Hi there,

 

I'm hoping one of you guys in the know can help with a few fundamental questions please 😀 

 

We have a single storey (double brick, no cavity) garage adjacent to the house, that were looking to extend over, with a sloping tiled roof

 

The architect & builder we spoke with viewed the garage & suspects the foundations might not be deep enough, & if this is the case suggested we may need to demolish the garage, ripping up the foundations & laying a new deeper foundation to start anew. The builder with him said somewhere around £20k for undertaking this

 

We weren't sure if this sounded a reasonable price for a 8m x 3m, but I can't imagine it'd be cheap.

 

It got me thinking: whether helical piles, or some other alternative might be just as good & a little cheaper?

 

Obviously we'd need to consult a structural engineer 1st, if we consider this. But wondered if anyone had experienced similar with insufficient foundations & had any advice?

 

Whatever happens, we'll only know once they dig down (the builder agrees nobody knows for sure till we excavate)

 

But any up front knowledge for your genius is most welcome 😀 

 

 

Thanks for your time

Shadow

 

 

Edited September 26, 20251 yr by SilverShadow

Could you do the extension above in timber frame. Stick built. Clad on the outside ? That way you would not be putting much additional load on the foundations.

Hi Jimbo, that's a good shout & something to bear in mind

 

We were hoping to have brick if possible, so it's in-keeping with the rest if the house. 

 

But it's a great alternative for saving a few ££

Edited September 26, 20251 yr by SilverShadow

' ... suspects the foundation might not be deep enough ....' 

 

And we all know that the architect's arse is now covered because he suspects . Everyone in the food chain you will be feeding is reducing their own exposure to liability and risk.

The only way of countering suspicion is with hard evidence. Get it.

 

Ask someone (you?) to dig down and look at the current foundation profile and / or have a couple of appropriate depth cores taken by a geotechnical firm. Send those results to a suitably qualified SE.

 

Spot ok, TBC - it's purely an arse covering exercise. But as you say, nobody can be sure yet

 

There is 2ft of cracking right through the bricks in 1 area, which I showed them, that's likely the reason for their suspicion

 

 

Thanks for your replies so far, guys

 

Do you guys reckon our next step is to hire the prowess of a structural engineer? I'm afraid I wouldn't have a clue, as regards foundation depth/suitability

 

If you think it wise, then I guess we could employ someone now & do this independently of the builder & architect

Easy enough to just dig down besides the foundation in a few places to see how deep it is and how it’s made. Probably a couple of hours work for someone who likes digging. My big question with those is how long will they last?

Edited September 27, 20251 yr by Alan Ambrose

Yes, helical piles are a solution.  They are often used to underpin, but you do need SE advice.

Thanks Adrian - always great to get a x-section of opinions, but also fab to know that's a viable alternative! 😀

 

One builder did use the word 'underpinning' when talking about the extension foundations, so perhaps he was referring to this as an option instead of relaying the foundations...

Hi - chartered structural engineer here. Definitely dig your own trial pit, take dimensions of the foundations - width from the wall face, depth, note the founding strata (clay, made ground etc), take photos. This is the first thing I would ask for. 
But if you have cracking already, sounds like you already have problems. Could underpin with mass concrete but time consuming, do mini piles or screw piles, loads of options or potentially just re-build might be easier to get the extension you want. 

20 hours ago, Sophiesbuild said:

...But if you have cracking already, sounds like you already have problems. ...

 

 - and so you need a properly qualified opinion from a reliable, trusted professional source. We buildhubbers are merely nosey, interested amateurs.