wattle and daub + earth roof on foundation poles

hi im querying if someone has answers to how many and how deep foundation poles to support the weight of a pole frame of a locally grown timber (manuka nz) and an earth roof. i thought to use treated foundation poles as i live remote with boat only access, its easier for me to transport out there rather than bags of cement. the rocks out here dont seem to be very strong and nz is a seismic area. i want to use the manuka poles for framing the structure. the manuka is easier to work with when it is fresh felled rather than waiting for it to dry when it is very hard to work with. it is heavy when wet.
the earth roof will be made with an EPDM lining with turfs placed on top (i have done this already on another structure and simply it works very well, the grass dies and creates compost and feed the next growth) the walls could only be compared to wattle and daub though i will use the brush from the tops of the manuka dipped into a clay slip and packed lightly between two layers of recycled milk bottle netting.
the structure would be within the ten square meter thresh hold.
i dont know how to calculate the weight.
thanks in advance for your thoughts

Hi Angela,

First...welcome, and thank you for sharing your project...

It is going to be almost impossible (probably is) to really give any good guidance with out a set of blueprints and/or CAD model to look at. "Earth roofs" exert a massive amount of load on frames and many that are being built without PE support and supervision are really pushing the envelope of "safe" in many examples. Others go for the "massive overkill" in frame work, and this can never really go wrong if attention to detail is kept up.

Understand well that "rubber roofs" alone have a short life span of only perhaps 20 to maybe 50 years before needing to be completely redone...sometimes including the roof deck. With "earth roofs" the more traditional and complex the longer they will last and good ones made of flat stone, layered materials, bentonite clays and related means and methods can last well over 500 years...It all depends on location, style and material detailing to achieve this. Fast and lighter version can be easier to replace. I like "double roof systems for all of these to facilitate maintenance and inspections. It adds some cost but also gives more security to the expensive building underneath it.

A green timber frame structure of wood is both traditional and should work just fine once the exact loads are understood and calculated. As for "depth of post" they don't need (nor really should) go into the ground at all. Most "traditional" and longest lasting frames just sit on stone plinths. This can be post to socle or plinth, or sill to plinth...

Get some drawings up or a CAD model and I can perhaps help more, but I strongly recommend a PE and/or doing the math yourself to really understand the work...

Regards,

j

Jay beat me to it and is absolutely correct. I can walk through the calculations and size the piers/poles if one can interpret and follow along, but the first thing I am going to ask for a plastic index of the soils at a good six inches below frost line. If it is high and expansive I am going to ask for a full geotech report. I''ll need to know the loads of your seismic and winds, snow loads if any, and how many stories...Weight/compression is only one check.

If you have building and safety code there that will size the piers. The area and strength of poles alone may not provide enough bearing area to be reacted by the bearing allowable of the soil, you may need a wider stronger rock or concrete pier, or even pile drivers to bedrock. If a person is not familiar with it or the loads, or has no any idea what Jay and I are talking about for your own safety hire an Architect to begin with and ask about their PE (Structures Engineer) and how much experience they have with the building method and land. Not all PE's are created equal, nor Architect Engineers.

If you are out in rural with no laws, I will walk you through the calculation but need the info above (a cad model or volume of structure calculated by hand starting with walls (exterior and interior, floor, roof_pitch separately, and a hand sketch so I can see how the weight is distributed on the floor plan). My legal disclaimer is since I am not there use the info at your own risk.

