Area calculation for 2 story extension

donquixte80

Hi,

I am planning to build an extension of size 7m x 5m on the ground floor. On top this extension i am planning to build a 3m & 3m storage room which will be an adjacent room in my first floor bedroom for storage usage.

Every builder quoting me for extension cost is calculating the construction area as 70m2 area (ie, (7mx5m) x2. Is this right? or how should be the calculation of cost needs to be done in this case?

bfclancy2

they are going to charge you their price regardless of what you calculate the area as, if you say it is in fact 41m2 they will just up the price per sqm

donquixte80

Thanks for your reply, for calculation purpose should i consider the external wall to wall distance for total area ?or should i be considering only the internal floor area?

Gumbo

https://www.boards.ie/discussion/comment/121951312#Comment_121951312

you can’t quote an extension by simply using the floor area. Yes upstairs is smaller but it will need a substantial steel structure to carry it as it’s not on the same footprint as the downstairs footprint.

Mellor

https://www.boards.ie/discussion/comment/121951312#Comment_121951312

The internal wall area of both floors is the building area. You don’t need to do calculations.

donquixte80

https://www.boards.ie/discussion/comment/121951847#Comment_121951847

ok, but how do builder's usually calculate the total construction area for cost calculations? they consider internal wall to wall or external wall to wall measure?

Mellor

https://www.boards.ie/discussion/comment/121953624#Comment_121953624

A proper estimate wouldn’t be based on floor area. It would break down the total into floots, walls, roof etc.

If a builder wanted to do a very quick price he might use ground floor area and use different rates for single story flat roof, pitched roof, converted attic, and two story.

bleaks

https://www.boards.ie/discussion/2058343913/area-calculation-for-2-story-extension

Just curious, how much are you being quoted for this, and what part of the country are you in? Or if anyone else has quotes for similar sized 2 story extension jobs.