Method of retrofitting an existing flat or flat-inclined roof of a building, flat or flat-inclined roof for a building and assembly for a retrofit system to be used on an existing flat or flat-inclined roof of a building

Abstract

The inventions relates to a method of retrofitting an existing flat or flat-inclined roof (1) of a building, the existing roof (1) comprising at least a first layer (3) of a combustible insulation being arranged on a substructure (2) and being covered with a first membrane (4) as a roof seal, whereby a second layer (5) of a preferably non-combustible insulation is arranged on top of the first membrane (3) before the second layer (5) of preferably non-combustible insulation is covered with a second waterproofing membrane (6) and before finally a photovoltaic system (7) with at least one photovoltaic panel (9) is arranged with a distance to and on top of the second waterproofing membrane (6).

Description

[0001] Method of retrofiting an existing flat or flat-inclined roof of a building, flat or flat-inclined roof for a building and assembly for a retrofit system to be used on an existing flat or f lat-i ncl i ned roof of a

[0002] The invention relates to a method of retrofitting an existing flat or flat-inclined roof of a building, the existing roof comprising at least a first layer of a combustible insulation being arranged on a substructure and being covered with a first membrane as a roof seal. Furthermore, the invention relates to a flat or flat-inclined roof for a building comprising a substructure, at least a first layer of a combustible insulation, which first layer is covered with a first membrane as a roof seal. Finally, the invention relates to an assembly for a retrofit system to be used on an existing flat or flat-inclined roof of a building, the existing roof comprising at least a first layer of a combustible insulation being arranged on a substructure and being covered with a first membrane as a roof seal. The membrane being a waterproofing membrane.

[0003] Flat roofs and flat-inclined roofs are well known in the art, e. g. as membrane roof systems which are generally divided into the following types, according to the position in which the principal thermal insulation is placed: warm roofs, inverted warm roofs, roof gardens or green roofs, and cold roofs. Within the current disclosure reference is made to traditional warm roof assemblies.

[0004] Membrane roof systems are used to protect flat roofs or flat-inclined roofs from all weather conditions likely to be experienced during their design life. They are often built as single ply roofing systems, in particular for larger roofs, or they are built up of bituminous membranes, in particular reinforced bitumen membranes (RBM). The latter are based on a carrier normally polyester and coated in bitumen, mostly two different layers of bitumen with varying softening performance. They are typically applied in two or more layers of sheet materials rolled out over the thermal and / or acoustic insulation element.

[0005] A typical membrane roof system comprises: a substructure providing continuous support, a vapor control layer (if required), thermal and / or acoustic insulation (if required), a waterproof membrane or lining and a traffic or load resistant finish (if required for functional and / or aesthetic reasons). In warm roofs the principal thermal and / or acoustic insulation element is placed immediately below the roof seal, namely the waterproof membrane or lining. The three principal options for securing roofing systems against wind loads are mechanical fastening, adhesion / hot bonding / cold gluing, ballast, whereby the insulation element and the membrane maybe either attached by the same or a different method.

[0006] The substructure, providing continuous support for the subsequent insulation and membrane layers, might be formed of e. g. a concrete deck or steel deck on structural supports. Across Europe these two types of substructures share an almost equal market size with some national variations.

[0007] Over time, above-described membrane roof systems often develop a reduced insulation performance. This may for instance be caused by damages to the roof seal, like perforations or cracks, and the penetration of water or humidity. Moreover, existing roof systems of a certain age might simply not fulfil today’s thermal requirements which might lead to a need for renovation and upgrading of said roofs.

[0008] A method for renovation of insulated roofs and a plate for renovation of insulated roofs is for example known from EP 1 052 343 A1. This prior art describes a method for renovation of insulated roofs whose top sides are provided with a roof-covering comprising a layer of insulating material covered with at least one water-repellent covering layer, wherein on the existing roof-covering, a new layer of insulating material is provided. The new layer is covered with a water-repellent top layer and wherein the top layer is attached with screws extending at least through the new layer of insulating material and beyond the water- repellent covering layer of the existing roof-covering. The existing insulating layer may consist of plates of suitable foam material, such as for instance polyurethane foam, which may have a protective layer, for instance a thin, gritted layer of bitumen, applied to the top and / or bottom sides thereof. Hence, such existing insulating layer constitutes a combustible insulation material.

