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Architectural Drawings

MEP Academy Instructor

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September 27, 2020

Chapter #2 – Architectural Drawings (How to Read Construction drawings)

You will need to understand how to read the Architectural drawings as they have information that can impact the cost of the Mechanical estimates. This section will cover some of the Architectural drawings and what to look for when bidding a Mechanical project. This section is not an extensive coverage of Architectural drawings, but is intended to provide you with the knowledge on what to look for when bidding the mechanical portion of the project.

Architectural Drawings

You should be able to understand how to read the basic information on the Architectural drawings as these drawings are the foundation upon which all the other trades are drawn. The Architect designs the building, while the structural engineer figures out how to support the design. The Architectural design set may include the following drawings.

Cover Sheet
General Notes, Drawing Index, Abbreviations, Code Info
Plot Plan (site plan)
Foundation Plan
Floor Framing Plan
Floor Plans
Roof Plans
Reflected Ceiling Plan
Window and Door Schedules
Wall Sections
Elevation Plan
Details and Section Views

Architectural Floor Plans

You can use the Architectural floor plans to identify the name and use of a room. The drawings will show the room layout with walls, doors and windows. Each room should be identified by a room number and room name.

If you’re not familiar with reading drawings then you’ll need to study the background carefully to discern the various ways in which building items are represented on the drawings. Just like in real life the first one or two letters of the room number will indicate the floor its located on, as in this example here all the room numbers begin with 1, so we can assume this is the first floor.

As can be seen in the above image of the bathroom area taken from the floor plan of an Architectural drawing, there are symbols for each of the bathroom fixture. We have highlighted all the walls in yellow to make it easier to see each room.

Reading a set of construction drawings requires that you learn basic drafting guidelines and the symbols used to convey meaning, much like a traffic sign tells you what to expect up ahead.

Reflected Ceiling Plan

The reflected ceiling plan shows you what type of ceiling is used in each room. Below is an example of a small portion of a building, showing the type of ceiling used. With each set of architectural drawings there will be a legend for the ceiling types used in the set. (See legend below)

The below reflected ceiling plan identifies the type of ceiling, light fixtures used and the height (yellow highlight) of the ceiling in each room. Looking at the reflected ceiling plan above you can also see that Supply (blue highlight) and Exhaust (green highlight) grills are shown on the ceiling in addition to the lights.

The HVAC system ductwork and air distribution grilles are overlaid on the reflected ceiling plan. By looking at the reflected ceiling plan below and the legend above you can identify the type of ceiling that each air distribution is set into.

For any volume damper hidden above a hard lid ceiling you will need a remote damper operator or an access panel to provide a means for adjusting the damper. The remote damper operator allows you to adjust the volume damper without needing to remove a piece of the ceiling (see Sheet Metal Specialties).

Fire Rated Corridors

In large commercial buildings you will often find that the corridors are fire rated to protect the occupants in case of a fire. There are several common methods of rating the emergency exit ways. Fire rated corridors are important to the HVAC industry because under certain circumstances when a supply, return or exhaust duct penetrates the fire rated assembly, which could be the wall or ceiling, a fire or fire/smoke damper could be required.

The corridor or emergency pathways are rated to allow sufficient time for the occupants to evacuate the building in the case of a fire. The rated corridor or pathway will prevent the fire from spreading long enough for the occupants to get out. The area shown in red above is the emergency pathway or corridor that is fire rated.

Fire Rated – Slab to Slab System

In this method of fire rating the exit way, the use of rated walls extending from the floor all the way to the deck above provide protection. There is no rated ceiling, as the deck above is considered a fire barrier.

Fire rated walls - slab to slab — Fire rated walls – slab to slab

Fire Rated – Tunnel System

This version of a fire rated exit way is constructed in a tunnel configuration that’s fire rated for the purpose of protecting the occupants during an emergency situation. With the tunnel rated system if you penetrate the rated tunnel ceiling to install a supply, return or exhaust grille you will be required to install a fire damper or a fire/smoke damper to maintain the fire rated construction.

Here are the two most common fire rated construction methods side by side for comparison.

