Finger in the wind estimate of extension cost

daivid

Any ideas of the ballpark figure to build above a double garage. The plan would be to add a good sized bedroom with walk-in wardrobe and a bathroom (sink, wc and decent sized bath). The waste pipe for bathroom should be fairly straightforward as would be above an existing bathroom. I would want the roof to be sloping, coming of the main roof to form a T shape. No idea how much strengthening of the existing garage (double brick) would be needed.

This is just an idea at the moment, to be done when equity could be released from the mortgage in a few years time so I don't want start getting quotes yet. On the North Wales/ Cheshire border if that helps for labour rates.

Thanks in advance.

ic

Twelfty pounds.

Rosa_Damascena

Can your garage actually support a FF extension? If not, it will send costs way into the stratosphere.

GDB2222

Extensions usually cost around £1-2k per sq m.  That sort of ball park. It's possible that you'll need to knock the garage part down and rebuild it. 

ka7e

Builder's merchants can't guarantee their prices for the next 3 months, let alone a couple of years.

FaceHead

The foundations of the garage will almost certainly not support the addition of a first floor to the standards of a modern building controller. 

It seems rather unlikely that someone built unnecessarily deep foundations in case they wanted to add a floor above, decided not to, and then you've come along, seen the garage and had the idea to build the first floor that the original planner intended but decided against. 

So, cost to knock down a, say, 7m x 7m double garage (=49msq) garage and replace with two floors of 49 msq each... obviously a massive number of variables, but ballpark 75k (say 1.5k per msq)  to a plastered finish, and 15k might cover kitting out a bathroom decorating the 3 upstairs rooms and reinstating the garage downstairs. 

Architects, planning, building control, engineers etc. plus the big factor of choosing the nice tiles etc. means I'd congratulate you if you kept it under 100k. I'd need at least 125k up my sleeve to consider this. Cost could easily hit 150. Running out of money half way is never good, so it's always critical to have access to further cash and then do your best to avoid needing it. Three years of inflation, the way things are, as potential to add 10k. 

Rosa_Damascena

GDB2222 said:

Extensions usually cost around £1-2k per sq m.  That sort of ball park. It's possible that you'll need to knock the garage part down and rebuild it. 

This may have been true a decade ago, its a different economic scene now.

Rosa_Damascena

FaceHead said:

The foundations of the garage will almost certainly not support the addition of a first floor to the standards of a modern building controller. 

It seems rather unlikely that someone built unnecessarily deep foundations in case they wanted to add a floor above, decided not to, and then you've come along, seen the garage and had the idea to build the first floor that the original planner intended but decided against. 

You say that, but there are plenty of historic build-over garage extensions on 1930s-40s properties, whether the garages remain as garages or they are converted into living accommodation. The same applies to 1970s-80s brick cornflake packets. Has BC suddenly become so much stricter?

Doozergirl

When you say sudden and refer to 1970/80, that's my entire lifetime!  National Building Regulations were only introduced in 1986.   Someone a bit older and wiser than me can probably say when minimum foundation depths were introduced across the board, but I suspect it was around then.  

We lived in a house with an extension that had been added onto in the 1990s and that was underpinned to comply with minimum depths.  

Whether the OPs garage needs underpinning or knocking down depends on when it was built. 

An attached garage (which I'm assuming from the OP) built in the last 30 years will have adequate foundations for a second storey, so what FaceHead says about 'unnecessarily deep' foundations for a single storey has not been a thing for a good amount of time.   The depth needed to provide solid ground for a single storey is the same as that for two.  

All we know is that the OP's garage is double skinned.  That doesn't answer any questions in itself.  

Rosa_Damascena

Double garage suggests to me 1970s/80 build. Something like this, for example:  

Silvertabby

A friend wanted to add a granny flat on top of their late 1990s build stand-alone double garage.  Despite being double skinned, the foundations were nowhere near suitable, meaning the whole lot would have to be pulled down and proper foundations dug.  She didn't even bother getting an estimate for that.

On the other hand, houses on the same estate which were  built with integral single storey garages could and have built over the top, as the foundations were built to the same standard as the house.