Warm flat roof insulation boost

[Jimbo37]

Hi

Can I put mineral wool between solid joists on a flat roof - see red on the graphic. TIA

[Mr Punter]

Often you can but it is worth doing a condensation risk analysis.

[Dave Jones]

as long as you have a proper VCL under the kingspan and sealed down onto the internal wall it will be fine.

[ADLIan]

Don’t do it!! Frowned upon by BS6229 & BS5250 and doubt insulation manufacturer would support it without lots of caveats. On your head be it.

[Jimbo37]

@ADLIan Is condensation the concern (presumably between the wool & board above)?

@Dave Jones @Mr Punter thanks