WO1995018899A1

WO1995018899A1 - Roof structure and a pressure equalization means for this roof

Info

Publication number: WO1995018899A1
Application number: PCT/DK1995/000016
Authority: WO
Inventors: Erik Frederiksen; Peter F. Collet
Original assignee: A/S Jens Villadsens Fabriker
Priority date: 1994-01-10
Filing date: 1995-01-10
Publication date: 1995-07-13
Also published as: DK4194A

Abstract

A roof structure comprising a support and a roof covering in the form of a roof membrane arranged on said support and optionally an insulation layer located between the membrane and the support, one or more pressure equalization means, each comprising an air duct including a valve which opens only when the pressure above the roof membrane is lower than the pressure in the space between the support and the roof membrane.

Description

Roo_f s_truc_tur_e and a pressure equalization means for this roof.

The present invention relates to a roof structure comprising a support and a roof covering in the form of a roof membrane provided on said support and optionally an insulation layer provided between the membrane and the support, and one or more air ducts through which the space between the support and the membrane is in communication with the area above the membrane.

When the wind blows across a roof, turbulence may cause subatmospheric pressure zones to be formed above the roof which will consequently be exposed to the influence of vertical suction forces. Such suction forces will have a tendency to remove the roof covering from the support.

It is well known to provide means for securing a roof covering as described above to the support. Usually this is effected by adhesion, by mechanical fixing means or by applying a layer of ballast material to the roof covering, e.g. a layer of stones. The known securing methods are labour consuming and require additional materials and consequently are costly. Besides they may cause leakages to be formed.

It is well known to provide roofs, such as horizontal roofs, with systems of roof ventilation caps having air inlet and outlet openings which are oriented in such a manner that, under the influence of the wind, they generate air flows parallel to the roof in the space between the support and the roof membrane. The purpose of such roof ventilation caps is to vent said space thereby preventing accumulation of moisture and the formation of steam bubbles.

However, experience has shown that instead of reducing the accumulation of moisture in the space between the support and the roof membrane, including the insulation layer, such ventilation caps often cause the water content of the roof to increase and thus reduce the insulating capacity of the insulation layer. The reason for such accumulation of moisture is that the ventilation caps, due to the prevailing pressure conditions, draw hot and humid room air upwards through cracks and gaps and into the relatively cold roof structure where the humid air gives off condensation water which is absorbed in the roof structure.

It is also well known to provide ducts which are evenly dis- tributed across a roof covering comprising an insulation layer in the underside of said insulation layer in order to vent off humidity, such as moisture originating from the construction of the roof or moisture coming from rooms below, said ducts being connected to a number of ventilation caps.

Since the caps are mutually connected through said ducts, a high pressure zone above the roof may cause air to be pressed through the caps and the ducts to a low pressure zone else¬ where on the roof and thus a desired pressure equalization between opposite sides of the roof covering is not obtained.

The invention is based on the discovery that the effect of the above-mentioned wind suction forces on the roof covering may be substantially eliminated without causing a harmful accumulation of moisture and ensuing reduction of the insulating capacity of the roof structure by arranging on the roof pressure equalizing means each comprising an air duct including a valve which opens only when the pressure above the roof membrane is lower than the pressure in the space between the support and the roof membrane.

When a roof structure according to the invention is exposed to suction forces caused by the formation of a subatmospheric pressure zone on the upper side of the roof covering, the valves in said ducts will open and thus allow a certain pressure equalization between the upper side of the roof covering and the space between the support and the roof membrane to take place, thus causing a complete or partial elimination of the sucking effect of the wind forces on the roof covering. As the valves open only when the suction on the roof covering reaches a certain value, the harmful movement of room air into the roof structure is reduced or eliminated. Moreover, it is avoided that a εuperatmospheric pressure in zones where such a pressure prevails is trans¬ planted to subatmospheric pressure zones thereby permitting a quicker pressure equalization in said zones.

By suitable selection of the dimensions and design of the pressure equalization means the time constants for said pressure equalization will be very small.

As a result of such quick pressure equalizations the need for means for securing the roof covering to the support is eliminated or substantially reduced.

