7/28/2019 Footing the (Strawbale) Bill

1/3

Footing The (Strawbale) Bill

John Glassford and Susan Wingate-Pearse run Huff n Puff Constructions, specialising in

strawbale buildings, from their base at Ganmain in south-west New South Wales.* In this

article John describes three types of cheap footings for strawbale buildings he has tried at

Ganmain.by John Glassford

Ganmain, New South Wales.

STRAWBALE walls require careful consideration before you build. You need to allow for the width ofthebales and, most importantly, for the weight that the render adds. So we always allow for the width ofthe footings to carry the weight of the render. We make the footings 50 to 70 mm wider than the bales.

Without well-engineered footings you will have trouble with the walls either sagging in the case ofpiers, bearers and joists or sinking in the case offootings in the ground. We strongly advise that

you consult a structural engineer once you have decided which type offooting suits your strawbalebuilding.

We are developing suitable foundations for strawbale walls that minimise cement. Cement consumes aninordinate amount ofenergy and resources in its manufacture and in our opinion is an unsusta inablebuilding material. In this article we w ill look at three of the foundations we have used in our ownstrawbale buildings in Ganmain. We do not have any preference as long as the method is sustainable,cheap and easy to accomplish.

Rubble trench footings (Fig. 1)

Have you ever wondered how thecombination ofblue metal and ironbark

sleepers can carry the weight ofalocomotive and various carriages that havebeen running along our railway tracks allthese years? Why would not the samemethod carry the we ight ofa house? Wellthis method can and does. Frank LloydWright has used this method extensively inmany ofhis houses that have stood thetest oftime. Frank began building homes in1893 and one ofhis most innovativebuildings was the Imperial Hotel in Tokyo,which was one ofthe few structures tosurvive the disastrous earthquake thatstruck Tokyo in 1923. The Imperial Hotel

used a system ofcaissons that were heldin place by the friction ofthe soil. The soilitselfwas composed ofapproximately 18metres ofmud covered by 2.4 metres offilled so il. The caissons supportedcantilevered concrete slabs that wereanchored at their ends.

We use a similar principle in that thefootings are dug to a depth of700 mm andyou can see by the drawing that we useagricultural pipe to drain any water thatmight get into the footings. It is importantto slope your footings so that ifany water

7/28/2019 Footing the (Strawbale) Bill

2/3

gets in it will easily drain off.

We also anchor the concrete bond beamevery 1.8 metres by using a cement pierthat is tied into the bond beam with re-bar. The bottom plate assembly is thenfixed to the concrete bond beam by usingdynabolts or a two-part chemical boltingsystem. This method not only uses one-tenth of the cement but also reduces the

cost to a quarter of a conventional cementand steel footing.

Rubber tyre footings (Fig. 2)

We have conservatively estimated thatAustralians consume some 18 million-rubber tyres per year (four million carsusing 4.5 tyres per year). What happensto them? We are all aware that thedisposal oftyres is a major environmentalproblem in the world. Tyres have anestimated half-life of30,000 years so theyare around for a long time.

Once they are filled with dirt andcompacted, tyres make the most earth-friendly and strongest foundations that Ihave seen. They w ill outlive any cementfoundations by thousands ofyears. Theywill not outgas once they are buriedbecause tyres only outgas when they areexposed to direct sunlight. They aretermite proofand, once buried, arefireproofas well.

This method uses a fair bit of labour butwe are working on methods ofpremixing

the earth fill and pouring this into the tyresin the ground. In most cases your localtyre supplier has to pay a levy for theirdisposal and this adds to the cost ofyournew tyres. We have used 55 tyres in asmall round building (four metres diameter)in Ganmain approximately ten yearsconsumption oftyres, in our case. This isalso the cheapest method offoundationsthat we have ever used.

The system is working out very well for thisbuilding and I can see no reason why itwould not work in the footings ofa much

larger building. In fact we know that thereare several large buildings in the USA thathave used this method not only for thefootings but also for the walls themselves.This method o fbuilding is know asearthship building. We visited one suchearthship built by Jack Ehrhardt inKingman, Arizona. Jack is the co-founder ofCERBAT, the Center for EnvironmentallyRespons ible Building Alternatives inArizona.

Recycled timber piers (Fig. 3)

7/28/2019 Footing the (Strawbale) Bill

3/3

This is probably our favourite method offoundations for strawbale buildingsbecause it is easy for owner builders touse, suits our climate we ll, and can beused on sloping blocks without soilexcavation.

It is, however, the most expensive ofthethree methods and takes the longest todo. You also need to be able to use a

chainsaw w ith some degree ofaccuracy.Once you have had your soil analysed forits stability you can have a structuralengineer design the size of the timbermembers for the piers, bearers and joists.Your engineer will also be able torecommend the span that you can carrywith your timbers.

We prefer to use recycled cypress pine forour piers west ofThe Divide and preferrecycled turpentine on the East Coast ofAustralia. These two timbers can be foundin many different types of structures such

as timber bridges, wharves and shearingsheds. They both are resistant to termitesand are to be found in many ofour timberbuildings that have stood the test oftime.There are several suppliers of recycledtimbers in Australia with the most notedbeing Nullarbor Timbers ofMoama in NewSouth Wa les.

*Huffn PuffConstructions, Moore Street, Ganmain, NSW, 2702, phone (02) 6927 6027, email, Web: .

FAQ| Resources| Strawbale home| Strawbale discussion board| Back to EG Web Page