Wimpey NoFines Houses

This form of construction involves the use of no-fines concrete, ie concrete containing cement and graded aggregate (often 12 or 19mm in size), but no sand nor fine aggregate. The lack of fines results in a wall that can be cast more economically than a normal concrete mix and which contains many air gaps, giving some improved insulating capability. It is also more resistant to damp penetration as its wide pore structure reduces capillary action (refer to Chapter 14 on Damp). The first recorded...

Cracking along edges of angle beads

Vertical cracks at quoins or at window jambs are often caused by problems with angle beads. In traditional work angle beads were rare but, nowadays, their use is widespread. It is, unfortunately, not uncommon to find angle beads bedded in gypsum plaster. This material sets quickly and is often seen as an ideal material in which to bed the beads. In wet conditions a chemical reaction between the cement and the gypsum (sulfate attack) causes expansion of the render and this will result in...

Conductance meters

These instruments, which are by far the most common form of meter, have two metal probes (the electrodes) which are firmly pressed into the material being tested. The electrical resistance between the two probes can then be measured. The meters (depending on type) can provide analogue or digital readings. The Mini meters have coloured LED lights (green, yellow and red) representing 'safe' , 'borderline' and 'decay inevitable' situations. On the extreme left, a Protimeter Mini Moisture Meter. On...

Natural slate

Slate covered roofs can be found throughout the British Isles and can range in colour from red black to green blue depending upon the source which, historically, was within the UK. The popularity of slate roofing declined in the first three quarters of the twentieth century but there was a revival in the last quarter. This has led to the re-opening of some formerly closed quarries to meet the increased demand. In recent years, foreign slates, in particular from Spain and China, have also become...

Frost attack

This is a problem that usually occurs in older bricks, and those that were underburnt on firing. In newer construction, failure through frost attack tends to be confined to areas of severe exposure. The ability of bricks to resist frost attack is determined by their pore structure (in particular the percentage Three examples of frost attack to bricks in exposed situations. Three examples of frost attack to bricks in exposed situations. of fine pores). Frost attack occurs through a combination...

Lead roofing

Lead sheet is commonly used as both a pitched and a flat roof covering, as well as for gutter linings, flashings, soakers and vertical claddings. Roofing and cladding panels of lead bonded to steel over a plywood, or other, building board, and lead bonded directly to building board are also produced. These may be used for roofing or cladding. Lead has been used as a roofing material in the British Isles for many hundreds of years. In medieval times, it was used as the roof covering on...

Conditions favourable to insect attack

The likelihood of attack will depend on a variety of factors, including the species of timber, its condition and the temperature and humidity of its environment. It is noticeable for instance that flight holes in floorboards to suspended timber floors often exist predominantly on the underside that is facing into the damper void rather than the dryer room. Although the insects generally like damp timber excessive moisture is by no means a critical factor. However low moisture content in timber...

The nature of stone

Stone is a natural material which is derived from one of three basic rock formations igneous, sedimentary or metamorphic. IGNEOUS. These rocks were originally formed from the cooling and solidification of molten magma - the name is derived from ignis, the Latin for fire. Building stones derived from igneous rocks are generally durable. Granite is an example of an igneous building stone. METAMORPHIC. As the name suggests these rocks were produced by changes brought about in existing rocks. The...

Essential conditions for wood decay

Fortunately fungi will only be able to survive and to thrive in certain conditions these are discussed briefly below FOOD Susceptibility to fungal decay varies between the different species of timber. In general, the sapwood will be attacked because it contains the food, although in certain timbers such as beech, birch and spruce the heartwood is equally susceptible. Modern construction tends to use timber from relatively young trees which therefore tend to have a high proportion of sapwood....

How Rising Damp Occurs

In liquids, surface tension is a result of cohesive intermodular forces. These cohesive forces are the reason why rain falls as small droplets. The molecules at the surface of the liquid are attracted inwards this attraction results in the liquid trying to minimise its surface area and forming the shape of a sphere. If the liquid is in contact with another material there will also be some adhesion between the molecules in the liquid and the material itself. So, there are two forces the cohesion...

Defects at upstands and skirtings

The junction of a roof with adjoining walls and penetrations, such as pipes, flues, access hatches and rooflights, is a common point at which failure occurs. The roof covering is required to be turned vertically through 90 degrees in order to form an appropriate upstand skirting that is watertight. Failure can occur for a number of reasons including Splitting along the 90 degrees turn in the covering, as it is weakened by the initial formation of the bend in the material, or by subsequent...

The remedial treatment of dry and wet rot

It is important that the cause as well as the symptoms of a rot outbreak is adequately dealt with. The first step in remedial treatment for rot is to determine the cause of the outbreak. This will involve finding and eliminating the source of dampness and rectifying those faults which have contributed to the problem. Fungal decay happens because conditions are created which allow for the germination and evolution of an attack and the key factor in creating and maintaining these conditions is...

Defects In Timberframe Housing

Timber frame became so popular that by the early 1980s nearly a quarter of house building starts used this method of construction. However, at this time reports of a number of defects in relatively new timber-frame housing began to emerge. These reports, which included a damaging television broadcast, led to a decline, (since reversed), in the construction of timber-frame houses. Volume house builders withdrew from timber-frame construction on the assumption that adverse publicity would affect...

