The Competition & Markets Authority (CMA) has already voiced concerns about the impact of the deal on the UK market for specialist insulation panels, as it brings together two of the big three suppliers.
Earlier this month, the CMA invited Kingspan and SIG to address it concerns or face a more in-depth investigation.
On 16th April 2020 the two companies told the CMA that they would not be offering any undertakings that might appease competition concerns.
The CMA has therefore decided to refer this merger for a phase 2 investigation, in line with sections 33(1) and 34ZA(2) of the Enterprise Act 2004.
The Kingspan-SIG deal was announced in October 2019. SIG Building Solutions includes the brands Steadmans, United Roofing Products, Trimform Products, and Advanced Cladding & Insulation. It made an operating profit of £3.3m in 2018 on revenue of £60m.