Foundation Types for Modular Homes: Slab vs Stumps vs Piers

The foundation is the most important decision in any modular home build. It determines durability, livability, and a meaningful chunk of the project cost. Your three main options in NSW for a modular home are concrete slab, engineered stumps, or piers. Here is how to choose.

Concrete Slab

A reinforced concrete slab poured directly on the prepared ground, with modules bolted down to the slab. The most common foundation for level suburban blocks.

Pros

• Lowest cost option
• Thermal mass benefits (good for passive solar)
• No floor-level voids for pests or moisture
• Quick to install once site is prepped

Cons

• Requires flat or near-flat block
• Not suitable for flood-prone areas
• Hard to relocate the home later
• Services must be precisely positioned before pour

Best for: standard suburban blocks with minimal slope, fixed-location forever home.

Engineered Stumps

Steel posts (sometimes timber, mostly steel in 2026) set on concrete footings, with the modules sitting on bearers that span between stumps. Floor level is raised above ground.

Pros

• Handles slope by varying stump heights
• Raises floor above flood lines
• Better airflow under the home (reduces moisture issues)
• Less excavation and disturbance to existing block
• Home can be lifted and relocated
• Services accessible from underneath

Cons

• Higher cost than slab
• Insulation under floor more important (no thermal mass)
• Pests can use the void if not screened

Best for: sloped blocks, flood-prone areas, blocks where minimising ground disturbance matters.

Piers

Engineered concrete piers drilled deep into stable substrate (rock or load-bearing soil), with bearers spanning between them. The most heavy-duty foundation type.

Pros

• Handles unstable soil (reactive clay, fill, soft soil)
• Handles severe slope
• Can raise the home very high above ground (flood-resilient, view enhancement)
• Suitable for difficult geological sites

Cons

• Most expensive foundation option
• Requires geotechnical engineering report
• Underfloor space needs structural enclosure if raised significantly

Best for: reactive or unstable soils, very sloped blocks, blocks where the home must be raised significantly above ground level.

How We Choose

For every Hi-Tech build we require a soil test (geotechnical report). The report tells us the soil class and movement potential. Combined with the block slope and any flood mapping, we recommend the foundation type that fits.

Most flat suburban blocks get slab. Most rural and sloped blocks get stumps. Difficult ground gets piers. See our process for how this fits into the full build.

Insulating Stumps and Piers

Homes on stumps or piers need quality floor insulation. We use R3.5 minimum under-floor insulation as standard, and recommend the eco-friendly upgrade package for any cold-climate build. See our eco-friendly options.

Get Started

For your block, the right foundation depends on a soil test and a site visit. Get in touch and we will arrange both.