.

Cheers.

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  • A 40 mm gap would be larger than what I read about. I thought 3/4" or 20 mm was usual. This gap would be perfect harbourage for roaches and other undesirables so provision must be made for excluding them at the top and bottom. There used to be a Tyvek wrap optimized for lap siding which had micro channels which supposedly would give some drainage but would not provide space for bugs. Jul 25, 2020 at 17:25
  • In the US the installation of plank siding on vertical battens is called a rainscreen wall. There seem to be many versions. Jul 25, 2020 at 17:36
  • @JimStewart Apologies. I meant to say 25mm not 40mm. I was gonna use Roof Batten which are 25 x 38 since for some reason both 19 x 32 and 19 x 38 are more expensive. I think it's because 25 x 38 is the standard size so is more of a commodity product.
    – Geoffry
    Jul 25, 2020 at 18:11
  • I wonder if mice could move behind a 25 mm gap, but not a 19 mm gap? If 19 mm is standard, then going to 25 mm might not be a good idea. I had to repair a section of lap siding (8 inch lap-and-gap) on an exposed west corner of our house where the bottom four courses had rotted. I investigated redoing the whole wall as a rainscreen, but in the end just replaced the lower third on the courses. I used new plywood sheathing, generic tyvek type wrap, then the new courses of cedar lap-and-gap directly onto the house wrap. I did use stainless steel ring shank siding nails. Jul 26, 2020 at 2:24

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It's really a matter of prerogative (which is why you get varied suggestions), but it sounds like you have your answer. You want to be "careful", which I interpret to mean you're willing to put in the extra expense and effort to get additional longevity. It might last 40 years instead of 30 if you let it breath.

In my experience, lap siding is installed directly over sheathing/house wrap. Wall shingles tend to be installed over strips, but that's because they tend to let more water through all the extra joints. Your mileage may vary.

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