A further advantage of the roof structure according to the invention is that, in case of decreasing wind forces acting on the upper side of the roof covering, the valves close and thus prevent the subatmospheric pressure from being equalized to the now reduced pressure on the underside of the roof co¬ vering. Thus, the subatmospheric pressure has been "saved" and the valves thus contribute to reducing the time constant for pressure equalization when the wind suction on the top surface of the roof covering rises again since less air should be removed from the space compared to the situation when the subatmospheric pressure in said space had been equalized relative to the surroundings.

In a preferred embodiment the insulation layer is provided with a system of ducts which are in communication with one or more of the above-mentioned pressure equalization means. This embodiment allows a quick equalization of the (subatmo¬ spheric) pressure across the entire wind-loaded portion of the roof and establishes the highest vacuum in said space within the regions where there is the highest need for such equalization, e.g. along facades, at corners and in case of pitched roofs at the ridge.

Preferably, the roof structure according to the invention comprises a system of pressure equalization means, such as pressure equalization caps, with cooperating pressure equalization ducts in the insulation layer. The number of pressure equalization means and ducts depends on several factors, e.g. the pitch and area of the roof, the structure and type of the insulation layer and the height of the roof.

For a given roof, suitable choice of pressure equalization means and ducts makes it possible to limit the suction acting on the roof covering (i.e. the wind suction minus the subatmospheric pressure in the space between the support and the membrane) to a value not exceeding the weight of the roof covering and/or the force which may be absorbed by mechanical fixing means, if any.

The invention further relates to a pressure equalization means for use in a roof structure of the type disclosed in the introductory part. The pressure equalization means comprises an air duct including a valve which opens only when the pressure formed in the portion of the duct which is located on the one side of the valve is lower than the pressure in the portion of the duct which is located on the other side of the valve.

In a preferred embodiment of the invention the pressure equalization means has the shape of a cap and comprises a perforated valve seat, the upper side of which being covered by a flexible valve flap, such as a rubber plate. The valve flap is preferably circular and is preferably connected to the valve seat at its centre. When a vacuum is generated above the valve flap it will be lifted from the valve seat and will allow a (subatmospheric) pressure equalization to take place. Furthermore the flap ensures that the valve is closed when the pressure above the valve is superatmospheric.

The valve of the pressure equalization means according to the invention may also be of the type in which the weight of the valve body determines the pressure difference at which the valve opens and closes.

It should be noted that the support described above may be not only a roof structure per se, but also an existing roof structure which is to be reinsulated, and further an existing roof covering to which a new roof covering is to be applied. Thus pressure equalization may be effected both between an insulation layer and a roof covering and between two roof covering layers.

The invention will now be described in further detail with reference to the drawings, wherein

Fig. 1 is a schematical vertical sectional view of an embodiment of a roof structure according to the invention,

Fig. 2 is a top view of a roof provided with pressure equalization means and ducts,

Fig. 3. is a vertical sectional view of a pressure equalization means for use in a roof structure according to the invention and shown with an open valve,

Fig. 4 is a diagram showing the magnitude of the subat¬ mospheric pressure above and within a roof structure according to the invention as a func¬ tion of time, and

Fig. 5 is a schematical vertical sectional view through a roof structure according to the invention comprising a support consisting of an existing roof covering.

The roof structure shown in fig. 1 comprises a supporting roof floor 1 which is composed of building elements 2 and bituminous strips 3 positioned over the joints between the elements 2 in order to seal the roof covering.

An insulation layer 4 is arranged on top of the roof covering 1, said insulating layer comprising elements 5. The insula¬ tion layer 4 is covered by a roof membrane 6. Moreover, the roof structure comprises a pressure equalization cap 7 including a valve (not shown) . The lowermost end of the pressure equalization cap is connected to ducts 8, 9 and 10 in the insulation layer 4.

Fig. 2 shows a rectangular roof 11 having pressure equaliza¬ tion means 12 arranged at its corners. Each of said pressure equalization means 12 is in communication with pressure equalization ducts 13 running parallel with the adjacent roof edges. The positioning of said ducts along the roof edges is due to the fact that these are the areas of a roof which are exposed to the most powerful wind suction forces.

