US3757477A

US3757477A - Fire barrier system for multi-family dwellings

Info

Publication number: US3757477A
Application number: US00230825A
Authority: US
Inventors: Crillis R Mc; W Fuller; R Dixon; J Oldani
Original assignee: Marcor Housing Systems Inc
Current assignee: Marcor Housing Systems Inc
Priority date: 1972-03-01
Filing date: 1972-03-01
Publication date: 1973-09-11
Anticipated expiration: 1990-09-11
Also published as: US3810335A

Abstract

In a dwelling construction system, a multi-story, multi-family building comprises prestressed concrete pallets which are supported between load bearing walls to form the floors and the ceilings of individual dwellings. Each dwelling includes a service core comprising an enclosure formed on one of the pallets and complete mechanicals for the dwelling. The service cores are fabricated by mass production techniques and are subsequently transported to the building site for installation. In some instances the service core comprises a complete dwelling, in which case the enclosure of the service core may form the exterior walls and the roof of the dwelling.

Description

iliiited States patent McQrillis et al.

1 1 Sept. ll, 11973 1 1 FIRE BARRIER SYSTEM FOR MULTl-FAMILY DWELLINGS [75] inventors: Raymond L. McCrillis; Walter T.

Fuller, both of Littleton; Richard H. Dixon, Lakewood; John F. Oldani, Littleton, all of C010.

[73] Assignee: Marcor Housing Systems,

Incorporated, Denver, C010.

[22] Filed: Mar. 1, 1972 [21] Appl. No.: 230,825

[52] US. Cl 52/79, 52/236, 52/317, 52/745 [51] Int. Cl E04b 1/94 [58] Field of Search 52/236, 79, 317, 5 2/404, 412, 262, 283, 745

[56] References Cited UNITED STATES PATENTS 293,617 2/1884 Bartlett 52/317 3,162,863 12/1964 Wokas 52/79 Primary Examinerlohn E. Murtagh Attorney- D. Carl Richards. E. Mickey Hubbard et a1.

[57] ABSTRACT In a dwelling construction system, a multi-story, multifamily building comprises prestressed concrete pallets which are supported between load bearing walls to form the floors and the ceilings of individual dwellings. Each dwelling includes a service core comprising an enclosure formed on one of the pallets and complete mechanicals for the dwelling. The service cores are fabricated by mass production techniques and are subsequently transported to the building site for installation. In some instances the service core comprises a complete dwelling, in which case the enclosure of the service core may form the exterior walls and the roof of the dwelling.

9 Claims, 28 Drawing Figures PATENTEBSEPI nan saw our 15 PATENTEIJ SEPI I 975 sum 02 or 7s PATENTED SEP'! 1 I975 sum 03 or 15 FIG. 7

PATENTED SEPI I I973 SHEET 0Q [1F 15 PATENTED SEP] 1 I975 sun-:1 us or 15 FIG. I!

PATENTED SEP] 1 I975 sum 08 a;

seo

PATENTED SEP] 1 I973 sum as or 1 PATENTED SEP] 1 I973 SHEET 11 [1F 15 PATENTED SEP] 1 I975 SHEET 12 0F 15 FIG. I7

SHEET 13UF 15 FIG. 2/

PATENTEUSEPI 1 I973 FIG. 20

PATENTEDSEPY 1 I915 $151.41?

saw u er 15 'FIG. 23

PATENTEDsEPn'ms- 3,757, 477

sum 150F15 FIG. 24 FIG. 25.

SYSTEM FOR MULTI-FAMILY DWELLINGS BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to dwelling construction systems, and more particularly relates to a system for fabricating a wide range of dwelling types using production line techniques.

Very substantial sums of money have been expended over the last decade or two to develop building systems which use production line techniques in the construction of both single family and multi-family dwellings. The basic considerations fueling this activity are rapidly increasing labor costs of tradesmen, and the hope that use of production line manufacturing procedures would reduce or eliminate the need for the highly skilled labor of tradesmen as well as provide other cost savings.