[0009] According to this prior art document, new insulation plates are readily fitted on the existing roof-covering and covered with a second water-repellent layer or top layer. Such plates can for instance be manufactured by foaming the insulation material on a substrate of a suitable sheet, such as for instance an aluminum foil, provided with a wafer pattern or other desired relief. Said plates having relief on the bottom side are highly suitable for use on existing insulating layers containing relatively much moisture. A further method for the renovation of a flat and / or flat sloping roof of a building, wherein the roof comprises a supporting shell and a thermal insulation arranged thereon and a first roof seal being arranged on the thermal insulation is known from EP 1 960 613 B1. This known method proposes to at least partly remove the roof seal, applying a second thermal insulation in a full-covering manner on the thermal insulation and a second roof seal in a fullcovering manner on a second thermal insulation whereby a hygroscopic storage layer is arranged between the thermal insulation and the second thermal insulation.

[0010] Both cited prior art documents center around upgrading existing roofs in terms of their thermal performance and handling of moisture in the existing roof construction. The latter may e. g. be caused by damages to the waterproofing membrane layer provided on the insulation layer as has also been described above. Said documents do not discuss fire- related aspects. And, due to the incorporation of foam-based insulation or of a hygroscopic storage layer, the proposed solutions do not improve the fire resistance of the renovated roof as compared with the original one.

[0011] Renewable or green energy becomes more and more important. Reducing the dependence on fossil fuels, solar energy plays a key role. Solar energy technologies convert sunlight into energy, either as electricity (typically photovoltaic systems) or in the form of solar heat.

[0012] Several countries already decided that new build buildings have to be equipped with photovoltaic systems to produce electricity and that existing buildings have to be equipped with photovoltaic systems if the roofs have a certain size. Especially roofs of industrial or commercially used buildings have often a large size and companies using these buildings for the production of goods, as offices and / or storage houses have a big need for electricity so that these buildings are perfectly suitable to be equipped with photovoltaic systems.

[0013] Following the Energy Performance of Buildings Directive (EPBD) by the European Commission, obligations for new buildings to install solar energy installations have recently been introduced (Solar Rooftops Initiative). According to these requirements all new public and commercial buildings with a roof larger than 250 m2shall have solar energy installations from 2027 on.

[0014] On all existing public and commercial buildings with a roof larger than 250 m2solar energy installations will be required starting from 2028 and finally on all new residential buildings from 2030 on need solar energy installations.

[0015] Solar energy installations will mainly comprise photovoltaic panels which likely will be the standard on all future flat roofs. Photovoltaic panel installations on flat roofs or flat-inclined roofs have been known for several years but have more recently been under discussion as they are considered an ignition source for roof fires. More specifically, photovoltaic panels radiate heat back to the roof covering, thereby increasing fire spread and intensity in case of such fires. Furthermore, it is well known that photovoltaic panel fires are difficult to extinguish. Especially flat or flat-inclined roofs comprising a first layer of a combustible insulation being arranged on a substructure and being covered with a first membrane as a roof seal are problematic with respect to the installation of a photovoltaic system on top. A fire caused by the photovoltaic system and being difficult to extinguish will cause damages on the insulation on top of the substructure and causes the risk of a collapse of the substructure. A combustible insulation material frequently having been used on respective flat roofs or flat-inclined roofs in the past is e. g. Expanded Polystyrene (EPS), often being covered with a bituminous sheeting.

[0016] It is therefore an object of the invention to provide a method of retrofitting an existing flat or flat-inclined roof of a building to be prepared for a photovoltaic system with at least one photovoltaic panel to be arranged on the existing roof, providing a practicable method at low cost and at high quality with respect to fire resistance and tightness of the retrofitted roof.

[0017] It is another object of the invention to provide a retrofitted flat or flat-inclined roof for a building being equipped with a photovoltaic system and being highly fire resistant.

[0018] Finally, it is a further object of the invention to provide an assembly for a retrofit system to be used on an existing flat or flat-inclined roof providing the possibility to extend the use of an existing roof to fulfill requirements with respect to solar energy installations on buildings and whereby an existing flat or flat-inclined roof is retrofitted and thereby made resistant against fire.

[0019] A typical build-up of an existing flat or flat-inclined roof to be retrofitted according to the present invention and for the further description of same here below comprises the following components: a substructure like concrete or steel deck, optionally a vapor barrier, a first combustible thermal and / or acoustic insulation and a first membrane as a roof seal. In an alternative build-up of an existing flat or flat-inclined roof to be retrofitted a vapor barrier is provided between the substructure and the first layer of the combustible insulation which prevents ingress of humidity from inside the building into the insulation.

