This is a guest post by Ed Clayton. Ed has previously written for GA about the benefits of ‘green-tracking’ light rail.

Light rail has been back in the conversation following the media release on route and mode selection last week (Greater Auckland post 29/10/2021). Three options were released, tunneled and surface light metro, surface light rail and a mixture of tunneled and surface light rail. Of these three, the surface light rail would travel down Dominion Rd with the other options being linked to Sandringham Rd. Minister for Transport, Michael Wood, has been very clear that while the mix of tunneled and surface light rail is the preferred choice of the ALR team, any of the three options could be finally selected by the Government. This post was written mostly before the announcement, and while it explores how surface light rail down Dominion Road could spur development, it could apply to any route and mode selection. As a declaration, I do support surface light rail over the other choices, partly due to the eye-watering costs of tunneling, but mostly due to the better environment and social outcomes possible with surface light rail. This is neatly summed up in the only dissenting view from the ALR board from Ngarimu Blair.

Summary of Ngarimu Blair dissenting view on ALR choice

The Government has made some positive moves with the just-released acceleration of the National Policy Statement for Urban Design (NPS-UD). This will effectively end single-house zoning across Aotearoa NZ and allow for, in some estimates, increased density in up to 92% of Tāmaki Makaurau’s residential zoning that in turn could mean 50,000 new dwellings.

What could this mean for planned light rail? The NPS-UD requires that rapid transit stops have a 10-minute / 800m walkable catchment and allowance for buildings of at least 6 storeys. This has been endorsed by Auckland Council in recent planning meetings. One of the goals for the LR project is not just improved transport connections but also allowing better urban development opportunities. Dense residential development around stations will surely support patronage and enable better transport choice, but just how much development could there be?

Map of Dominion Rd corridor with residential and business zoning, special character overlay and light rail walking catchments (from 2016 AT proposed route)

How much density is captured in the 10-min catchment?

If the Dominion Road route is selected (still unknown at the time of writing) then the answer may be, well, not much. Even with the allowed increased density rules, much of the corridor is surrounded by special character (SC) areas. the map above shows the proposed Dominion Rd route (as of 2016). Mapped on to this are the 400m and 800m isochronous walking catchments. When zoning is added with the SC it becomes very apparent – only nine parcels zoned single housing in the 800m walking catchment are not covered by the SC overlay!

The single housing zone covers 36% of the Dominion Road 800m catchment. The SC is a qualifying matter under the NPS-UD, meaning that the amount of development otherwise permitted can be reduced. The NPS-UD doesn’t allow blanket protection and Auckland Council knows that it will have to enable the requirements in some SC areas, but they also appear to want to retain as much of the SC areas as possible. It is unclear how the new rules will affect SC overlays (or others such as volcanic viewshafts), but it is certain that there will be fewer protections and that the ones that are kept will be weaker. Hopefully the recent changes mean council will step up to deliver the dense, walkable catchments around transit that will require removing the SC overlay.

Meanwhile, how could we enable dense development along the Dominion Road corridor through focusing on the other housing zones and the business areas?

Enhancing an ecological light rail corridor

Hopefully light rail is green tracked to reduce environmental impacts and focus on improving water quality.

Could we leverage this to create an ‘Ecological Build Zone’ (EBZ) where zoning restrictions are relaxed for achieving biological targets?

An EBZ would be a permissive overlay where bonus development rights could be awarded if developments and buildings incorporate certain features that promote not just water detention and treatment functions, but also reduced urban heat island effects, reduced embodied & operational carbon, improved air quality and improved biodiversity functions. A major focus of this would be green roofs but could incorporate green walls and raingardens too.

Light Rail – Green Tracks

The primary driver to implement an EBZ would be reducing site runoff and improving water quality through bioretention. While rules in local planning documents already stipulate that new residential runoff needs mitigating through retention and detention devices, these requirements are almost always met through hard engineering designs such as pervious paving or rainfall retention tanks. These do not address common roof derived contaminants such as zinc. Instead, an EBZ would focus on bioengineering to achieve goals.

Currently the Auckland Unitary Plan does allow for green roofs to be counted as pervious surfaces, meaning areas with a green roof do not count towards maximum site impermeability (generally 60% coverage). In Stormwater Management Area: Flow (SMAF) zones, building green roofs will not trigger stormwater management requirements and underground infrastructure and devices are not required to mitigate roof runoff.

