12.2 TSBPE 2-Story DWV Dollhouse Design & Layout

12.2 TSBPE 2-Story DWV Dollhouse Design & Layout

Core Principle: The TSBPE 2-Story DWV Dollhouse is the centerpiece of the Texas Journeyman Plumber practical examination. The station consists of a scaled wood-frame structure representing a two-story residential home. Candidates are required to design, draft, and assemble a fully compliant Drainage, Waste, and Vent (DWV) system. Success requires flawless integration of fixture unit calculations, wet-venting geometry, stack base transitions, cleanout placement, and fitting takeoff mathematics under strict code evaluation.

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1. Dollhouse Station Overview & Structural Layout

The dollhouse model simulates standard residential platform framing with a ground floor (1st Story), an upper floor (2nd Story), and a roof penetration plane.

============================== ROOF PLANE ============================== (VTR)
                                    |
                                    | Stack Vent (3" Min Thru Roof)
                                    |
----------------------------- 2ND STORY FLOOR -----------------------------
  [LAVATORY]            [TUB / SHOWER]                  [WATER CLOSET]
   (1 DFU)                 (2 DFU)                         (3 DFU)
   1-1/2" Trap             1-1/2" or 2" Trap               3" Closet Bend
      |                        |                               |
      +==== Wet Vent (2") =====+===============================+
                                                               |
                                                      Soil Stack (3" Min)
                                                               |
----------------------------- 1ST STORY FLOOR -------------------------|
  [KITCHEN SINK]      [CLOTHES WASHER]           [POWDER LAV]          |
     (2 DFU)             (2-3 DFU)                  (1 DFU)            |
    1-1/2" Trap         2" Standpipe              1-1/2" Trap          |
        |                   |                          |               |
        +=== Individual ====+                          +===============+
             Vents (1-1/2")                                            |
                                                                       |
========================== SUB-FLOOR / FOUNDATION =====================|
  Building Drain (3" or 4" @ 1/4"/ft slope) <====== [Stack Base Combo]--+
  +--- [Cleanout @ Foundation Exit]

Fixture Inventory & Drainage Fixture Unit (DFU) Allocations

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2. Venting Methodologies for the 2-Story DWV System

Proper venting protects the liquid trap seals of all fixtures against siphonage, aspiration, and back-pressure.

Upper-Floor Horizontal Wet Venting (The Classic TSBPE Design)

A single bathroom group on the 2nd floor can be vented using a horizontal wet vent (IPC 912 / UPC 908):

1. The Dry Vent Connection: The dry vent originates at the lavatory drain. Because the lavatory is the highest fixture elevation in the group, its vent remains dry above the flood level rim.
2. The Wet-Vented Pipe: Below the lavatory fixture drain connection, the pipe becomes a wet vent that carries liquid waste from the lavatory while simultaneously supplying atmospheric air to the bathtub/shower and water closet.
3. Sizing the Wet Vent:
   • A 2-inch wet vent is required to serve a complete bathroom group (water closet + lavatory + tub/shower).
   • The dry vent portion rising above the lavatory drain must be at least 1-1/2 inches.
4. Order of Fixture Connections (Crucial Rule):
   • The lavatory must be connected furthest upstream.
   • The bathtub/shower connects downstream of the lavatory.
   • The water closet must connect furthest downstream (or directly into the stack at the lowest point of the group).

+-----------------------------------------------------------------------------+
|                   HORIZONTAL WET VENT CONNECTION SEQUENCE                   |
|                                                                             |
|   [Lavatory Dry Vent 1-1/2"] (Rises to Roof/Stack Vent)                    |
|              |                                                              |
|   [Lavatory Drain 1-1/2"] (Upstream Inlet)                                  |
|              |                                                              |
|              v                                                              |
|   ================== 2" HORIZONTAL WET VENT =============================   |
|              ^                                             ^                |
|              | (Connects via 2" Wye)                       | (3" Wye/Combo) |
|     [Tub/Shower Drain 2"]                        [Water Closet Drain 3"]    |
+-----------------------------------------------------------------------------+

