Lightweight Earth Concrete  
Multilayered Carpentry  
Public Declaration  


Wood Reinforced Lightweight Earth Concrete is a construction system that integrates the insulation within the structure of a building.  The construction techniques are similar to those employed for reinforced concrete, but the materials employed are natural and available more or less everywhere.

It has an insulation value around half that of glass-wool (lambda = ~0.07).  A roof 40 cm thick has a thermal resistance (R) of 6 or 7.  Its fire resistance is of the order of M1 or M2 and its useful life will be a lot more than 10 years.

  It's ecological advantages  are enormous in relation to the alternatives available on the market.  The preparation of the materials employed is without heating and their availability reduces the transport that would be necessary.  It's high insulation value will help us to live with the inevitable planetary reheating.  The clay content of the BTA ensures it's structural stability, it's fire resistance, it's flexibility when confronted with earthquakes or mechanical shocks and it's capacity to control the hygrometry of the adjacent air.  It is this last quality which makes earth houses so comfortable in summer and in winter.   It's possible demolition presents no difficulties.

It is a system that is still in development and I invite you to contribute - I will try to publish your comments, or at least to create a link to your site.


The beginning

It all began with an unexpected situation. I am the owner of some old barns which were falling in ruins, without the necessary revenues to repair them.

It was in 1992 that I found an old adze among the rubbish, which I recognised by its shape and the steel which was harder than a hoe.

fro,t wall july 1995

front wall november 1995

Unbaked Earth

A friend, Paulo, recommended that I participate in a weekend course on building with unbaked earth with Alain Klein of Inventerre, after which I was able  to replace some old walls of rotting planks with timber frame panels, made from chestnut, from the coppice in my forest prepared with the adze; filled with wattle & daub made from earth and straw from my land.

wall outside after the fire

wall inside after the fire

Fire Resistance

 Then in 1996 there was a fire.  I lost my workshop  and most of my woodworking tools but I learned something which was extremely useful to me. A section of wall and a section of the roof had been insulated with a mixture of mud and straw, one of my first experiments with this material, and had resisted the fire; in spite of temperatures above 800 °C. I was on the road towards a construction system that used this 'magic' material.

roof outside after the fire

roof inside after the fire

Carpentry with square wood

The carpentry that I worked on was made from hewn coppiced spars which always produces square sections.  Mechanics teaches us that rectangular sections are more efficient for horizontal applications.

Reflecting on these two facts led me to observe that traditional roofs are made from square sections in a number of layers; battens, rafters, purlins, truss frames.  I reasoned that if each element of an upper layer was fixed at each intersection to an element in a lower layer, to share the load, we would gain efficiency.

ossature multicouche
Multilayered Carpentry

I imagined a structure constructed from a number of layers of wood, all of the same section.
I calculated the  resistance of the battens used and quickly concluded that a widespread distribution, and the possibility to concentrate the support where it was needed, could be obtained with smaller battens and more layers. On the other hand the fixing time increased with the number of elements.

A balance between these two considerations led me to make more serious calculations.  The optimal size came out at 4cm x 4cm.  Battens of this size can easily be fixed using self-tapping wood screws.  Multilayered carpentry was born.

Infilling with lightweight earth concrete

There is a serious fire-risk with such a carpentry, but filling it with something which is both insulating and fireproof would solve the problem. Starting from mud and straw, I experimented with different kinds of woodchips in order to replace the straw with a material that could be inserted with more regularity.  That provided by local joinery companies was perfect. I had found what I was seeking - Wood reinforced lightweight earth concrete. 





What is Lightweight Earth Concrete (LEC)?

Lightweight earth concrete is a mixture of  woodchips and only the koalinitic clay fraction extracted from the earth, which offers minimum shrinkage; with granular woodchips  <8 mm, shavings <2 cm and fibrous woodchips < 8 cm .  These are what are normally produced by woodworking machines and garden waste chippers.

(Research on mixtures containing different proportions of these three types of woodchips could help us to improve its mechanical qualities and its  thermal insulation and acoustic properties.)

