Plumbing work and the building fabric

Core idea

Pipework rarely exists independently of the building. Drilling, chasing, notching and making openings can affect structure, damp resistance, fire separation, sound and airtightness. Before cutting, identify what the element does and what services may be hidden. Restore the required performance after the service passes through.

What to recognise

• Do not notch or drill structural members outside accepted zones or design instructions.
• Maintain damp-proof courses, membranes and weathering where pipework crosses the envelope.
• Fire-stop penetrations with a suitable tested system for the wall or floor construction.
• Protect safety glazing and identify concealed electrical, gas and water services before drilling.
• Preserve required ventilation paths; sealing a grille to solve a draught can create another hazard.
• An intumescent collar closes the passage left by a softening plastic pipe during a fire. Use the specified arrangement for the pipe, wall or floor and opening, including the required fixings and gap seal; a collar on its own is not a complete repair.

Apply it

When routing a pipe through a compartment wall, plan the sleeve, movement allowance, insulation and compatible fire-stopping before making the hole. Photograph concealed work and record the product and installation detail. A neat pipe on show does not mean the barrier behind it has been restored.

Limits

Building-control notification, structural design and specialist fire-stopping can require other competent people. If the construction or hidden-service route is uncertain, stop and investigate. A general-purpose foam, sealant or patch will not suit every fire, acoustic or damp-control detail.

Notifiable work under the Building Regulations

For work in England that needs building-control approval, make the application or give notice before starting, following the procedure that applies and any exceptions. Gov.uk describes two routes for most work: a full plans application, the most thorough, with a decision within 5 weeks or 2 months with consent, and a building notice, only for smaller projects, which lets work start 2 days after the notice is submitted but gives no formal approval of plans. An installer registered with a competent person scheme can use the scheme instead for work within its scope, with the required notification and certification. Either way, the work must comply. Building-control arrangements and terminology differ across the UK, and higher-risk buildings in England have a separate regulator-led route.

Installing an unvented hot-water storage system is an example of plumbing work that engages Building Regulations and may require notification or a scheme certificate. In England, routine like-for-like tap or gland maintenance and adding an outside tap to an existing supply do not themselves require a building-control application. Water-fittings requirements remain separate.

Notching and drilling floor joists

For a conventional solid-timber domestic floor joist within the scope of these rules, top-edge notches lie between 0.07 and 0.25 of the clear span from a support and are limited to 0.125 of the joist depth. Centre-line holes lie between 0.25 and 0.4 of the span, with diameter limited to 0.25 of depth. The guidance also limits notch depth to 35 mm and hole diameter to 65 mm, spaces holes at least three diameters apart, measured centre to centre, and keeps them at least 100 mm from a notch. Check adequacy and the specific design before cutting. Engineered joists, beams and other structural members need their own instructions or design advice; these fractions are not blanket permission. Roof rafters are not notched or drilled for pipes at all. Pipe joist clips with a built-in metal plate protect a pipe in a notch from nails driven through the floor, and their shape is a ready template for a notch of the right depth.

Chasing masonry walls

Approved Document A keeps a vertical chase to a third of the wall's thickness, or of the leaf's thickness in a cavity wall, and a horizontal chase to a sixth of the leaf. In a 90 mm leaf that allows a vertical chase of 30 mm and a horizontal one of 15 mm at most. Do not place a chase where it would weaken the wall, particularly in hollow blocks.

Supporting copper pipework

The Copper Development Association's table gives maximum intervals between supports. Horizontal runs need closer supports than vertical ones, because a horizontal run sags between them: 15 mm tube is supported every 1.2 m horizontally and 1.8 m vertically, and 22 mm and 28 mm every 1.8 m horizontally and 2.4 m vertically. On long runs hung from brackets, fit anchor bracing at 12 m centres to stop the run swaying. Hot water lines also need room to move: each metre of copper tube changes length by about 1 mm for a 60 °C change in temperature. Anchor the run and take up the movement with an expansion joint or an expansion loop, and install and support a loop in the horizontal plane, so that it cannot form an air lock. In a home, bends, elbows and offsets usually take up this movement; Yorkshire Copper Tube's guide says to consider expansion bellows or loops on straight runs longer than about 10 m.