Sarking on Batons??

[SuperJohnG]

I've been pricing my roofing for my SIPS build. 

 

As it's a SIPS roof, I had been looking for membrane, counter batons running vertical then normal batons so I had the ventilation space. I will be using a slate roof (Cupa heavy 3) in Scotland. 

 

Now one roofer has said Batens are harder than sarking to fix slates on and hence says, I should do the counter batens, but then fit sarking (22mm thick, 150 wide, etc) and that would be better and reduce costs for labour install.

 

I need to check cost implications but thoughts anyone from a technical (or any other) perspective??? 

[Roys]

When I did my the slate roofs on my byre and workshop I did a fair of research on fixing slates to the roof even phoning up the membrane company tech line.

The two roof constructions were roof trusses then sarking, then breathable membrane,  one set of sarking was 18mm the other was 22mm bought them as different times as the projects were a year apart. Anyway we came to the conclusion that it was sarking with a 2mm gap between boards then the membrane then nail the slate directly on. When the sarking gets a couple of years older under the slate the gap has grown slightly to 3 or 4mm which is what the breathable membrane people were wanting.

So I can see why your roofer is suggesting batten then sarking as it will then in effect be a slate nailed direct job.

[Simplysimon]

2 hours ago, Roys said:

So I can see why your roofer is suggesting batten then sarking as it will then in effect be a slate nailed direct job.

it will still be a nailed direct job, just into battens as opposed to sarking, i have the same issue as i beam warm roof. had thought to clip them instead of nailing, biggest issue i have with slate on batten is someone going onto roof in future. must admit i hadn't thought to sark it, though would need to check whether 25mm would be sufficient or if would need to double counter batten.

[scottishjohn]

the disadvantage of just using batons is you are limited to where you can nail your slates

-with sarking  and even if you decided to use diminishing slates  then you can nail anywhere 

https://www.tntroofingspecialist.co.uk/portfolio/random-diminishing-slates-6/

 

Edited September 4, 2020 by scottishjohn

[SuperJohnG]

3 hours ago, scottishjohn said:

the disadvantage of just using batons is you are limited to where you can nail your slates

-with sarking  and even if you decided to use diminishing slates  then you can nail anywhere 

https://www.tntroofingspecialist.co.uk/portfolio/random-diminishing-slates-6/

 

But why would you need to nail anywhere if you have a specific headlap and holed slates. It woukdnt be level otherwise?  

[SuperJohnG]

18 hours ago, Simplysimon said:

it will still be a nailed direct job, just into battens as opposed to sarking, i have the same issue as i beam warm roof. had thought to clip them instead of nailing, biggest issue i have with slate on batten is someone going onto roof in future. must admit i hadn't thought to sark it, though would need to check whether 25mm would be sufficient or if would need to double counter batten.

Do you mean double counter batten on top of one another? or something else? 

 

Is sarking treated also? I see the advantage with being able to walk on the roof it is sarking, but If i do it this way, then I end up with abuild up like this:

 

Sips outer skin, membrane, Treated counter batens, 22mm sarking (fully covering) membrane (again?!), slates. Seems A lot! 

 

Can imagine what a great place that be for birds etc to next, nice big void. 

[Simplysimon]

39 minutes ago, SuperJohnG said:

Do you mean double counter batten on top of one another? or something else?

yes, if necessary to give sufficient air flow

 

40 minutes ago, SuperJohnG said:

 

Is sarking treated also? I see the advantage with being able to walk on the roof it is sarking, but If i do it this way, then I end up with abuild up like this:

 

Sips outer skin, membrane, Treated counter batens, 22mm sarking (fully covering) membrane (again?!), slates. Seems A lot! 

sarking is treated and yes it does seem like a lot! as i have the same issues.

 

41 minutes ago, SuperJohnG said:

Can imagine what a great place that be for birds etc to next, nice big void. 

insect mesh needed no matter what to close off cavity whilst still allowing air flow. will you have cavity outside walls?

[SuperJohnG]

41 minutes ago, Simplysimon said:

yes, if necessary to give sufficient air flow

 

sarking is treated and yes it does seem like a lot! as i have the same issues.

 

insect mesh needed no matter what to close off cavity whilst still allowing air flow. will you have cavity outside walls?