[0020] According to another alternative a third layer of a non-combustible insulation is provided between the substructure in the form of a steel deck and the first layer of a combustible insulation. Such third layer protects the first layer of combustible insulation against the impact of a fire from inside the building as well as the substructure from impact of a fire from outside the building even if the fire reaches and influences the first layer of a combustible insulation. Said build-up is sometimes referred to as a hybrid roof construction.

[0021] Preferably, this alternative is further developed in that a vapor barrier is provided between the third layer of insulation and the first layer of a combustible insulation which prevents the first layer of insulation from ingress of humidity from inside the building and as well from ingress of water from outside.

[0022] To keep the total load on the substructure of such existing roof build-up low, a third layer of a non-combustible insulation provided on the substructure may only have a thickness between 40 mm and 80 mm, preferably of 50 mm. Besides the low load on the substructure the third layer increases the value of sound and / or thermal insulation in a sufficient way.

[0023] A method of retrofitting according to the invention provides the step of arranging a second layer of a preferably non-combustible insulation on top of a first membrane before the second layer of the preferably non-combustible insulation is covered with a second waterproofing membrane and before finally a photovoltaic system with at least one photovoltaic panel is arranged with a distance to and on top of the second waterproofing membrane.

[0024] By using a second layer of a preferably non-combustible insulation, for example made of boards or slabs of mineral wool, especially stone wool, the existing roof is covered with a layer protecting the existing roof against fire. Thereby the existing roof can withstand a longer time an impact of a fire with a photovoltaic system being arranged on top of the roof. Furthermore, using a second layer of insulation on top of the existing roof has the positive result that the roof in total has better insulation values such as sound insulation and / or thermal insulation. The second layer of insulation is covered with a second waterproofing membrane so that the second layer of insulation especially made of mineral wool is protected against water ingress into the insulation. Both constructional elements, namely second layer of insulation and second waterproofing membrane have therefore the effect that a flat or flat-inclined roof of a building can be used as a basis for a photovoltaic system with a considerably reduced risk in case of a fire, e. g. caused by the photovoltaic system and of course with a considerably increased value of sound and / or thermal insulation.

[0025] Preferably, a second layer of the non-combustible insulation layer made of mineral wool is provided on the first membrane. Such a layer of mineral wool provides a high fire resistance and protects the existing elements of the flat or flat-inclined roof of the building. The layer of mineral wool maybe installed as several boards or slabs lying side by side and thereby neighbored to each other on top of the fist membrane of the existing roof. The layer of mineral wool can be provided as a multi-layered system of mineral wool boards or slabs being arranged offset on each other just to close joints between elements being arranged adjacent to each other and thereby giving a better protection against water ingress and / or consequences of a fire as for example smoke diffusing into the building or oxygen diffusing from the building. Furthermore, the boards or slabs can have layers of different bulk densities.

[0026] Mineral wool, especially stone wool, according to the present disclosure is to be seen in the context of European Standard EN 13162:2012+A1 :2015, with the title “Thermal insulation products for buildings - Factory made mineral wool (MW) products".

[0027] According to a further embodiment of the invention a second layer of the non-combustible insulation having a thickness between 40 mm and 100 mm, preferably of 50 mm is arranged on the first membrane. A layer of such a thickness provides increased sound and thermal insulation values on the one hand and as on the other hand not the disadvantage to build up an insulation in total being too thick and therefore being too heavy to be carried by existing substructures.

[0028] According to a further embodiment of the invention a vapor barrier is provided between the According to another embodiment of the invention a second layer of the non-combustible mineral wool insulation having a bulk density between 80 kg / m3and 180 kg / m3, preferably of 130 kg / m3is provided on the first membrane. Insulation elements having the before- mentioned bulk density are sufficiently compression proofed to carry a photovoltaic system without being deformed. A further aspect is that these bulk densities provide a sufficient bending stiffness so that the insulation elements can span certain distances between parts of the substructure. Last but not least insulation elements made of mineral wool and having the before-mentioned bulk densities provide and increase sound and / or thermal insulation performance values being sufficient in the area of flat and / or flat-inclined roofs.

[0029] To fix the second layer of the non-combustible insulation anchor elements like screws might be used. Said screws will be running through the first layer of the combustible insulation and the second and optional third layer of the non-combustible insulation and fixed in the substructure, typically a steel deck. In case of a concrete deck the layers will typically be adhesively connected.

