Builders' Rubble Under The Lawn

What's happening?

This is the standard new-build and post-extension garden. Construction leaves the ground compacted by plant and littered with broken brick, block, mortar, offcuts and plastic, and the quickest way to hand a garden over is to spread a thin layer of topsoil over the top and turf it. The lawn looks finished on day one and behaves badly ever after, because grass has almost no soil to root into. Two things follow. The thin layer holds very little water, so the lawn browns in the first dry spell and stays thin. And the rubble beneath sits in pockets, so the surface settles unevenly as those pockets consolidate — which is where the lumps and hollows come from. Anything you want to plant deeper than a bedding plant hits the same obstruction.

What usually causes it?

• Construction spoil and broken materials buried rather than removed at the end of the build
• Topsoil spread as a thin skim over compacted subsoil and rubble, then turfed straight away
• Subsoil compacted by tracked plant into a pan that roots and water cannot cross
• Mortar droppings and sand raising the soil pH locally, so grass and plants struggle in patches
• Trenches for services backfilled with arisings and not consolidated, settling later into lines and hollows
• Site levels finished to suit the build rather than the garden, leaving no fall for drainage
• Turf laid over the top too soon, hiding all of the above until the first dry summer

When should you call a landscaper?

Call a landscaper when there is less than a spade's depth of usable topsoil, when the lawn is settling into lumps and hollows, or when you want to plant anything with real roots. Get the trial-hole evidence together first, because on a recent new build this is often a defect worth raising with the developer or under a warranty before you pay to fix it yourself. If suspected asbestos-containing material turns up, that gets identified and removed under the right controls before any garden work continues.

What will the landscaper actually do?

• Dig trial holes across the garden to map topsoil depth, the rubble layer and the compacted subsoil beneath
• Excavate and remove the buried rubble and construction waste to a licensed facility with the right waste transfer paperwork
• Break up the compacted subsoil pan so water and roots can move through it
• Import graded topsoil to a workable depth for lawn and for planting beds, which are different depths
• Re-grade the finished levels so the garden falls away from the house to a defined low point, and install land drainage where the trial holes show water has nowhere to go
• Cultivate, firm and level the bed, then turf, seed or plant as designed