A

The effects of compressible sub-soils Cracking pattern will be unpredictable. Cracks tend to be wider at the bottom. Settlement due to a compressible sub-soil can be extensive and uneven Cracking pattern will be unpredictable. Cracks tend to be wider at the bottom. Settlement due to a compressible sub-soil can be extensive and uneven Any applied load will compress such a material and result in movement of the building above. These types of sub-soil should be completely removed or, if of...

A definition of damp

In a well ventilated room with a fairly constant relative humidity of about 30 a softwood timber skirting board may contain as little as 6 moisture (see previous chart). In a kitchen with a constant relative humidity of about 70 the moisture content of the skirting will be approximately 16 . In both cases the timber contains moisture but, because its moisture content fluctuates according to the relative humidity, and because a relative humidity of 70 will not encourage decay in timber, it can...

Above Ground Drainage Introduction

In the Georgian period sanitation was, when compared to modern standards, primitive. Better quality houses had rainwater pipes, made from lead, or in some cases timber. A crude system of brick sewers, often built around natural water courses, carried rainwater away to streams and rivers. Collection and disposal of foul matter, a much more hazardous material in terms of health, was dealt with in a variety of ways. Perhaps the most common was the cesspool. This comprised a pit dug in the back...

Acknowledgments

We would like to thank the following organisations and individuals who have contributed to this text Nancy Carlton, Sally Gilbert, lan Constantinides, Dr Brian Dury, Azadour Guzelain, Dr Susan Marriott, David McLaughlin, lan Stokes, British Gypsum, Peter Cox Preservation, Protimeter, Rentokil, The Brick Development Association, The Building Research Establishment, The Expanded Metal Company, The Timber Research and Development Association, Wardell Armstrong, Graeme Todd, Peter Smith, Robert...

Advantages of timberframed houses

The main advantages of timber-framed houses, when measured against brick and block construction, were initially thought to be those cost savings that accrued from industrialised processes, including standardisation and speed of on-site construction. Speed was associated both with quick erection times and the ease of making connections between uniform materials. Additionally, there was a significant reduction in time spent waiting for the finished structure to dry out, because fewer 'wet trades'...

Aid to diagnosis

The figure on the previous page, which should be read in conjunction with the charts on pages 256 and 277, explain the basic steps in trying to identify and pinpoint problems of penetrating damp. Mistakes in diagnosis are common, and where the problem is not obvious, remedial action should not be considered until all the steps have been carried out. Specialist advice is often necessary although it should be remembered that many of the so called 'Damp Specialists' have a vested interest in...

Airey Houses

Approximately 26,000 of these houses were constructed between 1945 and 1955. They were built with storey height pre-cast concrete columns at 450 centres. These had tubular steel centres and were erected over a cast in situ ground floor slab. They were connected at roof and first floor levels by timber or steel lattice joists. The external elevations were finished with horizontal pre-cast concrete slabs which were either smooth finished or pebble dashed and secured to the columns with copper...

And 40 years oldand 100 years old

Sapwood is that part of the tree that carries nutrients from the ground to the branches and leaves and, in the other direction, the products of photosynthesis from the leaves to the roots. Sapwood is susceptible to decay because it is carrying the nutrients that timber pests feed on. The physical nature of the cells is also a factor in durability. For example the water nutrient carrying cells in softwoods, known as tracheids, have walls which become thicker and more rigid as growth progresses....

Asbestos boarding and fibreboard

The use of asbestos products has been closely controlled for many years. However, there are still many houses where asbestos boarding has been used to dryline walls or finish ceilings. It was a very common material in the post Second World War reconstruction of Britain, particularly in non-traditional housing. Some grades of plasterboard were suitable for painting, others received a plaster finish. Where asbestos boarding is suspected specialist advice is necessary. Asbestos boards were usually...

B

Sulfate attack has just started to crack the horizontal bed joints in this retaining wall. The effects of sulfate attack in a garden retaining wait The effects of sulfate attack in a garden retaining wait A common consequence of sulfate attack in chimneys is a pronounced lean caused by the different wetting and drying cycles between elevations. In chimneys additional sulfates may be deposited by the combustion process and additional water may be introduced from condensation within the chimney...

Below Ground Drainage

Mains drainage is comparatively recent. Although a number of Georgian buildings had a rudimentary form of drainage, it was not until the end of the nineteenth century that it became an automatic requirement to provide a comprehensive system of mains drainage for all houses in urban areas. Early systems were 'combined' in other words rainwater and foul water (from WCs and wastes) shared the same drains. A typical terraced house from the early 1900s is shown in the diagram below. At this date...

Bitumen paint

Completely impermeable coatings such as bitumen paint can cause problems more serious than the ones they are meant to eradicate. They prevent moisture escaping from a wall and can, in freezing conditions, lead to frost attack in the render. In many cases this type of coating is often specified in an attempt to resolve perceived problems of penetrating damp. However, incorrect diagnosis of the causes of dampness is common surface condensation is often mistaken for penetrating damp. Where this is...

