Residential complex project of 12 passive single-family houses and a training centre in Koberovy – Cesky raj

Project authors:

Ing. Petr Morávek, CSc., ATREA s.r.o.
V Aleji 20, 466 01 Jablonec nad Nisou
Phone.: +420 483 368 111, Fax: +420 483 368 112, E-mail: atrea@atrea.cz

prof. ing. Jan Tywoniak, CSc., FSv ČVUT in Prague
Thákurova 7, 166 29 Prague 6
Phone.: +420 224 354 574, Fax: +420 224 357 071, E-mail: tywoniak@fsv.cvut.cz


Introduction
In August 2007 ATREA s.r.o. delivered for use a pilot residential complex of 12 passive houses and a training centre in Koberovy – the first large-scale experimental development project in the Czech Republic based on a wooden skeleton structure and certified to meet the parameters of energy-passive buildings.

Urban concept
The development fully respects the strict regulations of Natural Preserve Cesky Raj within the village’s built-up area, i.e. solely saddle roofs, entrances from lateral facades, limited glazing areas etc. The ridges of the houses are situated in the East – West axis while their fronts gradually turn South to South-West to guarantee a completely undisturbed view of the gardens and minimise the shade they put each other in. The decentralized concept of development intentionally abandons the current monotonous nature of terraced “street development” to rather create an optically closed form logically conforming to today’s character of development in Koberovy.

Individual house plans
The longitudinal wing of the main living space is oriented to the Southern front, with over 30 % glazed and protected by
a roof overhang of over 950 mm. The Northern wing contains entrance, sanitary and technical areas, staircases and loosely connected porches for cars and a garden shed. The attic space is conventionally divided into 3–4 bedrooms,
a bathroom and a walk-in wardrobe, with the East-West orientation and up to 15 % glazing to provide enough daylight for inhabited rooms.

Constructional and architectural design
  It follows up on the unique building type of the Cesky Raj region characteristic by a simple shape concept, the smooth surfaces of saddle roofs from black and grey slate from local quarries, the compact surfaces of wooden panelling and the overhangs of saddle roofs formed by ceiling beam consoles. 
With its characteristic gable orientation the new houses logically blend in with the existing urban development to virtually merge with it (Fig. 1). The main unification element of the new development are the dominant surfaces of black and grey roofing continued by the variable façade design with full or partial Siberian larch cladding and wooden porches with sloping or flat green roofs (Fig. 2, 3, 4, 5). The semi-closed spaces of the wooden porches at the same time create a very pleasant entrance area. The floor space of the basic 9.60 x 9.60 m size house is 132 m2 (plus 39 m2 in a walk-in attic), with a gross enclosed volume of 513 m2. Volume shape factor A / V = 0.57.

