Roof Construction

Abstract

A roof is prepared wherein the water barrier layer is placed on a metal roof deck and waterproof thermal insulation is placed over the water barrier layer. A non-combustible fire resistant insulating layer is disposed beneath the water resistant layers and above the metal roof deck. The water barrier layer is not subjected to the extremes of temperature that are encountered when the water barrier layer is the outermost element of the roof structure and the structure is resistant to fire originating above or below the metal deck.

Description

Built-up roofing has been employed for many years, wherein a roof deck supports a weatherproof membrane where often the weatherproof membrane comprises a plurality of felt and bitumen layers which prevent the penetration of moisture of the roof deck. Oftentimes it is desirable that such a roof be insulated and various insulating materials and methods have been utilized to accomplish this end. For example, oftentimes insulation is positioned below the roof deck on the interior of the building between rafters or similar roof deck support means. Frequently an insulating body such cellular glass, fiber board, plastic foams and the like are positioned on the upper surface of the roof deck and subsequently covered with alternating layers of felt and bitumen to provide a water resistant membrane. Gravel or like material is then spread upon the roof to provide protection from the sun. Considerable difficulty over many years has been encountered with such built-up roofs. Cracking of the water impermeable membrane often occurs and is probably due to the loss of volatile components from the bituminous material. Direct damage from foot traffic, condensation during cold weather on or about the roof deck, on the underside toward the building, are some of the many causes of failure of this type of roof. Many of these problems have been overcome by the use of the roof structure set forth in U.S. Pat. No. 3,411,256 wherein the barrier layer is positioned on the roof deck and the insulation layer above the barrier layer. When thermoplastic organic materials such as asphalt and plastic foam are employed for such a construction on a metal roof deck such as a steel roof deck, substantial difficulties occur when the structure is subjected to an internal fire. Usually within very few minutes the moisture barrier membrane such as a felt-asphalt built-up membrane and a thermoplastic foam insulation become heat plastified and can result in flaming drips from roof edges and fissures between the roof decking members.

It would be beneficial if there were available an improved roof structure and method of preparing such a roof structure which would preserve the integrity of the water barrier or barrier membrane and offer substantial resistance to internal fire.

Further, it would be advantageous if there were available a simplified roof structure and method of forming such a roof structure having improved properties.

These benefits and other advantages in accordance with the present invention are achieved in a roof structure which comprises a roof support means and metal roof deck having an upper surface and a lower surface, a fire resistant insulating layer disposed on a metal deck, a water barrier membrane disposed adjacent the fire resistant insulating layer on the upper side thereof, the water barrier containing heat softening organic combustible material, a layer of thermal insulation, the layer of thermal insulation comprising closed-celled water impervious cellular insulating material affixed to the roof membrane.

Also contemplated within the scope of the present invention is a method of preparing a roof comprising disposed upon the upper surface of a metal roof deck a non-combustible thermally insulating layer and above the non-combustible insulating layer a water impermeable membrane, disposing upon the membrane a closed cell water impermeable insulating foam.

Further features and advantages of the present invention will become more apparent from the following specification when taken in connection with the drawing wherein the FIGURE schematically depicts an isometric schematic cutaway view of a roof structure.

In the FIGURE there is illustrated a schematic, isometric representation of a roof structure generally in accordance with the present invention designated by the reference numeral 10. The roof structure 10 comprises in cooperative combination a metal roof deck 11. The roof deck 11 has an upper surface 12 and a lower surface 13. The roof deck 11 has supported means 11a. A non-combustible thermally insulating layer 14 is affixed directly to the upper surface 12 of the deck 11. Affixed to the insulating layer 14 is a water or moisture barrier layer 15. Beneficially, the water impermeable membrane 15 may comprise a plurality of alternating layers of felt and a bituminous material or asphalt. A thermal insulating layer 16 having a lower surface 17 and an upper surface 18 is adhered to the surface of the barrier layer 15 remote from the roof deck surface 12. The thermal insulating layer 16 is of closed cell configuration and is water resistant and water impermeable. A protective layer 19 is disposed on the surface 18 of the thermal insulating layer 16. A plurality of spaces or fissures 20 is defined by the layer 16.

A wide variety of materials may be employed in the preparation of roofs in accordance with the roof and the method of the present invention. The roof deck or metal roof support means may be prepared from steel, aluminum sheet or mesh. Advantageously, steel sheet is employed which has formed therein a plurality of ribs which give excellent stiffness without undue weight.

The roof deck may be supported in any convenient manner such as by being firmly affixed to the support means or beam by means of nails, screws, bolts and the like. The roof decking may be of panels and readily inserted into suitable recesses in a framework and prepared by like methods well known to the art.

