Knockdown Rebuild double storey house

sun99 · Aug 11, 2024 12:58 am

We are doing knockdown and rebuild in western Sydney. First timer building so looking for some advice and guide here.

It's a double storey house on land with 14 meters wide and sloping towards the street and backyard is in the north. As there is a significant slope, a split slab was suggested. Is it a good idea to cut and fill or go with a split slab? How will the roof heights impact with the split slab approach? Will there be extra costs in bulidling with split slabs?

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Thanks in advance for any advice.

Eng. B A · Aug 11, 2024 5:32 am

If the land is located within landslides hazard area (check with local council) then you need to follow the recommendations of the slope stability report in terms of cut and fill. In my opinion split slabs is less risk in terms of landslide and helps in stabilising slope than cutting and filling. I’m not sure if cutting and filling this area would be more costly than retaining walls in split slabs either.

sun99 · Aug 12, 2024 12:12 am

Eng. B A

If the land is located within landslides hazard area (check with local council) then you need to follow the recommendations of the slope stability report in terms of cut and fill. In my opinion split slabs is less risk in terms of landslide and helps in stabilising slope than cutting and filling. I’m not sure if cutting and filling this area would be more costly than retaining walls in split slabs either.

Thanks, if i go with split slabs , how will sealing height varies across the house. i want 2700mm hieght , what will be garage height with split slab.

Denali · Aug 19, 2024 3:59 pm

We completed our split double story in May and your question asks about additional cost and the answer is yes, just due to the complexity of having a less than perfectly flat site. Depending on your site, we required an edge beam and part of our house is 3.3mtrs ceiling (love it) and another is 2.4mtr ceiling in two bedrooms (not a fan but basically unused rooms) and upstairs is 2.7mtrs (which Im use to/had in the old house).

On the plus side, your storm water will be easier to deal with than ours and thats a cost benefit.

Eng. B A · Aug 19, 2024 5:52 pm

You can either continue with floor level and increase the garage ceiling or use suspended ceiling to lower it down or step the ceiling down as your slab goes down with upper floor step down as well.

sun99 · Aug 19, 2024 6:16 pm

Denali

We completed our split double story in May and your question asks about additional cost and the answer is yes, just due to the complexity of having a less than perfectly flat site. Depending on your site, we required an edge beam and part of our house is 3.3mtrs ceiling (love it) and another is 2.4mtr ceiling in two bedrooms (not a fan but basically unused rooms) and upstairs is 2.7mtrs (which Im use to/had in the old house).

On the plus side, your storm water will be easier to deal with than ours and thats a cost benefit.

Thanks I am ok with 3.3m ceiling at the entrance it will be grand entrance, but only worried with garage ceiling going to 4m
How expensive is edge beam?

Denali · Aug 19, 2024 6:25 pm

sun99

Denali

We completed our split double story in May and your question asks about additional cost and the answer is yes, just due to the complexity of having a less than perfectly flat site. Depending on your site, we required an edge beam and part of our house is 3.3mtrs ceiling (love it) and another is 2.4mtr ceiling in two bedrooms (not a fan but basically unused rooms) and upstairs is 2.7mtrs (which Im use to/had in the old house).

On the plus side, your storm water will be easier to deal with than ours and thats a cost benefit.

Thanks I am ok with 3.3m ceiling at the entrance it will be grand entrance, but only worried with garage ceiling going to 4m
How expensive is edge beam?

Edit: Unable to upload copy of site costs from contract but it was $60K exc the below

Every job is different and this (attached) doesnt include many items, like our storm water $13K, additional slab and piering $10K, power connection/pole, $3K, 2.7mt ceiling upstairs $3K, insulation, double glazing and many other nice to have we picked or the facade.

qrius · Aug 20, 2024 1:40 am

sun99

It's a double storey house on land with 14 meters wide and sloping towards the street and backyard is in the north. As there is a significant slope, a split slab was suggested. Is it a good idea to cut and fill or go with a split slab? How will the roof heights impact with the split slab approach? Will there be extra costs in bulidling with split slabs?

What is the length of your land, and what is the rise of over that distance ?

What is the height difference from street to the backyard ?
(or building envelope height difference, from front to back of house) ?

If you can use the contour of the land, and split level design,
you get some interesting internal private spaces,
like 2-3 different "apartments", eg. kids area, guest room, etc.

If you see some display homes for Montgomery Homes [ https://www.montgomeryhomes.com.au/ ], you will get the idea.
I am not linked to them in anyway, but I visited them last year,
because my own land has a slope, and I'm finding that the slope is causing a lot of builders,
to not want to give me plans without a split-level.

Besides, the split-design has other design implications for where my garage needs to face,
and I also need to worry about some 'flood affectation' on my property too.

So, that's why I was curious of the slope in your land.

Otherwise, you go for something like this design:
https://imaginekithomes.com.au/plans/varley/

(the garage is all downstairs, and no splits...so living space is only upstairs.

