The Honest Answer to the First Question
The London clay geology across much of the CM1 area means that ground movement from soil shrinkage and swelling can be a significant factor in driveway performance, and a professional contractor will excavate to the correct depth and specify a robust sub-base to prevent the cracking and settlement that poorly constructed driveways on clay soils frequently experience.
The area is a city in Essex, East of England, administered by Chelmsford City Council. The postcode districts covering the area are CM1, CM2, CM3. Nearby areas include Basildon, Brentwood, Braintree, Maldon. The sub-base beneath any driveway surface determines its long-term performance — a minimum 100–150mm compacted Type 1 MOT stone base is the standard specification for residential driveways.
Sub-base and Installation Standards in Chelmsford CM1
The clay causes ground movement as it shrinks in dry conditions and swells when wet — movement that will crack and deform a driveway laid without adequate excavation and a properly compacted Type 1 MOT sub-base. 150–200mm of compacted Type 1 is the minimum sensible specification in Essex's clay soils; less than this is the single most common reason for premature driveway failure in the county. Any contractor quoting without mentioning the soil conditions and their specification for sub-base depth is not engaging seriously with the job.
Driveway Planning Rules in Chelmsford and the CM1 Area
The area has a very large driveway contractor market, and Chelmsford is well served. The range of quotes for a similar job can be wide — sometimes reflecting genuine quality differences in sub-base specification, sometimes reflecting different views on what the soil conditions require. Getting three itemised quotes where the sub-base depth is explicitly stated gives the most reliable comparison. Resin bound aggregate has become extremely popular in Chelmsford given its permeable properties and the fact that it doesn't require planning permission for front garden replacement. Planning is required for impermeable surfaces over 5 square metres.