house lower than Street

[Gatoblanco]

I went and checked out a house it's an old timber cottage in good condition on stumps at about 1.8 metres. It has a driveway that goes sloping downwards under the house at the side of the drive way towards the end of the driveway slab under the house there is a drain under the house. At the back of the house there is also a drain on the sloping slab that slopes from the backyard under the house to access the (ex) laundry. The underside of the house wasn't damp and there is absolutely no evidence of every day water but I imagine what would happen when it rains is that rain would run down the driveway and also in from the back and that's what those drains are for. So that's not much of a problem given that the house is off the ground however if I wanted to raise it up to legal height and build under what are the issues associated with that?
There would be no intention for the water to go underneath at that stage if there were bedrooms underneath. You would need to keep the water out from under the house. I imagine it would be fairly expensive to be shifting drains any experience or advice?
does this write the place off as being feasible to lift and build under?
In the photo one drain is about a metre in front of the girl in pink you can see the hole. The other one is out of frame near those bricks where i am standing taking the photo.
Thank you

 

[gaiusb]

Firstly you should check with council whether the land is flood prone. Sometimes this precludes building in underneath instantly so it would not be feasible.

Ignore the fact that there's no dampness already, because you need to meet the building code of australia (BCA) anyway when you build underneath, which will basically make it weatherproof.

You'd need to install a new slab with the vapour barrier (plastic) to avoid rising damp.

You need a minimum 50mm stepdown from the inside floor level to the outside concrete level. The ground is also required to slope away from the building. If the slab level is below the road then your driveway slope will probably not allow you to get this slope away from the building at the front, so you will need to put a drainage line between the driveway and the house slab to remove any surface water coming in. The building certifier will need to approve this as an 'alternative solution' to the BCA. In QLD that's no problem as it's up to the certifier, whereas in other states you need to go to the government for dispensation. At the side and back of the house you will just need to remove any existing concrete and get the 50mm stepdown + slope to work.

Another thing is that if the walls of the ground floor are also retaining the outside soil, a waterproofing membrane needs to be installed to the wall.

All of the above is feasible (and I see it all the time) so long as the land isn't flood prone, which will require additional checking to see if it's permitted to build underneath.

 

[Gatoblanco]

Thanks for the awesome reply. I checked and the land is subject to overland flooding from drainage. It actually has a drain running under the property. But to take water from the property only. Ie it goes from the middle of the property to the stormwater in the street. I see that from a dial before you dig report.

 

[gaiusb]

If it's in Brisbane City Council and the land is in overland flow, then it will be hard to get approval to build underneath. You would need an overland flow report (aka hydraulic report) from a hydraulic engineer certifying that the build won't affect the upstream and downstream overland flow or affect the neighbours. Those reports can cost around $3k and still the engineer will be reluctant to certify that it won't worsen the current situation.

To confirm it's in overland flow go to http://cityplan2014maps.brisbane.qld.gov.au/CityPlan/, search fort the property and click the flood overlay.

You might be sitting on a council stormwater line which is usually the case when overland flow is involved. This isn't so bad but it's just another piece of red tape to get around.