This paper examines the home as an evolving product. Over the passage of time, the changing tastes of the population coupled with emerging technologies have fashioned the simple house into a series of stereotypes which reflect their era of building. Some changes in techniques, materials and form have brought benefits to homeowners, unfortunately others have not.
An examination of these changes has characterised their influence on structural defects found in real properties. This paper seeks to list those defects most commonly seen in particular eras and charts their origin.
Prior to the industrial revolution, houses were procured via one of two routes. The wealthy and landed entry would employ architects to design their properties, or re furbish them, in the latest architectural fashion. There would be a “keeping up with the Joneses” motivation and a need to reflect the very latest fashions. Such design work is now referred to as “polite” architecture.
Properties for the less wealthy would be fashioned by the local tradesman and artisans, who would nevertheless have an eye for form and detail. Many of the “chocolate box” villages we so adore today were designed in such a way, so called vernacular architecture. Properties would be built from locally sourced materials, as before the railway network existed, there was no viable means of hauling heavy loads over any great distance.
The main phases of house building can, for convenience, be divided up as follows;
- Victorian – pre WW1
- Edwardian – the inter war years
- Post War - the 50’s,60’s and 70’s
The Victorian Years
Although Queen Victoria reigned from 1837 until 1901, there was little change in house building practice up to the first world war. House building on a large scale commenced around 1850. Victorian house building, with the advantage of a national rail network, became industrialised. Materials such as bricks, which had previously be made on site or nearby in small quantities were now mass produced. Roof coverings were inevitably slate which could be distributed nationwide from the quarries of Wales and other locations.
Professional architects had virtually no involvement in house building. Instead, builders relied upon pattern books and magazines. In 1834 J C Louden published “the Encyclopaedia of Cottage, Farm and Village Architecture” and it quickly became the bible. In 1890 a pocket edition of “The Art of Building” was available for 2/-.
The use of pattern books and other guidance resulted in Victoria House becoming stereotyped in their form. Over the page is a layout of the most common Victorian House footprints. It should be noted that the walls forming the external WC’s and stores were often in 102mm thick brickwork, whereas the main walls were built in 215thk bricks. Often, the rear walls of properties have, in recent times, been taken out to enlarge kitchens. Issues with structure, weathertightness and insulation arise when the 102thk walls becoming the exterior envelope of habitable accommodation.
Walls of this narrower thickness were often be used for the gable spandrel above the purlin bearings. Party walls in Victorian properties seldom rose above loft floor level, leading to issues with the passage of fire and security.
Early Victorian roofs were dominated by Georgian idealology, which included hiding the roof behind parapets. The butterfly roof became a common type of roof covering. There are a whole host of servicibility issues with this type of construction. As well as being hidden, debris is easily collected in the central valley resulting in the gutter overflowing.
Overflowing gutters can lead to rot in the main timber beam carrying the roof. Not withstanding the above, the enclosure of the roof with parapets forms an ideal trap for drifting snow. Even if none of the above ills afflict a roof, the likely high deflections in the main timber beam can disrupt the necessary falls in the valley.
By the mid Victorian period, roofs became more traditional with a central ridge parallel to the front wall. It should be noted that roof spread, endemic within traditional agricultural buildings, can occur due to the high deflections in the inevitable undersized roof purlins, see diagram on the following page. Such a characteristic can be observed in circumstances where the ceiling joists have poor (or no) connection to the rafters, or where these joists run parallel to the eaves wall. Whilst there is an enthusiasm for solely stitch repairs to gable end cracking, the only satisfactory long term solution is to strengthen the purlins to prevent high deflections.
Victorian builders did not have the choice of off the shelf beams and lintels that bless the modern house builder. Timber beams were one option available, as was the use of arches. A more prestigious property could utilise stone lintels (or synthetic substitutes). Often the absence of access to the rear garden left Victorian house builders with no other option then a ground floor alleyway running from front to back.
The eaves wall can be carried over the alleyway, at the front and back by a simple arch. Arches are simple to construct and use components already on site eg brickwork. However, arches do produce a horizontal thrust at the springing point. Horizontal movement can be observed in circumstances where there is no lateral support eg an end of terrace.
