What is ORLIT construction?
A non-traditional method of constructing houses and flats between 1940’s and 1950’s as a cheap, quick solution to the housing shortage after the war.
PCC have 55 Orlit houses all built in 1949.
It is constructed with pre-reinforced concrete frame structure which is then externally clad with reinforced concrete panels or blocks with two leaves connected with wall ties. Sections of the concrete frame can be joined with high alumina cement poured in situ or bolted connections. It could either have a flat or pitched timber roof.
What are common defects in Orlit construction?
The expansion of steel reinforcements in concrete from corrosion can cause the concrete to crack and spall decreasing its strength. The steel can corrode from carbonation of the concrete which is the decreasing of PH level over time which protects the steel or water ingress from cracks which have a snowball affect growing in size.
Where high alumina cement joints were used they could have significant loss in strength from deterioration over time, the cement is very good at getting strength quickly so it was preferred for quick housing however over time the high alumina cement loses strength from being in an unstable atomic form reverting to a stable form becoming more porous therefore decreasing strength.
Orlit properties are often rendered which can fail from cracking from movement of the building, potentially allowing water ingress and worsening the spalling of render. Also on the corner beads of steel reinforcement they are prone to corroding as they have little coverage and often need repaired same with elements as the canopy & supports for the front door.
Why does steel rust?
Because it is thermodynamically unstable under normal atmospheric conditions therefore will react with the air and oxidise to iron oxide.
Thermodynamically unstable means the chemicals are unbalanced and the compounds try to fill their structures with other elements.
When were orlit properties built?
1940’s to 1050’s as a quick cheap solution to housing shortage after war
Any orlit properties in PCC?
We have 55, I did an EPC on one and the rating was
How would you identify orlit construction?
In the roof space you would see the PRC beams, typical wall thickness would be
Why are orlit buildings not constructed anymore?
Under the Housing Act 1985 (part XVI) it is considered a defective construction method due to the common defects such as the steel reinforcements corroding losing strength in concrete or the high alumina joints losing strength.
This was developed from an inspection done on an Airey construction house after a fire which identified structural problems in PRC construction resulting in further inspection of all similar types
Are there any variants of orlit houses?
There is a Blackburn variant that has a Blackburn aluminium pitched roof and simplified framing and cladding with prefabricated internal partitions. This was to overcome bricklayer shortages.
How are orlit houses sustainable performance?
The floor and roof are generally adequate as it is likely solid concrete flooring and roof spaces can be topped up with insulation. However the walls are often in insulated and have an empty cavity which does not have good insulation.
What is the Defective Housing Act? / Housing Act part XVI
Legislation that outlines defective construction types and produced a scheme to aid owners to either repair or get money back for their defective property.
It was developed after a fire in an Airey construction house exposed the prc frame that showed cracking and structural issues which led to similar prc non traditional construction methods being investigated and identified structural issues also.
Can you name and describe another type of non-traditional construction?
Starts with a solid slab foundation and a DPC on top, then concrete is poured in situ into moulds and strengthened with steel reinforcing bars. It is similar to traditional as it has two leaves with a cavity between.
It was used before the war and reintroduced after the war to help the housing shortage. And is not classed as a defective construction type but generally pre 1940’s have thinner walls and thicker after the war. Typical defect is the reinforcements corroding and cracking the concrete.
You can identify it by horizontal pour lines where each layer of concrete would have been laid.