Blocked drains

There are a number of ways in which drains can become blocked. Identifying the cause may take a surveyor minutes, although it may require specialist input and specialist equipment. Nowadays, there are a number of companies who can inspect drains internally using remote controlled cameras. These are relatively cheap when the alternative cost of digging up several sections of road or gardens is considered. Blocked drains can be caused by Internal problems Inappropriate materials finding their way...

Bond failure

If a plaster surface appears to be in good condition but sounds hollow when tapped, this usually indicates a failure to bond properly with the background. This may be due to top coats not adhering to base coats or base coats not adhering to the wall. Localised hollow spots do not necessarily mean that the plaster is loose and may not warrant further action. However, where hollow spots are extensive, or where there is associated cracking, hacking off and replastering may be the only option....

Brick and block partitions

Load-bearing partitions in modern housing are usually formed in blockwork and are most likely to be found at ground floor level where, besides dividing space, they support the upper-floor joists. They will usually be built on a foundation although, in some areas, they may be built on a thickening in the concrete slab. The partitions can be built from dense or lightweight blocks and are usually 100mm thick. In very small houses, where the joists can span from external wall to external wall,...

Brick categories

Brickwork is generally a durable material with modern methods of manufacture ensuring good quality control. Problems experienced in the past, such as underfiring (leading to softness) or overfiring (leading to brittleness), deterioration through reactive materials, lamination, distortions, and differing sizes, are now rare. Modern bricks are categorised by strength, salt content and frost resistance. The category of frost resistance considers whether or not a brick is suitable for use where...

Brief History

The aftermath of the First World War saw an urgent need for thousands of houses. The immediate reasons for this were a lack of any new construction and maintenance during the war years combined with the need to house large numbers of demobilised soldiers and their families. Post-war shortages of materials, such as bricks and timber, and labour, in particular, skilled labour (as the result of war casualties and the lack of training), meant that new methods of construction were encouraged by the...

British Iron and Steel Federation BISF Houses

Some 30,000 of these houses were erected in England and Wales together with over 4,000 in Scotland, out of a total of about 140,000 metal-framed houses, in all, of some 30 different types. There were three different types of BISF house, although the essential feature of each was a frame of either hot-rolled or cold-formed steel. A number of cladding systems were used of which the most common consists of an outer cladding of profiled steel sheeting at first floor level, cement rendering applied...

Brown rots

These can cause severe decay in timber. They attack both the cellulose and the hemicellulose elements of the wood. The lignin is generally not broken down although its characteristics might be changed. The lignin cracks into cubes as moisture is removed during the decay process and it is this cuboidal cracking which is a primary identifier of a brown rot attack. As a consequence of the attack the wood becomes darker in colour and often becomes so dry that it can be crumbled easily between the...

Building Conversion

Many large Georgian, Victorian and Edwardian buildings have been converted into flats. In many cases these conversions will have been carried out in the past when Building Control requirements were less onerous than today. It is the higher floors that are normally most at risk. In many of these early properties joist size varied from floor to floor. The top floor, for example, was possibly built as servant accommodation and would contain joists of modest size to reflect the modest intended...

Building Movement Walls

A building will suffer some degree of movement throughout its life. Often, it may not have its performance affected in any significant manner. On the other hand, the movement may be so great, or happen in such a way, that performance is adversely affected. The walls of newly constructed buildings commonly suffer cracking as a result of the initial drying out of the materials used in the building process. This is usually caused by the evaporation of the water used in the process and can take up...

C

Differential movement may be vertical (up down). It may also be rotational. Cracking may occur In walls, ceilings and floors along movement line. Dotted line indicates movement plane, le. interface of different forms areas of construction where cracking can occur. Dotted line indicates movement plane, le. interface of different forms areas of construction where cracking can occur. This lean-to extension (left) was built on inadequate foundations. The rotational movement is most evident at the...

Carbide testing

For masonry products, bricks, blocks, mortars etc, carbide testing can be used to assess moisture content. Its use should be regarded with caution because, as already mentioned, these materials will differ in the amount of moisture they can contain and still be regarded as dry. By drilling into a wall with a large slow bit (to minimise heating and, therefore, drying) a sample of suspect material can be collected. Part of the sample is weighed and tipped into a cylinder. A specific amount of...

Cavity insulation

Most forms of cavity insulation (complete cavity fill) are treated to make them water repellent. Unfortunately, if the manufacturers' recommendations regarding the sequence of construction are not followed, situations can occur which permit damp penetration. Where cavity batts are used there is the risk that mortar can collect on the top of each batt and create a bridge. This is a particular problem where batts are inserted down into the cavity rather than being positioned against the wall as...

Cavity trays

Problems of missing cavity trays or mortar build-up on trays have already been mentioned. There are two common situations, apart from over windows and in parapets, where correct installation of cavity trays is important. These both occur where structures abut a cavity wall. Problems may occur through incorrect installation but are more likely to be caused by subsequent building alterations or additions. If there Is no cavity tray (and proper flashings) water can penetrate the new addition. If...

