Balcony foundations

[bluebaron]

I am adding a self supporting balcony to my house. It will basically be a large 6x2m raised deck.

I'm planning on placing 4 or 5 150mm oak supports on the outside with a 6m 6x2 attached to house via either resin bonding or masonry bolts.

What type on foundation do you think will be required for the oak supports? BCO it coming back with 1m3 which seems a bit overkill to me?

Ground is basically 600mm clay then hitting shale.

Thanks for advice.

 

[noseall]

What type on foundation do you think will be required for the oak supports? BCO it coming back with 1m3 which seems a bit overkill to me?

Unless you pay for an SE to prove otherwise then you are best off going with the advice of the BCO. It's a fairly generic go-to standard foundation for a point loaded column. Look at the savings (or not) of either method. An SE might just end up speccing the same.

 

[bluebaron]

Seems silly that you can build a deck off a breeze block when 3" inches of the ground and it stays put for years but as soon as you elevate it then start digging!

Still thought that would be the case, better get the space out and start digging! Thanks

 

[John D v2.0]

Doesn't seem silly to me, the forces on a ground level platform are smaller and if it collapses or moves the consequences are less bad.
Don't forget that when you ask an SE to design something he is insuring against anything disastrous happening. Suddenly a couple of bricks to spread the load doesn't seem prudent to them as they're not paying to build it, only if it fails.

 

[freddiemercurystwin]

1m3 is bonkers, this was the last one I submitted to BC and was approved (without SE intervention):

 

[^woody^]

How deep is that? And on rock or sand? Asking for a friend.

 

[freddiemercurystwin]

Devon shillet just under the surface, basically it's slate on it's edge.

 

[noseall]

Devon shillet just under the surface, basically it's slate on it's edge.

Does Devon shillet have the same bearing pressure characteristics as clay?

 

[noseall]

Doesn't seem silly to me, the forces on a ground level platform are smaller and if it collapses or moves the consequences are less bad.

Correct. The taller the column the greater the exaggeration the movement will be (at the top) should the foundation decide to tilt. However, 1m cube per hole is a lot of digging and a lot of conc.

 

[bluebaron]

Well the guy that built my porch which is 5m x 1.5m just dug the posts in with post mix about 2 foot deep 200mm oak posts 2.4m.

That's supporting about 400 clay tiles and rafters!

 

[^woody^]

Yeah, and the bloke that dug the footings for Warwick Castle near me, just went down a couple of foot. The world has gone mad.

 

[John D v2.0]

Yeah, and the bloke that dug the footings for Warwick Castle near me, just went down a couple of foot. The world has gone mad.

That was the job that made your reputation wasn't it woody?

 

[freddiemercurystwin]

Does Devon shillet have the same bearing pressure characteristics as clay?

No, more like rock, when you hit the shillet BC don't expect you to go any further. Then there's the drain that needs a lower foundation anyway and then the digging gets fun!

 

[^woody^]

That was the job that made your reputation wasn't it woody?

Nah, I only did the Homebuyer survey for the Earl ,and then the LDC for the state room extension for Liz's visit. What a knightmare that was - planner said it was not PD! I think he's still hanging up in the Gaol.