This type of construction is particuarly promising in the case of dwellings to be erected at remote or relatively inaccessible building sites where labor and materials are not readily accessible.

To date the most successful adaptation of production line techniques to dwelling construction has been in the mobile home industry. As is well known, the fabrication of a trailer house, including the installation of mechanicals such as kitchen, bathroom, and temperature control facilities, is typically carried out to completion at a factory. By this means the labor required to install such a dwelling at a particular site is reduced to an absolute minimum.

A different but related method of adapting mass production to dwelling construction comprises sectionalized houses. Typically half or quarter house sections are fabricated at a factory using conventional building materials and techniques and are transported to a construction site by truck. At the site the sections are positioned adjacent one another and are joined to form a completed house.

Multi-family dwelling units have also been considered using production line techniques. By ay of example, one construction system that has been used heretofore involves the fabrication of box-like modules each including a floor, walls and a ceiling which are interconnected to form a structurally integral and transportable unit. The finishing of the modules, including the installation of mechanicals, is completed at a factory. Thereafter the modules are transported to a construction site and are stacked in various configurations to form dwelling units. In this case, the interrelationship of the floor, walls and ceilings of each module cooperates to provide the structural integrity and load bearing capacity necessary to permit the modules to be transported and handled. This type of system has the inherent disadvantage of greatly limiting flexibility of design, and also results in duplicate wall structures.

Although the modular building systems heretofore used have provided some cost reduction, the systems are inherently inflexible and greatly limit the architectural design and livability of the structures. In general, the greater the modularization of the system to achieve reduced costs, the more inflexible the system is to design change, the smaller the rooms, and the more unlivable the dwelling.

Another trend in the construction industry involves the use of prestressed concrete structural components.

FIRE BARRIER Thus, structures such as bridges, parking garages, warehouses and the like are presently being fabricated from various prestressed components including load bearing and non-load bearing walls, columns, beams, and floor and roof decks. I-Ieretofore prestressed members have been used solely as structural elements. This practice necessitates the use of labor at the construction site to perform such tasks as erecting interior partitions, installing mechanicals, etc.

The present invention comprises a novel dwelling construction system which incorporates many of the advantages that are characteristic of prior art modular construction systems while eliminating substantially all of the disadvantages that have long been associated with such systems. In accordance with the broader aspects of the invention, a service core is substantially completely fabricated on an assembly line using mass production techniques. The service core is formed on a prestressed concrete pallet which is also fabricated at a plant site using automated equipment for greatest economy. The service core includes a mechanical enclosure which may be fabricated from conventional drywall building materials of the type used in building houses, and similar buildings. The mechanical enclosure may include complete mechanicals for at least one dwelling, i.e., complete kitchen facilities, complete bathroom facilities, complete temperature control equipment, and electrical systems including telephone and television wiring.

Upon completion, each service core is transported to a dwelling site. The concrete pallet provides the only struc-tural integrity required, thus giving total flexibility in the design of the enclosures. In some instances the service core may comprise an entire dwelling. More often, however, each service core is employed in conjunction with additional prestressed concrete pallets to form a relatively large dwelling. In the latter case the pallets extend between and are supported by prestressed concrete load bearing walls to provide a clear span of substantial length. Additional combinations of service cores and pallets may also be supported on the load bearing walls to form garden apartments, high rise apartments, and the like.

In accordance with more specific aspects of the invention, the prestressed concrete pallets used in the service cores and used in conjunction with the service cores to construct dwellings each comprise a relatively thin deck, a plurality of integrally formed beams depending from the deck, and pretensioned members extending through the beams to prestress and maintain the concrete of the beams in compression such that the beams are adapted to span a substantial distance between two spaced load bearing points and still support large static and live loads on the deck. The deck may terminate at the load bearing points, in which case the deck is entirely enclosed by the load bearing walls. On the other hand, the beams may be cantilevered substantially beyond either of the load bearing points to support a deck portion located outside the load bearing walls to provide a balcony, an entry corridor, etc.