Cement plasters

Although the Romans discovered materials with properties similar to modern cement, the material used today has only become widespread since the early part of the twentieth century. Cement differs from lime in a number of ways. Unlike lime, it sets by hydration rather than carbonation in other words, the chemical reaction occurs when in contact with water, not carbon dioxide. Again, unlike lime, it cannot be 'knocked back' once the set has started. It is strong and brittle, virtually impermeable...

Central heating systems

The majority of central heating systems in the UK are vented. In other words, the boiler is fed by a storage tank and the water in the boiler can discharge back into this tank if the water overheats and reaches boiling point. Because of the risk of this discharge the storage tank for the boiler must be separate from the cold water storage tank which serves the cylinder. Typical central heating system from the late 1980s

Chemical Analysis

Moisture meters are helpful in providing a first step towards the diagnosis of rising damp. However, as described in the first part of this chapter, it should be remembered that they have limitations when used on materials other than wood and are easily confused by the presence of salts. The various stages in achieving a diagnosis are included in a chart later in this chapter. Definitive evidence can be provided by chemical analysis. Sub-soil naturally contains nitrates, from decaying plant...

Chipboard

Chipboard is common in modern construction. It is made from timber waste products, at the point of timber conversion, bound together in a resin and formed into large sheets. It is available in a range of grades. Standard grade chipboard is very sensitive to moisture. It can therefore be very vulnerable in a ground floor, not just because of the risk of rising and penetrating damp, but also because of spillage and leakage. A leaking washing machine can ruin chipboard in a few months. If the...

Chipboard Failure Ground Bearing Slabs

Chipboard flooring is becoming an increasingly popular alternative to traditional floor screeds. Chipboard is very sensitive to moisture and this has obvious implications for the type and position of a damp proof membrane. If the chipboard is covered with an impervious material such as sheet vinyl minor defects in the membrane can lead to wetting of the chipboard. Trapped construction water in the slab can cause similar problems which is why the chipboard manufacturers recommend an additional...

Clay tiles

Clay tiles have been used extensively in England and Wales for several hundred years. They have been manufactured in a great number of shapes and sizes ranging from the small and simple (eg plain tiles) to the large and more complex (eg double roman). Tiles such as the former merely butt up to the sides of each other but are heavily overlapped vertically, in a similar manner to slates, to form a weather resistant covering. Other types of tile, like the pantile and double roman, are more...

Co

0 10 20 30 40 50 60 70 80 90 100 Relative Humidity ( ) 0 10 20 30 40 50 60 70 80 90 100 Relative Humidity ( ) The relationship between relative humidity and moisture content of softwood is shown in the diagram below. Moisture evaporating from ground raises relative humidity of air below floor. The moisture content of the timber floor will increase until it is in equilibrium with the air below. If the relative humidity of the air below the floor is above 85 the timber floor will eventually reach...

Common Defects During Construction Process

Insufficient suction on smooth brickwork. Porous bricks provide too much suction. Flush mortar joints prevent key. Lack of bond, loose and hollow render. Single coats rarely satisfactory. They are not weatherproof and cause 'grinning'. Render mix too strong. Sand too fine, requires more cement and more water to get workable mix. Damp penetration caused by insufficient protection. Uneven drying after rain. Shrinkage cracking -lack of weather protection. Thick...

Common Defects Of Flat Roofs At Construction Stage New Build

Inadequate timber joist or steel member sizes. Insufficient thickness of reinforced concrete. Deflection of roof and water will collect in depression. Water unable to drain away. Greater leakage if covering fails. Reduced life of roof covering. Deflection of roof. Rainwater collects in depression unable to drain. Reduced life of covering. Greater leakage if covering fails. Inappropriate choice of sheathing felt for lead covering. Inappropriate choice of roof decking (eg chipboard). Lack of any...

Common furniture beetle

This has the Latin name Anobium Punctatum and is the most common form of insect to attack timber in this country. Despite its English name it does not attack just furniture (although it is often brought into a building by furniture which has been infested) and it will attack softwoods and hardwoods in many situations, from a damp underfloor area to the roof. The beetle attacks mainly sapwood, heart-wood is only usually attacked where it has suffered from fungal decay. If the sapwood is only a...

Common Site Errors During Construction Process

Choice of membrane not appropriate to floor finish. Concrete oversite (suspended timber floors). Timber joists (suspended floors). Sub floor ventilation. Insulation. Radon gas protection. Pre-cast floors. Some industrial wastes expand if wet. Hardcore not compacted in layers, or hardcore too deep. Trees felled or growing in clay soils. Cracking caused by shrinkage. Concrete not laid in bays. Concrete too wet when laid. No surface protection on hot days. Frost attack. Concrete too dry when laid....

Conclusion

When examining any building for movement problems, reference must be made to the date of construction of each part. Consideration will need to be given to the implications of dealing with different ages, types and styles of construction within the same property. Initially, records should be examined to determine previous use(s) of the land, eg an infilled pit. Unfortunately, it may be difficult to ascertain these facts without some element of detailed and, possibly, destructive investigation,...

