13. međunarodni simpozij o kvaliteti „KVALITETA I DRUŠTVENA ODGOVORNOST“, 15.-16.3.2012.
QUALITY IN WOODEN HOUSES BUILDING INVESTMENTS KVALITETA ULAGANJA U IZGRADNJU DRVENIH KUĆA
Ing. Renata Stasiak-Betlejewska, PhD. Institute of Production Engineering, Faculty of Management Czestochowa University of Technology Al. Armii Krajowej 19 B, 42-200 Częstochowa, Poland E-mail: renatastasiak@wp.pl
UDK/UDC: 005.6:502.3/.7+674 Pregledni rad/Review Primljeno: 31. siječnja, 2012./Received: January 31st, 2012 Prihvaćeno: 4. veljače, 2012./Accepted: February 4th, 2012
Izvor: Zbornik radova 13. međunarodnog simpozija o kvaliteti Kvaliteta i društvena odgovornost, Hrvatsko društvo menadžera kvalitete, Zagreb, Solin, 2012, str. 177-190.
ABSTRACT Current trends in building focus mostly on the sustainable development strategy promoted by European Union. It is not only trend or strategy but living idea in enterprises activity. The article shows an idea of wooden houses building with using prefabricating elements which cause shorter time of building process. There are some important problems which must be analyzed in the aim to support product quality in that kind of investment. Adventages and disadventages of wooden houses in the context of nonconformities and solutions noted in the chosen building company are the object of analysis presented in the article. Key words: sustainable development, quality, wooden skeletal house, passive house.
1. INTRODUCTION Current trends in building are focused around the principles of sustainable development. Sustainable development is development which meets the needs of the present without compromising the ability of future generations to meet their own needs.1 Modern home users increasingly expect both favourable economic balance and comfort for its inhabitants, as well as care for the environment. In the current sustainable building, system solutions include among others precast elements of house construction. The necessity of implementing the sustainable development principles since the 80s is one of the main point of international institutions dealing with environmental, safety and economics. These assumptions are intended to such global resources management to meet the current needs of society and also provide the opportunity to develop future generations. Building, as one of the most important areas of the economy, and puts such demands. Choice of the proper materials and building technologies support realization of sustainable development. Natural and renewable materials in building is one of the several 1
United Nations. 1987. Report of the World Commission on Environment and Development. General Assembly Resolution 42/187, 11 December 1987. Retrieved: 2007-04-12.
solutions of sustainable idea applying in building branch. The wood is a kind of material which meets with sustainable requirements and is healthy for users. It is also renewable and safety for environment. Wood is also a building block of moisture self-regulation capacity while giving warmth in the winter chill and relaxing on hot days. Moreover, in a wooden building there are primarily natural materials used such as: chipboard, mineral wool, plasterboard, wood salt preservatives impregnates. To join the fight against climate change and improve the life quality users decide to build a wooden house, for example, in the frame method. House made of wood reduces carbon emissions by about 10 t. Thus, if in Europe the number of houses built of wood has increased by about 10% is caused by a reduction of CO2 to the atmosphere by 1.8 million t. European experts in ecology have estimated that each wood cubic meter used instead of other material reduced by an average of 0.8 t of CO2 emitted amount to the atmosphere. One of the most important facts in wood using as the building material is that the construction of eco-wooden house uses a completely renewable resource, thus ensuring a healthy forest - the planned forestation. Healthy nature of a wooden house is indisputable, also allergy friendly. For example, where wooden architecture is distributed, statistical inhabitant of these houses live several years longer. There are also some other advantages of wooden houses. The wooden construction has lower price, which may be in some cases even one-third lower in relation to housing units built in traditional way. It should also be noted that timber houses are characterized by similar or often better standards for noise transmission or the temperature, than building a traditional building material of the ceramic. The time of "object life" is similar in both cases, although the wooden residential buildings require more frequent renovation. In addition, a factor which supports this structure is also a delivery time - much shorter than is the case of traditional technology. The main doubt of people reflecting on the wood house construction concerns fire protection issue. It is worth to note, that fire prevention measures currently used extensively to minimize the risk of fire. According to analysts' estimations of the Department's Research and Analysis Emmerson (research unit acting in Poland) the number of new residential timber construction for 2010 contained between 1.500-2000 of individuals. The best time for this kind of singlefamily housing, however, was a period including 2007-2008, when the total houses number significantly exceeded 3000. Recorded over two years decrease of this number can be explained rather by general situation in the real estate market, reversing the previous trend than a gradual increase in interest in wooden houses.
