Gas Pipework Installation: Materials, Sizing, Burial and Pressure Testing

Quick Answer: Domestic internal gas pipework must comply with BS 6891. Copper half-hard tube (BS EN 1057) is the standard for internal above-ground work; yellow MDPE is used underground at minimum 375mm depth (600mm under roads). All work must be carried out by a Gas Safe registered engineer. Pressure test at 100mbar working pressure, and perform a let-by test before connection.

Summary

Gas pipework installation is one of the most tightly regulated areas of building services. A gas leak or poorly installed pipe joint is a potential source of explosion, fire, or carbon monoxide poisoning. Every aspect of the installation — from material selection and pipe sizing through to burial depth and pressure testing — is governed by specific standards and Gas Safe registration requirements.

IGEM/UP/2 (the Institute of Gas Engineers and Managers installation guidance for domestic premises) is the primary technical document that engineers work to alongside BS 6891. Together these cover sizing methodology, materials, installation practice, and testing procedures for domestic and light commercial gas installations in the UK.

This article covers all aspects of domestic gas pipework — internal copper installation, CSST (corrugated stainless steel tubing), underground yellow MDPE service pipes, sizing methodology, testing procedures, and Gas Safe notification obligations.

Key Facts

Quick Reference Table

Need to quote gas work? squote generates accurate, professional quotes fast.

Try squote free →
Pipe Material Standard Applications Maximum Temperature Notes
Copper half-hard (R220) BS EN 1057 Internal domestic 250°C (not for direct burial) Most common; soldered or compression fittings
Copper hard (R250) BS EN 1057 Internal domestic 250°C Used for longer straight runs
Yellow MDPE BS EN 1555 / BS 1552 Underground external 40°C continuous 25mm minimum; yellow colour only
CSST (stainless) BS 7838 Internal commercial/domestic 200°C Requires bonding; must be clipped
Mild steel (black) BS EN 10255 Large commercial 250°C Welded or threaded; anti-corrosion coated

Detailed Guidance

Material Selection: Copper vs CSST vs Steel

Copper half-hard (R220): This is the standard material for domestic internal gas pipework. It is available in straight lengths (3m and 6m) and can be bent with a pipe bender. Jointing is by:

Do not use pushfit fittings (speedfit, JG Speedfit) for gas pipework — they are not approved for gas service.

CSST (Corrugated Stainless Steel Tubing): CSST (Gastite, Tracpipe) is a flexible corrugated tube in a yellow polymer jacket. It threads through voids and around obstacles more quickly than rigid copper. However:

Steel pipework: Heavy gauge mild steel pipe (black steel, internally painted yellow for identification) is used for large commercial installations and high-pressure distribution. Threaded steel joints require PTFE tape approved for gas use (yellow gas-grade PTFE, not white plumbing PTFE).

Underground MDPE Installation

Yellow MDPE (Medium Density Polyethylene, BS EN 1555) is the standard for underground gas service pipes:

Minimum sizes:

Burial depths:

Location Minimum Depth
Garden/landscaped area 375mm to top of pipe
Footpath/paved area (pedestrian only) 450mm
Road/driveway (vehicular traffic) 600mm
Agricultural land 750mm

Bedding and cover:

Above/below ground transitions: At the point where the service pipe rises from underground and enters the building, a transition fitting connects the MDPE to the above-ground copper or steel pipe:

Pipe Sizing: IGEM/UP/2 Method

Gas pipe sizing uses pressure drop calculations based on the total gas demand of all appliances connected:

Step 1: Calculate total gas demand Sum the rated inputs of all gas appliances in kW:

Step 2: Apply diversity Not all appliances run simultaneously. IGEM/UP/2 provides diversity factors (Table 1 in the document):

Step 3: Calculate pressure drop Using IGEM/UP/2 Table 5 (or approved software), find the pipe size that keeps pressure drop below 1mbar for each pipe run from the gas meter to the appliance. Maximum allowable pressure drop: 1mbar total across the entire installation.

Step 4: Check velocity Gas velocity must not exceed 25 m/s in any pipe section to prevent noise and erosion.

Quick reference sizing (natural gas at 20mbar inlet pressure, 1mbar max drop, 10m run):

Demand (kW, after diversity) Pipe Size
Up to 25 kW 15mm
25–60 kW 22mm
60–120 kW 28mm
120–300 kW 35mm or larger

For runs longer than 10m, increase pipe size by one step for every 10–15m of additional length.

Pressure Testing Procedure

All new gas pipework must be pressure tested before connection to the gas supply:

Working pressure test (tightness test):

  1. Isolate the installation from the gas supply
  2. Apply a test pressure of 100mbar using a manometer (U-gauge or digital gauge)
  3. Wait 1 minute for temperature stabilisation
  4. Record the pressure; maintain for 1 minute minimum (or as specified by BS 6891)
  5. No pressure drop permitted — any drop indicates a leak

Let-by test (valve seat tightness):

  1. With the manual emergency control valve (ECV) closed, apply gas pressure at the inlet
  2. Monitor the pressure downstream of the closed valve
  3. No pressure rise on the downstream side confirms the valve seat is gas-tight
  4. A pressure rise indicates valve seat leakage — the valve must be replaced

Leak detection:

Gas Safe Notification

After completing gas work:

Penalties for working on gas without Gas Safe registration: up to 6 months' imprisonment and/or unlimited fine under the Gas Safety (Installation and Use) Regulations 1998.

Internal Pipework Identification

Above-ground internal gas pipework must be identifiable:

Frequently Asked Questions

Can I use plastic push-fit fittings on gas pipes?

No. Push-fit fittings (Speedfit, JG Speedfit, Hep₂O) are approved for water only and must never be used on gas pipework. The only approved jointing methods for domestic gas are: capillary solder fittings, approved compression fittings, press fittings (Viega, Geberit with gas approval), or proprietary CSST fittings. Always check the fitting manufacturer's approval documentation before use.

Does gas pipework need to be bonded?

Main equipotential bonding must connect the incoming gas service pipe to the main earth terminal. This is a single bond (at least 10mm² copper conductor) at the point where the gas service pipe enters the building. CSST (Corrugated Stainless Steel Tubing) requires additional supplementary bonding at each appliance connection because of its susceptibility to lightning-induced surge.

What happens if the pressure test fails?

If the tightness test shows a pressure drop, the leak must be located and rectified before any further work. Use leak detection fluid on all joints. If the leak cannot be found by visual inspection, a more sensitive leak detection device (electronic gas detector) may be needed. Once repaired, the test must be repeated from the beginning. Do not connect the installation to the gas supply until the test passes with zero pressure drop.

Can I bury copper pipe underground?

Copper is generally not appropriate for direct burial underground. Copper is susceptible to corrosion in aggressive soil conditions (acidic soils, soils containing sulphur or chlorides, soils contaminated with salts). Where copper must pass underground (e.g. short sleeve through a wall foundation), it must be sleeved in a continuous protective sleeve and sealed at each end to prevent moisture contact. For all genuine underground runs, yellow MDPE is the correct material.

What size meter is needed for my gas installation?

The gas meter must be sized to pass the maximum instantaneous demand of all installed appliances. For domestic installations:

Regulations & Standards