Lightweight roof garden soil
Lightweight roof garden soil - image 2

Our Lightweight Roof Garden Soil brings intensive planting to rooftops and podium landscapes with its high-quality peat-free blend of high-performance sands, organic materials and lightweight LECA aggregate. The medium-graded sands and LECA create and maintain good porosity and permeability to avoid excess weight from water retention. Perfect for:

  • Podium landscapes
  • Intensive rooftop planting
  • Rooftop planters
  • Green roof systems

This innovative substrate supports healthy plant growth with excellent drainage while reducing structural loads on your building. Lightweight Roof Garden Soil is perfect for renovating your roof into a vibrant, sustainable garden space.

Lightweight Roof Garden Soil

Price range: £157.00 through £232.00 inc. VAT

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Topsoil Calculator

Tap a job to fill the depth in. For a raised bed, use the depth of the bed, usually 200 to 300mm.

Our Lightweight Roof Garden Soil blend comprises high-quality sands, soils, peat-free organic materials and a lightweight clay aggregate (LECA). The medium-graded sands and LECA help create and maintain good porosity and permeability levels within the substrate to avoid excess weight from water retention. A high-quality blend developed with the country’s leading soil scientist for use in rooftop and podium landscapes.

Latest Analysis Results
pH: 8.5
Saturated Hydraulic Conductivity: 157 mm/h
Bulk Density Received: 1.3 tonnes per m3 (BSEN 12580:2013)
Bulk Density Saturated at Field Capacity: 1.4 tonnes per m3

Copies of the latest certifications and test data are available upon request.

Quantity

Builders Bag (approx. 700L), Bulk Bag (approx. 1000L), 40 x 25L Bags

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Specifications, Inspirational Ideas & DIY Guides

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Why Professionals & Homeowners Choose, Applications, DIY Guides & Inspirational Ideas, Maintenance, Purchasing Tips, FAQs, Related Products

Overview

This blend is built around weight: high-quality sands, soils, peat-free organic material and LECA, clay pellets fired until they puff up and most of each one is air. It runs 1.3 tonnes per cubic metre as delivered and 1.4 tonnes at field capacity, roughly 20 to 30% under a saturated garden loam. Latest analysis has it at pH 8.5 and 157 mm an hour saturated hydraulic conductivity, so it drains fast rather than holding water. It is made for intensive roof gardens, podium landscapes and rooftop planters, not a sedum blanket on a shed. Here is why.

Why Professionals & Homeowners Choose Lightweight Roof Garden Soil

Five reasons this blend ends up on roof drawings, and one job it’s wrong for:

  • At 1.4 tonnes per cubic metre at field capacity it loads about 140kg per square metre for every 100mm of depth, against roughly 200kg for saturated garden soil, so a 300mm build saves 180kg on every square metre.
  • The expanded clay is fired ceramic and does not rot, so the build holds its depth where a compost-heavy starts to break down after a season or two.
  • Water drains through it at 157mm an hour, so heavy rain runs out of the soil instead of sitting in it.
  • The sands are medium-graded, so there is minimal fine dust to wash down and block the roof drains.
  • The organic fraction is peat-free, so it clears a planning condition or a client spec without argument.
  • The one thing it will not do is grow acid-lovers. At pH 8.5 it is firmly alkaline so rhododendrons, camellias, pieris and most heathers yellow in it, and a roof build cannot sensibly be acidified once it is in.

Lightweight Roof Garden Soil Applications

pH 8.5 settles the planting list before anything else does, and it points at the chalk-and-limestone crowd. Lavender (Lavandula angustifolia), catmint (Nepeta x faassenii), Russian sage (Perovskia atriplicifolia), bearded iris (Iris pallida) and red valerian (Centranthus ruber) all take a hot, dry, alkaline roof. What it is not is an extensive sedum substrate or a container compost, so don’t fill a patio pot with it.

  • Intensive roof gardens over a drainage layer and filter geotextile, at 300mm and up for lawn and perennials.
  • Podium decks and over-garage slabs, where the structure carries a garden but the loading allowance is finite.
  • Rooftop planters and raised beds, where the same volume of topsoil would push the planter past what the deck is rated for.
  • Semi-intensive schemes at 150 to 300mm, for ornamental grasses and low perennials (rather than shrubs).
  • Shrub planting at 450 to 600mm, and small trees from around 800mm, where the weight arithmetic bites hardest.

DIY Guides & Inspirational Ideas

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Lightweight Roof Garden Soil Maintenance

A roof build loses depth as the organic fraction breaks down, and you cannot dig a roof to fix that without risking the waterproof membranes underneath. Top-dress instead: 25 to 40 litres of compost per square metre, or roughly 5cm, once a year in autumn, worked gently into the surface. Irrigation is essential on an intensive roof garden, because there is nothing below to hold water and roof-level wind dries a surface far faster than it does at ground level. Yellowing between the leaf veins on an alkaline medium points to manganese rather than nitrogen, so feed for that. And keep the outlets clear, because one blocked outlet turns a free-draining build into a pond over the one part of a building that must never hold water.

Purchasing Tips

Work out the loading before the price. At 1.4 tonnes per cubic metre at field capacity, 300mm across 20 square metres is 6 cubic metres and about 8.4 tonnes. Get it signed off by a structural engineer before ordering. One cubic metre is 1,000 litres, covering 5m² at 200mm deep, 3.3m² at 300mm and 2m² at 500mm. The gravel calculator does the volume sum, but read the cubic metre figure and ignore the kilos, which are worked out on stone. The 4-10mm LECA we stock is the usual drainage layer used beneath it.

If you would rather talk your lightweight roof garden soil order through with a person, ring Outdoor Aggregates on 0330 043 7585. The office is open 7am to 7pm, seven days a week.

Lightweight Roof Garden Soil FAQs

How much does lightweight roof garden soil weigh per square metre?

Lightweight roof garden soil weighs roughly 140kg per square metre for every 100mm of depth once it is at field capacity. A 300mm build is therefore about 420kg per square metre, a figure for a structural engineer to sign off.

Can you grow acid-loving plants in lightweight roof garden soil?

Lightweight roof garden soil tests at pH 8.5, which is alkaline, so rhododendrons, camellias, pieris and blueberries sulk and yellow in it. Plant the lime-tolerant end instead: lavender and bearded iris thrive on a hot alkaline roof.

Is lightweight roof garden soil suitable for a sedum roof?

Lightweight roof garden soil is an intensive substrate for planting 300mm deep and more, which makes it too rich for an extensive sedum blanket. A sedum roof wants 80 to 150mm of a leaner mineral mix.

Does lightweight roof garden soil go straight onto the roof deck?

Lightweight roof garden soil sits on top of a full green roof build-up, never on the deck itself. Waterproofing, root barrier, protection fleece, drainage layer and filter geotextile all go below it, and skipping the filter layer is how fines block the outlets.

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