A permeable sub-base stores or conveys water as well as supporting the surface. Its aggregate must match the complete drainage design. Use the dedicated calculator to explore a guide budget for the work described below.
Estimate permeable sub-base installation from the measurements and work options below. Guide allowances are already included; a contractor’s quote is not required to use the tool.
Do not substitute a dense aggregate for an open-graded specification. Storage volume and infiltration need a site assessment.
Guide model reviewed 7 November 2026. VAT treatment varies between published guides and supplier quotes; no VAT is added automatically. Add it only where your allowances exclude it.
The guide covers sub-base construction by measured area. The depth field gives a quantity check, while the actual depth, aggregate and compaction are determined by the agreed specification. Do not interpret the displayed volume as approval of a particular foundation.
View the published guide used for the main allowance. Optional allowances are budgeting estimates and can differ from a site-specific quotation.
Use a measured specification to compare prices for your property. Ask contractors to confirm the work, preparation, materials, access, disposal and any exclusions before agreeing a price.
Permeable Sub-Base Installation planned around your property
A permeable sub-base stores or conveys water as well as supporting the surface. Its aggregate must match the complete drainage design.
Do not substitute a dense aggregate for an open-graded specification. Storage volume and infiltration need a site assessment.
A permeable sub-base stores or conveys water as well as supporting the surface. Its aggregate must match the complete drainage design.
Do not substitute a dense aggregate for an open-graded specification. Storage volume and infiltration need a site assessment.
Measure the length and width of the work area in metres. Split an irregular outline into rectangles and add their areas. Where a depth or unit-count field is provided, it gives a separate quantity check; it does not decide the correct construction specification.
The guide covers sub-base construction by measured area. The depth field gives a quantity check, while the actual depth, aggregate and compaction are determined by the agreed specification. Do not interpret the displayed volume as approval of a particular foundation.
The first guide option is open-graded type 3 sub-base construction. Its allowance is £55–£85 for the relevant unit shown in the result. This is a published-guide starting point; it is not a price offered by a contractor on this website.
This page models open-graded type 3 sub-base construction. A different construction or repair method needs a separate allowance rather than an assumption that every job has the same scope.
The project controls include:
The results show the measured quantity, the selected work allowance and any separately selected items. A volume, unit count or coverage result is a quantity check, not a construction design. Where the model uses a minimum visit allowance or whole bags, the displayed total will not fall in direct proportion to a very small area.
Use the optional contingency to make a separate budget provision. Add a quoted fixed allowance only for work outside the model’s stated scope. Check the VAT basis before selecting the VAT adjustment.
Give contractors the same measurements and work description. Ask them to identify the main work, preparation, disposal, access requirements, drainage and any making-good that applies to this project. An apparent saving can simply mean that a different part of the scope has been priced.
Do not substitute a dense aggregate for an open-graded specification. Storage volume and infiltration need a site assessment. Keep the agreed specification with the quote, including any exclusions and the way changes discovered during the work will be authorised.
Examples use the specification named on each card, the calculator’s example measurements and guide allowances. Optional extras, contingency and VAT adjustment are off. Supply-only models exclude installation.
The guide covers sub-base construction by measured area. The depth field gives a quantity check, while the actual depth, aggregate and compaction are determined by the agreed specification. Do not interpret the displayed volume as approval of a particular foundation.
Measure the length and width of the work area in metres. Split an irregular outline into rectangles and add their areas. Where a depth or unit-count field is provided, it gives a separate quantity check; it does not decide the correct construction specification.
A permeable sub-base stores or conveys water as well as supporting the surface. Its aggregate must match the complete drainage design. Do not substitute a dense aggregate for an open-graded specification. Storage volume and infiltration need a site assessment.
The figures are early budgeting allowances for the work described in the selected option. Do not substitute a dense aggregate for an open-graded specification. Storage volume and infiltration need a site assessment. Ask a contractor to confirm the measured scope, access, preparation, materials and exclusions after assessing the property. The written quotation, rather than the calculator, establishes the work and the agreed price.
The result separates the main work from selected options and any additional allowance you enter. Do not add an item again if the main rate or contractor’s quote already includes it. Contingency is optional and is shown separately.
No extra VAT is added automatically. Published cost guides and supplier prices can use different VAT bases, so check the source and any written quotation. The optional VAT control adds 20% to the calculated allowances only when you select it. Leave it off when the rates or quotation already include VAT to avoid counting tax twice.