Render of Prato Urban Jungle (Stefano Boeri Architetti)

Given that increased infrastructure cost is often an argument trotted out to oppose increased density, an EBZ could result in minimal increases to the carrying capacity of the stormwater network, as the simplest design of a green roof (low maintenance groundcovers over a 75-100mm media layer) is known to retain around 50% of rainfall. This is taken up by the plants and released through evapo-transpiration processes. The biofiltration actions help remove contaminants and dust particles that otherwise make their way into stormwater networks. Incorporating additional retention tanks within developments would then provide harvesting of excess rainfall to be used to water plants during summer months. Green roofs that include more extensive planting such as small trees can provide increasing benefits, shading adjacent streetscapes and reducing urban temperatures while providing additional insulation for buildings.

Bosco Verticale, Milan (Stefano Boeri Architetti)

Minimising the load on existing infrastructure

These rules would apply to any building that incorporated a green roof, and to some extent external green walls and perhaps raingardens. It could be as simple as rewarding every m2 or kg of green mass with a m2 of extra floor area. Or, as slightly more complex approach, the greater the coverage of the green roof and the greater the biological mass supported, then the greater the exemption from planning rules. A green roof that consisted of an accessible terrace with small trees and lawn space would qualify for a greater exemption than a simple green roof, which in turn would receive greater exemption than a green wall. Alongside these initiatives floodable gardens and pocket parks could be built for attenuation and detention functions, bringing rainwater back into the public realm.

Floodable pocket park in Philadelphia designed to be submerged during rain events (Philadelphia Water Department)

Designs that incorporated specific planting regimes designed to increase biodiversity, improve specific environmental indicators such as air quality or improve pollinator food sources could gain extra exemptions as well. Singapore allows increases in gross floor area (GFA) for green roofs with additional benefits for public access. Several USA municipalities also have incentives for green roofs, either GFA increases or tax credits and others apply penalties if green roofs aren’t built.

Namba Parks, Osaka (Yuji Kotani / Getty Images via The Guardian)

Increasing public green space

One important aspect to an EBZ would be granting public access to a green roof. Research acknowledges that access to green and blue spaces are linked to improved mental wellbeing. An interesting LinkedIn post by Jesse Prendergast, a transport planner and analyst at MRCagney, investigated access to green space in the Auckland isthmus in light of Covid-19 lockdown restrictions (highly recommended read: https://www.linkedin.com/pulse/novelty-mugs-new-zealands-problem-public-open-space-jesse-prendergast). The Dominion Road corridor has some of the lowest green space available in the central Tāmaki Makaurau area and if we are to expect greater density along the light rail line, increasing green space at every available opportunity needs to be pursued. This would allow more equitable access to nature and the benefits that come with it.

Map showing accessible park area for the central Auckland isthmus (Jesse Prendergast)

Green construction innovations

The NPS-UD also requires new policies on greenhouse gas emissions reductions and exemptions could be coupled with additional concessions for low embodied and operational emission construction so that cumulative exemptions could be realized. These could include the use of locally manufactured cross-laminated or other engineered timber products in structural engineering rather than steel and concrete. Diverting waste streams from landfill (eg. reuse of rubble), using eco-products such as hemp bricks for insulation and building to Passivhaus, Green Star / Homestar, or zero-carbon standards could all add cumulative concessions and exemptions from local rules.

Render of new Auckland City Mission building being built with engineered timber products (Auckland City Mission)

Green roofs aren’t cheap however. The added weight and waterproofing requirements of even the simplest designs add significant engineering costs and irrigation systems are often required to get plants through dry periods. There will be additional maintenance costs and, in a drought, dry vegetation could pose an additional fire risk. To expect that standalone single dwellings would build green roofs is probably beyond the budget of most renovations or new builds. Instead, the focus of an EBZ could be on apartment or commercial developments where the addition of a green roof will enable extra floors and units to be constructed. The benefits to building a green roof could be tax credits to offset the cost of the roof, increasing the GFA of the development or a fast-tracked consenting process. While undoubtably controversial, allowing extra height that enables more apartments could spur the uptake of green roofs.

Park Royal Hotel, Singapore (Patrick Bingham-Hall/WOHA)

A linear biophilic network

Allowing an EBZ around an extensive green light rail network could create infrastructure that improves water and air quality, access to nature, improves community wellbeing and urban biodiversity. The EBZ would allow extensive green roofs and walls in exchange for bonus development rules to encourage increased density around rapid transit. These could be coupled with water sensitive public realm features such as raingardens and floodable pocket parks. This would adhere to Te Mana o te Wai principles (see the Green Light Rail post for a deeper exploration of this) and could create a linear biophilic network where biodiversity, regenerative design and ecological net-gain can be realized.