2. WOOD IN BUILDING CONSTRUCTIONS Most often raw materials used in wooden constructions is softwood. As a natural material construction it is constitutes harmony with the environment. Wood used for building construction should have a moisture content within the limits of 18-19%. It is assumed, that during the construction phase, usually lasting several weeks, the wood gets dry to about 14% for maximum strength, constancy of dimensions and twist without causing structural elements of the building. This concerns the sunny, summer weather. In autumn and winter periods, when it's cold and chilly, the wood may increase its moisture content to 20-22%. But it is a superficial humidity, which in a few warm days should reduce the moisture content of the required technology. There are three basic, well known wooden building constructions kinds in Polish architectures. The most typical is the log construction, also called carbon construction. Balls, of which the walls were built, hewn on two sides. Layers were stacked and combined in a
special corner cuts. The second type of building wooden construction is the construction called sumik-Ĺ‚Ä…tkowa, including balls. This construction was joined often with carbon construction. The third type of wooden building construction is construction called pole-frame construction, which has appeared in Poland at the beginning of the fourteenth century. This design is based on the frame formed of vertical columns and horizontal logs connected by pins and jams. The term skeletal home includes all the houses which are based on the wooden superstructure of the building. This allows clients to build houses very quickly - house closed in the raw state is ready after 4-6 weeks, and a developer state it is ready after 2-3 months since building start. It is one of the most popular wooden houses building technology and there is another popular met name of that technology - Canadian technology, which origins from country where it is common solution in building. House is created in accordance with an individual project in a factory, then it is assembled at the construction place is on the foundation already prepared in advance. The technology used to build wooden skeletal house is subjected to the modern production process. Primarily of natural materials are used in that production process such as: wood, chipboard, mineral wool, plasterboard. Supporting structure of the house is the skeleton, which consists of wooden poles and beams, which are combined by using nails, glue or special connectors. Frame house construction is made of pre-prepared pine logs or other conifers, with C24 wood class. The skeleton is installed on the foundation, protected from moisture and thermally isolated. The skeleton is a framework, consisting of bars with spacing of about 50-60 cm axial, horizontal and diagonal struts bolts for structural rigidity. The design of the ceiling and the floor is created under strict control and under a big pain, so that the beams were stiff and durable load floor. Exterior walls are formed by encapsulating skeleton by the finishing layers, from the facade and the inside (Fig.1a). Thermal insulation is placed between them. Construction of internal walls is similar to the construction of external walls, but the insulation layer is thinner and also feature a fully acoustic insulation. The internal walls are finished by cardboard plates applying, paneling or smooth wood based panels. Many items are imported for the construction in the form of finished parts for immediate installation resulting in a relatively short construction time. The basic thermal insulation of the building is a mineral wool filling the inner spaces of wall panels, ceiling and roof. Mineral wool is put in the elements at the stage of fabrication house under strict quality control, ensuring that the insulation layer is sealed. In addition, the exterior walls have an air pillow, what guarantees the natural windisolation so that the house is breathing freely. Technology of light wooden frame construction puts quality requirements to the construction elements in the mechanical wood processing. It is required, that structural elements are four-sided planed. This treatment not only provides dimensional stability, which greatly facilitates the work of the building contractor, but also makes shorten the time for obvious reasons, erecting structures, and thus does not raise the work cost. Quadrilateral planning increases the fire resistance of the wooden structure of the building (Fig.1b). Planed timber, wood compared to the outgoing directly from the saw, is more resistant to fire, because flames "glide" over the smooth surface of the wooden parts quickly without causing inflammation and thus limit the spread of fire. For the same reason, and the wood drying process in the heating chamber, the wood is more resistant for insects.
Figure 1. The construction of the wooden prefabricated element: a) cross-section of the structure, b) constructive element - after planning process. a)
b)
Source: Made by author in analyzed company X.
