PREFALZ at the Luční House in the Krkonoš Mountains

Luzni House Yesterday and Today
The modern building of the residential project Luzni House is situated on a unique and valuable plot near the center of Špindlerův Mlýn. At this appealing and strategic location with a history stood the Wiesenhaus Hotel - Luzni House, owned by entrepreneur Hollman, since 1876. It took the form of a magnificent, multi-story building with Art Nouveau elements on the facade and wooden ornaments, featuring a stunning interior whose luxury was enhanced by wooden paneled walls and ceilings, high tiled stoves, beautiful Art Nouveau chandeliers, and furniture supplied by Thonet. The hotel was later replaced by accommodation facilities run by Aero, but that is now a thing of the past. The current form of Luzni House represents comfortable mountain living in an absolutely exclusive location, which has its own spirit and extraordinary history. Significant attention was paid during the design to the execution of the common areas, which evoke hotel standards and a sense of coziness that is generally lacking in the halls and corridors of apartment buildings. Overall, the newly constructed apartment building will offer 47 modern, logically and functionally designed residential units with breathtaking views of the surrounding landscape.

Luzni House is situated at an altitude of 770 m above sea level. The roof area made up of differently sloped planes and connected by more than 70 meters of valleys reaches 1532 m². The roofing material used is lacquered aluminum groove roofing Prefalz with a two-layer baked lacquer P.10 (with a 40-year warranty for material quality and color fastness) in a light gray shade. The material consumption exceeded 2000 m² overall due to the amount of segments and edging. However, with the weight of the Prefalz roll sheet at approximately 1.89 kg/m², the weight of the roofing on the apartment building did not exceed 4 tons. The installation was carried out on a full substructure using concealed anchoring (stainless steel fittings in the upright groove). The load-bearing capacity of the Prefalz roofing reaches a maximum of 800 kg/m², making it suitable even in terms of snow load in the given location.

Roof Slopes from 10° to 19°
The building of the new Luzni House is located at an altitude of 770 m above sea level, is oriented to the southwest, and stands out due to its spaciousness. The rough floor plan measures 53 x 33 m, but the above-ground part of the building is shaped like an extended letter "U," which the roof also follows. It consists of three interconnected units, on which several differently sloped planes are located due to a series of shed and gable dormers. The main section of the building has a shed roof with a slope of 19°, from which a total of 6 gable dormers with a very mild slope of 10° extend from the front and rear. The side roof planes are almost entirely formed at the eaves by large gable dormers with the same slope as the main shed roof. On these massive dormers, additional gable dormers (with a slope of 17.5°) follow on both the northern and southern sides, which, while visually connected to the main section, are already at the height of the side sections, of which they are also a part. The integrity of the remaining part of the gable roofs of the side sections (the southern slopes are 17.5° and the northern 17.0°) is almost perfectly disrupted across the entire area by another 8 gable dormers with a very mild 10° slope.

The pronounced subdivision of the roof area is visible only when viewed from the upper floors towards the inner courtyard or directly from the roof. The view from street level does not allow for the distinct complexity of the roof envelope to be seen, thus keeping it hidden from the ordinary passerby.

Composition of the Roof Envelope
The construction of the roof envelope of the building is executed as an insulated double-shell. Air intake openings are continuously located along all eaves, with air exhaust along the entire length of the ridge. The roofing envelope consists of a load-bearing reinforced concrete slab, a vapor barrier (heavy asphalt membrane with aluminum insert), a system of common and Italian rafters (80x120 mm) filled with thermal insulation, a safety diffusion membrane, a ventilated air gap of 80 mm from counter battens of 40x80 mm, complete boarding of planed boards with a thickness of 24 mm and a maximum width of 160 mm, a separating layer, and a final light aluminum sheet roofing.

The roof above part of the garage in the basement is designed as a flat single-shell roof. The roofing consists of a load-bearing reinforced concrete slab, a vapor barrier (heavy asphalt membrane with aluminum insert), polystyrene thermal insulation forming sloped wedges, and a hydro insulation membrane of mPVC type on both sides with a separating layer of geotextile. Stabilization of the roofing layers against wind uplift is ensured by weighing with stones of fraction 16-32 mm. Around the atrium, 2 m wide, instead of stones, an armored dilated concrete slab is proposed to protect the layers from heavy falling snow and ice from the roofs.

