Timber doors

[dumper]

I need to make two doors for my workshop 2.75m tall x 2.5m wide and thick enough to be insulated for sound and heat so about 125 MM thick also want to automate them so will need mag locks and motors 

Current design is to use two sheets of ply so to make them square frame the ply with box section steel then make a timber frame around the outside they need to be faced in tongue and groove or ship lap vertically on the face then filled with insulation and the rear faced in ply

anyone see problems or got better ideas workshop is in conservation area so doors need timber face and council have refused roller shutter

[woody paul]

My brother had some doors made from 50mm box each was 2m x 3,6m which he them boarded with tongue and grooved hang them on large cup hinges and have not moved in 12 years but are north facing. 

 

[Woodworks]

Can bond the ply to some PU insulation like SIPS panels are made?