The number of repairs left outstanding by the Housing Executive has more than doubled in the last three years - despite the body having over £100m of cash reserves.
Over 20,000 repairs are outstanding, according to the latest figures, leading to accusations that the NIHE is failing its tenants and causing them "upset and stress".
A well-placed source in the construction industry said there "needs to be root-and-branch reform of how repairs are delivered".
The number of repairs left outstanding had spiralled to 21,632 at the end of September this year - compared with 9,692 at the end of October 2016.
The figures were obtained through a Freedom of Information request and revealed by trade magazine Inside Housing.
They point to a surge in unfinished jobs in the wake of the collapse of giant contractor Carillion in January last year.
The number of repairs to be done within their housing stock of 85,000 properties peaked at 30,887 in March 2018.
While that figure has reduced, there is still a backlog of more than 21,000 repair jobs.
North Belfast MLA Nichola Mallon said tenants deserve better.
She said: "The fact that the Housing Executive has failed to carry out over 21,000 repairs isn't acceptable. The spiralling number of outstanding repairs and the upset and stress it is causing to people living in these homes is something we have been seeing more and more of in our work on the ground over the past three years.
"Families are being left to live in houses that are old and in a poor and unacceptable condition. They are being failed. In response the Housing Executive says it hasn't the money to carry all the repairs that are needed.
"But yet it is sitting with £102m in its reserves in the midst of a housing crisis. Serious questions need to be answered.
"This is yet another reason why we need a functioning Assembly that scrutinises and holds people to account."
Mrs Mallon was also a member of Stormont's Communities Committee - the department whose remit covers the Housing Executive - when the Assembly was last sitting.
Last month the Belfast Telegraph revealed that the Housing Executive is sitting on cash reserves of £102m.
The NIHE explained it is kept as a contingency for unexpected events such as a bad winter.
But it also admitted that another reason for its increased coffers is "because of legal challenges by bidders to procurement competitions".
Now, on the issue of repairs, the Housing Executive has defended its record despite the dramatic increase - and claimed staff are meeting their 'key performance indicator' targets.
A spokesperson said: "We complete over 400,000 repairs annually through our all-trades contractors and of those repairs, 95% are completed within the prescribed time period. Overall, these fall within our contracted key performance indicators.
"However, we have seen a gradual increase in the number of overdue repairs and this can be attributed to the current skills shortage within the relevant sectors in Northern Ireland.
"We are working with our contracting partners to address these shortages and to ensure all repairs are done within the prescribed timeframe."
On the 'skills shortage', a local construction industry source revealed that "the skills are out there - they just don't want to work for NIHE". They added that many contractors who either currently work with it or have in the past have been frustrated by how the Housing Executive operates and said action needs to be taken to reform how things are run before the crisis deepens.
The source said: "The nine NIHE maintenance contracts that are split across Northern Ireland are very difficult due to the management style, culture and raised expectation level of the customers.
"There needs to be a root-and-branch reform of how repairs are delivered which involves contractors being engaged instead of the internal reviews that have taken place.
"The suite of key performance indicators implemented as well as a new English schedule of rates and delivery model has not been successful for NIHE or contractors.
"The promised land made in 2015 of a 'tenant-focused' repair service that is 'best in class' has not materialised and that has to be questioned as to why."