They were also told temporary classrooms would arrive in four stages, starting August, with the last rooms scheduled for November.
Meeting organiser Miranda Cross said that was not as quick as many parents would like.
"For all of us the priority is getting our kids back at school and understanding how that's going to work, what it's going to look like, what the timing is going to be," she said.
"I have to say I am a little gutted to know that it's not going to be till the end of the year and it's three full terms that our Year 12 and 13 kids are going to be not at school all the time, which is sad."
The meeting showed the level of anxiety, concern and frustration in the school's community, Cross said.
She was considering trying to apply political pressure to get more funding for school buildings nationally, not just at Hutt Valley High School.
"A lot of the questions that the parents had around funding and systemic funding, to be fair to the ministry officials they can't answer those questions, this is actually political decisions about where money gets spent," she said.
During the meeting, the audience asked ministry staff if schools were adequately funded for maintenance.
They did not respond, but local MP Ginny Andersen did.
"The answer is no, from what I can see. There is insufficient funding provided to this school to enable it to operate in a healthy, safe manner, and that's disappointing," she said.
Earlier, the school's board of trustees chairman Hamish Bowen told the meeting that lack of funding was behind the school's building problems.
"If we look at the maintenance, we're given an amount but to really maintain, paint it properly, clean it properly we probably should be spending four or five times what we're given as an allowance," he said.
"I can look back at least 15 years and say we've had quite a substantial under-funding both in maintenance and in capital and that inevitably leads to roofs failing, water getting in and things like mould occurring."
The Education Ministry's associate deputy secretary for property delivery, Scott Evans, told the meeting the ministry would start working with the school today on a strategy for replacing C block.
"We're committed to ensuring that we replace that block and we also have an opportunity to expand the teaching spaces in that block.
"There's also a focus around how do we move forward with ensuring that we have a robust maintenance plan for the school."
Evans said the ministry would include in its thinking plans the school developed years ago for a C Block replacement.
Occupational hygienist Bridgette Jennings fielded questions about the risks posed by black mould.
The mould was unlikely to spread to more buildings in the school and there was not a high health risk, she said.
"Any mould spores that you might get on your skin, on your clothing, we have that on us anyway, there's mould present in the environment wherever we go. There may be spores that you transport from here to your home but it's not going to start mould growing in your home and it's likely to be a limited health risk because its going to be minor."
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