Where to start the journey to energy efficient home

Emily_Joy

OH and I are both finally home for Xmas and we got around to it. The loft floor is covered with loft boards, which presume date back to 2007. There is some 50mm insulation under the boards. We were initially thinking about removing it altogether, but I started to wonder if we should keep it? A slight problem that for some reason cables go under the insulation, but as far as I understand for fire safety they should go above.

markin

You could just roll out new on top, or use some foam board around the hatch for the Xmas tree, If the wood is only 60mm deep it cant take a lot of weight before you crack all the ceilings.

FreeBear

More likely to be 75mm or even 100mm there. Lift the boards and screw some loft legs to the joists at regular intervals after removing the plastic sheeting. Lay 200mm top-up insulation at 90° to the joists, and refit the boards. Standard loft legs are 175mm high, but the insulation will still work if compressed by 25mm.Assuming you have LED lighting all round, most of the cable up there will be hugely overrated and will not come to harm being buried under insulation. Cables for electric showers would be better on top if possible (depending on the size of cable & rating of the shower).

JSHarris

There may be a cable rating issue in increasing the insulation level above them.  The rating for cables under 100mm of insulation or less is higher than the rating for cables with more than 100mm of insulation over them.  The OSG to BS7671:2018 (current version of the wiring regs) references this and may help when making a decision as to whether it's worth the hassle of trying to relocate cables above insulation or not:

To interpret this usefully, lighting circuits are normally protected by a 5A fuse or 6A circuit protective device so 1mm² or 1.5mm²  T&E lighting cable under more than 100mm of insulation (line reference 101 in the above) is fine and doesn't need moving.

If there are 2.5mm² ring final cables up there (the cables that supply sockets and sometimes immersion heaters and perhaps other wired in loads with fused connection units) then things get a bit marginal, as these cables will be protected by a 30A or 32A fuse or MCB/RCBO and the ring relies on the current balance around it being OK so that it's shared fairly evenly along both sides.  17A x2 gives 34A, which is still just about OK, and personally I'd not be too bothered by it.

There may be 2.5mm² radials up there to feed things like immersion heaters (if the immersion is on a separate circuit).  A 2.5mm² radial will usually be protected by a 15A fuse or 16A protective device, and as this cable is still OK to carry 17A when under thick insulation it's just about OK left underneath it.

The problem cables are ones mentioned earlier, electric shower feeds, but also car charge points, cooker cables and any cable running a high current radial circuit.  Electric shower supplies are usually protected by either a 40A or 50A protective device and will be run in 10mm² cable usually.  Some very low power showers may be run in 6mm² with a 30A/32A protective device.  Either way, it's not safe to run either size of shower cable or cooker cables etc underneath insulation, so as mentioned those cables need to be relocated above the insulation.

My preferred way to run all cabling in lofts is to fit battens under the rafters and run them up there.  Pity more people don't do this IMHO, as there's nothing worse than a rat's nest of cables running across a ceiling, far neater (and easier when it comes to laying insulation) to just have cables drop down from the rafters where needed (although it does need doing carefully if the loft is to be used for storage).

Hope this is useful and doesn't over-complicate things too much!

Emily_Joy

@JSHarris thank you. Currently we have neither electric shower, nor immersion heater and the cooker is gas, there is no red power socket in the kitchen either. We don't have car charging points. There is no downlights. Does this mean that there are rather unlikely to be cables that need moving?

JSHarris

Emily_Joy said:

@JSHarris thank you. Currently we have neither electric shower, nor immersion heater and the cooker is gas, there is no red power socket in the kitchen either. We don't have car charging points. There is no downlights. Does this mean that there are rather unlikely to be cables that need moving?

Sounds like it, as long as none of the cables you come across look like big ones (around 15mm to 17mm across the widest dimension) then you should be fine leaving them where they are and just increasing the depth of the insulation.