Overcrowding – An Occupancy Overload

Good building designs rely on knowing a little something about their occupants.Not in a stalkerish way you understand; there’s no need for eye colour or icecream flavour preference. To design well we need to know about the people in the building; when they will be there; how many of them will there be; what do they want to do?

This weekend I found my interest sparked by an article published by Stuff (01/09/17) about an apartment with Japanese style sleeping pods installed in a residential unit.
It’s an apartment right? What could be wrong with people sleeping there?

The same could be said of the overcrowded homes the length and breadth of New Zealand.

Well actually, there are so many reasons why it might not be a great idea that it’s difficult to know where to start. Beyond all the obvious social ills of people living on top of each other, sharing too few resources with not enough privacy, there are the obvious and well documented issues of disease.

So much has been researched and written about the plight of people living in overcrowded conditions I’m not going to add to it here. I am however going to think through some of the indoor environment design implications for housing and where we are going to trip up if we allow too many people to share the same too small home.

Designing for People

Overcrowded sleeping arrangementsWhen we design homes we make some assumptions about the number of people who will be living there. Typically we allow two people for the main bedroom and one per bedroom thereafter. Ok, many homes have one or two people more than that particularly if they are children but the numbers are suitable to the size of the accommodation.

Once we’ve established how many people will be using the space, we can work out the loads they place on the building. How much heat they will add to the interior, how much moisture they will produce, how much will they pollute the air?


Overcrowding Leads to Design Failure

People produce an amazing amount of moisture. A single person through perspiration and breathing will produce over 350kg (or a third of a tonne) of moisture per year; that’s around a kilogram per day. And that’s before they start bathing, cooking, doing laundry and cleaning which creates more moisture for the home to deal with.
They also generate a lot of heat. Even seated, each person’s metabolism will create about 70 Watts of heat. If they’re more active that will increase too. We can add some more again for the heat from electronic devices, and hair driers, and lights etc.

Sleeping podsAnd then with the breathing we all seem to require, there is the issue of the oxygen we need and the pollutant carbon dioxide we breathe out (never mind the odour and other pollutants we can imagine). Assuming the room has the doors and windows closed the carbon dioxide may easily reach levels of around 5000 parts per million with just four sleeping people in a 24m² room. Some studies suggest 10000 ppm may be likely.

So, in a single room with four sleeping pods, if people are just there for eight hours at night it will be like having a small heater on all the time (not great in warm weather); they will produce almost 1.3 litres of water as vapour; and reduce the air quality well beyond the design maximum value of 1000 ppm of carbon dioxide allowed for naturally ventilated spaces.

Meeting the Issues

All that warm humid air is a problem. If we don’t plan for it, it has the potential to cause issues with condensation, mould growth and disease. There are safeguards in a good design which deal with the moisture, pollution and heat loads we place on a space. In essence they are quite simple:

  • Understand the indoor loads and the outdoor climate.
  • Remove the moisture at source before it gets a chance to get into the air by extracting close to where it is being generated.
  • Ventilate so that the moisture laden air is exchanged for drier outdoor air with less water content.
  • Heat the space so that the relative humidities stay low and room surfaces are kept high (oh, and so we’re comfortable as well!)
  • Design and insulate the structure in the correct way to allow vapour migration without condensation on cold surfaces.

Design Risks

Mouldy window sillIf we don’t do these things we are likely to get cold room surfaces and cold, moisture laden air. This is the perfect recipe for condensation and mould. We’re all familiar with internal condensation where cold surfaces like windows develop beads of moisture. We know too that moisture on these surfaces can help mould to develop. What a lot of people don’t realise is that this can be happening inside walls and other structures.

The wrong sort of mould and we get degradation. We can rot timbers; we can initiate or exacerbate health conditions; we can even grow mushrooms!
So is there a risk in overcrowding? You bet! Is there an even bigger risk in unplanned, un-designed-for occupancy? Definitely. So what shall we do?
We go right to the top of this piece and start by answering the questions:

  • How many people?
  • When will they be there?
  • What will they be doing?

With those an experienced designer, who can cross the construction materials, heat and ventilation design, and human health and comfort boundaries, supported by design evidence from appropriate simulation tools, can deal with the combinations of risk to avoid undesirable outcomes.

And for purely social reasons, we need to deal with overcrowding. It may be big but it’s not clever.


The sleeping pod Stuff article was published 01/09/17. Take a look here

Author: Ruth Williams – Principal, Buildings That Work InsideOut Ltd

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