Abstract:
The present invention concerns an insulating roof support assembly for a roof structure comprising a plurality roof elongated rafters spaced apart in a predetermined distance with insulation boards therebetween, wherein elongated mineral wool fiber insulation elements are provided on the top of each of the elongated roof rafters and elongated wooden elements on top of said insulation elements with at least one impermeable membrane between at least two neighbouring insulation elements sandwiched between the wooden elements and the insulation elements.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national phase of international patent application Ser. No. PCT/EP2014/061027, filed May 28, 2014, which claims priority to international patent application Serial No. EP 13171005.5, filed Jun. 7, 2013, the contents of which are incorporated herein in their entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to a thermally insulating roof support assembly, a method of installing such roof support assembly and an insulating roof construction for buildings. 
     BACKGROUND OF THE INVENTION 
     It is known to provide an insulating roof support assembly for a roof structure comprising a plurality roof elongated rafters spaced apart in a predetermined distance with insulation boards there between. On top of this roof support assembly, the roof tiles or other types of roof cover is mounted. 
     It is also known to provide solutions for the new-build but as well for the refurbishment sector in order to deal with the constantly increasing requirements being specified in respect to thermal insulation respectively energy savings. Just by way of example reference is made to  FIGS. 1 and 2  illustrating common solutions to deal with said increased demands.  FIG. 1  showing a rafter extension as it would be required in order to improve existing buildings, i.e. for refurbishment; simply to increase the height of the existing rafters and hence the space to accommodate additional insulation; whereas  FIG. 2  illustrates an on-rafter insulation system which actually would serve for both purposes, the new-build as well as for the refurbishment segment. Such systems have also earlier been described in e.g. EP0852275, DE19922592, or EP2354363. 
     In WO2009/153232 there is disclosed an insulating building system for an external building structure, such as a wall or a roof, or an internal building structure of the above-mentioned kind. This building assembly comprises a top and a bottom profile with a plurality of joining profiles between the top and bottom frame profiles. The joining profiles have a first and second side surfaces which are abutted by the contact sides of adjacent insulating panels on each side of said joining profiles, wherein the profile contact sides of the insulation panels are provided with a shape matching the profile side surfaces of the joining profiles such that the insulation panels are retained between two profiles. The insulation panels thereby support the joining profiles and provide stability and strength to the wall structure and prevent the joining profiles from buckling. 
     However, these known building assembly systems are often complex, not easy to install on a roof and furthermore, there are increasing demands for extra thermal insulation in roof constructions in order to provide a comprehensive thermal building insulation. 
     SUMMARY OF THE INVENTION 
     It is therefore an object by the present invention to provide a roof support assembly which is easy and fast to install on site and which allows for an efficient level of thermal insulation for avoiding thermal bridges in the roof construction. 
     This object is achieved by an insulating roof support assembly for a roof structure comprising a plurality of roof elongated rafters spaced apart in a predetermined distance with insulation boards there between, wherein elongated insulation elements are provided on the top of each of the elongated roof rafters and elongated wooden elements on top of said insulation elements with at least one impermeable membrane between at least two neighbouring insulation elements sandwiched between the wooden elements and the insulation elements. 
     By the invention, a roof support assembly may be provided which increases the insulation accommodating space between the roof rafters, but without extending thermal bridging by the wooden roof rafters. Due to the insulating properties of said insulation elements the thermal bridging is reduced compared to the use of similarly larger dimensioned rafters. The said insulation elements, like e.g. mineral wool fibre material, polymeric foams or other suitable insulation materials act as a thermal break or spacer. Moreover, the material is less expensive which results in a roof support construction which is inexpensive compared to the known solutions. 
     Today building requirements in many countries demand a roof insulation thickness of 400-500 mm. Existing roof constructions are not provided with rafters of such height and therefore an extension is needed when refurbishing the roof. By the roof support assembly according to the invention, a simple and cost-effective solution is provided. 
     Preferably, the elongated insulation elements are provided with the same width as the elongated roof rafters. Hereby the same dimensions of the insulation boards can be used for installation between the rafters and between the insulation respectively spacer elements. 
     In order to facilitate an easy mounting of the roof support assembly, the wooden elements, the at least one membrane and the elongated insulation elements are preferably mounted to the elongated rafters by a plurality of fastening members, such as screws. 