Detail Drawings

In order to show how certain aspects of the construction is to be built in greater detail each trade will provide a detail drawing. These drawings show various components of construction in greater detail. This allows the installers a more accurate detail of what the engineer expects in the way of material and methods in a visual format as opposed to the specifications.

Architectural Sheet Test-Question — Architectural Detail Drawing

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Now click the link below for Chapter #3 “Plan, Elevation, Section Views and Details” to get an overview of these drawings.

Chapter #1 – General Layout of Drawings
Chapter #2 – Architectural Drawings
Chapter #3 – Plan, Elevation, Section Views and Details
Chapter #4 – HVAC Mechanical Drawings
Chapter #5 – Understanding HVAC Symbols
Chapter #6 – Drawing Scales (How to Read Scales including Metric Scales)
Chapter #7 – S h eet Metal Shop Drawings

General Layout of Construction Drawings

MEP Academy Instructor

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September 27, 2020

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Chapter #1 – General Layout of Construction Drawings

Reading a set of construction drawings requires that you learn basic drafting guidelines and the symbols that are used to convey meaning, much like a traffic sign tells you what to expect up ahead. The larger and more complex the project, the more drawings will be contained within the set. All the drawings together will provide for a fully constructed project, covering everything from the structure to the mechanical systems.

Reading Construction Drawings

In this first chapter we will cover how to interpret the meaning of the various lines, references, sections and the general layout of construction drawings.

Drawing List could include the following Trade Drawings;

Cover Sheet
Index
“G” General
“C” Civil
- Roads
- Parking
- Site Utilities
- Grading Plan
“L” Landscape
“A” – Architectural
“S” – Structural
“M” – Mechanical
- HVAC Sheet Metal
- HVAC Piping
“E” – Electrical
- Power
- Lighting
“P” – Plumbing
“FP” – Fire Protection

Title Block

The main purpose of the title block is to identify the project and engineers involved in the design. Also included is a place for the individual responsible for the design and a date; a place to record the progression and date of any milestones such as a plan check set, addendums and their date. Title blocks can run horizontally along the bottom of the page or vertically along the right edge of the drawing. The title block should be visible when the drawings are rolled up, that way you can tell without having to unroll them which project it is related to.

Revision Block will show any changes made to the drawings since they were issued. You might also find the original issue date and comments such as “Issued for Construction”. A revision number will be given that corresponds to clouded areas on the drawing where changes were made under this revision number.

Grading plan – shows the new and existing grading, the contour of the land.

Location map shows where the property is located on a Google map or other source.

Key Plan – this shows you where in the building the current drawing is located in reference to other sections of the building.

Site Plan (Plot Plan) – this shows how the building structure is situated on the plot of land it’s built upon. The site plan shows the contours, boundaries, roads, utilities, trees, structures, and other significant physical features on or near the construction site. It shows the locations of proposed structures in outline.

The site planshows the survey marks, including the bench mark (BM), with the elevations and the grading requirements. Surveyors use the plot plan shown below to set up the corners and perimeter of the building using batter boards and the line stakes. The plot plan furnishes the essential data for laying out the building.

The yellow lines highlighted in the image below shows the property line, while the blue highlighted area shows the building area as it’s located on the property.

There will be a north arrow somewhere on the drawing providing the orientation of the building to North, this is especially important when doing heating and cooling loads. Depending on which hemisphere you’re in, this will determine which exposure get shade and how the sun hits various aspects of the structure, effecting its heat gain or loss. The north arrow is shown in the upper right hand corner of the below drawing.

The site plan is drawn at a small scale so that everything fits on one page including the property boundaries. As you can see in the example site plan below, the driveway is shown entering off of the roadway. A dimension is shown indicating how far each corner of the building is in relationship to the property line or boundary.

Another item of interest on the site plan is the building finished floor elevations for the garage and floor plan. The length of the properties boundaries are also shown.

Electrical Drawings

You should be able to find all the HVAC equipment that requires electrical power on the electrical drawings. Shown below are two VAV’s (VAV 1-5 & VAV 1-6) that are provided with electrical power. You can read the description as circled in red as the electrical panel number and the circuit in that panel, such as; P5-16 (Panel 5, Circuit 16).This indicates that VAV 1-5 has electrical conduit and wire coming from panel 5 and circuit #16 in that panel.

