It is believed the posts will be split equally across sites in Carlisle and Dalbeattie in Dumfries and Galloway.
An additional shift is being added at each plant as the company needs to service increased requests for items such as timber housing frames and building maintenance products.
Tony Hackney, chief executive of BSW Timber, said the business was now producing more home-grown timber than ever before. He added: "These are exciting times for BSW Timber and the UK forestry sector and I am delighted to see more jobs created here at our Carlisle and Dalbeattie mills.
"This is a direct response to the increased demand for UK timber and reinforces the importance of the forestry sector to growing both our local and national economies."
The Carlisle mill currently employs around 170 people, with a further 140 staff based at Dalbeattie.