# Forum Home Renovation Structural Renovation  Two storey v extension

## g_coopster

Hi All, 
I know this is perhaps has the potential to be a stupid question with all the possible variables involved ............. however here goes anyway !! 
Would there be a great deal of difference cost wise between adding a second storey vs adding the same floor space to an existing single storey floor plan? 
For example, say we wanted to add around 7m x 5m 
Would a second storey be in the order of twice the price? Deceptively comparable?? 
Very curious as to your opinions & thoughts! Someone asked me recently if we had considered a second storey as a option for our extension. To be totally honet, I had never considered it and don't even have a valid reason why!

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## Haveago1

Depends on how complicated the additional space would be to construct around your existing footprint and roof structure and how much inconvenience you are prepared to put up with during the process.  
Obviously a second storey requires some roof rejiggering and affects the area underneath (at least for stair access) whereas a ground floor addition does not.....bit more detail on what the additional space is for (bedrooms, rumpus, bathroom etc), existing building layout/fabric and how it is all going to mesh together may allow a better response to your query.  
There are standard building guides for estimating costs on a generic basis if you just want a ballpark idea.

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## GraemeCook

I asked that question to an architect thirty years ago when I was thinking about extending into an attic room.   Amongst the points he made were the following: 
*  With a second floor you must deduct space from both the ground and upper floor for the stairwell. 
* Alterations to roofs can be difficult and expensive. 
*  The original structure must be capable of bearing the increased loads, or expensive engineering may be required. 
* In my case, federation house with double brick external walls and brick internal walls, I would get the most value for money (ie (M2 per $ spent) by jacking up the roof and putting an entire new floor in basically replicating the ground floor. 
* Planning rules may be inconsistently interpreted. 
In the end, with a combination of reasons including council planning processes, heritage commission, national rust and the busy body on the corner, we decided it was easier to move than extend. 
Cheers 
Graeme

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## g_coopster

Thanks for the feedback. 
Thinking aloud, any second storey would probably only include 2 kids bedrooms and a bathroom. It would also be small enough to well & truly fit within the fooprint. Our current footprint is a simple H pattern & I would envisage that we could duplicate the horizontal joining part of the H pattern as a second floor. 
I note the issues you have both raised, particularly with the loss of floor space on both floors for any staircase. It's a strange one, in some way, building up would possibly alllow us to sacrifice a bedroom (smaller) to make room. 
I am pretty sure that it will be a path we don't choose to head down however I still felt it worth asking. 
In the long run, it may be easier to deal with the cost & disruption by moving an extrnal wall here & there than the inconvenience of adding a second storey!

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## Haveago1

By all means debate the pros and cons, but unless you are restricted by the size of your block or want to take advantage of a view, I would think a ground floor addition would usually work out cheaper than a 2nd storey addition. Also has the advantage of not being so disruptive to everyday life as work progresses 
Then again, if you are doing a ground floor addition outside your existing footprint, is it worth considering making that part 2 storey? In that circumstance the extra cost is much more reasonable if you are doing both from scratch as it can be designed and built concurrently....a nice big parent's retreat?

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## ric_b

Hello all, 
I wonder if anyone can advise me (pro or con) about adding a second floor to an existing house.  I have an AV Jennings Kit Home.  It's a brick veneer home.  
From what I understand so far from the discussion, my foundation/slab might not be good enough to support a second floor.  Is it still possible to build up?  What costly engineering work will have to happen to accommodate the extra floor?  :Yikes2:  
Thank you all for your time and advise.

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## brissyboy

Hi Ric B
It is definitely possible. One thing you can do is place steel right over the top of the existing building to support it all. depending on size of existing house you may need to put a post in the middle. I have seen it done were they actually put verandahs on both sides with stell beams reunning alll the way through. was very effective. if it is an avjennings you may be able to get the original engineering plan out of them for your build and that will tell you (or the engineer more) 
good luck

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## Black Cat

You may find that your neighbours object to a second storey where they might be happy to live with an extension. Consider whether raising the roof will reduce their privacy or possibly impact on their solar access. If either of the above, then you may have a neighbourhood battle on your hands. 
Also, unless you have a steeply sloping block, and extension will probably work out a lot cheaper and give you more floor space for the same expenditure ...

