Help - Insufficient fall for sewerage house connection

amitesh · Jul 12, 2024 4:57 pm

Please refer to the attached image of lot 7. The invert level of the house connection for gravity sewerage is 38.066, while the rest of the lot is approximately 38.8. Accounting for 400mm for the drain head and another 400mm for swivel and expansion joints (as the site is classified E2), this leaves only about 60mm of fall to the sewer house connection. This is insufficient to achieve the required fall of 1:60.

My builder proposes to charge nearly $40,000 to raise the house pad by 500mm with fill. However, according to the National Water Code, the house connection must sufficiently service the entire lot, which does not seem to be the case here. Additionally, the house connection is placed contrary to technical guidelines, being at the highest point of the land rather than the lowest where it should be.

I am wondering what you would do in this situation? Are there any cheaper workarounds? I have tried to contact the engineer, but they have not been helpful and are now not responding to my inquiries despite my courteous approach.

This is in SEQ. Thank you.

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Eng. B A · Jul 13, 2024 6:26 am

I’m not sure why do you need to lose 400mm going down for swivel and expansion joints. Those joints can be on horizontal level.
You can check this product https://www.stormplastics.com.au/installation.html

building-expert · Jul 13, 2024 12:25 pm

Who designed the house?

amitesh · Jul 13, 2024 6:17 pm

building-expert

Who designed the house?

The house was designed by the builder, Coral Homes. However, they didn't have access to the sewerage plans until well after the contract was signed and after the settlement of the land. It appears the house connection was installed quite late. Nevertheless, it seems that the lot does not meet the technical guidelines regarding serviceability if I understand correctly.

Bimbob · Jul 14, 2024 12:28 pm

Eng. B A

I’m not sure why do you need to lose 400mm going down for swivel and expansion joints. Those joints can be on horizontal level.
You can check this product https://www.stormplastics.com.au/installation.html

You’ve misunderstood the issue. The expansion joints must be installed vertically, it’s in the code

Eng. B A · Jul 14, 2024 5:59 pm

Which part of which code that says that?

amitesh · Jul 14, 2024 8:04 pm

In case it helps, here are the sanitary drainage articulation notes from the Soil Test and Foundation Design report. It states that vertical expansion joints are required only when pipe depth exceeds 6 meters, which I do not believe is the case here. However, I am not sure if there are code requirements that override this.
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Eng. B A · Jul 15, 2024 6:24 am

The recommendation from the soil report may meant >600mm in depth. However this recommendation is for deep dropper vertical pipes in class E (if you have to use one).
My question is why do you need to go that deep to exist the building perimeter?
Generally expansion joints is placed in vertical deep droppers to absorb differential ground movement between shallow pipe system that moves the most and deep pipe system that would move the least.

amitesh · Jul 21, 2024 10:23 am

For those following along, the engineers have kindly come to the party and will be implementing a solution that should ensure adequate fall to the house connection. This is likely the best possible outcome for the situation.