Building Glossary

Structure and groundwork

These are the terms that appear on structural drawings and engineers calculations, and the ones that carry the most cost if they are misunderstood.

RSJ: rolled steel joist, the beam that carries the load when a loadbearing wall is removed. Sized and certified by a structural engineer.
Padstone: a dense concrete block set into the wall beneath the end of a steel to spread its load. Omitting one is a common and serious defect.
Underpinning: deepening or strengthening existing foundations, usually because they are inadequate for a new load or because of subsidence.
Trimming: framing an opening in a floor or roof so that the cut joists or rafters transfer their load onto the neighbouring ones.
Lintel: the beam over a window or door opening that carries the masonry above it.
Purlin: a horizontal beam running along the roof slope that supports the rafters at mid span.

The vocabulary of the projects that dominate south west London.

Side return: the strip of land beside the back addition on a Victorian terrace. Filling it in widens the kitchen and is the highest value alteration on most terraces here.
Back addition: the narrower rear wing running down one side of the plot on a Victorian terrace, usually containing the original kitchen and scullery.
Wrap around: an extension combining the rear and the side return, taking the full width of the plot.
Hip to gable: converting a sloping hipped roof end into a vertical gable wall, squaring the roof to create loft volume.
Dormer: a structure projecting from the roof slope with a flat roof and vertical face, creating full head height in a loft.
Mansard: a roof reshaped to a steep near vertical pitch with a shallow top, giving the greatest loft volume but almost always needing full planning permission.

The approvals that determine whether a project can proceed, and in what form.

Permitted development: alterations you may carry out without a planning application, within defined limits. Removed in some conservation areas and never available to flats.
Prior approval: a notification process for larger single storey rear extensions, where the council consults neighbours but does not assess the design in full.
Article 4 direction: a council order withdrawing permitted development rights in a defined area, meaning a planning application is required for work that would otherwise be automatic.
Building regulations: the technical standards covering structure, fire, insulation, ventilation and electrical safety. Separate from planning permission and required in addition to it.
Listed building consent: a separate consent needed for almost any alteration to a listed building, including interior features. Working without it is a criminal offence.
Party Wall Award: the document produced by surveyors when a neighbour dissents to a party wall notice, setting out how the works may proceed and recording the condition of their property.

The sequence terms that appear on a schedule of works and in progress reporting.

First fix: the services work carried out before plastering, when cables, pipes and duct runs are installed inside the structure.
Second fix: the visible fittings installed after plastering and decoration, including sockets, switches, taps, sanitaryware and door furniture.
Strip out: the removal of existing finishes, fittings and services back to the structure before new work begins.
Snagging: the process of identifying and correcting minor defects at the end of a project before final handover and payment.
Schedule of works: the written document setting out every item to be carried out, in sequence, with the cost of each. It is what a quotation should be based on.
Variation: an agreed change to the schedule of works, priced in writing and approved before it is carried out.

The terms that matter most for durability, particularly in period property.

Tanking: the waterproof membrane applied behind tiles in a wet area. Tiles and grout are not waterproof, so this is what actually keeps water out.
Screed: a levelling layer laid over a floor structure, often containing underfloor heating pipes, on which the final floor finish is laid.
Lime plaster: the traditional finish on solid walls, which allows the wall to absorb and release moisture. Sealing a lime built wall with cement or gypsum traps damp inside it.
Damp proof course: a barrier in the wall preventing moisture rising from the ground. Absent or failed in much of the Victorian stock in south west London.
Decoupling membrane: a layer laid between a timber floor and tiling that allows slight movement without cracking the tiles or the grout.
Slim profile glazing: double glazed units made thin enough to fit into refurbished sash windows where standard units would not.