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joists

A joist is a horizontal structural member used in framing to span an open space, often between beams that subsequently transfer loads to vertical members. When incorporated into a floor framing system, joists serve to provide stiffness to the subfloor sheathing, allowing it to function as a horizontal diaphragm. Joists are often doubled or tripled, placed side by side, where conditions warrant, such as where wall partitions require support.
Joists are either made of wood, engineered wood, or steel, each of which have unique characteristics. Typically, wood joists have the cross section of a plank with the longer faces positioned vertically. However, engineered wood joists may have a cross section resembling the Roman capital letter "I"; these joists are referred to as I-joists. Steel joists can take on various shapes, resembling the Roman capital letters "C", "I", "L" and "S".
Wood joists were also used in old-style timber framing. The invention of the circular saw for use in modern sawmills has made it possible to fabricate wood joists as dimensional lumber.

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  1. T

    Getting a long kitchen sink waste across and out to main waste stack

    I have a project where we'd like to put a kitchen in the living room to create an open plan. The would mean the sink waste running the length of the kitchen circa 3m and then circa another 3m to get out to the waste stack. Most joists run the right way ( subject to any noggins) however we'd need...
  2. O

    Notching joists for 1” 1/2 waste bath/shower

    Guys I have read the labc advice on notching and I’m all ok, I have calculated a max 38mm notch allowed but that isn’t going to allow for my 1” 1/2 pvc.. what an earth do I do? Notch really needs to be 42mm deep Thanks!
  3. T

    Drilling joists to get into loft

    Good afternoon, im putting in a concealed shower unit into a cavity wall. It’s going to need 2 x 25mm holes for hot and cold supply and a 20mm hole for the shower head feed. every joistdrilling and notching advice I can see on the net is about drilling horizontally. But whatif you need to...
  4. Ricardo Napoli

    New build plumbing joists

    hey guys, we are starting on a load of new build houses on site just wondering about the joists. I take it you can’t just drill any where for the hep pipe to go through? All the other new builds we have done had the metal web joists so had no problems with pipe runs. Any advice would be good...
  5. M

    Waste pipe through joists

    I am fitting a shower tray upstairs. I want to run 42mm shower waste pipe for a run of 1. 6m. The problem I have is that I would have to drill a hole 45mm in a 120mm joist. These joists I don't think are structural as they run from rsj to rsj. I would have to go through 3 joists. Is this...
  6. V

    Holes in floor joists for waste pipes

    If you have to run a basin or shower waste perpendicular to the joists I understand that you need to make the hole in the middle of the joists.My question is how big a hole can you make without affecting the structural integrity of the joist and how can you put a fall on the pipe if you have to...
  7. J

    Anyone drilling holes through joists for waste pipes...?

    If you looking for a tool to drill through joists I used one of these recently on a house I 1st fixed... 51mm TCT holesaw, very fast & very easy to remove cut timber. Used the arbor from my bi-metal holesaw kit. (As you know there's rule & regs as to cutting/drilling joists so keep within...
  8. Scott_D

    Wood bits for drilling joists?

    Whats best for drilling joists? Realised today all my bits are blunt, old and useless. Need to upgrade
  9. N

    Plastic vs Copper

    I did a search but couldn't see the answers I was looking for as I believe this may be asked does any one know the exact pros and cons regarding these two pipes obv plastic is cheaper and to an extent more robust but is there any thermal advantages if so does any one have any links to the...
  10. C

    Plumbing speedfit pipe around metal joists - protection

    Hi, I need to plumb speedfit pipes around some metal joists without drilling into them. Should i protect the plastic pipe with something to prevent it rubbing on the metal joists? Also, what would you recomend to attach/clip the pipe? Thanks, Colin
  11. M

    asbestos water tank and cracked wood support advice

    Hi, I recently had a leak in the mains water pipe to my asbestos water tank. Ive fixed the leak and in the process ended up draining the tank down and refilling it. I have 2 questions - 1) ive noticed since the tank support beams have large splits in the wood (see pics). Im assuming they have...
  12. J

    Cut a 300mm hole in lath and plaster ceiling?

    I have to fit a condensation control fan (PIV) into the hall ceiling. The hole needs to be about 300mm and the ceiling is lath and plaster! Any tips for cutting the ceiling without damaging the surrounding lath and plaster? Cheers
  13. M

    Ground floor 75mm depth joists

    Evening all. Long time since being on here due to work being a bit crazy. I hope you're all doing well and enjoying yourselves. Need some advice on the best way to install some pipes on the ground floor with the joists just 75mm deep. Pretty much 3x2. Now the space underneath the joists is...
  14. M

    Identifying a water leak - insulation

    Got a potential headache on my hands. I have recently had my house refurbished- we went all the way back to the joists and I saw all new central heating pipes and electrics going in - as well as the floorboards and a layer of hardboard on the upstairs floor and plywood in the bathroom go on...
  15. B

    Flourescent dye detection

    I am in desperate need of advice, from a female who knows nil about plumbing but is learning fast following a huge amount of water discovered under my home! There was absolutely no indication of any of this going on in my home until laminate recently lifted in corner of my home! floor boards...
  16. T

    floorboard on gas pipe

    Hello ( new member) I am trying to replace my landing floorboards, having removed the last one i have discovered a gas pipe which has been fitted along 4 joists, there are holes cut into the joists to accommodate the pipe but there are 2 of the joists where the pipe is not flush and is...
  17. F

    Cutting tracks for pipework

    Hi guys, first post here. Joined up to do a bit if research into a CH system we're having installed in the coming months. Our flat has a concrete cap on the solemn, and no gap between joists and floor/concrete, so only way to go below floor is to cut channels/tracks into the caber floor/joists...
  18. E

    Gas pipes under joists

    Hi could anyone give me advice on where I stand with this. recently whilst investigating an uneven kitchen floor, my joiner cut a hatch to pack up the uneven floor, when the hatch was up it was noted that joists were sitting directly on top of 2 gas pipes, this is why the floor had a high point...
  19. S

    Sink & bath into Soil pipe horizontal

    Hello, I would appreciate some advice if anyone could spare the time... I have a soil pipe running horizontally (with correct fall) for 1m before it exits the house. Coming in from the side I have a 40mm which carries the waste from a bath and sink. This needs to connect to the soil pipe. The...
  20. M

    Joists runing parrel to external walls making it hard to get radiator pipes

    Hi I have a new build to first fix were the joist run parallel to the external walls, most rads are on external walls. The joists are about 50mm from the wall though to 125mm. So bang in the distances I would want to bring my 15mm copper storks up to the rads, from a 15mm plastic elbow and...
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