What Can Go Wrong If Your Builder Uses the Wrong Approach?
When it comes to renovating your home, most people worry about the obvious risks going over budget, running late, or not liking the paint colour.
But there’s a deeper, more dangerous risk that many homeowners never see coming.
The wrong building strategy can quietly destroy your home from the inside out.
It doesn’t matter how nice the finishes look or how energy-efficient the brochure says your new addition is if your builder doesn’t understand building science, especially how moisture, air, and heat interact, your renovation could be heading toward serious structural and health problems.
This blog reveals the hidden consequences of working with a builder who lacks a scientific approach, and how to avoid them.
The Risks of "Standard" Renovations.
Let’s be honest most builders are still doing things “the way we’ve always done them.”
That might have worked 40 years ago, when homes were naturally leaky and forgiving but today’s materials and expectations are completely different.
Here’s what can go wrong with a renovation built without building science knowledge:
1. Condensation in Walls and Roofs
Builders may add bulk insulation or wrap a home tightly to meet energy requirements, but forget to allow for drying pathways. This leads to:
Moisture trapped inside walls
Mould growth on insulation and framing
Swollen plaster and peeling paint
Long-term rot and decay
2. Rotting Timbers
Timber frames need to dry out after exposure — but some renovations “seal in” damp materials. Poor ventilation or incorrect vapour barriers can accelerate rot behind the scenes, even if everything looks fine on the surface.
3. Mould and Indoor Air Quality Issues
Incorrect use of sarking, membranes, and plasterboard can create cold surfaces where warm indoor air condenses. Over time, this leads to:
Toxic mould outbreaks
Poor air quality
Health issues like asthma, allergies, and respiratory infections
4. Buckling, Warping and Structural Damage
When materials expand and contract due to unregulated moisture levels, your home begins to move unnaturally. This causes:
Doors that don’t shut properly
Gaps in joinery and cornices
Cracks in walls and ceilings
Fastener failure
5. Energy Inefficiency Despite High Ratings
A tight house that can’t breathe properly will often require more mechanical heating and cooling to stay comfortable.
The result?
High energy bills, condensation, and discomfort the very things you were trying to fix.
Real-Life Examples of Poor Practice
We’ve seen it time and time again. Here are just a few case studies from around the region:
A double-storey weatherboard home was “upgraded” with foil-backed wrap and bulk insulation. Within two years, black mould was growing behind the plasterboard because moisture couldn’t escape.
An architect-designed extension in a coastal suburb had sleek finishes and high R-values but no roof ventilation. The ceiling cavity became a humid box, leading to timber warping and sagging plasterboard.
A builder installed a flat roof with no breathable layer beneath the metal. When seasonal condensation hit, it had nowhere to go dripping onto electrical cabling and ceiling lights.
Each of these could have been prevented with basic building science awareness.
The NCC Can’t Protect You from This
It’s important to remember: The National Construction Code (NCC) only mandates minimum standards — and those don’t include many critical aspects of building science.
For example:
The NCC might require insulation, but not how it interacts with vapour.
It requires water-resistant materials in wet areas, but not consideration for interstitial condensation in walls.
It sets ventilation requirements for bathrooms and kitchens, but not the whole building envelope.
Renovation can be compliant, look great, and still be doomed to fail in 5–10 years — especially in older homes not designed for modern construction techniques.
What a Scientific Builder Does Differently
At Shepherd Homes, we ask deeper questions:
Where will this wall or roof dry to?
Is this assembly vapour-open or vapour-closed — and is that appropriate for the climate?
Are we creating a sandwich of impermeable materials?
Will this insulation method reduce or increase condensation risk?
We don’t just install what looks good. We consider:
Material compatibility
Climatic drying potential
Seasonal changes in indoor humidity
Ventilation paths
Long-term maintenance impacts
That’s the difference between a high-performance renovation and a standard one.
How You Can Protect Your Home?
You don’t need to become a building scientist but you do need to choose a builder who understands these risks and can design around them.
Here’s how to safeguard your investment:
Ask your builder about moisture management not just waterproofing.
Question how walls and roofs will dry not just how well they’re sealed.
Request breathable wraps instead of foil-only sarking in cool climates.
Discuss mechanical ventilation if your home is being made airtight.
Work with someone who can explain the why behind every material choice.
If your builder can’t explain how your home handles water, vapour, and air… they might not be the right builder.
