Land - controlled or uncontrolled fill

We have an acre block that's mostly sloping downhill towards the road. The practical building area is about 600m2, with a 3-5m slope from back to front. We can't really afford to build a custom home, split level etc, so we are looking at project builders, and they want us to get the earthworks done ourselves, which we're happy to organize.

I've consulted a few contractors and rough estimate for site cut and fill varies from 10k-30k.

Options as I see it are...

1/ Get the site cut and filled and rolled over by the excavator (I guess that's uncontrolled, or rolled, fill). That looks to be the cheaper option for earthworks, however the slab would cost more as it require a piers and likely need to be engineered more.

2/ Get the site cut, filled and compacted properly, and have the site supervised and tested to ensure it complies with the relevant standards? This will cost more for earthworks, but presumably we would not need piers (or as many as in option #1).

Which would be the best (cheapest) option here? Would a project builder build on both options 1 and 2?


Also, what professional would I engage first to design a site cut and fill plan for the excavators to follow? This person would need to consider drainage, retaining walls/batters etc. Would this person be a civil engineer, or a civil designer or someone else?

Thanks in advance.

This can be an awesome home but will be terrible if you're going to cut 3m.

If you can afford a 600sqm project build, you can afford a smaller split level which will infinitely better on your block.

Use the slope of the land in your favour, not against you. Build on stumps.

chiggles
You will need a starting point
1. Budget, Contour , geotech report and Prelim BIM sketches
2. Track down a project engineer That uses Maplesim or Matlab always ask for proofs to solutions
3. Extract data from at least 3 alternative models & Compare the costs
4. Then you will need to go back prioritize what's important and solve for Optimize variables using matrix manipulation
5. or find an engineering student needing a final year project and pay him well
6. or Ask on the AEC BIm Apps & Simulations ..there are some clever guys on there that love a challenge..
Goodluck

Sorry I probably didn't explain it very well.

The lot is 4,000m2 but the building envelope is around 600m2. Our house will be between 300-350m2, probably single storey.

The slope over the building envelope is about 3m, so roughly a 1.5m cut/1.5m fill. The 2-3m cut behind the building envelope can be gradually sloped or terraced as there is enough room that (ie it shouldn't need a steep cut and retaining wall).

I wish I could afford to have something designed and built (its almost criminal not to with the views) but im pretty sure the cost of a custom builder (whether it be split level or on stumps) will still be a lot more expensive than the cost of earthworks to level the building envelope and using a project builder... But I could be wrong.

Thanks, I'll have to research all of that, it's a foreign language to me!!!

You won't know that until you do the calc$-> Numbers...my2c
1. Own copyright of your optimised design
2. Know what's involved in regards to l/m, m2,m3, Costs and time taken
3. Armed with this make an informed decision
4. It's also useful in persuasive discussions with Builders & Trades, eg what is a fair price, easy build, etc
Optimising the engineering will be the key component to your Design & Build
BTW...Math ( ie Data, Proofs & Equations ) is a universal language

My two cents from building on a slope. My lot is 900m2 and have a 5m slope (2m over the building envelope). My builder cut and filled before laying a concrete slab.

My lessons learnt:
- Engineer (not builder) will design your slab. They will always play it safe because the builder is passing on the risk of fixing any slab heave to the Engineering firm.
- The Engineer will play it safe and put a pier over any fill so you can’t escape the cost. For controlled fill (if you can give the certification to them), they will put a concrete pier. For uncontrolled fill, they will put a screw pier. Concrete pier is about 30% cheaper than screw pier. However you are not saving 30% because that saving is spent on getting controlled fill and the certification.
- Did you actually speak with a volume builder who does split level? I didn’t find any price difference (say between Metricon who doesn’t do split vs Steve Parcell who does split - the Steve Parcel house were 2-3 square smaller though).
- Your biggest cost will not come from leveling the building pad and putting piers. It will come later from driveway and landscaping. Slopes usually have large rocks underneath the soil which will be dug up during leveling, building pad, plumbing, driveway, pool. Slope isn’t usable for gardening or letting your kids play in backyard. So you have to build stepped retaining walls to further level the yard. Those costs will add up very quickly.

Yes you are absolutely right, we won't know until we do the numbers. The only problem is that we have to incur the time and cost of getting proper plans done to give to builders to quote on. My fear is that it will be wasted time and money.

...but it's probably the smart thing to do.

Most Engineers will design to what builders are comfortable building.
$30-$50K is the going rate and try as you may you won't see value in material & Labour Costs
.. unless you analyze the alternate breakdowns.
Here are some breakdowns for you-> low to high
Engineering 2%
Building Surveyors & Consultants 3%
Salespersons Commission 3%
Architects/Designers Fees >!0% + Commission 3%
Builders Margins >25% (Varies)
Engineers control Bugger all mate..the builders margins & profits dicate

Thanks Nabeelc. Very helpful.

The only volume who I could find who does split level is Metricon funnily enough and they said it was too steep for them.

Fortunately our site is large enough so excavators can place fill around the block and track over it to level it, then batter it with slope, so won't need much in terms of retaining walls etc for flat areas for gardening etc. Although we will need some retaining between the house and one side boundary. Also the driveway is 100m long and it's already cut and level, just needs to be graded a little at the start and filled with some kind of surface, probably crushed rock at this stage until we can afford to seal it.

Yea. I built with Metricon. Maximum slope they do is 2m which gives 2-3 steps inside the house with a high ceiling in one part of downstairs.

Here is an option to consider.

Hire a bobcat to push dirt around to level the area to less than 1m slope over the 600m2 building pad. Will take 3-4 hours so cost less than $500 and will be considered as uncontrolled fill. Then get a survey done on the new slope which will cost around $500. So for $1000 you are within the parameters of volume builders.

Then take quotes from volume builders. If the site cost of volume builders is less than $9000, you will be saving from doing a $10-30k proper controlled fill.

Thanks Nabeelc, that's a great idea, and low risk as if it doesn't work out then no harm done.

Do you have a thread for your build?