Structural Drawings

The structural engineer will design the support framing for the building in addition to miscellaneous equipment supports and concrete pads. They will do all of the calculations to ensure that the structure can support the various weights, wind loads, seismic activity and other stresses bearing on the building and its components. For the HVAC contractor this could include the design of special roof duct supports and equipment pads.

Below is a concrete pad designed by the structural engineer and shown as a detail on the structural drawings.

Column Lines

“Column lines help you find common areas on different floors.”

If you locate the intersection of column line “4” & “N” on the first floor, then you can find the same location directly above on the 2nd floor by finding the same column lines. This is helpful when trying to trace sheet metal, piping or utility risers that penetrate the floor.

Architectural, structural and all mechanical drawings should have the same column line references.

Dimension lines

Dimension lines are used to indicate the distance between two points.

Dimension lines can be shown many different ways, such as shown here with arrows as end points or hash marks.

Hidden Lines

Hidden lines represent lines traveling under or on the inside of an object. These invisible portions of an item are often represented by dashed lines. Hidden Lines give an indication of items that are behind or below another item, as shown here highlighted in yellow. If you see dashed lines, those are part of a hidden item. The hidden items in this drawing show other sheet metal air ducts traveling under the duct above.

Elevation View

This is the view that shows the outside or inside of the building from a standing position, eyes forward.

Elevation views are used to determine sheet metal riser lengths.

Watch this Video for a quick overview of a complete set of Construction Drawings.

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Now click the link below for Chapter #2 “Architectural Drawings” to get an overview of these drawings.

Chapter #1 – General Layout of Drawings
Chapter #2 – Architectural Drawings
Chapter #3 – Plan, Elevation, Section Views and Details
Chapter #4 – HVAC Mechanical Drawings
Chapter #5 – Understanding HVAC Symbols
Chapter #6 – Drawing Scales (How to Read Scales including Metric Scales)
Chapter #7 – Sheet Metal Shop Drawings

Sheet Metal Shop Fabrication Productivity

MEP Academy Instructor

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September 27, 2020

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Chapter #9 – Sheet Metal Shop Fabrication Productivity

You must be able to determine the productivity rate of your shop as measured in pounds per hour. How many pounds per hour of galvanized rectangular fittings can your shop produce? How many pounds per hour of coil line ductwork can your shop produce? If you fabricate round ductwork and fittings the same question would apply.

You must have some measure of productivity in order to measure whether or not your shop is becoming more or less productive over time. This measure of productivity will allow you to focus on those areas of your shop that need improvement to be more productive.

Also, does your shop ship its duct KD (Knocked Down, Unassembled)? The main reason ductwork is shipped to the jobsite knocked down is to be able to nest (stack) more ducts onto the trucks, or because access into the building is limited

The fabrication shop is the best place to assemble the duct and fittings because it’s done under a controlled environment, although this may increase your trucking cost.

Coil Line Productivity

Sheet Metal Coil Lines usually feed other pieces of equipment in a fully automated shop such as a Beader, Shear, Snap Lock or Pittsburgh Seamer, TDC/TFC Flange Roll Former, Duct Liner with Glue and Pins, and lastly a Break that bends the finished duct into the size required.

The sheet metal gets cut from the coil and then goes through all the processes of beading and forming seams and joints before being finished with liner if required, then bent into shape (Either as one piece or as two halves that get assembled together).

Productivity will vary according to how much of the work is being done by the equipment and how much has to be done by hand. How many pounds per hour can your coil line produce lined and unlined ductwork? For an example maybe the shop did 20,000 lbs. this week and incurred 160 hours of labor. This would equate to 125 Lbs./Hr. (20,000 Lbs. / 160 hrs. = 125 Lbs./Hr.)

Rectangular Fittings

If your sheet metal fabrication shop has been fortunate enough to have a plasma cutter you can avoid the time consuming method of hand layouts and cutting. If you don’t own some form of automation cutter, your productivity will probably be at least half of that of those that do. Either way you should know how many pounds of fittings your shop can produce per hour.

