How to check foundations for RSJ

[JDWHughes]

Hi,

I am 3/4 of the way through a loft conversion and have decided to do a bit of extra work to expand the kitchen slightly by incorporating what is currently my porch.

I need to install a beam to support the floors and walls upstairs. I have done the calcs for the beams but now need to check the foundations. the beam will be supported on 2 piers which will be left from the existing external that the beam is being installed in place of.

I'm guessing i need to excavate to find out what the foundations are actually like (1880 terraced cottage external wall). Once I have done this how to i check if they are sufficient? I can calculate the loads on the piers and the footprint to get a bearing pressure buut how can i tell if the existing foundation/footing can withstand the new bearing pressure?

Thanks

P.s. please don't tell me to ask a SE because my hose might fall down

 

[tony1851]

The truth is, you can't tell- it's mostly guesswork unless you pay ££££ for soil testing.

If it's 1880s, the foundation will most likely be one or two courses of bricks laid width-wise to form stepped footings.
If the span of the beam is not too great, and the brickwork each side in reasonable condition, it will probably be OK as the
load disperses as it goes down the wall, and becomes spread over a wide area of foundation.