does existing wiring in loft space need to be led thro holes in joists when building a loft conversion?

Question

the existing wiring in my loft space is laid over the joists. as i am considering a loft conversion - will the wiring have to be led through bored holes in the joists, to meet legal requirements. or can i build up the existing joists with timber (glued and screwed 38 x 48) before fitting the floor boards.
if holes must be bored, what is the distance below floor boards.

Answer 1

You can drill holes if you wish, but it may mean a lot of disconnecting and reconnecting. The holes should be 50mm from the top of the joists, to the top of the holes, and the same from the bottom, so if you have 6" joists you should drill through the centres to avoid weakening. If you build up or have to notch the joists you can protect with steel plates above the cables.

http://www.tlc-direct.co.uk/Main_Index/Cable_Accessories_Index/Necessities~Cable_Protection/index.html

http://www.worthing.gov.uk/Planning/BuildingControl/TechnicalGuidanceNotes/19NotchingDrillingofTimberJoists/

Answer 2

HI DREW,

Different States require different codes on precise hole boring in joists and beams. We sometimes would build a floor up 1 1/2 .to avoid "runnin" the wires.

Sometimes you can get away with "notching" the wood to drop the wires. As long as you protect the wires with metal strapping (to prevent nails from poking the wires).
But if you wood is nominal at best, beefing it up is best answer.

I like the fact that you said glue, and screws. You are on the right path.

Answer 3

yes- bore thru the center of the joist. Notching the joists will weaken them and is a very bad idea. BTW someone mentioned 2X6 joists-- if that's all you have then be aware the maximum span for that size is only 8 feet

Answer 4

Just think of the electrifying fun you will have when you fix the floor boards and forget that you could not be bothered to run the cables through drilled joists.

Answer 5

you must bore holes in the joists. the holes must not be larger than a third of the total width of the joist, and in the center of the joist

Answer 6

really depends on the loft converter!!! i would personally say that if it was a loft conversion done correctly and to the regs i would employ the services of an engineer to calculate deflection etc you may have to introduce steels and there is where you may have to introduce a secondary set of joists at right angles to the original for strenth etc there is where i would hide all my cabling etc

hth

regards

steve

Answer 7

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