     By the invention it is found advantageous that the insulation elements have a sufficient rigidity and good load-carrying capability, in particular in a new-built situation, whilst at the same time being sufficient resilient so that any unevenness in the wooden rafters can be absorbed and the roof surface may thereby be aligned. The latter will often be a challenge faced in a refurbishment situation. Therefore, it is essential that the insulation elements or spacer provide a certain compression strength at 10% strain (CS(10)) according to European Standard EN826. In an embodiment of the invention the said compression strength at 10% strain will be in the range of 15 kPa to 30 kPa, preferably in the range of 20 kPa to 25 kPa. It is the person skilled in the art who will be able to choose the adequate strength properties in respect to the individual situation at the site. In some cases it might even be necessary to reduce the strength properties, e.g. by additional flexing of the bottom part of the insulation element which will be in contact with the wooden rafters, in order to be as resilient as to compensate for unevenness in a broad variety of tolerances. 
     In a preferred embodiment of the invention the elongated insulation elements are made from mineral wool fibre material, preferably stone wool fibre material. Moreover, it may be preferred that the mineral wool fibre insulation elements have a density of 70 kg/m 3  to 100 kg/m 3 , preferably of 90 kg/m 3 . 
     The roof structure in which the roof support assembly will typically be mounted may be an inclined roof, i.e. a pitched or steep roof, or a flat roof. 
     In a second aspect of the invention, there is provided a method of installing an insulating sub-roof assembly, said method comprising the steps of providing a plurality of roof elongated rafters with an elongated insulation element on the top of each of the elongated roof rafters and an elongated wooden elements on top of said insulation elements with at least one flexible membrane for waterproofing between at least two neighbouring insulation elements sandwiched between the wooden elements and the insulation elements. Such membranes for waterproofing are commercially available and regulated according to European Standard EN13859-1. In a preferred embodiment of the invention the membrane provides a variable diffusion-equivalent air layer thickness (s d -value) of 0.01 m (depending on the moisture level) in accordance with European Standard EN12572 which ensures applicability of the membrane for a broad variety of different constructions. 
     By the invention, it is realised that the elongated insulation elements are mounted on the top of the rafters off-site. Hereby, the roof construction rafters may be prepared on the ground before being lifted to the roof, whereby a fast and easy insulating roof support assembly may be achieved. 
     However, it is also realised that the present invention is advantageous as the support roof assembly may be mounted on the roof rafters for refurbishment of an existing roof construction. 
     In yet a further aspect of the invention there is provided an insulating roof construction for buildings comprising a roof support assembly as described above and preferably provided by performing a method mentioned above. In the roof construction according to this aspect one or more insulation panels are provided in the space between the rafters and a top surface is mounted on the elongated wooden elements. 
     An insulating roof construction according to the invention is found advantageous as it is realised that it is possible to comply with e.g. the Passive House demands according to recommendations by the German Passive House Institute (PHI), Darmstadt as the roof construction can be provided with a U-value≦0.12 W/m 2 K, in particular as low as 0.1 W/m 2 K. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the invention is described in more detail with reference to the accompanying drawings, in which: 
         FIGS. 1 and 2  are cross-sectional schematic views of roof constructions according to the prior art; 
         FIG. 3  is a schematic side view of an insulating roof support assembly according to an embodiment of the invention; 
         FIG. 4  is another embodiment thereof; 
         FIG. 5  is an exploded schematic front view of the insulating roof support assembly; 
         FIGS. 6 and 7  are two variants thereof where the insulation roof support assembly is assembled; and 
         FIG. 8  is a schematic cross-sectional view of the roof support assembly of example described below. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 and 2  show examples of known roof constructions. In  FIG. 1 , a number of wooden roof rafters  1  have been extended with additional wooden rafters  1 ′. Membranes  4  are fitted around the rafters and insulation boards  2  are then fitted between the rafters  1 ,  1 ′ and a second membrane  4  is then provided on top of the rafters  1 ,  1 ′. The roof top structure is then mounted, i.e. the wooden support members  5  and the horizontally oriented laths  6  with roof tiles  9  or the like on top. In  FIG. 2 , there is no extension of the rafters  1  but instead a second layer of insulation  2 ′ is provided. 
