Understanding Building Plans

By Fred Bretze

Figure 1

Whether you are building a multi-storey building, or a house, they all involve plans or blueprints. The bigger the building, the more details in the blueprint, however they are basically all the same when it comes to plumbing.

Plumbers start at the bottom and work their way up, which means the plumber is one of the first trades in. If your company is going to spend millions of dollars on supplying and installing the mechanical system for a multi-storey high rise you better send your best to set it up.

In order to core the holes in the right spot and/or rough-in your stacks in the ground in the right area, you have to be within millimeters on some jobs. If this is done incorrectly, it could cost your company thousands of dollars. This can be quite stressful unless your guy paid attention in blueprint classes in school.

Let’s take a look at some generic blueprints.

Figure 1 architectural blueprint is for a senior citizen complex. We will look at a typical Suite Type A 1:50 scale, paying attention to the GL (grid lines) and the wall construction assembly’s PW2 purple arrow and PW3 red arrows.

Figure 2

Your benchmarks are the horizontal and vertical grid lines (GL) marked in red short dashes. As you can see the cen-cen measurement of the horizontal grid line is 4,500 mm. The vertical grid line is 7,300 mm. In order to rough-in the toilet you must place the WC flange 300 mm from the finished wall and space it out correctly from the lavatory on the right. The first measurement looked at is the 4,500 mm vertical measurement from the top horizontal grid line. You must be 300 mm plus the full width of the wall to centre of toilet flange. Hence you need to locate the full wall measurement. In order to do this, you cross reference to the construction assemblies legend as shown in Figure 2.

PW3–Plumbing Wall Construction in Figure 2 illustrates that you add 13 mm for water resistant gypsum wallboard (GWB), 140 mm sound blanket insulation and 13 mm GWB for a total of 166 mm plus the 300 mm centre of the water closet, which equals 466 mm plus 4,500 mm which equals 4,966 mm of the top red dashed horizontal grid line. This will get you the correct toilet flange measurement off the wall. Then all you have to do is centre the toilet tank off the left wall PW2 (purple arrow) and the vanity.

Figure 3

The next part of this senior citizen home is more fun to rough-in. It involves knowing your commercial kitchen equipment list (see Figure 4) and how to rough it in. We are going to look at just two things for now: #38 & #39 Tilting Kettle SS Floor Pan, and #37 Convection Oven but it should say Combi Oven.

Pay attention to the two red arrows in Figure 5 indicating the waste size (75 mm or 3 in.) for the floor pan and 50 mm or 2 in. waste for the oven. Kitchen equipment is roughed in uniquely. The oven or combi oven is indirectly connected while the Tilting Kettle floor pan has a waste basket in the ground to collect organic matter from soups or chilies.

Figure 4

3-D pictures in Figures 6 and 7 illustrate how each of these two pieces of equipment are actually roughed in.

We can now actually augment blueprints and plans into reality using mixed reality technology, which will make it easier to read plans and blueprints. I can’t emphasize enough how important it is to be able to read a blueprint correctly. Doing it incorrectly is one of the most common and costly mistakes in the field.

Figure 5

My first example of a poorly-planned job was a company I worked for in Edmonton that was involved with the mechanical installation for a group of townhouses in the early ’80s. My job as the all-brawn, no-brains apprentice was to fix 60 incorrectly measured toilet flanges in the basement concrete floors. As it said in our rough-in books at the time, WCs needed to be roughed in 12 in. from the finished wall. The finish wall is the benchmark as walls may have different thicknesses. Most plumbers just guess the thickness of drywall and tile and usually rough in the toilet flange ¾ in. off the rough two-by-four wall. In most residential cases it works, however on a commercial building you should always check the architectural drawings first or you may end up roughing in toilets too close or too far away from the wall.

Figure 6

In this case, I had to break out the concrete floor in 60 basements to adjust the toilets mostly with offset flanges or completely replace the flange and pipe.

Figure 7


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