The long term performance of an arch can also be adversely affected by decay in the mortar, resulting in bricks dropping slightly, and thus disrupting the performance of the arch. Cracking in the masonry above the arch can result.
Many terraces utilising an alleyway running from front to back had a flying freehold over, occasionally switching sides halfway along. The author has observed a small number of examples where the party wall is carried by a continuous arch, which relies upon buttressing from the internal loading walls and fireplaces at right angles to it. Removal of the fireplace caused the arch to start spreading and the need for emergency props to be inserted
Bay windows tend to be a common feature of Victorian properties. Where these bays are single storey, the masonry over is typically carried by a large timber beam, sometimes known as a “bressummer”. Poor construction of the flat roof to front wall intersection can cause water to soak into this important beam resulting in cracking over the bay. However, this damage is just as likely to result from shrinkage in the timber, occurring when central heating is installed into the house.
Two storey bays frequently rely on the window frames to support the rendered panelling as well as the floor and roof. It would be typical of the process of window replacement to provide poorly executed temporary support leading to cracking where the bay meets the front main wall of the house and a downward slope in the first floor in the bay area.
Victorian foundations were normally excavated by labourers working under the supervision of the bricklayers. Their depth would be nominal and the bottom compacted with a large rammer. Where the ground was not so good, the ramming would be more intensive. Unfortunately the influence of the weight of the building extends beyond that depth which hand ramming can be expected to compact the ground.
It is common to see high initial settlements in Victorian properties, particularly in the gable and party walls, as they are the most heavily loaded. Suspended timber floors are typically supported on an oversite concrete slab, but sometimes on their own foundation. The very limited presence of masonry on these sleeper walls means they settle much less than the external walls. For this reason it is common to see ground floors that are “dished”, ie they have settled around the edges but not at the centre.
The limited ventilation of the underfloor spaces along with the absence of DPC’s in crucial places means that rot in the timber is common place. Ground floor joists tend to be fairly shallow, typically 100mm, meaning that notches and holes for services cut in later life, can cause a major reduction in their stiffness.
Despite their shallow, and narrow foundations subsidence of Victorian houses tend to require some trigger for subsidence to occur in later life. Whilst trees can have an effect, by far the most common factor is a leaking drain. The Victorian habit for forming a rear projection utilising the kitchen and with soil and vent pipes and waste water drainage concentrated along the side wall leads to problems with subsidence when leaks occur.
Part basements are a source of differential movement where they exist.
The Edwardian Years
House building in the interwar years was dominated by the Arts and Crafts movement, which had started in the late 1800’s. It was basically a revolt against the standardisation of the Victorian house era and the uniform looks that resulted. There was a strong desire to make buildings look more like the vernacular architecture of old. Architects became involved in the design, and elevations were broken up with different materials, such as render, tile hanging etc. The typical rear projection of the Victorian era was incompatible with a desire to re-create a cottage look and was reduced to a single storey minor projections, sometimes housing a kitchen, other times a WC.
Many in-built problems of Victorian houses remained, arches were common over front entrances and foundations were perhaps a little better. Two important new aspects of construction introduced yet more hazards.
Changing consumer habits needed adjustments to room layouts. Kitchens were becoming larger and first floor and ground floor walls no longer lined up. Consequently, many first floor walls are built off the timber floor joists. Deflection, creep and shrinkage can result in some walls dropping and others not. The diagram shows a classic defect where the wall one side of an opening sits on a wall below, the other side sits on timber joists which have dropped, resulting in a distorted door opening.
The inter war years also saw the widespread use of walls with cavities. The need for tying together of the walls was anticipated, but the need for corrosion protections of ties was not. Inevitable wall ties suffered corrosion. One effect of corrosion is to “lift” the outer skin, another is to destroy the bond between the mortar and the tie making the outer skin unrestrained. Another aspect of wall tie corrosion is the development of horizontal cracks associated with a lean in the outer skin.
Post War Housing
Many changes to house building practice occurred after the war. The use of concrete became common. As a result stiffer mortars were on hand to create shrinkage problems, combined with concrete lintels. There were strong desires to hide anything structural, which meant that support for the inner skin could be provided by off the shelf pre cast lintels, but supporting the outer skin was a problem now cavity walls were the norm. Supporting the outer skin on the timber frame of the windows was common practice right up to and including the seventies.
