Different finished floor level between attached garage and house. Footing detail?

[flanagaj]

The attached single storey garage of our house has a finished floor level 450mm higher than that of the house and I am trying to work out how best to do the footings.  My original idea was to simply dig the footings of the garage to the same depth as that of the house and then just have an additional two course of blocks.  I mentioned this to a builder and he said that nobody will want to be in the trench to do the blockwork and instead I should just pour an additional 450mm of concrete. 

So I am a bit confused as to how to proceed.  I have read on the NHBC guide about stepped footings, but not sure how this works with the adjoining cavity wall that is shared between the garage and the house (see below)

[JohnMo]

Don't you have a design from either the structural engineer or architect or both?

 

You normally have a stepped strip foundation, but this is normally detailed on your drawings.

[flanagaj]

Just now, JohnMo said:

Don't you have a design from either the structural engineer or architect or both?

 

You normally have a stepped strip foundation, but this is normally detailed on your drawings.

The technical architect didn't provide details and the SE was as much use as a chocolate teapot

[Mr Punter]

1 minute ago, flanagaj said:

SE was as much use as a chocolate teapot

 

Get them to do the drawings and spec.  You don't want to be designing this yourself or winging it on site when you have paid a professional to do this.

[flanagaj]

Just now, Mr Punter said:

Get them to do the drawings and spec.  You don't want to be designing this yourself or winging it on site when you have paid a professional to do this.

Ok.  I will see if I can find another SE who is local to us.

[JohnMo]

1 minute ago, Mr Punter said:

 

Get them to do the drawings and spec.  You don't want to be designing this yourself or winging it on site when you have paid a professional to do this.

And don't trust your builder to make engineering decisions - he isn't qualified 

[saveasteading]

17 minutes ago, Mr Punter said:

when you have paid a professional to do this.

But perhaps they haven't. What was their brief? 

[flanagaj]

1 hour ago, saveasteading said:

But perhaps they haven't. What was their brief? 

I enlisted an SE 'Barrat Associates' online job.  I am most likely to blame, they were quick and cheap.   I sent across the building control drawings to them and got back nothing more than the structural calcs for the steels.  I wasn't sure what to ask for, so I said I want full calcs for the drawings.  These were submitted to building control and they signed the drawings off.

[Nickfromwales]

1 hour ago, flanagaj said:

Ok.  I will see if I can find another SE who is local to us.

You don’t need local, it’s a desktop job .

 

If you need someone just PM me. 

[Temp]

Ok so the issue is where the higher garage founds meets the lower house. The ground must slope down to the house in this area so you also need to think about drainage and the visuals. You don't want to be looking at exposed concrete.

 

I would expect a standard stepped foundation a few feet along the garage wall away from the house depending on how the ground rises. Some engineered bricks might be needed where partly burried?

 

Check ground levels carefully to avoid the wall of the house accidentally becoming a retaining wall.

 

I agree an SE needed to design how the garage floor slab abuts the house.

Edited 3 hours ago by Temp

[Russdl]

@flanagaj I presume you won’t be attempting to access the garage from within the house? And if not, why are you planning an ‘attached’ garage and not ‘detached’?
 

Detached would be a whole lot easier I suspect.