The woodchips should be air-dry, around 15% moisture content.  Green woodchips, covered with sap, adhere better if they are washed by the rain and dried in the sun.  During this process, they should be turned regularly to prevent them from fermenting and the possibility of spontaneous combustion.

The clay  is extracted by washing earth,  non-organic subsoil, followed by sedimentation in tanks or pits. The consistency of the resulting mud should form a patch 15 cm dia. when 100 ml is poured onto a clean, dry sheet of glass.

The woodchips and mud are mixed with 20 to 30 litres of mud for 80 litres of woodchips by hand or in an ordinary concrete mixer, poured into  vertical shuttering or onto  more or less horizontal shuttering and tamped or vibrated.  Vertical shuttering can be removed after several hours.

Horizontal shuttering must be properly supported during the entire drying period considering that the weight of the material is in the order of 1200kg/m³; 3 months at 25°C during the day or more quickly with artificial heating.

Lightweight earth concrete sets by the evaporation of the water and the formation of electrostatic links between the micelles of clay and the woodchips.  The drying rate, within the limits of the possible, that means < 60°C, does not modify the integrity of these linkages.

When dry the LEC typically has a density of 4-500kg/m³.  The carpentry that supports it must be calculated with regard to this weight plus the weight of additional charges.

Fire resistance experiment:

(en construction)

Persistent leak experiment:

(en construction)


drawing - 3 layers

All moments in cm³
moments for 10 layers
10 layers of elements  4cm x 4 cm

What we all know

We can say that it is do-it-yourself carpentry.  Everyone has nailed two pieces of wood across two others.  For a fence we have three layers, or for a roof its four.  Why not more?   More layers, that means more elements.  If we go on, we have a composite; a wooden structure becomes a fabric with new qualities.

It is this web, filled with lightweight earth concrete that becomes wall, roof, partition, ceiling, floor, pillar, arch....  The distribution of the battens throughout the volume provides a uniform and flexible support.  The concentration of the battens around the critical points assures optimal resistance.

Mathematical model :

We need to analyse the structures that we propose in order to calculate the stresses imposed on each member. A mathematical model is required to understand what is happening in each element and liaison.

Consider the elements in a horizontal structure.

The setup shown to the left is a simple junction between three elements, disposed in three layers.

To calculate what support it gives we must find the value of it's moment of section which is given by: bh²/6cm³

If the vertical rectangular section were continuous its moment of section would be:
 bh²/6 = 4 x 144/6
                                         = 96 cm³
However the central horizontal element is not continuous in the direction perpendicular to the image and must be removed from our total:
4 x 16/6 = 10.67 cm³
and                       96 - 10.67 = 85.33 cm³

Each element contributes : 85.33 / 2 = 42.67 cm³

Viewed from left to right the central
element contributes its moment which is :  10.67 cm³

In this manner we can calculate the value for any number of elements and layers no matter how they are distributed.  The values of all the elements perpendicular to the image can be added to calculate the moment offering support in this sense over the length envisaged and the left to right values are similarly added to obtain the moment supporting over the length in this sense.

We have thus two values, the sum of the moments of all the elements, one for each direction.  For a  horizontal structure with a square plan these two values can be added together, for a rectangular plan they are considered separately.

Taking the coefficient of resistance of wood as 80bars/cm²  the moment of resistance is given by PL/640cm³  where P is the load in Kg and L is the length between supports in cm.  

This value must equal the sum of the moments previously calculated.  We can ensure that this is the case by adding elements to the structure.
(to be continued)



Peter Lorien, the system's inventor, offers it free to the world

This is freeware, please acknowledge it with help to develop and spread the system.

Demonstrations, technical assistance & short courses available on demand.

Site : http://lorien.free.fr   

Mail : lorien@free.fr

Declaration in the public domain 

15 February 2001


Wood reinforced lightweight earth concrete, (WORLEC). A construction system which comprises a wooden armature filled with lightweight earth concrete.