Studies conducted in the United States have shown that drying of wood at elevated temperatures (around 60oC) deprives the wood all natural substances, which could provide a breeding ground for pests of wood. However quadrilateral planning of structural elements prevents among others the insect eggs submission on the smooth wood surface, thereby reducing their reproduction within the wooden structure of the building. Unfortunately, building codes have not yet take into account the wood quality processing as a method of pest fight management. There is nowhere to be saved, obligation of the wooden structural elements protection by using chemical sealants, which by the way, in most cases are incorrectly used. The most serious and most common mistake on many construction places carried out with wooden frame technology applying is using of wet and not planed wood. Such wood is not only adversely affects the structural strength, but also reduces the durability of the building. Here are some examples of the risks caused by the using of wet wood in the building constructions: • Reduction of the structure strength; the wood of trees freshly cut (with a moisture content above 30%) has a bending strength of about 60-75% less than wood with a moisture content below 18%. • Rapid destruction of the timber; closed in the wall, not being able to quickly dry, the wood is brewing, and exposure to blue stain, mold and fungi. Destructive action of fungi on wooden structure can lead to total destruction of the building. • Destruction of thermal insulation properties of external walls; moisture coming from the wood penetrates the layer of insulation reduces its insulating properties. Thermal properties of thermal insulation layer of damp can be compared to the thermal properties of wet clothes during the cold winter. • Cracking of plasterboard walls and ceilings; during drying process wooden pieces are shrinking and twisting. Wood dimensional stability is achieved only when the humidity below 14%, but before reaching such a degree of humidity is shrinking by 1% for every 4% loss of moisture through which, not having the freedom of deformation, rigidly fixed plasterboard burst. • Yellowish patches on the plaster walls, caused by excess moisture in the wall in case of damage or improperly arranged vapor barrier.
3. ANALYSIS OF THE PREFABRICATED WOODEN BUILDING PRODUCED BY CHOSEN ENTERPRISE Majority of the building enterprises which are dealing with producing wooden elements for building investment prefer prefabricated elements which present cost-efficiency on high level in building investments. It is connected with such factors as: cost of produced elements, time of building realization and energey efficiency of the house. The object of the analysis (wooden house) is the main product of two chosen Polish building companies which are dealing with building wooden houses as well as passive (low energy) houses. They use common type of building construction method - skeleton construction with applying constructive glued wooden elements KVH. Analyzed companies realized their production and building investment with applying of sustainable idea, which focuses on the passive house building. The Passive House Standard constitute of several house building features set being a quality standard. Passive design is a promising strategy for sustainable housing design both in developing and rich countries: it permits the improvement of thermal comfort at low ecological and economical cost.2 The Passive Houses Standard is a sustainable construction standard. A Passive House is a building, in which thermal comfort (ISO 7730) can be provided solely by post heating or post cooling of the fresh air flow which is required for good indoor air quality (DIN 1946) - without using recirculated air in addition.3 Passive idea was introduced in those two companies on different level what is connected with the awareness of the passive house definition and sustainability idea. Analyzed companies has join element which concerns used building technology (KVH elements and skeleton construction) and the number of building investment realization per year (15 building investment done per year). Those two enterprises employee 45 workers which are divided into 3 teams working on the production and construction positions. Wood frame buildings in analyzed companies are realized in the form of prefabricated large-size elements (walls, floors, roof), or directly on the construction place with previously prepared individual items such as: posts, beams, lintels, foundations, rafters. Nowadays, prefabricated large-sized buildings are increasingly realized, what results in shorter cycle time for a better quality of construction and prefabricated factory-prepared. From a structural point of view, the most sensitive elements are made on the construction place.4,5 Ensuring adequate level of safety expected by the users of buildings becomes in this case particularly important. Understanding the behavior and response of the structure is also necessary for considerations such as: damages control or middle-elemental connections or the effect of use time. Prefabricated elements are ready-made building elements, which are supplied to the building site and assembled there directly from the factory or warehouse (Fig. 1). They are not a novelty in the construction market - their advantages have already appreciated a few decades ago. Also today, ready-made building elements are very popular, however, from modern prefab requires much more than before. Mentioned technologies are based on the prefabricated small-format and large format elements. These elements are usually boards or panels, which compiles the walls and ceilings, or consists of the form of requiring a complete mix of concrete. The construction of such 2
Ernst M체ller탑, Crucial Building parameters as a novel approach for the design of passive solar house in a mediterranean climate, Building Research Institute, University of Kassel, Germany, 2006, pp. 37. 3 Resolution of the European Parliament of January 31st, 2008 calls for its implementation by all member states by 2011. On November 17th, 2009 the European Parliament and the Council fixed 2020 as a deadline for all new buildings to be nearly zero energy buildings. 4 Donald E. Breyer, Design of Wood Structures, Mc Graw-Hill, Inc. Third Edition, 1993, pp. 43. 5 Horst Schulze, Holzbau, Wande-Decken-Dacher, B. G. Teubner, Stuttgart, 1996, pp. 45.
prefabricated house takes a bit longer than the installation of large plates (Fig.2). During the construction is not required a large crane, the work is often performed manually, without the aid of heavy equipment. The most large-format technologies, each element corresponds to one wall of the house.
