Detail design for roads and footpaths

3b. Road build tables

Soft spots and sub-grades with less than 1.5% CBR shall be laid with both an approved geotextile and geogrid or an approved geo-composite of both and the sub-base may be reduced to 300mm over an additional 410mm of 6F5 capping layer granular fill.

Low trafficked residential new roads with either a single access or accesses at both ends to the same road with no bus stops proposed shall be built to the following build depths in millimetres (mm).

Table 1 – Low trafficked asphalt residential new roads


Subgrade CBR value	Sub-base without geotextile	Sub-base with geotextile	Binder course	Surface course	Total depth without geotextile	Total depth with geotextile
Below 1.5% & soft spots	N/A	620	130	40	N/A	880
1.5 %	N/A	440	130	40	N/A	610
2 %	400	340	130	40	570	510
3 %	310	300	130	40	480	470
4% or greater	300	N/A	130	40	470	N/A

Table 2 – Low trafficked block paved residential new roads


Subgrade CBR value	Sub-base without geotextile	Sub-base with geotextile	Binder course	Laying course	Block paver	Total depth without geotextile	Total depth with geotextile
Below 1.5% & soft spots	N/A	620	90	30	60	N/A	890
1.5 %	N/A	440	90	30	60	N/A	620
2 %	400	340	90	30	60	580	520
3 %	310	300	90	30	60	490	480
4 % or greater	270	N/A	90	30	60	450	N/A

60mm pavers may be replaced with 80mm pavers.

In specific exceptional circumstances, we might allow reducing the build depths in Tables 1 and 2 to 200mm binder course over 150mm sub-base with an approved subsoil strengthening technique on a subgrade below 2% CBR.

Table 3 – Low trafficked permeable paved residential new roads


Subgrade CBR value	Sub-base Type 3	Binder course	Laying course	Block caver	Total depth
2.5% or greater	300	130	50	80	490

Permeable paving is not suitable on a subgrade with a CBR value less than 2.5%. Additional sub-base may be proposed to meet hydraulic requirements. Binder course shall be perforated by 75mm cores at 750mm centres.

High trafficked residential new roads with access at both ends to different roads or to the same road with bus stops proposed and all industrial new roads, shall be designed with the following build depths in millimetres (mm).

Table 4 – High trafficked asphalt residential and industrial new roads


Subgrade CBR value	Sub-base without geotextile	Sub-base with geotextile	Binder course	Surface course	Total depth without geotextile	Total depth with geotextile
Below 1.5% & soft spots	N/A	620	180	40	N/A	930
1.5 %	N/A	440	130	40	N/A	660
2 %	400	340	180	40	620	560
3 %	310	300	180	40	530	520
4 %	260	260	180	40	480	480
5 % or greater	230	N/A	180	40	450	N/A

Table 5 – High trafficked single access block paved residential and industrial new roads


Subgrade CBR value	Sub-base without geotextile	Sub-base with geotextile	Binder course	Laying course	Block paver	Total depth without geotextile	Total depth with geotextile
Below 1.5% & soft spots	N/A	620	120	30	80	N/A	940
1.5 %	N/A	440	120	30	80	N/A	670
2 %	400	340	120	30	80	630	570
3 %	310	300	120	30	80	540	530
4 %	260	N/A	120	30	80	490	N/A
5 % or greater	220	N/A	120	30	80	450	N/A

In specific exceptional circumstances, we might allow reducing the build depths in Tables 4 and 5 to 260mm binder course over 150mm sub-base with an approved subsoil strengthening technique on a subgrade below 2% CBR.

Public road improvements

Public road improvements shall be designed to the relevant road type build as confirmed by us during the review. The surface course for road type 0 and type 1 shall be Hot Rolled Asphalt.

Table 6 – Public road improvement
Road type	Sub-base	Binder course	Surface course
0	Subject to CBR testing	310	40
1	Subject to CBR testing	310	40
2	Subject to CBR testing	250	40
3	Subject to CBR testing	200	40
4	Subject to CBR testing	140	40
5	Subject to CBR testing	110	40

Regardless of the CBR value, unless the subgrade has been proven to be non-frost susceptible, sub-base must be thick enough to provide 450mm of frost cover.

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