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## DvdHntr

Ric B, 
Be careful with this one. The piers/footings have been designed for single storey only and if you are not on a rock or very stiff clay strata the extra weight could quite possibly cause an over loading and extra settlement, which will crack brickwork. 
Best advice is to try and get plans and to ask the engineers on the plans the advice, they would be the only ones to have a record of the sub strata conditions and any pier locations and depths. 
Also any internal columns would not be acceptable and would most likely need to locally cut out the slab and pour in a pad footing. 
What is the age of the house?

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## dazzler

Dont forget to factor in the cost of land that you are going to cover with an extension that may be of value for resale. As blocks get smaller useable land is of value.

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## Moondog55

We just had our house re-stumped, NOW we are talking about adding the extra story. 
I want a BIG room for listening to music and watching movies, we can pull out a wall with few problems and little cost but where would wwe sleep?? 
Just what is involved in adding a second story to a weatherboard house built on stumps?? 
This is an interesting building, ex housing commission, built 1950, the house was made off-site in 2 halves and brought to the site on a semi, then bolted together ; this means the center wall is 8 inches thick 2 layers of 4 * 2 Hardwood walls,rafters joists etc:  are hardwood

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## Bloss

> Just what is involved in adding a second story to a weatherboard house built on stumps??

  Mostly lots of cash and a fair bit of disruption. Most things are possible given time and enough money - but some are better than others. Going up is rarely the cheapest option, but if space at ground level is restricted then your choices are limited anyway. There are still many companies offering the 'cape cod' type additions that place modularised and lightweight framing and cladding extensions above the existing level. 
This requires engineering advice based on the specific existing structure - not really something that this forum could or should be giving except in the most general terms IMO. It is standard building though - need to have a way to get the net increased load of the new structure carried through the ground (ie; roof structure will be removed and a new structure plus its roof will be added). That means not just the timber framing, but the foundations - and that's where it can get tricky. 
Especially on reactive soils (mainly clay), but more generally too, the minimum specs for foundations have increased over the years and most certainly since 1950. Any extensions will need to comply with current BCA and although that can be done it will cost more to modify or bypass existing foundations to support a new floor than to build a ground level extension. 
Of course if getting views is the main driver that's a different set of choices about how much you are prepared to pay for the view vs more space or same space for less money on the ground. 
So - have a look at the options, but if you can do it at ground level you'll get more space for your buck.  :2thumbsup:

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## Cecile

> This requires engineering advice based on the specific existing structure - not really something that this forum could or should be giving except in the most general terms IMO. It is standard building though - need to have a way to get the net increased load of the new structure carried through the ground (ie; roof structure will be removed and a new structure plus its roof will be added). That means not just the timber framing, but the foundations - and that's where it can get tricky. 
> Especially on reactive soils (mainly clay), but more generally too, the minimum specs for foundations have increased over the years and most certainly since 1950. Any extensions will need to comply with current BCA.

  The just-finished restumping specs are for single story, 600mm deep 100x100 concrete on 450d min concrete pads.  It was only afterwards that he started to contemplate the possibility of going up.  I'm not actually convinced, used to be in the building industry some years ago and have a general idea about what's required.  Very deep pockets and a lot of patience.

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## Moondog55

> What Moondog didn't mention is that we have JUST finished restumping and the specs are for single story, 600mm deep 100x100 concrete on 450d min concrete pads.  It was only afterwards that he started to contemplate the possibility of going up.  I'm not actually convinced, used to be in the building industry some years ago and have a general idea about what's required.  Very deep pockets and a lot of patience.

  That is 100*100 stump, hole size is 300 * 300 * 600 deep 
My argument is that I do not want to loose any garden bed or chook room

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## Bloss

> That is 100*100 stump, hole size is 300 * 300 * 600 deep 
> My argument is that I do not want to loose any garden bed or chook room

  Duh - that's what she said .  .  .   :Biggrin:  
Going up rather than out makes for some damn expensive chooks and veggies!   :Rolleyes:

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