Flood-Damaged Buildings: What to Check Before You Repair
Flooding can leave a home looking fine on the surface while hiding damage underneath. Before any repairs start, it pays to work through the building systematically - foundations, framing, linings and wiring - so nothing gets covered up or re-lined before it has dried out or been checked properly.
Start with safety, your insurer and your council
Before you do anything else, isolate the electrical supply until it has been checked, and isolate gas until a registered gasfitter has looked at it. Take photos and videos of the damage as you find it, and talk to your insurer and council before starting any repair work - this confirms what's covered and what the Building Act requires for your situation. If a Rapid Building Assessor has placed a red or yellow placard on the property, follow that guidance first.
What to check for structural damage
Foundations and slabs
Look for ground that has eroded away from around footings, and for any settling, sagging or tilting. Check piles and subfloor walls for tilting or bowing, and look at timber piles and concrete pads for exposed or damaged sections. On concrete slabs, hollow-sounding patches, new cracking or sagging can mean the slab has lost support underneath.
Subfloor and framing
Uneven, bulging, swollen, soggy or springy flooring, and new gaps or cracks, all point to water having got into the subfloor. Particleboard flooring that has been wet for any length of time will generally need replacing. When removing linings to check framing, take care not to damage studs, plates or connections - and keep in mind that linings can be part of a wall's structural bracing, so leaving them off for too long can affect how the building performs.
Linings, insulation and walls
Check whether linings were submerged, including water wicking up above the visible water line in absorbent materials. Look for swelling, cracking, bulging, staining, or doors and windows that have started sticking. Wet insulation should be identified and generally replaced. Concrete and masonry walls can hold onto moisture and need time to dry before relining. Any fire-rated wall or ceiling lining that's damaged must be replaced with a lining of equal or higher fire rating.
Electrical and gas
Any outlet, switch or fixture that was underwater should stay switched off until a registered electrician has checked it. Watch for a flooded meter or distribution board, tripping fuses, failing circuits or flickering lights, and have a flooded heat pump or air conditioning unit checked before it's used again.
When to bring in an engineer
Ongoing ground movement, cracking or tilting in retaining walls, foundations or slopes, cracking in masonry linked to settlement, or cladding that's bent, cracked or pulling away are all signs the structure itself may need assessment, not just drying out and relining. If you've seen any of this, it's worth a structural engineer looking at the building before repairs are finished off.
Drying out and consents
The building needs to be sufficiently dry before repair work goes ahead - rushing to re-line damp framing just traps moisture in. Check with your council on whether your repairs need a building consent and what you're able to do yourself; restricted building work still has to be done or supervised by a licensed building practitioner. Councils also have discretion under the Building Act to allow some flood-related repair work, such as replacing damaged plasterboard, without a full consent in certain circumstances - your council can confirm whether that applies to your situation.
Reducing damage next time
If the property is in a flood-prone area, talk to your council or an engineer about practical ways to reduce future damage - sealing the building envelope well, using water-resistant materials lower down, and keeping gutters, drains and catch pits clear. If flooding or land instability has affected the site, that needs factoring into any rebuild.
Every flood event is different, and the right next step depends on what's actually happened to your specific building. If you've had flood damage and want a second opinion on the structure before repairs continue, get in touch with Fil Engineers - we're happy to help you work through it.
This article is general information, not site-specific engineering advice. Every building and flood event is different - talk to a structural engineer about your specific situation before carrying out repairs.