@Simplysimon I will have renderboard on battens. When are you due to do yours Simon ?

[Russell griffiths]

I have two lots of membrane, metal roof but similar, 

membrane

counter batten,

sarking fitted hit n miss style 

membrane

metal roof. 

[Cpd]

1 hour ago, Russell griffiths said:

I have two lots of membrane, metal roof but similar, 

Seen this used locally to me, it’s a good solution and provides plenty of ventilation, it was also for a standing seam metal roof, the only difference being they covered the whole roof in sarking whereas I think the hit and miss would have been more than sufficient. Covering the sarking with membrane and then letting the sarking dry to the local conditions should also help it settle and lessen the chance of movement once the tin goes on. 

[Russell griffiths]

1 hour ago, Cpd said:

Seen this used locally to me, it’s a good solution and provides plenty of ventilation, it was also for a standing seam metal roof, the only difference being they covered the whole roof in sarking whereas I think the hit and miss would have been more than sufficient. Covering the sarking with membrane and then letting the sarking dry to the local conditions should also help it settle and lessen the chance of movement once the tin goes on. 

If I did it again I would use sarking boards but with 10mm gaps

one thing I wouldn’t do is the design method that all the roof companies specified and that was ply wood with no gaps, didn’t make sense to me. 

[scottishjohn]

10 minutes ago, Russell griffiths said:

If I did it again I would use sarking boards but with 10mm gaps

one thing I wouldn’t do is the design method that all the roof companies specified and that was ply wood with no gaps, didn’t make sense to me. 

my guess plywood by its nature is more  stable --so no need for gaps  maybe?

[Cpd]

I would not recommend ever using plywood on a roof.... my personal experience with it has always been bad. Treated Sarking is what I would always recommend As it’s stood the test of time in many buildings I have worked on and seems to last indefinitely when used under roof membrane. There may be a case for OSB but given the choice I would alway go for treated 22mmx150mm pine sarking. 

18 minutes ago, Russell griffiths said:

If I did it again I would use sarking boards but with 10mm gaps

Interesting as the guy who’s roof I saw was specified at 5mm gaps, I told him that if the sarking was wet (Check by cutting boards and measuring dampness in centre) to put it up tight as it would shrink And leave 5-10mm  gaps but if it was dry to space it out as recommended. Either way I would always recommend leaving it for as long as possible to dry out before putting on the tin to prevent movement in the fixings, though I think his standing seam roof had oblong holes to allow for a bit of movement. 

[SuperJohnG]

4 hours ago, Russell griffiths said:

I have two lots of membrane, metal roof but similar, 

membrane

counter batten,

sarking fitted hit n miss style 

membrane

metal roof. 

@Russell griffiths looks a tidy job a d food to see someone else that has dine it. How come you chose the sarking instead of batons? What construction is the main roof? 

[Russell griffiths]

@SuperJohnG metal roof, cannot go on battens needs full support. 

Main roof is I joists. 

[SuperJohnG]

I have now reached the point where I need to buy battens or sarking for the top layer, SIPS roof will be fitted next week and then its over to me to fit them before roofers come on site. 

 

I had made my mind up to use sarking as it's what the roofers wanted however of late changed my mind somewhat for two reasons:

 

1) Reading the STA (structural timber association) guide it says minimum 50mm ventilation gap for SIPS roof. but the counterbatten (25mm) and sarking option (22mm) kind of means i only have a 25mm gap as the sarking forms a full covering - albeit the gaps in sarking help air flow. 

 

2) I checked the cost difference. Ignoring the counter battens as in either case I require these:

 

Sarking costs: 350m2 - £3055 for materials only - then I would need more nails and also another membrane on top of the sarking. 

 

Counterbattens: 350m2 - £1872 for materials only (this could comedown if I use 22mm battens to £1372) - but less less nails also plus I don't see why a membrane would be needed over the battens, makes no sense as there is a membrane on the SIPS outer layer.

 

 

For me - it seems if I ignore the roofers wants then with battens rather than sarking I can reduce costs but also I can provide that 50mm ventilation gap. 

 

Is there anything I am missing?

 

[LA3222]

@SuperJohnG why are you sarking a SIP roof you nutter?