Also, any short straight pieces that are not run on the coil line should be figured as a fitting. As an example you might have 10,000 Lbs of metal run through the plasma cutter and have spent 250 hours of labor. (10,000 Lbs. / 250 Hrs. = 40 lbs/hour).

Round Ductwork

If your sheet metal fabrication shop owns a spiral machine, then you will want to know the productivity of this machine. This can also be figured in pounds per hour, or feet per hour per size depending on how the shop prefers to inventory materials. As an example if you produced 20,000 Lbs in 100 hours, you would get a productivity of (20,000 Lbs. / 100 Hrs. = 200 Lbs./Hr.)

Round Fittings

If you cut and assemble your own round fittings it is imperative that you keep track of the cost to fabricate. How would you know if it is cheaper to fabricate then to purchase them? The only way to know for sure the true cost of fabricating is to measure the cost.

Also it can be very difficult to compete against a shop that uses Blue Label Workers; these are production, assembly line type of workers that have limited work task and a lower pay scale.

If a sheet metal fabricator is only in the business of fabrication and not contracting, they might have an advantage of being able to combine multiple orders from many contractors into to one fabrication run that helps optimize efficiency and increase productivity, making their prices highly competitive.

Remember that the examples here are just that, examples! Do not use these values for your adjustments. Each fabrication shop produces at various levels of productivity based on the machinery they own and the talent and experience of their shop labor. You must know your shops productivity factors in order to make the appropriate adjustments based on your unique circumstances.

Galvanized Rectangular Duct Chart – Fabrication Shop Report

Above is a rectangular duct & fitting report from a popular computer estimating program. This report shows the total full-length pieces which can be considered from your coil line, plus the total quantity of short pieces and fittings (#1). From this report we can analysis the fabrication shops productivity. If your computer program summarizes these numbers in the format you need, you’re a step ahead.

The first thing to do is to determine what type of productivity the program is coming up with. If you rely 100% on the database numbers that printout of your estimating program then you can skip this step, but you should still verify the numbers from time to time.

If you notice from the report above there is no way of using the numbers without doing some type of calculation to get it into the format that is comparable to your shop reports of Lbs./Hour. Your Estimating program or if by manual takeoff you should obtain the following information.

#1 (Total Full Length Pieces, Total Short Pieces and Total Fittings)

#2 (Quantity of Pieces). This will help you determine how many hours it takes to fabricate or install each piece.

#3 (Total Linear Feet). Again we use these values to measure productivity.

#4 (Total Pounds). You will use the total pounds for each category to determine how many pounds of metal can produced within an hour.

#5 (% of Total Pounds). This is important to analyze the fitting ratio when thinking about field labor. Projects with more fittings will take longer and thereby have a slower productivity value.

#6 (Total Material Cost). The sheet metal material cost that is in your computer program or that you calculate by hand.

#7 (Total Fabrication Hours). These should be your unadjusted values from your computer estimating program or if you have already put the net values into your database for shop labor, then those values are represented here.

#8 (Total Field Hours). Just like the shop hours, these are based on your labor database values unadjusted or net. If they are net labor units, then you should still review them to ensure they still make sense.

Sheet Metal Fabrication Shop Analysis

Put the numbers from the report above into the Shop Fabrication Analysis portion of the Sheet Metal Labor Review form shown below and calculate the productivity of the report without adjustment. The spreadsheet will automatically calculate LBS/HOUR (#1) and HRS/PIECE (#2) after you enter the information from the estimating program. You’re fortunate if your program provides these metrics as this will help avoid these extra steps.

After you complete filling out the form and doing the calculations compare it to the form shown below. You can see that for each item (Straight Duct, Short Pieces, Fittings) there is now a calculated productivity metric shown by item #1 in the chart below. Straight Duct has a productivity of 150 LBS/Hr, while Short Pieces 75 LBS/HR. and Fittings 60 LBS/Hr.

This is the value that has come from the computer estimating program, now its time to adjust these values (#2) to that which is derived from your companies historical data or performance metrics. This will provide you with an Additive or Deductive Hours (#3) which you will enter into your estimating spreadsheet.

