I know this thread is two years old but I want to clear up a lot of miss information and inform those who read this in the future the correct facts.
Firstly a gas pipe, gas service pipe and a gas main are three different things.
1) A gas pipe is what is installed after the gas meter inside your house/building.
2) A service pipe is what supplies gas to your meter from the street.
3) A gas main is the pipe that runs down your road supplying the service pipes.
In brief the gas main and service pipes can have anything between 24mb to 75mb of gas pressure in a low pressure main and in a medium pressure main it will be anything over 75mb.
For gas pipe installed in a house/dwelling the following regulation/document is applied
BS6891:2005 + A2:2008. This document covers copper, steel and polyethylene (PE) which is yellow.
All three types of gas pipe can be buried although copper and steel need protection from corrosion.
PE pipe is plastic and requires no protection under normal installation. Old steel gas service pipes tend to have PE pipe slid up the middle to save digging up the old service pipe. This steel sleeve adds protection but is not a genuine sleeve for the PE service pipe and there would require adequate sleeving if required/demanded.
The regulations are not completely clear cut on buried gas pipes/service pipes under buildings, however.
If you know your service pipe comes down your drive to a meter box on the side of your house and you decide to build an extension over it the following applies.
Don't listen to your builder.
Don't listen to the building control officer.
These two people don't know the correct regulations or where to find the correct information.
Your builder if digging near a gas service pipe cannot use a mechanical digger within 0.5meters of it and must hand dig around it. If the builder exposes the gas service pipe, PE or steel they must inform the responsible person of the house/property and stop work immediately.
Builders, building control officers will just tell you that it is ok to build over it. WRONG WRONG WRONG.
As the responsible person (the home owner) you must do 1 of 2 things, or both. Call a Gas Safe registered gas engineer. Go to
www.gassaferegister.co.uk and find a local registered gas engineer.
They will advise (if they know, which they should like I do) to call national grid or who ever looks after the gas mains/service pipes (0800111999). These people are the gas transporter and are responsible for all gas pipe work infrastructure up to the isolation valve before the meter. The gas meter belongs to the supplier. Your installation belongs to you.
In my area it is National Grids responsibility to look after the service pipes and gas mains. They are very helpful. You, the home owner/responsible person or the gas safe registered engineer will tell them that your builder as uncovered the service pipe to your house. They will demand you stop the builder from working and that your turn of the gas at the meter and all appliances etc.
They will send out someone to survey what has been uncovered and may uncover more to expose more pipe.
Firstly they will say your meter must be moved. Although, depending on the depth the pipe is buried may affect his decision. However, most service pipes are not at the correct depth of below 375mm from the surface as I know all to well.
If deeper, like deeper than 1 meter or more you can build small foundations either side of the pipe before putting foundations over it. However this will not be the case trust me.
I have seen builders lay a foundation under the service pipe and build a lintel over the top. This is not adequate. The service pipe would need to be sleeved first by Nation Grid. They will not do this however for a number of reasons.
1) If the service pipe is PE and has fittings, like elbows, couplers etc then you cant build over it as you can't builder over pipes with joints. BS6891:2005 (yes this is normally used after the gas meter) states regulation 8.15.1 table 4 that PE pipe with fittings can not be build over or be installed under a building.
2) The service pipe is not your property and you cannot not conceal it from inspection. Your drive can be dug up, you house cannot without damaging the foundations.
3) Tha Gas Act 1995/2000 comes into play and this is one big document riddled with dos and don'ts.
You also have IGE/TD/4 which covers gas service pipe and gas mains etc. I have not read this document as it cost £165 and I have purchased loads of these documents in the past at a cost of thousands of pounds.
If your builder decides to build over the gas pipe in anyway and even if the building control officer signs off on it this situation will bite you in the arse.
The pipe will either get squashed or the joint that 9 times out of 10 that puts the service pipe at a right angle to the meter box may crack and leak gas. The gas will build up and up and up until the ground is saturated with gas and only has one more place to go, YOUR HOUSE. You wake up one morning, if you are alive and you turn a light on, or the kettle. You will more than likely be killed within 1000th of a second from the almighty gas explosion. You and your family will be killed.
The ground will hold a massive amount of gas before seeping upwards.
The gas transporter, supplier and an half decent builder, gas safe registered engineer will tell you not to build over any form of gas pipe. If you do and, because you can in some situations and it isn't done correctly then you may be screwed.
99% of the time no gas service pipe or mains gas pipe will ever be built on. You can put a gas pipe downstream (after the gas meter) of the gas meter under a structure but only as long as you protect it correctly by following the regulations in place for the type of installation you have.
Gas suppliers and companies like National Grid are fighting to have a clear cut regulation added to the Gas Safety (installation & Use) Regulations 1998 to prohibit any gas pipe being build over.
Just don't do it. Simples.