EP1464772B1

EP1464772B1 - Fire-proof construction of a thatched roof

Info

Publication number: EP1464772B1
Application number: EP04007742A
Authority: EP
Inventors: Erling Bach Pedersen; Carlo Christensen
Original assignee: Carlo F Christensen AS; Erling Bach Pedersen Brandsikring ApS
Current assignee: Carlo F Christensen AS; Erling Bach Pedersen Brandsikring ApS
Priority date: 2003-04-01
Filing date: 2004-03-31
Publication date: 2007-07-18
Anticipated expiration: 2024-03-31
Also published as: DE602004007565T2; PL1464772T3; EP1464772A1; ATE367491T1; DK1464772T3; DE602004007565D1

Abstract

The present invention concerns a roof construction (20) for a thatched roof (30) with side edges (47), eaves (24) and ridge (27), including a glass matting (23) placed on the laths (22) of the roof construction (20), preferably covering the entire roof construction (20), and a mineral wool mat (25) disposed between the thatched roof (30) and the glass matting (23) along the side edges (47) and eaves (24) of the thatched roof (30), where along the ridge (27) of the thatched roof (30) between the thatched roof (30) and the glass matting (23) furthermore there is placed a mineral wool mat (28) having a melting point of 800 DEG C or higher. <IMAGE>

Description

Field of the Invention

The present invention concerns a roof construction for a thatched roof with side edges, eaves and ridge, including a glass matting placed on the laths of the roof construction, preferably covering the entire roof construction, and a mineral wool mat disposed between the thatched roof and the glass matting along the side edges and eaves of the thatched roof.

Background of the Invention

On old buildings deserving restoration, e.g. timber frame houses from previous centuries but also on new houses, thatched roofs are still laid so that the houses will appear as originally intended or with a rural and pleasant appearance. A real thatched roof may furthermore contribute to increasing the value of a house due to the nice appearance and because it provides the house with a certain charm as compared with houses with tile or asbestos cement roofs.
That which many people see as the disadvantage of a thatched roof is the increased fire risk and thereby the increased cost of a fire insurance. Therefore, in the thatching business much time and money has been used for finding possible fire-proofing systems that can reduce the risk significantly.
One of these methods has been to install a piping with sprinklers in the thatched roof itself, where the sprinkler delivers water if the roof catches fire. The device has appeared to be efficient; however, unfortunately it increases the costs of laying a thatched roof too, since more man-hours are to be used in assembling and integrating the piping in the thatched roof.
A roof construction according to the preamble of claim 1 is described in DE-A-3220536 .
Another fire-proofing method is described in the folder from Dansk Brandteknisk Instituts (DBI) entitled "Brandteknisk Information 29 - Brandsikring af stråtage", 3rd edition July 1998, where the constructions are described in which the thatched roof is laid on the laths of the roof construction and mineral wool is disposed between the laths and/or under the laths, after which a sheet covering is fitted at the inside.
The disadvantage of the above method is that the thatched roof cannot "breathe", since natural ventilation of the straw material cannot occur, whereby the straw material rots and the thatched roof is decomposed.
Subsequently, it has appeared that some thatched roofs laid according to the regulations in the DBI folder has a considerably reduced service life of only 5-10 years, after which investments in re-laying the thatched roof are to be made, meaning unexpected costs and which afterwards have kept the house owners from laying a new thatched roof.
The skilled people in the thatching industry have therefore examined the possibilities in order to find other materials and/or methods that may reduce the fire risk and simultaneously prevent rotting of the straw material.
The trend has pointed towards a method where the laths of the roof construction are entirely or partly covered with a fire-resistant and very diffusion permeable glass matting. Fire tests have shown that this method is functioning very well, and that it reduces burn-through on the face sections of the thatched roof.
By fire in a thatched roof, only smouldering fire will occur on the face sections as the fire does not ignite any straw material. The fire will seek to the edges of the thatched roof, where it has possibility of getting at the straw material while at the same time there is a lot of oxygen available.
The drawback of the glass matting is that it melts at 600°C - 800°C, and that considerably higher temperatures can occur at the edge areas due to heat radiation and a surplus of oxygen, whereby the glass matting melts and the fire can get free access to the underlying roof construction.
In order to avoid melting of the edge area of the glass matting, a narrow mineral wool mat of maximum 15 cm was laid up along side edges and eaves of the thatched roof during fire tests.
The principle of placing a narrow mineral wool mat along the side edges and the eaves is about the mineral wool mat in the edge area protecting the underlying glass matting against the high temperatures. At the same time, the mineral wool mat is not to cover too large roof face area, whereby the ventilation of the thatched roof is considerably reduced, causing areas with risk of rotting in the straw material.
The above fire test showed that the combination of underlying glass matting and a mineral wool mat along the side edges and eaves of the thatched roof partly functions as fire-proofing of the thatched roof.