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29 comments

  1. I agree that green roof roofs look nice – but how much Stormwater function will they serve along Dominion Road? Most of the area highlighted is overlying basalt and stormwater from each site will be discharged to ground. Attenuation thus isn’t required as no water will be leaving the site as is. And roof water is considered functionally clean and not requiring treatment (in most cases) under the Unitary Plan.

    Instead of trying to increase density by providing low carbon construction, developments that needed to support the heavy weight of wet soil and trees on their roofs will more likely be made of concrete and steel, or at a minimum will have larger concrete foundations even when made of timber. Additional plastic waterproofing will be required under the roof that requires increased maintenance and replacement over time as it leaks compared to a typical roof.

    I guess green roofs are really a pet peeve of mine as a civil engineer – they look nice so people think they are ‘green’ but without considering the location they’re placed in they often just increase carbon emissions for no benefit for the Stormwater network. And I rarely see discussion of the trade off of green roofs (more Carbon emissions during construction and maintenance) in the discussion of them.

    1. +1

      Not to mention that green roofs have the opportunity cost of not being able to use that roof space for solar panels.

        1. Yeah so you can stick solar panels on a green roof but you’ve compromised both in order to do that. You get less solar panel area than if it was all solar, you get a green roof that is no longer usable for recreation because of the solar panels, the whole installation is heavier etc etc. You’d get more benefits by having half a roof that is 100% solar panels and half a roof that is 100% green than mixing the two.

        2. Solar panels compromise the use of green roofs for recreation, but you can still get 100% of the solar power generation and 100% of the water management and thermal insulation benefits.

        3. Well in theory, the medium the plants grow in will dry out less if the plants have a period of each day in some shade…

    2. Thanks James, you raise some good points that will of course need careful consideration when designing and building green roofs. However, I think that many of these points could be considered and valued differently.
      I believe aesthetics, especially the visual amenity of green and blue spaces, are vastly under-rated in our urban areas. We know that mental wellbeing (and recently evidence to support childhood development too) is improved with such access, but how do we value this when we assess buildings?
      As for roof runoff, you’re correct that it is considered clean under current plans and rules. Yet we also know that zinc in roofs is a massive contributor to zinc found in marine sediments, to me this indicates that we do have an issue with roof runoff which probably should be addressed through a review of environmental rules.
      I dispute that green roof construction and maintenance increases carbon emissions, comparison to a simple single dwelling timber frame and zincalume roof may be correct, but as we scale up to large apartments construction materials change. A well constructed green roof will be less intensive than a concrete roof and also sequesters carbon over its lifespan. If we use engineered timber products here (again, vast scope for NZ and our plantation timber industry) this could be a great win-win: reduced runoff and reduced carbon

      1. I just think that the Stormwater angle, particularly given the current stormwater disposal around Dominion Road, is less of a strong selling point. Is reducing some small amount of Zinc runoff from new roofs worth the extra materials required to provide green roofs? Designing for the wet weight on soil on top of the building will always require larger beams and foundations, and thus greater carbon emissions.

        100% agree that visual amenities and greenery/trees are lacking from many of our public spaces, and that this is only going to become more pronounced as intensification occurs. Green roofs can be a very good way of addressing this on individual lots while still increasing the building coverage – and that’s one of the strongest benefit I see from them. Could the increased density also cause less vehicle miles to be travelled and help offset some emissions? I don’t know, but maybe?

        There can be many benefits and reasons to encourage them in a district, I’m just not sure Stormwater benefits are one of them

  2. Great post Ed. I think green roofs have some drawbacks (as outlined by James above) but there’s lots of potential to use zoning rules to incentivise better construction methods and urban development outcomes. Lots to think about.

  3. Such inspiring photos. Thanks, Ed. I really enjoyed this. This sort of thinking is needed for all areas of Auckland, and some of it will apply best to those places with different underlying geology but it’s still useful to consider here.

    One of my pet peeves, to use James’ term, is the use of “retention” and “detention” tanks instead of doing a proper ecological design for a site, or at least using that water for household use – in Aussie they use rainwater for toilets, washing machines and hot water cylinders even if they don’t use it for drinking water. This means the storage offered across each suburb from the rainwater tanks will be useful during rainfall events because they’ll have been drawn down by water use – whereas in Auckland where we generally only use rainwater tanks for garden use, there’ll have been little drawdown whenever the ground is already wet.

