Extension over integral garage

Brebal

I’m considering options for extending my house and looking at building over the existing integral garage to add an extra bedroom. Firstly, I need to know if the foundations are sufficient. If I have to demolish the garage and start again, that rules this out, it’ll be too expensive.

So, Who do I get to check the foundations? A builder? I know they have to dig down.. there’s block paving at the back and tarmac at the front. Is it a big hole? Will it be able to be filled in and restored to normal?
I’m not sure if the garage was built at the same time as the house or added on... don’t know what the chances of the foundations being good enough are??

If the foundations were suitable, how much roughly would building over it cost? I’ve seen estimates for single storey extensions of about £1k-2k per square metre. Is that the same even though there’d be no foundations to dig?
(I’m in the north of England, fyi)

Any help/tips/advice is appreciated?

Thanks

SHAFT

Are you sure it's an integral garage?

If it is it must have been built at the same time as the house.

George_Michael

Integral garage foundations are normally the same as the rest of the property.
The main reason for this is to reduce the possibility of differential movement between two different specifications of adjoining foundations which could result in cracking or separation of the structure.

Davesnave

The usual method to check is to dig holes on the side and rear elevation, exposing the foundation to its full depth.

If a mini-digger can be used this will be easier/quicker. A manual hole ends up about a metre square. It's best done at this time of year, rather than winter, when it may fill with water before completion.

markin

Its not an Integral garage is it? that means inside, What you describe sounds like attached garage.

Brebal

I was under the impressions a garage that is attached to the house is called integral if it has a door providing access into the house. Is that wrong?

Robin9

An integral garage is an attached garage that is built within the walls of the main property and is an element of the building's structure. These garages can allow admission to the house through an integral door.

I have similar built as such.

What I think you have is a single story built (possibly as new) attached to the main building.

In addition to the foundation concern what is the ceiling made off - asbestos ?

Brebal

Ah, I’ve been wrong all these years!!

It’s single storey attached to the house, with a door through to the house, as well as one to the garden, and the main door at the front.

I don’t know about any asbestos. I can see rafters and some sort of felt covering above them. The roof is tiled the same as the roof of the house.

Brebal

I’ve been searching planning records and the garage was built in 1995, if that gives any indication of anything.

TELLIT01

To me, rightly or wrongly, an integral garage is one built within the footprint of the house, not one on the side of the building irrespective of whether there is direct access. What the OP describes is, to me, an attached garage, but that's really incidental to the question.
To check the existence of suitable foundations a hole about a metre square will need to be dug. Another problem is going to be a single skin wall to the garage. That will not be able to support another storey above, so a second skin would need to be constructed, probably inside the existing walls. That will narrow the floor space by 6 to 9 inches and will shorten it by roughly twice that amount.
If, as is actually likely, the garage wall is built directly off the concrete raft floor of the garage, I don't think it would comply with building regs to add an upper floor. The only option then would be demolition and start from scratch.

Mistral001

There could be more than foundations that need to be thought of. If the existing garage is not a cavity wall and you want to build an extension over it which does have cavity walls, you are likely to need steel beams to support the extra skin of wall.


With regards to the foundations, these and any other structural elements will need Building Control Approval. They will or your architectural designer will advise you on what is required to satisfy the Building Regulations.