Basement Garages

Basement Garages

This is the big question that only you will be able to answer. If the basement is to be a new granny flat, what rent would I get? Is this rental return better then my superannuation performance? How much valuation would this addition add to my property considering you will be losing much less of a footprint then an on ground extension or separate on ground granny flat that eats up your back yard. { 60+ square meters}

Suffice to say you will need to consider these items to make that decision.

  • Council Approval. Have a chat to local council town planner, he’ll give you a good idea of feasibility.
  • Value of existing structure. Check out real estate websites your suburb
  • Value of site. How much is a square meter of land worth in this vicinity? Check websites, agents opinions. As site densities and values go up so does the viability of a new basement man cave/garage/granny flat. Inner city, waterviews and steep sites are mostly economical viable propositions.
  • How much do you value off street parking/the inconvenience factor of having to walk blocks and paying parking fines.
  • Possible usable spaces to be gained, 30 / 60 sqm
  • Architect, engineer, builder, underpinner
  • Cost of getting the new /car/kids retreat/granny/ spaces.
  • The New net value of your property as a result of the works
  • Your basement soil profile, sand, rock or clay.
  • Excavation underpinning engineering required
  • The placement /rerouting existing services to home
  • Existing subsoil drainage

Recently completed double garage and store under house at Flood St. Clovelly

Keep it Healthy Underground

A garage often contains a number of toxins in the form of paints, solvents, fertilizers, insect sprays, etc. But the largest polluter is generally the family car. Possibly more so than Radon gas and mould spores from damp rock. A hot automobile inside an attached garage can give off a variety of offensive odours that easily seep into the living space. Houses with attached garages typically have gasoline concentrations that are 10 times outdoor levels. One study found that benzene concentrations from gasoline-fuelled vehicles can reach hundreds of parts per billion in attached garages, and the benzene can migrate into the main house exposing the occupants.

Today if we had horse and buggy, we’d never have a barn attached to the house because the animal odours would be objectionable. Yet houses routinely have an attached garage which contains much more unhealthy odours. Detached garages don’t have the problem of keeping exhaust gases, and other pollutants, from seeping into the living space of a typically constructed new home. So extra care in planning for light, air and soil moisture is required for basements.

An underground or attached garage should have an exhaust fan installed to minimize any contamination of the air in the house. A fan can be controlled by a timer or activated by auto when garage door is opened when a car pulls in.The fan then allowed to run for an hour or so until the exhaust gases have dissipated. As an alternative, you can run a pair of 150mm diameter ducts from the garage ceiling up through the roof to a pair of turbine roof ventilators, such as the Whirlybird ventilators. These are passive ventilators and will continuously ventilate the garage without the electricity or a solar powered fan could be installed and ducted through wall or ceiling to side of the house. It is good practice to start and shut off the engine with external panel lift door open and internal access door with seals attached shut.


This is one way to dig out a confined sub-floor space