    1. Thanks Heidi, yeah we are water-rich here in Aotearoa compared to Australia. I think this is shown in how stormwater is still very much assigned ‘nuisance’ value rather than viewed as a resource

  4. You’ve got me thinking about the Special Character overlay and stormwater.

    A 300 m2 roof can house one dwelling, or 15. The stormwater burden per dwelling is created by the single houses, not the apartments.

    So in terms of all these impervious areas per dwelling:
    – roof space
    – driveway space
    – carparks all around the city, as residents’ travel habits are determined in large part by the carparking they have at home.

    “special character” homes will have far higher numbers, on average, than apartments will.

    It’s not the apartments that should have extra requirements for dealing with stormwater, but the single houses.

    The Council should take this into account if they try to retain “special character” overlays at all. For example, let the property owners say no to having a “special character” overlay, but if they say yes, they need to:

    1/ Remove all car storage from the site.
    2/ Reduce impervious areas.
    3/ Provide raingardens and gardens designed for stormwater infiltration, sufficient to absorb the rainwater of, say, the new roads and widened motorways and housing and carparking that would be otherwise required to build 10 houses in sprawl – since that is the “stormwater opportunity cost” of keeping the special character single house.

    Chuckle. I’m actually serious.

    1. Haha I love it! Given that most (all?) of the SC areas were built when there was very little private vehicle use I think removing provision for cars is very much in keeping with the original character!

      1. Yip. Basically, this is the difference between:

        1/ assuming that “change” is “significant”
        2/ assuming that “change” is normal and required, and that “retaining the status quo systems” is “significant”.

  5. Maximum site impermeability is a bit of a joke having recently brought a new build in the North Shore

    We looked at a bunch of houses, as we recently sold our 1970s concrete block place with big garden as it was losing all privacy due to a set of very large (~300 sqm) houses being jammed in on ~400sqm sections overlooking our place.
    Just on those:

    I have been following this blog for ages and welcome better public transport & active modes for getting around, and also a fan of more and better intensification; it’s insane that in some very valuable real estate around Milford on the North Shore, NIMBYs have stopped/slowed most of the development around the town centre (most of which is 1 or 2 stories) and seem to want to retain the classic ugly 1 level brick & tile units.

    But councils & developers have pretty much given up on trying to ensure quality. The new builds next to me violate hight, boundary and access restrictions, which all approved by the council, and appears to me to be built overscale just to appear large and expensive. I get it maximises value from the land, but really disappointing to see 3 huge overscale houses built where 4-5 decent sized townhouses could have fitted in better

    For our new house, we ended up doing detailed investigation on ~3 properties and looked at a few more before signing contract on the one which has gone unconditional.

    Quick summary:

    every single one exceeded impermeability guidelines. Just massive amounts of concrete and a tiny strip of (ready laid) grass if any greenery at all.
    The developers put in stormwater tanks and pumps to get consent, but these will require active systems, which makes me wonder how these will look in 20+ years

    Everyone we looked at had gas connections, which can’t help with emissions, but claws back a square metre of space that would otherwise have been lost to a HWC system. Are gas supply companies offering deals to developers, as I stull don’t understand in 2021 why these are still being installed as primary energy source for hot water, heating, and cooking

    Not a single one had solar system, PV panels or hot water boosting. The house we brought could have had PV array installed cheaply and easily, but they have taken down scaffolding, so to get installers back onto the 3 story high roof and drop cables, is going to add thousands to the cost of the solar panel install.

    One offered an EV charger as a token, but most developers we spoke to via agents just seemed to not understand why any buyer might be interested in efficiency or emissions on a $1.5 to $2m dollar house.
    I couldn’t help but notice the vehicle of choice appeared to be large Audi SUVs for the people we spoke to, which didn’t inspire confident in approaches to green builds

    I really like the recent changes to penalize high emission vehicles and reallocate that money to a tax neutral fund which incentives low emission vehicles; we are now looking at an EV for our next car once we have moved house (though the house is close enough to a village centre we intend to walk/cycle more).

    I would really like to see a similar scheme; say $1k charge to all new town or fixed bottled gas installation, reallocated to a fund for a basic solar panel install. If a big chunk of those consents got panels installed at the time of build (the best time to do it) then Auckland and other centres could be reducing daytime energy consumption by several Megawatts, meaning that Huntly could be burning less coal, and hydro could be throttled back a bit.
    Would also have a flow on effect to reduce cost of panels and installation

    1. Would you be interested in writing a blog post?

      If you don’t have time for that, would you be interested in sending me the details of the properties? (The parts I’m particularly interested in are the stormwater calculations and the plans.)

