2 Storey home extension - cost estimate advice needed

dinoman

Hi all,

We are buying an existing 1950's house with the plan to extend it. In a nutshell it will be a 2 storey extension where the ground floor will see the existing kitchen extended, new shower room downstairs and study room. On the upper floor there will be new family bathroom, ensuite, bedroom extension and an additional bedroom at the rear added. Total new extension part approx 85metre.sq.

Before we even start we wanted to grasp more accurately how much this project will cost us.
We've been told there is a good rule of thumb being a cost per metre/sq we can apply. Which is ground floor £1500/metre.sq and first floor £750metre.sq.

But we have no idea what this does or does not includes. We don't want to proceed on this basis assuming everything is included as that would be risky to our budget. Because we know it will not be. We was wondering whether this would be include: windows/doors? All drainage / Insulation / Roofing to new part of extension?/ Internal plastering and decorating? electrics / plumbing? Flooring? 
Does anyone here know what this might be included or not? Or any other better rules of thumb we can apply? 

We have so far only allowed separate cost for Architect/structural engineer fees / Kitchen fit out and some loose furniture.

Any advise from people with experience would be much appreciated!!
Thanks. 

Doozergirl

Not a good rule of thumb.  That comes in at an average of £1,125 per square metre, which wouldn't build you a basic new build box.  

I really think the minimum for any standard has to be £1500 a metre but there is no rule because it depends on how you build and also the design and the cost effectiveness of it.    Kitchens, bathrooms, flooring etc need adding to that, as does any consideration of renovation to the existing property.  

You're proposing something as big as a small three bedroom house.  

dinoman

Doozergirl said:

Not a good rule of thumb.  That comes in at an average of £1,125 per square metre, which wouldn't build you a basic new build box.  

I really think the minimum for any standard has to be £1500 a metre but there is no rule because it depends on how you build and also the design and the cost effectiveness of it.    Kitchens, bathrooms, flooring etc need adding to that, as does any consideration of renovation to the existing property.  

You're proposing something as big as a small three bedroom house.  

Thank you. Good to know and we appreciate every build will be different depending on complexity. This is why we want to try and keep it simple and make sure we are comfortable with the costs.
In your mind - would the £1500 per sq metre, include all the basic interior plastering and windows and doors or would all those be extra aswell?
The existing house is a basic 3 bed semi-detached. We want to turn it into a 4 bed property.

ComicGeek

It's not cheaper in all areas of the UK to extend rather than just buying a bigger house in the first place. Does spending £150k-£200k plus professional fees on an extension in your area make sense?

dinoman

ComicGeek said:

It's not cheaper in all areas of the UK to extend rather than just buying a bigger house in the first place. Does spending £150k-£200k plus professional fees on an extension in your area make sense?

Exactly our thoughts and this is what partially concerns us. Hence wanted to understand the costs to see whether it's a like for like comparison.
The nearby house prices for those that have been converted into 4 beds already (but not to a layout that works for us) - are telling us it's worth doing - but only if we can keep the total extension costs to circa 160K. 
However, saying that, we of course plan to live in this for a very long time, so assume house prices can only go up we technically will most certainly re-coup what we paid as a minimum - should we sell in the future.
It's the uncertainty with cost etc - having not done this before that worries me....

Doozergirl

I'd need an idea of the house and projected floorplans to come up with a gut feeling figure.   

Grumpy_chap

£30k for ground floor.
£20k for upstairs.  Flat roof.
They were our costs 15 years ago, so add inflation.

Any extra for your taste and desires.  Kitchen, for example, could cost £5k to fit out or £105k. Same for the bathroom.

This is really too broad a question for an internet forum because of the many variables and assumptions involved.