The non-combustible first or lower insulating layer may comprise or consist of any one of a variety of materials such as cement/asbestos board, gypsum board, foamed glass, ceramic foam, thermoset plastic foam scuh as phenolic resin foam, epoxy resin foam and the like. A particularly advantageous non-combustible insulating layer is board prepared from a mixture of gypsum, inorganic fibers such as glass fibers and expanded mica such as vermiculite. Such a composite gypsum board provides excellent fire resistance to the roof structure of the invention.

The water impermeable membrane may comprise or consist of a wide variety of water impermeable materials including conventional asphaltic and bituminous compositions employed for roofing as well as laminates of the bituminous material with fibrous products such as roofing felt employing organic or inorganic fibers. Beneficially, such felt and bituminous materials may be applied in alternating layers to provide a water impermeable membrane of the desired thickness and mechanical strength to resist movement of the roof deck and associated supporting structure. In certain instances, a water impermeable membrane can be formed of synthetic thermoplastic resinous film or sheet such as polyethylene, polyvinyl chloride, chlorinated polyethylene and the like which is adhered to the roof deck by a suitable adhesive.

One or more layers of such material may be employed, depending on the characteristics which are desired from the finished structure.

The upper or second thermal insulating layer employed in the practice of the present invention beneficially is a closed cellular material which is substantially water impermeable. Particularly beneficial and advantageous for use in the present invention are cellular plastic foams of a closed cell configuration including styrene polymer foams, styrene/acrylonitrile copolymer foams, styrene/methylmethacrylate copolymer foams, polyvinyl chloride foams, polyethylene foams and other water impermeable materials available in cellular foam form which are well known to the art. Foam glass is particularly advantageous when it is desired to omit a protective layer over the thermal insulating material. A protective layer beneficially is employed when synthetic resinous organic cellular thermal insulating layers are utilized. Such organic materials are generally subjected to decomposition when exposed to weather and more particularly when exposed to sunlight. Therefore, it is advantageous to place a protective layer on the outside surface of thermal insulating layer.

Beneficially, such a protective layer may comprise or consist of a particulate inorganic material such as gravel, spread over the foam layer, or if desired, a relatively thin weather and sun-proof protective coating is readily provided by employing an inorganic mortar such as is formed from a mixture of portland cement and sand and is spread thinly upon the surface of the insulating layer in such a manner as to provide protection from the sun and the weather. In certain instances, depending on weather conditions and pitch of the roof, it may be desirable to provide an intermediate or bonding layer to adhere the protective layer to the thermal insulating layer.

In preparation of roof structures in accordance with the invention, usually the metal roof deck is affixed to the suitable support means or structure, the non-combustible layer is affixed to the uppermost surface of the metal roof deck and the water resistant membrane applied to the non-combustible insulating layer; for example, by applying a layer of bituminous material thereto, applying a suitable roofing felt to the bituminous material and providing the repeated applications of roofing felt and bituminous material until a suitable membrane is formed. Advantageously, the uppermost or closed cell thermal insulating layer is joined to the water impermeable membrane by the use of the same or different bituminous composition employed in preparing the water resistant membrane while the bituminous material is in a heat plastified condition, pressing planks or sheets of the heat insulating material into the bituminous layer to provide a suitable bond. When employing a heat insulating layer of a thermoplastic synthetic resinous material, it is necessary that the bituminous material not have a temperature sufficiently high to destroy a large portion or proportion of the cellular insulating material. For example, when foamed polystyrene sheets are utilized as the heat insulating layer, it is generally desirable that the bituminous material have a temperature not greatly in excess of about 100.degree. C., in order that undue distortion or melting of the polystyrene foam insulating material occur. It is essential and critical to the practice of the present invention that the insulating layer be of a closed cell configuration. The particular density or physical strength of such an insulating material need only be sufficient to meet the mechanical demands of the particular installation. Generally, foamed polystyrene sheets having a density of about 1.5 pounds per cubic foot are adequate for roof installations which are not subject to heavy foot traffic. If lower density and/or lower physical strength closed cell foamed materials are employed as the insulating layer, it is often desirable to provide the protective layer of sufficient strength to resist mechanical damage. Thus, in a region where little or no foot traffic is expected on a roof, a loose gravel coating is applied directly over the closed cell thermal insulated layer and provides adequate protection; however, in regions where frequent or heavy foot traffic occurs, it is often desirable to employ a layer of cementitious material as is obtained from a mixture of portland cement, sand and water or magnesium oxychloride cement and the like.

