Patent Application
20120151869
The invention relates to improvements in building construction and, in particular, to improved fire resistance in insulated, covered metal joist construction.
A type of building construction for floors and roofs utilizes C channel sheet metal joists. A roof deck or flooring is secured on upper flanges of the joists and drywall sheets are attached to lower flanges. Lengths of fibrous insulation batts are often disposed in the spaces or cavities between the joists to reduce heat transfer and noise transmission through the roof or floor.
The invention provides a simple, reliable, and economical way to improve the fire resistance of steel C channel joist construction. It has been found that a drywall ceiling will remain in place in the event of a fire where insulation batts are supported so that they avoid contact with the drywall and, thereby leave an air space at the upper face of the drywall.
It is believed that the inventive technique avoids trapping heat in the zone immediately above the drywall and thereby delays temperature rise in the drywall and its eventual failure. As disclosed, the insulation can be suspended above the drywall sheeting by steel wires spaced along the length of and transverse to the joists. The wires bridge between adjacent joists and are located well above the bottom flange of the joists.
Preferably, the joists are manufactured or otherwise provided with aligned wire anchoring sites strategically located along their respective lengths. In the illustrated example, anchoring elements take the form of holes punched or otherwise formed in the channels at or near the center of their webs. This hole arrangement allows the use of lengths of steel wire to be assembled in pairs of aligned holes and to be locked in place by simply bending their ends at or near right angles to the main section of the respective wire bodies.
A roof or floor and ceiling construction 10 is illustrated in
The joists 12, ordinarily being identical in a particular building area, are elongated sheet metal channels having a C-shaped cross-section. A joist 12 has a web 16 oriented in a vertical plane when installed. Commonly a web may be 9¼″ or 10″ in width corresponding to the depth or size of the joist; other regular web depths are normally 8, 12, 14 and 16 inches. Along each longitudinal edge of the web 16, is a flange 17 with an in-turned lip or secondary flange 18. Generally, the ends of the joists are vertically supported by load bearing walls, not shown.
The roof deck or flooring panels 11 are typically screwed to the upper flanges 17 of the joists. Similarly, sheets of drywall 14 are fixed to the lower flanges 17 of the joists 12 with self-drilling screws.
The insulation 13 is in the form of a fibrous batt, most commonly fiberglass or mineral fiber. The batts 13 have a nominal width equal to the joist spacing and a nominal thickness less than the depth of the joists 12. The insulating batt 13 is placed in the space or cavity between adjacent joists 12 prior to the installation of the drywall 14. It has been found possible to prolong the ability of the drywall 14 to remain in place when its lower surface is exposed to the heat of a fire by installing the insulation batt 13 so that it remains out of contact with the upper surface of the drywall 14. Under this circumstance, the air space between the insulation 13 and drywall 14 delays heat build-up in the drywall which allows it to maintain its integrity for a longer time period.
The invention affords a reliable, simple and economical manner of holding the insulation batts above the plane of the lower flanges 17 of the joists 12 and out of contact with the drywall 14. In the illustrated embodiment, anchor points 21 in the form of punched or drills holes in the mid area of the webs 16 are provided. The anchor holes 21 are located along the lengths of the joists at regularly spaced intervals, for example, at 12″ centers or 24″ centers. Lengths 22 of moderately stiff wire, for example, of 12 gauge mild steel, are threaded through the anchor holes 21 and are mechanically locked into the holes. The wire 22 can be cut to a length that spans the distance between a pair of joists with an additional length so that an end portion 23 on each length of wire, can be bent at or near a right angle on the far side of an anchor hole 21. One end of the wire 22 can be pre-bent before the wire is threaded through a pair of aligned holes 21 in adjacent joists 12. Once the wire 22 is in place, the second end 23 can be manually bent to mechanically interlock the wire to the respective joist. By interlocking the wires 22 in place on the joists 12, they are prevented from migrating or slipping out of position over time due to vibration or thermal expansion and contraction or, importantly, in case of distortion in the event of a fire. The holes 21 can be large enough, i.e. ¼″ diameter, to accommodate two wires 21 so as to receive the wires on both sides of a particular joist 12. Alternatively, multiple holes can be provided. Other anchoring elements, besides the holes 21, can be provided on the joists 12 such as tabs punched out of the web 16 or separate elements welded or otherwise fixed to the joist 12.
Normally, the insulation batt 13 will be installed from below the joist 12 before the drywall 14 is installed. Some or all of the wires 22 in a particular joist cavity can be in position in their respective holes 21 before the batt is threaded over the wires. Alternatively, the wires 22 can be progressively installed under a batt as the batt is temporarily supported by the installer.
It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.
