Section Through Building

Minimum And Maximum Dimension Drawing

3.11 Assembly detail from PSA Standard Library. Its simplicity contrasts sharply with the complexity of the detail illustrated in 3.12. What they have in common is that each conveys clearly and precisely the information needed by the operative carrying out the assembly an appropriate scale for the benefit of the assembler. Figure 3.11, taken from the UK Department of the Environment's PSA Library of Standard details, is an assembly drawing. Figure 3.12, part of Foster Associates' highly sophisticated detailing for the Willis, Faber and Dumas head office building in Ipswich, is another. A world of technology lies between them, but each drawing has in common that it defines how a number of component parts are to be put together.

With the assembly drawing we arrive at the very heart of the information package. If the location drawing is in many ways simply an ordered confirmation in building terms of planning decisions made long before, whilst the component drawing is frequently a documentation of the architect's judicious selection, the assembly drawing poses that most searching of all our questions, 'How is it

Willis Faber And Dumas Window Details
3.12 Assembly detail from Willis Faber and Dumas Head Office Building (Foster Associates)

to be built?'. Before he attempts to document his answer in a manner which is going to be acceptable to the users of the document, the detailer must not only be confident that he knows the answer, but also that he is aware of the full implications of the question.

It was stated at the outset that this book is not intended as a textbook on building construction, but it would be futile to pretend that the preparation of a set of working drawings can be regarded as an academic exercise, to be undertaken without reference to its content. Clearly form and content interact, and the point is raised now because it is precisely here, in the area of assembly detailing, that the really fundamental questions of adequacy emerge:

• Will the construction function adequately?

• Is the method of presentation adequate?

• Does the range of detailing anticipate adequately all the constructional problems that will be encountered by someone trying to erect the building?

Check lists are of limited value. There is really no substitute for the complete involvement of the detailer in his task, for an intelligent anticipation of the possible difficulties, for an alert awareness of the total problem while individual aspects of it are being dealt with. Nevertheless, it is useful at times to review one's work formally, if only because to do so concentrates the mind wonderfully. Since two distinct aspects of detailing are involved, two lists may be formulated.

The first, aimed at establishing the adequacy of the individual assembly detail, is a series of questions:

1. Is the chosen method of construction sound, particularly with regard to:

• possible movement

• water or damp penetration

• condensation

• cold bridging

2. Has it been adequately researched, particularly if non-traditional methods, or the use of proprietary products, are involved?

3. Is it reasonable to ask someone to construct it? Figure 3.13—taken from a real but anonymous detail and calling for an improbably dexterous plasterer—is an example of the sort of thing that can occur when this question isn't asked.

4. What happens to the construction in plan (if the detail happens to be a sectional view) or in section (if the detail happens to show a plan view)?

5. Is the result going to be acceptable visually, both inside and outside?

6. Does the information concerned give rise to any possible ambiguity, or conflict with other information given elsewhere?

These questions are self-evident, and the conscientious draughtsman should have them in mind constantly from the outset of the detailing. They are noted here because it is probably better to pose them once more, formally, on completion of the series of details, than to have to worry about them at random in the small hours of the morning at some later date.

The second check list, aimed at determining the completeness of assembly detailing throughout the building, is more capable of precise definition. The objective is to cover the building comprehensively, identifying those aspects which merit the provision of assembly information about them. A logical progression is essential, and a suitable vehicle is readily to hand in CI/SfB table I (see table I in chapter 1) for not only does this provide an analysis of the building in elemental form but it also affords a framework within which the necessary details, once they are identified, may be presented.

It should be noted here that almost all the assembly detailing with which the architect will be concerned is confined to the primary and secondary elements, sections (2-) and (3-) of table I. (The range of built-up fittings inherent in section (7-) should in general be regarded as components rather than assemblies.) Nevertheless, the exercise should be undertaken comprehensively.

3.13 Not an easy task for any plasterer 58

if up

Amco Barrier Foundaion

3.15 Scale of 1:5 is necessary to show this detailing adequately

The important things to note about assembly drawings are these:

1. The scale must be appropriate to the complexity of the construction being detailed In practice this will involve a scale of 1:20 being used for a wide variety of constructions, with a scale of 1:5 being used where greater detailed explanation is required—eg where the exact positioning of relatively small components such as bricks or tiles is a vital part of the information to be conveyed.

The level of draughting ability may well be a deciding factor when details are drawn manually. But don't be over-optimistic, the mere fact of drawing to a larger scale will force you into consideration of problems which might have been glossed over at a smaller scale. It is the operative ultimately who will be asking the questions and requiring the drawn answer. And he will be building full size.

Figures 3.14 and 3.15 at scales of 1:20 and 1:5 respectively are appropriate examples of the information it is necessary to convey. Note that the damp course in 3.14, being a simple layer of lead-cored bituminous felt, can be shown adequately at the smaller scale, whereas the damp course in 3.15 is a much more complex piece of work, with all sorts of hazards should it be installed incorrectly, and justifies its more expansive 1:5 treatment.