[0030] According to a further embodiment of the method according to the invention the first membrane is removed before the second layer of insulation is arranged on top of the first layer of insulation. To remove the first membrane has the advantage that the first layer of insulation can be inspected with respect to damages especially caused by water ingress and if necessary, the first layer of insulation can be dried before the second layer of insulation is arranged on top of the first layer of insulation. Furthermore, removing the first membrane may have the advantage that a non-even layer is removed which facilitates to provide a retrofited flat or flat-inclined roof providing the necessary characteristics of the retrofitted roof with respect to sound and / or thermal insulation values and / or the ability to carry a photovoltaic system and being protected against an impact of fire caused by the photovoltaic system. Areas with distances between the two layers of insulation can be mostly avoided be removing an uneven layer on top of the first layer of insulation.

[0031] According to yet another embodiment of the invention with respect to the method a foil of metal, preferably of aluminum and preferably being part of a laminate, is arranged on top of the first layer of insulation before the second layer of insulation is arranged on the foil and preferably after the first membrane is removed from the first layer of insulation. Preferably, the foil, preferably as part of the laminate is fixed to the second layer of insulation before the second layer of insulation is arranged on top of the first layer of insulation.

[0032] With respect to the roof according to the invention a second waterproofing membrane is provided on top of the second layer of the preferably non-combustible insulation, thereby covering the second layer, and comprising a photovoltaic system with at least one photovoltaic panel being provided with a distance to and fixed on top of the second waterproofing membrane.

[0033] Such a retrofitted flat or flat-inclined roof provides superior protection against impacts caused by fire due to e. g. a photovoltaic system on the one hand and on the other hand provides a roof with sufficient and increased values of sound and thermal insultation, and that can be easily installed on a building with an existing roof.

[0034] According to a further embodiment of the roof according to the invention the second layer of the non-combustible insulation is fixed by anchor elements like screws running through the first layer of combustible insulation and the second and optional third layer of noncombustible insulation and being fixed in the substructure. The anchor means are covered by the second waterproofing membrane so that the second waterproofing membrane does not allow ingress of water in the area of the second layer of non-combustible insulation and thereby protecting it against damages. Furthermore, it is of advantage that a foil of metal, preferably of aluminum and preferably being part of a laminate, is provided between the first layer of insulation and the second layer of insulation. This foil of metal protects the first layer of insulation additionally against the impact of a fire caused by the photovoltaic system in that heat from the fire is radiated on the one hand, and on the other hand the foil of metal closes the area between the two layers of insulation in a nearly gas tight manner. In case of fire the foil prevents ingress of gas, especially smoke, into the building or oxygen diffusing from inside the building and feeding the fire.

[0035] Preferably the foil, preferably as part of the laminate, is fixed to a major surface of the second layer of insulation, preferably made of insulation boards or mats being arranged adjacent to each other. Further preferably, the foil fixed to the major surface of the second layer insulation extends over at least one, preferably two side faces of the second layer of insulation in form of boards or slabs. Extending parts of the foil underlay boards or slabs being arranged adjacent to each other and close joints between them.

[0036] The assembly according to the invention is characterized by a second layer of a preferably non-combustible insulation to be arranged on top of the first membrane, a second waterproofing membrane to be arranged on the second layer of preferably non-combustible insulation and a photovoltaic system with at least one photovoltaic panel to be arranged with a distance to and on top of the second waterproofing membrane. Such an assembly can be provided to retrofit an existing flat or flat-inclined roof of a building according to the method of the invention. The assembly contains all necessary components to build up a roof on an already existing flat or flat-inclined roof being able to carry the photovoltaic system and being protected even in case of a fire caused by the photovoltaic system.

[0037] According to an embodiment of the assembly the second layer of insulation comprises boards and / or slabs preferably made of mineral wool and preferably having a thickness between 40 mm and 100 mm, more preferably of 50 mm. Other boards and / or slabs can be part of the assembly. The use of boards and / or slabs has the advantage that the assembly can be delivered as a building kit which allows to install the second layer easily on an existing roof. The small thickness of the boards or slabs has the advantage that these boards and / or slabs are easy to handle and the weight of the elements which usually have a bulk density between 80 kg / m3and 180 kg / m3can be handled by one or two workers without going beyond allowed weight of a building element to be carried by a worker.

[0038] To fix the parts of the assembly to an existing flat or flat-inclined roof, anchor elements like screws are to be arranged running through the first layer of insulation and the second and optional third layer of insulation and to be fixed in the substructure, more specifically a steel deck, as getting part of the assembly. In the same way, a suitable adhesive might be part of the assembly in case an existing flat or flat-inclined roof based on a concrete deck is to be retrofitted.

