I have a bit of a tricky detail I've been mulling over for weeks. Anyone who's got a spark of inspiration on this please let me know.

I'm currently detailing a beam and block flat roof, got as much insulation over it and along the edge as I can get, which means at the perimeter I have effectively tried to maintain a consistent layer of insulation to keep the slab warm. Over the insulation I've got my membrane, then paving slabs to create a deck. Obviously the deck needs a handrail, but how do I fix it without creating a cold bridge or puncturing my membrane? I can't really go over the edge and fix to the wall either, as I've got render on to mesh, over more insulation down there! Thats the problem I guess when your entire outer skin is insulation, what do you screw stuff too! Railing is to be stainless steel and glass (recycled), set on to a new green oak ring beam (300x125ish) which will sit over the membrane and have the paving running up to it with some gravel for drainage.

Current best option is to have some stainless plate fixed to the base of the oak protruding from the inside face say 600mm, so that it gets laid under the slabs and the railing is effectively held in place as a cantilever by the weight of the slabs. The Oak ring beam will be fairly chunky and 22m along the full length, so I don't know how much more force I need to resist really?



See sketch, without oak and railings.

I guess it depends on how big the cantilever is and how big a force you have to resist to comply with building regs. A quick googling turned up the following

For external balconies & also in light office areas non susceptible to overcrowding - 0.74 kN/m (this can be compared to having one averagely weighing person 75kg applying the full force of their body on every metre of the balcony)

Point load: 0.25kN/m For external balconies & also in light office areas non susceptible to overcrowding 0.5kN/m.

What sort of returns (at ends of roof) do you have? is there an abutting structure that you can run the oak and hand railings to and fix into? That might provide sufficient support at the ends of the rails, and then rely on mass and cantilever effects in the middle?

If the cantilever idea doesn't work out, isn't this an ideal case for one of those proprietary plastic thermal break pads for use between two bits of stainless steel? i.e. thermally broken stainless column(s) going down to the beam.

Could you elaborate on "plastic thermal break pads" djh? Not seen anything like that, but sounds interesting.

In the end I went for a design not dissimilar to that of FH Bundles, only with the support bracket affair and a lengthways strip hidden beneath the paving slabs. It's going to need a bit more looking at when we come to actually do it.

Many Thanks.