4.3 Pipework Jointing, Sleeving, Corrosion Protection & Concealed Routes

4.3 Pipework Jointing, Sleeving, Corrosion Protection & Concealed Routes

Quick Answer: Under BS 6891, gas pipework passing through external walls, floor structures, or fire-rated partitions must be enclosed in a continuous protective sleeve sealed at both ends with a flexible fire-retardant compound. Gas pipework in screed or concealed voids requires strict protection against mechanical damage, corrosion, and gas accumulation.

---

1. Pipework Sleeving Standards (BS 6891)

Passing gas pipework through structural elements poses risks of mechanical stress, abrasion, corrosion from alkaline building materials, and unmonitored gas spread through wall cavities.

Sleeve Construction & Installation Rules

• Sleeve Materials: Sleeves must be constructed from durable, corrosion-resistant tube such as copper, carbon steel, or heavy-duty rigid plastic (UPVC).
• Continuous Enclosure: The sleeve must pass completely through the structural wall, floor, or cavity. No pipe joints are permitted inside the sleeve.
• Wall Projections: Sleeves must extend beyond finished wall or floor surfaces by at least 1 mm to 2 mm to prevent ingress of wash water or floor cleaning chemicals.
• Annular Space Sealing: The space between the outer surface of the gas pipe and the inner surface of the sleeve must be sealed at both ends using a flexible, non-hardening, fire-retardant sealant (e.g., silicone mastic). This prevents water ingress, gas migration into wall cavities, and draft transmission while accommodating thermal expansion.

---

2. Concealed Routes & Duct Ventilation Requirements

Routing gas pipes inside unvented concealed voids, timber frame floor structures, wall chases, or dedicated service ducts requires meticulous design to prevent gas accumulation in the event of a microscopic leak.

Pipework in Voids and Wall Chases

• Floor & Ceiling Voids: Pipe runs inside joist spaces should ideally use continuous unjointed runs of R220 soft copper or CSST tubing. Where joints are necessary, only capillary soldered or press-fit joints are allowed.
• Wall Chases: Gas pipes buried in wall chases must be protected against corrosion, covered with continuous plaster or masonry to a depth of at least 15 mm, and must contain no mechanical compression joints.
• Prohibited Concealed Locations: Gas pipes must never be routed through unvented lift shafts, chimney flues, drainage ducts, or primary fire escape routes.

Service Duct Ventilation

Where gas pipework passes through a dedicated enclosed vertical or horizontal duct, the duct must be continuously ventilated directly to external air to prevent gas accumulation.

• Ventilation Openings: Ducts must feature high-level and low-level ventilation grilles positioned to discharge safely to the outside atmosphere.
• Fire-Stopping: If a duct passes through fire-rated compartment walls or floors, fire dampers or intumescent seals must be integrated in accordance with Building Regulations Approved Document B.

---

3. Embedding Pipework in Concrete & Screed

Embedding gas pipes directly in concrete subfloors or floor screed is permissible under BS 6891 provided rigorous protective measures are applied:

• Protective Coating: Bare copper pipe must never come into direct contact with concrete or screed due to chemical attack from moist alkaline compounds. Pipework must be factory plastic-coated (e.g., Kuterlex) or manually wrapped with continuous overlapping self-adhesive petrolatum tape (e.g., Denso tape).
• Joint Restrictions: Joints embedded in screed are restricted to capillary soft solder or silver brazed joints. Compression fittings are strictly prohibited in screed.
• Screed Depth: Embedded pipework must have a minimum top cover of 25 mm of screed to prevent surface cracking and mechanical crushing under point loads.
• Expansion Provision: Long straight embedded runs must incorporate flexible expansion joints or sleeving at building movement joints to absorb thermal expansion.

---

4. External Protection & Atmospheric Corrosion

Pipes installed outdoors or in damp environments require protection against atmospheric degradation and aggressive chemical attack.

Corrosion Protection Protocols

• Underground Metal Pipework: Steel or copper pipes buried underground must be protected by factory plastic wrapping or spirally wrapped with petrolatum tape applied with a minimum 55% overlap to ensure double-layer coverage over the entire pipe surface and fittings.
• Dissimilar Metal Contact: Direct contact between copper and carbon steel pipework in moist environments creates a galvanic cell, causing rapid galvanic corrosion of the steel. Dissimilar metal connections must use insulating dielectric fittings.
• Masonry Protection: Where copper pipes emerge from damp floor slabs or plaster walls, they must be wrapped with protective tape for at least 50 mm on either side of the masonry contact point.

---

5. Pipe Support Intervals & Clip Spacing Guidelines

Gas pipework must be securely anchored using approved pipe clips (malleable iron, brass, or plastic-coated steel) to prevent sagging, vibration noise, and mechanical stress on joints.

BS 6891 Maximum Pipe Support Intervals

---

6. Regulatory Checklist for Concealed Installations

1. Verify no compression fittings are installed inside screed, wall chases, or unvented voids.
2. Confirm sleeves are continuous through walls with annular gaps fire-sealed at both ends.
3. Check that plastic-coated copper embedded in screed has a minimum 25 mm top cover depth.
4. Ensure vertical service ducts feature functional high and low level ventilation grilles to outside air.
5. Verify pipe support clips are installed within maximum allowable distance limits.