Another two central heating Q's - timber notches and feed pipes routing

Yet another Q for pending central heating install.

I need to run the 22 mm flow and return across all the wooden timbers under the 1st floor rooms (a 50's 3 bed semi). Making the notches is ok but these seem mighty big "notches" to me. Also they need to be a little larger than 22 mm as want some clearance to the floorboards above and plan to put some "patches" of pvc for the pipes to expand in. Not being a structural engineer, is it safe to make such large notches in the timbers? Not too keen on the floor collapsing in!

Supplementary Q: The flow and rtn to each rad will tee off from these "bus-like" 22 mm's. What is the best way to do this ie both 15 mm pipes are going to tee off in the same direction from the 22 mm's so one 15 mm has to loop under the other. (Hope that makes sense!)I see Screwfix sell a 15 mm loop pipe, which I thought to use. Is there a better way perhaps?

Thanks

Reply to
dave
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When notching try to keep to the edge of the room, as a rule of thumb no mo re than a quarter of the span of the joist in from the edge. It is at the c entre of the joist that you need the greatest depth of material so notches towards the centre will weaken the joist. Also if you have T&G flooring and you are installing say flow and return pipes then lift 2 planks and aim yo ur notches down the middle of each that way when you replace the boards you will have joist into which to nail or screw the planks back.

Richard

Reply to
Tricky Dicky

Make sure they are in the 'middle' of a floorboard, and when you replace those screw i down firmly either side of the notch. That will add back a considerable amount of the strength lost.

Reply to
Dave Plowman (News)

dave scribbled...

I once cut a row of notches for 28mm pipes across the middle of a house to fix a major design cockup in a new build wooden framed house. The arsetech turned up to see what we had done to ensure the heating would work and nearly shit himself when the saw how large the notches were. He'd designed the house with very small margins on the joists and we'd gone beyond the allowance he'd made. As there was sod all we could do about it - the house was occupied and so were the other 5 that required similar treatment, we carried on. The houses never fell down, but I don't know if the arsetech still has a job.

Oh - we had to replace the boilers too, which meant larger holes for the balanced flues - he was lucky, we got away with only cutting through only one upright by a matter of an inch so-.

Reply to
Jabba

The joist sizing rules are based on deflection rather than breaking strength. So the floors would have felt a bit extra springy - but they're unlikely to have collapsed.

You'd have done better to drill through the centres of the joists - with the holes carefully lined up, of course - and then fed the pipes in through a small hole in an outside wall.

Reply to
Roger Mills

A notch can be no more than 1/8th times the joist height in depth. Notches must be toward the ends of the joist only - between 0.07 and

0.25 times the span. So with a 4m joist that would be anywhere between 280mm and 1m from either end.

one tee rotated with its spigot at 45 degree, then a pair of 45 degree bends to miss the other pipe and continue, or a preformed crossover bend.

Reply to
John Rumm

The general rule is that if drilling, in the middle of the height and near the mid span of the joist is best. (hole diameters of no more than

1/4 of the joist height - and no nearer the ends than 1/4 of its span). Notching is best at the ends. (see my other post for building regs specs)
Reply to
John Rumm

In article , John Rumm writes

Useful info John, thank you.

All in all, maybe plastic would be easier, fine for notches or drilled joists and no bother to flex under/over the main feeds.

I would suggest copper feeds on the verticals to the rads though, no point in tempting fate with carpet fitters cutting close to plastic pipes.

Reply to
fred

You could run two 15 mm pipes in parallel.

Or put the minimum 22 mm loop in and take 15/10 mm feeds from it. You probably only need a couple of metres of 22 mm.

Run the feeds in plastic and you can drill small holes in the middle of the joists.

Reply to
dennis

Why not drill the holes and use Hep2O ... much smaller cut out, less weakening of joists, and usually a lot less joints in the pipe.

Reply to
Rick Hughes

Agreed. Read the Building Regs as regards notching, so you can be pretty sure you will not be weaking the joist too much if you do go ahead. Basically: between 0.07 and 0.25x span on TOP of the joist. Max. depth 0.125x depth of joist.

Holes: max diamter 0.25x joist depth, in the centre line of the joist between 0.25 and 0.4 x the span.

Notching under the joist is a bad idea.

There is a good diagram in this .pdf:

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Reply to
A.Lee

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