Section 5: element definitions
1 Substructure
1.1 Substructure
Definition: All work below underside of screed or, where no screed exists, to underside of lowest floor finishes including damp-proof membrane, together with relevant excavations and foundations (includes walls to basements designed as retaining walls).
Functional definition: To transfer the load of the building to the ground and to isolate it horizontally from the ground.
Measurement: Area of lowest floor measured to the internal face of the external wall (as for gross internal floor area) (m²).
The cost and area of any lowest floor slab that extends beyond the external wall for a veranda and the like should be shown separately.
Cost and area of basement walls should be shown separately.
Design criteria to be stated:
- Permissible soil loading (kN/m²);
- Nature of soil;
- Bearing strata depth (m);
- Site levels: main gradients;
- Water table depth (m);
- Design load (kN);
- Thermal requirements;
- Average pile loading (kN); and
- Volume of basement requiring excavation (m³) measured to the internal face of the perimeter walls, i.e. volume of basement below ground level.
1.1.1 Standard foundations
All standard foundations up to and including the damp-proof course.
| Includes | Excludes |
| Wall and column foundations | Preparatory earthworks to form new contours to site (see 8.1 Site preparation works) |
| Foundation walls to underside of damp-proof course |
Columns and stanchions with relevant casing (see 2.1 Frame) |
| Pile caps | |
| Ground beams | |
| Insulation | |
| Damp-proof course | |
| All relevant excavation, dewatering, backfill, compaction and disposal for the above | |
1.1.2 Specialist foundations
All specialist foundations up to and including the damp-proof course.
| Includes | Excludes |
| Piling | Vibro-compaction to the site in general (see 6.1 Site preparation works) |
| Caissons | |
| Ground anchors | |
| Vibro-compacted columns | |
| Grouting | |
| Underpinning | |
| All relevant excavation, dewatering, backfill, compaction and disposal for the above | |
1.1.3 Lowest floor construction
The entire lowest floor assembly below the underside of screed or lowest floor finish.
| Includes | Excludes |
| Beds, slabs, basement slabs | Applied floor finish (see 3.2 Floor finish) |
| Raft foundations | Non-structural screeds (see 3.2 Floor finish) |
| Suspended floors | Hardeners and sealers to slab (see 3.2 Floor finish) |
| Inclined and stepped slabs | Excludes venting to entire site (e.g. for methane) (see 0.1 Toxic/hazardous/contaminated materials treatment) |
| Retaining walls at changes in level | Basement walls (see 2.5 External walls) |
| Lowest floor surface where construction does not provide a platform (e.g. floor boarding to joisted floors) | Basement floors (see 2.2 Upper floors) |
| Lift pits, etc. below the lowest floor | Basement roofs (see 2.3 Roof) |
| Ducts, etc. below the lowest floor slabs | Machine bases constructed on top of slab (see 5.14 Builder’s work in connection with services) |
| Swimming pool walls and the like | |
| Slab thickening for loadbearing walls, machine bases, etc. | |
| Structural screeds | |
| Drainage below or within the lowest floor up to the external face of the external wall; including gullies, floor outlets, manholes, etc. | |
| Sump pits, chambers and the like | |
| Damp-proof membranes | |
| Insulation | |
| Membranes, clayboard, etc. beneath slab | |
| Expansion and contraction joints | |
| Groundwater drainage below lowest floor | |
| Venting below building (e.g. for Radon) | |
| All relevant excavation, dewatering, backfill, compaction (including vibro-compaction) and disposal for the above | |
| Special filling beneath slab | |
1.1.4 Basement excavation
All work to basement excavation.
| Includes | Excludes |
| Excavation required for construction of floors below ground level | Preparatory earthworks to form new contours to site (see 8.1 Site preparation works) |
| Temporary support to the excavation (e.g. caissons, sheet piling, and the like) | Basement construction (see 2.1 Frame, 2.2 Upper Floors, 2.5 External Walls, etc.) |
| All relevant dewatering, backfill, compaction and disposal | |
1.1.5 Basement retaining walls
Up to and including the damp-proof course.
| Includes | Excludes |
| Basement walls in contact with earthwork |
Applied finishes to inner faces of external walls (see 3.1 Wall finishes) |
| Permanent support to the excavation (e.g. contiguous and secant piling, diaphragm walls, etc.) |
Internal linings to retaining walls to basements (see 2.5 External Walls) |
| Tanking to walls |
Basement walls not in contact with earthwork (see 2.5 External Walls) |
| Applied protection to external tanking |
Retaining walls not providing external walls to building (see 8.4 Fencing, Railings and Walls) |
| Insulation, membranes, etc. |
|
| Ground anchors to basement wall |
|
| Groundwater pressure relief drains connected to the drainage system |
|
Retaining walls