Concrete Ground Bearing Floors Construction Summary

Although there are examples of concrete ground bearing floors from the1930s, and even before, it was not until after the Second World War that they became the most common method of forming ground floors. This was, in the main, due to a shortage of timber caused by government restrictions on imports (eventually relaxed in the mid 1950s). Nowadays, although timber floors can be found, concrete ground bearing slabs are much more common. At its simplest the floor comprises a slab, or bed, of in...

Concrete slab

The concrete slab is usually about 100-150mm thick. Nowadays the required strength of the concrete is set out in the Building Regulations. Prior to this it depended on local by-laws and generally accepted good practice. In some cases the slab is reinforced with a steel mesh, for example where soft spots exist in the ground. The mesh prevents the slab from cracking. The surface of the slab can be power floated to produce a very smooth surface, usually smooth enough for vinyl tiles of sheet...

Condensation

A key element in the design of most timber-frame houses is the vapour barrier (vapour check or vapour control layer). Its purpose is to prevent the passage of moisture vapour from the warm side of the insulation to the cold side where there is a danger that it might condense within the wall structure. This phenomenon is known as interstitial condensation (see Chapter 13). The vapour barrier is usually The vapour check prevents moist air from reaching colder parts of the structure. Interstitial...

Construction of stone walls

Stone walls are defined by the manner employed in dressing the stone. The two general categories are Ashlar Rubble This is the description given to squared stone which is presented by being dressed to a smooth face. Ashlar consists of mathematically precise blocks separated by very thin joints to produce a 'classical' appearance. This was a popular approach in the Victorian era. It was used because it was cheaper than ashlar but, in many instances, it was deliberately chosen because of its...

Construction Summary

Most houses have upper floors made from timber. The construction has changed very little in the last two or three hundred years although current controls such as the Building Regulations should ensure that modern floors are structurally sound and free from problems of penetrating damp. They are made from a series of timber joists covered with floorboarding or sheet materials such as chipboard. The floor structure is usually hidden from view below by a ceiling, originally made from timber lath...

Construction Summary Function of the roof

The primary function of the roof is to provide protection to the building beneath from the weather. It should be constructed in a form that will meet the following five key criteria. It must be capable of supporting both its own weight and any loads that might be imposed upon it, eg snow, standing water, water tanks and other plant. The various components should not be subject to excessive movement nor should they create instability in other elements. The materials used, especially coverings,...

Contraction of a material due to initial drying

Brief reference has already been made in this chapter to the effect of the cracking caused by initial drying out of a building once the construction process has been completed. Shrinkage cracking of this nature is quite normal. It is the most common form of cracking found in newly constructed buildings. Portland cement products, lightweight concrete, sand-lime bricks, calcium silicate bricks, some plasters and timber are all subject to initial drying out and cracking. With cement-based...

Corrosion Of Steel And Iron Components

Unprotected steel and iron will rust when in the presence of water. The formation of the rust (or hydrated iron oxide) results in a four-fold increase in the volume of the affected metal. The only way to prevent this is to coat the metal to provide a barrier between it and any water. This is often achieved by the use of hot or cold galvanising. This process involves applying a coat of zinc over the complete surface of the metal. It will offer protection for between 20 and 60 years depending...

Cracking

The nature and pattern of cracks will help to diagnose their cause. Perhaps the first stage in any diagnosis is to identify whether the cracking is caused by movement in the background, ie the wall, or is confined to the plaster itself. Some cracks are usually attributable to a fault in the building itself. These can take many forms (see Chapters 2 and 3). Diagonal cracks, either stepped or in fairly straight lines, are usually caused by building movement. In new buildings these may be fairly...

Cracking of ceiling finishes

This is most likely to occur where plaster finishes have been applied directly to the soffit of the beams. It may be caused by incorrect or inadequate grouting of the floor surface, the load from heavy partitions built directly on a single beam, or the use of wet infill blocks which will shrink slightly as the floor dries out. It could also be caused by using undersized beams which suffer excessive deflection although this defect should not occur if the manufacturer's design guidance is...

Damage by foot traffic andor human activity

Most flat roofs are not designed to accept foot traffic, except for maintenance purposes. Where access is needed for maintenance and repair, it may be necessary for crawling boards to be used. Any access, approved or otherwise, may result in mechanical damage to the covering, especially if it is of a softer material such as felt, asphalt or lead. Examples of this type of damage include gouges, rips, tears and indentations caused by human movement itself, or the placing or dropping of heavy...

Damage from aircraft wake vortices

This phenomenon affects the roofs of properties situated beneath, or close to, the flight path of a busy airport by dislodging the tiles or slates. All aircraft trail powerful air currents, or 'vortices', behind them and, in general, these are at their strongest when the aircraft is heavy and flying slowly - exactly the conditions when a modern passenger plane is taking off or landing. The likelihood of damage is greater when an aircraft is landing, as it is closer to the ground for a longer...

