Gas leaks, damp, holes in the floor and cracks in the walls - for some, their new homes have become "uninhabitable" less than a year after moving in.
"Slugs, worms, beetles, spiders - they have their own personal entrance and exit route into our house," Karen Stacey-Pope tells the BBC's Victoria Derbyshire programme.
"There's a gap underneath the [patio] door and the doorframe," she says, explaining how the bugs get in. "It's fairly deep, about 2ft [60cm] down."
Karen is angry, upset and drained of energy.
She has a long-term disability - a form of severe arthritis - and was diagnosed with breast cancer this year.
She says the fight to have her home's numerous issues resolved has become so stressful it has made her even more ill.
The wrong porch was built on, airbricks meant to stop the house from getting damp and rotten were buried underground, and her driveway is sinking.
She says the issues continue to surface.
"There was a leak on Sunday that just drenched the walls and the ceiling. Nothing's been fixed, we're just left with a hole in our ceiling," she says.
Karen bought the property from housebuilder Bovis for £325,000 in December 2016, under the government's Help to Buy scheme.
After numerous complaints to the company, she eventually hired an independent surveyor to assess the house - who uncovered major structural issues.
Movement joints - which stop the house cracking up if the land shifts - had been completely forgotten.
The surveyor concluded the house was "not fit for habitation" and some parts were "unsafe".
He also questioned how inspectors could have signed it off.
When contacted by the BBC, Bovis apologised to Karen "that she did not receive the quality that she and her family deserved and rightly expected".
The company said work to rectify the issues with Karen's house had stalled at different stages this year because she had not given authority for them to proceed.
Karen said she had stopped some work from going ahead because - on advice from her independent surveyor - she was not happy with the way Bovis had proposed to carry out the repairs.
Bovis said it is absolutely determined to deliver a quality home and is confident that the works it has proposed will achieve that.
It added that it had made "significant changes" to how it operated in the past 12 months - including reducing the number of homes it planned to build.
Karen is not alone in her experiences. The Victoria Derbyshire programme has spoken to many people with similar issues, who bought from various housebuilders.
Defects, referred to as "snags" in the industry, included holes in the roof, badly fitted windows and doors, cracks in the walls, toilets overflowing with sewage, damp and mould, and sloping floors - all occurring within 12 months of residents moving in.
One man described coming home to a maggot and fly infestation.
A survey by the House Builders Federation this year suggested 98% of those who had bought new homes reported defects to their builder within a few months of moving in, with 41% reporting more than 10 problems.
It comes at a time when Prime Minister Theresa May has promised to build "more homes, more quickly" to tackle the housing shortage.
The government says the country needs 300,000 new homes a year to meet demand.
But as it pushes developers to build faster, there are growing concerns that the quality of homes being built has drastically dropped.
Phil Waller, a retired construction manager with 35 years' experience, says standards are at the worst they have been for 20 years - describing the situation as "atrocious".
"How people walk away and give someone the keys to their home when there's a great big hole in the wall I don't understand," he says.
"No-one in the process is really checking that the quality is going to be there and that the houses comply with building regulations and warranty standards."
The National House Building Council (NHBC), which inspects and signs off finished homes, says: "Every home registered with NHBC is inspected at approximately four or five key stages of construction, including foundations, superstructure and pre-handover.
"These visual, spot-check inspections are designed to target critical elements of the build process and allow us to identify and highlight potential defects to the builder, who is ultimately responsible for ensuring that homes conform to the building regulations."
When things do go wrong, many homebuyers - like Karen - say they feel powerless in their attempt to get their issues resolved.
In 2016, a group of MPs - the All Party Parliamentary Group for Excellence in the Built Environment - called for a new homes ombudsman to be introduced to offer quick, free, independent mediation, saying levels of accountability and means of redress were currently inadequate.
"At the moment it feels like buyers are buying a promise that they see in advertising, which is unrealistic," says Maria Miller, a Conservative MP on the panel.
"Then, if their new house doesn't live up to those unrealistic expectations, they have very little recourse other than trying to get those things changed through the housebuilder themselves."
A spokesman for the Department for Communities and Local Government said it was considering whether housing should have a single ombudsman.
"It's only right that developers and builders are held to a higher standard," he added.
New homes are guaranteed by the builder for two years.
Most also come with a 10-year warranty issued by the NHBC.
But the organisation has faced criticism from some campaigners and MPs who say it is too cosy with developers, something it denies.
Karen, at the end of her tether, is hoping her home's issues will be resolved.
"It is just heartbreaking, because we can't even fight any more because we've run out of energy, run out of money," she says.
"We can't do anything any more - we're just stuck here and we've got no choice but to be stuck here.
"There is no other way for us to turn any more. There's nothing we can do."
Watch the BBC's Victoria Derbyshire programme on weekdays between 09:00 and 11:00 on BBC Two and the BBC News channel.