The elements in a building are roughly divided into two parts
- the envelope of the building like walls floors, doors etc.
- the services such as wiring and drainage.
Thinking of a house as a number of elements is the traditional way of organising the construction process and works well around the various trades involved. However the challenges which arise with selfbuild and green building are often as much to do with the relationships between the elements as with the elements themselves. This is particularly true with thermal bridgingthis is a pathway where heat can easily escape (or get in) through some part of the structure. It is usually caused by some element of structure such as a steel lintel or wooden studwork. Also known as a cold bridge. see more on thermal bridging and air tightnessA measure of how leaky a building is to air. In other words, how draughty it might be. There are now standard fan pressure tests to check how air tight a house is and the Building Regulations have minimum standards for all new houses (L1A – Conservation of fuel and power in new dwellings (England)). A much higher degree of air tightness is covered by the Passivhaus standard. The services also pose a challenge in terms of their efficiency, and take on a new dimension where energy harvesting is concerned.
Until quite recently the building regulationsThese are the mass of regulations that cover safety, health, welfare, convenience, energy efficiency etc. in the way buildings are constructed. Not to be confused with Planning consent (which is more to do with whether you can put up the building in the first place), parts L1A and L1B, have been mainly based on an ‘elemental’ calculation for heat loss. This was a fairly crude method of calculation of the U valuemeasurement of how much heat escapes (or gets in). The units are W/sq.m./°c. see Insulation properties of each element of the building and simply adding all the bits together to give a total heat loss. What is becoming a more important aspect now is the actual performance of the whole house when it is built. Hence the introduction of fan testingHow 'leaky' a house is (in other words how drafty it might be) can be measured by fixing a large fan in an external doorway and measuring the pressure difference between the inside and the outside. (see Fan testing) to find out if all the elements fit tightly together.
The other factor which becomes important is how the materials used in the various elements are sourced and eventually disposed of and how much energy goes into making them (the embodied energythe total amount of energy it takes to make a material (or a building). See more on embodied energy).
If you purchase a kit house you are very much in the hands of the supplier and you need to check out their materials and design whereas if you go down the route of designing and building it yourself then you have (hopefully) more control over all the ingredients.
The building site
There are two main challenges that arise once you actually get to the on-site work
- Reducing waste on site and recycling.
- Reducing transport associated with the building work
Reducing on-site waste is often harder than it first seems. Obviously a great deal can be achieved at the design stage by carefully working out the quantities of materials required and who can supply them in the correct batches at the right time.
Well organized storage is necessary especially where materials need to be kept dry so as to avoid damage due to waste.
Containers and packaging needs to be considered carefully because it is such a complex issue. Some items such as pallets are returnable, some such as cardboard boxes are probably recyclable while some plastics such as polystyrene may not be. Local recycling schemes are improving rapidly in many areas of the country so check out what they will and won’t take.
Transport associated with building sites can be enormous, especially when the work becomes more specialized. For instance the ‘shopping’ needed for plumbing or electrics can be a major part of the job especially for someone who doesn’t carry a large range of fittings etc. in the back of a van. Particularly if you are going to undertake this type of work yourself and especially if the building site is remote from a town with a good selection of merchants, the golden rule is to plan shopping trips carefully and phone beforehand to make sure they have it in stock. Also take the phone numbers of alternative suppliers so you can phone round as you go. This can avoid a lot of repeat journeys.
Manufacturers are generally good at giving technical information on their own products.
The NHBCThe National House-Building Council describes itself as being "the leading warranty and insurance provider and standards setter for UK house-building for new and newly converted homes" have a considerable amount of information about construction details on their Technical Guidance pages and their Technical Extra
Trade associations often publish information on good practice e.g.
Glass and Glazing Federation A Guide to Best Practice in the Specification and Use of Fire-Resistant Glazed Systems