Qualification - Foundation Diploma in Sustainable Construction

Learn to build with wood, stone, mud and other environmentally friendly materials to create interiors and exteriors that are more people friendly. 

Modules

Note that each module in the Qualification - Foundation Diploma in Sustainable Construction is a short course in its own right, and may be studied separately.

Any Sustainable Building Needs Good Foundations

Throughout history, solid buildings that last were always built on a solid foundation (eg. stone buildings were often erected on rock surfaces). When foundations had to be laid, the building pit was first filled with water and the resulting horizontal lines were marked on the walls. The water was then removed and the pit filled with sand up to the marks, and the foundation started from there.  Luckily we have many other choices and options to have our foundations made out of in today’s time.  

The aim of footings/foundations in any building is to spread the load of the building so that the capacity of the foundations to support the building is not exceeded.  In a domestic situation, strip foundations are usually adequate, however in soils which are highly reactive, pier and beam footings will minimize cracking (you will get some cracking due to seasonal variations, even with good foundations).
Any type of foundation can be part of an energy-efficient house if the details are done right. Many factors, such as soil type, slope of the site, local experience, and material availability enter into deciding what to rest your house on for the next 50-100 years. Besides supporting the weight of your house, your family, all your relatives at holidays, your piano, waterbed, and hot tub, the foundation needs to control the flow of heat, moisture, and air. 

Specialist engineering advice should be obtained in the following cases:

• Where you are building on filled ground
• Building on limestone soils where there might be underground caverns
• Where there might be subsidence due to mining
• Where there might be subsidence due to underground water.
• Where there is a statutory requirement for engineers certifications or calculations

There are two main options for foundations:

• Strip Foundations - creating a solid base in a series of trenches
• Slab Foundations - creating a solid base with a large solid slab

For normal soil conditions, footings twice the width of the wall are adequate. Concrete foundations are usually extended above ground level to 300 mm or so (to avoid the bottom layer of mud bricks eroding). Alternatively a layer of masonry brick or stone may be laid to bring the level to 300 mm or more above the surface of the ground. The depth of a concrete foundation will depend on the type of soil it is placed in, and upon the weight of wall it is to support.

Foundations are perhaps the most important part of any building or wall.  They must be properly designed and properly constructed. A poor foundation will result in cracking of walls, and even the collapse of a building.

For standard housing or garden walls, strip foundations are normally suitable, however, in some soils a pier and beam footing may be necessary to minimise movement and hold firm as the soil moves from season to season. Expert advice from a civil engineer is advised in situations where the soil is suspect i.e. filled ground, limestone soil where there could be underground caves, underground water courses, subsidence due to erosion, mining etc.

Rock Or Rubble Foundations
Strip foundations composed of stone rubble (carrying sized rocks) have been widely used for mud brick walls in some countries (including China). These foundations are constructed in a rectangular trench at least 35cm deep.  A depth of 50cm is better. If the walls are extra heavy (tall or wide) a deeper or wider foundation may be necessary.

The foundation should extend above ground level for up to half a metre (depending upon susceptibility to erosion). The top of the foundation can be either flat or stepped.  Whatever the choice though, surfaces should be level. This is important not only for appearance, but also for the strength of the wall. Mud walls that are built on a sloped foundation will distribute forces unevenly throughout the wall, and that can weaken a structure. A stone/rubble foundation should ideally use mostly medium to large rocks that are 15 to 30 kg in size. Smaller stones down to 2.5kg can be used to fill gaps but these should not be more than 10% of the total volume of the foundation.

The stones are joined together by mortar. There are various options for mortar:

• Cement mortar
• Soil-cement mortar: 1 part cement to 10 parts sand has been used successfully for mud brick foundation in Egypt
• Lime mortar: 1 part slaked lime, 1 part clay, 1 part sand, mixed with water.
• Mud mortar: made from sandy clay and water. This has been used for foundations in drier climates (including China). Under certain conditions (eg. On the crest of a hill in a desert) it may be adequate. This type of foundation is more likely to erode though under moist conditions.

Note: A well constructed foundation gains strength mostly from the interlocking of stones. If stones are arranged so that they will not move, the mortar becomes more of a “filler” and less important to the actual strength of the foundation.