House On Stilts- Dig Down How Much ?

[swissie]

I know there is a real-estate section, but it covers Frarang-Type houses for the most part. But I have a question concerning a Thai-House on stilts. So I believe the Isaan-Forum is the right place.

Here we go: I am planning on putting up a Thai-Style House (fairly small, wooden structure, rather lightweight, on 6 stilts, I reckon).

Need a rule of thump as to how far down I would have to dig for the stilts, in order to avoid "sagging" and keep it level in the future.

In my case, the land is level, not prone to flooding = Not rice-paddy land !

As mentioned, need only a rule of thump, something like: Is it closer to 1 meter or closer to 3 meter ?

Thanks & cheers.

[toffo9]

Im also interested in this but building a 1 storey home with bricks that has stilts to prevent flooding

[Mrjlh]

That's a loaded question. You say a small wooden house. Well how small? one room total? You need to know what your final floor plan is going to be. Wooden houses are not light weight as you suggested. You really need to know what the total load of the house is. And that's the job of a structural engineer to figure out. There are pre-design house plans available I just don't know where you find them. I do know if you drive past Pak Chong near the Corn farm there is a small company opposite side of the road that builds just what you are describing. Best check there first. This old worn out engineer would think 3 meters or to bed rock and 6 concrete pillars aren't enough.

[swissie]

That's a loaded question. You say a small wooden house. Well how small? one room total? You need to know what your final floor plan is going to be. Wooden houses are not light weight as you suggested. You really need to know what the total load of the house is. And that's the job of a structural engineer to figure out. There are pre-design house plans available I just don't know where you find them. I do know if you drive past Pak Chong near the Corn farm there is a small company opposite side of the road that builds just what you are describing. Best check there first. This old worn out engineer would think 3 meters or to bed rock and 6 concrete pillars aren't enough.

Thanks Mrjlh,

If that helps: 1 room, approx 10 x 5 meters ( 50 square meters). With an equally sized veranda (roofed) also on stilts (that would definitely be the lightweight part.)

As you can see, certainly not a Mansion on stilts ! If I could get a so-called "knock-down" pre-fabricated structure, that would be ideal.

PS: Not shure, if the average Rice-Farmer hires a structural engineer when he builds his shack on stilts. That's where my "rule of thumb" question comes from.

Thanks & cheers.

[swissie]

Me again: Just thought of the "KISS" approach: = Keep It Simple and Stupid.

Something like this: Any farang resident may want to ask the parents of the wife / girlfriend: "how far down did you dig down when you built your stilt-house ?". If the house should happen to be near my size parameters (10x5m = 50 square meters), this could give me a clue, right ?

Again: For now, a "rule of thumb" will suffice and above practical approach might just do it.

Thanks & cheers.

[sinbin]

The biggest question is, how wide the foot will be on the bottom of each stilt/leg ? The foot spreads the load, making it more stable than a stit/leg with no foot. The original question should be 'how long's a piece of string ?'. Answer ' the longer, the better'.

[Cuban]

Rule of thumb, given the length of the vertical pre-cast columns used, a hole about 1 Metre deep is dug. If you put some rubble and part fill with concrete below and above the flange to set your columns it will be firmer than most. If you might consider to later build a ground floor room, start as you mean to go on and dig a trench between the column holes to lay a wall foundation, tie in to the column footings and the ground that you seek to later be the room's floor. A brick walled room is ideal if you seek to have a place that has air conditioning.

[Jezz]

Rule of thumb, given the length of the vertical pre-cast columns used, a hole about 1 Metre deep is dug. If you put some rubble and part fill with concrete below and above the flange to set your columns it will be firmer than most. If you might consider to later build a ground floor room, start as you mean to go on and dig a trench between the column holes to lay a wall foundation, tie in to the column footings and the ground that you seek to later be the room's floor. A brick walled room is ideal if you seek to have a place that has air conditioning.

Don't forget to consider height from ground to 'ceiling' (floorboards above) if you plan to build under later. Use long pillars. The two pics show an old stilt house which we modified.

Edited July 1, 2011 by Jezz

[Mrjlh]

Those prefab house companies are all over Thailand. I suggest you check them out first. Save you time and energy. You only to provide the land and title deeds, they do the rest. my GF got a 300K Baht quote for one. And that's "complete".

Looking at the pictures of the house, he has 12 pillars and each pillar being 3 meters tall are probably 1-2 meters down to a concrete footing at least 1/2 meter thick and double the with of the beam. My guess. how soft is the soil is a big question. Also, people like to "add", so plan for that.

[ballpoint]

In much of Isaan you'll have to dig down a fair way before you hit bedrock. When my Thai style place was built, which was 15 years ago. they dug holes about 2m deep and 2m x 2m across. In each hole they made a wire mesh "basket" which was filled with rocks and then concrete, giving a stable pad about 1m below the ground level. The teak posts were placed upright on these and the holes filled with concrete. No sign of sagging or cracking at all.

