House Raising and Build Under
Residential building design specialists
Blue Planet Design are experts when it comes to house raising and build under projects. House extensions of this type are a great way to double your floor area without sacrificing yard space. The increase in height of your existing home can create city or mountain views and provide access to cooling summer breezes. A new lower level can provide direct access and connection to outdoor recreation or swimming pool areas. Whatever result your wanting to achieve our vast knowledge and experience with Queenslanders and timber framed post war homes will ensure a positive outcome.
Check out the special report “Upwards and Onwards” in the October 2014 issue of Australian House & Garden magazine. Article written by Harvey Grennan, featuring comments by Scott Dawson, principal building designer, Blue Planet Design.
Upwards and Onwards
The conventional way of extending a home is to build up or out. But there is another possibility, writes Harvey Grennan.
Queenslanders have been doing it for decades: building an extension beneath an existing home. In the suburbs of Brisbane and beyond, builders are well practised in jacking up a house and creating more living space at ground level.
In the fashionable London boroughs of Kensington and Chelsea, however, it’s not so simple – they have to go underground; a concept of building dubbed the ‘iceberg’ home. There, the super-rich are excavating Georgian terraces to build subterranean pools, gyms, ballrooms, cinemas and even bowling alleys. Those underground caverns can be up to four-storeys deep, with more floor space than the original house, hence the term ‘iceberg’ – you only see a small part of the whole.
Back in the ‘real’ world of ordinary folk, there are circumstances where lifting an existing house to create a new living zone below is an attractive and viable alternative to going out or up. Going ‘up and under’ can be a solution on a very small block where you would lose too much yard space with a single- storey extension, or where the local council’s footprint restrictions would be exceeded. Or where the existing house structure is not suitable to take a second storey, or the height already underneath is short of the legal requirements for habitable rooms.
Another possibility is removing a house from another location and doubling the accommodation by using it as a top storey with a new storey underneath. Not all houses are suitable for this treatment; they must be timber-framed structures on stumps or brick piers, not on a concrete slab. Full brick or brick-veneer houses are a no-go.
"Brisbane has a lot of areas where prewar Queenslander-style houses aren’t allowed to be demolished."
The ‘up and under’ approach can maintain the character of an existing house and be a good way of complying with heritage regulations, says building designer Scott Dawson of Brisbane’s Blue Planet Design, which specialises in this type of renovation. “Brisbane has a lot of areas where prewar Queenslander-style houses aren’t allowed to be demolished,” he says. “Raising a home and building underneath will usually result in more floor area than a rear extension, and it’s an effective way to stay within council restrictions relating to site coverage (the percentage of building area compared to site area), which is commonly 50 per cent.” Dawson says there are two design approaches to building underneath an existing home. These are to:
- Reconfigure the existing upper level to contain the bedrooms, bathroom and perhaps a secondary living space, then move all the main living areas to the new lower level.
- Retain the upstairs with minimal changes and put additional bedrooms, a laundry, bathroom and secondary living area on the lower level.
“Clients wanting to go with the first option usually don’t have much of a view and want to orientate their living toward the backyard/pool area. Those favouring the second option usually have views and breezes they want to capitalise on,” says Dawson. “Both these types of projects usually incorporate a new covered rear deck and car accommodation in the form of a lock-up garage as part of the new lower level. Or, a carport between the house and the front boundary.”
The usual building procedure is to employ a re-stumping contractor to lift the house on hydraulic jacks and sometimes the house is relocated by sliding it on rails. Then the house is temporarily supported on steel beams and timber cribs while any stumps and brickwork are removed. The site is levelled for a concrete slab, pier holes are bored, steel columns are placed in the pier holes and steel beams attached to the existing timber-floor bearers. Concrete is poured into the pier holes, the temporary supports are removed and the slab poured. New timber- framed walls are then built on the new slab in the conventional manner.
Any steel columns within the internal floor area can be positioned so they are built into the new timber-framed stud walls, says Dawson. “The new steel beams bolted to the sides of the existing bearers gives the bearers the ability to span further with fewer supporting columns. The result is a more open-plan space under the house.”
"Finding a location for the new internal stair within the existing layout usually results in the loss of a small room."
There are design challenges, however. “Finding a location for the new internal stair within the existing layout usually results in the loss of a small room,” says Dawson. “The location of this internal staircase somewhat dictates the lower-level layout as the stairs will divide up the available space.”
Buying a house that has already been developed underneath requires caution, says building inspection firm Australian Building Inspection Services (ABIS). “A lot of older homes have DIY-built areas below the house that are used for storage, car accommodation, bedrooms etc. These are usually poorly built with very low ceiling heights, and present a risk of termite attack and infestation,” says Dawson.
ABIS says it’s important to check that the floor has been raised at least 150mm above ground level to avoid flooding in the case of heavy rain, that moisture and termite barriers have been installed at ground level, that the head height, ventilation, glazing and any other aspects of the room comply with requisite building codes, and that the building work has been approved by the local authority.
Australian House and Garden