Finger in the wind estimate of extension cost

FreeBear

Doozergirl said:  National Building Regulations were only introduced in 1986.

A bit earlier than that... Building regulations kicked off after the Great Fire of London in 1666 which, whilst only covered London, was loosely adopted by other towns & cities. Various changes were made in the (many) years that followed, but it wasn't until 1858 when central government set out guidelines for local bye-laws regulating buildings. Most local authorities adopted the recommendations, but standards & enforcement was not consistent across the country. National building regulations were introduced in 1965 via various pieces of legislation. The Building Act of 1984 finally set the foundations of today's building regulations and inspection/enforcement framework.

For foundations, UWE has some useful history - https://fet.uwe.ac.uk/conweb/house_ages/elements/section1.htm

It is unlikely that a garage would have sufficient foundations to support a second floor especially if it is only single skin brick construction. However, that doesn't preclude extending over the garage - It may be possible to do some piling, insert steel supports/framework and build a lightweight structure on top. Piling & steel isn't going to be cheap, so demolition may work out a more cost effective solution.

Doozergirl

Silvertabby said:

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.

Different rules apply to attached and detached garages.  A detached garage is usually classed as an outbuilding and so the regs don't apply at all.  

Silvertabby

Doozergirl said:

Silvertabby said:

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.

Different rules apply to attached and detached garages.  A detached garage is usually classed as an outbuilding and so the regs don't apply at all.  

Just remembered - she also wanted a covered walkway, linking the first floor landing of the house to the granny flat..... 

stuart45

There are methods of building over a single skin garage, either using steels on piers, or can be as simple as 3 joists bolted together to take a timber frame for the inner skin.

daivid

FaceHead said:

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. 

Thank you. £100k - £150k would be viable. Do the other knowledgeable people on here think it is a reasonable estimate?

Doozergirl said:

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.  

Thanks for your input Doozergirl. It is indeed an attached garage, built (with the house) in 1974. Part of the garage is house in that under the 'garage roof' is the hall, downstairs wc and utility, wether this has any bearing on the standard of foundations and walls, and what the standards were at the time I (clearly!) have no idea. 

stuart45

Foundation's in the 70's were normally around 3 ft deep, with 9 inches of concrete at the bottom, depending on the ground. Is the garage.part of all a cavity wall?

daivid

stuart45 said:

Foundation's in the 70's were normally around 3 ft deep, with 9 inches of concrete at the bottom, depending on the ground. Is the garage.part of all a cavity wall?

I think not. The house has cavity walls of block and brick, the garage walls don't seem to be thick enough for there to be a cavity.

Rosa_Damascena

Doozergirl said:

Silvertabby said:

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.

Different rules apply to attached and detached garages.  A detached garage is usually classed as an outbuilding and so the regs don't apply at all.  

Mine was detached, and combined with neighbouring trees and approximately 0" of foundations, was rapidly subsiding. It's now got 2m of thick foundations ready for a second floor should the fancy take me, and that's where a lot of the build money went. 

stuart45

daivid said:

stuart45 said:

Foundation's in the 70's were normally around 3 ft deep, with 9 inches of concrete at the bottom, depending on the ground. Is the garage.part of all a cavity wall?

I think not. The house has cavity walls of block and brick, the garage walls don't seem to be thick enough for there to be a cavity.

Very often another storey can be built on top. Obviously it would need to be checked on site.