Crawl Space Pillow Tanks

Pillow tanks from 1 to 50 m³ designed to be installed in a crawl space or underfloor void. They turn dead space into a rainwater reserve without taking up usable ground, without groundworks and without a buried rigid cistern.

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Why put the tank under the floor

A crawl space is a volume you already have — shielded from light, from frost and from temperature swings. Putting a pillow tank there buys you storage without losing garden or garage space, and without the excavation a concrete cistern would need.

Space recovered: uses a void that serves no other purpose.
No groundworks: the tank goes in folded and takes shape as it fills.
Shaped to the void: narrow, low-profile formats, or a bespoke build to your actual dimensions.
Protected: out of the light and away from frost, with no direct exposure to weather.

Typical applications

Rainwater harvesting from the roof
Reserve for automatic garden irrigation
Non-potable domestic use: WC flushing, washing machine, outdoor washdown
Temporary attenuation storage on plots with limited drainage

Technical specification

Specification	Detail
Material	PVC-coated reinforced polyester, high tensile grade
Thickness	0.85 mm to 1.5 mm depending on capacity
Treatment	UV-stabilised; closed opaque membrane that admits no light
Capacities	1,000 to 50,000 litres
Fittings	Overflow, venting, connections sized for the void
Warranty	5-year manufacturer’s warranty

Where the stored water is intended for human consumption, the membrane and fittings must meet the minimum hygiene requirements of Directive (EU) 2020/2184 for materials in contact with drinking water. Confirm this specification before ordering. For non-potable domestic supply, installation design is covered by BS 8515.

Installation, step by step

Survey the void: usable dimensions, headroom, access hatch and ventilation.
Prepare the base: level it, clear rubble and sharp objects, lay a geotextile mat.
Place the tank: pass it through the hatch folded, then unfold it in position.
Connect: gutter feed, overflow to the drainage system, and draw-off point.
Check: joint tightness and continued access for maintenance.

The critical constraint is access: the hatch must admit the folded tank and still allow you to reach the fittings later. Send us those dimensions before choosing a model.

Maintenance

Annual visual check of fittings and overflow
Occasional flush if the inlet filter has let sediment through
Keep the void ventilated as originally designed

Frequently asked questions

How much headroom does a crawl space tank need?

Low-profile models work from roughly 80 cm of usable height, but headroom alone does not decide it: bearing area and hatch dimensions matter just as much. Send us all three measurements and we will confirm the right format, or quote a bespoke build.

How is the overflow handled?

The overflow connects to the existing drainage or to a soakaway. It must be sized for the inlet flow — in heavy rain, water the tank cannot take has to leave without pooling in the void.

Will the tank cause condensation?

The tank is sealed and adds no moisture to the void. Condensation depends on ventilation, which should be maintained as the building was originally designed.

Can the tank be removed later?

Yes. Drained and folded, it comes back out through the hatch it went in by. That is one of the practical differences from a buried concrete cistern.

Request a survey for my crawl space