Is Tarmac Permeable?
Although there are ‘open graded’ options within the tarmacadam industry, in general, tarmac is NOT permeable. Open graded tarmacadam is classed as ‘semi-permeable’, meaning rain water WILL drain through it. The rate of absorption is considerably less in comparison with a permeable grid system or resin bound.
OPEN GRADED TARMAC driveways
If your main objective is a permeable surface, then we do highly recommend getting comparative quotes for a completely permeable solution also.
Using ‘open graded’ tarmac for your driveway will provide the surface with some form of ground drainage as it is partially permeable. This being said, open graded tarmac has not got the small fines inside of the mix, which means the surface is going to look and feel rougher.
This is usually an unpopular choice of surfacing for driveways that have to remain permeable. Normally if SUDS compliance is an issue, homeowners will choose to have closed graded tarmac and have added drainage installed for surface run off.
CLOSED GRADED TARMAC DRIVEWAYS
You would have seen plenty of these driveways before. You may already have one! They’re a popular choice on new builds because of how cheap they are. Yes, they do provide a solid surface which when installed can last for 30 years but they are not permeable. Are they aesthetically pleasing? As they say, beauty lies in they eyes of the beholder.
Tarmacadam is very similar to asphalt, which is used on 96%-97% of all UK motorways. It is also used on most other main roads. The reason for its popularity that it is cost effective, smooth and can be accessed almost everywhere. You will notice that main roads will either have drains on them or will have slopes either side to allow water run off, as the surface is not permeable.
SUDS compliance has become, and will become, more and more important as time goes on. This is because a lot of pollution is cause by rain water gathering unwanted toxins as it flows over road surfaces and into grids. This of course does affect homeowners, as previously it was acceptable for a driveway to be installed with falls towards the exit of the driveway. Now, with non permeable surfaces, there must be suitable drainage in place to catch the surface water before it reaches the road. This means higher costs in drainage, as soak-aways need to be constructed.
3 MOST COMMON PERMEABLE SURFACES
- Resin Bound. A hard wearing, durable and aesthetically pleasing surface designed to be completely permeable. Resin bound is quickly becoming the most popular paving solution due to its stunning appearance and very few flaws
- Gravel. When installed correctly, gravel should be permeable and should not sink overtime. Permeability goes beyond the surface. In order to ensure complete porosity, every material used underneath the surface should be permeable. Gravel is often installed with gravel grids, which creates a hard wearing, solid surface, preventing constant movement of the gravel.
- Permeable Block Paving. There are a few alterations needed to make block paving permeable. The base must allow for water to drain through, therefore the use of sand is replaced with fine aggregate. The MOT used must be type 3, and the blocks should be labelled as permeable.