40 yrs old house subsiding - builder/underpinner or engineer? (Brisbane)

Hi all,

I am based in Melb and I have an IP in Brisbane and my existing tenants have reported an issue where one of the bedrooms upstairs has been on a slight downward slope towards then road (room highlighted in floorplan). Issue appears to be reactive soil.

There is a granny flat at rear of property separated with a dividing fence. My realestate agent has sent a builder to do an assessment ($600) as well as our plumber ($500) to perform camera check on drainage pipes blockage. A solution proposed by builder is to dig trench from back of house to the road, and will cost at least $8k. Plumber disagrees as he can't see issue with the drainage issue apart from service water, plumber suggests to get quote from underpinner. I contacted my insurance too and but I don't expect much this is covered by the policy (based on what I read on this forum),but hoping for another opinion. I am reaching out here to see if you guys can share your opinion what I need to do next.

More info below:

Builder:
Builder proposed a trench to be dug from the backyard all the way to the side of house then out to the road for service water to flow away from the house (plumber think this is too much and not needed). Estimated cost of minimum $8k. Underpinning and internal fixes would be extra once soil is stabilised. He also stated a crack on the brick wall above garage due to this issue.


I am not 100% clear from this report if this issue has just happened, or it is actually movement over 40 years and I am not clear if the trench is really needed. The crack above the garage has been there since I bought this in 2018, and gap does not appears to be expanding. The crack appear to have been there for quite some times, digging up the internet, I found an old listing picture back in 2013 and crack was already there. Which suggest maybe movement has been over time and not a single event?


Plumber:
Our plumber checked all drainage pipes and did leakage test and there do not appear to be leakage. He does not agree with the builder and thinking the trench work is too much. There can still be service water (my understanding it is rain water flow through the soil/lawn), he suggests to get quote from underpinner and get them have a look at it. I have attached his recommendation in screenshots below if that help.



My Building Insurance:
Insurance company contacted the tenants and is aware of check completed by builder and plumber, they requested these info to sent through and I did. They said they are independent and will arrange their own guys to check if there are conflicting information... I am not hopeful this is covered under insurance, but hoping to get another opinion on what needs to be done.


Thanks in advance,
Berns

 

FYI, the builder disagrees with what plumber said and said the trench is needed, plumber is wrong. Although we have pictures and footage of the camera check from plumber, builder refused to look at them and requested they do the drainage pipes check themselves. This was last week.

Today builder contacted the real estate agent and offer free drainage pipe check, but I asked to put that on hold, there are a lot of information and I want to wait for information from insurance and also want to post this here for opinion from you guys.

I can't 100% trust the report from builder not because it cost an arm and leg, but I guess he is not in a neutral position as there is money involved if he get the job. I see some other posts where forum members have suggested engineer to check as they are not bias and will give you proper advice. I am not sure if this is what I need to do, or get underpinner to check it out. Probably same issue with underpinner.

 

Best bet is a report from an independent structural engineer.

 

Thanks, this is what I am leaning towards to. If advice is to stay put and monitor, then I can get them check again next year to compare if movement has worsen before doing any underpinning work.

 

I'm confused - are there any cracks / identifiable issues directly related to the apparently sloping floor?

 

I forgot to mention, there is a door issue in the same bedroom (the one facing to the road far left), it cannot be shut, this issue was reported same time as the slope issue. From what I was told there are no visible cracks inside. As for exterior, the crack on brick above sunroof (above garage) is the one visible crack and appear to have existed for quite sometimes, not sure the cause of that one, but assume it is probably due to movement over time

 

There was a mould issue in the same bedroom reported back in April which caused by water dripping from roof into wardrobe causing the mould. A section of flashing above main bedroom was loose and not sealed. This has been primed sealed and secured since. Not sure if this is related.

 

I did read about your story in another post and this align with builder recommendation. By the sound of it, your son's first property was in a deep slope landscape given double storey front and single back which probably have a lot more service water running off against the property. My land is relatively flat, with right side neighbour on higher ground, probably half a meter higher, so it is possible there are water coming from that side, but majority of drop appears to be on left hand side of house.

Do you know how much your son's first house has dropped?

Did your builder/underpinner say it definitely wont have movement overtime once soil is stabilised? Or it will still have movement over long period of time (let say over 40 years)?

 

Thanks for the additional information, it helps, I think I need to find out how much engineer report cost and make a decision from here.

 

As the property hasn't fallen down after 30 or more years (based on the use of vc pipes) and the cracks have been known about for 8 years, so there even longer, I suspect it is not particularly serious. If water is ponding near the house, then this definitely needs remedying as it will exacerbate ground movement and I would want to deal with the drains - either the remedial work recommended by the plumber or replacement with upvc pipe.

 

Thank you, would you get structural engineer to check first?

 

Quite a good read here, Underpinning made simple: A Step by Step Guide to Underpinning

I am going to get some quotes and get a strucutral engineering report done prior further action. Thanks everyone commented on this thread

 

Some good advice in this thread already.. I would just recommend including Booth Engineers in your list of quotes.. I’ve read many reports and underpinning scopes (including my own), and I don’t think you’d get better advice than from these guys.

Booth Engineers & Associates | Home Page
p.s I’m not affiliated with them

 

Thank you for the contact, will reach out for a quote too.


Would you guy disclose the report from builder as well as plumber when getting the structural engineer to assess this slope issue? or just see what they find?

 

Definitely show them all plumbing info you have. They will need this and may undertake another leak detection otherwise..

 

When you do underpinning, do you need structural engineer design prior underpinner quoting on the job? or do they quote the job based on preliminary report from structural engineer and they will get the design separately and generally include soil test/engineer design in their quote?

I have contacted a couple of Structural Engineers.

1. First one I contacted has two price structures, where they would first do a preliminary inspection on the issue (check level of house, crack and etc), and if recommendation is to do underpinning, I can then upgrade to a more detailed report which include design and soil test, and I can then provide it to underpinner to quote.
2. The second structural engineer I contacted will do preliminary inspection same as per above, and if recommendation is to do underpinning, then I would then take the preliminary report (includes estimate number of under pin needed) and get quote from underpinner. This structural engineer said the underpinner generally has their preferred structural engineer they work with and their quote includes this cost.

I probably should call a couple of underpinners to see what the process is.

 

Just an update to this. I found an underpinner which both engineers recommend on their website and I spoke to the underpinning company (not quite sure if I am allowed to name it here). the first engineer #1 (the upgrade option) is what they prefer to work with as that guy has better drawing and does all the soil test prior and they would be able to give firm quote.

As for the #2 structural engineer, this underpinning guy also worked with, they can quote based on site visit and preliminary report from engineer, but they can only provide estimate due to no engineer design.