Damp Penetration

In cavity walls problems of damp penetration are usually due to faulty workmanship. This can occur in a number of ways. One common problem is caused by bridging of the cavity which can allow moisture to penetrate the joist ends. This can occur where careless bricklayers allow mortar to accumulate in the cavity. The problem is exacerbated if the joists project into the cavity and form a ledge on which martar droppings can collect. The cavity can also be bridged where insulation has been fitted...

Damp proof membranes

Although some early ground bearing floors incorporated waterproofing agents in the slab or screed (the most common finish) most floors contain a separate damp proof membrane. They can be formed from a variety of materials, some of which are no longer readily available. They include bitumen (distilled from oil) asphalt (bitumen and aggregate) pitch (distilled from coal) bitumen solutions bitumen rubber emulsions To be effective these materials need to be continuous and need to form a good joint...

Dampness

There are a number of defects which occur in raised timber floors. It is the early floors which are particularly at risk. Most of these defects are caused by dampness. Rising damp and penetrating damp can occur in a number of circumstances and these are shown in the diagram opposite. If the cause of the dampness is not addressed promptly dry or wet rot may occur. Adequate ventilation of the sub-floor void is vital if problems of rot are to be avoided. If moist air lingers in the sub-floor void,...

Dampness and moisture content

The word 'damp' is potentially confusing because most building materials (with the exception of plastics and metals) are porous and will always contain some moisture. Assuming there are no problems of condensation, spillage, or damp penetration through the fabric the moisture they contain will vary according to the relative humidity of their surroundings. This is why it is so important to ventilate timber ground floors. Inadequate ventilation, particularly if the ground below the void is wet,...

Dampness condensation and thermalmoisture movement

Penetrating and rising damp can affect partitions in a number of ways. Where partitions are built into solid walls or into defective cavity walls, damp may penetrate the edge of the partition. In studding and proprietary plasterboard partitions this can cause rot in the framing materials and deterioration of the plasterboard. Rising damp can affect partitions at ground floor level. This can be due to failure (or non-existence) of DPCs. Where partitions are built directly on concrete ground...

Death watch beetle

This beetle tends to be well known because it is associated with attacks on the type of hardwood, particularly oak or elm, which may be present in more prestigious or historic buildings. Other hardwoods including walnut, chestnut, elder and beech, are also at risk from attack as are softwoods which are in the vicinity of the hardwood. Death watch beetle will usually only attack damp decayed timber. Infestation is often therefore restricted to, for instance, timbers or parts of timbers built...

Decking problems

In domestic flat roof construction, the structure is normally formed with a reinforced concrete slab or by timber joists. The former will usually be finished with a screed topping laid to a fall, or insulation boarding with an integral sloping top. On the other hand, a timber joist roof will be covered with board or sheet decking. The roof slope is formed by either installing the decking on firring pieces fixed to the joists, or shaped insulation boarding. There are a number of materials that...

Defects

Stone is a natural but complex material. Within the general headings of sandstone and limestone there are many stone types, with different durability and weathering characteristics. The discussion of defects is therefore inevitably generalised. There is still much debate about the key factors affecting durability in stone and empirical evidence is somewhat contradictory. However, it would appear that whilst natural durability can be affected by a number of factors, probably the most significant...

Defects In Concrete Houses And Steelframed Houses Introduction

It would be impossible in a textbook of this nature to detail the problems experienced by the complete range of concrete and steel houses currently in use. The following sections, therefore, initially describe some important defects that are commonly found across a number of different types of system-built houses and then briefly examine, in more detail, a representative sample of systems. It should be noted that the individual housing systems frequently had variations in design and or...

Defects in houses constructed between 1945 and 1955

This section concentrates on those houses constructed with components of either pre-cast reinforced concrete (PRC), cast in situ concrete or steel. Many thousands of these were erected in this period. A great number have subsequently been demolished for the reasons briefly referred to above. The remaining houses, which number in their thousands, are still in use. Some are in good condition, although many suffer from problems similar to those already demolished. Their continuing use is normally...

Defects In Precast Concrete Floors

These floors are comparatively recent and, as such, their long term durability is unproven. However, there are a number of problems which have manifested themselves, most of which are due to inadequate site preparation or specification rather than failure of the floor components themselves. Beam and block floors are not usually designed to carry internal load bearing walls. Deflection in a floor below a wall or horizontal cracks in the wall itself may suggest that over loading has occurred....

Defects In Systembuilt Houses Constructed After 1955

Many of the defects associated with earlier system buildings are found in dwellings of this later period. Problems caused by carbonation, chloride attack, lack of thermal insulation, damp penetration and inadequate sound insulation are all too common across the broad range of industrialised (or system) buildings constructed - low, medium and high rise. Over 150 different systems were authorised in England and Wales alone, with the individual numbers erected ranging from single figures to over...

Deflection

Deflection or sagging can occur if the joist ends have started to rot. It can also occur for a number of other reasons and systematic inspection is necessary if the cause is to be correctly identified. Deflection can be caused by any or all of the following undersized joists excessive loading from furniture joists at incorrect centres or partitions bearing on the floor excessive notching for services rot or insect attack In extreme cases deflection can affect the stability of the external...

