Sean Maxwell

Within a few hours of moving in, we had spotted a cockroach. The little beast was trying to hide in the shadows of a corner. My wife, always humane, collected it and tossed it out the window to pursue a fulfilling life elsewhere. Just not in our apartment.

I had come to accept that big bugs were a fact of life in Australia when a short time after moving here in 2015, I met my first huntsman lurking under the bed. But if the ecosystem of my Bondi apartment was robust enough to support a big spider, what was he snacking on?


Cockroaches, and the spiders who eat them, are often relatively free to pass between apartments in search of sustenance. Roaches can survive weeks without food and days without water. So when the neighbour downstairs does some cleaning, they come to my place looking for food. A cockroach doesn’t have far to travel between food sources in an apartment building. In fact, because most of the big holes in apartments are near plumbing lines, my kitchen is at most a few metres from at least three others, if you follow the piping. Bugs love to hang out in these dark places because they offer warmth, water and ready access to food.

Here’s where the building science comes in. I do building air leakage testing and consulting for a living. That might sound pretty obscure until you learn that in many parts of the developed world, an air leakage test on new buildings is required by law before getting a construction completion sign-off. That’s because sealing air leaks has a huge number of benefits for energy efficiency, as well as occupant health, safety and comfort.

It also has the side benefit of being one of the central tenets of Integrated Pest Management in buildings. IPM is an approach to pest control that uses knowledge of pest biology and often commonsense actions to keeping bugs out of people spaces, often with little or no use of pesticides. It’s sustainable in a real sense because unlike sprays, the application of sealing measures are hopefully a one-time thing.

Being a building science nerd and thinking and writing about testing buildings non-stop, of course one of the first things I did when I moved into my new place was an air leakage test. It’s also called a blower door test because… basically it’s a fan in a door. Turn the fan on and suck air out of the house, and leaks blow in through all the gaps and cracks to replace it. My apartment came in at around 30 air changes per hour at 50 Pascals. That’s nerdspeak for “very cold in the winter”. A more respectable number is about 10. With a blower door test you can walk around and feel the air leaking in with your hand. And sometimes you find stuff that grosses you out.


The linoleum flooring in our kitchen was apparently simply laid over a clearly high-quality newspaper underlayment. The result when I turned on the blower door was that the flooring actually floated up on a cushion of air coming from my neighbour’s place downstairs. And with it, little brown balls from where the skirting should be (why there’s no skirting in our kitchen, I don’t know). The little brown balls, I found out, were egg cases for the German cockroach. A dead mamma cockroach lay entombed beneath the linoleum. Gross.


I sprang into action with a caulk gun hitting every last hole and crack that I could find. I thought I had the place sealed like a bath tub. But with the blower door running, I could still feel a draft near the cabinets, and this is where it gets tricky. In essence there are only a few true entry points for bugs in a kitchen: the pipes and the joints in the major building materials like floors and walls. There’s an easy way to seal them and a hard way. Once a building is built you’re stuck with the hard way.

In every room in a house, there’s a crack running along the floor that is usually covered by skirting. Rooms with tiled or hardwood floors may have the skirting caulked to the floor, which is done mostly for appearances but also it provides a seal. In rooms where carpet is installed, a little gap is left so the installer can slide the carpet under the skirting. This looks just fine but the gap is still there. I know because I can feel the leak with the blower door.

In the kitchen, a much worse situation exists. Almost always in new homes and apartments, there is no skirting and no seal created at that wall/floor joint in the area behind where the cabinets go. It makes some sense because no one will ever see this gap once the cabinets are in – except a cockroach. Once the bug waltzes through this open crack behind the cabinets, they have free access to the whole area behind them, and the trip from the neighbour’s kitchen to yours is awfully short.

In order for me to seal up these cabinets, I have to get inside and find every little crack on every joint inside and outside the cabinets. It’s a very labor-intensive job, and as I sealed along one crack, I noticed a draft further along. Imagine that this is a cockroach simply trying to make an end run around your seal. In my apartment I did not stop until I could feel a complete absence of draft created by the blower door.


This problem is so easy to avoid for new apartments. Just have the builder, before the skirting goes on and before the cabinets go in, walk around and seal every gap, pipe and electrical penetration with plaster, caulk or a can of low-expansion foam sealant. For a whole apartment it realistically takes only an hour, and demonstrable performance benefits result. I know this because I’ve studied apartment leakage, ventilation and building performance for years, and I’ve done the sealing myself.

The benefits are many. Ventilation systems work more reliably in buildings with sealed apartments. Sound transmission is reduced. Secondhand smoke and other pollutant transfer is reduced. Smells between apartments are reduced. And using a blower door to check for air tightness helps reveal serious lapses of fire-stopping between apartments that may be hard to see – an added level of attention that has real safety benefits. And of course, sealing up the big gaps in apartments reduces the number of ways that pests can travel between them.

And before anyone quips that you need to let your apartments breathe: no you don’t – you need to let your residents breathe. Seal up the apartments and let them use those wonderful things called windows…

  • If you are a builder or developer, especially if you are pursuing Green Star for a residential project, make sure you include the Innovation Challenge for Building Air Tightness. It’s one relatively inexpensive credit that will deliver real benefit to your project and make your tenants happier and more comfortable.
  • If you are a resident, look at this list of items to seal in your own apartment to help get rid of bugs, or get your landlord to do it.
  • If you are a manager of apartments, use the same list to fix up apartments, especially in buildings with complaints of pests. It’s a much more environmentally friendly approach to pest control than pesticides, and it’s a lot better for your tenants.

Sean Maxwell is NSW and QLD manager of Efficiency Matrix, an air tightness testing and consulting company. He is a member of AIRAH and ASHRAE and lives in Bondi with his wife and no bugs.

Join the Conversation


Your email address will not be published. Required fields are marked *

  1. Hi there,

    Great article – it shows the painstaking process taken just to seal every gap if not done right the first time. More importantly, I read somewhere that sealing/caulking only accounts about 1% of total building costs. The benefits are countless – less roaches, less noise transmission, efficiency of ventilator systems. Great article!
    Would you be kind enough in sharing some insight? If yes, please contact me on


  2. Sean,
    For years I have tried to convince my clients of the benefits of air leakage testing using energy efficiency and comfort as my most convincing argument. Integrated Pest Management however is now on top of my list!
    Love you article!