Buildings age and defects

Question 1

ALL PERIODS

Answer 1

• Over notching of floor joists – reduction in strength
• Removal of chimney breasts – lack of support
• Provision of installation blocking ventilation paths – condensation
• Blocking of air bricks – lack of ventilation and cause of decay
• Removal of loadbearing walls – possible long term structural consequences
• Removal of planting and trees – rehydration of subsoil, damage to drains or foundations
• Replacement window – poor support, distortion to brickwork. Poor sealing of new windows to existing fabric leading to loss of airtightness and water penetration.

Question 2

PRE-1900 (19th Century)

Answer 2

• Alterations to trussed partitions
• Damp penetration through solid brick walls
• Defective rainwater goods
• Delamination of brick skins
• Failed or lack of DPC
• Failure of brick arches and timber lintels
• Insect attack in roof and floor voids
• Lack of restraint to flank walls
• Lead lined parapet gutters – poor sizing of lead sheet causing splitting etc.
• Lead water mains – hazardous to health.
• Over notching of floor joists for services etc.
• Poor quality repairs to roofs and gutters.
• Poor ventilation of floor voids.
• Retrofit of concrete interlocking tiles – additional weight loading.
• Settlement of bay windows – poor foundations.
• Settlement in internal partitions.

Question 3

1900 – 1939 (Pre-War)

Answer 3

• Poorly fitted timber sash windows.
• Corrosion of steel windows.
• Corrosion of rainwater goods.
• Corrosion of steel frame (Regent Street Disease).
• Corrosion of roofing nails.
• Delamination of cement renders.
• Lead water mains.
• Outdated electrical services.
• Decayed external timber joinery.
• Use of Mundic concrete – poor integrity when damp.
• Wall tie failure in cavity brick.

Question 4

1960 – 1980 (Post War)

Answer 4

• Failure of aluminium sash windows.
• Asbestos containing materials.
• Failure of asphalt roofs.
• Calcium chloride concrete – additives or sea-dredged aggregates.
• Calcium silicate bricks – prone to shrinkage.
• Cladding system – steel and aluminium - distortion, operation, security, sealants etc.
• Cold bridging and condensation – poor insulation standards – little consideration.
• In 1975-80 thermal insulation standards were increased - particular problem for industrial warehouse with condensation problems.
• Cold flat roof construction - Vapour control, insulation and ventilation overlooked – risk of condensation and decay of structure.
• Concrete - Mixed quality, poor compaction, lack of cover, calcium chloride added.
• Concrete boot lintels – projecting nib to support outer leaf – eccentric loading and opening of joints.
• Concrete bricks – similar to calcium silicate – prone to shrinkage
• Concrete frame – were common in 1960’s often with brick infill panels and cladding - risk of brick panels becoming stressed as a result of concrete shrinkage.
• Corrugated ‘big six’ asbestos cement sheets – Health risks, fragile, corrosion of hook bolts and poor remedial works, missing foam fillers etc causing water ingress.
• Cracking brickwork outer skins – failure for movement joints and expansion of brick size.
• Cut edge corrosion of plastisol roof sheets
• External ceramic tiling – delamination of background material.
• Mosaic tesserae – small tiles applied to render background – adhesion failure – hammer test to identify hollow areas – vacuum injection techniques.
• Mosaic tesserae overhead – soffit finishes – applied over expanded metal lathing – fixing bolts or metal lathing may corrode and large section may collapse if water ingress. Potentially rot timber supporting battens.
• Dark coloured plastisol – high temps and deterioration of coatings
• Glass reinforced concrete – Lightweight panels etc early forms deteriorate in alkaline conditions, loss of strength, cracking bowling etc. later alkaline resistant types perform better.
• High Alumina cement – precast and prestressed work – loses strength with age – susceptible to chemical attack in damp conditions.
• Hollow clay pot floors – common during 1960’s – concrete poured between pots – clay spacer tiles can conceal honeycombing of concrete, lack of fire protection. Can be structural and non-structural – in some cases non-structural may have been removed to increase floor to ceiling height.
• Lack of movement joints – cement walls are prone to thermal and moisture movement – cement mortar is less flexible than older lime mortars and stresses induced by thermal movement form cracks.
• Poor cavity tray details
• Poor installation of lateral bracing to trussed rafters.
• Poor quality joinery.
• Reconstituted stone used for window sills, surround etc – carbonate fairly quickly resulting in damage in reinforcement or fitting cramps.
• Reliance on mastic sealant – poor durability – over-optimistic expectation of longevity.
• Render backgrounds used in conjunction with tile finishes – strong Portland cement used – poor adhesion to sub-surface, inflexibility, high vapour resistance and risk of water entrapment.
• Sand faced fletton bricks i.e. London Bricks – found in 1960s housing or industrial applications – work well in sheltered conditions – in exposed situations such as parapets, chimneys stacks where saturation is common can lead to sulphate attack. Bricks contain high level of sulphate that reacts with cement mortar resulting in it expanding and damaging brick face.
• External softwood joinery with low life expectancy.
• Spontaneous failure of glass – nickel sulphide inclusions.
• Trussed roof construction – introduced in mid 1960s – trusted rafters are usually jointed with factory-fixed galvanised steel fasteners – shrinkage can affect the adequacy of the trusses and metal connections fail – lateral buckling if not properly braced. Lack of restraints to gable walls can cause unacceptable degree of movement.
• Tying in of precast floor and roof slabs can lead to elevations gradually parting company from the floors – collapse could occur under accidental loads.
• Use of brick slips – detaching from structure.
• Use of built up roof coverings – poor life expectancy.
• Use of deleterious materials - HAC, chloride, asbestos, wood wool.
• Use of reinforced concrete frames, carbonation and chloride attack.
• Wall ties – thin steel sections and poor galvanising standards – tend to corrode away and lead to sudden collapse of wall. Thicker corroded ties may lead to horizonal cracks and lifting of brickwork.
• Wood wool as permanent shuttering – perhaps where extra insulation is required – risk of poor compaction around rebars. Could prejudice fire protection, durability and lead to a lack of strength. Intrusive investigation required to determine whether steel is covered properly.