Purpose of the Invention

The purpose of the present invention is therefore to provide an improved fire-proofing of a thatched roof while simultaneously ensuring sufficient ventilation of the thatched roof.
This is achieved with a roof construction as described in the preamble of claim 1, and where along the ridge of the thatched roof between the thatched roof and the glass matting furthermore there is placed a mineral wool mat having a melting point of 800°C or higher.

Description of the Invention

In the following, there is described a roof construction for fire-proofing thatched roofs with a number of edges in the form of side edges, eaves and roof ridge. For a skilled person in the thatching industry there is clear difference in these edges, since by thatching there is made different closing sections of thatching depending on whether the case is a side edge, eaves or a ridge.
With the term thatched roof is preferably understood roofs built up of reeds, but a thatched roof may be built up of other organic materials, as e.g. straw, rushes, seaweed and the like.
Large-scale fire tests showed that the combination of underlying glass matting and a mineral wool mat along the side edges and eaves of the thatched roof partially functioned as fire-proofing for the thatched roof. In order to improve the fire-proofing, it is necessary to use a mineral wool mat having a melting point of 800°C or higher, as the flame temperature can rise close to this temperature.
The said large-scale fire tests furthermore showed that problems arise around the ridge of the thatched roof, since the thatched roof has less material thickness around the roof ridge, simultaneously with the roof ridge is typically closed with a ridge part of porous material, as e.g. heather, seaweed or straw, and by cross-pieces, entailing that the fire has some material to ignite.
Due to the less material thickness around the roof ridge, the heat radiation from the flames may more easily cause melting of the underlying glass matting and burn-through into the roof construction. In order to avoid this, a mineral wool mat is provided along the ridge of the thatched roof.
As opposed to previous cases, where only a narrow mineral wool mat was provided along the side edges and the eaves during test for keeping the ventilation of as much of the face of the thatched roof as possible, the fire tests showed that it is necessary to compromise this concept in order to achieve satisfactory fire-proofing of the thatched roof. Therefore, broader mineral wool mats are to be placed around the edges of the thatched roof.
By igniting fire on a thatched roof in a test set-up, it was observed that the flame border moves from the side edges and/or eaves into the roof face of the thatched roof, and that the flame border moves with a speed determined by the humidity of the straw material and by the wind conditions.
In order to protect the underlying glass matting and at the same time to attain sufficient response time for alarm and fire extinguishing, the mineral wool mat along the eaves and the side edges of the thatched roof is 50-80 cm wide, preferably 60 cm.
Along the ridge of the thatched roof, the flames propagated a little faster due to the ridge part and the thinner thickness of straw material, and therefore the mineral wool mat along the ridge of the thatched rood is 50-80 cm wide, preferably 60-70 cm.
The wider mineral wool mats are considered as being sufficient for preventing melting of the underlying glass matting and thereby to achieve sufficient time for commencing fire extinguishing, while at the same time good ventilation of the other roof faces of the roof is achieved.
In order to achieve optimal fire extinguishing of the roof construction, there is used mineral wool mats with a melting point higher than 1100°C. For the fires not involving lighter fuel or inflammable liquids, e.g. petrol and the like, the flame temperature will rarely exceed 1100°C, and the mineral wool mat will therefore be able to protect the underlying glass matting until the fire is extinguished.
The fire tests showed that is was necessary that the mineral wool mat is a rockwool mat for ensuring that the mineral wool mat could resist the heat radiation and protect the underlying glass matting.
Particularly suited mineral wool mats for covering the edges of the thatched roof have a density of 100 - 350 kg/m³, are dimensionally stable and without any surface protection in the form of plates, bags or impregnation.
Mineral wool mats with a density between 100 - 350 kg/m³ imply that the mineral wool material is so densely packed that it can be formed into plates (mats) which are easy to handle during transport and laying.
In order prevent that the fire jumps from the thatched roof and into the roof construction in spite of positioned mineral wool mats, these are to be without any surface protection in the form of plates, bags or impregnation which can be ignited.
In order to establish a roof construction for a thatched roof, the following steps are performed:

glass matting is placed and fastened directly upon the laths of the roof construction;
mineral wool mats, preferably having a width of 60 cm, are placed along the side edges and eaves of the thatched roof;
straw material is laid from the eaves and upwards on the roof construction;
mineral wool mats, preferably with a width of 60-70 cm, are placed along the ridge of the roof; and
the roof is thatched and finished with a ridge part.