Diagnosing Penetrating Dampness

Pinpoint damp contours with moisture meter Readings show sharp change from wet to dry Patches of efflorescence (crystallisation of sulphates and carbonates present In building materials) Timber in area of damp has high moisture content. External inspection may reveal obvious defects including cracked render or brickwork, cills without drips, damaged downpipes etc. Deep wall probes indicate high readings in centre of wall Salt analysis shows zero level of nitrates and chlorides (eliminating...

Differential movement

A flat roof may be affected by differential rates of movement between the roof itself and an adjoining element of construction. The element may be at the same level as the roof (eg a parapet wall or another area of roof, perhaps of a separate construction) or below it (eg an internal wall). The effect upon the flat roof will be horizontal and or vertical movement stress which can manifest itself in a number of defects Stepping, unevenness or sagging The problem may affect only the roof covering...

Differential Settlement

This is the term used to describe the circumstances in which separate parts or elements of a building are subject to quite independent movement, eg a bay window or rear annexe of a house settles downwards whilst the main part of the building remains stable. This is often due to the fabric of the separate areas being quite distinct in form and or construction, or the foundations being formed at different depths. Any part of a building formed in lighter construction will impose lower loads on its...

Direct cold water systems

These systems are the most cost effective, providing there is a reliable and continuous water supply and the building has no need of a stored water supply. As water enters the property directly from the mains it is at a high pressure and the fittings throughout the system are required to be suitable for this high pressure. This applies especially to the 'ball valves' feeding cisterns and tanks for heating, hot water and toilet facilities. Water hammer is a problem experienced with variations in...

Direct hot water systems

The main problems which occur are related to water discoloration, possible scale formation, poor temperature control and noise. Older systems are usually associated with coal fired back boilers and more modern assemblies are single multi-point gas and electrical water heaters of both storage and non-storage types. A typical coal fired back boiler system is shown below. Direct hot water supply was quite common before the 1960s. The water from the cylinder was heated by a cast-iron heat exchanger...

Direction of joists

The floor joists are supported by the external walls, the internal load bearing wall between the lounge and dining room, and intermediate sleeper walls (shown as dotted lines). Timber floors require ventilation below the floor to keep the underflow space dry. This was achieved by providing vents in the external walls. These early floors vary in quality, particularly in their resistance to problems of dampness. Late Victorian houses, for example, were usually built with DPCs in the external...

Double floors

Where floor spans are considerable the joists have to be very deep to resist deflection. Wide floor spans also require long joists but lengths above 4.8m or so have never been readily available. In these situations it is more economic to use a double floor. Double floors were quite common in grand Victorian and Edwardian houses and usually consisted of one of more large timber beams, spanning the shortest possible distance and supporting smaller bridging joists. In modern housing, spans of over...

Dry rot

Dry rot is often referred to by its Latin name Serpula Lacrymans. It is the term given to a particular identifiable brown rot. The popular name refers to its effect on wood - which becomes dry and crumbly - rather than the conditions that create it. Dry rot spores are probably present in most buildings, although some buildings are more prone to attack than others. This is because of the presence of excessive moisture, perhaps due to defects, but it can also be because once a successful attack...

Durability And Defects

The durability of any plaster depends on a number of factors. These include background key number and thickness of coats background suction dampness background movement chemical attack strength of the mix defective workmanship Defects which occur through the above problems manifest themselves in a number of ways. There may be cracking, either in the plaster itself or in the walling material as well. There may be surface deterioration accompanied by loss of bond, and in extreme cases, partial or...

Early floor finishes

In the 1940s and 1950s timber floor finishes were popular. These often took the form of floorboards fixed to dove-tailed battens secured by a screed or rectangular battens fixed by clips or nails. This gave the floor the appearance of a traditional raised timber floor and was suitable for a period when few people had fitted carpets. The membrane below the screed was most likely to be formed from a hot liquid materials such as pitch or bitumen although cold membranes, applied in two or three...

Effect of wall structure and heating pattern

In a well heated dwelling, with average levels of humidity, condensation will only occur locally after long hot baths, cooking or drying clothes. As you would expect, kitchens and bathrooms are most at risk. However, when houses are heated intermittently condensation may also appear on living room and bedroom walls even houses with central heating are at risk. Few people keep their central heating on permanently and a more typical arrangement is to have heating for a few hours in the morning...

Efflorescence

Efflorescence is a common sight in new brickwork. It is caused by soluble salts in solution being brought to the surface as water in the wall dries out. It is usually a harmless, temporary problem, often occurring in spring following a wet winter. The main concern is the unsightly appearance caused by the white staining that it produces. Persistent efflorescence may indicate a design or construction fault which allows the brickwork to become, and to remain, saturated. White soluble salts...

Electrical thermal storage heating

During the 1950s the power supply industries were trying to find means of levelling out the peak demands for electricity and one of the ways introduced was to offer electrical power at a cheaper rate during the times of low demand. The most significant period was overnight, and the introduction of electrical thermal storage heaters proved very effective. The economies to the user however, were questionable under certain circumstances and led to a generally poor reputation for this type of...

