You are planning a renovation. You have a vision for your Aussie home. You chose the builder. You picked the tiles. You budgeted for the new kitchen. But you have missed something vital. Air. Fresh air moving in. Stale, damp, and polluted air moving out. This is ventilation. It is not an optional extra. A $100,000 renovation fails if the house feels stuffy.
It fails if it smells of damp. It fails if black mold grows on your new walls. You must plan for ventilation during renovation, not after. This is about protecting your health and your investment. This blog will tell you why ventilation is so important.
So you may be thinking, why is ventilation so important when I am renovating my house?
Your renovation is a process. This process creates pollutants. It happens in two phases. First, the demolition and construction. Second, the finishing and "off-gassing." Both are dangerous to your air quality.
What Happens in Home Renovation?
When your home gets old, there may be various safety hazards as well as aesthetic challenges to address. A home renovation is done to fix some minor issues by repainting the walls, replacing furniture and replastering bits and pieces to something major like introducing proper ventilation systems, remodelling entire rooms, changing the plumbing system and so on.
It is common for people to consider renovating their homes every 10-20 years. Ventilation is one of the most important things to consider when renovating your home.
What Happens During Finishing?
When you reach the end of your renovation process, your new carpets, cabinets, and vinyl plank floors will look great. However, they are also "off-gas" materials. This means they release chemicals into your air. These chemicals are called Volatile Organic Compounds, or VOCs. The smell of new paint? That is VOCs. The smell of new carpet? Also VOCs.
Paint, primers, sealants, and glues all release fumes. Engineered wood, like MDF in your cabinets, uses formaldehyde-based resins. Without ventilation, these chemicals build up inside your home. You and your family breathe them in. This can cause headaches, dizziness, nausea, and "sick building syndrome." You are trapping these pollutants inside your new rooms.
Why Airtightness is a Trap?
Modern renovations focus on energy efficiency. This is a good goal. You add high-R-value insulation. You install double-glazed windows with perfect rubber seals. You use vapour barriers. You seal every gap to stop draughts. This is great for your heating and cooling bills. It is a disaster for your air quality.
Your house can no longer "breathe." Old, draughty homes had accidental ventilation. Air leaked in around windows and under doors. Your new, energy-efficient home is a sealed box. It acts like a plastic bag. It traps everything inside. Every pollutant, every smell, and every drop of moisture.
A sealed home creates a cascade of problems. The biggest enemy is moisture. You create this moisture every single day. It has to go somewhere.
Where Does Moisture Come From?
You are a source of moisture. A family of four breathes out 6 to 8 litres of water vapour daily. A 15-minute hot shower releases over a litre of water into the air as steam. Drying a load of laundry on an indoor rack? That adds 4 to 5 litres.
Pot plants release moisture. So do pets. In an old, draughty house, this moisture would find a way out. In your newly sealed reno, it is trapped.
This warm, moist air moves through your home. It eventually finds a cold surface. When it hits that surface, the air cools. It can no longer hold the moisture. The moisture condenses back into liquid water. This is the "dew point." You see this clearly on windows in winter.
But it also happens in places you cannot see. It happens on the cold "thermal bridge" in room corners. It happens on the wall behind your new wardrobe. It happens inside the wall cavity itself.
This condensation is a problem. It is water. And water feeds mold. Mold is a fungus. Its spores are everywhere, waiting. All they need to grow is moisture and a food source. Your new home provides both. Mold feeds on the paper lining of your plasterboard. It feeds on the cellulose in your timber studs.
It feeds on the dust in your carpet. It loves the silicone in your new bathroom. That small spot of condensation becomes a patch of mold. Common molds like Aspergillus and Penicillium trigger allergies. Stachybotrys, or toxic black mold, is worse.
It releases mycotoxins that can cause severe respiratory issues. Mould does not just look bad. It is an active threat to your family's health.
The Impact on Your Renovation
Mold destroys your investment. It ruins your new paint job, causing it to bubble and peel. It creates a musty, damp smell that never leaves. This smell gets into your furniture, your clothes, and your new carpet. It rots the timber structures inside your walls. It causes your new timber floors to warp and cup.
It turns your dream renovation into a damp, unhealthy box. All because the moisture had no way to get out. A high-quality home reno exhaust fan is the only solution.
How Do You Ventilate Specific Areas?
You cannot solve this with one fan. Ventilation is a system. It has two parts.
Exhaust: Removing stale, moist, polluted air.
Supply: Bringing in fresh, clean air. Your renovation needs to plan for both. The most effective strategy is "point-source ventilation." This means you target the problems where they start. The main sources are bathrooms, laundries, and kitchens.
Bathrooms and Laundries
This is non-negotiable. Your new bathroom will create more steam than any other room. A powerful, ducted exhaust fan is critical. The fan you choose matters. A cheap, noisy fan from a hardware store just makes noise.
It does not move enough air. You need a fan with the right capacity for the room size. This is measured in cubic metres per hour (m³/h). A fan should replace all the air in a bathroom 10 to 15 times per hour.
Ducting is just as important. Never vent a fan into your roof space. This is lazy. It is also dangerous. You are just moving the warm, wet air from your bathroom into your ceiling. This creates condensation on the underside of your roof. It rots your roof trusses and feeds mold in your insulation. The duct must terminate outside. Through the roof or a wall. Use rigid or semi-rigid ducting.