It is used in the construction of relatively flat parts of buildings; e.g. walls, floors and roof surfaces.


It addresses two categories of problems encountered in building construction.

  • The first is the contradiction between the structural and the protective functions of a building.

 The structure of a building presents a support for the protective elements such as thermal insulation, acoustic insulation, rain and wind resistance and hygrometric stability to maintain the internal atmosphere in the comfort zone.

 It must be solid enough to support its own mass and that of the occupants and their belongings, and it must be strong enough to resist the impact of the external forces that can be anticipated.

We are frequently required to make compromises or to make complex structures.

I will address these compromises more precisely when I consider the existing solutions.

  • The second are of an ecological nature.  The problems in this category are related to the high cost of the energy required in the manufacture and transport of building materials; or to the chemical or fibrous emissions given off during the construction, useful life, or the demolition, of current constructions.


  • Concerning walls:

The contradiction between the solidity of a structure and its thermal isolation is manifest in the case of masonry or reinforced cement concrete structures.The proposed solutions are to use hollow bricks or blocks, no-fines or expanded concrete, or adding insulating fillers. Timber embedded in cement or lime is subject to fungal attack. Masonry, especially when it is rendered with plaster, dries the atmosphere inside the building.  It is complicated to produce earthquake resistant masonry.  The raw materials, requiring large amounts of energy for their manufacture and transport, have a high ecological cost.

Modern, composite, timber-framed structures resolve this contradiction by means of assembling complicated multi-layered structures using many different materials.  There remain problems of waterproofing, condensation and acoustic insulation which are not fully resolved. The ecological balance-sheet starts with the emissions given off by the chemical products used to protect the wood and the fibres used for insulation, both during the construction and the useful life of the building and returns when we have to demolish these complex structures.
  • Concerning roofs:

Traditional carpentry uses an excessive quantity of wood being based on the principal that each layer must support those above and itself.  It has no redundancy and requires qualified workmen to produce it.  It is difficult to insulate. 

Roofs built with lightweight truss frames are difficult to insulate to a great thickness. Their mass is not sufficient, in themselves, to prevent the roof from flying off in heavy winds. Similar remarks to those above mentioned apply to the products used to protect the wood. 

  • Concerning floors

Floors made with concrete beams and blocks require additional insulation and fall down in earthquakes.  See my remarks in relation to masonry walls. 

Wooden floors display problems with acoustic insulation and fire-resistance; and need to be protected with chemical products.

  • Concerning fires:

In spite of being built to the norms, classical roof and floor structures often fall, before the occupants can escape.  The prolonged stability of a building on fire is only to be welcomed.

horizontal section


figure 1

Typical example of a more or less horizontal structure employing 10 layers.

vertical section

figure 2

Typical example of a vertical structure employing 7 layers.


The armature consists of superimposed layers of parallel strips of identical dimensions; each layer being fixed at an angle different from the preceding one. 

The strips can be more or less square or round and can be of wood, bamboo or bundles of fine stalks. 

The layers are fixed together at each intersection by means of bolts, screws, nails, dowels, rivets; of metal, plastic or rawhide; or with cords. 

These multiple fixations offer a high degree of redundancy, which insures stability in the case of damage to the structure. 

The number, dimensions and spacing of the strips are calculated to support the determined load within the total thickness chosen for that element. 

This thickness is determined from the degree of thermal insulation required and the thermal resistance of the infilling material. 




A continuous horizontal layer is fixed to the foundations at the bottom of the walls, above and below openings and at the junctions between walls, floors and roofs, within the diagonal layers and using the same materials. 

One or both of the outside layers could be of traditional timber-framed construction, either existing or made to measure; the shuttering being fixed to the outside of this framework with a layer of elastomer foam,  or panels of polystyrene, plywood or fibreboard cut to fit between the framework, to set back the concrete to make space for the rendering.  The armature being set into the infilling, no extra support is necessary between the timber frames.       

To improve acoustic insulation adjacent layers can be made to move independently by means of inter spacing them with blocks of a soft material such as cork or fibreboard.   