Question 5

1980 – PRESENT (Modern)

Answer 5

• Using thinner stone as cladding material – used as rainscreen cladding - some stones prone to curling, visible distortion, damage to fixings, loosening or cracking of stone and in worse case detachment of panels.
• Toughened glass used at height – risk of spontaneous fracture due to NSI – could result in collapse – laminated safety glass preferred.
• Warm edge spacers in insulated glass units – risk of debonding and gradual creep into the sight line.
• External rainscreen systems – defects in fire stopping within cavity leading to rapid fire spread.
• External wall insulation systems - delaminate at high level due to water ingress without a drained or ventilated cavity.
• Synonymic drainage – water disposal from roof relying on symphonic condition – can be very effective if designed and installed correctly – prone to issues owing to poor specification etc. poor maintenance and blocked outlets.
• Composite panels – expanded foam and total loss in fire.
• Liquid roofing systems – risks of failure due to poor preparation and detailing.
• Indoor air quality – improved airtightness and greater need for MVHE / HVAC – a failure to service and maintain adequately can lead to a decline in indoor air quality and consequential health issues. Poor access to equipment to service – poor installation can lead to poor performance and reduction in efficiency.
• Shrinkage or distortion of timber frame – Lack of provision for movement with relatively static external envelope can lead to distortion in windows, internal finishes etc.
• Poor or inadequate fire stopping / cavity barrier in multi-storey structures – risk of rapid and uncontrolled fire spread.
• Hydrogen embrittlement of steel bolts – Entrapment of hydrogen gas during manufacture process leads to gas concentrating around high stress areas leading to sudden failure of bolt or component. Tends to affect high strength steels rather than lower grade metals.
• Decay in timber floors and roof cassettes – poor vapour control and lack of effective ventilation as a result of a failure to properly dry out structure following unintended saturation during construction.
• Timber rainscreens – defects with breather membranes and poor cavity tray details leading to uncontrollable water entry and passage behind cladding and subsequent water ingress into building. Moss and algae growth in poorly detailed joints leads to water retention, staining and gradual deterioration.