In the use of the present invention to construct a multi-family dwelling such as a garden apartment, a pair of load bearing wall panels are initially erected at points spaced in accordance with the positioning of the support points of the beams of the concrete pallets. After the load bearing wall panels are in place, a service core and then one or more additional pallets are set in place on the load bearing wall panels to form the floor of a first story dwelling. in the case of the first floor dwelling, the beams of the pallets may rest on members projecting inwardly from the load bearing wall panels. Non-load bearing shear wall panels interconnect the load bearing wall panels and serve the dual functions of enclosing the dwelling and maintaining the load bearing wall panels erect.

A service core and then additional pallets which form the ceiling of the first floor dwelling and the floor for a second story dwelling are set in place on the top edges of the load bearing walls of the first floor unit. The beams of the pallets of the second dwelling are preferably received in notches formed in the upper ends of load bearing wall panels that enclose the lowermost dwelling. Also, the decks of the pallets forming the floor of the second dwelling preferably either end at or are interrupted at points corresponding to the positioning of the load bearing wall panels. This permits mounting a second pair of load bearing wall panels directly on the first pair of load bearing wall panels to form the walls for the second floor dwelling.

When the second set of pallets are in place, a second pair of load bearing wall panels and a second pair of shear wall panels are installed. Then a third set of pallets including a service core for a third dwelling are mounted on the second pair of load bearing wall panels to form a ceiling for the second floor dwelling and the floor for a third dwelling. This procedure is repeated until all of the dwellings in the apartment are formed. Then prestressed concrete pallets are mounted on the uppermost load bearing wall panels to form the roof of the uppermost dwelling, and of the stack of dwellings. The interiors of the several dwellings are then grouted, and floor and wall coverings installed, whereupon the structure is ready for occupancy.

As will be appreciated by those skilled in the art, prestressed concrete pallets of the type employed in the practice of the present invention can be supported only at the two design load bearing points. In most instances, the blank pallets are handled by means of eyes cast in the concrete. However, the pallets upon which the service core is formed make this method of handling the pallets impractical. Accordingly, each service core is set in place by means ofa pair of picking bars which extend under the support points of the beams of the pallet, a harness including members for connection to the opposite ends of the two picking bars, and ammo which operates through the harness and the picking bars to lift and position the pallet. On the other hand, both for fire prevention purposes and for the sake of appearance, it is highly desirable that the enclosure of each service core extend substantially into engagement with the pallet located next about the service core. To this end the enclosure of each service core is equipped with at least one picking bar slot positioned to permit withdrawal of one of the picking bars that will be used to install the service core or pallet above the service core. The picking bars used in the installation of the pallets weigh approximately 400 pounds. This necessitates reinforcing the picking bar slots to such an extent that the picking bar does not damage the service core as it is withdrawn.

The building codes of the various cities and states typically require a fire barrier having a one hour rating between adjacent buildings in a multi-family dwelling. In the practice of the present invention this requirement is easily fulfilled with respect to pallets that do not comprise service cores by simply filling the spaces between the decks of the pallets and the load bearing wall panels and the shear wall panels with grouting. On the other hand, the enclsoures of the service cores prevent access to these spaces and thereby prevent the filling of the spaces with grouting. For this reason the service cores are preferably installed with one edge of the deck engaged with the adjacent wall panel. At the other end of the deck a strip of sheet metal is secured between the enclosure and the deck. The strip of sheet metal is extended over the upper edge of the load bearing wall panels that supports the deck and is engaged by the load bearing wall panel that is mounted on the supporting panel to provide the necessary fire barrier.

In accordance with a particular embodiment of the invention, double loaded service cores are utilized in the construction of adjacent dwellings. That is, a single prestressed concrete pallet is equipped with two complete but separate sets of mechanicals, one for each of the adjacent dwellings. in such a case it is necessary to form a fire barrier having a one hour rating between the portion of the service core that is individual to one of the dwellings and the portion that is individual to the other dwelling.

