Introduction:

As an example of a low-impact, environmentally friendly building technique, it is hard to better the use of recycled car tyres as foundation material. If not exposed to ultra violet light via sunlight, their estimated life expectancy is 30,000 years! Significantly longer than environmentally high-impact concrete. They have been widely used, particularly in the USA, to build whole houses, known as “earthships”. The first earthships are now being built in England (near Brighton) and Scotland (near Fife) with full Planning and Building Regulation approval.

Most buildings need to have some sort of foundation on which to build. This fulfils several functions:

1. To provide a solid, stable base that distributes the weight of whatever is built upon it over the ground beneath.
2. To raise the walls above ground level, to protect them from groundwater and rain.
3. By using a damp proof course within the foundation, the walls can be protected from damp below them.
   

Why car tyres?

The main reason for using recycled car tyres is that there are lots of them about, and they are free! Of course, the reason there are lots of them about is that they are difficult to dispose of, and this is a negative aspect of their use and production for the car industry. Garages and others have to pay to dispose of them, which sometimes leads to illegal dumping. They come into their own, however, when we can use them because they are difficult to dispose of.
There are tyre recycling plants that chew up old tyres and re-use them for road surfaces, or cut them up and make them into door mats etc. And they are now being ground down and stuck together again with polymers to create roof tiles, but car tyres cannot be melted down usefully. Some recycling plants burn them under special conditions and use the heat energy released for other things. Under normal circumstances, car tyres are not burnt because they give off noxious fumes and a dense black smoke.

So in car tyres we have a free, plentiful, durable and easily worked material that can also be its own damp proof course, as it is made of rubber/butyl. Generally, the only thing that causes them to deteriorate is the ultra violet light in sunlight.

What sort of buildings can use them?

They can be used as a foundation for any well designed, low-impact building. This includes sheds, garages, workshops, offices, and living spaces. They can also be used for much larger buildings too, we are currently building a whole residential school with car tyres for foundations.

When would you use them?

• When concerned about the environment
  
  By low-impact, we mean that we wish to disturb the environment as little as possible, and to leave little or no trace of ourselves and our building when the need for it has passed, either through using compostable materials, or ones that can be re-used again and again. Low impact does not mean short term or temporary, although car tyre foundations would be ideal for this type of structure as well.
  
• When concerned about cost
  
  They can be used when cost is an important factor, as they only require the price of transport to collect them from the nearest car tyre centre or garage. Sometimes, these places will deliver free if you need a lot.
  
• When concerned about fun
  
  The actual experience of physically filling the tyres ready for use is ideal as a community activity, and usually generates a lot of excitement, play and storytelling.
  

What about Building Regulations?

There are three buildings in the UK that have both planning permission and building regulation approval for rammed car tyre foundations, all designed by Amazon Nails. One is a loadbearing residential school that is under construction in Richmondshire, North Yorkshire, with the first phase completed, another is a large meeting room, also loadbearing, with kitchen and disabled access toilet to be built for Agbrigg and Bellevue Allotment Association, in Wakefield, and the third is a loadbearing sauna and jacuzzi in Calderdale which has never yet been built.

Approval in Calderdale was given for:

“foundations…of recycled car tyres, with side walls packed solid by clay and rubble, the central core being filled with free-draining gravel. The tyres themselves, being made of waterproof material, act as a damp proof membrane.”

A condition was imposed that the tyres should be plastered over, so that they would have a more beautiful appearance.

Richmondshire County Council asked for several loadbearing tests to be carried out on site and approved the method using well-compacted stone as the ramming material. These tyres will also be coated in an ultra violet reflecting paint to ensure durability.

The fact that there are only three buildings so far should not put you off; it is still a new and experimental technique. Also, other buildings have used this method, but have not needed to ask for building regulation approval due to their size. The existence of the school now gives a strong case for “precedence” when applying for Building Regulation approval. Also, with the changes to rules governing Building Regulation in the UK, it is possible to use an independent Approved Inspector rather than your own Local Authority to ensure compliance with the Building Regulations, so if you meet with resistance you can appoint an inspector who is already familiar with the method. In general, however, it is best to credit your building inspector with sound knowledge and experience. Their job is to make sure you are building something that is safe and healthy, they can and do access the experience of their colleagues, and most of them are able to offer invaluable help.

How to Choose Car Tyres.

Tyres come in many sizes. They have different diameters and are different heights. You can usually work with different diameters, but it can be hard to level the tyres if they are of different heights.

When you look at a tyre, it always has its dimensions stamped on the tyre wall, it says something like: 185/60 x R14
The first (larger) number is the most important; it tells you the width across the tread in millimetres, so when you lay the tyre flat, this is the height it will be. Eg. 185mm

Sometimes this number has a second number with it (/60) and this tells you the depth of the tyre wall in millimetres, (the measurement from the rim to the tread) eg. 60mm. This number is not always shown.
The third number after the letter tells you the size of the rim, or the size of the hole in the middle, but this is measured in inches.

Eg. R14 = 14 inches. Beware!
So the diameter of the above tyre is:
depth of the tyre wall + the size of the hole in the middle
60 millimetres + 14 inches = approx. 415mm

So, when choosing tyres for your foundation, it is helpful to use ones that are all the same, ie. all 185 or all 155 etc. Using the same diameters is also helpful, especially if you are stacking them up in pillars.

So how do you do it?

