Neighbours of the $1.75 billion Waterview motorway project say no amount of finessing will disguise a planned ventilation stack that has been likened to a "dark tower" from the Lord of the Rings.

Architects plan a 25m-high "urban sculpture" of thick, rusted steel "reminiscent of spear-like leaves" to act as a huge ventilation shaft for the Waterview tunnel.

Several associated factory-like buildings will also be constructed around the stack, which would be next to a kindergarten and primary school.

Residents say the plan is an eyesore.

Eden Albert Local Board deputy chairwoman and Waterview resident Margi Watson said the stack would look like a "dark tower in Lord of the Rings" found in Mordor and Isengard.

"No matter how they dress it you've still got a monster factory-like building with blank walls as the face of a suburb," said North West Community Association chairman Bill McKay of a new design proposal from the Transport Agency.

Architect David Gibbs, who led a team which redesigned buildings at both ends of the motorway tunnels for the Transport Agency in response to concerns raised in public submissions, says in a brief of evidence prepared for a board of inquiry hearing in February that he recognises "the potential of the stack to be a dominating visual element in its context. The solution in my opinion is for the stack to be designed as [a] large-scale urban sculpture."

He describes the proposed structure as "an assemblage of self-rusted thick steel plates that are both tapered and curved - in some ways reminiscent of spear-like leaves".

As for the tunnel building, which will be 6.5m high and more than 60m long, he said each of its four parts would be adorned with symbols "reminiscent of sea organisms and objects that might be found in the inter-tidal zone".

But Ms Watson, who is also chairwoman of the Waterview Primary School board, said the Transport Agency was not listening to community calls for the building to be buried and the ventilation stack moved to the other side of Great North Rd.

She said the new design moved the stack 10m closer to the school andkindergarten than in a plan lodged with the Environmental Protection Authority.

Auckland Council member for the Eden Albert ward Cathy Casey is crying foul over the redesign of buildings at both ends of the tunnel, saying the Transport Agency should not be allowed to "keep changing the goalposts" after submissions closed.

She is upset about a proposal to construct the control building for the tunnels in Alan Wood Park at their southern end, where there will also be a 27m ventilation stack, saying more Mt Albert residents would have prepared submissions had they known the park was to be "so heavily built on".

An earlier proposal to erect the control building at the Waterview end was changed after the Transport Agency decided it needed a larger structure.

But although it will be 640sq m, Mr Gibbs says a ventilation building he has designed for the southern tunnel portals will be 1330sq m smaller than planned.

It will be longer - at 133m - but will taper to just 12m at its northern end with a "green" turfed roof to lessen its visual impact. Its materials and forms are intended to reinforce a "volcanic highway theme".

Transport Agency highways manager Tommy Parker said the changes followed concerns raised in submissions. "We got submissions saying it was very imposing and dominant so the architects have been doing their best to try to break that up a little bit and make it less dominant," he said.

Mr Parker said Waterview Kindergarten would be temporarily moved while the tunnels were dug, and it was possible that would become permanent. The exact location of the ventilation stack had yet to be settled.

The agency was satisfied the tunnels would improve air quality around the school but "we know there is a stigma attached to this and we're trying to work with the school to see if ... we can overcome that."