# Forum Contacts & Links Estimating & Quoting  Underground Garage & Workshop

## Mayyam

So, this is why I need to stay busy, as when I'm not, I dream up these sorts of things. Long story short, the previous owners built a single carport in a cutout space for two cars. :No: As she must be obeyed, the wife parks under the carport and I park down the hill on the street. I started getting some ideas a while ago and sketched up how I think we can convert to a double garage, create some workshop storage area and add a herb garden/decorative area or grassed area to add some more flat land area to what is our very steep block. 
Below are a range of pictures of site, rough drawings/plans & some inspiration. I was originally looking to put a skillion roof carport in and reinforcing but through looking in to it further it feels like it's really building a raised subfloor, laying a floor with drainage & waterproofing to create the area. I'm happy to be challenged by anyone with better ideas! 
This forum has excellent advice from a range of contributors so I'd love to get any ideas/builds and a rough idea on what those in the know think would be the damage. I've broken it down by tasks but I'm in marketing so a newb at this so it's my best guess as to what needs doing. My brother in law is a landscaper so I'll probably work with him to achieve some of the steps but would be keen to know total cost if I outsourced everything. 
Sorry for the long post but thought I'd get as much info down for those that will read!  :Wink 1:   *1. Pre-advice* Geo-tech engineer advice?Council approvalPlanning  *2. Earthworks* Options are to go it ourselves with hand tools or get a crew in with excavator for a day or two Widen 1.5-2m, deepen 1m & level floor approx 50-75cm depthCombination of soil & sandstone (varying consistency)Waste to be re-used on site to fill & level other areas  *3. Structure Build* Basically building a subfloor 3m high to meet the level of the stairs Base is currently solid sandstone - Concrete slab required? or just core-drill for posts and level with levelling or rubbercrete?Options - Brick, Block, Wood or Steel6x6.5m garage area & 3.2m x 2.8m storage/workshopRetaining wall along storage L shape to fill and level top areaSubfloor structure sufficient to hold green roof/garden area  *4. Roofing/Sealing* Flooring material to cover over subfloor & waterproof with drainageBase above TBC - Artificial grass, crushed granite, pavers, etc  *5. Enclosing* Enclose 2 x sides on storage L & 1/2 side next to stairs with cladding. Likely to be sandstone cladding or similiar.Double garage door across opening *
6. Above Landscaping* Most of this we can do but would be: Fill & level where possibleLay floor/grass/graniteBalustrade around exposed edges *
7. Plumbing & Electrical* Reroute above ground stormwater & waste around back of new garage & under driveway. (joins above ground)Relocate water tapExtend existing power, install external sensor lights, internal light & 3-4 GPOs for tools & garage opener  *8. Ashphalting* Reseal exposed area where drains are run under the driveway *
First Sketch*     *Site Photos*    *Existing & Planned (Rough)*     *Sub-floor Frame*     *Inspiration*

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## Uncle Bob

I reckon it's a fantastic idea, but it looks like it ain't going to come cheap. My tin garage (5x10) came in about $12K (built myself on the cheap) so I reckon you can at least double that.

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## Mayyam

> I reckon it's a fantastic idea, but it looks like it ain't going to come cheap. My tin garage (5x10) came in about $12K (built myself on the cheap) so I reckon you can at least double that.

  Agreed, not expecting it will be a cheap one but based on the improvement of land area (potential kids play area) and increasing from 1 car spot to DLUG I've got confidence that the increase in house value should outweigh the cost. Or come close to and save my legs from the trek up that driveway everyday. 
I did get a rough first quote for supply of a 3m raised pre-cut steel sub-floor which came in at ~$7K which gave me some relief that I'll likely play in the 15-30K bracket and not the $50K+ that it might cost to build an equivalent brick DLUG. Will all depend on quality of materials we choose and how much we do in our own-labour vs getting in the pros (in particular the earthworks). 
There's a few pictures from the US via google but haven't been able to turn up any build threads or further detail.

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## witheng

Have you looked at ICF - check out Eco - ICF builders website ( look it up on google ) they have a  block system which cuts out block layers and suspended slab system which cuts out expensive formworkers

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## Oldsaltoz

Bricks or blocks are prone to let moisture through when underground, steel is subject to corrosion. 
With proper treatment it is possible to treat the above but inly on the outside. 
I think I would be looking at something like a tilt slab construction. It still needs waterproofing on the outside and the joints need a really good sealing method, the good news is that any leaks down the track can be repaired from inside, unlike the materials above. 
Depending the product/s used you are looking at $35 to $48 per square metre plus drainage in the form of a porous drain in a gravel filled trench that may need a pump and sump at at the rear of the garage.  
The ICF system can be a bit tricky in that the styrene tends to dissolve when in contact with most waterproofing materials containing solvents, there alternative products but they do not perform as well as the commonly used materials. 
All external waterproofing should be covered with a protective sheeting soon after it has cured and before backfilling. This not only protects the membrane from getting damaged during the backfilling but also ensures the pressure on the walls and membrane is better spread and allows the soil to settle without peeling the membrane off as it goes. 
Good luck and fair winds.  :Smilie:

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## witheng

With anything you will have to waterproof on the cut side and install a geothermic matting ..... I've done many ICF retaining walls as part of construction jobs and have had ZERO problems waterproof , Geothermic matting, AGGY pipe and Gravel.
I use Parchem waterproofing products they are not solvent based

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## Mayyam

Thanks oldsalt & witheng. Waterproofing is going to be the most crucial part being on the downhill side of a sandstone hill.

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## aaronskeates

Wow, this is exactly what i am trying to do right now. but about twice the size. we have a property with a fire trail (on our land) which would be the entrance to the carport/workshop. with grass on top as a continuation of the lawn from the house. how do you certify something like this. do you need an engineer to draw up plans etc?

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## witheng

depending on the height of the wall and looking at your photo's, you will need it to be drawn up by an engineer ( usually about $300 to $400 ) they will also certify it the easiest and possibly the cheapest would be from Eco ICF block , then assemble it on site stack it like big boys Lego with the reinforcing and pour concrete you will save on block layers and blocks . you can also pour a suspended floor with the Eskydeck ( which goes with Eco ICF blocks and needs virtually no formwork and can be done D.I.Y )  and you can get the Spanish villa look like your pictures
but then again you could just go traditional concrete blocks and get them laid but then suspended floors need formworkers which are expensive.
this is the sort of thing we build with rooftop terraces

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