Unity Precast Concrete Properties

• Manufacturers: Unity Structures Ltd / Unity House Construction
• Alternative Names: Butterley, Unity Brick clad
• Period Built: 1950s
• Number Built: 19,000 (includes Types I and II)

Unity Precast Concrete Properties

Built as bungalows and 2-storey semi-detached and terraced houses. This system was also used to construct flats.
Having a medium pitch hipped or gable roof covered with concrete tiles.
External walls have stack bonded Precast Concrete  panels, or partial or
all brick cladding.
Hanging tiles were fitted to gable apex.
Splayed Precast Concrete blocks to corners.

The following issues have been noted in some properties. This may not be representative of all stock.

• Longitudinal cracking of PRC columns.
• Cracking and spalling of PRC lintels.
• Corrosion of steelwork at interface between PRC columns and RSJ first floor beams.
• Corrosion of copper fixings to cladding.
• Significant levels of chloride in PRC panels.
• Asbestos cement roofing sheets should be inspected for signs of damage or decay.
  

Unity House Background information

The Unity system was devised by architects Kendrick, Findlay and Partners. An early Unity design, was used to construct less than 100 houses during 1947-48 and a second re-design was introduced between 1948 and 1950 during which approximately 3,000 properties were built.
A further re-design in 1950. led to 10 years of production during which the majority of the 19,000 Unity dwellings were constructed. Despite the historical development of three build types, only two are commonly referenced as the Unity Type I and Unity Type 2.

The basic construction elements of both systems are very similar, with only a limited number of variations between version type. It should be noted here that both variations are Designated Defective in England & Wales. Scotland repealed the designation status is 2018.

Foundations
Foundations consist of a concrete slab on top of concrete strip footings in both Type1 and Type II

Load Bearing Frame
The load bearing elements in both Unity house Variants shown, consist of storey height, reinforced concrete columns of 3 1/2″ x 6″ cross section, at 3′ 0″ centres around the house perimeter.

Both versions employed PRC columns and steel column support/ connecting brackets however, the earlier Unity Type I design has PRC columns with a side indentation, which gives a dumbbell shaped cross section appearance. See Below Gallery.

The later Unity Type II columns, have rectangular cross sections without any indentation and slightly more compact steel support plates, which can be a useful aid to identification where columns are exposed. 

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Street View of Refurbished & Standard Unity Type II Houses Great Shelford.

Columns are connected by cold-formed steel bracing. Ground floor columns are longer than those at higher levels and have a boot shaped projection at one end. During construction, the boot ends of the ground floor columns were stood on the footing. Typically, the spaces between the columns were in-filled with masonry to retain fill below the ground floor structure. On some sites, mass concrete infill has been found in the spaces between the columns. The columns form window reveals and mullions.

External walls

Walls are clad with stack bonded, unreinforced concrete panels, each just under 3′ 0″ long and 11″ high, with a clinker block-work inner leaf. The individual panels have shaped, interlocking upper and lower edges to reduce water ingress through rain penetration. Façade panels are tied back to the columns by copper straps. These hook onto wires cast into the back of the panels at one end and are fixed to the side of the columns at the other. Front faces of the columns were treated with bitumen to form a vertical damp proof course between column and cladding.

Generally, the clinker block-work inner leaf is rarely continuous through the floor void, being supported at each floor level. Tying of the inner leaf to the columns is more primitive than that for the outer leaf. Typically, nails are partially driven into timber plugs cast into the rear face of the columns, hopefully aligned with the bed joints in the block-work, and built into the wall.

Post 1950 type Unity houses generally have distinctive square comer panels, which typically are only held in place by steel wire in the bed joints, embedded in generally poor quality concrete infilling in the void behind.

Floors
The ground floor is of solid concrete construction. The first floor is formed from 4″ deep steel joists, spaced at 3′ 0″ intervals. The floor is finished with tongue and grooved floor-boarding, nailed to timber joists that are notched into the webs of the steel joists.

Roofs
The roof is of timber trussed rafter construction, lined with felt and battens and clad with interlocking tiles.

Other

• The party wall construction comprises two leaves of 2 1/2″ clinker block-work separated by a 2 1/2″ cavity.
• Load-bearing spine walls are generally of masonry construction, although in some variants there is a load-bearing PRC beam spanning the opening between the lounge and dining room.
• Internal partitions are typically of clinker block-work or masonry construction with a hard plastered finish.
• Ceilings are formed with plasterboard.
• Chimneys are of masonry construction.