The majority of the fire barrier for a double loaded core may comprise a wall including at least one layer of inch sheet rock. A pair of diverging sheet metal flanges are provided at the upper end of this wall for engagement with a beam of the pallet that is installed above the double loaded core to form the upper portion of the fire barrier. The fire barrier wall is also provided with a stub wall which is slidably supported at the end of the deck that will be engaged with a load bearing wall. During installation of the double loaded core the stub wall is retracted. Then, after the load bearing wall panels adjacent the double loaded core have been installed, the stub wall is moved outwardly and is engaged with the adjacent load bearing wall panel. By this means the fire barrier between the portions of the double loaded core that are individual to the separate dwellings is extended to the full height and the full width of the core.

In addition to the foregoing, the present invention incorporates numerous features which contribute greatly to its overall practicality. For example, notwithstanding the strength of prestressed concrete pallets, it has been found that a direct connection between a particular pallet and the enclosure of a service core situated beneath the pallet is not workable. lnstead a slip joint is employed to provide a pleasing appearance while permitting relative movement between the pallet and the service core as a result of live loads.

Another important feature of the invention involves the manner in which convenience outlets are provided at spaced points around each dwelling. Thus, electrical conduits are formed in the load bearing wall panels when the panels are manufactured. After the panels are installed, electric service lines are directed from the adjacent service cores through the conduits in the load bearing Wall panels and along the shear wall panels. The shear wall panels are typicaily covered with wood panelling or the like, so that the resulting dwelling is equipped with suitable convenience outlets and yet has no exposed conduit or wiring.

Still another important feature of the invention involves an improved method of forming the enclosures of the service cores. It has been found that a great deal of time is wasted if the enclosures are formed by finishing the walls on one side, installing the walls on the pallet by fastening through the panel frame into the pallet, and then finishing the walls on the other side of the panel. In accordance with the present invention holes are formed in the pallets along the lines that will comprise the walls of the enclosures. This permits the walls to be completely finished and then secured to the pallets by means of lag screws which are inserted through the holes in the pallets from the bottom.

DESCRIPTION OF THE DRAWINGS A more complete understanding of the invention may be had by referring to the following Detailed Description when taken in conjunction with the accompanying Drawings, wherein:

FIGS. 1-7 are illustrations of progressive steps in a method of fabricating dwelling units incorporating the invention;

FIGS. 8 and 9 are illustrations of presetressed concrete pallets utilized in the practice of the invention;

FIG. 10 is a view taken generally along the line l0l0 in FIG. 5 in the direction of the arrows;

FIGS. 11 and 12 are perspective and end views, respectively, showing a method of and apparatus for installing service cores which is utilized in the practice of the in-vention;

FIG. 12A is an end view of an alternative type of prestressed concrete pallet that can be utilized in the practice of the invention;

FIG. 13 is an elevational view of an apartment complex constructed in-accordance with the invention;

FIG. 14 is a plan view of the apartment complex shown in FIG. 13;

FIGS. ISA-15C are an enlarged plan view of one of the apartments comprising the apartment complex shown in FIG. 13; I

FIG; 16 is an enlarged plan view illustrating the service core of one of the apartment buildings shown in 'FIG. 14;

FIG. 17 is a sectional view taken generally along the line 17-17 in FIG. 16 in the direction of the arrows;

FIG. 18 is a sectional view taken generally along the line l818 in FIG. 16 in the direction of the arrows;

FIG. 19 is an enlargement of the upper portion of FIG. 18;

FIG. 20 is a sectional view taken generallyalong the line 2020 in FIG. 16 in the direction of the arrows;

