Installing gas pipe under solid floor

[Tournifreak]

All, I am in the process of building an extension, and need to re-route the gas pipe from the meter box to the boiler. I plan to have a CORGI in to do the connections at each end, but I really want to do the pipe run myself as the plumber is very busy at the moment and waiting for him will hold up the build.

The bit I need advice about is running the pipe below the new solid floor. Currently, there is a concrete block & beam floor. This will then be covered with 90mm Celotex, then 65mm screed.I am planning to do the following. Does anyone have any objections/suggestions?

I want to run the pipe clipped to the concrete block & beams, cut into the Celotex. Pipe will be 22mm copper, with several solder ring straight couplers. I will need 1 solder ring 22-15 reducing tee. Some sort of sleeve where the copper pipe goes through the screed. (I have some Speedfit conduit which might do the job).

Plumber will pressure test and commission. I have plenty of experience soldering pipework.

Is this the normal way to run a pipe in a new solid floor?

My biggest (slight) worry is what happens if there is a leak (somehow) under the concrete floor. The gas could then seep throughout the whole floor, between the Celotex sheets. Then /if/ there was some kind of spark, I dread to think what could happen. Am I being over-concerned? I suppose the probability is pretty small.

Will discuss with the plumber, but want to know the group's (extensive) collective wisdom. (grovel grovel...)

Thanks for any advice...

Jon.

[Lobster]

I don't know what the rules are about burying gas pipes in a solid floor, but personally I wouldn't feel very comfortable with it. Is there no other potential route, eg up'n over the ceiling, or even boxing it in?

If it was a must though, I'd definitely try to run it within ducting, enabling a future duff copper pipe to be replaced with minimal disruption (maybe using the nifty technique described by SetSquare in a reply to a query of mine to enable access to the ends?):

tip would be to ensure that whoever is signing off the installation is happy with you running the gas pipes. Technically, a CORGI shouldn't sign off pipework done by you (although some will) even if it pressure-tests OK, because that's still no guarantee that the joints are properly done and durable - as one CORGI pointed out to me that a joint assembled with flux alone (ie, the soldering forgotten!) is capable of passing a standard test. So it would be a pity if you had your pipe concreted under the floor, and then nobody would agree to pass it!

David

[Mr Fizzion]

I'm curious as to what pressure would blow flux out of a joint. Would pressure testing with 10 bar be good enough?

This is something I have to test in the garden! :-)

Mr F.

[Tournifreak]

I could run it up to 1st floor then notch the joists, but seems messy for a new build. If only one could use Speedfit for gas...would be so much easier because then I could put holes in the centre of each joist. Very hard with copper though. Underfloor would be by far the least messy solution, if it is allowed, and is "normal" practice.

What do others think? I don't see how I'd ever be able to replace/fix a problem with a non-flexible pipe even if it was in a duct. Both ends of the pipe are would be inside, (gas box is cavity type) and would have several bends.

Regards,

Jon.

[Richard Conway]

ISTR that you aren't allowed joints in gas pipes buried under concrete floors. This topic has come up many times before so a good search in google groups may be helpful

[Tournifreak]

I couldn't find anything very conclusive when googling for this topic. In particular, I couldn't find anything about having joints in what is effectively a very small duct. Regs are here:

'm sure this is something which is done all the time, Id just like to feel a bit more informed before I speak to my plumber about it.

Thanks & regards,

Jon.

[Dave]

I recently had to do something similar. When we discussed it with the BCO he wouldn't let me run the pipe in the cellotex and insisted it was in the screed, because of this we had to put the cellotex below the slab and the pipe in the screed on top. Everyone was happy with this solution. I would recommend using iron pipe wrapped in denso-tape rather than copper, if you don't have the threading dies they're available cheaply from the usual culprits. Remember that you must sleeve if you're going through any structure.

Dave

[Lobster]

OK, with lots of bends that would be tricky.

Thinking further on this, how about instead of burying it, you form what would essentially be a trough or gutter in the screed, following the course of where the pipe will run. You allow for a rebate in the screed at the top of the gutter to allow removable pieces of 0.5" WBP plywood to be inset, and which will be flush with the screed.

Still don't know if that is compliant with the regs (particularly vis-a-vis running pipes in confined spaces) but to me it sounds better than burying them! Hopefully Mr Sirett will be along shortly with the definitive response (although - have you tried searching the archives of this ng?)

David

[Ed Sirett]

This type of work is not a common part of my job. It may be that others here are more familiar with these aspect of the regs.

The gas pipe may not go under the footings of a wall unless there is load protection - i.e. a Lintel above the pipe - I think this is the same for waste pipes too.

Gas pipes must not be run in unventilated voids - it is possible that part of your proposed route violates this requirement?

Gas pipes must be protected from possible corrosion due to contact with cement/mortar/plaster.

Gas pipes must be inspected and tested for gas tightness BEFORE the above protection is applied. If you are not able to test for tightness (requires inspecting each joint) then you are not able to install the pipework.

[Tournifreak]

The problem I will have running the gas pipe in the screed is the underfloor heating pipes which are also in the screed ;-) Oh well.

I'll talk to the builder, plumber, and possibly BCO.

Out of interest, why would you recommend iron pipe? Copper can be wrapped in denso tape can't it?

Thanks & regards, Jon.

[Tournifreak]

Good idea, but will clash with meters and meters of carefully planned under-floor heating pipes! ;-)

[Dave]

In my (very limited) experience I've only ever seen jointed iron in concrete floors, not copper. It's much more robust and easy enough to work with.

Dave