Greensted Colchester prefab identification  



Hi, I have looked at a house in Blackthorn avenue, CO4 3QD, the whole street and some of the smaller street around seems to be made of the same type but there are some small variations.

Some have dark wood siding on the opposite to party wall, other are painted all over, yet others have some white plastic siding at front and back. The roofs also vary from some sort of tiles to something smooth like metal sheets. All have entrance doors on the side of seemingly standard front extension but some of these extensions have sloped roof others flat.

From looking up a document on this site I saw Hawthorn Leslie being listed for that street but the number of houses given is much smaller than what can be seen on street.

Could you please see if you can tell me whether these houses are indeed the Hawthorn Leslie or some other type? They do not look exactly like the example given here and elsewhere, more like some sort of mix between BISF and HL but it could just be superficial and they are HL?

The agent is very vague and was guessing it is some concrete build, however I could not find a solid wall other than the party wall, making me doubt his guess.

The vertical corners (stanchions?) of and end-of-terrace are often clad in some white plastic, underneath seems to be some layered wood material, making me suspect the real load bearing material is further below the wood? Do you know if these are known to rust or are the layers of plastic and wood enough to guard it?

How would you classify such house for insurance purposes? Does the flat roof on the front door extension make it "partially flat roof property"? What would your guess of a rebuild cost be (insurance purpose again)?

There are many questions and I'll be happy with any information you can provide.


4 Answers

Hello DMT

The house is definitely Hawthorne Leslie Construction and possibly built as a variant with UPVC or timber cladding which you have already noted, or this may have been added later. It would also appear that the original large picture windows have also been replaced with a 50/50 split of window and foma filled composite board, presumably to increase insulation a little and also to keep glass replacement costs low.

The location documents that we hold, only refer to properties that are still under local council ownership. This would suggest that many of the properties not listed, have since been purchased under the right to buy scheme and are now under private ownership and thus no longer recorded on the local authorities register.

Regarding the frame, let me first post the following detail for you:

hawthorn leslie house sm
hawthorn leslie

A Little background; (Courtesy of the BRE).
The system, originally called 'Plasteel', was developed by Mr P Keate, a builder and surveyor, in association with Mr F Mould, an architect. In production little seems to have remained of the original design except perhaps for the concept of large panels of sandwich construction to form the external walling.
The company formed to produce and market the system, Hawthorn Leslie (Buildings) Limited, was backed by R W Hawthorn Leslie Limited, Shipbuilders of Tyneside. The company offered a complete package from the design of the site layout according to Radburn principles, to house types designed to Parker Morris standards, through manufacture and delivery, to erection on site. With a planned capacity of 6,000 dwellings per year the sales of the system did not match the production capability of the factory and the building company went into liquidation in the late 1960s.
Some confusion exists over the total number of dwellings built by the company. A survey of local authorities non-traditional housing stock shows around 1,800 Hawthorn Leslie dwellings whereas a compilation of planning applications shows a total of over 3,600 being built between 1964 and 1969. The system was also sold through private developers. 

Hawthorne Leslie 

Consist of bungalows and 2-storey detached, semi-detached and terraced houses.
Having a Shallow pitch gable roof covered with interlocking concrete tiles, or shallow pitch gable or flat roof covered with bituminous felt.
External walls of storey height cladding panels coated with various coloured aggregate finishes.
Large section timber cover strips mask corner and separating wall junctions.
Gable apex clad with timber shiplap boarding.

General Construction

hawthorn leslie frame

Having concrete pads below stanchions [1].
A Perimeter kerb formed in oversite concrete and damp proof course (DPC).
The frame consists of 9 Rolled Steel(RS) hollow box stanchions [2] (one single storey) and 1 Rolled Steel Angle (RSA) floor support beam [3], see frame layout [A] above.
The frame has a Protective coating of Brown Primocon paint.
The external walls consist of Storey height dwelling width, galvanised Mild Steel (MS) channel panels shown at [4], complete with door and window frames, clad with asbestos cement sheets and coated with various coloured aggregate finishes, and lined with plasterboard which was then filled with polyurethane insulation.
The Panels are bolted through the stanchions and over-lapped at the first floor level. The Timber cover strips are shown at corners [5] and at separating wall.
The Gable apex is clad with timber shiplap boarding.
Separating wall: Block cavity wall, 9" block laid flat in roof space.
Partitions: Honeycomb plasterboard.
Ground floor: Chipboard on timber joists.
First floor: Chipboard on timber joists.
Ceilings: Plasterboard.
Roof: Timber trusses, bituminous felt and interlocking concrete tiles.

Build variations:
Ground floor slab sometimes thickened around perimeter to form ground beam.
Intermediate stanchions are sometimes omitted in narrow fronted dwellings.
Gable external wall stanchions sometimes omitted.
Stanchions omitted in small detached bungalows.
External wall panels are sometimes flush jointed with timber cover strip.
External wall panels are sometimes overclad with timber or PVC shiplap boarding.
Additional linings of plasterboard or honeycomb plasterboard.
Some properties have been found to have concrete ground floors.
Timber stud partitions sometimes lined with plasterboard.
Flat or shallow pitch roof sometimes covered with bituminous felt..

Notes for surveyors of possible issues:

  • Superficial corrosion at bases of RS hollow box stanchions.
  • Loose or missing holding down bolts.
  • Corrosion of plain metal panel frames.
  • Separation of aggregate coating from cladding panels.
  • Warping of asbestos cement cladding sheets.
  • Rain penetration at panel-window frame joints.
  • Poorly constructed roof space separating walls.
  • Deterioration of bituminous felt roof cover.
  • Racking of roof trusses in detached dwellings.
  • Asbestos cement sheet claddings and fire protection
  • This system was also used to build flats.

In relations to classification for insurance purposes, I would suspect that these houses are, Prefabricated, non-combustible.

Generally, when taking into account flat roofs attached to the property, most insurance providers state that you should not include porches or out-houses etc, but I would recommend checking your insurers guidance or  terms and conditions regarding this.

Incidentally, you can purchase a more detailed document on the Hawthorn Leslie house direct from the BRE Press Library (Building Research Establishment) HERE.

I hope this helps and please fire away if you have any further questions.






hawthorne leslie terrace
hawthorne leslie semi
hawthorne leslie flats
hawthorne leslie bungalow
hawthorne leslie 2
hawthorne leslie (4)
hawthorne leslie (3)

Hi Marc, Thanks for the detailed answer! I've also found and bought the br152 pdf if someone else has this house and would like me to lookup something in it. Beyond this and your info there seems to be not much else on the net.

I think the first picture may well be from one of the side streets (or "walks") in that neighbourhood.

Best wishes



You're very welcome Dimitar and thank you for offering to share details contained within your document.

As you rightly state, there are very few internet resources available regarding Non-Traditional constructions. As far as I am aware, is the worlds only website dedicated to Non-Standard U.K housing but we ourselves may be forced to close in the near future due to lack of funding and other reasons.

I'm just glad to be able to assist you whilst we are still in operation.

Best regards and good luck in the future





Scroll to Top