      1. Will pull up the plans for a couple of places and see if I can summarize with supporting detail

        TL;DNR version of my comment; we need to build more housing and the infrastructure that supports that housing (light rail, cycleways etc) but we need to try and ensure good quality housing outcomes and take energy efficiency into consideration

    2. FYI, electric hot water only occupies about 0.5m2. Most houses have a linen cupboard, which can easily be used to accommodate your cylinder,

    3. In a housing crisis it’s a sellers market: The developers know they can sell whatever they produce no matter how much of a McMansion it is. They know a lot of house buyers aren’t clued up enough to be thinking about ongoing running costs. They know a lot of buyers are investors who don’t care about energy costs because the tenants will pay for it.

      1. Right now people are desperate. They will buy whatever so long as it says x bedrooms and costs y on the mortgage.

        I think when there are hundreds of smaller redevelopment projects going on, it will become a far more reasonable market. Why pay x, when you could pay basically the same thing, but for one that the developer spent a bit more on an architect to make the place not stupid. I think they could struggle to sell places that are really ugly etc because there will be actual choice in the market.

        The best marketing money the developer could do is make the development look nice or comply with some basic extra standards that will lower operating / maintenance costs.

    4. Oh man I must take a photo of the horrendous water detention system on a new build down the street.

      The duplex at the front has two 2 metre high water tanks next to the footpath, blocking the kitchen windows.

      Each townhouse at the back of the section has the same set up but instead of the tanks being against a wall or section fence, they’re next to the garden fences.

      Unbelievably ugly and I’m guessing this was a shortcut to save money.

  6. Talk does get down into “bad redevelopment” problems quite easily – not that we don’t need to debate those thoroughly.
    The whole ALR route dips into all the range of ecological/rainwater contexts, so should include every solution imaginable somewhere along its route. The issue of street trees and visual amenity overlaps with the rainwater issue, for example green walls/terraces offer more visual amenity to the public as well as street-level heat mitigation. Even along Dominion Road, ground conditions vary from impervious clay and some of the basalt to pervious basalt and “swallow anything” tomos. So the measures and calculations vary wildly and blanket rules become problematic. But for definite, the mode choice will have a big influence on how blue/green design is enabled by ALR.

  7. These buildings look great with all that Greenery have they thought about what all those roots will do to the structure when they find a small crack and they start expanding ? .
    And don’t say it won’t happen , as pipework under ground , buildings with Ivy on the face of them and the greatest example are the construction’s of ancient societies where the roots of the trees have blown supersize blocks of stone apart .

    ;- https://www.123rf.com/photo_14240298_close-up-of-tree-roots-growing-through-and-slowly-destroying-the-ancient-khmer-temple-of-ta-som-part.html

  8. While in the topic of zoning, Auckland really needs to remove most volcanic view shaft restrictions. Large parts of the CBD are currently maxed out while city fringe areas like Freeman’s Bay etc are severely restricted in places. One of the biggest culprits is from Northcote point to Mt Eden.

    1. Its pretty concerning in the ALR documents mana whenua were strongly supportive of keeping the viewshafts.

      With that kind of support, and more and more power being given to local Iwi we may never see any removed.

      It would be good to see if somehow there could be a bit of a win win. Where they agree to compensation from developers for building into that airspace. Some of the view-shafts are really ridiculous. Already grown out by trees, extremely distant, exist for the view from the porch of a single house (so not even any public benefit), cause ENORMOUS economic losses. So much land near the downtown core is made way less useful for one of the view-shafts. The induced transport is huge.
      The payouts to mana whenua could really be quite huge and it would still work out to be a net societal benefit.

      I’m not at all qualified to talk about it, but if someone was then it would be a fascinating read.

      1. Compensation for the airspace you are legally otherwise entitled to?
        If anything compensation should be going the other way… that is if mana whenua want to protect viewshafts, then they can pay property owners compensation for loss of amenity.
        The mountains are magic, as are taniwha.. *groan* no wonder why building in this country is so fkd.

  9. Good article. I got a scholarship in 2005 that took me to North America, Japan and Europe to research local government policy to promote ‘greener’ development. My research was referenced in several international publications, including a journal of the European Union. Unfortunately no one was interested in NZ, and still hardly are.
    All of the upzoning we have done in Auckland should have been contingent on both green development and affordable housing requirements.
    We give away development rights and property value uplift in little ole NZ!
    And we are doing it again with the Housing Supply Bill!
    c’est la vie.

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