 

Batten and counter batten, job done.

 

The roof is already 'sarked' by the OSB outer sheaf. I suspect the roofers want it sarked because it is easier to walk on and the lizards have probably never seen a SIP roof so have no idea what they're working on.

 

The number of trades I've had who go all glazed in the eyes when you mention SIP and how it is constructed. They know block, they know timber frame, anything else is black magic?‍♂️

Edited June 2, 2021 by LA3222

[LA3222]

For what it's worth, my garage roof will be sarked but that is timber trusses so open. I like the idea of sarking for reasons such as ease of working on, rigidity etc but with SIP its pointless, you're putting timber sheet over timber sheet?

[LA3222]

32 minutes ago, SuperJohnG said:

plus I don't see why a membrane would be needed over the battens, makes no sense as there is a membrane on the SIPS outer layer.

My roof buildup

 

SIP outer sheath

Membrane - housewrap

Battens

Proctor roofshield

Counter battens

Tile

 

I did put an extra membrane on mine, reasons being it is a good quality non tenting roof membrane rather than a generic house wrap. Figured it can't do harm, only good?‍♂️

Edited June 2, 2021 by LA3222

[SuperJohnG]

6 minutes ago, LA3222 said:

The roof is already 'sarked' by the OSB outer sheaf. I suspect the roofers want it sarked because it is easier to walk on and the lizards have probably never seen a SIP roof so have no idea what they're working on.

It's mainly due to them wanting it like that (and that's all the roofers I have talked to) it's down to them being able to position the slates for the headlap easily. But if you have a good slate that is consistent then I don'tsee the point - exactly as you say I just don't think they get it (yet). 

 

Did you counterbatten then batten? only go with the existing membrane also on the SIPS roof?

[SuperJohnG]

4 minutes ago, LA3222 said:

I did put an extra membrane on mine, reasons being it is a good quality non tenting roof membrane rather than a generic house wrap.

why???? lol. this is where I get confused. lol

[LA3222]

7 minutes ago, SuperJohnG said:

It's mainly due to them wanting it like that (and that's all the roofers I have talked to) it's down to them being able to position the slates for the headlap easily. But if you have a good slate that is consistent then I don'tsee the point - exactly as you say I just don't think they get it (yet). 

 

Did you counterbatten then batten? only go with the existing membrane also on the SIPS roof?

SIP house wrap

Then vertical battens

Proctor roof shield

Then horizontal battens

 

I used 25x50mm JB red battens iirc

Edited June 2, 2021 by LA3222

[LA3222]

7 minutes ago, SuperJohnG said:

why???? lol. this is where I get confused. lol

I view the house wrap as just a generic membrane, good at everything, Master of nothing. The Proctor roofshield is designed to be a roof membrane so I see it as belts and braces. Got generic wrap which was a bonus prize but got the good stuff doing the job it is supposed to do?‍♂️

 

I think the intimate contact between the wrap and the SIP didn't sit well we me either, happier having the roofshield with a ventilation gap under it between it and the SIP. Its probably all in my sward but I sleep easier having done it. The roof shield is expensive but pennies in the build budget.

Edited June 2, 2021 by LA3222

[SuperJohnG]

3 minutes ago, LA3222 said:

I view the house wrap as just a generic membrane, good at everything, Master of nothing. The Proctor roofshield is designed to be a roof membrane so I see it as belts and braces. Got generic wrap which was a bonus prize but got the good stuff doing the job it is supposed to do?‍♂️

I think I have a VP400 roofing membrane on mine - so hoping that would suffice. 

 

What did you end up attaching the battens with? the engineer has specced nails, and from what I have seen so far looks like it'll be fine. I think you used screws though eh ?

[LA3222]

8 hours ago, SuperJohnG said:

I think I have a VP400 roofing membrane on mine - so hoping that would suffice. 

 

What did you end up attaching the battens with? the engineer has specced nails, and from what I have seen so far looks like it'll be fine. I think you used screws though eh ?

Yeah mate, screws. I went with the fixing details as given by kingspan tek. I emailed them about it and got directed to ejot technical department. They had done all the pull out strength testing etc and advised me on the type to use.

 

Nails - not sure I'd want to go with them when all you have is 15mm of osb holding them in.