FIG. 21 is an illustration of special slots which are utilized in the practice of the invention to facilitate the installation of prestressed concrete pallets on previous-ly DETAILED DESCRIPTION METHOD OF DWELLING CONSTRUCTION Referring now to the Drawings, and particularly to FIGS. l-7 thereof, a method of dwelling construction incorporating the present invention is employed to construct an apartment building 48. As is best shown in FIG. I, the first step in the method comprises the erection of a pair of load bearing

wall panels

50 and 52. The

wall panels

50 and 52 are both formed from prestressed concrete and are both nominally six inches thick. The

wall panels

50 and 52 are further similar in that they are both provided with a plurality of slots or notches 54 formed in the upper ends and with a plurality of support members 56 which project inwardly from points adjacent their lower ends. The notches 54 are generally U-shaped, but comprise inwardly tapered side walls, and some of the notches 54 in the wall 50 extend only part way through the wall so as to provide a flush outer surface. The supporting members 56 may comprise any convenient construction, but preferably comprise pipe stubs cast into the

panels

50 and 52 and extending inwardly therefrom. One difference between the

wall panels

50 and 52 is that the wall panel 50 is provided with a door opening 58.

Referring now to FIG. 2, the next step in the method of dwelling construction comprises the installation of a service core 60. The service core 60 comprises a prestressed concrete pallet 62 and an enclosure 64 formed on the pallet 62. The service core 60 further comprises complete mechanicals" for a dwelling unit, i.e., complete kitchen facilities, complete bathroom facilities, and complete temperature control facilities.

The prestressed concrete pallet 62 of the service core 60 is shown in FIG. 8. The pallet 62 comprises a deck 66 and three beams 68 which depend from the deck 66. Thus, the pallet 62 isof the type commonly known as a triple T deck. A plurality of tension members extend through each beam 68 of the pallet 62 and serve to prestress the beams, whereby the beams 68 are adapted for support at spaced points indicated by the arrows 72 to support a load on the deck 66. As is well known in the art, a prestressed concrete pallet of the type shown in FIG. 8 is subject to breakage unless it is properly I supported. g l

The cross sectional configuration of the pallet 62 is shown in FIG. 12. Those skilled in the art will appreciate the fact that the invention may also be practiced using either solid core or hollow core prestressed concrete pallets 62' of the type shown in FIG. 12A. The pallet 62' comprises a deck 66 and a plurality of beams 68' which depend from the deck 66' between cylindrical passageways 69'. A plurality of tension members 70 extend through a lower portion 7l One difference between the pallet 62 and the pallet 62' is that whereas the beams 68 of the pallet 62 are exposed, the bottom of the pallet 62 is flat.

Referring again to FIG. 2, the enclosure 64 of the service core 60 is formed on the deck 66 of the prestressed concrete pallet 62. The enclosure 64 is preferably formed from materials of the type used in constructing conventional homes and similar buildings, i.e., two by four and two by six studs, drywall panels, and similar materials. The enclosure 64 includes interior partitions which separate the various mechanicals of the dwelling unit into kitchens, bathrooms, and the like, and further includes at least one end wall .and a'dropped or false ceiling 76.

In accordance with the illustrated embodiment of the invention, the service core 60 is completely fabricated at a factory by means of mass production techniques. The fabrication of the core 60 comprises construction of the walls, partitions, and ceilings in suitable jigs and fixtures, installation of the walls, partitions, and ceilings, installation of all mechanicals, installation of electrical, plumbing, and heating/air conditioning risers for the mechanicals, installation of all doors and cabinetry,

installation of floor and wall coverings, and painting. Thus, when the service core 60 is installed between the load bearing

wall panels

50 and 52, it is complete and ready for use. This feature of the invention is highly advan-tageous in that it not only reduces the cost of a dwelling by applying mass production techniques to the construction of the service core, but also reduces the time that is required to finish a dwelling following the beginning of construction at the dwelling site.

Upon completion of the manufacture of the service core 60 at the factory, it is transported to the site of the building 48 by truck. During such transportation, the service core 60 is supported solely at points corresponding to the support points of the beams. This is accomplished by means of members positioned under the support points of the beams to maintain the remainder of the pallet out of contact with the bed, etc. of the truck.