It is necessary to dig down to something solid. Sometimes this is as simple as removing the topsoil, if you are building in a place where rock is close to the surface. Or you may need to dig down 4 or 5 inches to find clay/gravel subsoil, or rocky soil. In any case, you should not need to go beyond 18 inches. If you do, you should consider changing your site or using a different type of foundation, such as posts or compacted gravel holes with car tyres on top.

If you do have to dig a foundation, it will either be holes beneath each pillar of tyres, or a full trench the same shape and size as your building. It may be the same width, wider or narrower depending on the type of subsoil, the load (weight) of the building, and the choice of wall materials.

Fill the trench/hole with drainage gravel or round river rocks. These must be well tamped down every 6 inches (150mm) depth to prevent them settling further later. In effect you are creating a French drain, which is underneath the building rather than outside it, it’s an idea that Frank Lloyd Wright (American architect) used 40 years ago to avoid excessive use of concrete.

You may be able to use whatever came out of the trench to pack tightly into the tyre walls, but the first tyre on the ground should be packed with stone or urbanite (broken up old buildings) with draining gravel in its centre so that there is no possibility of moisture coming up through it into the building. Then you can use a mixture of clay (roughly 20%), sand and small stones, rammed into the tyre walls with a heavy hammer or piece of wood.

Other materials could be used, including concrete, but do not use anything organic, such as topsoil, as it will rot or grow and cause movement in time. The aim is to pack the tyre walls solid so that they are firm and will not move. It is best to do this close to where they will be laid to avoid any material dropping out on movement, and so as not to have to carry them when heavy! Be careful to keep the packing material only in the walls and not to drop any onto the drainage gravel, or it won’t drain!

Carefully place the tyres onto the trench. You may need to adjust them slightly to make sure they fit tightly around the shape of the building. Now fill the central hole with more drainage gravel, again, well tamped down.
If you need to build higher than one car tyre, place the second one directly onto the first. Tyre foundations usually act like pillars rather than being a continuous strip, and have a timber floor grid placed on top into which hazel stubs can be placed to secure the bales, or act as a perimeter wall for a limecrete solid floor.

And Finally…

Once the walls have been built, you may want to plaster or otherwise cover over the tyres to protect them from sunlight. This can be done with a clay, lime or cement plaster, or with a reflective paint. The whole building can be surrounded with a woven willow wall to hide the tyres, or you can use left-over pieces of timber from the building as slats. The decision will depend on how long you expect the building to last for (sunlight will only slowly cause deterioration of the tyres) and what you want it to look like. In any event, make sure you do not bridge the damp proofing effect of the tyres by covering them with something that creates a path for water from the ground into the walls. Leave a gap between the covering and the wall. When using tyres with a timber grid on top it is usual to fix a tilted timber piece to the grid so that water drains off rather than sitting on the top of the tyres.

Using Rammed Car tyres for Foundations

Type of Infill

The tyre walls will be rammed full with stone, urbanite, or the subsoil that is found on the site. Suitable subsoil would be a clayey gravel, which has glue-like qualities and also allows for some plasticity, whilst still giving load-bearing capabilities and a solid, immoveable fill.

How to infill the tyres

The tyre walls are compacted with infill by the use of either a lump hammer or a pneumatic ramming device, ensuring that the infill is packed completely solidly, leaving no movement gaps between it and the tyre walls. First, the empty tyre is taken to the place where it will lie in the foundation, and the ramming device brought into position. This is to minimise the amount of movement of the tyre once it is filled with compacted infill. The procedure requires 2 people to work together, one to fill the tyre with infill, and the other to operate the rammer or use the hammer. The tyre is laid flat in its correct position and completely filled to the rim edge, compacted with some force ensuring that the whole inside ring of the tyre is solidly packed as well as the central hole. The stone in the centre is well compacted with a heavy device such as an upturned sledgehammer at a depth of 100mm, and also when full (approximately 195mm). Care must be taken to ensure that the stone makes full contact with the infilled tyre walls and forms a solid core to the tyre, to avoid the possibility of later settlement.

The second tyre is lifted onto the top of the first and filled in exactly the same way, the stone making a level surface. They are placed so as to form vertical columns 2 tyres high.

Construction of Foundation

For Timber floors:

The ram-filled tyres are placed around the footprint of the building at centres dictated by the dimensions of the floor grid (usually between 1.5 and 3m apart). They are laid directly onto the subsoil, or trench.
Once all the tyres are in place, the floor grid is laid on top of them, and the separate grid sections securely fixed together. The grid, usually made of 150-220 x 50mm timber, is designed to act as a whole unit that could theoretically be lifted off the tyres entire. (No pun intended!)
The grid is levelled on top of the tyres by packing underneath it at appropriate points with slate, or other such solid and waterproof material.

For solid floors:

The ram-filled tyres are placed around the footprint of the building in a continuous ring or line. They are laid directly onto the subsoil, or trench.
Once all the tyres are in place, the limecrete floor is laid on top of insulation (usually leca – blown clay particles), alternatively a rammed clay floor can be used.

Other comments.

The rammed infill is a permanent part of the structure, providing stability to the tyres, which operate in a similar way to gabions – stone filled metal cages. There is no possibility that the filling could wash away or otherwise be removed from the position it is in. It is held securely in place by the tyre walls themselves, which are steel radials, and the gravel central core, and is protected from above by the floor. There is no access to the central core of the tyre once the floor grid or solid floor is in position. The grid itself has a vermin-proof mesh on its underside, which completely covers the top of the tyre.