House raising

Why people raise a house

Queensland housing stock is unusually suited to being lifted. Timber framed, relatively light, and already up off the ground on stumps. Raising one is a well established piece of work here in a way it simply is not in most of the country.

There are three common reasons.

Space. The most common by a distance. Lifting a house and building in underneath adds a floor of living area without extending the footprint or losing yard. On a tight block it is frequently the only way to get more room.

Flood. Parts of the Gold Coast carry flood overlays, and raising a habitable floor above a defined flood level is a recognised response. It can change what the property is exposed to and, over time, how it is insured.

Access and condition. Some houses are lifted simply because the existing subfloor is too low to work in, or because the whole stump system is being replaced anyway and going higher costs comparatively little extra at that point.

How it is done

Long steel beams are threaded through under the floor frame, transverse to the bearers, so the load of the whole house is picked up at a small number of controlled points rather than at every stump. The beams sit on hydraulic jacks, which sit on stacked hardwood cribbing. Those cribbing towers look precarious and are anything but. They are extremely stable under vertical load and they get built up progressively as the house rises.

The lift itself happens in stages, a small amount at every jack, moving around the house in sequence, packing the cribbing up as it goes. Nobody lifts a house in one motion. The whole art of it is keeping the frame in plane while it travels, because a house that racks on the way up cracks on the way up.

Once it is at height, new stumps or columns go in underneath, the house is lowered onto them and fixed down, and the temporary works come out.

What actually costs money

The lift is only part of it, and often not the largest part.

• Services. Plumbing, drainage, gas and electrical all have to be disconnected before and reconnected after, by the relevant licensed trades. Stairs, both internal and external, generally need rebuilding because the height has changed.
• New supports. Going higher increases the load on each support and the slenderness of it. A taller stump does more work, so material and size often change, and engineering input is usually required.
• Approval and design. Building approval, engineering, and often a building designer or draftsperson for the new lower level.
• Building in underneath. If you are enclosing the new space as habitable rooms, that is a full construction project in its own right, with slab, framing, waterproofing, insulation, ceiling height requirements, egress and everything else. It typically dwarfs the cost of the lift.
• Accommodation. You will be out of the house, usually for weeks. Budget for it.

Approval is not optional

This is the main practical difference between raising and restumping. Straight restumping at the same height is often treated as repair work and commonly does not require building approval. Raising changes the height and form of the building, and generally does require approval, obtained either through the City of Gold Coast or through a private building certifier.

On top of the building approval, planning overlays can apply depending on where the property sits. The Gold Coast has flood overlays across parts of the city, and character or heritage provisions apply in some areas. Height limits and boundary setbacks can all bear on how high you are allowed to go and what you can do with the space underneath.

The practical sequence is to check the property against the planning scheme first, before spending money on design. The council's online mapping tool will show you the overlays that apply to a specific address, and a building certifier or town planner can tell you what those overlays mean for your plan.

Height underneath

People often ask how high they can go. There is no single number, because it depends on the planning controls for the site and on what you intend to use the space for. What is worth knowing is that there is a meaningful difference between raising a house enough to get useful storage and access underneath, and raising it enough for legal habitable rooms. Habitable space has minimum ceiling height requirements under the National Construction Code, and hitting them changes the whole scope, cost and approval picture.

Decide which of those two you are actually after before anyone quotes, because they are very different projects.