Add an extra internal block wall - possible?

[apples12]

Hi all

Our garage conversion saga continues.

It is a single skin blockwork construction

My question is, is it feasible to add a second internal cavity wall? The blocks would be on top of the concrete slab inside. I'd assume the cavity wall would need tying somehow to the existing wall?

The roof will be an EPDM rubber roof, kit already purchased. Will need to break the existing felt roof down (which has leaked everywhere) to the joists before laying any decks or vapour barriers over the top/deck/rubber

Option 1.
Insulate between joists, leave an air gap, vapour barrier, ply/OSB then the EPDM

Option 2.
Replace the rotten 9mm ply with 11/12mm, apply vapour barrier, add foam insulation, overboard, then EPDM roof .

Which would be more advantageous/less likely to cause problems in the long term

Any ideas welcome.

 

[^woody^]

Any masonry wall will need a foundation

 

[mrrusty]

Why blockwork? If you want a second layer construct an insulated stud wall inside the single skin garage. Leave a ventilated cavity in case any penetrating or condensing damp appears on the inside of the outer skin.

 

[Mr Chibs]

My brother is looking at do this shortly, he’s had some plans from the architect, but it has generated another set of questions.

He’s adding to the garage (single skin)
Roof wall plate is on this skin.
Been suggested to have an insulated stud work wall, but he’d prefer masonry.
he suggested building internal block work off the slab, but He’s no idea how thick this is, or what’s underneath.

Reading the posts above it seems building a block second skin is overkill.