It is not essential that the protective layer be resistant to the passage of moisture, nor is it essential that the insulating layer have a surface which prevents moisture from contacting the water resistant membrane.

Beneficially, in the fabrication of a roof in accordance with the present invention, thermal insulating panels such as planks or sheets or cellular polystyrene or other cellular material are positioned adjacent each other in edge to edge relationship and no attempt has been made to seal the cracks or fissures therebetween. Indeed, in some installations employing incompletely cured or stabilized synthetic resinous foams, shrinkage of the foam occurs wherein the foam cracks in random patterns similar to mud cracking and mortar on the surface thereof ruptures in a similar pattern. Such cracking does not appear to cause loss of serviceability or desirability of the roof structure.

Roof structures in accordance with the invention do not appear subject to damage by freezing of water in the minor spaces between adjacent foam insulating elements. The foam insulating elements appear to have sufficient resilience to resist rupturing by the expansion of freezing water in crevices. Furthermore, in installations on a heated building the temperature adjacent the water resistant membrane usually does not reach freezing temperatures. In buildings having a roof applied in accordance with the present invention, little or no tendency is observed for moisture to condense on the inner surface of the roof deck. Generally for most applications the thermal conductivity of the lower or non-combustible insulating layer will be from about 100 percent to about 1,000 percent of the upper or closed cell insulating layer, and most beneficially from about 100 percent to 500 percent. Thus, the normal temperature cycling of the membrane layer will be relatively small compared to the cycling of the ambient external temperature while reasonable protection from internal fire is obtained; i.e., a time lag of many minutes is obtained between initiation of the fire and melting of the moisture barrier layer and/or the closed cell insulating layer.

By way of further illustration, a plurality of roof panels are evaluated for fire resistance by evaluating the panels for life in a test furnace. The furnace is a hollow, square, firebrick structure having an upper opening 12 inches square. All samples are prepared using a 14 inch square of 22 gauge (about 0.025 inch) steel roof deck sheet having 1-1/2 inch deep by 1 inch rectangular ribs formed therein by adhering on a sheet 6 inches. The ribs are removed adjacent the edges thereof so that the ribs fit into the upper opening of the furnace. A plurality of roof panels are prepared, each having the general structure shown in the FIGURE. In each sample the moisture barrier layer is three layers of 15 pounds per square roofing felt, each layer of felt being bonded to adjacent layers (including both insulating layers) by asphalt. The closed cell insulating layer is one inch thick polystyrene foam having a density of about two pounds per cubic foot. The upper surface of the polystyrene foam is covered with pebbles to provide a coating weight of 0.1 pound. A propane gas burner is positioned within the furnace; the burner is upwardly facing and is about 4 inches below the ribs of the steel roof deck sheet. A thermocouple is positioned immediately below the steel deck sheet and temperatures indicated during evaluation of the samples at given times are as follows:

TIME IN TEMPERATURE MINUTES .degree.F. 0 Room Temperature 2 1100 5 1200 10 1350 15 1400 25 1475 30 1500

Five samples are prepared employing the following materials as the layer 14 of the FIGURE, together with the time in minutes to sample failure. Sample failure is considered to be ignition of the combustible asphalt or polystyrene foam or collapse of the polystyrene foam. ##SPC1##

In a manner similar to the foregoing illustration, other beneficial and advantageous roofs are prepared by disposing closed cellular water resistant insulating material above a water impermeable membrane from a roof structure, such insulating materials including foamed glass, foamed polyethylene, foamed copolymers of styrene/acrylonitrile and the like.

As is apparent from the foregoing specification, the present invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. For this reason, it is to be fully understood that all of the foregoing is intended to be merely illustrative and is not to be construed or interpreted as being restrictive or otherwise limiting of the present invention.

Claims

What is claimed is:

1. A roof structure, the roof structure comprising

a roof support means and

a metal roof deck having

an upper surface and

a lower surface,

a fire resistant, thermally insulating layer of gypsum board disposed on the metal deck,

a water barrier membrane disposed adjacent the fire resistant insulating layer and on the upper side thereof and remote from the roof deck, the water barrier layer containing

heat softening, organic, combustible material,

a layer of thermal insulation affixed to the water barrier membrane, the thermal insulation comprising closed-cell, water impervious cellular insulating material affixed to the water barrier membrane.

2. The roof of claim 1 wherein the water impermeable layer comprises a plurality of layers of bituminous material and roofing felt.

3. The roof of claim 1 wherein the cellular insulating layer is a synthetic resinous foam.

4. The roof of claim 1 wherein the gypsum board contains inorganic fibers and expanded mica.

5. The roof of claim 1 including a protective layer disposed on the uppermost surface of the closed-cell insulating material.