Tapered roof insulation

[gravelrash 1]

Tapered roof insulation...I am struggling to get my head around the u value on tapered roof insulation.  Surely cold bridging is unaware of an average U value...and will occur at the thinnest point of insulation.

Am I overthinking this unnecessarily. 

[PeterW 4,008]

You won’t get a bridge but the idea is target the minimum uValue at the taper end. 

[ToughButterCup 2,063]

3 hours ago, gravelrash said:

...

Am I overthinking this unnecessarily? 

 

No.

The level of information support that the industry gives to self-builders is poor at best. I needed to ask exactly the same question - of several people - before I trusted the answer. You are right, logically. But what they (the industry) don't tell you is that the thickness required to achieve the U value required is calculated at the lowest end of the slope: the minimum insulation needed to obtain the target value.

 

Then additional insulation is added to create the slope needed. So at the opposite end (the high end) the U value will be even lower.

[ADLIan 82]

The U-value of tapered roofs may be based on the maximum U-value/minimum thickness (subject to back stop values in Approved Docs L & C) or the 'average' thickness for the desired U-value. With most tapered systems the U-value is not the simple arithmetic average, the calculation method is in BS EN 6946 and involves splitting the roof down to various set shapes. This is probably a job for the system designer.