Most campuses and estates need parking that is full a few days a year: visitors on an open day, guests at an event, the weekend at a resort. The rest of the time it stands empty. Paving it in blocks or asphalt adds hard surface to the site plan for a car park that is mostly unused.
GridMats S3 keeps that area as a lawn that cars can park on. We ran one overflow car park through the GridMats Design Engine to see what that costs against the usual choices, and when blocks are the better buy.
The car park
- 1,500 m² (about 16,100 sq ft) of overflow and visitor parking
- Cars, SUVs and light vans up to 3.5 t, about 20 a day; soil CBR 5%
- Moderate rainfall (750–1,500 mm a year); Bengaluru rates, ex-GST
Four sections for the same cars
- GridMats S3, 235 mm in all. The 30 mm grass paver (GP-30), filled with a sandy root-zone mix and seeded or turfed, on 30 mm of sharp sand bedding and 175 mm of open-graded GSB that stores the rain, over a 200 gsm non-woven geotextile separation layer, with perforated pipes along the low edges to the outfalls.
- Concrete paver blocks, 240 mm. 60 mm pavers on 30 mm of bedding sand and 150 mm of GSB, with a lined surface drain.
- Asphalt, 325 mm. A 25 mm premix carpet on 150 mm of WMM and 150 mm of GSB, with a lined surface drain.
- Concrete slab, 300 mm. 150 mm of concrete on 150 mm of GSB, with a lined surface drain.
All four have kerbs on both sides.
What it costs
| Section | To build | Over 35 years, in today's money |
|---|---|---|
| GridMats S3 (grass) | ₹117 per sq ft (₹1,261 per m²) ₹18.9 L for the car park | ₹183 per sq ft (₹1,967 per m²) ₹29.5 L for the car park |
| Concrete paver blocks | ₹90 per sq ft (₹969 per m²) ₹14.5 L | ₹115 per sq ft (₹1,242 per m²) ₹18.6 L |
| Asphalt | ₹92 per sq ft (₹990 per m²) ₹14.8 L | ₹158 per sq ft (₹1,696 per m²) ₹25.4 L |
| Concrete slab | ₹203 per sq ft (₹2,185 per m²) ₹32.8 L | ₹235 per sq ft (₹2,532 per m²) ₹38.0 L |
The geotextile separation layer under the base is a separate BoQ item and is not included in the GridMats figures above.
What the numbers say
- Paver blocks cost less, to build and over 35 years: ₹90 per sq ft against ₹117 for S3 to build, and ₹115 against ₹183 over 35 years. If the only aim is the lowest cost, choose blocks.
- A lawn needs looking after. Mowing and watering are the reason S3 costs more over 35 years. We plan upkeep at 3% of the build cost a year for S3, against about 1% for asphalt and 1.2% for blocks.
- Against a concrete slab, S3 costs 42% less to build and 22% less over 35 years.
The installed range recorded on our completed S3 sites is ₹125–167 per sq ft (₹1,350–1,800 per m²); this design came out just below it. Freight, the base and local rates move the figure on every site.
When grass is worth it
- Green-cover and permeable-area rules. S3 supports green-cover rules and permeable-area requirements, subject to local approvals.
- Rain. In this design the open-graded base stores about 62 mm of rain and releases it through the perforated pipes along the low edges: about 1,350 m³ a year goes into the ground instead of a surface drain (Design Engine estimate). Edge and outfall drains go in only where the levels need them.
- The space does two jobs. On the days it is not a car park, it is a lawn: an event ground, a play area or a garden.
- No cement and no saw-cut joints. About 4.5 t of recycled polypropylene is put to use in the pavers (Design Engine estimate for this car park).
When to choose something else
- Cars every day, in the same bays. Grass under daily parking struggles. S2 stone chip keeps the car park permeable and opens the same day; in the same run it came out at ₹157 per sq ft (₹1,694 per m²) to build.
- You need it in a hurry. Feet can use S3 at once, but cars wait until the grass is 60 mm tall and rooted, in 4–6 weeks.
- No water in the first season. New grass needs watering until it is established.
- Trucks. S3 is for cars, fire-lane access on a base we design and walkways. Daily truck traffic needs S1 or S2.
In service
At Waters India, Bengaluru, the amphitheatre and event lawn are on GridMats grass pavers, built in 2022: foot traffic from day one, mowed like a lawn. At Svamitva Floresta, Bengaluru, grass-top roads and paths have been in service since 2021.
How we worked out 35 years
As in our other cost articles, we follow the US Federal Highway Administration's practice for life-cycle cost: a 35-year period, a 4% real discount rate, and credit for the service life left at the end. Paver blocks: 20% relaid every 10 years. Asphalt: mill and 40 mm overlay at 12 and 24 years. Concrete: joints resealed every 10 years, with grinding and slab repairs at 20 years. S3: mowing and watering only, our planning assumption.
At an 8% real rate: S3 ₹158 per sq ft, paver blocks ₹106, asphalt ₹129 and concrete ₹222.
Your car park will differ
These are indicative figures for one typical overflow car park. Soil, traffic, rainfall, local rates, freight and the base design change them, and every GridMats site is priced from its own design. Ask for your free estimate: our engineers follow with the design, the bill of quantities and the cost comparison against your conventional section.