Avoid cheap flexible foil, which kinks and fills with water. Install a timer switch. Run the fan for 10-15 minutes after every shower. This clears the steam and stops moisture from spreading. The same applies to your laundry. Dryers release moisture and lint. A dedicated fan keeps this room clean and dry.
Kitchens
Cooking releases steam, grease, smoke, and odours. A quality rangehood is your kitchen’s dedicated exhaust fan. It must duct to the outside. Recirculating range hoods are not ventilation. They just pull air through a cheap filter.
They filter some grease. They do nothing for moisture, smoke, or heat. All that moisture gets trapped in your kitchen. A properly ducted rangehood protects your new cabinets from greasy buildup. It helps control cooking smells. It removes the steam from boiling water. This is a key part of your home's moisture management. Plan the duct run before the cabinets go in.
Sub-Floor (The Aussie Problem)
This is the area most renovators forget. Many Australian homes, especially older ones, have a sub-floor space. This area gets damp. Moisture from the soil rises. Poor drainage lets water pool. If this space is sealed or poorly vented, that damp has nowhere to go.
It rises up through your floorboards. This causes rising damp. It makes your home smell musty. It is the perfect breeding ground for termites and other pests.
It will destroy your new timber or carpet floors from below. Your renovation is the perfect time to fix this. Traditional passive vents (grilles) often do not move enough air. You need an active sub-floor ventilation system. These systems use powerful fans to pull the damp air out.
They create a cross-flow of fresh, dry air under your home. This keeps the foundations and timber bearers dry. It stops that musty smell. It protects your new floors.
Roof Space
Heat builds up in your roof cavity. On a hot Aussie summer day, your roof space can reach 60-70°C. This space acts like a giant radiator. It pushes that heat back down through your ceiling. Your brand-new air conditioner has to fight it. It runs constantly.
Your power bills skyrocket. Your renovation insulation helps, but it cannot stop all of it. Roof ventilation expels this hot air. Whirlybirds are a passive option. Powered roof fans (solar or electric) are much more effective.
They actively pull the hot air out, drawing cooler air in. In winter, this system also helps remove any moisture that drifts up. This prevents condensation and mold growth in your attic.
Living Areas
You cannot just pull air out. If you make your home airtight and install powerful exhaust fans, you create a new problem. Negative pressure. Air will try to get back in. It will pull air from a wall cavity. You must provide a source of fresh "supply" air.
This can be as simple as dedicated "trickle" vents. The best solution for a sealed home is a mechanical ventilation system. A Heat Recovery Ventilator (HRV) or Energy Recovery Ventilator (ERV) is the gold standard. This system is a set of two fans. One fan exhausts stale, moist air from inside.
The other brings in fresh, filtered air from outside. The clever part is the "core." The two streams of air pass each other. In winter, the heat from the outgoing stale air is transferred to the incoming fresh air. You get fresh air without the cold. This is a balanced system. It is the key to a healthy, efficient, modern home.
Why Plan Ventilation Early?
You must include ventilation in the design phase. Do not leave it as an afterthought. Ventilation during renovation is simple. Retrofitting is hard. It is easy to run ducting when the walls and ceilings are open.
Trying to feed a 150mm duct through a finished wall is complex. It is messy. It costs much more. It often means cutting into your new paint and plaster. You may have to build ugly bulkheads to hide ducts you forgot.
Talk to your builder and your architect. Specify what ventilation you want. Ask them:
- Where will the bathroom fans go?
- How will they be ducted to the outside?
- Where will the kitchen duct run?
- Do I need sub-floor ventilation?
- Is my roof space vented properly?
- Is my home sealed so tight that I need a balanced HRV system?
Good planning makes the system invisible. You get the benefits. You see none of the mechanics. A quiet, efficient ventilation system is the cheapest insurance you can buy. It protects your renovation. It protects your home. It protects your family's health.
FAQs
1. What’s more important: sub-floor or roof ventilation?
They solve different problems. If you have a damp, musty smell or are getting new timber floors, solve the sub-floor first. If your home gets extremely hot in summer, start with the roof. A healthy home often needs both.
2. Can I install exhaust fans myself?
You can buy DIY kits. If you are handy, you might install the fan unit. However, a licensed electrician must do all the wiring. Proper ducting is also tricky. A poor install (like a kinked duct) will kill the fan's performance.
3. Are modern exhaust fans noisy?
No. Old fans were loud because of poor motors and bad mounting. Quality new fans are designed to be quiet. Look for a low "Sone" or "dB(A)" rating. An "in-line" fan, which hides the motor in the roof space, is almost silent.
4. How much capacity do I need for my bathroom fan?
Calculate your room's volume (Length x Width x Height). For example, a 3m x 2m bathroom with a 2.4m ceiling has a volume of 14.4 m3. To get 15 air changes per hour, you need a fan rated for at least 216 m3/h (14.4 x 15). Go higher if you have a large shower or long duct run.
5. How much does a good ventilation system cost?
Costs vary. A single, good quality bathroom exhaust fan (supply and install) might cost a few hundred dollars. A full sub-floor or roof ventilation system is a larger investment, often costing a few thousand dollars.