Lateral Pressure On Retaining Walls

Retaining walls are subjected to a mixture of lateral pressures and they must always be designed and constructed to withstand them. The principal pressure is normally formed by the force exerted by the volume of soil supported but this is often increased by further applied forces. These may include groundwater pressure, loads from adjoining buildings and loads from traffic on nearby roads. The higher the ground being retained, the thicker the wall, although it can be of stepped width -retained...

Builtup mineral felt

This roof covering consists of two or, preferably, three layers of felt, bonded with hot bitumen. The exact number of layers depends on a number of factors (eg whether a partially bonded first layer is needed to accommodate substrate movement the type of reinforcement in the individual layers -polyester felt membranes normally consist of two layers, glass and other fibre membranes of three). The top layer is normally finished with small chippings or, sometimes, reflective paint to provide...

Wind related damage

There are a number of potential problems that may be experienced by flat roofs because of the effect of the wind. They are discussed below. (The general background to this subject is discussed in Chapter 7 in the section entitled 'Wind-related damage'.) THE EFFECT OF SUCTION. As with pitched roofs, negative pressure (suction) is a greater problem than positive pressure and affects the edge of the roof (the eaves and verges) more than the central area of a flat roof. This is because maximum...

Flemish Garden Wall Bond

Brick Wall Corners With Rendered Wall

In 'true' bonds headers must be exactly the right length If the wall Is to have a fair face both sides. In garden wall bonds, with their fewer headers, waste Is reduced. English Bond comprises a row of stretchers followed by a row of headers. English Bond comprises a row of stretchers followed by a row of headers. A quarter brick known as a Queen Closer is required to line up corners and openings. A quarter brick known as a Queen Closer is required to line...

Typical installations of the early twentieth century

During the first 40 years of the twentieth century millions of low rise houses were built, as towns expanded and the suburbs were created. Most of these houses adopted the two pipe system of drainage. Discharge pipes were made from cast iron, with yarn and lead joints, or asbestos cement with cement mortar joints. The discharge stacks were connected to the mains drainage by salt glazed clay pipes (salt glazing provides a smooth surface and improves impermeability). An interceptor, or rat trap...

Drip Problems

Lead Chase Into Mortar Detail

Too small an overlap may lead to moisture penetration. A minimum overlap of 100mm is required for the overcloak to prevent capillary problems. Too small an overlap may lead to moisture penetration. A minimum overlap of 100mm is required for the overcloak to prevent capillary problems. Undercloak should be minimum 90mm long. A ridge step will be formed if the deck is not rebated (ponding may result). Undercloak should be nailed at 50mm centres (not less than 25mm from end). Minimum height of...

Common Defects In Pitched Roofs At Construction Stage New Build

Weakening of timbers due Rafters, purlins and other roof components inadequately sized. Roof structure too weak to cope with roof covering and or imposed loads and or wind. Bowed and or split timbers. Deflection of overstressed roof members. Dishing of roof. Rafters, purlins and other roof members omitted. Structural integrity of the roof compromised. Bowed and or split timbers. Deflection of overstressed roof members. Dishing of roof. Roof trusses inappropriately...

Wall tie failure

Failure of wall ties has become a significant problem in recent years. The main cause of failure is rusting of metal ties, although there can be other causes, such as a failure to properly bed the tie in the mortar joint, poor quality mortar reducing the bond between tie and mortar, or not installing the requisite number of ties. The obvious danger with rusting wall ties is the possible collapse of the outer leaf of the cavity wall. These rusted mild steel galvanised ties are from a house built...

Common defects of PRC houses

This is a problem that affects reinforced concrete and has been discovered across a broad range of PRC houses. Carbonation is a natural process that takes place in all concrete but, where insufficient allowance has been made for its effect, it can have disastrous consequences on reinforced concrete, as it can lead to corrosion of the steel and cracking spalling of the concrete. Fresh concrete contains calcium hydroxide which is highly alkaline and protects the steel reinforcement, preventing it...

The form of pitched roofs

Green Roof Post Joist

The simplest form of pitched roof is the lean-to or monopitch roof that is commonly found above many rear extensions of Victorian houses. It can also be found as the roof form on a great number of housing estates built since 1960. Originally such roofs were constructed on site from individual timbers but the modern version is normally formed with trusses and often has an extremely low pitch 17.5 degrees or less . A lean-to roof can only span a short distance but a simple double pitch or couple...

Statutory Nuisance

Some bad housing conditions can amount to a statutory nuisance, which is a criminal offence. The low relating to statutory nuisance is now set out in the Environmental Protection Act 1990 EPA , which largely, but not entirely, replaced the Public Health Act 1936 PHA . The definitions of different types of statutory nuisance are set out in the EPA and the PHA and include the following which may be relevant to bad housing conditions i any premises in such a state as to be prejudicial to health or...

Late Victorian Terraced Housing

Victorian Load Bearing Walls

1905 - middle class terraced housing in Plymouth with basements . 1905 - middle class terraced housing in Plymouth with basements . Foundations Until about 1890 or so most walls were laid direct on subsoil. Larger properties sometimes had brick footings. From about 1890 many houses had shallow concrete footings. Walls One-brick thick external walls in Flemish bond or English Garden Wall bond. Stone walls still common where stonework occurred locally. A few houses had cavity walls external leaf...