The service core 60 is installed by means of apparatus of the type shown in FIGS. 11 and 12. A pair of picking bars 78 are positioned under the beams 68 of the pallet 62 at points corresponding to the support points of the beams. The picking bars 78 are engaged by a harness 80 comprising a plurality of cables 82 and a spreader frame 84 which functions to cause the cables 82 to extend vertically upwardly from the picking bars 78 to points above the enclosure 64 of the service core 60. The cables 82 are connected to a beam 86 which is in turn supported by a cable 88 extending from a crane (not shown). By this means the crane functions through the harness 80 and the picking bars 78 to lift and position the service core 60.

Referring again to FIG. 2, the service core 60 is installed between the load bearing

wall panels

50 and 52 with each beam 68 of the pallet 62 engaged with one of the support members 56. It will be appreciated that due to manufacturing tolerances and in order to facilitate the installation of the core 60 between the

wall panels

50 and 52, the length of the pallet 62 is necessarily somewhat less than the distance between the interior surfaces of the walls. The resulting gap is accommodated by positioning the deck 66 closely in engagement with the wall panel 50, whereupon a suitable entry in the enclosure 64 is aligned with the door opening 58 in the wall'panel 50. This forms a small gap between the deck 66 and the wall panel 52. However, an end wall is provided at the end of the enclosure 64 remote from the door opening 58, whereby the gap is not visible from within the service core 60.

The next step in the method of dwelling construction comprises the installation of a pair of blank prestressed concrete pallets 90 between the lead bearing

wall panels

50 and 52. The pallets 90 are handled by means of cables 92 which are connected to eyes 93 in the pallets. The same procedure could be employed in handling service cores except that the enclosures of the service cores prevent access to the eyes of the pallets. Thus, the service cores must be handled by means of picking bars.

The blank pallets 90 are identical to the pallet 62 of the service core 60 in that they each comprise a deck, three beams depending from the deck, and tension members extending through the beams for prestressing the pallets. The pallets 90 are positioned between the wall panels 50 and S2 with their respective beams engaged with the support members 56 of the walls. The decks of the pallets are therefore aligned with the decks 66 of the pallet 62, whereby the pallets 90 cooperate with the pallet 62 to form the floor of a dwelling unit.

As is best shown in FIG. 4, the installation of the pallets 90 is followed by the installation of a pair of

shear wall panels

94 and 96. The

wall panels

94 and 96 are formed from prestressed concrete, but differ from the load bearing

wall panels

50 and 52 in that they are nominally four inches thick. The shear wall panels include window openings 98 and a door opening 100 and serve the dual functions of enclosing the ends of the dwelling unit and maintaining the load bearing walls erect.

The

shear wall panels

94 and 96 are preferably connected to the load bearing

wall panels

50 and 52 by forming welds between suitable members which either comprise part of or are connected to the reinforcing structure of the wall panels. The load bearing wall panels and the shear wall panels may also be joined by other techniques of the type commonly employed in the construction industry to connect prestressed concrete structural members. The various prestressed concrete pallets which are employed in the practice of the invention may be connected to the load bearing wall panels by similar techniques, however, it has been found that it is often unnecessary to connect the pallets to the load bearing wall panels in any fashion.

Upon the installation of the

shear wall panels

94 and 96, the lowermost apartment of the apartment building 48 is structurally complete. Thereafter, a service core 102 for a second dwelling unit is mounted on the load bearing

wall panels

50 and 52. As is shown in FIG. 5, the service core 102 com-prises a prestressed concrete pallet 104 and an enclosure 106 formed on the pallet 104. The service core 102 further comprises complete mechanicals for the second apartment.

The pallet 104 of the service core 102 is illustrated in FIG. 9. The pallet 104 is similar to the pallet 62 in that it comprises a deck 108 and three beams 110 which depend from the deck. A plurality of tension members 112 extend through the beams 110 to prestress the beams and thereby adapt the beams for support at spaced points indicated by the arrows 114 to support a load on the deck 108.

