The system for adapting elderly or disabled people's homes is complicated, inconsistent and lacks respect for their wishes, says a new report.
A customer charter setting out people's rights and how long work should take is being called for by assembly members.
Their review also says the means-testing system for disabled facilities grants is both complex and unfair.
Older People's Commissioner Sara Rochira said adapting homes saves pressure on the health care system.
The Welsh government welcomed the report and said it was committed to continuing to improve services.
The Local Government Committee is also raising concerns about different standards and services being offered by local authorities.
Committee chair Christine Chapman said: "People need adaptations to their homes for different reasons and at different stages of their lives.
"In all cases it can take time for someone to adjust to being less able and it is vital that the support services they need are there when they need them.
"The committee was told that the current system is too complicated, inconsistent and doesn't do enough to respect the wishes and needs of the most important people in the process, the people who need these adaptations to their homes."
She said a customer charter, guaranteeing what people can expect would bring "clarity and confidence".
Ms Chapman urged the Welsh government to set minimum quality of service standards and to investigated the disabled facilities grant means testing system, which the report said was "too complicated and unfair".
Ms Rochira called for the report's findings to be implemented swiftly.
"Quite simply, the cost of failing to get this right and deliver home aids and adaptations effectively to older people now and in the future is just too great - not only in terms of the cost to the public purse, but more importantly the cost to an individual's health, wellbeing and independence," she said.
Welcoming the report, a statement from the Welsh government said: "Whilst home adaptation services vary across Wales, it is important to note that significant improvements have been made to service delivery in recent years and we are committed to continuing this.
"As part of the housing white paper we are reviewing the range of aids and adaptations programmes to see whether there is any scope to make further improvements to the current range of services provided for citizens in Wales."
The College of Occupational Therapists called for a "thorough overhaul" of the housing adaptations system in Wales, which it said was "bewildering, discriminatory, and failing those in need".