It's comforting to know that, even as I type, Dermot Bannon is probably in someone's garden wearing a high-viz jacket and obsessing about windows. The man is an elfin folk legend and the only way to deter him from renovating your home is to run around it backwards reciting lines from Bungalow Bliss.

Room to Improve (RTE1, Sunday) is a spiritual experience. In modern Ireland where people circle Ikea like pilgrims at Lough Derg and declare "Jesus, Mary and Joseph" when gazing in estate agents' windows, this programme is basically mass. Indeed, when I hear the words "a decade of Room to Improve" (it's been on since 2007) I picture devout families kneeling around the television, fingering paint swatches like rosaries and gently murmuring "more light" and "east facing" and "Open up that kitchen a bit, Dermot" in unison.

In this episode, chirpy, quippy Dubliners Robbie and Julie want to build their "dream house" around a "dingy, smelly" (Dermot's words) cottage in Malahide. I find this alarming, because my "dream house" has secret rooms and a ghostly little boy who whispers "deaaaaath!". It turns out, however, that when people on Room to Improve say "dream house" they mean their "ideal" house and not the creepy building in their Jungian nightmares.

And what Dermot Bannon hears when someone says “we would like to build our dream house” is “We would like somewhere to park our aeroplane” and he instantly pictures a cavernous white space with no internal walls and loads of windows. He’s a martyr to the old windows is Dermot. Indeed, when I learn that Robbie is a window cleaner by trade, I think, “Good luck hanging on to your man, Julie.”

At this point, Dermot wanders off to meet his new quantity surveyor. Her name is Lisa and Dermot wants to check how good she is with animal metaphors.

“Are you a bit of a Rottweiler on site?” he asks.

“My nickname is The Wasp,” says Lisa. “Because I’ll sting you.”

“YOU’RE HIRED!” shouts Dermot (he doesn’t really shout “YOU’RE HIRED” but it’s implied). Lisa goes on to liken herself to “a nodding dog” when listening to Dermot, which is laying it on a bit thick. “Steady on Lisa, you already have the job,” I yell. “Keep that one for next week.”

The next part is the bit where couple's expectations do not match their budget. Sad music plays as Dermot informs Robbie and Julie that they can only afford two bedrooms not their desired three bedrooms, a turret and a moat, and for some reason no one thinks of just getting Mexico to pay for it.

“I’m gutted, I really am,” says Julie, and they don’t even look at Dermot’s model, which makes Dermot sad. There’s more melancholy music.

In order to save money, Robbie takes on some of the demolition work himself and we cut to a gleeful Robbie smashing things. “I came here like a wrecking ball,” he sings. We cut to Miley Cyrus singing the same song. This stuff writes itself, think the producers.

“No injuries, thank god,” says Robbie, and the producers get another idea. We cut to Robbie now sitting with his leg in a cast. This delays things somewhat. To make matters worse Robbie’s efforts at demolition have obscured where the sewer pipe is and relaying the pipe is going to cost $1 million (I didn’t write down the actual figure). Dermot sighs a lot at this point.

Then we get a sequence in which Robbie and Julie discuss their 23-year-old love story which is quite sweet until it culminates in Robbie, Julie and Dermot Bannon shopping for kitchen cabinets together to the sound of Dolly Parton's Jolene (it's not really soundtracked by Dolly Parton's Jolene).

Dermot wants an impractically pristine white kitchen, like I imagine Jesus owns. Julie wants one that’s the same colour as a shampoo bottle she has taken a photo of, the mad bitch. And Robbie doesn’t know what he wants, because it’s just dawning on him that Dermot Bannon lives with them now, as he does with all of his “wives” and “husbands” (if you draw a line on a map between the properties that Dermot has TV renovated over the past decade, it spells out the words “I own you”).

And so now it's the part of the show in which everyone is annoyed with each other. Sometimes I think they should just rename the programme, or indeed, the nation, The Project is Over Budget and Everyone Is Annoyed. There's some footage of Dermot driving around in his car angrily muttering: "I've been to college for six years to study this stuff and I've worked for nearly 20 years in the industry." I like to think this is how he goes on even when he's not being filmed.

He then makes Robbie and Julie come with him to look at a radioactively white kitchen with loads of windows. “Have Robbie and Julie finally seen the light?” asks the narrator. How could they not with all those windows?

But then, in an unexpected dramatic twist, Robbie and Julie go against Dermot’s wishes and plump for a grey kitchen. Dermot falls to his knees and screams “NOOOO!”

Okay, he doesn’t do that, but he is upset and his eyes are red like he’s been crying. “I feel like I’ve failed a little bit,” he says. It’s a classic Irish mammy manoeuvre, the equivalent of “Don’t mind me, I’ll just sit here in the dark… if only this place wasn’t so well lit due to all the windows.”

There’s a fast-forward montage in which all the boring building, plastering and painting gets done and soon Robbie and Julie have their dream home – a cottage with a big bit in the back in which they can park light aircraft.

Dermot comes to visit. There’s a bit of an edge to things because of how they betrayed him.

“We’ll hug it out,” says Robbie.

“We’ll hug it out,” says Dermot, less convincingly.

He talks about the “space” for a while, because this soothes him. Then they have a look at the coveted third bedroom and Robbie tries to cheer him up by saying, “You in our bedroom, that’s exactly what we wanted, Dermot” even though swinging is the last thing on Dermot’s mind now.

There’s a bit of a party and Dermot has his last word: “It may not be everything that I had imagined it would be but it’s close,” he says. “But far more importantly, Robbie and Julie are happy and I really hope that this is the house of their dreams.”

This is his way of saying: “I hope you choke on your grey kitchen you f***ing traitors.”

Then we all bless ourselves, check our gardens for Dermot Bannon and go to bed.