[0039] Finally, a foil of metal, preferably of aluminum and preferably as part of a laminate, to be arranged on top of the first layer of insulation underneath the second layer of insulation is present in the assembly according to the invention. The foil of metal, preferably as part of the laminate is preferably fixed to a major surface of the second layer of insulation. To fix the foil of metal to a major surface of the second layer of insulation facilitates the installation of the assembly on top of the existing flat or flat-inclined roof thereby reducing the labor to install the elements.

[0040] Further advantages and features of the invention are described in the following description and the accompanying drawings showing preferred embodiments of the invention. The drawings show in

[0041] Fig. 1 a first embodiment of a part of a flat roof in cross-section;

[0042] Fig. 2 a second embodiment of a part of a flat roof in cross-section;

[0043] Fig 3 a third embodiment of a part of a flat roof in cross-section;

[0044] Fig. 4 a first top view on an EPS-layer of a flat roof according to Fig. 1 with an arrangement of thermocouples on the EPS-layer (test#1);

[0045] Fig. 5 a graph showing the temperature data for the thermocouples of Fig. 4;

[0046] Fig. 6 a second top view on an EPS-layer of a flat roof according to Fig. 1 with an arrangement of thermocouples on the EPS-layer (test#2);

[0047] Fig. 7 a graph showing the temperature data for the thermocouples of Fig. 6 and

[0048] Fig. 8 a graph showing the temperature data measured at different heights within the insulation of the flat roof according to Fig. 1 .

[0049] Figures 1 to 3 show different embodiments of a flat roof 1 , each comprising a substructure

[0050] 2 and a first (insulation) layer 3 of a combustible insulation. The first (insulation) layer 3 is part of an existing flat or flat-inclined roof 1. Additionally, the existing flat roof 1 already comprises a first membrane 4, e.g. a bituminous sheeting, as a roof seal.

[0051] According to Fig. 1 the substructure 2 is a concrete deck on which the first (insulation) layer

[0052] 3 of the combustible insulation, e. g. EPS, is arranged directly.

[0053] On top of the first membrane 4 a second (insulation) layer 5 of a non-combustible insulation namely made from mineral wool is arranged and covered by a second membrane 6.

[0054] The second membrane 6 comprises a waterproofing layer and may be constituted by another bituminous sheeting. To protect the second (insulation) layer 5 several bituminous sheeting are arranged side by side thereby overlapping each other partly. On top of the second membrane 6 a photovoltaic system 7 is arranged and comprises at least one supporting frame 8 and at least one photovoltaic panel 9 mounted in the supporting frame 8. The photovoltaic panel 9 is arranged non-parallel to an upper surface 10 of the second membrane 6.

[0055] A void 11 of triangular cross-section is constituted between the upper surface 10 of the second membrane 6 and therefore of the flat roof 1 and the photovoltaic panel 9.

[0056] To limit the additional load on the existing flat roof 1 the second (insulation) layer 5 has a thickness of 50 mm and a bulk density of 130 kg / m3.

[0057] The flat roof 1 according to figures 1 to 3 is build up in that on the existing flat roof 1 comprising the substructure 2, the first (insulation) layer 3 and the first membrane 4, the second (insulation) layer 5 is arranged on top of the first membrane 4. The second (insulation) layer 5 is made from several boards of mineral wool insulation, which can additionally be fixed by not shown anchor elements, e. g. screws to the substructure 2 before the second membrane 6 is arranged on top of the second (insulation) layer 5.

[0058] After covering the second (insulation) layer 5 with the second membrane 6 the photovoltaic system 7 is installed on top of the second membrane 6 by installing supporting frames 8 and photovoltaic panels 9 in the supporting frame 8.

[0059] It is possible to remove the first membrane 4 first before the second (insulation) layer 5 is arranged on top of the existing flat roof 1.

[0060] Compared to the embodiment of Fig. 1 the embodiment of Fig. 2 provides a substructure 2 formed of steel deck on which an additional vapor barrier 13 is arranged which covers the substructure 2 totally.

[0061] Compared to the embodiment of Fig. 2 the embodiment of Fig. 3 additionally contains a third layer 14 comprising boards or slabs made from mineral wool, especially stone wool. The vapor barrier 13 is arranged between the third insulation layer 14 and the first (insulation) layer 3 and increases the values of sound and thermal insulation characteristics. The embodiment according to Fig. 3 is also called hybrid solution and often . used in Nordic countries. The insulation of the roof 1 according to the embodiments of figures 2 and 3 corresponds to the before-mentioned description of the insulation of the roof 1 according to embodiment of Fig. 1.

