The purchase price is an initial £4m cash and further deferred consideration of up to £12.5m depending on performance over the next two years.
Permavoid's products are used for urban water management. Its core technology is a patented plastic subbase replacement system containing capillary cones capable of storing surface water (to prevent flooding) whilst passively wicking the stored water to irrigate soils and substrates above.
The core subbase technology is complemented by further patented solutions for managing surface water runoff from pavements whilst providing treatment to remove oils and other contaminants before discharge.
Applications include the recent installed under-pitch drainage system at Liverpool Football Club's Anfield stadium.
Polypipe already manufactures and sells Permavoid's products under exclusive licence for the UK and Irish markets.
For the year to 30th September 2018 Permavoid is expected to post revenue of £3.8m and adjusted Ebitda of £0.5m.
Polypipe chief executive Martin Payne said "The acquisition of Permavoid is a small but important step towards delivering on our strategic goals. The acquisition brings new intellectual property into the group with exciting opportunities for further product integration and innovation, allowing Polypipe to enhance its market leading water management and attenuation solutions in the UK, as well as provide opportunities to leverage those market leading solutions in Europe and other markets."