Our Dream Renovation: 04 Excavation

Its time to get dirty and get this home out of the ground! The excavation stage can sometimes be the most daunting stage of the construction project. When a builder prices up for excavation for a client, 9 times out of 10 it will be an allocated sum known as a provisional sum.

A provisional sum in a contract is an allocated sum of money that is estimated to complete a certain stage of construction.

The excavation stage is unkown. You can get an idea of what is expected when digging your foundations. But, you truely cannot know what is down there until you start digging.

Lucky for us, we didn’t come across anything too unexpected during excavation. This stage for us came in right on budget. Being mostly a bearers and joist floor system, the excavation stage was never going to be too drastic.

A Few Tips Before Excavation Starts

Here are a few tips that could help you breeze through the excavation stage of your construction project:

• Always use dial before you dig before any excavating starts. Usually this is done in the planning stage anyway to make sure existing serivces won’t affect the build. Visit Dial before you dig here > www.1100.com.au
• Have a sediment control plan! Councils are coming down hard on projects not taking sediment control seriously. Take your time and strategically install a sediment control fence and sand bags down the road gutter to catch any escaping sediment from your site. As an individual you could be fined as much as $7500 for not taking proper precautions.
• Do you have a good excavation tip? Let us know below in the comments section?

Excavating The Pier holes

Our home had a total of 83 piers we had to dig, with a majority of them being a size of 400mm in diameter and a depth of 500mm.

Our engineer called for 6 piers to be larger to account for some point loads coming down from the build. Four piers were taking loads coming down from two large roof beams. Being a large raked ceiling, these beams were going to help take the roof weight over the living room. The two other piers that were beefed up were designed to take the weight of an intermediate deck bearer as well as the weight of the house.

Unlucky for us, we were caught out with bad weather making our site very muddy and hard to work with. Our pier holes filled up with water and had to be pumped out numerous of times, but we got there in the end!

Excavating The Garage Slab

Excavating wise there also wasn’t much involved with the garage slab foundation works. Our engineer nominated 2 sizes for our strip footings for various reasons, 300W x 500D and 400W x 500D. These strip footings were designed to hold a 9inch brick wall which would then eventually support the concrete slab.

Originally, our garage was designed to be a suspended concrete slab on Bondek sheets. Because of the amount of soil we had stockpiled so far, and with our engineers input, we decided to fill under the slab with the stockpiled material.

Excavating The Site Cut

As bed 3 and bed 4 were extending out from the existing house, we wanted to make sure we had a minmum clearance of 400mm under our floor to the ground. This helps with better air circulation under your subfloor.

AS 3660 calls for a miniumn clearance of 400mm, except for the last 2 metres around the perimeter, where it can slope to a clearance of 150mm.

For us, the ground height was too high and had to be cut to achieve our designated 400mm ground clearance. Luckily we were aware of this by taking various level points during the design phase and through our survey plans that were drawn up, and budgeted for it accordingly.

Our Method Of Excavation

There was only one way we could attack the excavation of our site. With narrow side boundaries, we only had one choice, to start from the back and work to the front.

I took some levels of the site and set up profiles to set out the house. From a rectangle grid of string lines I was able to set out all our piers ready to be excavated. We hired a 1.7 tonne excavator, purchased a few shovels and got all hands on deck to help out. So we started digging the rear piers of our home.

Moving on from the piers, we got into the garage slab. Digging the trenches for the strip footings was an easy process. Once set out, all we had to do was dig the trench to the right width and depth to satisfy our engineers plans.

Our southern boundary, unfortunately, was a lot more labour intensive. Due to a decent sized driveway situated where we were extending out to. Half the driveway, we were able to cut 400×400 sections out of for our pier footings. We had the ground clearance. The other half was encroaching on our minimumn 400mm clearance under the subfloor. So up it came!

In conjunction with our hired 1.7t excavator, we also hired a quick cut concrete saw. This helped cut the concrete into smaller sections so they can be picked up with the excavator. Unfortunately for everyone involved, and our neighbours, this was a three day process :/

The result was going to leave us with a lot of concrete to get rid of. While we had the machine, we sourced a well priced hard waste skip bin, and loaded it up with the concrete sections.

After all that hard work one final area was leftto take care of, the extension of bed 3 and 4. To gain our designated 400mm clearance under our subfloor we had to use the machine to do a minor bulk cut of the area. Essentially we had to go down 600mm and scrape it back to nothing to achieve our desired levels.

The site was now ready to pour concrete. Then it rained, :(.

Excavation Stage Costs

Total Project Costs To Date

• (02) Designing and planning stage: $13, 428.20
• (03) Council application stage: $6,171.20
• (04) Excavation stage: $1,163.82
• Total costs: $20,763.22