[0062] Testing procedure:

[0063] In the absence of specific requirements and harmonized Standards for testing flat or flat- inclined roof constructions comprising a photovoltaic system, a test method has been developed following some pre-considerations supplemented with knowledge gained from some pre-tests and calculations.

[0064] Large-scale testing on roof segments was chosen with the aim to analyze how a roof buildup behaves during and after being exposed to a fire, to observe events during the fire spread, to evaluate data from thermocouples and visual inspection, and to assess the damage done to the underlying materials.

[0065] A roof build-up on a test rig representing a roof segment was used to assess the extent of damage a fire can exert on the insulation layers under a PV installation. A build-up with dimensions 4.000 mm x 3.500 mm was prepared with a pitch (slope) of the roof at 2.5 %, which corresponds to a 1 :40 slope.

[0066] A PV system was mounted on the roof build-up following the roofing practices and industry standards. The base troughs of the system were in line with the short side of the roof. The ends of the base troughs were aligned with the end of the roof on the long edge and with a 150 mm distance from one of the short edges. To simulate the wind-lift mitigation load of a roof corner in a typical / representative line loaded support structure, heavy metal plates (about 20 kg / piece) were placed in the middle of each base trough (total load of 120 - 130 kg).

[0067] For the ignition source, a wood crib with an estimated heat release rate of about 15 kW was chosen.

[0068] The extent of impact / damage was assessed / compared in the tests via:

[0069] - measurement of temperature (measured with thermocouples (TCs) positioned on different layers in the roofing structure and on the PV installation during and after the test);

[0070] - extent of flame spread (assessed via visual inspection during and after the end of the test);

[0071] - depth and extent of damage (assessed via visual inspection after the end of the test); - ignition or no ignition of the combustible insulation;

[0072] - compromise of the roof assembly.

[0073] Testing followed aspects of different Standards, such as CEN / TS 13501-5:2016, FM Approvals 4478, and CEN / TS 1187 (tests 1 and 2), to establish conditions and results that could be compared with other test results.

[0074] The general roof build-up for the test setup comprises the following layers:

[0075] 1. photovoltaic panels 9, fire rating: UL type 1 or 2 IEC Class C. Protection class: Class II;

[0076] 2. PV panel support system 8;

[0077] 3. second membrane 6, i. e. bitumen layer (base and top layers), Broof (t2) [as system];

[0078] 4. second (insulation) layer 5 of mineral wool;

[0079] 5. optional first membrane 4, i. e. existing membrane, only for test #2;

[0080] 6. first (insulation) layer 3 of EPS 150 (W30), Euro-class E;

[0081] 7. substructure 2.

[0082] The invention has been analyzed in how a flat or flat-inclined roof 1 being retrofitted according to the invention and with a photovoltaic system 7 being built on top behaves during and after being exposed to a fire, i. e. to observe events during the fire spread, to evaluate data from thermocouples 17 and to assess the damage done to the underlying materials. A first test (test#1) according to figures 4 and 5 is based on an area 15 of the flat roof 1 shown in Fig. 4 as a top view on the first insulation layer 3 in one of the figures 1 to 3. This first (insulation) layer 3 is made from EPS. The area 15 is divided into sixteen equal parts 16 of square shape, each part 16 being equipped with a thermocouple 17 (TC 17 to TC 32) on top of the first (insulation) layer 3. The thermocouples 17 are arranged in the middle of the parts 16 being of identical size.

[0083] During the test#1 it has been discovered that six thermocouples 17 (TC 20, TC 23, TC 25, TC 30 to TC 32) being indicated with a cross 18 were before or during the test#1 malfunctioning.

[0084] The first (insulation) layer 3 and the thermocouples 17 were covered with the second (insulation) layer 5 made from stone wool, having a thickness of 40 mm and a bulk density of approx. 185 kg / m3. On top of the area 15, namely above the second (insulation) layer 5 the photovoltaic system

[0085] 7 has been arranged and fixed to the flat roof 1 . A wood crip placed 10 cm under the photovoltaic system 7 has been used as the ignition source and led to flame spread beyond 5 the second (insulation) layer 5 above the area 15 and to a self-sustaining burning as a result of re-radiation of the heat from the ignition source from the rear face of the PV panel to the roof surface.