Another solution was the use of a boot lintel, with a nib to support the outer skin. For aesthetic reasons these nibs stopped at the face of the support. The loading on the lintel now became eccentric. Sometimes, if the construction sequence was undisciplined, these lintels would rotate causing cracking in the structure above. Even without the rotational element, shrinkage in the concrete lintel could cause characteristic cracking in the brickwork above the opening. Occasionally, the use of poorly or untreated steel angles will be encountered with inevitable corrosion.
Before uPVC gutters became available, there was a desire to utilise alternative durable materials for eaves gutters. Remarkably, pre cast concrete units, typically 600mm long, were seen as the answer. The joints between them require a seal that inevitably suffered a short life. Yet again, the introduction of a shrinking component into a brittle material such as brickwork caused cracking.
The sixties saw the introduction of trussed rafter roofs. Their use had first been established in the States, where plywood decking was traditionally used. No thought was given initially to the absence of this stabilising diaphragm when first used in the UK. Consequently, some roofs built in the 60’s and 70’s suffered instability in the rafter members caused by sideways bending in the rafters. The S bend often manifests itself in an uneven overhang at the verge of the gable end.
In the post war years, the structures used to form houses became more ambitious. Trussed rafters allowed the whole of the first floor walls to become non loadbearing. This means the ground floor and first floor wall layouts became almost independent of each other. However, a need for beams still arose and these were typically formed with either steel beams or with reinforced concrete beams. The bars in concrete can, if the “cover” of concrete around them is insufficient, corrode causing the beam to split. Often a problem with lintels. Similarly, steel beams in vulnerable positions can also corrode.
By the early sixties solid ground floors tended to be the norm, having replaced timber ground floors. Builders of the day did not have small compaction plant available. Where hardcore was of some depth, complete compaction was not possible meaning slabs often settled leaving a gap under the skirting. Slabs can also settle unevenly as a consequence of masonry walls being built off a weak slab or a slab supported by poorly compacted hardcore.
During the sixties a variety of unsuitable hardcore materials became available. Some formed from waste from the power generating industry and some from mining. When in contact with moisture, reaction with sulphates could either cause the slab to expand and lift (generally leaving a void) or for the hardcore itself to expand. A heaving slab will normally require replacement.
Another characteristic of post war housing is the detached garage built upon a plain concrete slab. When on clay near trees, some subsidence is inevitable. However, instances of subsidence and cracking along the middle of the slab are common. Even today, there is a bad habit for buttresses to detached garages to be built off the slab. Experience has shown that any tendency for slight heave in the slab can lift the whole of the superstructure.
The second world war caused a shortage of certain traditional materials and left a shortage of certain trades. However, there were many wartime industries that had been making munitions, aircraft etc that were now under utilised. It goes without saying there was a huge demand for housing in the post war period. Methods were devised to use these industries to produce as many components in the factory as possible and to cut down on the use of materials in short supply.
Non traditional Housing, as it become known, is a huge subject beyond the scope of this paper. The main types are
- Steel framed
- Concrete framed
- Large Concrete Panels
- Small concrete panels
Steel framed houses have suffered from corrosion, particularly at their base. Concrete houses have suffered from corrosion of reinforcement resulting in splitting, and caused by poor construction practice, inappropriate admixtures and a tendency for the concrete to become porous.
Many non traditional house types can be identified by either the nature of the roof structure or the manner of the gable and party wall construction.
Hopefully most problems that existed before have been overcome in modern times. Where problems do exist, they are most commonly caused by poor workmanship. One recurring theme is the inappropriate use of raft type foundations. The diagrams below illustrate two situations on a recently built site using controlled fill, with rafts designed by “signature” consultants. Rafts are suitable for spreading the rectangular load of a building onto a material which is slightly compressible but evenly so.
If, for instance, a building straddles the edge of a backfilled quarry, where part is on firm natural ground, the rest on compressible material, a raft will tilt, probably dramatically.
If the building to be supported is irregular, or is linear with varying load, it will settle differently in different places.
Paper written by Brian Margetson BSc CEng FIStructE