Clare Dunne is the young Irish stage and screen performer who takes a commanding role in this heartfelt and engrossing personal movie: she is the star and co-writer with Malcolm Campbell (who scripted Lenny Abrahamson’s What Richard Did). The director is Phyllida Lloyd, known for mainstream films like Mamma Mia! and The Iron Lady, and she shows a confident touch with both the subdued moments, the intestine-clenching spasms of domestic abuse and the big C-major chords of emotional uplift. It’s a really unexpected drama: unexpected for a heartwarmer, unexpected for a tough social-realist picture, these being the two genres in which it finds a Venn overlap.

Sandra (Dunne) is a young woman in Dublin who has had to separate from her toxic and violently abusive husband Gary (scarily portrayed by Ian Lloyd Anderson), taking her two young daughters with her, taking cleaning jobs and living in state-funded hotel accommodation near the airport where she is humiliatingly told to come in through the service door at the back so her evident distress and poverty won’t upset the well-heeled customers. The hatchet-faced concierge icily reminds her of this arrangement whenever she cowers past the sleek flight attendants and pilots in their uniforms who are overnighting there. Here is how Sandra gets her nose rubbed in the glamorous world of international travel, a brutal reminder of how she is imprisoned at home – and doesn’t even actually have a home.

So Sandra is desperate for somewhere to live, and she has an entrepreneurially bold and imaginative idea, which she stumbles upon online. Why not build a house herself, using self-build templates she’s stumbled upon online and one of the council’s many derelict brownfield sites? If the council could loan her the capital and then rent her the resulting property, it would cost far less than paying years of hotel bills. Of course, the narrow-minded officialdom is obstructive, but fortunately Sandra has a friend in one of her cleaning clients: Peggy (Harriet Walter), angular and patrician in her plain-speaking candour and loyalty. There is also a friendly builder, Aido – a typically likable performance from Conleth Hill – who responds instinctively, if a bit reluctantly, to the good karma of what she wants. But the poisonous situation with Gary is not wished away as easily as that, and the movie effectively conveys the white noise in Sandra’s head that can still be triggered at any time by Gary’s wheedling requests for a second chance and specious promises of having received “help”, together with his mood shifts and the theatrical displays of good humour he puts on for the benefit of the children.

Naturally, the existence of the well-heeled and sympathetic Peggy is a bit convenient for the plot, and perhaps the film’s self-build premise is exotic and does not realistically address the issue of homelessness as it is actually experienced, as in, say, Roddy Doyle’s script for Paddy Breathnach’s 2018 film Rosie. But the clue is in the title: the spirit of the film is self-help and self-empowerment, and the simple idea of building something – rather than passively and miserably withstanding callous bureaucracy, or just waiting for the next sickening display of abuse – is very sympathetic. There’s a great odd-triple emotional dynamic between Sandra, the defiantly unconventional Peggy and the avuncular Aido, who has to shepherd the job. There’s a strong basis of originality here, and the warmth and good nature of the movie carries it along.

• Herself is released on 10 September in cinemas.