Step 2 – Preparation of the sub-base
Sub-base should be prepared by using Methods 2, 3 or 4 from Table 6/4 of the Specification of Highway Works Volume 1 Series 600 Earthworks and in accordance with NHBC recommendations:
- The plot should be set out as normal, ensuring that a completed ‘Construction Issue’ drawing showing the Insulslab foundation layout and details is available. For severely sloping sites, individual conditions have to be addressed. In case this happens, please contact Insulslab support.
- Excavate to reduce general level to a depth of 600mm below top of slab level over the polystyrene pod area and 675mm under edge beams and party walls. Additional fill may also be necessary to ensure that all topsoil, degradable material and soft spots are removed.
- Ground conditions may require the placing of an additional hardcore bed under the whole area to overcome the influence of trees/shrinkable soils in accordance with the NHBC Standards Chapter 4.2 and 4.5. Position, excavate & install all services and drainage entries. The accuracy of this operation is paramount, as correction of inaccuracies is very difficult.
- Place granular hard-core and compact to a level 550mm below top of slab level. Compaction with a Wacker Plate or Trench Roller to the hard-core in the trenches or a larger twin drummed roller to the whole of the formation area is acceptable. Tolerances on top of the finished sub-base should be within +10/-20mm with an average of -5mm.