The pallet 104 also differs from the pallet 62 in several important respects. First, the deck 108 is discontinued at spaced points 116 corresponding to the positioning of the load bearing

wall panels

50 and 52. Second, the deck 108 and the beams 110 extend beyond one of the support points 114 to form a cantilever portion 118 of the pallet 108. At least some of the tension members 112 extend through plastic tubes 120 or are otherwise disengaged from the material of the beams 110 in the cantilever portion 118. This is necessary in order that the portion 118 can be supported in cantilever fashion.

The installation of the service core 102 is illustrated in FIG. 10. The picking bars 78 of the lifting and position-ing apparatus shown in FIGS. 11 and 12 are engaged with the beams 110 of the pallet 104 at points adjacent the support points 114. At the end of the pallet 104 comprising the cantilever portion 118, a picking bar 78 may be positioned at a point located outside the positioning of the load bearing wall panel 50. Therefore, no problem is encountered in removing the pick

Claims

1. The method of fabricating a habitable building including dwelling units situated one above the other including the steps of: installing all of the kitchen, bathroom and temperature control facilities for a dwelling unit on a prestressed concrete pallet; mounting the pallet between the upper ends of a pair of prestressed concrete load bearing walls with one end of the pallet substantially in engagement with one of the load bearing walls; and forming a fire barrier between the opposite end of the pallet and the other load bearing wall.

2. The method of fabricating a habitable building according to claim 1 further characterized by forming an enclosure on the pallet which extends substantially the entire length and width of the pallet, and wherein the fire barrier forming step is characterized by extending a length of fire proof material between the portion of the enclosure at the opposite end of the pallet and the other load bearing wall.

3. The method of fabricating a habitable building according to claim 2 wherein the fire barrier forming step is further characterized by securing a length of fire proof material between the portion of the enclosure at the opposite end of the pallet and the upper surface of the pallet and securing the length of fire proof material between the upper end of the prestressed concrete load bearing walls and another portion of the load bearing wall.

4. The method of fabricating a habitable building according to claim 1 wherein the fire barrier forming step is further characterized by positioning a length of fire proof material between the upper surface of the prestressed concrete pallet and the upper surface of the adjacent load bearing wall and extending the entire width of the prestressed concrete pallet.

5. A multi-family dwelling unit comprising: a first pair of spaced, substantially vertically extending prestressed concrete load bearing wall panels; a first prestressed concrete pallet supported by the first pair of load bearing wall panels and extending between the upper ends thereof; an enclosure formed on the first prestressed concrete palleT and extending the entire length and width thereof; fire retarding means extending between one end of the first prestressed concrete pallet and the adjacent load bearing wall panel and extending substantially the entire width of the first prestressed concrete pallet; a second pair of spaced, substantially vertically extending prestressed concrete load bearing wall panels mounted on the upper ends of the first pair of wall panels and enclosing the opposite ends of the enclosure on the first concrete pallet; and a second prestressed concrete pallet extending between and supported by the upper ends of the second pair of prestressed concrete pallet load bearing wall panels.

6. The multi-family dwelling unit according to claim 5 wherein the fire retarding means comprises a body of fire retarding material gripped between the first prestressed concrete pallet and one end of the enclosure thereon and between the upper surface of the adjacent one of the first pair of wall panels and the lower surface of the adjacent one of the second pair of wall panels.

7. The multi-family dwelling structure according to claim 5 wherein the enclosure comprises complete mechanicals for two dwelling units and further including a fire barrier wall extending continuously between the second pair of wall panels and the first and second prestressed concrete pallets and separating the two sets of mechanicals within the enclosure.

8. The multi-family dwelling structure according to claim 7 wherein at least the second prestressed concrete pallet includes at least one depending beam and wherein he fire barrier wall includes opposed members for receiving the depending beam and thereby extending the fire barrier wall to the second prestressed concrete pallet.

9. The multi-family dwelling structure according to claim 7 wherein the fire barrier wall comprises a stub wall mounted for sliding movement outwardly to engage one of the panels comprising the second pair of wall panels and thereby extending the fire barrier wall continuously to said panel.