The Quick Answer
Yes! Gravel driveways are the most permeable option by far. This stays true as long as the base is also permeable. The used of type 3 MOT will be essential to ensure complete permeability, and this can be sourced from builders merchants, granted it is not as readily available as type 1 and some digging around, (pun intented!) may be required. When installed, Gravel naturally lays with gaps between the aggregates, this is what makes Gravel driveways permeable.
Type 1 MOT & Permeability
As stated before Type 1 (MOT) is much more readily available however it consists of hardcore aggregate ranging from 40mm down to as fine as dust. The high levels of dust content make this sub grade choice, less permeable than its counterpart, Type 3 (MOT)
Type 3 MOT & Permeability
The use of Type 3 (MOT) ensures that the sub-base will be fully permeable therefore, SUDS compliant. Type 3 is made from crushed granite and limestone. The aggregate size is usually maxed at approx 40mm and is screened to remove most of the fines (dust). The reason that we won’t remove all fines is that this would weaken the base significantly. The fines element within the aggregate helps to allow a solid and sturdy base once compacted.
Out With The Old And In With The New
The only possible way to ensure that your finished gravel driveway will withstand anything the English Weather can throw at it, whilst staying fully permeable, is to have your existing driveway excavated and have a whole new sub-base installed. It’s recommended to have a new base installed with any surface option however it is essential when it comes to gravel as gravel is a loose product with spaces between the aggregate meaning that displacement can happen. A solid and flat base can help ensure that displacement is kept to a minimum whilst allowing water to pass through.
Having the old base excavated also helps the contractor understand what is lying beneath the sub-base. It would be extremely rare that a gravel driveway would ever need extra drainage however if the ground below the sub-base is not permeable then extra measures may need to be taken.