[0086] Fig. 5 shows a coordinate system with the temperature in degrees Celsius at the y-axis and the time after starting the burning on top of the flat roof 1 in minutes at the x-axis. Fig. 5 io shows the different graphs for the thermocouples 17 and it can be seen that the general i curve progression is given with an increase of temperature after approximately 30 min of fire

[0087] : increasing up to approximately 160°C followed by a slow flattening of the curve within the next approximately 160 min. The increase of temperature is similar for all thermocouples 17 measuring the temperature. is Fig. 6 shows the same arrangement of thermocouples 17 in the parts 16 of the area 15 for test#2. The same first (insulation) layer 3 was used and instead of a second (insulation) layer 5 of stone wool with 40 mm thickness and a bulk density of 185 kg / m3a second i (insulation) layer 5 of stone wool with a thickness of 50 mm and a bulk density of i approximately 170 kg / m3has been used. Such a layer 5 can be a double density product

[0088] I 20 with two layers of different bulk densities. A first layer of the dual density product may have

[0089] : a thickness of 15 mm and a density of 220 kg / m3whereas a second layer of the dual density product may have a thickness of 35 mm and a density of 150 kg / m3.

[0090] Fig. 7 shows the curve progression during test#2. It can be seen that the curves of the different thermocouples 17 are more linear and very close to each other compared to Fig. 5 i 25 and that the maximum temperature has not exceed over 100° C. The first (insulation) layer

[0091] ; 3 made of EPS is therefore affected to a layer temperature because of the second i (insulation) layer 5 having a greater thickness compared to the second (insulation) layer 5 used in test#1. i Conclusions from the testing; The selected fire source (wood crib, approx. 15 kW, 10 min.) created sufficient energy to enable fire spread beyond its own area without burning through the photovoltaic panel 9, In the absence of dedicated fire tests for solar energy installations such as photovoltaics on flat or flat-inclined roofs 1 , the selected crib following some pretests and calculations, provided for a feasible and realistic fire source.

[0092] The fire eventually spread to the entire area below the photovoltaic panels 9 and became a significant fire due to the involvement of the second membrane 6, which eventually was contributing to the fire.

[0093] For a significant fire with a duration of about 20 minutes according to test #1 , the 40 mm thick second (insulation) layer 5 of mineral wool prevented ignition of the first (insulation) layer 3 of EPS, but the significant heat transfer from the fire still resulted in melting of some of it.

[0094] For a significant fire with a duration of 30 minutes following test #2, the 50 mm thick second (insulation) layer 5 of mineral wool rendered the first (insulation) layer 3 of EPS practically undamaged.

[0095] A repetition over a longer test duration and up to full burn-out of the setup according to a test #3 (not described in further detail here), i. e. up to the fire being self-extinguished, proved the first (insulation) layer 3 of EPS to remain intact. And, although minor melting of the first (insulation) layer 3 of EPS was observed, there was no ignition and the temperature monitored on top of the first (insulation) layer 3 of EPS only slightly increased above 140 °C, namely to around 150 °C after more than 90 minutes of said fire test.

[0096] Finally, Fig. 8 shows three curves 19, 20 and 21 each showing the temperature over the elapsed time of the fire before extinction of the fire after approximately 90 min. Whereas curve 19 shows the temperature on top of the second (insulation) layer 5, curve 20 shows the temperature inside, approximately in the middle of the second (insulation) layer 5. Finally, curve 21 shows the temperature on top of the first (insulation) layer 3. It can be seen that the first (insulation) layer 3 is protected by the second (insulation) layer 5 against high increase of temperature.

[0097] It can thus be concluded that a second (insulation) layer 5 of mineral wool with a thickness of 50 mm in combination with an existing membrane 4 ensures a retrofited flat or flat-indined roof 1 to be safe in case of photovoltaic-fires.

[0098] Reference signs:

[0099] 1 flat or flat-inclined roof

[0100] 2 substructure

[0101] 3 first (insulation) layer

[0102] 4 first membrane

[0103] 5 second (insulation) layer

[0104] 6 second membrane

[0105] 7 photovoltaic system

[0106] 8 supporting frame

[0107] 9 photovoltaic panel

[0108] 10 upper surface

[0109] 11 void

[0110] 13 vapor barrier

[0111] 14 third (insulation) layer

[0112] 15 area

[0113] 16 part

[0114] 17 thermocouples (TC 17 to TC 32)

[0115] 18 cross

[0116] 19 curve

[0117] 20 curve

[0118] 21 curve

Claims

Claims:1 . Method of retrofitting an existing flat or flat-inclined roof of a building, the existing roof comprising at least a first layer of a combustible insulation being arranged on a substructure and being covered with a first membrane as a roof seal, characterized in that a second layer of a preferably non-combustible insulation is arranged on top of the first membrane before the second layer of preferably non-combustible insulation is covered with a second waterproofing membrane and before finally a photovoltaic system with at least one photovoltaic panel is arranged with a distance to and on top of the second waterproofing membrane.

