Foundation depth check

[Timberframeguy]

Hello there - I’ve had the attached design from our SE for a garage conversion with a second storey above.

 

My builder has said the footing depth of 670 is ‘ridiculous’ and I should look to have this redesigned as it’s complete over kill. Can anyone shed any light on this? Thanks 
 

Normal ground, no trees nearby. 

[nod]

Your SE will probably no more about ground conditions than your builder 

670 isn’t deep 

Our last build was 1800 detached garage also 

[Timberframeguy]

Thank you for your reply, the total depth is 900 with a 670 depth strip. 1800! Wow

Edited May 22 by Timberframeguy

[ETC]

I’m presuming your SE has two things on his or her mind:

 

1. The foundation is asymmetrically loaded.

2. He doesn’t want to get sued if shit hits the fan.

[Temp]

Did you dig a test pit to check out the foundation depth of the main house? 

 

 

[Timberframeguy]

8 hours ago, Temp said:

Did you dig a test pit to check out the foundation depth of the main house? 

 

 

We didn’t, this wasn’t requested. 

[Gaf]

I'm just a civilian but have done a build and run into trouble between the various professionals involved. I am currently going through some structural issues requiring remediation and, based on my experience, I would trust your SE above all others. I've had the 'ridiculous' comments and the 'overengineering' comments thrown at me when communicating the SE's evaluations - but everyone went quiet when the SE produced the data. Your SE will be the one who can provide the most robust rationale via calculations cross referenced to building regulations. Everyone else, in my experience, will provide unbelievably confident opinions but if things hit the fan, opinions will count for naught. 

 

Based on my conversations with an SE, base foundation depth of 600mm is a minimum best standard to ensure your deep enough for suitable soil stability and frost protection, so (although just a civilian) this doesn't look ridiculous. 

[Timberframeguy]

Thank you for your reply. Building inspector is due round on Friday so I’m sure they will also have something useful to add.

[G and J]

If our experience is anything to go by the BCO will simply ensure the SEs design is followed.