guess at the foundation, earthworks, pilings

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kingdragonfly

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#233601 24-Apr-2018 10:42

I was thinking of buying a lot, for a small 2 BR house.

I created these footprint mock ups, using Google Sketchup.

Below is just a basement, 5 meters deep.

The men are standing inside the lot.

Anyone willing to take a guess at the foundation, earthworks, pilings?

Cheers

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#2001487 24-Apr-2018 11:22

Anyone willing to take a guess at the foundation, earthworks, pilings?

There is no way you can tell any of this until you get a geotechnical report on the site,

What is the soil, is it cut or fill, what is the general slope stability of the area, etc, all will impact on the design of any foundations....

Fred99

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#2001508 24-Apr-2018 11:41

Why not put the garage under - if there's 5m clearance and the space would otherwise be wasted?
I expect that building a garage with 5m elevation at one end, then building the foundations and suspended floor for that is going to be an expensive exercise because of the weight loading.

But yeah - there's no way to even guess what cost could be. To scare you, our neighbour rebuilt a 200m2 house on a similar site in Chch, by the time the geotechs had determined that part of the site had been backfilled with loose soil at some time in the past and needed to be removed and filled/compcted, then cost for assorted retaining walls etc, total cost was $1.3 million, paid for by their insurer.

kingdragonfly

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#2001529 24-Apr-2018 12:00

Holey mackerel!

I guess I'm getting a geo-technical survey first, before putting in an offer.

nickb800

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#2001556 24-Apr-2018 12:38

Assuming you have good ground, a cheaper way to achieve your garage might be a retaining wall and backfill, rather than suspended floor

kingdragonfly

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#2001588 24-Apr-2018 13:06

I made these changes, based on advice.

It doesn't show the driveway, but the brown door is the garage.

The outside lines are for visualizing the lot boundaries, not an actual fence.

The "sunshine" / recession plane should be OK, but there's something in the council rules about 40% coverage. I think I'm OK for that too.

kingdragonfly

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#2001628 24-Apr-2018 13:35

From QV

Earthquake Hazard Earthquake frequency

high

This property is in an area which has a high level of earthquake activity by New Zealand standards. Moderate shaking (MM6) is likely to be experienced once in every 7 years and strong shaking (MM8) is likely to be experienced once in every 110 years. MM7, MM9, and MM10 shaking is likely to be experienced every 27, 405, and 1700 years respectively.

Landslide Hazard
Susceptibility to landslide as assessed from slope/rock strength model

Very Low

This property is in an area with a very low susceptibility to slope instability as assessed from the combination of slope and rock/soil materials.

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mattwnz

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#2001631 24-Apr-2018 13:40

Fred99:

To scare you, our neighbour rebuilt a 200m2 house on a similar site in Chch, by the time the geotechs had determined that part of the site had been backfilled with loose soil at some time in the past and needed to be removed and filled/compcted, then cost for assorted retaining walls etc, total cost was $1.3 million, paid for by their insurer.

Insurance jobs always seem to be a lot higher cost for some reason. Neighbours got a timber paling fence replaced under insurance, about 20 metres, and it ended up being about 10k.

It is interesting about building prices, because I noticed that some insurance companies won't insure you if the building cost (replacement build cost) is too high. eg over 1 million, and you have to go to another insurer. But I would have thought 1 million to build a large modern house that is decent spec, isn't that uncommon these days.

wellygary

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#2001641 24-Apr-2018 13:53

kingdragonfly: From QV

Earthquake Hazard Earthquake frequency

high

This property is in an area which has a high level of earthquake activity by New Zealand standards. Moderate shaking (MM6) is likely to be experienced once in every 7 years and strong shaking (MM8) is likely to be experienced once in every 110 years. MM7, MM9, and MM10 shaking is likely to be experienced every 27, 405, and 1700 years respectively.