Structural design
 It is based on the economical unified timber frame structure by ATREA. The ground floor is formed by a set of posts spaced between 1.5 and 3 metres from each other, set in the foundation sill and linked at their ends by a set of lateral bonded beams and cross bracings (Fig. 6). Spatial stiffening is provided by angular diagonal bracings. All elements are joined by BOVA gusset plates and anchors and KH nail joints.  The attic and roof part of the house is formed by large-span in-situ trusses whose bottom chords act as joint beams to directly form ground floor ceilings (Fig. 7). This collar beam system without purlins makes the entire attic space free of any supports to achieve a fully variable layout. The lateral reinforcement of the roof truss system is provided by wind braces at the bottom face of the rafters and hard ceiling plates from bonded OSBs.
 The whole skeleton structure is assembled in-situ from dried spruce/fir timber with a moisture content of 12-14 % without impregnation. The higher profiles are from bonded KH profiles up to 13.2 metres in length. The in-site assembly of trusses is highly productive (0.3 hours to assemble one piece).
From the material demand point of view it is a very economical structural system, with 3.1 m3 of timber required for the ground floor and 4.8 m3 for the entire attic and roof section (including ground floor ceilings) in a house with a built-up space of 9.6 x 8.6 metres!
The 400 mm thick outer walls consist of two separate non-load bearing skins filled with folded mineral wool boards. The envelope has either wood cladding on battens with an aired cavity before a TYVEK barrier or thin-layer rendering on FASCROCK façade insulation. The inner envelope consists solely of 12.5 mm thick FERMACELL plaster fibre boards bonded together on a batten grid with installation space. A JUTAFOL N vapourtight foil layer thoroughly bonded at the joints with butyl-rubber tapes and secured with battens. Verification measurements of air permeability were conducted before covering all internal surfaces with plaster fibre boards. The peculiar problem of connecting vapourtight foil sheets to the window structures was solved by using additional corner brackets. The roof skin is made of ROCKMIN (U = 0.092 Wm-2K-1) mineral wool boards fitted on CD battens on extended and reinforced brackets. Windows by Slavona have wooden frames and triple glazing (Ug = 0.5 Wm-2K-1), with the large windows on the ground floor being installed as fixed glazing.
All significant structural details of the house were verified by a thorough thermal and engineering calculation, establishing the effects of thermal bridges and thermal couplings. Floor structures on the ground floor, with 200 mm insulation, are untypically made of inexpensive EPS Stabil 200 whose rigidity and compressibility generally meets mechanical requirements, with support grids installed underneath localized loads (fireplace stoves, baths).

Technical installations
 Warm-air heating, ventilation and cooling are provided by a double-zone system of a Duplex RB unit connected to a ground-coupled circulation heat exchanger and a warm-air distribution network from the fireplace stove into the entire house. Flat floor channels lead to floor outlets below the windows (Fig. 8). HVAC ducts generally run in the ceiling space and centrally into the utility room (Fig. 9).
An IZT 615 (Fig. 10) with connections from solar panels and hot-water fireplace inserts using block wood fuel is used as a centralized heat accumulator. Heating water outlets from the IZT 615 heat the hot-water register of the ventilation unit and heating rails in the bathrooms. The outlet of hot water heated via a continuous flow system is connected directly to the sanitary facilities and then through a thermostatic valve to the dishwasher and washing machine to provide savings of up to 60 % compared to direct electrical heating! Low voltage electrical and TV wiring and IT networks are run strictly in integrated raceways in the installation cavity along the entire perimeter of the ground floor and attic. This significantly reduces the time needed for electrical installation and virtually eliminates the risk of subsequent damage to cables. The solar thermal panels on the saddle roof are arranged into vertical strips to eliminate the formation of ice crusts at the bottom with the subsequent permanent layer of snow on the collectors in a low-mountain area with higher snowfalls. A photovoltaic system is installed across the entire roof area of the training centre, with an output of 8.5 kWp and distribution to the public network (65 KYOCERA KC 130 GHT – 2 PV panels on Schletter rails ventilated from the bottom) to classify this building as a Zero House.

Conclusion
 The large-scale project of passive houses in the wooden frame system, the first of its kind in the Czech Republic, brought a range of experiences together with ideas for optimizing the technical design as well as the management of construction. The permanent presence of a site inspector during the handover of individual constructional phases proved absolutely necessary, as well as the importance of coordinating the work of subcontractors as the straight-line flow method of construction is in place. The developer (ATREA s.r.o.) strictly implemented a system of regular weekly inspection days with daily task scheduling which proved very effective in practice. BAK a.s., the general building contractor, managed to coordinate – especially towards the end of construction – the schedule of all of its subcontractors’ commencement on site and their work by the hour, which is truly unique under standard construction conditions in the Czech Republic. Despite the experimental nature of the development the construction work was highly efficient as the assembly of a single structural frame did not take more than a day and a half, while the turnkey development project of thirteen experimental houses was completed in just seven months!
The specific investment costs for the contractor system in the basic energy passive standard with “turnkey” equipment did not exceed CZK 20,000 per square meter of floor space (i.e. CZK 5,070/m3) to match the costs for conventional construction in the Czech Republic with significantly worse utility parameters for a really uncertain energy future.