andreas

That is my point - as it already stands, the majority of houses I've seen have enough outlets per circuit that if you plugged a high draw device in every outlet, it would surpass the rated current carrying capability of the circuit even without insulation being a factor. I'm not saying to derate the circuit with stickers, I'm asking how you're supposed to calculate it nowadays. As far as I am aware you can still have as many outlets on a circuit as you want, unless modern houses that are fully insulated have only got a couple of double sockets per circuit? Very few of the cables can be moved easily, to the degree I think it would be easier to rewire, but that seems a ridiculous requirement just so floors can be lifted. Also laying cables over the insulation but under the floor would mean it's almost touching the underside of the floor.

All floors throughout.

I have been told that as I am pulling up all flooring, I have to add insulation. I know that running a cable through insulation means that you have to derate it. I have done the maths on all the lighting circuits, even derating the cables 50%, and assuming a worst case scenario of max lamp wattage per fitting possible with worst power factor, the lighting circuit has a massive safety margin, max current would be half the derated capacity. What I don't understand is the power circuit - how do you work that out? In theory in pretty much every house I've been in, it's possible to overload the *cable's* current capacity if you were stupid enough to plug a 2kw heater into every outlet. I don't want to have to replace all the perfectly good power circuits that are in place just because I want to take the floor up and have to add insulation as a result. Best way to work around it?

I need to pass a 15mm pipe through a 175 x 50 joist, then through a 175 x 80 trimmer joist perpendicular to the first joist. There is no other possible route for it to take. I have read guidance on drilling through joists but none of them mention if that is all types of joists, or if it is different with trimmer joists? Also when they discuss the span, does it mean any individual span where a single joist spans several supports? The 175 x 50 starts on one wall, rests on a second wall 2.2m away, then a third wall 0.9m further on, then finally supported by the trimmer joist 0.3m further on. I need the hole ideally to go between the second and third wall, so do I just calculate the position based on a span of 0.9m, or on the total span?

How big a section would you be thinking, and what would you see the advantage being in cutting the slab rather than using a core drill to make the hole where I want? I have dug out the other side of the wall to have a look, I can get a plastic pipe in from above, and a bend in from below relatively easily. I'm just worried about disturbing the slab too much!

My bungalow appears to have a raft foundation below the floorboards. Either that or it has no foundations at all!. I have to replace some of the old clay drains in the garden as they have broken. While I am doing so I would like to replace the toilet waste. At the moment, the toilet waste is 12 inches to the centreline away from the wall, so the pan sits out a very long way into a room which is already cramped as it is. Lifting the floor boards it looks like the pipe was originally much lower and has been extended upwards with a cemented in section and is over 2 inches proud of the floor so I cannot even replace the bottom-exit toilet fitted with a bottom outlet Would it be safe to just core drill a new waste through the slab behind where the clay pipe is currently? What do I need to consider when doing so? If that is a bad idea what are the chances of breaking off the extension and cleaning up the original end of the clay pipe and then adapting that outside to the new plastic pipe? Grateful for any suggestions.

Thank you. Fortunately it is well below 50% as there is a large window on the elevation that needs repair, so it is probably more like 25%. If common practice has been 25mm ventilation space, could I fit 75mm PIR between the rafters safely and then the 25mm over the top. I don't think that would meet the 0.16w/m2k either but it would be closer.

Thank you, I agree it will be frustrating but also frustrating would be losing the money I spent on the sound block plasterboard and then disposing of it haha

I can get away with 40mm total, so 25mm insulation and then 12.5mm plasterboard is fine. Any more than that and the plasterboard will start to cover the windows. Will building control accept that the original design of my house means that is all that can be done? I am also keen to know if there is any reason not to put separate insulation and plasterboard up as I already have the plasterboard.

very little which is why I looked at 25mm insulation below. Is there any reason not so use separate plasterboard and insulation? I already have the sound blocking plasterboard so it would be most economical to buy only the insulation.

I have had to remove the plasterboard on one face of our pitched roof due to water damage and would like to put some insulation up at the same time as there is currently none. The roof is going to be re-tiled and a breathable membrane fitted during summer 2025 but at the moment it has the black bitumen type non-breathable membrane. There is no ventilation. The rafters are 100mm deep. What are the best options? It would be best if any solution can consider that work is going to be done in the not too distant future and capitalise on upgrading again later. Could I fit 50mm PIR between the rafters and then use 25mm PIR below the rafters before boarding over with soundbloc plasterboard, then when the breathable membrane is fitted in the future back-fill will another 50mm PIR? Will anything done now be required to meet building regulations?