Landslide Hazard
Susceptibility to landslide as assessed from slope/rock strength model

Very Low

This property is in an area with a very low susceptibility to slope instability as assessed from the combination of slope and rock/soil materials.

QV reports tell you pretty much nothing specifically about your property, they simply describe the region it is in,

Until someone actually goes on site, there is no way to tell what the foundation requirements will be....

Fred99

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#2001703 24-Apr-2018 15:13

mattwnz:

Fred99:

To scare you, our neighbour rebuilt a 200m2 house on a similar site in Chch, by the time the geotechs had determined that part of the site had been backfilled with loose soil at some time in the past and needed to be removed and filled/compcted, then cost for assorted retaining walls etc, total cost was $1.3 million, paid for by their insurer.

Insurance jobs always seem to be a lot higher cost for some reason. Neighbours got a timber paling fence replaced under insurance, about 20 metres, and it ended up being about 10k.

It is interesting about building prices, because I noticed that some insurance companies won't insure you if the building cost (replacement build cost) is too high. eg over 1 million, and you have to go to another insurer. But I would have thought 1 million to build a large modern house that is decent spec, isn't that uncommon these days.

In that case, the section was a bit smaller than the present city plan allows for dwellings in the area, probably also outside recession plane boundaries, and the homeowner insisted that the house be rebuilt "like for like". So they could only get consent using existing rights, they were a bit limited in what they could do, same footprint, height etc, the insurance had no choice as the policy was "as new" full cover - and the costs just kept increasing. If it was me, I'd have probably tried to play hard-ball with the insurer, their initial cash-settlement offer was "indemnity value", they based that on pre-quake market value and said that they wouldn't budge, but my guess is that they could have been encouraged to settle much higher than that original offer.

I also came across situations where people got paid what seem to be ridiculously high sums for minor work, then also plenty of cases where people got utterly shafted - especially when Fletcher EQR had been involved.

MikeAqua

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#2001721 24-Apr-2018 15:48

I'm concerned by the lack of diversity among your human figures. They all appear to be white men. At least they aren't old.

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kingdragonfly

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#2001754 24-Apr-2018 16:24

They are all Google software developers

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froob

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#2001855 24-Apr-2018 18:06

kingdragonfly: Holey mackerel!

I guess I'm getting a geo-technical survey first, before putting in an offer.

It would be a very good idea to include geotechnical investigation as part of your due diligence on the purchase of a vacant lot.

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kingdragonfly

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#2002057 25-Apr-2018 08:53

I don't think the garage under the house is going to work.

I guess the only option is everything on piles.

Maybe not a good idea to buy the property.

Any solutions I'm missing?

Fred99

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#2002064 25-Apr-2018 09:20

froob:
kingdragonfly: Holey mackerel!

I guess I'm getting a geo-technical survey first, before putting in an offer.

It would be a very good idea to include geotechnical investigation as part of your due diligence on the purchase of a vacant lot.

I do think it's probably a good idea to have some reasonably accurate concept of what you'd want to build on a site and where, before calling in the geotechs, unless all you want is an all care - no responsibility expert opinion along the lines of "soil types/bearing capacity around here is typically good/bad" etc. When they start poking holes in the ground with penetrometers, taking and looking at core samples etc, writing reports for engineers to use for design - it starts getting very expensive - and it's at that stage something unexpected might appear. It wouldn't be good to have a test done telling you that the patch of land you eventually want to use for a vege garden is great, then find out too late that the places you want to put foundations need to be excavated 3 metres, retained, and filled.

Fred99

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#2002067 25-Apr-2018 09:28

kingdragonfly:

Any solutions I'm missing?

Drop the floor level of the house a couple or three metres by excavating and retaining, then see if a garage at floor level might work. Some of the stuff excavated might be able to be used for backfilling/levelling under the garage, then again (and very likely) it might have to be dumped and new fill brought in. Maybe you can guess cubic metres required to be shifted and get some cost indication from a builder who's worked on similar sites.

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