Figure 2. The asssembly of wooden prefabricated house.
Source: Made by author in analyzed company X.
The analyzed building is made from imported laminated wood panels KVH. These are high quality wood components in a form of a timber (Fig. 3). In the production process, elements which adversely affects the strength wood quality are removed from the timber. Each item is also automatically checked for the required humidity and rejected in case of differences. Bonding is performed by using glue which is proven and approved in accordance with DIN1052-1, able to withstand high loads. These elements are connected to the wedge slings, one of the safest, most effective and modern methods. The connection is not a weakening of the structure and need not be included in the static calculations.
Figure 3. The constructive wooden element KVH used in analyzed enterprise.
Source: Made by author in analyzed company X.
The wood is kiln dried to a moisture content of +/-16%. Using wood KVH it is possible to build durable and complicated wooden buildings, ideal for a complete loadbearing structures.
Wood KVH meets the rigorous standards for static and load - standard DIN 1052 as well as parameters relating to the width of annual rings, wane, slope of fibers, cracks, discoloration, etc. specified in DIN 4074-1. The finished item is labeled with embossed numerals archived at the manufacturer's bar code, allowing producer to trace the path that it traveled in the manufacture and assembly on construction site (Fig. 4).
Figure 4. The constructive wooden elements KVH used in analyzed enterprise: a) with bar code, b) with identification number. a)
b)
Source: Made by author in analyzed company X.
In traditional carpentry constructions the main condition of the construction rigidity and power transfer occurring is appropriate carpenters jam called differently depending on the location of notches etc. Places of joints are linked by using of ring nails or screws. To ensure the highest stiffness of these connections and the building's, analyzed companies use SPAX connections that carry a maximum tensile and compressive strength by up to 67% more than the screw. These connections also have a high resistance to wind suction force, which allows to use them at roof construction elements. To improve the quality of window installation for tightness in the order of integrity standards supporting analyzed companies use additional external seal in the form of acrylic tape expansion steam-permeable Soudal. This tape is resistant to weathering and UV radiation, while allowing water vapor diffusion of thermal barrier assembly foam. In the finishing phase of the interior, the investor must pay attention to whether the inner seal is used to prevent moisture due to steam generated in the rooms.
Figure 5. The assembly of the window element in the house frame construction with the made by workers of the analyzed enterprise.
Source: Made by author in analyzed company X.
4. THE MOST COMMON FAILURES MADE BY THE WOODEN BUILDING Analyzed technology has no long tradition in Polish building what is connected mostly with using concrete technology, which is used for years and very well known on the market because of materials. Even cost of concrete house is lower than wooden house, current building enterprises have started interesting in using wooden elements as renewable and easy to process and use at construction process. The low of wooden building advantages is also caused by lack of proper law regulations in Polish building law. The lack of clients interests in wood as a building material is also caused by belief that wood is not fire resistant material what is not truth. The increasing number of enterprises which are dealing with wooden prefabricated building doesn't cause the increase of clients awarness of wood advantages. There are still several failures made by producers of prefabricated elements and workers who assembly elements on the contruction place. The most often failures made by building companies in the wooden house building are following (Fig. 6): a) lack of the insultation in all proper places, which eliminates thermal bridges (places which cause heat losses) - identified in 10 constructions per year (Fig. 6a), b) lack of proper insulation and strengthen construction in the corners of the hosue identified in 6 constructions per year (Fig. 6b), c) improper assembly of construction elements with improper sizes - identified in 4 constructions per year (Fig. 6c), d) improper joints - identified in 3 constructions per year (Fig. 6d), e) improper assembly of foil vapor barrier (Fig. 6e) - identified in 15 constructions per year.
Figure 6. The most often failures made in wooden houses buildings. a)
c)
b)
d)
e)
Source: Made by author in analyzed company X.
