There is an undoubted move towards developing upwards, with an increase in 3 and 4 storey walk-up apartments. It’s generally what major urban areas do, so really is no surprise. Yet some of the issues which come with developing upwards may surprise some. One of them is stairwell ventilation. It’s easy to get right if you know what you’re doing. If you don’t, then like most things, it’s easy to get wrong. The following guide talks to some of the basic considerations and recommendations for stairwell ventilation. This does not include fire and smoke safety. That’s a more complicated and serious issue, demanding sole focus in a dedicated article.
It was in late 2021 when Labour and National, in a rare show of bipartisanship, announced changes to housing density laws. It was a reaction to the urgent need for more housing. As was the recent re-zoning by Auckland Council to make way for higher density housing. It continues the rise (no pun intended) of apartment style complexes. In particular, Auckland has seen an increase in 3 and 4 storey walk-up style apartments, such as those at Fraser Avenue.
Architecturally designed, the walk-up apartments are characterised by the need to maximise space and brightness. The use of glazed stairwells is highlighted in the guidance from the Auckland Design Manual, who note glazed staircases are used to “...break up the horizontal length of the building, provide a very obvious front entry to each collection of apartments and also provide a vertical transparent space between the blocks”. Additionally, glazed stairwells reduce the often claustrophobic nature of the internal area and provide a connection from the exterior to the interior. Perhaps more important than all that, they help foster a sense of community and break down the barriers between apartments and occupants. But all of this does not come without issue.
A 3 storey high fully-glazed stairwell will introduce a greenhouse-like level of thermal discomfort without adequate ventilation. Even on a clear Autumn or Spring day, without adequate air flow, the stairwell can heat to an uncomfortable level. Especially if your apartment is on the top floor and you're carrying bags of groceries from the weekly shop. So what level of ventilation is required to counter this? And what do the standards demand?
A stairwell can be naturally ventilated if the louvres, windows or opening doors, are 5% of the overall floor area of the staircase. This will meet NZBC G4. To calculate this we take the footprint of the stairwell and multiply it by the number of levels. For example, a 3m wide x 5m deep stairwell with 3 levels would have an overall floor area of 45m2 and need ventilators measuring 2.25m2 (the ventilator measurement is the overall size of the vent).
As noted, windows can meet the code requirements but in an apartment building, they have some drawbacks. Windows introduce a certain level of risk (although it depends on the windows used). However, it’s more a case of what can be opened, can be closed. So ventilation becomes dependent on someone to open the windows, and on making sure an occupant who prefers the temperatures a few degrees higher, isn’t constantly closing them.
With louvres, there is no real security risk and they can be set in position, without the need for any physical manipulation to work effectively. Aesthetically, they are often incorporated into the design to such an extent that they disappear from conscious sight. Whilst we certainly don’t believe louvres to be unattractive, the ability to powdercoat louvres to match the colour scheme of a building can effectively camouflage the functional parts of the building (if that’s desired).
The choice of louvre model and decision where to place them is paramount, needing to take account for both the prevailing weather conditions and the use of material in the stairwell. For example, a bare concrete stairwell will have no issue with a small degree of windblown rain. A louvre such as the VL-55S is ideal. It’s a slimline, single bank louvre system providing a medium level of weather protection and perfect for such situations. But where the weather might be more challenging, or the stairwell is carpeted and/or the internal wall lining is gib, then additional protection is needed. In such cases, either the VL-104D or VL-2SD are more suitable, both decreasing any wind blown rain so no harm or damage will come to the interior.
In both instances, placement is important. The natural buoyancy of warmer air needs to escape through louvres towards the very top of the stairwell. As this warmer air rises and departs the building, it draws in the cooler air from outside and through the louvres at the bottom. The result is passive ventilation which is naturally self-adjusting, requires no physical manipulation and little maintenance. They are also silent. More importantly, it reduces the energy consumption of the complex, which benefits not only the environment but also the occupants who may have lower site fees as a result. A big advantage given the need for affordable housing and the current pressure of rising inflation.
Returning to the greenhouse-like effect of fully-glazed multi-story stairwells, if a mechanical ventilation system is being used, then it has to meet the specifications of NZS:4303. Yet these do not go far enough and even if you do satisfy them, will likely result in dissatisfied occupants. The reason being with NZS:4303, the code requirements for mechanical ventilation might be as low as 1 air change per hour. We know from experience the amount of ventilative cooling is actually much higher than often required and will typically be closer to 5 air changes per hour.
This means the fan used to extract the hot air out of the top of the building needs to have sufficient capacity for the air changes per hour required. Additionally a passive ‘make-up air’ louvre at the base of the stairwell is needed. The size of this louvre is based on airflow calculation and not the 5% rule applied to passive ventilation systems.
Regardless of the choice of passive or mechanical ventilation, there is a requirement whenever a louvre is used for ventilating a glazed stairwell that should never be ignored. The visible lights behind the glass will serve as the most attractive beacon possible for flying nasties, so an insect screen is a must. Without one, any issues of possible thermal discomfort will soon be superseded by tiny teeth and buzzing annoyances.
As 3 and 4 storey walk-up apartments continue to gain in popularity, the level of examination between options for buyers (or renters) will grow. You certainly get a ‘sense’ of the place when you visit. So if that visit is likely to include entering a glazed stairwell, the right ventilation solution will have a big impact on that ‘sense’. Getting it wrong is easy. Getting it right can be easy too…contact us and we’ll show you how.
