The comedian will take over from the regular presenter for the one-off episode in Hull in September.
Knowles is missing the special because it coincides with his appearance in a Shreddies ad campaign, but he will be back on the programme in 2022.
Gilbert will join the regular team of carpenter Mark Millar, plasterer Chris Freidiani, builder Jules Perryman and electrician Billy Byrne, alongside playground engineer John O’Driscoll and local tradesmen and volunteers for a project aiming to improve the physical and emotional health and wellbeing of children and young people.
Gilbert said: “It’s a great honour to step into Nick’s enormous steel toe-capped boots and be involved in Children in Need. I’m looking forward to joining the infamous DIY SOS team, and rallying an enormous group of local volunteers on a wonderfully ambitious and important project.
“After having tried my hand at over 30 jobs on my Work Experience TV programme, I’m hoping I may even be of some use around the site. My vis is high and my hat is hard, so bring it on.”
The programme will see the DIY SOS team, with the help of trade volunteers, attempt to transform an empty two-and-a-half-acre field into a purpose-built adventure camping site for St Michael’s Youth Project in Hull.
They plan to create a field kitchen, a landscaped campfire, a pizza oven, an exterior covered classroom, a mountain bike course, a birdwatching tower, an adventure playground, a toilet and shower block, and a storage unit.
DIY SOS executive producer Paolo Proto said: “We are delighted to have Rhod join the team for this incredibly special build in Hull for St Michael’s Youth Project.
“We can’t wait to see him get his hands dirty, and we’ll need his humour and empathy as we transform an empty field into an adventure camping site that will benefit children and young people across Hull, for The Big Build BBC Children in Need special.”
The programme is appealing for landscapers, gardeners and tradespeople to offer support with the transformation in September and is looking for donations of timber, aggregates, steel containers, a septic tank or treatment plant, solar panels, wind turbines, mountain bikes, tents, rope, outdoor furniture, play equipment and an internal fit-out of a shower block and field kitchen.
The two-week build will take place from September 8-16 and the programme will be broadcast in November 2021.