Probably at some future time needs some more tests done, to determine temperature rise in the new situations for new reference cases.
Or cables to be routed on the indoors side of the wall. 
Or a move to cables with a higher withstand temperature.

Oddly I've just been looking at something using 1.5mm2 railway cables (RL1131 types) and the max core temp of 120C makes for surprisingly high current ratings, almost automotive, so long as routed only in locations that cannot be touched. Just the ends need to be cooled where they terminate onto 'normal' fittings. (given the fun we have with SY I wonder what some folk would make of this ENs but no BS ;-) )

Mike

"Or a move to cables with a higher withstand temperature"

This would seem to becoming a necessity if the current roof void and wall insulation design approaches are sustained and get worse; although how one 'cools' for incompatible accessories will be a challenge. 

Perhaps the way properties are constructed needs a proper review and more thought by building designers to reduce the impacts on wiring and to limit waste as such.  May be the lead and a push should come from the electrical industry.

In one new build I recall, very thermally effective insulation was packed into an internal stud wall and its only purpose was sound dampening ! 

Perhaps Building Regs, where insulation is required/wanted, should mandate that insulation be built into the the materials used for of wall/ceiling, or in cavities, whereby no other is required and cables can be run along surfaces without general issue.

Nothing will be perfect it would seem, but still a little help and from building design would be great especially if specified is 10+ sockets on an insulation packed wall and so on.

:-)

direct bonded construction

Is that plasterboard 'glued' to the substrate? or plasterboard with thermal insulation backing? or something like SIPs with an outer skin of brick?

Perhaps the way properties are constructed needs a proper review

+1 for that! With passivhaus levels of thermal insulation often the only sensible way is to keep all the wiring on inside of the insulation - e.g. in a 25mm service void between plasterboard and insulation. Trying to hide wiring inside or behind thermal insulation opens up many cans of worms - not just heat loss from the cables, but also things like air tightness and condensation control - far better to design out the problems than try to work around them.

   - Andy. 

I reckon some overthinking might be going on here. Think for a moment about how a house heated with a heat pump will actually have a lower ambient temp than one with a gas boiler turned up to full. Then of course, we have lower rated appliances, lamps etc, so the cable itself most likely won't be carrying anything like it's design current in future.

so the cable itself most likely won't be carrying anything like it's design current in future.

Unless it's the cable that feeding the new fangled EV point, or the heatpump....

  - Andy.

hello Andy - 'glued' to the substrate  (as in 'dot dab') - with some insulation in play (however it may be).

I was just curious (as to the installation method classification where there is plaster board, insulation then cable on the brick wall for instance ... and what method if the insulation is touch and not touching.

Thank you

helo whj

perhaps

but  ib <= In <= Iz   regardless isn't it   accepting that lower Ib's reduce excessive waste of copper.

One person's excessive waste of copper is another person's lower running costs over the lifetime of the installation.

In which case it'll have to be done in oversized SWA to compensate.

And it's a one-off fee! Just for a change!