Overrating socket ring?

[jayc89]

BCO is being a stickler for the regs. My proposal for IWI would achieve a u-value for 0.35, for a couple of reasons; keeps the build up reasonable, allows "some" heat to escape, especially around floor joists pocketed into brickwork (this is a reno, not a new build). I've queried it, citing traditional building, risk of damage etc etc, so we'll see what he says. He's been pretty pragmatic so far... 

 

If he does dig his heals in, I could get around it by in-filling the service cavity with 25mm PIR, which would get me to 0.25, but it would mean I'd be encasing my socket ring with that 25mm PIR too... 

 

It's currently 2.5mm T&E, what would I likely have to upgrade it to if I did have to put 25mm PIR in the service void? Would 4mm be enough?

 

Note: This is a renovation, not a new build. I'm aware I'm not achieving PH-level standards.

[Sparrowhawk]

OT but what level of changes are you doing that got BCO involved? More than just sticking IWI internally while renovating I guess? I'm considering a remodel and so curious at what point BCO can start looking beyond the structural "internal load bearing walls removed" and start prescribing what's done with floor/wall U values?

[jayc89]

1 hour ago, Sparrowhawk said:

OT but what level of changes are you doing that got BCO involved? More than just sticking IWI internally while renovating I guess? I'm considering a remodel and so curious at what point BCO can start looking beyond the structural "internal load bearing walls removed" and start prescribing what's done with floor/wall U values?

 

It's been a wide spreading project, I'm sure our BCO loves us.

- Replaced rotten suspended timber floor with a new slab

- Covered over cellar with block and beam floor

- Windows/Insulation/MVHR (did these all through BC as I couldn't find a window fitter to supply windows without vents until we had MVHR and didn't want to rip the house up once to fit MVHR to do it again after windows had been fitted for insulation/airtightness etc, so a bit of chicken and egg situation)

We're also doing an extension on the same Building Notice, so we're locked into regs as they were in '21, which gives us some nice wiggle room. 

[ProDave]

I was considering adding extra insulation in my service void.  If I had done so, I would have left a gap either side of any cables so they were not "in insulation"  I have not found any definition of how wide that gap would need to be.

[Redbeard]

@Sparrowhawk, BCO becomes interested in U values when you are 'renovating' (adding or replacing a layer to) more than 50% of a thermal element, and that's not 50% of, say, all the walls in the house, it's the external wall(s) *in the room you're stood in*. For example if you rip off the plaster from the one external wall in your inner terraced front room, you arguably have an obligation to insulate to meet the requirements of Part L.

 

I have found that if I am using (thin) PIR, BCO wants to see 0.3W/m2K, but if I am using wood-fibre with an insulation value only just over half as good, BCO accepts arguments re trad building and 'safety' re interstitial condensation risk.

[TonyT]

You could derate the RCBO rather than the cable depending on the load?