Casa Buna: A low cost, energy-efficient residential building with a lightweight steel frame

Detailed information

A simple design for decent and affordable housing

The Casa Buna model is based on Romanian vernacular architecture. It is a compact and sober house, covered with a conventional roof with two slopes. Its principle of setting up and of lying out takes into consideration both the harsh continental climate and the relative shortage of building land. Thus, two levels measuring 10 m by 12 m comprise four apartments of equal measure under one roof.

Each apartment occupies one fourth of the house cut in the vertical direction: all the apartments are duplex and each faces a different direction – northwest, northeast, southwest, and southeast – and each has a private entrance and a private garden on the ground floor. The parking is outside along the road.

A reproducible construction principle

The constructive principle is simple and makes use of modern and traditional products.

The limited number of components facilitates easy assembly and the simple plan allows it to be assembled by non-professionals.

Thus, the frame structure is made of thin, cold-formed steel profiles. The metal sheet is made up of galvanised steel S350 of 1.5 mm thickness. Mounted on a 60 cm conventional frame, it is associated with OSB (Oriented Strand Board) wood panels and plasterboard. The windows are made of PVC with double glazing. All these parts are of standard size and composition.

Their assembly was essentially carried out with the help of bolts and screws, and the structure is bolted to the traditional concrete slab. OSB panels are attached directly to the profiles using deck screws. The insulation boards are in turn attached to the OSB. The finishing is either in stucco or steel raiment. The roof is made of organic-steel-coated tiles. These tiles are actually large strips of previously stamped steel measuring 7 m by 1 m - very quick and easy to install as half a day is enough to cover a house.

A construction adapted to its environment

In this part of Romania, buildings must be able to withstand earthquakes measuring 7 to 8 on the Richter scale. The bracing is provided by a St. Andrew’s cross. Furthermore, the continental climate, characterised by abundant snowfall in winter, causes large surges which must be taken into account when calculating the proportions of the framework.

Overall, the bioclimatic design of the house helps in achieving the right temperature by varying the compactness of the house, the distribution of glazed surfaces, and insulation from outside, all of which contribute to reducing energy costs.

Accurate management of materials for a speedy construction

Prefabricated parts, easy to assemble, fast to construct: The entire house is made from standard industrial components purchased from a distribution centre in Romania. A single truck is sufficient to transport the material to the site, which is assembled by volunteers who are supervised by a professional. The simplicity of the structure and tools required to build the house do not require advanced skills. However, the assembly is carried out under the guidance of technical supervisors of the NGO who follow strict technical specifications pertaining to the design and implementation plans along with ArcelorMittal personnel and its partners who are present, if necessary.

By building three houses in succession, Habitat for Humanity is now in a position to gather the manpower needed to conduct workshops. The tasks are distributed and repeated from one workshop to another. These workers who will tomorrow own the houses acquire the skill that will later come in handy to maintain the house and, possibly, to participate in subsequent workshops. In addition, it contributes towards the first step in building human bonds.

An 'optimised' house

Casa Buna responds to a severe economic necessity without which it would have been difficult to provide basic amenities. The low cost of this house was made possible due to a number of measures put in place from conception to completion.

The price of all materials excluding that of the foundation amounts to 50 000 Euros (inclusive of all taxes) for a house with an area of 240 m2. The planned cost was possible to achieve as all the items purchased are of standard quality and available with special traders. The sites and their development are negotiated in advance by Habitat for Humanity with the competent local authorities. The fact that unqualified workers can be used for this simple construction contributes to the decrease in the overall cost of construction.

A high-performance steel solution

The steel structure based on thin sections, combined with other materials like plaster and wood, is perfectly suited to the construction of houses such as Casa Buna which must not only be of high quality, but suit the climatic and seismic conditions and still be very affordable.

The durability of materials is of course essential, which is assured due to the use of galvanised steel.  With only 10 tons of steel per house with four apartments, the material is optimised. This light structure is also able to absorb the shocks of a major earthquake. Thus, although less steel is used, the same safety measures are inbuilt as in a modern car.

Moreover, another advantage of this structural solution is in relation to its foundation – it allows the house to be shifted, if necessary, and can be adapted to other types of housing.

The entire design follows a sustainable development approach - now a must for any responsible industry.

Text: Eve Jouannais