As shown above, the coil line or straight duct pieces are reporting out at 150 Lbs./Hour or 0.28 Hrs./Piece. However you analyze your productivity, now is the time to adjust the factor to your shops productivity. The Computer Estimating program may be setup with SMACNA labor units and your fabrication shop may be doing better or worse than these values, so an adjustment will be required.

After you have entered the numbers from your computer estimating report, it’s time to decide what factors to apply for the shop adjustment. Let’s use the numbers in the examples shown above at the beginning of this chapter of 125 Lbs./Hour for straight pieces and 40 Lbs. / Hour for short pieces and fittings as shown below by item #1. After these new adjustment factors (#1) you will either have additional hours to add to your estimate or hours to deduct (#2).

Sheet Metal Shop Productivity Adjustments

As you can see we have adjusted the straight pieces to 125 Lbs. / Hour, and the short pieces and fittings to 40 Lbs. / Hour. This gives us a shop add of 95.22 hours, which equates to a 47% add. (95.22 / 202.99 = 47%)

Other things to consider when adjusting the shop are how many pounds are on this one project compared to your average job. Is this considered a smaller job than usual? Will it be penalized at fabrication time because the shop is slow? Will the foreman submit cut sheets one at a time or in complete batches to improve productivity? Some of these factors are out of your control, but it is good to be aware of those things that have an impact on productivity.

If your productivity numbers are as those shown in our example at the beginning of this chapter, your adjustment might look as shown below.

Shipping

How do you figure the cost of transporting the ductwork from the fabrication shop to the job site? Does your company use an independent trucking company, or do they own their own trucks, or do you purchase your duct FOB job site?

If you fabricate your own ductwork and fittings you will have to determine the cost to ship it from the shop to the jobsite. A common way of figuring shipping is by determining the amount of pounds that can be shipped per truck load. If you know that you have 20,000 lbs of ductwork and that your truck can deliver 4,000 lbs per trip, the formula would look like this; (20,000 Lbs. / 4,000 Lbs. = 5 Truckloads.

The next thing to consider is what the cost to the company is for operating and maintaining the truck. This will include items such as fuel, lease payments, insurance, maintenance, all other burdens in addition to the labor for the truck driver, warehouse loading and delivery time.

The charge can be handled in many different ways, such as a burden rate added on top of the shop labor hourly rate, or by the hour for the labor and a fixed rate of recovery for the truck for each trip or miles driven.

For example you might figure using 12 hours per truckload at a rate of $50/hr. Based on our previous example of 5 truckloads, this would equal (5 Truckloads x 12 hours/Truckload = 60 hours) = (60 Hours x $50/Hr = $3,000). Or, you could use a combination of the two, where you separate the labor cost from the truck cost. Whichever method you use, be sure to consider all cost associated with shipping.

Remember to consider whether you are shipping your ductwork KD (Knocked Down) or if it is pre-assembled by the shop. You should be able to get a little more than twice the pounds per truckload in K.D. form.

Watch the below video to get a sense of the magnitude of the work required in a sheet metal shop. This shop by McCorvey Sheet Metal Works will give you an idea of what a large sheet metal fabrication shop entails. Most fabrication shops will not be this large, but this will give you an idea of what is capable on a larger scale and how productivity is also related to how well a shop is organized and professionally operated.

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Chapter #1 – Introduction to Sheet Shop Fabrication
Chapter #2 – Sheet Metal Materials
Chapter #3 – Sheet Metal Coil Line
Chapter #4 – Plasma Cutting Table
Chapter #5 – Spiral Machine
Chapter #6 – Sheet Metal Seams
Chapter #7 – Sheet Metal Joints
Chapter #8 – Casings and Plenums
Chapter #9 – Sheet Metal Shop Fabrication Productivity

Sheet Metal Casings and Plenums

MEP Academy Instructor

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September 27, 2020

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Chapter #8 – Sheet Metal Casings and Plenums

There are projects that will require large plenums or casings, such as in built up system where components of the air conditioning system are bought in separate pieces and then assembled. In order to build these larger sheet metal plenums you will need to use additional methods of construction than those for traditional duct fabrication. These larger sheet metal plenums are often built the size of a small or large room and house fans, coils, filter banks and dampers. These large plenums will have doors to provide access to the various sections.

