Back to basic - understandable, readable and constructable shop drawing

Posted by mashrabiya | Posted in | Posted on 2:35 AM


A shop drawing is a drawing or set of drawings produced by the contractor, supplier, manufacturer, subcontractor, or fabricator. Shop drawings are not produced by architects and engineers under their contract with the owner. The shop drawing is the manufacturer’s or the contractor’s drawn version of information shown in the construction documents. The shop drawing normally shows more detail than the construction documents. It is drawn to explain the fabrication and/or installation of the items to the manufacturer’s production crew or contractor's installation crews. The style of the shop drawing is usually very different from that of the architect’s drawing. The shop drawing’s primary emphasis is on the particular product or installation and excludes notation concerning other products and installations, unless integration with the subject product is necessary.

(http://en.wikipedia.org/wiki/Shop_drawing)

From my perspectives and experience here shop drawing is derives from coordinated drawing between all disciplines (architecture, mechanical, civil, structural and electrical) and suppliers details. The coordination task is mainly under the main contractor’s responsibility.

Architect / Draughtperson should put in mind these 2 things :
1. What kind of information required
2. Who will read the drawing

Its like when you buy furniture from IKEA which you have to assemble yourself, you’ll be given a diagram on how to put up the furniture together. The diagram should be easily understandable by the customer be it the customer is a skilled class worker or a layman. It’s the same when we are talking about shop drawing. It should be able to be read by the installer/builder.

For this project, all the drawing are organized and prepared by the main contractor. It is contractor’s responsibility to ensure it is fully coordinated to meet the specifications as prescribed in the contract documents/drawings. The architect as the head of design department should ensure the drawing issued for approval is properly coordinated with structural, civil, mechanical and electrical discipline.

I remember during my matriculation centre, we have been taught about technical drawings in our graphic communication subject. We have been introduced to architectural floor plan, elevation, section and axonometric. These are common communication tools used in building construction. There are even various kind of plans depending on what purpose of the plan or what information to show. For example, site plan, building plan, landscape plan, reflected ceiling plan etc. Different plan require different set of information. Plan with crowded information not always the best as it may be confusing and distracting if it is filled with unnecessary and repetitive information. It goes back to 2 aspect to be taken into account as noted previously. To summarize, here are the things that I have gone through during checking the shop drawing.

LETTERING SIZES – specifications sizes too small. No standardization on the lettering format. Not to mention the arrows for the specs, too small, missing and incorrect point. I got to admit that looking at drawing that is hardly to read is frustrating and affect the emotion of the checker. Though I as possible as I may to be professional, I just couldn’t help if the mistakes repeat more than twice.


DIMENSIONING – dimension is the most important information to give rough idea on the sizes especially to the fabricator even they have to do site measurement for confirmation. Unnecessary dimension should be avoided. Give clearer point of dimension from A to B. Give set out point, think on how the builder going to start, what dimension do they need. More consideration on dimensioning if the shape of the building is curvy or irregular such as angle, radius etc.

LINE WEIGHT – basic aspect on graphic communication in drafting. One should able to identify on which one need bold line and which are not. In elevation, one that stands out or much to the front is bolder than the one beyond. In details, the one with solid/rough build up should use thicker line such as concrete, structural I beam. The lighter materials use thinner line. The thinnest line should go to hatching as I just an indication of materials and in some cases its better not to hatch than the opposite.

SCALE – scale of drawing will determine the complexity of the information delivered. Depends on the size of the project, some drawing require blow ups or enlarge details up to five times. The drawing should able to give information required and readable. If the drawing is too crowded, some section/part may be excluded and blow up with bigger scale for clarity. Nevertheless, the sizes of lettering should remain the same/standardize even the drawing scale is different.

BUBBLE REFERENCES / ANNOTATION – reference bubble are use to indicate a blow up or section details to be referred to another drawing. Reference number should refer to correct drawing/details. This mistake could have been avoided if proper drawing management is developed.

CONSTRUCTION SPECIFICATIONS WRITING – specifications is very important to be written correctly as it will incur cost, procurement and contractual implications in a construction project. As the shop drawing will be a legal document, it is essential to thoroughly checked and standardize the specifications. I have encounter a few cases where the specs in one drawing differ with another drawing even it’s the same thing. It is the architect / coordinator’s responsibility to ensure the specs is as per approved materials and method statement.

PRESENTATION – aesthetic is the most important consideration in architecture. The way we want the building look nice, it’s the same with the drawing. It should be presentable and neat. Things such as alignment of lettering, overlapping of specs and drawing, blank space occupy most of the drawing area and arrangement of drawings/details should be taken care of in the 1st place.

I could not refrain myself from putting half of the blame to the technology. With the advance drafting method using computers, Computer Aided Design (CAD), by right it should make the drafting more accurate and less mistakes. However, it as per says about computer technology, ‘garbage in garbage out’. It still depends on the users/drafters itself. The architect in charge / coordinator should ALWAYS do the final checking of the drawing before issuing it for approval by the consultant.


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