[Atmos]

Last year we dismantled a traditional-style Thai house, it had been built around 1970; timber posts were 3m apart, four on each side so house 9m x 9m, the posts went right up to the ceiling on 2nd storey.

They were only in the ground about 800mm, with concrete about 20cm on each side.

[afarang]

The Thais have been building these houses for longer than you have been having birthdays. Forget all the nonsense,here. Trust the Thais ,they know what they are doing. I see people talking about bed rock .Well ,I sunk a bore -25 metres NO bed rock.The "Moo Ban" sunk a bore 80 metres, NO bedrock. All your concrete pillars are prefab, come complete with "feet". The locals will tell you how many you need for your soil type and building size. They will also know how deep to dig. And if you need to pour extra concrete in the "hole". In building here, I never interfere. I trust local knowledge. I have NEVER seen a house have any structural problems. But, then again ,I have only been observing for about 20 years.Maybe not long enough !!!

[swissie]

The Thais have been building these houses for longer than you have been having birthdays. Forget all the nonsense,here. Trust the Thais ,they know what they are doing. I see people talking about bed rock .Well ,I sunk a bore -25 metres NO bed rock.The "Moo Ban" sunk a bore 80 metres, NO bedrock. All your concrete pillars are prefab, come complete with "feet". The locals will tell you how many you need for your soil type and building size. They will also know how deep to dig. And if you need to pour extra concrete in the "hole". In building here, I never interfere. I trust local knowledge. I have NEVER seen a house have any structural problems. But, then again ,I have only been observing for about 20 years.Maybe not long enough !!!

I am the OP and would like to thank all the folks that have given inputs concerning this matter. I believe above statement from "afarang" makes a lot of sense.

As a footnote: The land (1 Rai) is not in the Isaan, but in Suan Phung (West of Ratchabury), but I figured I would get the best answers regarding this subject in the Isaan-Forum. I think I was right.

BTW: Wife is currently on vacation in Thailand in the Suan Phung aerea, so I Skyped her and told her to find out about the "Bed-Rock"-Level in the aerea, as this is of importance.

Her initial comment: "Why would we want a to have a house resting on beds?". Nevermind, I managed to convey to her that "Bed-Rock" has nothing to do with "bed for sleep". Hilarious !

Cheers.

[F4UCorsair]

You could try giving this company a call. http://www.thailannahome.com/

They erect timber houses all over Thailand, so would know the figures, but local knowledge would be invaluable also. There must be local builders who would know how deep, without doubt, and without soil tests, figured out the hard way over the years.

My observation would be that the more sandy the soil the deeper you would have to go, the more clay, less deep, but no idea of numbers.

Interesting point your wife made, but more importantly, why would you want a bed made of rock??!!

Edited July 2, 2011 by F4UCorsair

[ralston3057]

I think you would be ok at a 3 meter embedded depth. Piles work by skin friction and end bearing (in your case, end bearing). The installation of the piles is important. You should make sure that your wood is treated so that it does not decay.

You should use 10x10 wood columns.

Your bay spacing (column to columns spacing should not exceed 16 feet.

You will have 2x12 wood beams at 24 inches on center running from column to column (you can notch the columns to support the beams).

Cover the wood joists with 5/8 inch thick plywood sheathing (nailed to the joists).

Then, you will have 2x10 joists supported by the beams.

Keep the above general rules and you should be fine (typical construction guidelines for wood structures).

could keep going on and on but you get the picture.

[ralston3057]

I think you would be ok at a 3 meter embedded depth. Piles work by skin friction and end bearing (in your case, end bearing). The installation of the piles is important. You should make sure that your wood is treated so that it does not decay.

You should use 10x10 wood columns.

Your bay spacing (column to columns spacing should not exceed 16 feet.

You will have 2x12 wood beams at 24 inches on center running from column to column (you can notch the columns to support the beams).

Cover the wood joists with 5/8 inch thick plywood sheathing (nailed to the joists).

Then, you will have 2x10 joists supported by the beams.

Keep the above general rules and you should be fine (typical construction guidelines for wood structures).

could keep going on and on but you get the picture.

[Cattracks]

As somebody posted, the locals have this down pat. I ran mine a little deeper 3m because I wanted to make sure I was below the fill I imported to elevate my land. They ended up 2m x 2m x 2m, we also poured (placed) a concrete pad W/rebar first under the Pre-Cast columns. I built a Western Style house but, they started as they would a Thai house, Post and Beam.

[shadiadi]

I would imagine the standards for foundations would be about the same. 1.80x1.80 concrete block 0.4 m thick with 12mm rebar about 1.50-1.80m down should make sure your house doesn't fall down

I would imagine you would need at least 9 stilts 3 on each exterior and 3 down the middle

Edited October 25, 2011 by shadiadi