Is It Ok To Place The Timber Poles On Top Of Conc Pads Or Into The Concrete ?

[steven100]

Hi all ,

I'm looking to build the thai house as shown below in Australia and have just a couple of questions as I'm not sure what's the best and proper procedure ...

When building a teak wood / hardwood thai house should the timber poles be buried into concrete a couple of metres and if so should there be a waterproof between the pole and the concrete and not just straight into the mix ?

Also, if no need to bury the pole and as such placing them on 500x500x300mm pads as shown, will this be sturdy enough when trampling around upstairs, I mean will there be any movement/vibration ? will council allow it built this way ?

When pouring a raft foundation for the house, should there be anything under the concrete where conc meets the compacted rock & soil ?

Thanks for any feedback .. much appreciated.

[cooked]

A tentative reply: I was always told never to concrete wood in. I often did it for fencing jobs and they held up for 20 years, which would have been normal for (pressure treated) posts that hadn't been concreted in. I might suggest screwing a strong endless screw (is that the correct term) or two into the post and concreting that in. I have done this a few times on small construction projects and was able to use the screw to adjust the height of the post with some precision, you might need to think about the details of that process.

And finally you might want to Google coolthaihouse, good advice there

[Kwasaki]

Yes OK, don't know about Oz councils requirements though.

If you do same as the picture, you can anchor posts / columns on the concrete slab in many ways, just make sure you comply with your county's building regulations or what ever they call it in Oz on the depth of the floor slab.

[canopy]

When building a teak wood / hardwood thai house should the timber poles be buried into concrete a couple of metres and if so should there be a waterproof between the pole and the concrete and not just straight into the mix ?

Burying posts in earth or concrete below grade will rot even teak as moisture will wick into it. But if you don't bury them then you'll probably need cross bracing so the structure is rigid and cannot be blown over as well as need attachment from post to slab to prevent lift. Best to consult an engineer if your goal is a long lasting, stable design rather than making something up.

My eyes are drawn to the blue pvc in that photo which is a bit of an eyesore. At minimum I would use black hdpe for the plumbing/conduits and run them flush against a post on a side out of view.

[overherebc]

If the posts are concreted in you can fix a couple of small diameter tubes to the post before pouring in the concrete. This means that you can regularly pour wood preserver/wood oil down the small tube to the base of the post inside the concrete, helps to stop the water that will wick down between the post and concrete causing the wood to expand and contract as it it gets wet and then dries which may eventually crack the concrete.

[Crossy]

Many of the houses in that style that are located in the Bang Sai culture centre have tree-sized round concrete posts right up to the floor level, the teak beams etc are attached to steel plates cast into the top of the posts.

The posts are painted teak coloured and look pretty ok from a bit of a distance, not 100% authentic but keeps the wood away from damp rot and potential timber munching creatures.

Could be a way of satisfying local building regs too.

[sluggo50]

Hi Steven 100

Check with your local Building Department. If you do your house legally, you'll need permits, and plans. The plans should have footings for the poles.

In the pictured house, with slab, I would think the slab is about 4" thick. Either wire mesh, or a rebar grid throughout. Maybe a 24" X 24" X18" deep footing under poles.

Then , with added rebar grids in the holes. Then a steel bracket, in the cement, at each post. Bracket would be anchored in the cement. Pole bolted to the upper portion of the bracket. Google Simpson Strong Ties. This has what you would need. Post Bases.

These will keep the pole off the cement, and hold the poles, so your house doesn't lift in the wind. Sluggo 50

[bbradsby]

In Oz, you could use eucalyptus posts - very sustainable and cost-conscious compared to teak logs. Better for longevity would be concrete columns, finished to mimic a log, but requires some artistry to pull it off. Never bury wood posts for a house into concrete, as they'll rot out quickly as water pools inside.

In any case, the columns/posts will require concrete footings set on solid, compacted sub-grade stratum. All site soil bearing capacity conditions vary, and need to be investigated.

[Kwasaki]

Don't get the wood post posts just pulled out of the ground some old teak post on the Muma inlaws old house, built some 80 year or more, very little rot.

Setting wood posts in concrete is not necessary a bad idea it simply depends on the way it is done.

From some building text comments.

A potential remedy is created in two parts. First, the post hole can be dug deeper than is needed to seat it and filled partway with gravel to promote drainage. The concrete can be poured only around the sides of the post. The post will then be permitted to extend through and beyond the concrete rather than being encased by the concrete. When the post is tamped down into the hole, it will extend into the gravel. Water will have no opportunity to become trapped. It will simply drain away into the gravel nested in the deeper hole.

Edited July 28, 2012 by Kwasaki

[bbradsby]

Don't get the wood post posts just pulled out of the ground some old teak post on the Muma inlaws old house, built some 80 year or more, very little rot.

Setting wood posts in concrete is not necessary a bad idea it simply depends on the way it is done.

From some building text comments.

A potential remedy is created in two parts. First, the post hole can be dug deeper than is needed to seat it and filled partway with gravel to promote drainage. The concrete can be poured only around the sides of the post. The post will then be permitted to extend through and beyond the concrete rather than being encased by the concrete. When the post is tamped down into the hole, it will extend into the gravel. Water will have no opportunity to become trapped. It will simply drain away into the gravel nested in the deeper hole.

The post in the ground itself is not the problem if it's teak or redwood other suitable rot/insect resistant species. Even some Cedar can last fifty years, but eventually all woods break down naturally into a point shape, and punch through soil easily as a sharpened pencil! Now, concrete encasement traps moisture in the wood, then forms a gap as the wood shrinks in dry periods, then actively collects water through the gap and quickly destroys the wood. I've seen the results quite a few times; the post disintegrates in only a few years. Posts extending through the concrete solves the problem I suppose, but then the concrete has become a useless expense, except for lateral strength, and it's down to the post footing to carry the load. Best in-ground material is reinforced concrete, full stop.

