Dermot Bannon certainly doesn't hold back.

The architect behind RTÉ's Room To Improve knows what he wants from a build - and it's often something different from what his clients have envisioned. He's at his best when trying to change a client's mind but, to be fair to the man, he knows what he's talking about. After ten years in business, he's revealed that the biggest mistake Irish people make with their homes is not putting enough thought into their existing space when building an extension. "In the 80s and 90s, a lot of people would have put a kitchen extension on to the house," he told RSVP. "The biggest mistake people make when they are extending their home is not planning what they are going to do with the rest of the house. "A lot of the time you don’t even need the extension or it doesn’t need to be that big. So sit down and look at your brief. What do you really need and plan your extension around that. "If you’re extending a home you’re sort of reworking the whole ground floor anyway so it’s not just about the extension, it’s about the space behind too." This week's episode of the show will see Dermot throwing what RTÉ has called a 'temper tantrum'. On a boat trip, he thinks he is about to set foot on Lambay Island, home of Lambay Castle, designed by his hero, Sir Edwin Lutyens. Until he finds out that he’s not because the island is private and not accessible to the public. Check out the sneak peek here. Room To Improve continues on RTÉ 1 at 9.35pm on Sunday.