The above method for establishing a fire-proof thatched roof is performed when the laths have been fitted on the rafters of the roof construction.
The glass matting is put on the roof and are attached directly on the laths and straightened during the mounting, so that the inner side of the thatched roof appears as a relatively smooth and nice structure.
The glass matting is a combination tissue which is composed of a layer of glass fabric and a layer of glass splinters, providing the glass matting with the required strength and stability during construction.
The glass matting is turned so that the glass fabric layer faces the laths. This also entails that even if melting of the seams holding the glass matting together are melted, the glass fabric layer will hold up the glass splinter layer, and thereby the protecting function of the glass matting will not be critically reduced.
After the glass matting having been laid out across the entire roof construction, mineral wool mats can be placed long the side edges and eaves of the thatched roof. These mats are fastened with e.g. wood concrete nails that hold the mineral wool plates in position until the straw material is laid on and fastened to the roof construction.
When the straw material is laid from the eaves and upwards on the roof construction and before it reaches the ridge, mineral wool mats wider than the mineral wool mats at the side edges and eaves are placed along the ridge of the thatched roof. Then the thatched roof is finished with a ridge part.
Mineral wool mats are only to be placed on the spots of a thatched roof having a free edge. For example, on an attic where there is a gradual transition to other surfaces of the thatched roof, mineral wool mats are only to be placed along the eaves edge. At annular edges, as for example a valley between two buildings, no mineral wool mats are to be placed since the thatched roof does not have a free edge which the flames may ignite.
Typically, the mineral wool mats have a thickness of at least 45 mm which is found sufficient to protect the underlying glass matting, and at the same time the thickness fit with the typical displacement of barge board and fascia board which the roof construction is typically made with, providing that openings between the thatched roof and the roof construction are closed around the edge parts. It is furthermore an advantage that these openings/channels are closed with one i that may transport cold air into the house or may transport air (oxygen) on to the flames, increasing the speed of the fire. Furthermore, they may function as habitat for vermins, as e.g. mice, rats, polecats and the like.
Fire tests made in co-operation with DBI have resulted in that the regulations of DBI are re-written as to how thatched roofs can be fire-proofed according to the present invention, and since DBI has approved this roof construction as being fire-proof, house owners can attain reduction in their insurance premium and thereby achieve better economy by establishing or renovating thatched roofs.
The invention is explained in more detail in the following in connection with the drawing, where:

Fig. 1: shows excerpts from the information folder issued by DBI;
Fig. 2: shows a sectional view of a roof construction according to the invention;
Fig. 3: shows a sectional view of a roof construction with thatched roof;
Fig. 4: shows a perspective view with a roof construction according to the invention;
Fig. 5: shows a perspective view of an attic construction according to the invention, and
Fig. 6: shows glass matting according to the invention.

On Fig. 1 is shown three illustrations from the DBI folder "Brandteknisk Information 29 - Brandsikring af stråtagett" (3rd edition, July 1998), where three different methods approved for fire-proofing thatched roofs are illustrated:

In the upper illustration "Oven på spær" 1a a thatched roof 2 lies upon a layer of mineral wool mats 3 which are laid down between the laths 5 of the roof construction. The mineral wool mats 2 and the laths 5 are placed upon a spacer 4 laid on a fire-resistant plate covering 7 upon the rafters 6.
In the intermediate illustration "Mellem spaer" 1b a thatched roof 2 lies upon laths 5, and there is a layer of mineral wool mats 3 between the laths 5 and under the laths 5. There is a plate 8 for securing the mineral wool mats 3 between laths 5 and rafters 6. In order to support the plates 8, fillets 9 are mounted at the side of the rafters 6.
In the lower illustration "Påsprøjtet" 1c a thatched roof 2 lies upon laths 5, and fire-resistant plaster 10 has been sprayed on the underside of laths 5/thatched roof 2.