The construction of external walls form a cross-section bars 38 x 140 mm, connecting the lower foundation wall girt. Spacing of bars shall be 40 or 60 cm depending on the axial loads taken. Due to construction of bars 140 mm width is a dimension often inadequate. Stresses encountered in the construction of a wooden house to successfully move the elements with smaller sections, but for reasons of building thermal protection (insulation thickness) dimension of 140 mm bars seem to be adequate, unless of course does not provide additional insulation to the walls. The most often failure of the building companies is using wet wood. Wood brought to the building should have a moisture content greater than 18-19%. It is understood that during the construction phase, usually lasting several weeks, the wood gets dry to about 14% for maximum strength, constancy of dimensions and without causing warpage of the building construction elements. The other common failure made by workers is improper foil laying on the construction. The foil vapor barrier is laid from the house interior before attaching gypsumcardboard. Building envelope protects against excessive ingress of water vapor vented from the element room. The lack of the foil or assembly failure can result in moisture vapor barrier plating. Condensation of water vapor condensation in the chamber and it could in turn lead to mold wood elements in the building and reduce the insulation and thermal properties.
5. CONCLUSION Analyzed adventages of wooden prefabricated building and failures made by building enterprises can create the opinion about quality level of building works needed for wooden house building investment. In the construction process the most important role is played by used raw materials. One of the reasons responsible for the failures occurrence in the building investment process may be low quality materials (such as wet wood). In order to overcome this problem companies decided to introduce pre-process control of materials. Raw material quality improvement has a considerable impact on improving the quality of the building process. To choose the best way to achieve this objective, process decision program chart (PDPC) was applied (Fig. 7). The result of the application diagram is specifically defined, the best way to achieve improved quality materials.
Figure 7. The process decision program chart (PDPC) for building investment process. ISO standards Division of the responsibility
Elaboration of the criteria set
Technical standards
Preliminary inspection Control tools
Method’s selection
Methodology identification
Raw materials quality improvement
The process of suppliers qualifying
Selection criteria for suppliers
Analysis technical and quality requirements
Source: Made by author in analyzed company X. Applying diagram in both analyzed companies caused increas the quality level of houses built in last year (2011). The owners of those two companies stated that programming selection of supplies and suppliers supporting by control tools let to modify building process.
Sažetak: KVALITETA ULAGANJA U IZGRADNJU DRVENIH KUĆA Sadašnji trendovi u izgradnji usredotočeni su uglavnom na strategiju održivog razvoja promoviranu od Europske Unije. To nije samo trend ili strategija već ideja prisutna u poslovnim aktivnostima organizacija. Članak donosi ideju o izgradnji drvenih kuća upotrebom prerađenih elemenata koji zahtijevaju kraći procesni ciklus izgradnje. Pri tom postoji nekoliko važnih problema koji trebaju biti analizirani radi doprinosa kvaliteti izgradnje i ove vrste investicija. Prednosti i nedostaci drvenih kuća s obzirom na nesukladnosti i varijante do kojih se došlo u odabranoj građevinskoj organizaciji, predmet su analize prezentirane u ovom radu. Ključne riječi: održivi razvoj, kvaliteta, drvena konstrukcija kuće, pasivna kuća.
6. LITERATURA 1. Borkowski, S., Stasiak-Betlejewska, Renata, „Value Analysis in the Insurance Services Concerning the Construction Investment”, Chapter 6. [in:] Service Processes Improvement. Monography, Editing and Scientific Elaboration Stanisław Borkowski, Denis Jelacić, Renata Stasiak-Betlejewska, Publish Damir Jelacić, Zagreb, 2011. 2. Borkowski, S., Stasiak-Betlejewska, Renata „Quality Reception of the Building Services on the Basis of the Service Quality Analysis”, Chapter 5, [in:] Service Processes Improvement, Monography, Editing and Scientific Elaboration Stanisław Borkowski, Denis Jelacić, Renata Stasiak-Betlejewska. Publish Damir Jelacić, Zagreb, 2011. 3. Breyer, D. E., Design of Wood Structures, Mc Graw-Hill, Inc., Third Edition, 1993.
4. Drljača, M., "Uloga menadžmenta u uspostavi sustava kvalitete prema normi ISO 9000," Slobodno poduzetništvo, Broj 10, TEB, Zagreb, 2001. 5. Müller, E., “Crucial Building parameters as a novel approach for the design of passive solar house in a mediterranean climate”, Building Research Institute, University of Kassel, Germany 2006. 6. Schulze, H., “Holzbau, Wande-Decken-Dacher”. B. G. Teubner, Stuttgart 1996. 7. Resolution of the European Parliament of 31 January 2008. 8. United Nations. 1987. Report of the World Commission on Environment and Development. General Assembly.