Building on sloping rock

[Lukey13]

Not being a builder myself, I would like to know how much more expensive it is to build a house on sloping rock than it is on a flat soil surface?

I'd imagine that there would be at least two options - a pole home or cutting into the surface to make it flat before laying the usual slab. Which would likely be the cheapest option?

Also, if a block on a rocky hill appears to be fairly flat and with soil covered in grass and weeds, however nearby blocks are rocky, is it possible that there is only a thin layer of soil and that the same difficulty of having rock underneath will be an issue?

At this stage I have no idea and am unsure whether it's possible to roughly say that it would cost $50k more or $150k more to build on such a site, so any feedback and experiences would be welcomed.

Cheers

 

[Propertunity]

Not being a builder myself, I would like to know how much more expensive it is to build a house on sloping rock than it is on a flat soil surface?

It can be quite a bit more. So this needs to be reflected in the purchase price of the land in the first place.

I'd imagine that there would be at least two options - a pole home or cutting into the surface to make it flat before laying the usual slab. Which would likely be the cheapest option?

Pole house definitely. Rock excavation can cost a fortune or not depending on how much of it there is & how hard it is.

Also, if a block on a rocky hill appears to be fairly flat and with soil covered in grass and weeds, however nearby blocks are rocky, is it possible that there is only a thin layer of soil and that the same difficulty of having rock underneath will be an issue?

Yes. Add to that, that rocks can be 'floaters' - meaning not stuck to anything underneath and therefore you can't build on floaters and solid rock at different points of the building because they may move independantly of each other. You'll need a geotechnical report. And the geotech engineers will need to dig bore holes.

At this stage I have no idea and am unsure whether it's possible to roughly say that it would cost $50k more or $150k more to build on such a site, so any feedback and experiences would be welcomed.

Impossible to say - refer geotech guys

 

[Lukey13]

Thanks for your advice Propertunity.

It sounds as though there's no general rule to estimate the additional costs of building on sloping rocky terrain.

However, does anybody have any experiences they can share of building this way? Or does anybody have any experience with geotech reports or know how much they cost?

 

[Shadow]

I'm based on Sydney's Northern Beaches, which is full of pole homes (comes with the hilly territory).

A pole home is definitely the best option for a sloping site. Cutting into the surface is more expensive, impacts the environment more severely, and can destabilise the land if not performed correctly.

There are heaps of pole home designs, and sloping sites usually have the best views. I find pole homes can be very interesting, architecturally, but that's just me. I actually prefer sloping sites and pole homes, compared to regular boring flat blocks.

A geotech report costs around $900 in my area. Pretty much essential if buying a steeply sloping block. I order a geotech at the same time as the building and pest inspections.

Regarding the 'floater' rocks, I have seen designs where one pole is embedded in the 'floater' but attached to the house on a movable 'rail' so that the pole can be adjusted as the floater moves downhill (at a speed of maybe a centimeter every 10 years!)

Below is an excellent book on pole homes - you can order online.

Practical Pole Homes - Building Solutions for Sloping Sites, By Ray Crawley

Cheers,

Shadow.

 

[craigb]

i agree if it was a choice beetween a flat block and a pole home i would prefer the later,
large machines can remove any large rock, once the cut is done, its over with.
Think about incorporating the two, and get three landings, using the top one as a nice out door entertaining area.

 

[Lukey13]

Thanks for the hints Shadow and craigb. It sounds as though you've both had experience in building on such sites.

Of those instances that you know about, how much "extra" did it cost to build a pole home rather than say the equivalent home on a slab on a flat soil block?

I'm just trying to gauge whether it's worth even looking at rocky, sloping land and if so, whether it should be say "$100k cheaper" than an equivalent flat block due to the additional build costs. Obviously it all depends on the size and complexity of the house, but if it were possible to compare the same house on a sloping rock site versus a flat soil block what range of additional costs would be involved. Eg. 50% more in cost or 5,000% more in cost?

 

[Shadow]

Hi Lukey,

Pole homes are not particularly expensive. You can get an idea of costs below...

http://www.polehomecentre.com.au/favorite.htm

Rocky slopes are no worse than grassy slopes - the poles need to be embedded in stable rock anyway, so if the rock is near the surface then that's fine since you don't have to drill down so far.

Here is an example of the type of pole home design that is quite common around my neighbourhood...

Cheers,

Shadow.

 

[Lukey13]

Thanks heaps Shadow.

That link provided a basic estimate of $1,200 to $1,500 per sqm for the average pole home, which at least gives me some kind of idea.

The pole homes in the photos looked like a much more expensive level of finish to me though!

Just one more question; generally, is it much more expensive to have a two or three level pole home than it is for a single level?

I'm asking this because obviously on some sites the view from a second or third level would be far superior to that on the first level.

 

[Shadow]

I don't believe the price per sqm would increase significantly with 2 or 3 level designs, but probably best if you give one of the builders a call, really depends on the block and design. The majority of pole homes that I have seen are multi-level, and often split-level. A local pole home builder will probably be happy to visit your site to give an appraisal of what is possible.

 

[The Y-man]

Was this The Rock you were thinking of building on the side of?

Cheers,

The Y-man

 

[burty85]

Hey mate,

Are you looking around "the ville" to build your house??

 

[burty85]

Hey mate,

Are you looking around "the ville" to build your house??

 

[CADAN]

Was this The Rock you were thinking of building on the side of?

Cheers,

The Y-man

if so, forget a geo report, it aint gonna move.