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Basement Conversion Part II: Excavation, Waterproofing, and The Build

In Part I, we covered the vision, the consents, and the insurance required to get a basement project off the ground. Now, we move to the phase where the real transformation happens: construction.

Converting a basement is not a standard renovation. It involves turning a sub-floor void or a garage into a warm, dry, and habitable space. At Retro Construction, our motto is “Traditional Experience/Modern Style”. This means we apply time-tested construction methods to ensure structural integrity while delivering the modern finish you crave.

Here is what you can expect during the construction phase of your basement conversion.

1. Site Setup: The “Temporary Factory”

Before the first shovel hits the dirt, we establish the site. As we mentioned in our guide on costs, a building site operates like a temporary outdoor factory. This is especially true for basement conversions, where we are often digging beneath an existing home.

We manage the Preliminaries—the essential operating costs required to keep the site legal and safe. This includes:

• Conveyor Belts & Soil Removal: Efficiently moving earth out of tight spaces.
• Temporary Support (Propping): Ensuring your existing home remains stable while we work beneath it.
• Safety Barriers: Fencing and hoardings to protect your family and the public.

These preliminaries ensure that the site runs efficiently, preventing budget shocks and ensuring compliance with the Health and Safety at Work Act 2015.

2. Excavation and Concrete: Getting the Best Price

The heavy lifting of a basement conversion involves excavation and pouring new concrete foundations or slabs. This is where costs can escalate if not managed correctly.

To ensure you get the best value, Retro Construction utilizes a Competitive Bidding process. We do not rely on a single subcontractor for these heavy trades. Instead, we obtain multiple quotes for excavation and concrete work. This ensures:

• Competitive Pricing: Subcontractors offer their best rates when they know they are competing.
• Quality Assurance: We can assess the reputation and equipment of different teams to ensure they can handle your specific site conditions.
• Reduced Risk: We aren’t dependent on one supplier who might be unavailable.

3. Waterproofing (Tanking): The Critical Layer

The biggest risk in any basement conversion is moisture. Because the room is partially underground, it requires “Tanking”—a specialist waterproofing system that creates a barrier against ground moisture.

We treat this stage with extreme care. Just as we do with our Reclad projects, we focus on weather-tightness to future-proof the design. We ensure that proper drainage is installed behind the walls and that the tanking membrane is applied by certified specialists. This ensures your new home office or granny flat doesn’t turn back into a damp cellar in winter.

4. The Fit-Out: Creating “Hidden” Space

Once the structure is dry and secure, we move to the interior fit-out. This is where our practical design experience shines.

• Smart Laundries: If you are moving the laundry downstairs, we can design a space-saving area with hidden pipelines, wall-mounted sinks, and sliding shelves to keep the space clutter-free.
• Storage Solutions: We often find extra “packing space” in areas you wouldn’t expect, maximizing the floor plan.
• Visualizing the Finish: Struggle to read 2D plans? We use immediate 3D visualization technology to render photos of the space on-site. We can overlay different flooring or bathroom layouts, so you can see exactly how the finished room will look before we install the first fixture.

5. Managing the Process

Throughout the build, we handle the documentation and council inspections. Our team includes in-house specialists who manage the process from the structural phase right through to the Code of Compliance (CCC) application.

We also ensure transparency with costs. As Angie, our Office Manager, highlights, we provide detailed quotes and manage documentation to ensure there are no surprises at the end.

Ready to Transform Your Space?

Whether you are creating a “legal” granny flat for income or simply need a teenage retreat, a basement conversion is a significant project that adds massive value to your home.

With over 30 years of industry experience, Retro Construction is ready to guide you from the first dig to the final coat of paint.

Contact us today to discuss your project.

Retro Construction Ltd Quality Building Solutions in Auckland Web: www.retroconstruction.co.nz Email: info@retroconstruction.co.nz

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