For a buried wood post, the best is a concrete footing or maybe a compacted gravel base on undisturbed stratum, depending on imposed loads - but without concrete encasement. I don't mention these alternatives on forums where I don't know the design, loading, site, soil bearing capacity, design wind speed or seismicity. Every project is different, and there are no blanket solutions that are appropriate for all conditions.

The take-away is: structural engineers are really cheap insurance against the cost of a failed foundation! I hire one on every new house I design unless it's on solid rock in a non-seismic zone.... let's just say it been a few decades since I was that lucky.

[bbradsby]

If tree trunk posts are the aesthetic one is after, hold them up on concrete plinths, off the ground; use galvanized steel, concealed vertical locating pins and fab-up some thick hold-down strap steel "hold-downs" with massive galv. through-bolts safely up the trunk length. If done well, these are strong & beautiful. But, these are not lateral force-resisting, so use stair walls or store rooms or garage walls as shearwall(s), if the force so moves you

[cooked]

Wood will not rot when it is permanently immersed in water ( vis 1000 year old pilings found in wet environments etc). It is the variation of moisture that allows fungi to complete their life cycle and thrive. So drainage at the bottom of the post might do more harm than good. Just face up to the fact that wood will eventually recycle itself into soil.

[Kwasaki]

" Wood will not rot when it is permanently immersed in water "

" Just face up to the fact that wood will eventually recycle itself into soil."

[cooked]

Archaeologists will agree with me I'm afraid.

[Kwasaki]

Archaeologists will agree with me I'm afraid.

Yeah !! just having a bit of fun pointing out the contradition in time.

[bbradsby]

ya, some naturally- pest/microbe-resistant woods such as cypress are dredged up from the swamps after a hundred years of submersion and sold for big money, so teak may do as well - but permanent submersion is not the condition we're talking about in our OP's example. The timber posts at most building sites will see a continuous cycle of saturation and drying out.

Sorry, but this is a completely academic discussion - who in their right mind would take super expensive & valuable teak logs and bury at least a meter's length of every log laid out in a 4 to 5 meter grid large enough to build a decent house? No one. In-ground, or under water, we use concrete for a reason.

[steven100]

Hi Steven 100

Check with your local Building Department. If you do your house legally, you'll need permits, and plans. The plans should have footings for the poles.

In the pictured house, with slab, I would think the slab is about 4" thick. Either wire mesh, or a rebar grid throughout. Maybe a 24" X 24" X18" deep footing under poles.

Then , with added rebar grids in the holes. Then a steel bracket, in the cement, at each post. Bracket would be anchored in the cement. Pole bolted to the upper portion of the bracket. Google Simpson Strong Ties. This has what you would need. Post Bases.

These will keep the pole off the cement, and hold the poles, so your house doesn't lift in the wind. Sluggo 50

Sluggo50

I tend to agree with placing them on footing as you mentioned , that way there is no concern at all about moisture getting in etc ....

Then there is the question of support & vibration, however I believe this can be eliminated with some bracing, although I prefer not to have exposed bracing as it looks horrible and takes away the use of openess under the floor....

I will get an engineers opinion/design before going ahead as pointed out in another post.

Thanks for the information on this.

Edited September 1, 2012 by steven100

[steven100]

When building a teak wood / hardwood thai house should the timber poles be buried into concrete a couple of metres and if so should there be a waterproof between the pole and the concrete and not just straight into the mix ?

Burying posts in earth or concrete below grade will rot even teak as moisture will wick into it. But if you don't bury them then you'll probably need cross bracing so the structure is rigid and cannot be blown over as well as need attachment from post to slab to prevent lift. Best to consult an engineer if your goal is a long lasting, stable design rather than making something up.

My eyes are drawn to the blue pvc in that photo which is a bit of an eyesore. At minimum I would use black hdpe for the plumbing/conduits and run them flush against a post on a side out of view.

yes, they do look like a bit of an eyesore .. i'm sure there are better types & colours to use. I think there is brown pvc available .. i'll check it out. tks.

Yes OK, don't know about Oz councils requirements though.

If you do same as the picture, you can anchor posts / columns on the concrete slab in many ways, just make sure you comply with your county's building regulations or what ever they call it in Oz on the depth of the floor slab.

Thanks , and I will check on the building regulations as required.

Wood will not rot when it is permanently immersed in water ( vis 1000 year old pilings found in wet environments etc). It is the variation of moisture that allows fungi to complete their life cycle and thrive. So drainage at the bottom of the post might do more harm than good. Just face up to the fact that wood will eventually recycle itself into soil.

Thanks for your comment, I do think the drainage idea is a lot of problem and as such would opt out of tackling that one.

[trogers]

I would treat the timber posts like steel. Cast a steel anchor plate into a 10 cm high raised concrete pad. Weld a steel box to the anchor plate and place the timber post into the steel box and bolt through.

Edited September 1, 2012 by trogers

[Morakot]

Weld a steel box to the anchor plate and place the timber post into the steel box

A bath tub for the timber?

[trogers]

Weld a steel box to the anchor plate and place the timber post into the steel box

A bath tub for the timber?

Is your bathtub a box?

All you need are 4 steel plates tacked welded together to form a box with the bottom edges fully welded on to the anchor plate. The timber post will be held fast in x-y-z directions.

Edited September 6, 2012 by trogers