New gas pipe - through wall or under floor?

[Richard Conway]

Hi,

I'll be doing some work on the kitchen in the near future, and having moved things around to measure them I have found that the gas pipe to the cooker is in very poor condition - it is buried under the concrete floor with seemingly no protection and at the point where it exits the floor it is very green and corroded looking. I am assuming that I have no other option but to replace it (tell me if I'm wrong to save me some work!) Am also planning to replace cooker with gas hob/electric oven.

While I'm at it, I'm going to upgrade the pipework to the boiler to 22mm as it is currently only 15mm.

The gas supply and meter come in to the front of the house in a cupboard in the living room. The kitchen is in a single storey extension at the back. My options are as follows:

1) Take 22mm pipe under living room floor (this isn't concrete, only the extension is) from meter, up through the cupboard where the boiler is, T off to boiler with short lenght of 15mm. Carry on up the cupboard with 15mm to under the floorboards on the landing. Take it accross the landing, through back bedroom and down into dining room where it will be boxed in vertically until going through the wall into the kitchen roof space. Then down through the ceiling to below hob height, across the wall behind the units and into hob.

My main question relating to this option is what I am supposed to do when running the pipe through the wall into the extension. I know that you are supposed to sleeve the pipe and only seal it at one end - but which end? If I seal it at the house end and there is a leak it will spill into the roof space of the extension which is enclosed so would allow gas to build up - if I seal it on the extension side then it will build up in the boxing in on the house side. Any ideas what would be best?

2) Dig up channel in kitchen floor to replace the current run of pipe.

Not sure if this is easier or harder - I'm assuming my trusty SDS with a chisel bit would make fairly light work of digging up the channel (probably cut the edges with an angle grinder) - but how do I go about filling it or covering it afterwards? I would preferably cover it with wood as opposed to refilling it to aid future access.

Any adivce/ideas/criticisms on the above would be greatly appreciated.

Thanks, Richard

[Andy]

I had a vaguely similar problem. I can't quote the regs, but had to run some gas pipe in a stud wall cavity. I eventually settled for running the pipe in some solvent weld plastic gutter pipe, after asking around a bit. This allowed the pipe to enter an unvented area, but still itself be vented by the ends of the gutter pipe, which emerged into the room ( the gas pipe went into the studding for a bit then reemerged ).

You know that the main reason behind the gas pipe needing a plastic sleeve when it goes through a cavity wall is that the consequences of a build up in the cavity, if ignited, could lead to collapse of that wall. I imagine that a leak into your (unvented?) kitchen extension roofspace would have bad conortations, if not as bad as the cavity wall. The boxed in section seems to me to be the least worst place for a gas leak, being non-structural and with a small enclosed volume. The other reason for sleeving a pipe as it goes through a wall is that it is most vulnerable there, to scraping and distortion in case of movement of the house due to settling or seasonal heave or thermal expansion etc.

I would put a couple of uncloseable louvre vents in the boxed in section, one top, one bottom. I would vent the pipe sleeving into the boxed section, and seal the end of the sleeve going to the wall at the kitchen roof space end. This leaves the sealed volume of the roof space as the one place where a leak could build up, although the pipe will not be particularly vulnerable there. After all, if it is permissible to run a pipe under the floorboards, that gives the same sort of problem.

A belt and braces measure would be to sleeve the gas pipe where it enters the roof space with 4" diameter gutter pipe ( else you can't assemble things ) and seal that gutter pipe where the gas pipe + wall sleeve emerges into the roofspace, then have the gas pipe and gutter pipe sleeving emerge through the kitchen roof. Any gas leak then has a small volume path to a ventilated area.

I'm sure this is OTT but will at least give you a warm fuzzy feeling! I don't know the regs as they pertain to unventilated roof spaces.

Of course, don't recover with concrete as this corrodes the copper, unless you run it in plastic conduit or wrap it in denso tape. The wood sounds a good idea, you could seat the edges of the wood on a little mortar run along the edges of the channel you grind/chisel, that way it'll sit perfectly. DYOR.

I'm sure others on this NG will have suggestions.

Andy