Plas-2-Point House

(project)
Marcel Breuer, architect

Location

History

The building we chose for this project was Marcel Breuer's "plas-2-point" house designed in 1942. To understand the thought process and reasoning behind this building, first address the atmosphere in which it was created. The years that immediately foll owed the second world war saw the use of new methods of construction on a scale never before seen in this country. this reliance on new technologies in the housing industry arose from the anticipation that need for post-war housing would be far greater t han the traditional building industry could produce, thus creating a massive housing shortage throughout the country. This need for cheap, easily constructed and mass produced housing created the Prefabrication Movement into which Breuer's "plas-2-point" house fits. This building was in fact never built, but is well documented as a pioneer in prefabricated housing types because of its ability to be mass produced with all the benefits this entailed in terms of cost improved quality, and above all, given post-war demand, rapid production.

Physical Description

The "plas-2-point" design was not the most aesthetically pleasing, but it was eminently practical. It owed this practicality to the fact that it was demountable, meaning one unit could be picked up and moved to another foundation with minimal effort, and conceived as an assembly line product that could easily be mass produced and shipped all over the country. Two features make this house unique in its design and construction. First, it rests on two short piers (see foundation plan), thus avoiding the n eed for expensive foundation and cellar costs that are common to nearly all housing types. Second, and probably most interesting, is that it is entirely supported by two vertical posts at the ends of the structure. These posts hold a central plywood gir der that, in turn, supports cantilevered plywood trusses which form the roof and floor. The side walls are made of rigid plywood panels that are in tension, holding down the roof like a tent. This construction system allows for all the forces to be res olved internally and transfered down to the ground at two specific points, thus becoming cost efficient in the reduction of materials needed in construction.

Building Process

Structural Descripton/Aspects

The "plas-2-point" house is a stick frame and plywood structural system. The roof consists of a plywood girder which runs along the apex of the roof (the ridge) and acts as a stabilizer for the roof trusses. Vertical loads applied on the roof would trav el through the roofing material (plywood sheathing) and into the top chord of the truss, which resists the load by acting in compression. the wall panels are acting in tension; therfore, in the absence of a vertical load, the top chord of the truss would be in tension, because the walls are exerting a downward force on the ends of the truss. As such, the top chord of the truss could be said to be "pre-tensioned".

The load is then primarily transfered from the top chord of the truss to the plywood ridge beam. Additionally, two purlins run on either side of the ridge beam, about halfway between the ridge beam and the side walls. These members resist the load in be nding, which occurs due to the existence of both tensile and compressive forces within a structural member. The load is then transferred to the intermittent vertical members of the truss, which are acting in compression. The vertical members of the trus s are transferring the load down to the bottom chord of the truss, which is acting in tension, due to the downward force exerted by the vertical load on the top chord of the truss. Because of the tension in the walls, the bottom chord of the truss could possibly be said to be "pre-stressed" in compression.

The entire roof load (both live and dead loads) must be transferred downward through the plywood ridge beam and onto one of two columns which support the ridge beam at either end. Initially, however, the ridge beam and the two purlins are supported by a triangular end panel, at either end, which in trun transfers the load onto the two columns. These columns obviously act in compression, and transfer their loads downward onto a plywood girder, similar to the ridge beam, which supports the floor structure . The floor structure appears to be a mirror image of the roof strucutre. The members that were acting as framing for the roof are inverted and used as joists in the floor, and the ridge beam and purlins in the roof are replicated and used as load-beari ng supporting girders for the joists in the floor.

The plywood supporting girder which acts in compression and bending transfers the entire load of the structure onto two foundation blocks which in turn, transfer the load down into the ground by acting in compression. The majority of the floor structure is cantilevered beyond the two foundation blocks. Again, this was intended to reduce the cost of these houses by eliminating the need for a foundation.

As mentioned above, the side walls of this structure are in tension. This serves to "pinch" the structure together on both sides, adding stability. By designing the walls to act in tension, Breuer ensures that the entire load of and on the structure is transfered through the two end columns, which are acting in compression.

The pre-tensioned side walls serve as lateral stabilizers for the structure as well. A leteral load applied to these side walls would be transferred through the end walls, acting as shear walls, into the roof and floor structure, and be resisted by the t wo end columns. These two end columns would then transfer the lateral load down into the ground via the two foundation blocks. A lateral load applied to the end walls of the building would in part be reisited by the side walls as they act as shear walls to provide bracing against the shear components of the lateral load. Additionally, the two foundation blocks would resist a lateral load applied to an end wall.

What is not clear is whether or not the building is attached to the ground at any other point other than the foundation blocks. It seems that this building would want to topple off its foundation blocks when the side walls were subjected to a lateral loa d. We believe that there must be some sort of moment connection between the plywood girder and the foundation blocks, although we are not sure exactly how this could be achieved, as moment connections are difficult to execute between wood and concrete. We surmise that the concrete piers are shaped in such a way as to cradle the floor trusses at the plywood girder to prevent the structure from toppling.

Conclusions

It is a very light and simple structure, ideal for mass prodution, and perfectly able to withstand the loads of the single family within, as well as the live loads of mild climate areas.

Bibliography

Associated Buildings

Tony Salas and Steve Bolinger
ARCH 461/561 Spring 1995

Do you have questions about adding a case? or a building to suggest??????? send a message to me....... chrisl@aaa.uoregon.edu