Sustainable Urban Construction

It is well known that different materials used in construction are harmful to householders’ health. Although most of them are no longer permitted, it is still possible to find them in restorations. In addition to these materials inherent to the construction, there are others that do not depend on the building itself, but rather on the soil characteristics. One of such substances is radon. Therefore, the effect of this substance can be noticeable in those buildings where the soils upon which they are built contain it.

These hazardous materials and substances can be classified as:

3.3.1 Asbestos
Asbestos has been widely used because of its high fire resistant and thermal insulation characteristics, and as a resistant matrix for fibrocement products. It is made of different iron, aluminium, and magnesium metasilicates, fibre shaped. Inhalation of this product can develop lung related problems and cancer. The main diseases caused by asbestos are:

3.3.2 PCBs
These products are non-flammable and have dielectric characteristics. Their disadvantage is that when temperatures above350ºC are reached, like in a fire, they turn into a highly toxic substance, releasing hazardous gases such as dioxins.

PCB products are not biodegradable; therefore, pollution from these substances builds up in the environment, and can even remain in waterstreams like rivers or seas indefinitely, polluting them. PCBs produce cancer in animals, and they are thought to cause the same effect on people. They are currently considered potentially carcinogenic agents. PCB also affects the immunologic, nervous, reproductive and endocrinal systems.

3.3.3 Smoke ionic detectors
These are very radioactive fire detectors. The radiation emitted is not necessarily problematic, but there is always the latent risk of radioactive isotopes combining with the air if an accident should happen. This situation poses an important threat for radioactive pollution both on human health and environment.

The intensity of their radioactive emissions makes them unharmful at 5 cm away from their source. These detectors can be replaced by optic and thermovelocimetric detectors.

3.3.4 Radon
Some rocky materials such as granite release radon radiations. Radioactive particles from radon can get trapped in the lungs, damaging the tissues and causing cancer. Smokers are more prone to develop cancer, although it may take many years before it happens. Since radon is a gas coming from the soil, it can enter the buildings through little cracks in the foundation as well as floor structures and it can build up in basements and other upper parts of the building. For this reason, it is recommended to separate the housing’s floor from the ground and create a perfectly ventilated space.

3.3.5 Creosote
This term includes a wide range of products such as mineral tar, wood creosote plus mineral tar, and coal tar and its volatile compounds. These products come from the treatment of wood, and mineral coal and resin obtained from the creosote shrub at high temperatures. They were used as wood protectors and also in construction materials in parks and gardens. Creosote is classified as a possible carcinogenic product in the 2A group by the International Agency for the Research on Cancer, which means that there is not enough evidence proving that they cause cancer in humans but enough to prove they cause it in animals. Other institutions do consider it as a carcinogen.

3.3.6 Sick building syndrome
Lately, a new syndrome related to the building characteristics has been diagnosed on those who spend large periods of time in it. Its symptoms include skin, eyes, and neck rash, as well as other discomforts regarding smell and taste. It is usually due to a deficient ventilation, suspended particles, and ionic and electromagnetic charges. Office buildings with airtight curtain wall are the most likely to make people develop this syndrome. The ventilation in these buildings is artificial, and if it is not adequately calculated, it will favour the appearance of allergies and the transmission of diseases such as the flu.

On the other hand, humid, dustily, and scantly ventilated areas favour the appearance of acaruses and molds, which can cause allergy problems. In addition, there are some materials in the office that by releasing mineral fibres, containing volatile organic compounds, and releasing toxic vapours, contribute to the appearance of the syndrome.

To avoid the use of products containing volatile organic compounds (they are present in paints, varnishes, carpets, and curtains).
Restrict as much as possible the smokers’ zones
Enhance natural ventilation over mechanical one.
Good maintenance of air conditioning conducts, cleansing filters and conducts often.
Keep carpets and surfaces prone to accumulate pollutant agents clean
Separate zones with special air quality, specially combustion and machinery rooms, bathrooms, and kitchens, allowing independent ventilation.
Minimize radon emissions by using radon free materials or creating ventilated spaces over the ground they are built on.

3.3.7 Comfort
Comfort is achieved by the proper combination of several parameters such as temperature (25º-26ºC during the summer and 18º-20ºC during the winter), pressure, humidity, ventilation, air quality, low sound levels, and lighting. The aim is to create a comforting ambient with the least energy consumption possible in an environmentally friendly way. As it has been mentioned in section 1.2.8, thermal mass is a key feature in materials to help reach the right temperature. Depending on the weather conditions, the right choice of materials will vary. In dwellings used regularly, materials with a high thermal mass (associated with high mass) are recommended (i.e. brickworks). They take longer to accumulate heat energy from the ambient in their mass, and they also take longer to release it into the ambient when the temperature in the walls is higher than that in the room. Weekend households are better suited with low thermal mass materials (materials that build up energy in their mass faster and are also faster releasing it into the ambient; i.e. wood). The reason is that, when the heater is turned on, these households will reach a comfort temperature sooner than high thermal mass materials and will keep it until the habitants leave because the heater is usually on all this time.

Another way to keep a comfortable temperature indoors during the winter, and preventing excessive heat from entering the building during the summer, is using materials that provide thermal insulation, such as polystyrene. By properly and carefully installing thermal insulation (it has to be continuous to avoid spots through which heat is lost) it is possible to keep a pleasant temperature with little energy consumption. Thermal insulation is applied in façades, roofs, slabs, and windows, which constitute important heat loss surfaces.

Besides thermal mass, another way of controlling temperature is ventilation, caused by a difference of pressure between opposed facades. Ventilation can also be created by plants. Plants are capable of creating microclimates that contribute to cooling spaces by the evaporation occurring in the photosynthesis and by giving shade to the buildings next to them, therefore controlling the quantity of sun radiation entering the dwelling.

Sound is also controlled by sound insulation materials, such as wool rock and also double windows are very efficient reducing sound levels. Even plants can create sound screens. The table below shows the acceptable sound levels depending on the time of day:

Table 1. Sound levels in different parts of the housing. Source: www.c-sostenible.com

	DAY (07:00-22:00)	NIGHT (22:00-19:00)
Bedroom	35 dB	30 dB
Living room	40 dB	35 dB
Kitchen, bathroom, etc.	55 dB	40 dB

dB (decibel): measure unit for sound intensity level. The human ear is capable of noticing sounds starting at 0 dB, and those above 130 dB cause pain. As a reference, the breeze is dB, a normal conversation is 50 dB, a speeding motorcycle is 90 dB, and a plane take off is 130 dB.