thankyou jay and terry
i appreciate your answers.
the land where i live is very remote and a fortune is spent on bringing professional people out here and then they charge a fortune on top of that. of course they have their studies experience and livelihood to pay for.
i rather like the idea of not having to use treated timber and or cement but using stone plinths. and i get you with your suggestion for doing the math my self to understand how it all works, to be honest i didn't have a good relationship with math while at school so never applied, so i really don't know how to go about learning the math.
and terry i appreciate your offer (a cad model or volume of structure calculated by hand starting with walls (exterior and interior, floor, roof_pitch separately, and a hand sketch so I can see how the weight is distributed on the floor plan) i will have to get back to you with those
included is a photo of a wall section for the greenhouse i built with a manuka scissor frame roof, since then i learnt to dip the brush in a clay slip before enclosing in the netting. probably the mice have a very nice place to live in the green house walls.
the shed, i buried concrete in the earth on four corners sunk in an anchor to each then bolted the manuka poles to that and tying down the tin roof to the concrete anchor blocks, i built this shed after the green house so applied what i had learnt from the green house the walls are on earth bags there are two tin walls and two earth walls with large enough overhangs.
i just want to build slightly different with the raised floor try different techniques for the next project.
im not a builder but i love to build i started by building my compost toilet by hand till i got a tennis elbow (now i use an electric chainsaw a silky saw and battery drill) but by making the mistakes, i have learnt.
so i guess i will just keep learning and try my hand at maths
jay i read some of your replies to people after i had posted my question and i really appreciate you your advice and your patience for possibly replying to the same questions over again..thank you again

Hi Angela, I'm not as knowledgeable as Jay with these building methods so he can help you determine the volume of mass that the foundation of choice is seeing. For walls it is simply thickness x length x height. Roof the same and give me a pitch of the roof. If the flooring is resting on ground and not beaming load over to the foundation we do not need it for now. You need to identify load bearing walls/points in your sketch of the foundation only. There are some basic field test you can do to estimate Plastic Index PI: Learn about it here: https://en.wikipedia.org/wiki/Atterberg_limits

Once we have the volume and understand how load is getting to the ground we can estimate wall/roof density and get a building weight. That we distribute to the foundation depending on design to get a pressure (PSF (pounds per square foot or meter) to the ground including the weight of the foundation at each pole/footing/etc after applying a safety factor of 2-3. We'll need the weight of the foundation (rock, etc) if you know it or look on the internet.

See the attached.....then you need to figure out what soil type at depth in PSF you have so we can see if it can react this vertical compression downward load. If it is less than 1500 PSF that can be problematic. As you can see heavy structure defeats itself in weight to the ground below grade but, it can be beneficial above grade to reduce wind and seismic bending moments we look at next, so we need that info too.

After we get through the foundation sizing you need to do the same structures checks to make sure it can take the loads.

I hope your not in a rush my time is limited since I have my own design going on so please convert all units to feet.

terry WoW thanks, it all seems a bit over whelming right now this new language and mathematics, so i'm not in a rush in that aspect and not in a rush in another aspect as i'm currently away from home working. I posted my question hoping that the answer would be easier to understand but i'm glad i posted well in advance of my application to the question.

No worries I'll help you through it I know what being on a budget is like. I suggest you work with The Master Jay to come with a design, I'll help you analyze it and make it work pro-bono. Once you have a foundation drawing with the loads I'll help you determine where to take the DIY soil samples at 6" inches below whatever frost line may be there, I have no idea where this building site is and what environmental loads we need to resist. On any given site floor plan soils can change drastically causing issues. If there is anyone local there that understands structures bring them out here to act as a proxy.

Pm me when you get the info and let me know it is up. Keep up the good work!

There is no other place on the internet other than The Ranch you can get this level of help and professionalism on any building method, you came to the right place! Welcome!

hello
as and when i have had a spare moment i have jumped online. to my wonder i have found this site http://www.theroundhouse.org/images/2intro/gallery2.htm these are very heavy structures and this site even shows how it is built, tony wrench is teaching how to build round wood henge framed houses with reciprocal roof now on pad stones
here is another site in the uk http://www.wholewoods.co.uk/page.cfm?pageid=ww-traditional-buildings this site shows that reference is available for teaching building techniques on building round structures on pad stones
so i now see the way in which i would like to build my next project, i have started a very simple pencil drawing, but as yet not ready to work with

still dreaming....

Well those are great guides thanks of sharing them...

It gives a much better understanding of you style and goals...

Look forward to seeing your plans develop...