End bearing

Most manufacturers recommend a minimum end bearing of 100mm. Where brickwork has been badly set out or built out of plumb there is the danger that the end bearing can be reduced. In practice this can be avoided by careful site supervision or insisting that the beam manufacturers provide beams to suit the as-built dimensions rather than the dimensions shown on the drawings. While this will inevitably cause some delay the associated costs outweigh the potential costs of remedying incorrectly...

Entrapped moisture

This is a problem suffered by flat roofs that are wholly, or partially formed with in situ-cast concrete or topped with a screed. These construction processes require considerable amounts of water and the Migration of trapped moisture may take many years. Initial appearance is often around light fittings, vertical pipes or low points In the roof.

Eradication of beetle attack

Insect attack may die out naturally due to a number of reasons. These might include desiccation of the larvae in timber where the moisture content has been lowered, or attack by parasites, or because the nutrients in the timber have become exhausted. A detailed description of remedial treatment is inappropriate in this publication although the following brief points are worthy of note insecticides are usually applied as a liquid or as a paste. In certain circumstances smoke, gas or heat...

Establishing if condensation is taking place

A psychometric chart enables the incidence of condensation to be predicted (psychometric - from the Greek 'a measure of coldness' in fact the Greek name for a thermometer). The horizontal lines show moisture content, the vertical lines show air temperature and the curved lines show relative humidity. In practice measuring the moisture content of the air during a building inspection is difficult but it is fairly easy to establish the RH and the air temperature. If these two variables can be...

Expansion of a material due to moisture absorption

On the other hand, clay products, such as bricks, undergo initial expansion as moisture is re-absorbed after firing. This is only slight - between 0.1 and 1.0mm m in unrestrained brickwork - but the effect is increased in long large areas, where the overall movement can be considerable and results in vertical cracking that is similar in appearance to that of thermal movement. Brick panels in concrete-framed buildings can also be affected - the brickwork is constrained by the frame floors roof...

Failure Of Arches And Lintols

Often, movement cracks in a wall will be observed above window and door openings. They may be indicative of failure of the wall itself or its foundations. However, the problem may be as a result of the failure of the arch or lintol above the opening. In traditional masonry walls, openings were normally formed with brick flat or segmental rough arches above. If the mortar in the joints of the arch weathers excessively, or the wall around the opening is subject to some movement, the result can be...

Failure Of Protective Coatings

Coatings are often applied to stone in an attempt to protect it. They are usually applied in order to Additionally, given the number of bay windows where the stonework is painted, some coatings are presumably added because they are judged to improve the look of the stone. Whilst there may theoretically be good reasons for applying a silicone based water treatment to stone (ie where penetrating damp is occurring), they should not be used to try to arrest the effects of stone decay. Where they...

Failure Of The Ceiling Finish

Any deflection in the floor is likely to induce cracking in the ceiling finish. Cracking can also be caused by lack of floor strutting, inadequate nailing, plasterboard of insufficient thickness for the joist centres, lack of noggings between joists and plasterboard fixed without staggered joints or with joints incorrectly taped. Wall board, which tends to be in large sheets (often 2400 x 1200mm), is more likely to crack than plasterboard lath (not to be confused with traditional lath and...

Failure of the surface finish

Screeds laid on a resilient layer will crack if they are not reinforced (the usual recommendation is galvanised chicken wire) or if they are of inadequate thickness they should be at least 65mm thick. Screeds can also crack if they are laid too wet or are not sufficiently compacted thus reducing their bond with the wire reinforcement. Chipboard can fail if it becomes wet and this can occur through spillage or where wet flooring components are used and a polythene vapour check is omitted above...

Fire

In timber-framed buildings with an external cladding of brickwork there is a danger of fire spreading in the cavity. The fire can start within the building but spread into the cavity through an incorrectly fixed internal plasterboard lining. Fires can also result from careless soldering of pipes adjacent to the cavity. Most breather papers are flammable and the spread of fire can be rapid. Cavity barriers are required to limit the spread of fire within the cavity itself. In modern construction...

Fire Protection

In a modern two storey house the use of plasterboard ceilings and tongued and grooved boarding both contribute to the floor's resistance to the spread of smoke and fire. In many older properties lath and plaster ceilings together with square edged boarding are more likely to be found. Square edged boards are not effective in limiting the spread of smoke (the main risk to life) and lath and plaster ceilings may fail quickly if a fire starts. Early construction does not necessarily require...

Floor Boarding

Dampness apart, there are a number of defects which occur in floor boarding. Square edged timber boards were common until the 1950s. These can give sterling service. Although square edged boards do give rise to draughts because of the gaps between the boards (in centrally heated houses shrinkage can be quite high) they are easy to lift for maintenance purposes and generally of substantial section. However, if incorrectly fixed, the boards can damage surface coverings a rippled appearance to a...

