My first roof

[Ben100]

Hi all,

 

I've just started my first roof on my extension and have a few question.

 

The design is like so.

 

1. Timber frame, with pre-built trusses

2. Exposed rafter tails

3. OSB sheet material over exposed rafter tails to hide the felt/membrane and battens

3. Felt/membrane over OSB with enough overhand to go into the gutter when installed

4. First batten to create a kick-up on the bottom tile

5. Additional battens to fix tiles

6. 20/30 tiles for 30 degree pitched roof

 

How does this design sound? Am I missing anything?

 

One concern I have is with the OSB and felt. The OSB creates a flat surface for the felt to site on, and the battens fix firmly to the OSB and rafters. This means that I do not have any gap between the last 2 battens and the felt. Is this an issue? The other felt and battens have a small gap between them so any water can escape. I'm concerned that water may/will get stuck here and rot the lower battens?

 

Thanks in advance for any advice!

 

Ben

 

 

 

Edited August 29, 2021 by Ben100

[ProDave]

Sheet the WHOLE roof in OSB, the Scottish way, we call it "sarking"  It makes for a so much better roof in so many ways for little extra cost.

[Ben100]

18 minutes ago, ProDave said:

Sheet the WHOLE roof in OSB, the Scottish way, we call it "sarking"  It makes for a so much better roof in so many ways for little extra cost.

Could do, but it’s probably a bit overkill for the south of England ?

 

But that does raise a question. How do you allow water to run out under the battens if you fix them to the flat OSB?

[James Newport]

Counter battens that follow the line of the rafters, then fix the tile battens to those. 

[James Newport]

41 minutes ago, ProDave said:

Sheet the WHOLE roof in OSB, the Scottish way, we call it "sarking"  It makes for a so much better roof in so many ways for little extra cost.

Her in South Wales, our joiner called it scotchboarding. 

[Ben100]

8 minutes ago, James Newport said:

Counter battens that follow the line of the rafters, then fix the tile battens to those. 

Again, counter battening seems a bit overkill for just the bottom two battens. Maybe I can lift the problem battens a few mm using shims or something similar? 

[Onoff]

Tack some 50x6 ply strips over that bottom OSB up the line of the trusses?

 

If that OSB is just to hide the battens/felt, then cut pieces that sit between the truss ends rather than on them? You'd need a little batten either side flush with the truss tops then screw the infill up to them.

 

Overall though I'd agree, OSB the lot and counterbatten. 

 

I'm in the SE too btw. Has other benefits, felt sag allows vermin in. Ask me how I know! ?

[Ben100]

Thanks guys, all great information!

[makie]

1 hour ago, ProDave said:

Sheet the WHOLE roof in OSB, the Scottish way, we call it "sarking"  It makes for a so much better roof in so many ways for little extra cost.

 

OSB is overkill for that, counter-battens down the rafters would be more than enough. (the cost is definitely not little now anyway)

Also sarking is small boards around 150mm wide, not OSB.

[Dave Jones]

On 29/08/2021 at 18:14, ProDave said:

Sheet the WHOLE roof in OSB, the Scottish way, we call it "sarking"  It makes for a so much better roof in so many ways for little extra cost.

 

at £45 a sheet, hahahahha

 

you could have used the black plastic eaves trays instead of osb, stapled to the truss then membrane over and batten nailed through.

[Ben100]

19 hours ago, Dave Jones said:

 

at £45 a sheet, hahahahha

 

you could have used the black plastic eaves trays instead of osb, stapled to the truss then membrane over and batten nailed through.

 

Wouldn't you end up with the same issue? The plastic eaves tray would stop the membrane from sagging in between the rafters and allowing any water out.

[Dave Jones]

the trays are purely aesthetic so when you look up from underneath you just see black rather than membrane. You can use osb and paint it black if you have money to burn.

[Onoff]

I'm all for reinventing the wheel believe me but I did wonder why you didn't go for plastic eaves trays in the first place.

 

If you read the instructions on some of the modern, breathable felts it specifically says about fitting 1/4" thick or so strips along the line of the trusses so the subsequent battens sit up off the felt and allow free drainage. 

[scottishjohn]

13 hours ago, Onoff said:

I'm all for reinventing the wheel believe me but I did wonder why you didn't go for plastic eaves trays in the first place.

 

If you read the instructions on some of the modern, breathable felts it specifically says about fitting 1/4" thick or so strips along the line of the trusses so the subsequent battens sit up off the felt and allow free drainage. 

single batons will always cause a gather up of dust and bugs over time which is then a condensation dam  it then holds  damp and causes rot 

I would always for sarking   it will always be stronger +stiffer in wind loads and  make it easy to work on the roof while tiling  or slating it

 

[Ben100]

On 31/08/2021 at 18:37, Onoff said:

I'm all for reinventing the wheel believe me but I did wonder why you didn't go for plastic eaves trays in the first place.

 

If you read the instructions on some of the modern, breathable felts it specifically says about fitting 1/4" thick or so strips along the line of the trusses so the subsequent battens sit up off the felt and allow free drainage. 

Yeah, after thinking it through a bit more I ended up installing an plastic eaves tray.