The necessary trunking and pipe work are placed within the armature before fitting the shuttering.  

This armature is shuttered either by means of a permanent shuttering which remains in place  made from masonry, weather boarding or wooden, chipboard or straw board panels, or strip mats to take a rendered surface ; or by shuttering made from wooden or metal panels, full and covered with paper to prevent sticking or in the form of a mesh ; fixed to the armature with screws, nails or bolts which traverse the element or supported on props in the case of more or less horizontal surfaces; which are removed after the infilling has solidified. 

In preparation for a rendered finish the shuttering can be spaced from the armature by means of blocks so that no wood remains apparent.

The armature covered with shuttering is poured with earth concrete made from a clay mud, filled with cellulose particles such as chopped dried plant materials, straw, paper or fibres; or wood chips; or other insulating materials such as expanded clay, vermiculite or plastics.  The cellulose fillers can be waterproofed with silicone or wax in order to speed up the drying process and to make the material waterproof.  The concrete can be poured manually or by means of a blower and is compacted by vibration.  The degree of compaction and the proportions of the mud and the filler determine the degree of solidity and inversely the level of thermal resistance of the element.  Different particle sizes in the filler influence the solidity and the sound insulation at specific frequencies. 

As soon as the earth concrete has solidified, the shuttering can be removed and after thorough drying, a plaster, lime or earth rendering can be applied to the exposed earth concrete; or panels of other materials can be fixed to the walls and ceilings. 

The roof can be covered with sheet roofing, tiles, slates, shingles or thatch fixed by traditional means, the outer layer of the armature taking the place of the battens normally employed; or set in a lime or earth mortar. 

Floor surfaces can be finished with the planks and wooden tiles normally available, or they can equally be finished with beaten earth or a lime mortar to take ceramic tiles.   

No waterproof film is required because the earth concrete, being permeable to vapour, it is preferable that it respires from both sides.  It is therefore important that the external finish is impermeable to liquid water but ventilated if it is not permeable to vapour. 


The proposed system can be used for all flat elements within buildings, even for the panels used in geodesic domes and zomes and to construct pillars and arches. It is even easy to make curved forms. 

It is constructed with only one size of strips without any difficult cut joints. 

At one and the same time it satisfies the structural and thermal insulation requirements. 

It can be easily built without the need for specialised tools or workers, with materials available locally almost everywhere. 

Its vapour permeability avoids the use of impermeable products thus eliminating condensation and the need for air conditioning.

There are no thermal bridges. 

It has a high level of acoustic insulation both for airborne and transmitted noises.  Built from multiple continuous layers, it will be earthquake resistant. 

The lightweight earth concrete filling has a high degree of fire resistance protecting the wood for several hours, and it also protects against wood boring insects and fungus attacks, with the exception of termites. 

It must be protected at ground level against termite attack in affected zones.   


The advantage of this system of construction rests in the simplicity of its methods of construction and the local availability of the basic materials almost everywhere as well as their natural qualities. 

It may well be the cheapest way to construct buildings. 

In horizontal elements there is a saving in the amount of wood used as the upper layers are solidly fixed to the lower layers and help to support them. 

It can be used to construct all imaginable forms, even complex curves and large or multi-story buildings. 

It satisfies all the demands that we make of buildings in relation to their structural, and thermal or acoustic insulation requirements; (given the thickness of the insulation which goes all through each element, it presents the quality of super insulation permitting no heating requirement throughout much of Western Europe).  

The use of clay with its vapour permeability contributes to the control of the hygrometry inside the building.

It is fire resistant (which can be improved by treating the wood with a fireproofing agent), earthquake resistant, hurricane resistant and flood resistant (with waterproofed filler), and the wood being unexposed is protected from insect and fungus attack without using dangerous or toxic products. 

It can easily be taken apart offering the possibility of recycling the wooden elements into other structures.  The earth concrete can be remixed with water and used again, or thrown on the ground where the cellulose materials will become compost with the earth and clay.