       FIG. 3  shows an embodiment of the invention, where a roof rafter  1  is provided with an elongated mineral wool fibre insulation element  3  on the top of the rafter (see also  FIGS. 5-7 ). A flexible membrane  4  for waterproofing as it has been described before is provided on top of the elongated insulation element  4 . A wooden support member  5 , e.g. a Kerto board is then placed above the insulating spacer element  3  thereby clamping the membrane  4  between the insulation spacer  3  and the support member  5  when the assembly is mounted via glue and/or fastening screws  8  (see  FIGS. 5-7 ) penetrating the membrane  4  and the spacer elements  3 . On the support members  5  a number of horizontally oriented laths  6  are provided onto which the roof cover (not shown) can be mounted. 
     The rafters  1  and thereby the roof construction are fixed to a wall plate  7  on the top of the wall of the building. 
     As shown in  FIG. 4 , the insulating roof support assembly according to the invention may be mounted on rafters  1  of an existing roof construction. The mineral wool fibre spacer elements  3  may due to their resiliency absorb any unevenness  1   a  on the top surface of the rafters  1  so that when the spacer elements  3  are mounted the top wooden member  5  becomes aligned with the roof inclination. Said spacer elements  3  are mounted together with the support members  5  and the membrane  4  via fastening screws  8  as described before. In case of considerable unevenness  1   a  of the rafters  1  it might be adequate to apply additional flexing to the bottom part of the spacer elements by means per se known in the art to influence the resiliency to the extent needed. This “extra flexing” for refurbishment situations makes the roof support assembly according to the invention particularly advantageous. 
     The mineral wool fibre spacer elements  3  advantageously provide a very low thermal conductivity, expressed as the Lambda declared value according to EN13162 of between 0.030 W/mK and 0.035 W/mK, preferably of about 0.034 W/mK. 
     As indicated in  FIGS. 6 and 7 , insulation boards  2  may be provided between two adjacent rafters  1  with an insulating spacer element  3  mounted thereon. The insulation boards  2  may be traditional low-density mineral wool insulation boards as they are commonly known, being installed in one or more layers in order to provide the predetermined thickness of the thermal insulation required for the roof system. 
     The rafters  1  are normally made of wood and are normally part of the roof construction sections. When providing a roof construction to a new building, the insulating spacer elements  3  may advantageously be mounted as extensions on the rafters  1  during the production of the rafter sections. Advantageously, the insulating spacer elements  3  are provided with the same width dimensions as the rafter  1  (as shown in  FIGS. 6 and 7 ). This makes the fitting of the insulation boards easy and simple. 
     EXAMPLE 
     The main purpose of the roof solution in a modern building is to have a balanced and efficient thermal performance defined by the U-value or overall heat transfer coefficient. This value indicates the rate of heat transfer through a specific component over a given area if the temperature difference is exactly one degree (1 Kelvin). The measurement unit of the U-value is therefore W/m 2 K; the smaller the U-value the better the level of insulation. 
     With a system according to the invention it is found possible to complete a coherent un-broken fibrous insulation shell. A shell ensuring that the buildings structural parts are efficient protected and thermally well insulated. The building envelope does not impair the thermal performance significantly, except for those necessary penetrations that must be handled separately. 
     As an example of the thermally insulated roof support assembly, shown in  FIG. 8 , the system is made of components described below. 
     Wooden rafters  1  are provided at an axial distance (L 1 ) of 1.000 mm, having a density of approx. 500 kg/m 3 , and with a width of 45 mm, a height of 180 mm and a Lambda value of 0.12 W/mK (at approx. 12% moisture content). 
     The spacer elements  3  on top of rafters  1  are made of mineral wool fibres with a density of 90 kg/m 3  and with a width of 45 mm, a height of 180 mm and a Lambda declared value of 0.034 W/mK according to EN13162. 
     The intermediary insulation boards  2  are of the type Super flexibatts® produced by Rockwool A/S and with a thickness of 180 mm (T i ) and a Lambda declared value of 0.034 W/mK according to EN13162. 
     The rafters  1  are provided on a layer of wooden fibre boards  10  of the OSB type having a density of approx. 650 kg/m 3 , a thickness of 12 mm and a Lambda value of 0.13 W/mK. 
     By choosing the above described design and the said materials, the total thickness of the roof support is 372 mm in order to achieve a total U-value of 0.10 W/m 2 K.