Levelling the house: Steep slope foundations

[Bernmc]

Wondered if anyone here has some advice or contacts: Our house is built on a steep slope (about 6m rise over 25m block width). Some of the pillar foundations have shifted slightly (long dry followed by big wet!). We'll need to get this corrected. Problem is twofold: the steep slope, and difficult access - it'll all need to be done under the house, and getting any big machinery near will be all but impossible.

We've had the mining subsidence bunch out for an assessment - I think we're unlikely to get any cash out of them, but will end up with a full geo survey (poor buggers were here for the day with spades and hand arbours!). Waiting for the report to help inform a builder/fixer

We've had a couple of tradies around, and a local engineer, some of whom never even bothered to get back to me, and others that gave limited/poor advice which suggested they weren't up to the task of sorting it out.

Does anyone have any recommendations for companies that might specialise in this area, or foundation systems that might be used to sort things out? I'm tired of getting the local tooth-suckers out to tell me that it's difficult - I know this already!

[Mobyturns]

Restumping / levelling pier foundations is always a challenge, steep slopes make it more so. My experience from decades back was with my Dad, a registered builder in Cairns FNQ sorting out older style Queenslanders and low sets in the hilly areas of Whitfield, Edge Hill etc. Those days it was all hard yakka with the old manual Wallaby Jack, Trewhella Jack's & Acrow props etc.

Modern specialist restumping / levelling contractors have a range of hydraulic options that make life easier and safer. WOMA is the best recommendation so I would ask around.

Search out House Restumping & Reblocking in NSW ... Expert house re-stumping services; Re-stumping and re-blocking specialists ..

[ian]

What type of foundation do you have?
concrete piers -- which would allow the house to be jacked and shimmed back into position.
timber piles -- which would similarly allow the house to be jacked and shimmed
a form of braced steel lattice attached to concrete piles? -- which makes access more complicated.


Access. is it just difficult or nearly impossible?
Search for equipment types (boom lifts, scissor lifts) that can safely operate on the slope you have. You will likely be surprised what is available.

[Beardy]

Look for an underpinning specialist, there should be plenty of companies that would deal with it and have the appropriate equipment

[riverbuilder]

newcastlehouselevelling.com.au

[Bernmc]

Concrete piers, and it's just bloody difficult to get at them. We can't even crane machinery to the levelled part of the slope as the power lines are in the way.

It's all do-able, but at a cost, and with someone willing to do it - I think there's so much work around that the buggers are turning up and going 'too hard, see ya'.

We have to redo retaining walls and other bits of construction, so I'm happy to have someone turn up with a digger and build switchback ramp up to the levelled bit - that'll give us some access, but the piers under the house will remain difficult. Hydraulic jacks and I think adjustable piers that can be wound up a bit in the future if things shift would be ideal, rather than packing and having to do it again in five years.

[ian]

Concrete piers, and it's just bloody difficult to get at them. We can't even crane machinery to the levelled part of the slope as the power lines are in the way.not really an impediment. Depending on the power line voltage, you just to arrange for the power lines to be de-energised and possibly a bigger crane.



We have to redo retaining walls and other bits of construction, so I'm happy to have someone turn up with a digger and build switchback ramp up to the levelled bit - that'll give us some access, but the piers under the house will remain difficult. Hydraulic jacks and I think adjustable piers that can be wound up a bit in the future if things shift would be ideal, rather than packing and having to do it again in five years.adjustable props will mean that your house will permanently look as though it is "under repair". Probably not a good look for SWMBO.
Also, your house should be tied-down to the concrete piers. I'm not sure how adjustable props and permanent tie-downs would work together.


Are you prepared to post a photo or two of the current problem -- including a couple of the existing ground surface?

[aldav]

Also, your house should be tied-down to the concrete piers.

:? :no: What say the builders to this clanger? My reading is that the Op has brick piers not precast concrete. Even if he does have precast concrete piers the point of them being attached to the floor framing is to stop the piers moving in relation to the floor framing not to tie the house down.

[Beardy]

What sort of machinery are you thinking is needed under the house? If it is just redoing some piers it is pretty much hand work with the likes of a spade bit in a Kango to make it easier and then pour a concrete pad using a mixer and either use steel posts or brick up new piers.
Without more information I am making a number of assumptions but it is not a complicated process apart from the access hinderence

[ian]

Also, your house should be tied-down to the concrete piers. I'm not sure how adjustable props and permanent tie-downs would work together.


:? :no: What say the builders to this clanger?
The OP has confirmed that his house is on concrete piers.

It's a very long time since I studied wind loading on structures but my recollection is that on a slope as described (approximately 1:4) the main wind related risk is that the wind gets under the OP's house and lifts it off it's foundations -- not a good look.

leaving that aside, the BCA (Building Code of Australia) requires that domestic structures (e.g. houses) be tied down to their foundations (the details depending on the materials use to construct the structure) and not rely on gravity alone to keep them in place.