2. The information given should be limited Perhaps concentrated is the better word. For it is more helpful to produce twenty assembly sections, each covering a limited portion of the structure, than to attempt an elaborate constructional cross-section through the entire building purporting to give detailed information about almost everything.

Figure 3.16 reduced here from its original scale of 1:20 is a good example of how not to do it. All that has been achieved is a very large sheet of paper, consisting of an internal elevation at an inappropriately large scale

Section Through Building

3.16 Old-fashioned section through entire building. Far too detailed for its role of conveying information about the form and nature of the building; insufficient for anyone to build from with confidence 60

surrounded by a margin of detailing which through necessity has been portrayed at a smaller scale than would have been desirable. The drawing has clearly taken a considerable time to produce. This in itself may well have led to some frustration on the part of the builder or the quantity surveyor, who needed urgently to know the damp course detailing in the bottom left-hand corner, but had to wait for the gutter flashings at the top right-hand corner to be finalised before the drawing could be issued to him.

At the end of the day we have been shown in some detail what happens to the construction along a more or less arbitrary knifecut through the building at one point. It is to be hoped that the detailing is consistent right round the perimeter, because the detailer is not going to be anxious to repeat the exercise whenever the construction changes. Were he to do so he would find himself re-drawing 80 per cent of the information time and again in order that changes in the other 20 per cent could be properly recorded.

The more sensible way to deal with providing this sort of information is to prepare the assembly details in conjunction with, and related back to, the series of location sections described and advocated in the previous section on location drawings. The relevant information would then be cross-referenced on the lines of 3.17 and 3.18.

3. The assembly drawing should not be used to convey unnecessarily detailed information about the components from which it is to be produced. Consider the assembly section shown in 3.19. The window frame is a standard section and will be bought in from a supplier ready for fixing into the structural opening. There was no need therefore to detail so lovingly and so explicitly the profiles of the frame and sub-frame, right down to the glazing beads and the throatings—they are matters of moment to the manufacturer in his workshop, not the erector on site. (The matter of prime importance to the erector, the method of fixing, is not mentioned at all—let us charitably assume that the point had been covered in the specification.) The only piece of information this assembly detail need convey about the window is its relationship to the surrounding components.

The detail might have been produced more simply and speedily as shown in 3.20.

On the other hand it would be pedantic, especially on smaller projects, to reject the possibility offered by its large scale and availability of space round its margins, of providing descriptive annotation which it might be inconvenient to provide in another form. As elsewhere, comprehensiveness and common sense are the deciding factors.

4. The information conveyed should be both comprehensive and, within the limits already defined for an assembly drawing, exhaustive It should be comprehensive in the sense that the individual detail must contain all that the operative is going to need when he comes to that point on site. The detail may have been produced primarily to show the detailing of the window cill at a particular junction, but if it purports to show this junction then others will expect to use it for their own purposes, and it is no use being explicit about the window cill and vague about the wall finish beneath it. An assembly drawing is, by definition, a correlation of all the elements and trades involved.

So too the information should be exhaustive in the sense that no aspect of the construction, no variant on a basic detail, should be ambiguous or left to the discretion of the operative. 'Typical details' are just not good enough.

Coding assembly drawings

A complete system for coding the drawing package is discussed in chapter 5, but a note here on the coding of the drawings illustrated in 3.17, 3.18 and 3.20 may be helpful.

The location sections (3.17) are coded L for location, (2-) for primary elements (see location sections earlier for the reasoning on this), 017, 018 and 019 because that is their sequence in that particular series.

The references in the circles are to external wall details or to external wall opening details ie, to windows) and are therefore coded respectively A for assembly, (21) for external walls, followed by their number in the sequence of such details; and A for assembly, (31) for external openings, followed by their number in the sequence of such details.

The assembly section (3.18) is coded: A for assembly, (21) for external walls, 021 because that is its number in the series.

The assembly section (3.20) is coded: A for assembly, (31) for external openings, 001 because it is the first in that series.

It is not unreasonable to give a (21) coding to the section shown in 3.18, for it clarifies the construction of an external wall. But then so does the section illustrated in 3.20. Why not code that (21) also?

The answer is that it would be perfectly in order to do so, and if you elected to produce a series of details devoted to the assembly problems encountered in constructing the external walls, then you would code them A (21) 001, etc accordingly. But it is more likely that in commencing a series of details showing the junctions of two elements—for example, the junction of external openings components with the external walls within which they sit—you would find it more convenient, and a better guarantee that you had covered the subject comprehensively, to produce a series of external openings assembly details—and these would naturally fall into the (31) series.

The examples of assembly details illustrated have consisted of vertical sections through a particular construction, but of course the plan section also requires illustration and enlargement at certain key points—doors and window jambs, for example.

Where this is the case, and where space allows, it is better to group plans and sections together by their

Building Section Through GlassSection Drawings Spaceships

3.17 Location section provides references to where more detailed assembly information may be found

External Door Vertical Section

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  • robert
    How to do a building section?
    4 years ago

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