2. Method according to claim 1 , characterized in that as second layer of the non-combustible insulation a layer of mineral wool is provided on the first membrane.

3. Method according to claim 1 , characterized in that as second layer of the non-combustible insulation a layer having a thickness between 30 mm and 100 mm, preferably of 50 mm is provided on the first membrane.

4. Method according to claim 1 or 3, characterized in that as second layer and / or third layer of the non-combustible insulation a layer having a bulk density between 80 kg / m3and 180 kg / m3, preferably of 130 kg / m3is provided on the substructure.

5. Method according to claim 1 or 3, characterized in that the second layer of the non-combustible insulation is fixed by anchor elements like screws running through the first layer of combustible insulation and the second layer of non-combustible insulation and being fixed in the substructure.

6. Method according to claim 1, characterized in that the first membrane is removed before the second layer of insulation is arranged on top of the first layer of insulation.

7. Method according to claim 1 , characterized in that a foil of metal, preferably of alumina and preferably being part of laminate is arranged on top of the first layer of insulation before the second layer of insulation is arranged on the foil and preferably after the first membrane is removed from the first layer of insulation.

8. Method according to claim 7, characterized in that the foil, preferably as part of the laminate is fixed to the second layer of insulation before the second layer of insulation is arranged on top of the first layer of insulation.

9. A flat or flat-inclined roof (1) for a building comprising a substructure, at least a first layer (3) of a combustible insulation, which first layer (3) is covered with a first membrane (4) as a roof seal, whereby a second layer (5) of a preferably noncombustible insulation is provided on top of the first membrane (4), whereby a second waterproofing membrane (6) is provided on top of the second layer (5) of the preferably non-combustible insulation, thereby covering the second layer (5), and comprising a photovoltaic system (7) with at least one photovoltaic panel (9) being provided with a distance to and fixed on top of the second waterproofing membrane (6).

10. Roof according to claim 9, characterized in that the second layer (5) of the non-combustible insulation is fixed by anchor elements like screws running through the first layer (3) of combustible insulation and thesecond layer (6) of non-combustible insulation and being fixed in the substructure (2).

11. Roof according to claim 9, characterized in that a foil of metal, preferably of alumina and preferably being part of a laminate is provided between the first layer (3) of insulation and the second layer (5) of insulation.

12. Roof according to claim 11 , characterized in that the foil, preferably as part of the laminate is fixed to a major surface of the second layer (5) of insulation, preferably made of insulation boards being arranged adjacent to each other.

13. Roof according to claim 12, characterized in that the foil fixed to the major surface of the second layer (5) insulation extents over at least one, preferably two side faces of the second layer (5) of insulation in form of boards or slabs.

14. Assembly for a retrofit system to be used on an existing flat or flat-inclined roof (1) of a building, the existing roof (1) comprising at least a first layer (3) of a combustible insulation being arranged on a substructure (2) and being covered with a first membrane (4) as a roof seal, characterized by a second layer (5) of a preferably non-combustible insulation to be arranged on top of the first membrane (3), a second waterproofing membrane (6) to be arranged on the second layer (5) of preferably non-combustible insulation and a photovoltaic system (7) with at least one photovoltaic panel (9) to be arranged with a distance to and on top of the second waterproofing membrane (6).

15. Assembly according to claim 14, characterized in thatthe second layer (5) of insulation consists of boards and / or slabs preferably made of mineral wool and preferably having a thickness between 40 mm and 100 mm, more preferably of 50 mm.

16. Assembly according to claim 14, characterized by anchor elements like screws to be arranged running through the first layer (3) of insulation and the second layer (5) of insulation and to be fixed in the substructure (2).

17. Assembly according to claim 14, characterized by a foil of metal, preferably of alumina and preferably as part of a laminate to be arranged on top of the first layer (3) of insulation underneath the second layer (5) of insulation.

18. Assembly according to claim 17, characterized in that the foil of metal, preferably as part of the laminate is fixed to a major surface of the second layer (5) of insulation.

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