The pressure equalilization means shown in fig. 3 comprises a tube 20 with a foot 21 for attachment of the pressure equalization means to a support. A tubular insert 22 of e.g. plastics is arranged at the uppermost end of the tube 20. The insert 22 is provided with a collar 23 which extends over the uppermost end of the tube 20. The pressure equalization means further comprises a cap 24 having a lower cylindrical portion 25 comprising openings (not shown) . At its lower end the cap 24 is secured to the collar 23 on the insert 22 and the tube 20 by means of screws 26.

A perforated plate 27 is secured to the collar 23 by means of screws 28 and a flexible rubber membrane 29 is provided above the perforated plate 27. The rubber membrane 29 iε attached to the perforated plate by means of a screw 30.

Under normal pressure conditions the rubber membrane 29 is located parallel to the perforated plate 27 and thus closes the holes therein. When the wind generates a suction in the zone around the cap 24 a pressure is established which iε lower than the pressure within the tube 20 and thus lower than the pressure in the subjacent roof covering, and the peripheral portion of the rubber membrane 29 is lifted off the perforated plate 27, e.g. to the position shown in fig. 3, thus permitting a quick pressure equalization to take place between the zone around the cap 24 and the interior of the roof covering.

In the diagram of fig. 4 the curve 31 shows the vacuum (wind suction) above a roof structure according to the invention and the curve 32 the corresponding pressure in the interior of the roof covering.

As will appear from the curves 31 and 32 the suction force acting on the roof covering corresponds to the pressure difference C. When the vacuum (the wind suction) decreases and the valves of the pressure equalization means close the pressure difference is reduced, and at the point B it reaches the value 0. In the following period when the wind suction continues to decrease the vacuum in the interior of the roof covering exceeds the vacuum on the exterior side of the roof. Not until the wind εuction increases again a condition is obtained where the two pressures are identical, viz. in the point A where the valve is once again opened. The roof structure shown in fig. 5 comprises an existing roof comprising a support 40 and an existing roof covering 41 and a renovation roof covering 42 situated on top of the existing roof covering 41. A layer of polystyrene pellets or dis- continuos bituminous strips may be provided on the underside of the renovation roof covering 42 so as to form air gaps between the roof covering 41 and the underside of the renovation roof covering 42. The latter covering extends over the lower end of a pressure equalization cap 43 with a foot 44, the edge of which comprises openings 45 which are in communication with an internal duct wherein a valve (not shown) is arranged, which valve openε when the pressure above the roof membrane 42 is lower than the pressure between the roof coverings 41 and 42.

Claims

C l a i s

1. A roof structure comprising a support and a roof covering in the form of a roof membrane provided on εaid support and optionally an insulation layer provided between the membrane and the support, and one or more air ducts through which the space between the support and the membrane is in communication with the area above the membrane, c h a r a c t e r i z e d in that it comprises pressure equalization means each comprising an air duct including a valve which opens only when the pressure above the roof membrane is lower than the presεure in the εpace between the support and the roof membrane.

2. A roof structure according to claim 1, c h a r a c ¬ t e r i z e d in that it further comprises a syεtem of ductε arranged between the support and the roof membrane and being in communication with one or more of the pressure equalization means.

3. A roof structure according to claim 2 and comprising an insulation layer, c h a r a c t e r i z e d in that it comprises a system of pressure equalization means with corresponding pressure equalization ducts provided in the insulation layer.

4. A roof structure according to any one of the preceding claims, c h a r a c t e r i z e d in that the pressure equalization means comprises ventilation caps with valves.

5. A pressure equalization means for use in a roof structure according to claim 1, c h a r a c t e r i z e d in that it comprises an air duct including a valve which opens only when the pressure in the portion of the duct which is located on the one side of the valve is lower than the pressure prevailing in the portion of the duct which is located on the other side of the valve.

6. A pressure equalization means according to claim 5, c h a r a c t e r i z e d in that it compriseε a duct the uppermoεt portion of which iε in the form cap and including a perforated valve seat, the top surface of which being covered with a flexible or movable valve flap.