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How to begin costing


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Whilst we're deciding on architects/designs and all of that kind of thing, I'd like to start getting to grips with costing out our project.  It's a bit chicken and egg because, of course, I can't price up exactly what we need until we know exactly what we want, but I'd like to try and understand ballpark figures.  So, for example, if we have a 200sq m house with a 100 sq m footprint and start with the most basic form of a box, how much wall will I need?  This will allow me to compare the costs of different construction materials, assuming that suppliers are forthcoming with their prices.  Likewise, once I have a basic understanding of vertical exterior wallspace, then I can understand how much cladding we need, how much each type costs, and so on.  Clearly, there is far more to it than this, but I have to start somewhere.  I have the Housebuilder's Bible which is very informative but also a little overwhelming at first.


I don't know how much we will do ourselves in terms of project management, but we have the capacity to do a lot as long as we can understand what it is we are supposed to be doing!  I'm working on the assumption that this will save us money and another assumption that everyone else is out to spend our money for us, but not necessarily on us and our house.  A healthy streak of cynicism has done me no harm in the past.


Any pointers would be most welcome.






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I'll be honest with you, . I found this very challenging.  We used the ball park figs widely available per m2/area/house type and used that to give us an overall budget. 


Going lower level however,  I didn't find the house builders bible very helpful in terms of overall cost. Even at a lower level I found it only vaguely useful. And ICF barely gets a lookin there! 


I think to us being the builder and procuring everything direct, as well as a slightly over engineered/non standard design make it less relevant. I use the HBB as a post-reference rather than my baseline for costs. 


We have the overall budget but just manage everything very carefully as we go through each stage. We have a tracker and should come in on budget if we don't go OTT on the internal fit out. 


In terms of project managing, i would suggest an 'all or nothing' approach - probably limited scope to do only some bits unless you get a main contractor to get you wind and watertight and complete the rest yourself. 

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Pricing a the actual house is kind of the easy bit as you can use the general figures of between £1000-£1500 sqm and you won't be too far away. It's the unknowns that catch you out. What's the ground like as in will be be standard concrete foundations either strip or a slab or do you need it piled. Same goes with the connection charges of all the services as although a house is already there you might get stung if something needs upgraded.

First step is getting a rough design done. Draw it out yourself on paper and make tweaks and then use the like of sketch up to make it 3d. Then when you go to an architect or technican or even a timber frame company you will have it refined to what way you want it. Then it's a case of deciding on the build method and  by this stage then it's easier to get a better view of the costs involved.

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Hi Vivien,

One route (and not the only one by any means) is to engage with a Quantity Surveyor - I'm getting mine for €500-600 but they can cost a % of the build which can = €x,xxx! Just get a reputable / recommended one - the Architects can advise here also. At least you get a baseline cost and can adjust the design and push things in or out budget-wise on an informed basis. Less surprises later on but keep that 10%-20% contingency handy for when they happen! 


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Like any problem, costing is easier if you divide it into chunks.


Site specific services etc- absolutely no point using someone else's figure here, you need to get quotes from the elec, water, gas etc as applicable. For sewerage, I think you mentioned that you would be off mains, so you need to dig some holes and do some percolation testing to get an idea of what options are feasible (my system ended up about double the budget that I had hoped for, entirely down to my ground conditions). Also, access/driveway- will you need to buy in material, how long will the drive be, etc. Will you need special founds like a raft or piles, or will normal strip founds do. This is the hardest bit to cost out.


Basic shell- this is easier to cost out, and you can read up for general ballpark figures. Depends largely on construction type, and how simple the design is.


Fit out- this is where the spend is entirely up to you. Some people spend £50k on a kitchen, some spend a couple of grand. But the costs are pretty much under your control.

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