Common to all three methods is that thatched roofs 2 are placed directly down against a closed surface where there is little air through-flow. This implies that the thatched roof 2 cannot breathe, and rot can arise in the straw material, whereby the useful life is strongly reduced.
On Fig. 2 is shown a roof construction 20 including rafters 21 and laths 22 on which is mounted/suspended a glass matting 23 that extend from barge board edge 26 up over roof ridge 27 and down on the other side of the roof construction 20.
Along eaves 24 is placed an about 60 cm wide mineral wool mat 25 that lies upon glass matting 23 and up to barge board edge 26. Along ridge 27 is a mineral wool mat 28 that lies upon glass matting 23 and across the ridge 27 and extends about 70 cm down on both sides of ridge 27.
On Fig. 3 is shown the roof construction 20 of Fig. 2 with a thatched roof 30. At ridge 27 is furthermore arranged a ridge part 31 which can consist of heather, straw or the like for achieving a nice finish on the thatched roof 30.
At eaves 24 it can be seen that the mineral wool mat 25 fills up the opening between lath 22, thatched roof 30 and barge board 26, whereby air access is prevented. The material thickness of both the mineral wool mat 25 and the mineral wool mat 26 is reduced when the thatched roof 30 is laid upon roof construction 20.
Between the upper edge of the mineral wool mat 25 and the lower edge of the mineral wool mat 28 there is only the very diffusion permeable glass matting 23 separating the thatched roof 30 from the loft 32, whereby the thatched roof 30 can breathe freely.
On Fig. 4 is shown a roof construction 40 on a building 41 where a centrally placed attic 42 is provided. The side faces of the roof construction 40 and the side faces of the attic 42 are mounted with glass matting 43.
Along ridge 44 and ridge 45 on the attic 42 is placed a mineral wool mat 46, while along the side edges 47 and eaves 48 there is placed a mineral wool mat 49.
On Fig. 5 is shown an attic construction 50, where around eaves edge 51 is placed a mineral wool mat 52 surrounding the attic construction 50, and which lies upon glass matting 57 and up to barge board edge 53.
Furthermore, a mineral wool mat 54 is disposed along eaves 55 of roof construction 56 which lies upon glass matting 57 and up to barge board edge 58.
Between attic construction 50 and roof construction 56 no mineral wool mats are laid out, since a continuous junction of the thatched roof (not shown) is made.
On Fig. 6 is shown a glass matting 60 which is a combination tissue composed of a layer of glass fabric 61 and a layer of glass splinters 62 which e.g. are sewn together via seams 63.
The combination of glass fabric 61 and glass splinters 62 provides the glass matting 60 with the required strength and stability during mounting. The glass matting 60 will be mounted with the glass fabric 61 facing downwards so that by melting of the seam 63 or breakage of seam 63, it may hold up glass splinters 62 and thereby retain the fire-resistant effect of the glass matting 60

Claims

Roof construction (20, 40) with side edges (47), eaves (24, 48) and ridge (27, 44), including a thatched roof (30) and a glass matting (23, 43) placed on the laths (22) of the roof construction (20, 40), preferably covering the entire roof construction (20), characterized in that a mineral wool mat (25, 49) is disposed between the thatched roof (30) and the glass matting (23) along the side edges (47) and eaves (24, 48) of the thatched roof (30), and along the ridge (27, 44) of the thatched roof (30) between the thatched roof (30) and the glass matting (23, 43) furthermore there is placed a mineral wool mat (28, 46) having a melting point of 800°C or higher.
Roof construction according to claim 1, characterized in that the mineral wool mat (25, 49) along the eaves (24, 48) of the thatched roof (30) and the side edges (47) is 50-80 cm wide, preferably 60 cm.
Roof construction according to claim 1, characterized in that the mineral wool mat (28, 46) along the ridge (27, 44) of the thatched roof (30) is 50-80 cm wide, preferably 60-70 cm.
Roof construction according to any of claims 1 - 3, characterized in that the melting point of the mineral wool mat (25, 28, 46, 49) is higher than 1100°C.
Roof construction according to any of claims 1 - 4, characterized in that the mineral wool mat (25, 28, 46, 49) is a rockwool mat.
Roof construction according to any of claims 1 - 5, characterized in that the mineral wool mat (25, 28, 46, 49) has a density of 100 - 350 kg/m³ and is dimensionally stable and without any surface protection in the form of plates, bags or impregnation.
Method for establishing a roof construction (20) for a thatched roof (30) according to any of claims 1 - 6, characterized in that
- glass matting (23) is placed and fastened directly upon the laths (22) of the roof construction (20, 40);

- mineral wool mats (25, 49), preferably having a width of 60 cm, are placed along the side edges (47) and eaves (24, 48) of the roof construction (20, 40);

- straw material is laid from the eaves (24, 48) and upwards on the roof construction (20, 40);

- mineral wool mats (28, 46), preferably with a width of 70 cm, are placed along the ridge (27, 44) of the roof construction (20, 40); and

- the roof is thatched and finished with a ridge part (31).