[aldav]

Despite what Beardy has said in the post prior to yours Ian, you must be right. You're always right! I definitely have better things to do than argue against you, so I acquiesce. Pray tell, what holds the concrete pier to the pad that it's sitting on?

[ian]

Ian, you must be right. You're always right! I've been known to be badly wrong on more than one (make that many) occasions :doh:




Pray tell, what holds the concrete pier to the pad that it's sitting on?The earth just sucks :q

seriously,
if the foundation is as I think Bernmc described -- 7 to 8 m long concrete piers embedded up to 2 m into the ground -- the piers are held "down" by skin friction between the pier itself and the ground. Alternately, the piers could be sitting on concrete pads that in turn are anchored to the ground.
I'd be surprised if there wasn't some level of structural engineering design involved with a house sitting 6 m above the ground level, which in turn leads me to think that mine settlement shouldn't be ruled out as a contributing factor to the situation Bernmc is trying to address.

[Bernmc]

I'll take some pictures this weekend when I get home from work

I was thinking along the lines of replacing the piers, but that may be overkill. The house was built in the sixties, and extended a couple of times, so there's a bit of a mix between concrete piers and brick. One end of the house (a single bedroom extension on the left) just sits on a 100mm slab - there doesn't seem to be anything going down deep. So I think that will need something more substantial than packing.

Here are a couple of pics of us clearing the slope to the side of the house of lantana, so you get the idea of the gradient.

477525. 477526

And the front of the house - floor level is above the garage door you can see, so everything to the left of the garage is on piers sunk into the slope. Drive to the garage is 18 degrees!

477527

Will get some pictures of the foundations themselves later on. It's a) getting machinery up that slope, and b) having enough room under the house to do anything

[rustynail]

Despite what Beardy has said in the post prior to yours Ian, you must be right. You're always right! I definitely have better things to do than argue against you, so I acquiesce. Pray tell, what holds the concrete pier to the pad that it's sitting on?
Tie downs should extend from within the footing, not just from the pier. It is standard building practice.

[Mobyturns]

Building design and hence "tie down" requirements have changed over time with major revisions to the BCA in response to events such as the Newcastle Earthquake (1989), Tropical Cyclone research, to improve bush fire resilience etc.

Newcastle is in Wind Region A (normal) and given the slope of the site its probably Terrain Category 2 with a Topographic Multiplier of T2 -T3 so there would definitely be requirements for wind loading "tie down."

Movement in buildings over time is inevitable. How much, the type of movement, cause etc will determine the remedial actions required and IF it is considered minor or major structural works. Taking on major structural work i.e. underpinning foundations etc is not a task to take lightly and should be done in consultation with a Structural Engineer, registered building designers, experienced specialist contractors and most likely will require local authority approvals etc. Really time to get expert advice.

[Beardy]

Tie downs should extend from within the footing, not just from the pier. It is standard building practice.

What type of construction and State are you referring to and what type of tie down are you referring to?

[aldav]

I've been known to be badly wrong on more than one (make that many) occasions :doh:

Oh come now ian, don't be so modest. Posts on this thread this afternoon/evening indicate that you are probably correct. And I expect to see a response to this post, we all know how you love to have the last word. And this time you've even got some firm ground to stand on. :D Apologies to Bernmc. :B

[ian]

Oh come now ian, don't be so modest.
[snip]
I expect to see a response to this post ...
yes, I was a bit too insistent in the other thread ... I should have known better

[Mobyturns]

Hope this helps, I found a copy of AS1684.2 2010 "Residential Timber Framed Construction - Non Cyclonic Areas" at https://www.renovateforum.com/attachments/3/1/8/7/4/85884.attach

Its worth a read to see what the requirements are for "new" construction and what you may have to upgrade to with renovations / rectification works. Section 9 details "tie down" requirements as either "nominal" or "specific" with the "nominal minimum fixings per joint" requirements to be found at page 169 in Table 9.4.

Having past experience in residential construction in Cyclonic areas means that I'm more familiar with beefier hold down requirements.

[rustynail]

What type of construction and State are you referring to and what type of tie down are you referring to?
Domestic Construction,Steel rod, Australian Standards Section 9.

[riverbuilder]

Here, on the river, most houses are built on the bottom of at least a 30 degree slope of ground above, some even more, and ALL of them, without exception, sink down towards the water. The reason? The water that falls on the catchment above the houses, up the hill and on the plateau above, runs down the hill, into the ground and keeps going downhill to the river, generally once it hits the bedrock base it runs on top of that and follows down any soft pockets until it runs into the underground aquifers and into the river. I’ve had excavations down to rock that have had water streaming in through the ground 3 metres down and filling the holes up. I’ve been to bernmc’s house, and the hill above it would certainly have subsurface water runoff during rain events and that water would certainly be capable of underscouring foundations. It’s why most engineers that I deal with here, where there are major geotechnical issues to overcome, want foundations to go down to solid rock, whether it is 300mm down or 5 metres down, not an easy exercise when everything is done by hand, including digging.