Costing difference of SIP upper / roof with traditional construction method

[flanagaj]

I suspect this has been talked about a huge amount, but given I am going to be managing our project and doing the first and second fix carpentry myself I am unsure how I go about costing up the difference between having the upper storey and roof constructed with SIP Vs having it constructed with traditional block / cavity / block and me cutting the roof myself.

Exterior of the upper will be vertical timber cladding and the roof is standing seam.

Footprint of the dwelling is ~ 110m2 

If anyone has recently looked into this and can give me some guidance as to what their findings were it would be most appreciated

[Nickfromwales]

Not needing a crane will be one saving. 
 

I'm not a fan of a SIPS roof, particularly with a metal rain screen, due to the noise / acoustic transparency of the PIR vs say blown in cellulose or other similar higher performing material.

 

SIPS will need manufacturing, cut roof will be DIY / builder and more flexible / forgiving for you to work with.

[flanagaj]

3 minutes ago, Nickfromwales said:

Not needing a crane will be one saving. 
 

I'm not a fan of a SIPS roof, particularly with a metal rain screen, due to the noise / acoustic transparency of the PIR vs say blown in cellulose or other similar higher performing material.

 

SIPS will need manufacturing, cut roof will be DIY / builder and more flexible / forgiving for you to work with.

Thanks.  I wasn't aware of the acoustic transparency of the PIR.  

The one positive I do like of the SIP is around the fact that the cladding can then be flush in the vertical plane of the wall when it adjoins the lower floor brick exterior skin.  Having the lower in brick / cavity / block and the upper block / cavity / block, means that the counter batten + cladding (~ 75mm thickness) will sit proud of the lower floor brick face.  Aesthetically it doesn't quite look as nice.   I don't think there is anyway to avoid that?

[jfb]

1 hour ago, flanagaj said:

The one positive I do like of the SIP is around the fact that the cladding can then be flush in the vertical plane of the wall when it adjoins the lower floor brick exterior skin.  Having the lower in brick / cavity / block and the upper block / cavity / block, means that the counter batten + cladding (~ 75mm thickness) will sit proud of the lower floor brick face.  Aesthetically it doesn't quite look as nice.   I don't think there is anyway to avoid that?

Why can’t you just build the bottom section so it sits 75mm proud of the top section?

[flanagaj]

17 minutes ago, jfb said:

Why can’t you just build the bottom section so it sits 75mm proud of the top section?

But how does that work with regards to the inner skin?  Are you saying have a wider cavity on the ground floor?

[Nickfromwales]

2 hours ago, flanagaj said:

The one positive I do like of the SIP is around the fact that the cladding can then be flush in the vertical plane of the wall when it adjoins the lower floor brick exterior skin.

Not so sure that's practicable? Ventilation and rainwater runoff, moisture behind cladding needs to be able to drip, dissipate etc so I don't see how the cladding can finish flush with the lower course.

 

Pretty much anything is 'doable' with time, imagination, and budget, but I think you need to look at sectional examples first to decide if the flush finish from one discipline to the next is actually going to work in real life.

[jfb]

On 15/05/2025 at 10:38, flanagaj said:

Are you saying have a wider cavity on the ground floor?

Why not?

[Nickfromwales]

2 hours ago, jfb said:

Why not?

What do you propose for the change in footing of the upper course of block, which would then be straddling the lower, wider cavity?