Laidlaw is backed by Rutland Partners, a UK private equity firm.
Completion of the deal expected after a period of employee consultation.
SIG supplies of insulation, interiors, exteriors and specialist construction products. Already in recent months it has exited the scaffolding and PPE businesses by selling Beaver 84 and SIG Safety & Workwear.
SIG Interiors Manufacturing designs, manufactures and supplies doorsets, partitions, washrooms and glazing products in the UK, principally to non-residential markets. The business trades under the brands of Leaderflush + Shapland, Komfort Workspace, Cubicle Systems and SIG Glazing Services.
For the year ended 31 December 2010, the Interiors Manufacturing business made a loss before tax of £49.2m (after restructuring and goodwill impairment charges), and a pre-exceptional operating loss of £2.4m on revenues of £83.2m. Gross assets of the business as at 31 December 2010 were £41.8m.
The proceeds of the sale will be used to reduce SIG's net debt.
SIG chief executive Chris Davies said: “Consistent with our key strategic initiative to improve performance by actively managing the group's portfolio of businesses, we are pleased to announce the sale of SIG Interiors Manufacturing to Laidlaw and Rutland Partners.
"This divestment, together with the recent disposals of our scaffolding and safety & workwear businesses, enables us to better focus on our core distribution and merchanting operations and helps to rebalance the group's exposure further towards residential markets."