Lower-Floor Fixture Venting

• Kitchen Sink & Clothes Washer: Must be individually vented (continuous waste-and-vent) or circuit vented if configured in a battery. Their dry vents must rise vertically at least 6 inches above the fixture flood level rim before turning horizontal or tying into the stack vent.
• Distance from Trap to Vent: The maximum developed length of the fixture drain from the trap weir to the vent fitting must comply with code limits:

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3. Soil Stack, Building Drain, & Cleanout Sizing

Main Soil Stack Rules

1. Stack Sizing: A vertical soil stack serving water closets on two floors must be at least 3 inches in diameter. A 3" stack can handle up to 24 DFU on a multi-story building (IPC Table 710.1(2)).
2. Stack Vent Extension: The soil stack must extend full size as a stack vent through the roof or increase to 3" at least 1 foot below the roof to prevent frost closure.
3. Base of Stack Transition: The transition from the vertical soil stack to the horizontal building drain undergoes severe hydraulic turbulence. Code requires this connection to be made using:
   • A Combination Wye and 1/8 Bend, OR
   • A 45° Wye and 1/8 Bend, OR
   • Two 45° Ells (Long sweep).
   • PROHIBITED: A Sanitary Tee or standard short-turn elbow is strictly illegal at the base of a stack.

               VERTICAL SOIL STACK (3" or 4")
                             |
                             |  <-- Base of Stack Cleanout (Full Size)
                           [CO]
                             |
                             |
                            /    <-- Combination Wye & 1/8 Bend (Sweeps Downstream)
                           /     
   =======================+=======================> TO BUILDING SEWER
     HORIZONTAL BUILDING DRAIN (1/4" per foot slope)

Cleanout Requirements on the Dollhouse

1. Base of Stack Cleanout: A full-size cleanout is required near the base of every vertical soil/waste stack.
2. Building Drain Cleanout: A cleanout must be provided at the upstream end of the building drain and near the junction where the building drain exits the foundation wall (within 5 feet of the wall).
3. Directional Changes: Cleanouts are required for horizontal drainage directional changes greater than 45° (unless the change is made with two 45° fittings with cleanout access).

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4. Fitting Takeoffs & Practical Dimensioning

When cutting pipe for the physical dollhouse model, fitting takeoffs must be calculated exactly to prevent assembly binding or improper centerlines.

PVC DWV Takeoff Reference

$\text{Cut Pipe Length} = \text{Center-to-Center Travel} - (\text{Fitting Deduction}_1 + \text{Fitting Deduction}_2)$ $\text{Fitting Deduction} = \text{Center-to-Face (C-to-F)} - \text{Socket Depth (Makeup)}$

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5. TSBPE Grading Rubric & Common Deductions

Texas examiners grade the dollhouse practical station with a zero-tolerance policy for code violations and poor workmanship.

+-----------------------------------------------------------------------------+
|                   CRITICAL TSBPE DOLLHOUSE GRADING DEDUCTIONS               |
+-----------------------------------------------------------------------------+
|   DEFECT / CODE VIOLATION                       | POINT PENALTY             |
+-------------------------------------------------+---------------------------+
|   Sanitary Tee on its back / horizontal drain   | -25 pts (AUTOMATIC FAIL)  |
|   Reverse grade / back-pitch on drainage run    | -20 pts (AUTOMATIC FAIL)  |
|   Water closet upstream of wet vent lavatory    | -15 pts                   |
|   Vent taking off below drain centerline (<45°) | -10 pts                   |
|   Wrong fitting at base of stack (San-Tee)      | -10 pts                   |
|   Exceeding trap-to-vent maximum distance       | -10 pts                   |
|   Missing required cleanout                     | -10 pts                   |
|   Cut length dimension off by > 1/8"            | -5 pts per occurrence     |
|   Piping not plumb or level (> 1° out)          | -5 pts per occurrence     |
+-----------------------------------------------------------------------------+