Ashington Homes · Aug 20, 2024 6:08 am

sun99

We are doing knockdown and rebuild in western Sydney. First timer building so looking for some advice and guide here.

It's a double storey house on land with 14 meters wide and sloping towards the street and backyard is in the north. As there is a significant slope, a split slab was suggested. Is it a good idea to cut and fill or go with a split slab? How will the roof heights impact with the split slab approach? Will there be extra costs in bulidling with split slabs?

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Thanks in advance for any advice.

Hi Sun99

I had a look at the plan you posted and below are a couple of answers:

1. On your site you have no choice unless you can afford to do something funky like a basement garage and lift that whole first level out of the ground. That would cost you anywhere from $200-400,000. If you can't do that then you will need a split level. NSW planning laws wont allow a site to cut more than 600mm for most councils and some rarely allow 1000mm. As one other post mentioned, depending what council and geotechnical zone you are in there are also site slippage issues which may require a geotech report and site monitoring.

2. Drop edge beams are $300/sqm.But your builder may charge you more depending on how much profit they want to make. Without seeing your elevations I can not calculate how much that would be in total. If you want to send me your plans I can do a quick measure for you....my email is simeon@ashingtonhomes.com.au as a guide, we are doing one similar and we are estimating $8000 as there are drop edge beams down the site and front of the home as well.

3. Lastly, yes based on the plan you posted your garage height will be 4,000mm and your entrance 3,400mm. I have the same thing in my house. Seriously love it, Embrace the extra storage!

Good luck with your build

Cheers

Simeon

sun99 · Aug 20, 2024 2:38 pm

Denali

sun99

Denali

We completed our split double story in May and your question asks about additional cost and the answer is yes, just due to the complexity of having a less than perfectly flat site. Depending on your site, we required an edge beam and part of our house is 3.3mtrs ceiling (love it) and another is 2.4mtr ceiling in two bedrooms (not a fan but basically unused rooms) and upstairs is 2.7mtrs (which Im use to/had in the old house).

On the plus side, your storm water will be easier to deal with than ours and thats a cost benefit.

Thanks I am ok with 3.3m ceiling at the entrance it will be grand entrance, but only worried with garage ceiling going to 4m
How expensive is edge beam?

Edit: Unable to upload copy of site costs from contract but it was $60K exc the below

Every job is different and this (attached) doesnt include many items, like our storm water $13K, additional slab and piering $10K, power connection/pole, $3K, 2.7mt ceiling upstairs $3K, insulation, double glazing and many other nice to have we picked or the facade.

Thank you Denail, got rough idea on how much it costs

sun99 · Aug 20, 2024 2:46 pm

qrius

sun99

It's a double storey house on land with 14 meters wide and sloping towards the street and backyard is in the north. As there is a significant slope, a split slab was suggested. Is it a good idea to cut and fill or go with a split slab? How will the roof heights impact with the split slab approach? Will there be extra costs in bulidling with split slabs?

What is the length of your land, and what is the rise of over that distance ?

What is the height difference from street to the backyard ?
(or building envelope height difference, from front to back of house) ?

If you can use the contour of the land, and split level design,
you get some interesting internal private spaces,
like 2-3 different "apartments", eg. kids area, guest room, etc.

If you see some display homes for Montgomery Homes [ https://www.montgomeryhomes.com.au/ ], you will get the idea.
I am not linked to them in anyway, but I visited them last year,
because my own land has a slope, and I'm finding that the slope is causing a lot of builders,
to not want to give me plans without a split-level.

Besides, the split-design has other design implications for where my garage needs to face,
and I also need to worry about some 'flood affectation' on my property too.

So, that's why I was curious of the slope in your land.

Otherwise, you go for something like this design:
https://imaginekithomes.com.au/plans/varley/

(the garage is all downstairs, and no splits...so living space is only upstairs.thanks

Thanks Qrius, its 2.5M slop from back to front. total legth is lot is 14.02 x 42.67 . Thanks Montgomery Homes helped to visualize the build and also videos of them explaining pros and cons of split.

qrius · Aug 22, 2024 7:42 am

sun99

its 2.5M slop from back to front. total legth is lot is 14.02 x 42.67

That slope is very, very similar to mine, but my land is a little wider.

I got advised by some normal 'volume builders', that kind of slope will require a small stair case, to rise up about 30cm - 40cm (I think) in the middle of the house.

So, for a double-storey house, even with the stair-case to go upstairs, the ground-floor will have that split.

In the Montgomery Home designs, you get kind of around "3 floors",
so that's how the split works in favour of the land, rather than little riser on the ground floor.

This is all to ensure the total height of the house, does not exceed past whatever the Council has set
(and also if there's any precedence with the neighbours around you).

However, I looked for a design where the entire ground floor can be a basement car park, with the split.
whereas the living area can be on the 2nd floor (and without any splits).
It's hard to explain this words, so that's why I showed the Imagine Kit design,...anyway,
I need to look further into the "cut & fill" requirements too, as I don't know about those details yet.