Sarking

[Big Neil]

I don't quite understand another thing, please can someone in the know confirm. I get that Sarking boards increase the strength of the roof as a whole. What ideally should they be made out of? Can you just use normal sheets of say OSB or Ply etc? I know there are plenty of other products available, But is there a specific reason why you wouldn't use either of these for example. Also, If i've read correctly the membrane goes on top of the rafters but under the sarking? Why?

 

Thank you all once again.

 

 

[Jeremy Harris]

Our sarking is 18mm OSB.  The last house we owned when we lived in Scotland used ~9mm birch ply as sarking.  Traditionally it used to be planks that were spaced a few mm apart, but it seems that now pretty much anything could be used.

[SteamyTea]

  On 14/05/2019 at 12:04, Big Neil said:

Also, If i've read correctly the membrane goes on top of the rafters but under the sarking? Why?

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I would like to know that too.

[scottishjohn]

  On 14/05/2019 at 12:21, SteamyTea said:

Also, If i've read correctly the membrane goes on top of the rafters but under the sarking? Why?

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that seems wrong to  me 

water proof/ breathable membrane is last thing before tile batons  surely?

 

[Big Neil]

  On 14/05/2019 at 12:17, JSHarris said:

Our sarking is 18mm OSB.  The last house we owned when we lived in Scotland used ~9mm birch ply as sarking.  Traditionally it used to be planks that were spaced a few mm apart, but it seems that now pretty much anything could be used.

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bang on that thanks. So just lay the board on, screw down and bobs your uncles yes?

 

 

 

[Big Neil]

  On 14/05/2019 at 12:24, scottishjohn said:

water proof/ breathable membrane is last thing before tile batons  surely?

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well i thought so , but i'm sure ive seen it as described before, at least on the net somewhere possibly on here

[Jeremy Harris]

  On 14/05/2019 at 12:25, Big Neil said:

bang on that thanks. So just lay the board on, screw down and bobs your uncles yes?

 

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Yes, the sheets were just nailed to the tops of the rafters.

 

  On 14/05/2019 at 12:26, Big Neil said:

well i thought so , but i'm sure ive seen it as described before, at least on the net somewhere possibly on here

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We have counter battens nailed through the sarking, in line with the rafters, then membrane, then the battens for the slates.  The idea is to allow a free ventilation path up under the roofing to the ridge vents.

[bassanclan]

I went rafter then sarking then counter batten (in line with the rafters) breathable membrane then tile battens

[ProDave]

Membrane can go straight onto sarking as long as it is "non tenting"

[SteamyTea]

Could it be different for a warm/airtight roof?

[Big Neil]

  On 14/05/2019 at 12:35, JSHarris said:

We have counter battens nailed through the sarking, in line with the rafters, then membrane, then the battens for the slates.  The idea is to allow a free ventilation path up under the roofing to the ridge vents.

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is the menbrane over the in line battens taught?

[Jeremy Harris]

  On 14/05/2019 at 12:47, Big Neil said:

 

is the menbrane over the in line battens taught?

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No, it's laid to sag slightly.

[Russell griffiths]

The membrane needs to go on top of the sarking board, or else any wind driver rain or moisture would get onto the sarking board and soon turn it into a mess, membrane on top to protect everything from the elements. 

 

It would also also depend on your roof finish, slate tile, metal sheets. 

[scottishjohn]

  On 14/05/2019 at 12:35, JSHarris said:

 

Yes, the sheets were just nailed to the tops of the rafters.

 

 

We have counter battens nailed through the sarking, in line with the rafters, then membrane, then the battens for the slates.  The idea is to allow a free ventilation path up under the roofing to the ridge vents.

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thats an "English type roof ",

older houses built there had the tar paper done like that  or even no tar paper  at all just slates/tiles  into  a cold roof void 

certainly all SIPS roofs are done the other way  membrane then counter batons to give the vented area ,but to the outside of the membrane 

membrane goes direct to sips 

 the house i have now built in 70.s  has-plywood sheathing ,then tar paper ,then batons and tiles .

 

[scottishjohn]

  On 14/05/2019 at 13:33, Russell griffiths said:

The membrane needs to go on top of the sarking board, or else any wind driver rain or moisture would get onto the sarking board and soon turn it into a mess, membrane on top to protect everything from the elements. 

 

It would also also depend on your roof finish, slate tile, metal sheets. 

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thats how i see it.

and i  dont think it matters what type of roof finish you have ,that where you stop the water,before it gets to sarking 

put an extra one if you like between vertical batons and counter batons ,if you like --seen that done 

[scottishjohn]

I suppose if you have a live in roof space ,then I can see you might put VCL/air tightness barrier under sarking  and then breathable membrane above it ?

I just cannot see any good reason for allowing sarking to get wet /damp  or have the possibility of the membrane flapping and over time failing because its moving about with high winds 

seen some sips roofs that use full stick on membranes  as well,

fine provided you definately will never  get any moisture on inside which will start rot over time 

 

[Onoff]

  On 14/05/2019 at 12:47, Big Neil said:

 

is the menbrane over the in line battens taught?

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Dunno, maybe someone offers a course?

[scottishjohn]

  On 14/05/2019 at 12:25, Big Neil said:

Traditionally it used to be planks that were spaced a few mm apart, but it seems that now pretty much anything could be used.

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that was when you had drafty attic spaces -and the gaps were to allow the WET sarking boards to  expand -the drafty attics were your ventilation void up to the ridge vents and there was no membrane of any type just plenty of tile overlap and not low an angle on roof 

so that kind of goes against any modern thinking 

[scottishjohn]

  On 14/05/2019 at 13:54, Onoff said:

 

Dunno, maybe someone offers a course?

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 slight sag is what they do usually ,  not stretched tight

[Big Neil]

So maybe - OSB as the board, stretch MEmbrane over that, vertical battens and counterbattens (per @JSHarris) then the final roof covering.

[Big Neil]

  On 14/05/2019 at 13:54, Onoff said:

Dunno, maybe someone offers a course?

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If there's ever a Buildhub annual puntest - bags me you as a partner

[Russell griffiths]

  On 14/05/2019 at 13:59, Big Neil said:

So maybe - OSB as the board, stretch MEmbrane over that, vertical battens and counterbattens (per @JSHarris) then the final roof covering.

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You want to delete the term stretch, should be laid with a little bit of floppy ness, to allow for expansion and contraction. 

[Gone West]

 

  On 14/05/2019 at 12:04, Big Neil said:

I don't quite understand another thing, please can someone in the know confirm. I get that Sarking boards increase the strength of the roof as a whole. What ideally should they be made out of? Can you just use normal sheets of say OSB or Ply etc? I know there are plenty of other products available, But is there a specific reason why you wouldn't use either of these for example. Also, If i've read correctly the membrane goes on top of the rafters but under the sarking? Why?

 

Thank you all once again.

 

 

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Our old 1920s bungalow had T&G sarking boards covered with roofing felt and slates nailed into the sarking. Our new roof has 15mm OSB3 raking/sarking covered with Protect TF200 thermo membrane then 100 x 50mm rafters with 50mm Rockwool between and Protect A1 tight over the rafters then NuLok roofing.

[Simplysimon]

sarking used if slating as to allow nailing. nailing into osb with slate nail will mean quite a few broken slates. if tiles are to be used then i'd go osb, faster sheeting, does the same job for racking strength but don't need to be careful in the nailing as tiles fixed to battens. yes you can osb and slate, however, you will need to batten/counter batten out as well

[Redoctober]

Hope this helps. Nothing like a photo to assist. It shows our roof having been fixed with Sarking and then a "loose" or floppy fitted membrane attached.