Overview
Open System Building houses, also known as OSB, Poulson, or Dare houses, form a distinct group of non-traditional housing developed between 1967 and 1970. Designed by J G L Poulson and manufactured by Open System Building Ltd, around 500 properties were constructed during this period, largely in response to post-war housing demand.
These houses are generally two-storey semi-detached or terraced properties, most commonly found in urban settings.
Open System Building houses were constructed using a precast reinforced concrete structural system, combining factory-produced components with on-site assembly.
Typical characteristics & construction
Open System Building houses are constructed around a precast concrete structural frame, with storey-height precast reinforced concrete panels forming the external envelope to the front and rear elevations.
Roofs are shallow pitched and gabled in form, finished with interlocking concrete tiles over timber trusses and bituminous felt. Gable walls are generally of brick or PRC construction, returning around the corners of the front and rear elevations.
Asbestos cement sheeting is used to infill panels up to ground floor window sill height, with PVC boarding above. Exposed edges of precast slabs are coated with bitumen for weather protection.
| Element | Typical construction | Inspection focus |
|---|---|---|
| Substructure | Concrete raft foundation thickened at perimeter | Settlement, cracking, bearing performance |
| Structural frame | Precast concrete stanchions and beams | Corrosion protection, alignment, support details |
| External walls | PRC panels with asbestos cement and PVC cladding | Cracking, bowing, fixings, weatherproofing |
| Gable walls | Brick or PRC cavity construction | Support to beams, movement, cracking |
| Floors | Concrete ground floor, timber first floor | Level variation, deflection, bearing points |
Potential hazards & inspection priorities
The primary concerns with Open System Building houses relate to the condition of the precast reinforced concrete panels and the integrity of the supporting frame. During inspection, cracking and bowing to front and rear wall panels is frequently evident and can be severe.
Missing or inadequate concrete bearing pads at gable wall beam supports are a known issue and can result in uneven load transfer. Internally, uneven floor levels are commonly associated with timber boarding spanning over precast support beams.
Is this house right for you?
Open System Building houses require purchasers to be comfortable with non-traditional construction and to rely on condition-led assessment rather than age or appearance alone.
- Commission a full building survey by a surveyor experienced with PRC housing
- Pay particular attention to structural movement and panel condition
- Be prepared for targeted repairs or ongoing monitoring
Mortgage & resale considerations
Mortgage and resale acceptability for Open System Building houses depends heavily on construction clarity, structural condition, and the quality of professional reporting. Lender requirements can vary, particularly where significant cracking or structural alteration is present.
Clear evidence of maintenance, remedial works, and professional assessment is often critical.
What a survey can — and cannot — tell you
A building survey provides an informed assessment of the visible condition and construction of an Open System Building house. Inspections are non-intrusive and limited to areas that are accessible at the time of inspection.
- Identify visible cracking, bowing, or displacement of PRC panels
- Assess signs of dampness, moisture ingress, and condensation risk
- Comment on roof coverings, drainage details, and external envelope condition
- Review the general condition of accessible floors, ceilings, and structural elements
- Highlight defects that may require repair, monitoring, or further investigation
However, there are limitations to what a survey can determine without intrusive investigation.
- Confirm the condition of concealed reinforcement within PRC panels
- Assess hidden structural elements behind linings or finishes
- Determine the extent of internal concrete deterioration
- Inspect areas that are inaccessible at the time of inspection
Where higher-risk indicators are identified, further specialist or intrusive investigation may be recommended.
For a thorough building survey in Greater London, an instant quotation can be obtained through the online survey calculator.
Considering a Open System Building house?
A detailed building survey can help clarify construction-specific risks before committing to a purchase.
Get your instant survey quoteDisclaimer: This article is provided for general educational purposes only and is based on industry research, professional knowledge, and experience. It does not relate to any specific property and should not be relied upon when making a purchasing decision. Prospective purchasers should always commission an independent RICS-qualified surveyor to conduct a full inspection and provide a report on the actual condition of any property of interest.
