John Lewis is planning to expand its offering from furnishing homes to extending and renovating them.
The employee-owned business said it wanted to be involved in every area of home improvement from design to construction.
John Lewis already runs a booking site for tradespeople and last year it acquired a home improvement firm, Opun.
But now it is planning on bringing both of those services under one roof to design and build extensions.
Opun designs and installs bathrooms and kitchens as well as undertaking loft conversions and extensions.
Since it was acquired by John Lewis in September 2018, Opun, which undertakes large-scale construction projects, has been operating independently but now it will work alongside Home Solutions, which finds tradespeople for smaller jobs.
John Lewis director Sean Allam said the deal to buy Opun demonstrated the department store's ambition to grow in the home services market.
The firm is now looking at how best to bring these services to its customers.
Both Opun and Home Solutions sit in a part of the business that is supposed to create new products for both John Lewis and Waitrose, which is also part of the partnership.
John Lewis had a difficult year in 2018. Profits plunged by more than 45% to £130m, as department stores fight to stay relevant in the face of competition from online retailers.
But retail analyst Richard Hyman told the BBC that building up the home improvement business was unlikely to make a difference to short term profitability at John Lewis.
Instead, Mr Hyman said it was probably a response to a slowdown in the housing market, which he attributed to the "prohibitive" cost of stamp duty.
He said that had an impact on "connected markets" like John Lewis, which sells the furniture for those homes.