Electrical

Collaborative Electrical Rewire – Part 2 : Installation Day 1 – Design & running cables…

Wednesday 14th December 2016

Underfloor discoveries… Upstairs

We already knew that the original plaster and lath ceilings remain throughout much of the property due to the cracked, ‘characterful’ and undulating nature of them when viewed from below. Seeing them from above revealed that they are the same dark, black-ash lime plaster mixture used on the walls – very brittle, and very dusty.

Formed in a semi-regimented pattern of individually random extrusions over 100 years ago; there is something quite striking and aesthetically pleasing about these functional, hidden ‘hooks’ of ridged plaster.

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The plaster ‘nibs’ poking through the lath that hold up the ceiling below

Some of the old wiring installed by the previous owner was truly quite alarming, with exposed inner wires taped together with electrical tape!

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This is definitely not up to modern regulations & looks like a ‘temporary fix’ or poor diy job. Much of the wiring in the house had no earthing whatsoever.

It always feels like finding treasure when you come across snippets of history like this crumpled newspaper sheet in old houses. Possibly not ideal to have such a flammable thing next to wiring in such poor condition…

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Modern wiring has at least three cables (brown, blue & green/yellow) inside the outer sheath, rather than the green/black red/black shown bodged together here. The grey cable is the modern wiring …1.5mm twin & earth for lights, 2.5mm twin and earth for sockets.

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Wonderful fine curls of wood tell the story of a bygone time when hand planes were used, to ensure floorboards sat level, true and snug against each other…

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Bouncy floor …could this be the main cause?

I had previously been aware that the middle bedroom upstairs has quite a bouncy feel to it. I have quite a heavy filing cabinet and a desk which both exhibit a slightly irritating slope, demonstrating that the floor sags slightly towards the centre. I had previously worried that the joist ends might be deteriorating or some structural issue with the back wall might be contributing to this. Cursory inspection indicates the joists are in sound condition with no rot or woodworm. I have not ruled out a issue with the supporting walls just yet.

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Two rows of notches in the centre of the room, approximately halfway across the span of joists. Note the noggins made from offcuts of wood – some have a skirting board profile on them.

Walking around the room causes the filing cabinet to move and make clanging noises, indicating that the floor is springier than other rooms upstairs in the house. When we took up the floorboards in this room, we found that the joists had been notched more than once towards the centre of the room. Basic intuitive understanding of physics would suggest this is not good practice, which can be confirmed by checking structural guidelines that explain the best locations for drilling or notching joists.

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There’s a reasonable likelihood that these notches are causing the springy feeling floor in the middle bedroom – we will look at methods to strengthen these in future.

I am guessing that the notch on the left may have gone to a gas fire or gas lamp since there doesn’t seem to be any other reason an electrical cable would run in this direction. The notch on the right is for the cable to the dining room light fitting.

Running cables in old notches and newly drilled joists

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Sam suggested using the old notches to run cables where possible to avoid weakening the joists further. He explained that metal plates were needed to protect the cable from mechanical damage from nails etc,  & he advised that these jointing plates from Screwfix should do the trick.

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A metal plate is marked out over the notch, recessed using a chisel, then screwed down

A head torch is invaluable for working on this sort of thing to give good directional light whilst leaving your hands free… especially when your mains lighting is out of action

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Care is needed to avoid damaging the cable…

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The modern alternative to notching for cables involves drilling through the joists, although it is preferable to minimise any new damage where possible to avoid weakening the floor structure. These do not require protection with metal plates due to the cable sitting below the level where nails or screws are likely to penetrate.

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In the middle bedroom, notches from the old, single, surface-mounted socket you can see on the skirting board are repurposed to run a new cable down to the 1st socket in the dining room radial circuit, which is located in the alcove to the left of the chimney breast

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Carefully chiselling recesses for protective metal plates over cables running in notched joists.

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There is a gap in the central ‘spine’ wall of the house between the front and middle bedrooms where a half-brick has been removed to allow for the running of services. I found it interesting to note that the joists for each room sit alongside each other – it makes complete sense – I mean… where else would they be? I just find it an endlessly fascinating journey learning how buildings are constructed… the unseen parts that are vital to the whole functioning well, but that most people pay little attention to.

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The 22mm copper pipe runs to the boiler on the rear wall of the middle bedroom, the grey pipes are the flow/return for the front bedroom radiator and there are various cables for sockets and lights. This gap allows quite a bit of sound transmission between the rooms; it will be better sealed once all services have been finalised.

Taking overview photographs of the lifted boards is a useful reminder in future of where various services run, the route they take, which boards are already cut & how best to easily access various areas with minimal disturbance. I plan to draw or create a 3d model of all the wiring in the house, to simplify any future works that myself, tradespeople or future occupants might want to carry out.

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A well deserved cup of tea!

Read more about the rewire in Part 3

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