Foundation Defects The Causes

Not all defects are as dramatic as these. Temple Church (in Bristol) was started in 1398. The tower soon leant because the alluvial soil was too weak to support the heavy load of the tower. The upper stage (built at a different angle in an attempt to straighten it) was built in 1460. According to local history the Americans, stationed in Bristol at the end of the Second World War, intended to demolish the tower, incorrectly assuming the lean was a result of bomb damage. The 'defect' on the...

Foundations A Brief History

Historically, buildings were constructed directly on the surface of the ground until it was realised that removal of at least the topsoil normally provided a firmer base. This was considered sufficient for cheaper brick and stone buildings although timber-framed structures were often built on a stone plinth. In the nineteenth century a thin layer of fire ash or furnace clinker was commonly spread over the exposed sub-soil to provide a level surface on which to build. The pier of brickwork in...

Foundations Construction Summary

The purpose of the foundation is to fully and efficiently transfer the load from the building onto the sub-soil beneath. The exact type and performance requirements of a foundation will depend upon a number of factors including building type, use, load, etc and or sub-soil type, formation, condition. The width of a simple foundation varies according to the bearing capacity of the sub-soil. The width of a simple foundation varies according to the bearing capacity of the sub-soil. The building...

Fuel burning appliances

Nearly all fuels (coke is an exception) contain hydrogen. As part of the combustion process the hydrogen combines with oxygen to form water. In addition some fuels contain water coal or coke stored outside can be quite wet. As these burn the water evaporates. Both of these factors combine to ensure that the exhaust gases from the fuels contain high levels of water vapour. As the water vapour rises up the flue it may condense. In open fires substantial amounts of air are added from the room and,...

Fungal attack

They are present in great numbers in many situations and they play a number of roles. They are responsible for the breaking down of organic matter, they can cause disease both in animals and in man, they are the basis of fermentation and they help to produce chemicals and medicines (such as antibiotics). They are important factors in enhancing the growth of living trees but are responsible for the decay of timber in service. In very simple terms, fungi are a group...

Fungi

The risk of damage by timber pests for any given piece of timber will be affected by a number of factors including the natural durability of the species of timber the food value that the timber contains. (Food value will be determined by the amount of sap wood in the timber. This is explained later.) adverse environmental conditions - particularly dampness protection afforded through treatment by chemical preservatives The existence of timber frame buildings dating from the Medieval and...

G

Steel covers easily damaged by vehicles. If rainwater gulleys are not trapped, smells from an incorrectly connected drain can be a nuisance. Drive not laid to falls or gully too high will prevent proper drainage. In cold weather, ice can be a threat to safety. Foul drain incorrectly connected to storm drain. No access to main drain where branch connects. Blockages could be expensive to clear. Plastic inspection chambers in roads may collapse if not surrounded in concrete. Deep but narrow...

Gauge and lap problems

The gauge or distance between the centreline of the battens determines the headlap (lap) or cover that a tile achieves when laid above another tile. The amount of headlap is important - too little and it will not prevent weather penetration. Unfortunately, many roofs suffer from this problem, either because of ignorance by a contractor or because an extended gauge reduced lap can lead to savings in material, time and cost. Occasionally, exactly the opposite may occur. The gauge may be reduced....

General defects

The diagram below shows some of the common routes for damp penetration in houses with solid and, in some cases, cavity walls. Render with a longitudinal crack just above DPC level. A temporary repair to a Render with a longitudinal crack just above DPC level. A temporary repair to a A butterfly roof with inadequate A cill with the drip or throating A slipped plain tile sized lead gutter steps rendered over

General Problems That May Be Experienced By All Types Of Flat Roof

There are a number of defects that are not strictly related to a particular form of flat roof construction, nor the actual covering. Generally, these lead to moisture-related problems. Internal evidence that the defect has led to such a problem includes water staining to soffit ceiling and or adjoining walls at high level water damaged plaster and other finishes and moisture on the soffit ceiling walls at high level. Further evidence may be provided, such as the brown staining that is produced...

Gypsum plasters

The mineral gypsum (hydrated calcium sulfate CaSO4.2H20) was formed by the deposition of salts in inland lakes during the course of many geological periods. As these lakes dried, and as the surface formation of the region altered, the mineral so formed was buried to varying depths. Pure gypsum is white in colour, but small proportions of various impurities cause the colour to vary to shades of grey, brown and pink. The use of gypsum plaster spread to this country from France in the 13th...

Hardcore

The hardcore below the slab fulfils a number of functions. It provides a cheap bulk filler to make up levels and prevents the concrete from being contaminated by the sub-soil below. It helps spread the load evenly across the ground and should reduce the incidence of rising damp (a good quality hardcore has an open, porous structure which limits capillary action). A good hardcore should be chemically inert, easy to compact and should not be affected by water. It should be compacted in layers to...

Historical background

Brick is perhaps the main material which helps define the appearance of a modern house in this country. However, brick has competed with stone in terms of popularity and status for many centuries. Up until the sixteenth century timber had been the dominant structural material for most vernacular buildings. Brick and stone started to be adopted more commonly for a number of reasons, including timber supply shortages and, perhaps more significantly, the disastrous experience of fires which led...