The purpose is to provide an area for supply, return or exhaust air to accumulate before or after the fan section, so they will need to be built to the appropriate pressure class. In some cases walls and floors of the building will make up one or more of the sides of the plenum, requiring that the plenum be sealed tight at this connection. Any penetration of the casing or plenum will require proper sealing to prevent leakage or infiltration.

SMACNA states that all ductwork fabricated on the suction side of the fan are built to 2 in. wg (500 Pa) pressure classification, while the discharge matches the design pressure classification of the system. If the casing or plenum exceeds negative 3 in wg (750 Pa) then you may build according to SMACNA’s Rectangular Industrial Duct Construction Standards.

As the height or width (#1) of the Casing/Plenum increases, the thickness (#2) of the material, Steel Angles (#3) and Standing Seams (#4) will increase as shown in SMACNA Figure 9-1 below.

Construction methods include the use of Standing Seams, Gas Station Panels or TDC/TDF Flanges. As can be seen from the chart above, as the height increases so does the requirement for a thicker gage material, larger angle and standing seam. Openings in the plenum or casing will be framed with angle to provide reinforcement.

Gas Station Panel Roll Forming Machine

There are not many fabrication shops that own their own Gas Station Panel Roll Forming Machine because the cost of these machine are high compared to the volume of this type of sheet metal required by the average commercial construction company. Unless your company builds a lot of large built up systems, then chances are they won’t own one of these, but will use other methods that are less productive but yet provide a similar product.

The below chart shows what determines the requirements for building a large Plenum or Casing. The columns are as follows: Span (#1) defines the Panel Height of the casing, Panel Gage (#2) defines the thickness of the metal, Depth (#3) is the Panel Thickness (2”, 3” or 4”), Load Class (#4) is determined by the pressure class (Static Pressure wg.) of the system.

For example in the chart above, if you had a Panel Span (#5) of 8 feet and a system Static Pressure (#6) of 4” wg., and you wanted to use a Panel Depth (#7) of 3” with a Panel Width (#8) of 16”, this will inform you to use a Panel Gage (#9) of 20 Ga. The above chart includes additional Panel Span Heights: 10’, 12’, 14’, 16’ and 18’, (See SMACNA Manual for Additional Chart Data)

Sheet Metal Fabrication shops that have a roll forming machine will want to make efficient use of the coil sizes in inventory without waste. The below image shows a panel that was made from a standard 24” coil without any waste. If you add up all the dimensions of the below panel you will come up with 24”. Although the panel width in the below example is only 15-1/2”, you would use the 16” panel width and 3” wide column for all your panel requirements.

Many of these roll forming machines are used to fabricate metal roofing panels on large industrial projects.

The casing can be lined with insulation and a solid (Double Wall) or perforated sheet metal interior skin. There are vendors, who sell prefabricated insulated plenum wall panels, but they are usually more expansive then those that your shop can fabricate or that the shop you purchase your duct from can fabricate for you.

Estimating Built Up Casings / Plenums

In order to determine how much sheet metal is included in the design you will need to measure the linear feet of the Panel walls and ceilings across its Face Area. As shown below a typical Panel Width of 15-1/2” when stretched out or flatten, the actual width is 24”, which includes all the sides and parts of the metal that was rolled formed. The stretch-out of the panel above would look like the panel below. This would allow the fabrication shop to use a standard 24 inch wide panel or coil.

Example:

20 linear feet of a 16” (15-1/2”) Panel Width would be equivalent to much more because an additional 8” or 50% of the metal is consumed in the roll forming process using a 24” sheet metal coil.

#1 Panel Height 8 Feet

#2 Casing Wall Width 25.83 Feet (310 Inches)

#3 Casing Wall Width 5 Feet

A rough way to estimate how much panel material there is in the above casing walls is as follows;

Step #1 (Calculate Quantity of Panels in Casing Wall #2)

The first step is to determine how many Full Height Panels (#1) are required in Casing Wall Width #2 by turning the total footage into Inches and then dividing by the Panels Face Width.

