direct vertical load , wall will not fail. . 1 ~w all tied at level. roof I I . ~parallel joists provide no tying action. eccentric loading accelerates wall failure. Left: A wall will not usuallyfoil under compressionand thefloors and roofjoists often provide sufficient support. Right: Paralleljoints, however, provide no tying action and this can lead to bowing and failure. the outer skin to move away. This is not disastrous because, again, simple stainless steel resin anchors can give the outer skin lateral restraint. In such properties the construction of the floor related to the walls is very important in that sometimes in the rather better built houses there are main beams with secondary beams whilst in those of poorer quality the floor joists span directly onto the wall. When it has been established which way the floors span, the question as to whether there is adequate lateral restraint to the walls can be decided and additional restraint provided if necessary. The floors themselves will provide adequate lateral restraint by their place action. Quite often we ask for floor boards ro be screwed down, or in extreme circumstances plywood laid over the floor in two layers screwed down and then the floorboards replaced. U nfortunacely this inevitably causes problems with skirtings and doors, bur it sometimes is the least of several evils. When surveying brick-built structures, I have rarely felt it necessary for there to be any major rebuilding. If a wall is standing at the time of the survey, logically if one provides it with some additional support it can remain for a very long time. An example of this CONTEXT 40 occurred recently when I surveyed a house in Belgravia after two surveyors had surveyed a property and indicated that the front and side walls ought to be rebuilt because they were bowing. I was able to establish fairly quickly that the front wall had been in its bowed and outof-pl u mb condition for some time because the floor boards were cut to it. There was very little restraint of the gable wall in the total height of the wall because the floors did not span onto it; there was also an open well staircase. We have simply specified some additional restraint to be provided through the floors. Bear in mind once again that the restraint force required is very little. Ian Hume in his talk indicated simple load-test methods by hanging buckets of water from the underside of joists, particularly to check on their deflection, and there are many simple tests chat one can carry out to give one an idea of the overall stability of a particular element. An example is simply to jump on the floor, feeling the bounce. When this has been done a few times experience is gained as to what one should expect and what is acceptable; the effect of a large man suddenly jumping up and down in the middle of the room generally amuses most clients! If the strength of a timber member is in doubt because of some form of infestation, the use of a rechargeable drill with a masonry bit acts as a first class probe to tell whether the core of the timber is still sound. Probing of timber members or mortar joints in brickwork with a long chin screwdriver will give one a very good impression of the overall condition of structural elements. More scientifically, of course, the use of a borerscope into hollow structures will help out with the overall analysis. I carry in the boot of my car a 4ft builders' level which has proved to be of enormous value in assessing the plumbness of walls and the our-of-level of floors. Particularly good use of the level is when looking at a call building with internal timber stud wall construction, such as in the Nash terraces around Regents Park, where it will be found that the central area of the building will have sunk possibly up to two or three inches at the upper floors and very little by the rime one gets to the ground floor. In these circumstances the level will indicate whether the same situation is occurring in the lower floors. With this form of construction, shrinkage of the timber head plates and sole plates at each floor level causes the downward movement. We have found that clients sometimes find this difficult to believe. Inevitably, of course, the movement is great at the upper level and decreases as you come down through the building; the builders' level will show this up even if the movement is quite minor at the lower levels. I remember looking at a Church in Wales where an engineer had condemned the building because he said that the gable end was moving out. Visiting the site with my level, I found that the lower 10ft of the wall indeed leant out quite considerably, but the upper level was absolutely plumb. Investigation of the ground indicated that it was grossly overloaded at the time of construction. The initial movement had occurred and then the upper section had been built on plumb. This is quite a usual situation to find in churches and cathedrals where perhaps only I Oft a year was built. The structure was allowed to settle and they simply corrected the out of plumbness when they continued building. To sum up, look at the form of the structure and assess the problem areas; jump on the floors; check with a builders' level, and generally form con cl us ions based around these simple facts that I have attempted to outline in this article. Brian A Morton CEng MICE Dip Conservation (AA) is Consultant to The Morton Partnership Ltd. 25
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