The article is from A&B's 11/22 issue.
Mass production is present in many areas of life. In architecture, building materials - masonry units, ceramics or roof tiles - are produced on a large scale. However, houses built using concrete blocks or ceramic hollow blocks are not called prefabricated. So when are they referred to? Usually when the factory-prepared elements that make up the block are larger and allow for quick assembly.
Prefabricated technologies is an extremely broad term that accommodates a huge variety of production methods. One possible division of this category can be the construction material used. Then we can talk about prefabricated concrete, expanded clay, wood, steel and so on. Further differences and divisions occur between individual manufacturers or the products they offer. For example, in timber frame technology, the structural elements have different cross sections, and the buildings differ in the amount and type of thermal insulation used. Another issue is the degree of prefabrication. Some buildings are almost entirely constructed in a production hall and arrive at the project site with windows, internal installations and finishes inserted, while assembly on a pre-prepared foundation slab takes a few or a dozen hours. At the other extreme are timber-frame houses, whose structure of factory-prepared beams is assembled on site and only then are more elements added: insulation, membranes, finishing.
What are the possibilities in terms of prefabrication and what technologies can be used to build a house in Poland? And also - what are the advantages of this choice? This text is an attempt to answer the above questions. However, given the enormity of the possibilities and the myriad of technological nuances between different methods, this will be a selection of available solutions using examples from specific manufacturers.
Wood is the most popular material that comes up in the discussion of prefabricated houses. Manufacturers offering timber frame houses are by far the most numerous. In terms of typology, a distinction is made between light Canadian frame and heavy German frame. The difference between these types lies, among other things, in the cross-sections of the structural elements: in heavy timber framing, these are larger cross-sections, and OSB (or gypsum-fiber board) appears twice in the wall layers - outside and inside the structure. Wood as a construction material is solid and warm - it does not create thermal bridges. It is also a renewable material. In frame systems, in addition to the structure and insulation, membranes are hugely important: windproofing on the outside and vapor barrier on the inside. Thanks to them, the structure and thermal insulation remain dry, and the optimal microclimate is maintained indoors.
LD frame house is just one example of a house that can be configured from modules available at Simple House
photo: Bartek Warzecha © Simple House
Lightweight, wooden structures are offered by Simple House. The timber-frame houses are available in three energy standards: Simple with a demand of about 105 kWh/m2/year, Simple Energy: 40 kWh/m2/year and Simple Passive: 15 kWh/m2/year. Depending on the choice of standard, the thickness of the insulation (rock wool) changes, so the cross sections and the envelope. "Simple House carries out the project comprehensively. We build the house from the foundations to the development stage (or we also handle the interior finishing, if that is the will of the client or customer). Investors are minimally involved in the implementation process, all logistics related to construction are handled by our team," says Adam Czajkowski of Simple House. To build a 150-square-meter energy-efficient house, the company needs five-six months and the price of the investment in developer condition starts at 750 thousand zlotys gross. The bodies of the houses can be customized to individual preferences - the starting point is the ready-made designs offered, but they can be modified to suit the customer's needs. For example, you can change the angle of the roof or the layout of the rooms. Simple House is characterized by a modular approach - thanks to this, the form of the house can be easily changed at the design stage or later expansion.
The issue of houses in the heavy German system is slightly different. The cross-sections of the structural elements of the exterior walls in HausWerk are 16 by 6 centimeters, and the floor joists are 24 by 6 centimeters. With this comes greater load-bearing capacity, and this technology can be used with screeds on the first floor and clay tiles on the roof. Double-sided reinforcement with gypsum-fiber boards further stiffens the structure. More materials, however, means a higher construction price. "The cost of building a prefabricated house in the heavy German system depends on the scope of cooperation, the complexity of the body of the building, the choice of finishing materials and the type of heating. HausWerk houses are realized as standard to the developer's state with complete installations, heat pump and mechanical ventilation with recuperation. In the case of simple blocks, the cost of the house starts at PLN 5,500 per square meter. With complex design solutions, the price can reach 7,000. Usually the implementation of a foundation slab is not included in the scope of work, but at the request of the investor we can make such a slab". - Lukasz Maćkowski of HausWerk says.
The simple form of a modern barn built in timber frame, in the heavy German system
Photo: © HausWerk
Thus, there are higher costs than in the case of traditional masonry technology. However, Maćkowski points out that cheaper construction is an apparent savings: "The energy standards of the house mean that our operating costs will be significantly lower. The energy demand of most HausWerk houses fluctuates around 20 kWh/m² per year, and at the request of the investor we can even achieve energy self-sufficiency of the house, which translates into long-term savings, which is particularly important in conditions of rising fuel and electricity prices from year to year." How long does it take to build a 100-foot house at HausWerk? The prefabrication process in the production hall takes about a week. It then takes about a week to erect the shell of the house - the walls are built from previously prepared modules. It takes about four months for the development state.
Assembly of the walls of the house in the heavy German system; it takes about a week to erect the shell-closed state (on a previously prepared foundation slab)
Photo: © HausWerk
Steel prefabrication for houses is not as popular as wooden, although the technology itself is very popular if only in industrial construction. Houses are offered as an ordered frame, which is assembled on site, filled with wool and cladding. Some steel-framed buildings are built almost entirely in the factory. This is the case with QMODULAR's realizations, which are 95 percent prepared in the hall, with finished building modules roughly the size of a shipping container arriving on site. On site, the buildings are erected by crane. The modules already have cladding and windows inserted. The manufacturer gives the example of the 56-square-meter Phoenix+ two-story house, which arrived on site sixty days after signing a contract with the developer. The interior of the bathroom and kitchenette was already finished, and the on-site installation itself took only a few hours. What are the prices of houses using this technology?
The use of modular technology is a good idea for investments - it allows to shorten the time of construction of an object, such as the motels produced by QMODULAR, which are part of the Lemon Resort Spa in Gródek nad Dunajcem
photo: © QMODULAR
In the case of a one-hundred and fifty-meter house, the cost of building a square meter in developer condition is PLN 4500-5500. Of course, building and finishing materials choices have an impact here. Interestingly, QMODULAR houses are point-supported, so a full foundation slab is not required. In the case of steel, fire resistance issues are important - the manufacturer uses proven, tested solutions, but also develops and commissions tests of innovative partitions if the solutions available on the market are insufficient. In the production hall, the necessary internal installations are created independently for each module. On site, the connections of the individual components are sealed, and the installations are connected to each other (e.g. with quick connectors in the case of the electrical system) and checked.
The modular approach also results in the construction of larger facilities using this technology, such as the Lemon Resort motels in Gródek nad Dunajcem. Within three months of contracting, twenty finished suites were built on the water, ready to receive guests. Interest in the technology is growing: "The greatest interest is in large-scale buildings: hotels, office buildings, apartment blocks, dormitories, housing estates. We anticipate a significant increase in investment in 2023, which is related not only to the growing demand of investors for such facilities, but also to the expansion of our production line. The factory we are building next year will reach a production capacity of up to 4,000 square meters of floor space per month, and all indications are that we will fill it to capacity." - admits Andrzej Kukułka of QMODULAR.
timeline traditional vs. modular construction
photo: © QMODULAR