Roof Covering as a Basis
Given the low slopes, demanding mountain conditions, and snow load, aluminum roll sheet Prefalz with a thickness of 0.7 mm from Prefa Aluminiumprodukte in a smooth finish was selected for the roof covering. The grooves of the roofing sheets, unrolled to a width of 500 mm, are connected at double standing seams and attached to the full substructure using movable and fixed stainless steel fittings (according to the requirements of ČSN 73 3610), ensuring adequate protection against the weather and climatic conditions of Špindlerův Mlýn, as well as the material's ability to expand during large temperature changes. The same execution is applied to the side edging of the gable dormers and several projecting parts of the facade, where a ventilated facade made of Prefalz grooved cladding is implemented on a small area. In addition to the large roof area (over 1500 m²), an interesting aspect of this implementation is the number of differently inclined and independent roof planes. The most prominent are large gable dormers with a flat roof of always over 20 and 30 m² respectively. There are a total of 14 of these on Luzni House, with an average slope of 10°. Optical refinement and complexity are complemented by another 3 gable dormers and one combined dormer, creating a total of 7 valleys (of which 2 are heated) and 4 corners. In the valleys, a system element of safe valley PREFA was used with a total length of 70 running meters. Simple tubular snow guards were used as snow barriers on all larger planes with slopes greater than 10° and except for fields directing to the inner courtyard. Among other standard roofing details are window edging, concealed outlets for rainwater drainage, ridge ventilation, or penetrations for inspection anchor points.

Questions for the head of the technical department of Prefa Aluminiumprodukte, Roman Vanek What are the advantages of Prefalz sheet? Prefalz is a rolled sheet in excellent seam quality (H 41). It is predisposed for individual and creative solutions of roofs and facades. Thanks to its flexibility, it can be shaped more easily than most comparable materials, thus offering designers and architects nearly unlimited possibilities. Another advantage is uniformity, or rather systematism. All roofing elements used are made from the same material in the same color and seam quality, including outlets, edging, etc. They therefore act and function as a single unit throughout the lifespan of the roof. Why was Prefalz specifically used on Luzni House? Prefalz has an undeniable advantage compared to heavy tiled coverings in that it can be laid from a minimum roof slope of 3°. Although the roof on Luzni House has a minimum slope of 10°, we must realize the complexity of the roof envelope and the demanding climatic conditions that prevail in Špindlerův Mlýn. The stress on the roof is enormous. In winter, tons of snow fall here, which subsequently load the roofs; in summer, storms or sudden storms with hail are not uncommon. It is clear that no heavy tiled roofing would be suitable for these conditions. Here, it is necessary to plan for a durable and reliable covering that the investor can trust without having to resolve the roof again for several more decades. The properties of aluminum sheet Prefalz, such as rust resistance, strength, unbreakability, color stability, wind resistance, and others are of course standard. Moreover, it allows for trouble-free and economical installation. In this case, even light-sheet metal tiles would not suffice. Luzni House is a typical example for the use of the most reliable material. Do you see potential risks in the complexity of the roof on Luzni House from a functionality perspective? The potential risk of improper function of roofing envelopes usually lies in the complexity of the individual roof details. It is of course logical that even with a larger number of interlocking standardized elements and procedures, the risk of improper functionality can arise. It is similar to other fields. Only the correct procedure in all steps of the implementation, such as the connection of differently sloped surfaces, thorough anchoring of the covering, correct use of safe valley, edging, adherence to expansion rules, or precise anchoring, are prerequisites for 100% resistance to all forces that may act on the roof throughout the year. A metaphor comes to mind that every whole is only as strong as its weakest part. However, if all basic rules for roofing work are followed, the reward in the case of rolled sheet Prefalz is a reliable whole that will function for many decades, Luzni House included.

Material Used PREFALZ – Rolled Sheet:
Brief Description: colored aluminum rolled sheet is predisposed for individual and creative solutions of roofs and facades due to its excellent seam quality and surface treatment.
Product Advantages: wide selection of PREFA accessories (drainage systems, fastening materials, snow guards,…); universal application (from arched roofs to intricate roof extensions to vaulted roofs); consistent quality; low weight (approx. 1.89 kg/m²); long lifespan; recyclability; rust resistance; available upon request with protective film.
Colors: 16 standard colors in stock, surface finish smooth or stucco, warranty for color stability and quality for 40 years.
Temperature Resistance: from -50 °C to +80 °C.
Cleaning: with high-pressure water, sponge or brush.
Processing: easy and lightweight to work with even at low outdoor temperatures below 0 degrees.
Installation and Attachment: on complete boarding (24 mm) with separating layer, attached with stainless fittings.