25.83 feet x 12 inches/Foot = 310 Inches

310 Inches / 15-1/2” Inches/Panel Width = 20 Panels

Step #2 (Calculate Quantity of Panels in Casing Wall #3)

6.458 feet x 12 inches/Foot = 77.5 Inches

77.5 Inches / 15-1/2” Inches/Panel Width = 5 Panels

Step #3 (Calculate the Total Square Feet of Material)

Sum the total quantity of Casing Panels.

20 Panels + 5 Panels = 25 Casing Panels

Figure the Total Stretch-out Square Footage based on Panel Face Width and Material Width used to create the panel. The width of the material is determined by the wall width (2”, 3” or 4”). In the example above we were using a 24” coil width with a 3” Casing Panel Width, so we will use 24” for a stretch-out material width. Remember that the visible Face Panel Width is only a portion of the total material that you see or use in creating a panel, the rest is used in making the roll formed panel width (2”, 3” or 4”).

Using Panel Height (8 Feet) we can now calculate the total Square Feet of the material required to make this plenum or casing.

25 Panels x 24” width/Panel = 600 Inches / (12 Inches/Foot) = 50 Feet total width of material stretched out.

50 Feet (Width) x 8 Feet (Panel Height) = 400 Ft2

Answer 400 Ft2 of Material

Step #4 (Determine Total Poundage of Material)

Using the Maximum Allowable Panel Width chart above, we can see that with a Panel Height of 8 feet (#5) and a width of 3” (#7), and a static pressure of 4” wg, we find that using a panel width of 16 inches (#8) we get the required sheet metal gage of 20 ga. Note that we are using a panel width of 15-1/2”, and not 16”. The chart allows any size smaller then that listed, but not one greater than the listed panel width. The reason we are using 15-1/2 inches is that allows for you to use a perfect 24” sheet metal coil are flat stock without any waste.

Now that we know the Gage and the square footage of the material required to make the panels we can determine the total poundage.

400 Ft2 x 20 ga (1.656 Lbs/Ft2) = 400 x 1.656 = 662.4 Lbs

Whenever you have a bunch of calculations to perform its best to use a computer program or application for this like Microsoft’s Excel program.

There are additional materials when figuring out the cost of a Casing or Large Plenum, such as Angles, anchors, gaskets, sheet metal screws, Access Doors, etc . There are also other methods of fabricating casings, but these are the ones illustrated in the SMACNA manual.

Access Doors

With large built up HVAC systems there will be a need for access doors in the plenum walls to provide a means for maintenance staff to replace the filters, clean the coils or to replace fan motors. SMACNA prefers that you limit the amount of doors so as to maintain the integrity of the plenum.

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Now let’s look at chapter #8 on how to figure shop fabrication productivity.

Chapter #1 – Introduction to Sheet Shop Fabrication
Chapter #2 – Sheet Metal Materials
Chapter #3 – Sheet Metal Coil Line
Chapter #4 – Plasma Cutting Table
Chapter #5 – Spiral Machine
Chapter #6 – Sheet Metal Seams
Chapter #7 – Sheet Metal Joints
Chapter #8 – Casings and Plenums
Chapter #9 – Sheet Metal Shop Fabrication Productivity

Chapter #2 – Architectural Drawings (How to Read Construction drawings)

Architectural Drawings

Architectural Floor Plans

Reflected Ceiling Plan

Fire Rated Corridors

Fire Rated – Slab to Slab System

Fire Rated – Tunnel System

Detail Drawings

Chapter #1 – General Layout of Construction Drawings

Title Block

Electrical Drawings

Structural Drawings

Column Lines

Dimension lines

Hidden Lines

Elevation View

Chapter #9 – Sheet Metal Shop Fabrication Productivity

Coil Line Productivity

Rectangular Fittings

Round Ductwork

Round Fittings

Sheet Metal Fabrication Shop Analysis

Shipping

Chapter #8 – Sheet Metal Casings and Plenums

Gas Station Panel Roll Forming Machine

Estimating Built Up Casings / Plenums

Step #1 (Calculate Quantity of Panels in Casing Wall #2)

Step #2 (Calculate Quantity of Panels in Casing Wall #3)

Step #3 (Calculate the Total Square Feet of Material)

Step #4 (Determine Total Poundage of Material)

Access Doors

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