Sup roof on masonry build

[Lewis88]

I am considering a SIPs roof on my masonry/cavity build however most local SIPs manufacturers are indicating that my project isn’t suitable for SIPs - having said that I haven’t found one that has fitted a SIPs roof to a masonry build before.
 

Please can any shed any light as to what the issue is likely to be? I’m assuming that it’s a difficulty with the span as the main ridge beam would need to be 13m long.

 

Is there anyone that has a masonry build with a SIPs roof, and would the span be an issue?

[Russell griffiths]

I looked into sips roof on an icf house and forgot about it because of the spans. 
sips cannot span very far on their own without intermediate structural timber. 
you either need large splines of timber between the sips which leads to cold bridging which then needs additional insulation, or you need to put additional purlins at mid span to stop the droop from eaves to ridge, these then project into the room space. 
 

I would build a cassette type roof on site using I joists and insulation then osb. 

[SBMS]

I looked at this. Realised that if the rest of the walls weren’t being done in SIPS there was little point. No SIPs manufacturer would install as they need your masonry walls to be within a very small tolerance - fine if they are putting them up in sips, otherwise they just said they’d supply only. 
 

Reason number 2 - in my research of all the places a SIPS panel could fail it’s along the ridge where the two panels meet. If this detail is imperfect you’ve got osb weetabix. 
 

Reason number 3 - long ridge spans don’t work very well with sips. A glulam ridge was looked at for ours… then they said steel…

 

Reason number 4 - I was attracted to sips because we are doing attic rooms and having them vaulted was a desirable. But many on here have said the noise is quite high when it rains.
 

Instead we are going with a 304mm posi rafter hanging off a steel Ridge, filled with warmcel blown in. Fully vaulted and should be excellent u value, and quiet in the rain. And can be assembled by a normal roofing gang. 

[torre]

You've not mentioned why you're considering this route?

I looked briefly at it as it seemed seductively easy to get a roof on but building in masonry, very tight tolerances so little adjustability and most importantly cost weighed against it (seemed a huge gap between the cost of the panels and a whole roof even supply only). I was surprised to learn it's still classed as a cold roof and so needs ventilation above meaning you need counter battens above for example so the build up isn't quite as thin as you'd think either.

[Lewis88]

Thank you all for your responses. The SIPs company have now told me that it is the span that’s the issue so it is likely that there is no way around this and it is probably better to choose standard attic trusses. 
@Russell griffithswhat is a cassette styled roof?  Is this essentially using I-joists from a main ridge beam and covered over with OSB? Would you happen to have a detail showing this? Sorry, this is my first self build so not Ai fait with the process or terminology.

[Mr Punter]

If most SIP manufacturers think your roof is not suitable it probably isn't.

 

Trusses or cut roof and maybe some steel are what is widely used.

 

Who is doing the structural design?  They should be able to help.

[SBMS]

1 hour ago, Lewis88 said:

Thank you all for your responses. The SIPs company have now told me that it is the span that’s the issue so it is likely that there is no way around this and it is probably better to choose standard attic trusses. 
@Russell griffithswhat is a cassette styled roof?  Is this essentially using I-joists from a main ridge beam and covered over with OSB? Would you happen to have a detail showing this? Sorry, this is my first self build so not Ai fait with the process or terminology.

Do you have rooms in the roof?

[Russell griffiths]

What exactly do you want to achieve 

vaulted ceilings to the bedrooms, or 1-1/2 storey with room in roof. 
some context needed really as to why you wanted a sips roof. 

[SBMS]

29 minutes ago, Russell griffiths said:

What exactly do you want to achieve 

vaulted ceilings to the bedrooms, or 1-1/2 storey with room in roof. 
some context needed really as to why you wanted a sips roof. 

That’s why I was recommending posi rafters if vaulted ceilings. I discounted attic trusses because I didn’t want to insulate with PIR and couldn’t get trusses deep enough for cellulose blown insulation.