SE specifying foundation underpinning for RSJ

[turpis]

I've had an SE come up with specs for a RSJ to support a 2.6m span of a load bearing, internal wall (see floorplan below)

Within their specifications they 'assume' a 600mm wide / 800mm deep concrete trench foundation, and suggest underpinning if this is not the case.

Given the house is from the 1930s, the foundations are all but guaranteed to be much smaller than this, and underpinning would be far too disruptive and costly.

This exact work has been done on millions of houses of this type, neighbours and friends included, and I've never heard of underpinning being needed except for huge spans or 'goalpost' structures.

I have already gone back to the SE to ask if they have overdone it on the foundations, and also sent the plans to the BCO who will review them when time permits.

Is the BCO likely to waive that part of the structural plan?

Otherwise, what are my options? New SE? Private building inspector?

 

[stevie888]

Certainly seems OTT to go deeper than existing, but not uncommon to have to create pads. You have a fairly small beam so my sense is that the SE is being overly cautious (though this is not a totally bad thing).

Certainly ask him if he's sure but no BCO is going to tell you your SE has overdesigned something and a lesser design will do.

Others may disagree but I always advocate LA BC: there are too many horrer stories about private

 

[noseall]

I've had an SE come up with specs for a RSJ to support a 2.6m span of a load bearing, internal wall (see floorplan below)

Within their specifications they 'assume' a 600mm wide / 800mm deep concrete trench foundation, and suggest underpinning if this is not the case.

Given the house is from the 1930s, the foundations are all but guaranteed to be much smaller than this, and underpinning would be far too disruptive and costly.

This exact work has been done on millions of houses of this type, neighbours and friends included, and I've never heard of underpinning being needed except for huge spans or 'goalpost' structures.

I have already gone back to the SE to ask if they have overdone it on the foundations, and also sent the plans to the BCO who will review them when time permits.

Is the BCO likely to waive that part of the structural plan?

Otherwise, what are my options? New SE? Private building inspector?

View attachment 377398

Looking at that arrangement and loading, I'd say you will be fine. I doubt the inspector will bat an eye.

 

[^woody^]

You have used an inexperienced engineer who has designed from his uni coursework.

If the engineer won't come to his senses, then ask for the design to be in two parts - one for the beam, one for the foundations and just submit the beam design

 

[stevie888]

Just for interest OP, what size steel does he reckon you need?

 

[turpis]

Just for interest OP, what size steel does he reckon you need?

178x102x19
The unfactored load is 54.3kN, factored is 76.8kN

 

[noseall]

178x102x19

Piece of cake.

 

[turpis]

Could the suggested foundation size be due to the reduced size of the walls it is bearing onto?
The factored load of 76.8kN distributed over the 2.6m span of existing wall comes out to 29.54kN/m
With the 2.6m span of wall removed, that only leaves 1.1m (total wall width = 3.7m) which is 69.82kN/m or a 2.3x increase

 

[turpis]

SE has revised the foundation requirement thankfully so crisis averted