Wall Foundation

[sleepyjohn]

I'm transferring this from DIY as no replies.....

Hi

I am presently preparing a plan and spec for building a third, en-suite, bathroom as an addition/extension around the corner of a house. An existing, second, bathroom on the same side has started leaning off the main house by an inch and more at the top suggesting soft soil or settlement as the water pours off the roof for a year or two (house 8yo). It's a fairly sizeable and proper house and no settlement elsewhere so maybe this other second bathroom was added as an afterthought.

The new one will have a typical single thickness block wall with a mortar finish only averaging 2.5 m high, and I see no reason why the roof should be other than lightweight, as I'm intending for it to be open to the sky at one end with plants growing up the inside wall.

As this is more or less the same spec as the leaning bathroom I'm inclined not to just let a builder decide and I'm concerned about what to specify for foundations. The last time I dug for concrete foundations (got the blisters to prove it) in England was under the building inspector's leery eye and I had to go down 120cm!! But if it's at all deep, unless I get down to a hard layer, then I'm only adding to the weight of the foundation bearing downwards on topsoil, and spreading the load acrossways with a slab might be better eh?

Any help appreciated....I could easily guess but interested in what's normal for this modest load....

cheers

Edited December 27, 2009 by sleepyjohn

[jaapfries]

This is where you stop 'guessing' and engage the services of a "Structural Engineer". The cost of such "calculations" is very low and you'ld only be kidding yourself if you don't.

Builder Pattaya

[Crossy]

Agreed ^^^

Without knowing your soil and subsoil type it's going to be impossible to 'guess' what you need, which is likely why you got no response in DIY (in the 2 days you waited).

What type of foundations does the house have? The leaning bathroom?

Since TV does not permit cross-posting I've removed the thread from DIY, next time just hit the 'report' button and ask for the thread to be moved

[trogers]

Agreed ^^^

Without knowing your soil and subsoil type it's going to be impossible to 'guess' what you need, which is likely why you got no response in DIY (in the 2 days you waited).

What type of foundations does the house have? The leaning bathroom?

Since TV does not permit cross-posting I've removed the thread from DIY, next time just hit the 'report' button and ask for the thread to be moved

Is your house on a hillside with super hard clay beneath, or in a swamp floating on 30m of soft marine clay?

[sleepyjohn]

Is your house on a hillside with super hard clay beneath, or in a swamp floating on 30m of soft marine clay?

It's in a good quality flat farmland area 20-30 minutes south of Chiangmai and not far from the river, but not floodable. Just after the road which comes across east from Hang Dong/Baan Tawai towards Sarapee. I guess you'd call it the Chiangmai basin or plain. Out of interest anyone know what general soil type that would be?

Edited December 28, 2009 by sleepyjohn

[trogers]

Is your house on a hillside with super hard clay beneath, or in a swamp floating on 30m of soft marine clay?

It's in a good quality flat farmland area 20-30 minutes south of Chiangmai and not far from the river, but not floodable. Just after the road which comes across east from Hang Dong/Baan Tawai towards Sarapee. Out of interest anyone know what general soil type that would be?

If it is on previous rice field, I would think the first 60cm will be soft planting darkish clay followed by firmer red clay.

Constructing a single floor extension on such soil will require reinforced concrete beams and slab, and footing pads on short concrete piles of 5-6ft length that can be driven in using a sledge hammer.

But be prepared for some differential settlement between old and new structure, probably 35-50mm over a 10-year period. What you should aim for is even settlement, and since the extension is a bathroom, there will be a natural drop of 1 to 2 inches. So start off with the floor of the new bathroom being the same level as the existing house and slope the floor finish of the bathroom (1:100) towards a floor drain at an inside corner.

[sleepyjohn]

If it is on previous rice field, I would think the first 60cm will be soft planting darkish clay followed by firmer red clay.

Constructing a single floor extension on such soil will require reinforced concrete beams and slab, and footing pads on short concrete piles of 5-6ft length that can be driven in using a sledge hammer.

But be prepared for some differential settlement between old and new structure, probably 35-50mm over a 10-year period. What you should aim for is even settlement, and since the extension is a bathroom, there will be a natural drop of 1 to 2 inches. So start off with the floor of the new bathroom being the same level as the existing house and slope the floor finish of the bathroom (1:100) towards a floor drain at an inside corner.

Really 5 to 6 feet that much eh?

Now you suggest it the differential settlement thing makes sense to me.......but not sure why you're suggesting sloping towards the inside corner ( I would normally choose an outiside corner due to the position of the septic tank and the fact there's already a 90cm wide concrete walkway around the house which I would have been going over with the floor of the bathroom.....I would be going altogether about 2 metres wide off the house and 3 metres long, just a little en-suite affair).

Thanks for your interest.....

Edited December 29, 2009 by sleepyjohn

[trogers]

If it is on previous rice field, I would think the first 60cm will be soft planting darkish clay followed by firmer red clay.

Constructing a single floor extension on such soil will require reinforced concrete beams and slab, and footing pads on short concrete piles of 5-6ft length that can be driven in using a sledge hammer.

But be prepared for some differential settlement between old and new structure, probably 35-50mm over a 10-year period. What you should aim for is even settlement, and since the extension is a bathroom, there will be a natural drop of 1 to 2 inches. So start off with the floor of the new bathroom being the same level as the existing house and slope the floor finish of the bathroom (1:100) towards a floor drain at an inside corner.

Really 5 to 6 feet that much eh?

Now you suggest it the differential settlement thing makes sense to me.......but not sure why you're suggesting sloping towards the inside corner ( I would normally choose an outiside corner due to the position of the septic tank and the fact there's already a 90cm wide concrete walkway around the house which I would have been going over with the floor of the bathroom.....I would be going altogether about 2 metres wide off the house and 3 metres long, just a little en-suite affair).

Thanks for your interest.....

I suggest sloping to an inside corner as wet areas of the bathtub/shower would normally not be near to the entrance door. The area between the WC and wash basin should remain dry as much as possible for comfort during use and this area is adjacent to the entrance door.

Edited December 29, 2009 by trogers