Low emissivity cavity

[WVDV]

Hi,

Im new to the site: Stumbled across it when trying to resolve my querry.

 

Does anyone know how to account for low emissivity cavities in U-Value calculators? I'm using the BRE calculator, trying to calculate yhe U-Value of the following timber frame closed panel build-up:

• 12.5mm Plasterboard
• 35x50mm vertical battens to create a service cavity
• Reflective AVCL layer
• 25mm PIR Insulation
• 38x89mm timberframe studs at 600mm centres, with 100mm lambda 0.044 insulation between the studs
• 9mm OSB
• Reflective breather membrane
• 50mm Cavity
• 102.5mm brick

 

I come up with the calculation below, but it seems to me that the reflective membranes on the inner and outer cavities have a far to large impact on the calculation?

 

Walter V

[A_L]

hello and welcome,

 

Attached are the BRE conventions for most situations, specifically pages 19-21 for what you are looking for.

 

 

BR443-October-2019_consult.pdf