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Subrough Plumbing and HVAC

Temporary Services  | Surveying and Layout | Excavation | Footings/Foundation  |  Foundation Options | >>Subrough Plumbing & HVAC | Dampproofing, Waterproofing and Window WellsWater and Sewer Laterals | Foundation Drain, Backfill and Rough Grade | Basement Slab

The sub rough plumbing is located under the basement floor on a basement foundation, and under the slab on a slab on grade foundation. Depending on the foundation, the sub-rough plumbing takes place at different stages (see
Foundation options ).

Basement foundation/slab on grade.
Sub-rough plumbing- After the foundation walls are poured, the DWV pipe is installed. The plumber digs trenches for the pipes. He digs under the footings to put the main Drain pipe. The pipes are placed below the slab according to the location of the plumbing fixture. Residential plans usually don't show a plumbing schematic. The pipes are placed high enough so that they are above the finished slab. The pipes are leak tested by filling them up with air or water. After the leak test, the pipes are covered with sand. The sand protects the pipes from punctures.

HVAC- Like the plumbing pipes, the installer digs trenches for the ductwork (if forced air is used). The ductwork is inspected and then covered with sand for protection. The heat registers coming from the floor is more efficient than coming from above. However, it is still more common to put the registers in the ceiling in basement foundations. If the registers are placed under the slab you will need a downdraft furnace for the basement heating and updraft furnace for the main floor. Such an arrangement creates a better heating system but is more expensive.

The sub-rough plumbing and HVAC takes place at different times in the project depending on the type of foundation.

Basement foundation- With a basement foundation the sub-rough work begins as soon as the foundation wall forms are stripped. Once both systems are installed, tested, inspected and covered the floor slab is poured.

Slab on grade- When a slab on grade is poured the sub-rough work must go in before the slab is poured the same as a basement foundation.

Monolithic pour- When the floor and foundation is poured in one pour as it is often done in the Southwest, the sub-rough work is installed after the foundation is formed. It also should be noted that because areas where monolithic pours are popular the HVAC is not often placed in the slab. One reason is it is generally cheaper to put the HVAC system in the attic space. The other reason is that Air conditioning which is used heavily is more efficient blowing down from the ceiling.
The water supply lateral is also installed as part of the sub-rough plumbing for monolithic foundations

Crawlspace- The work on the under floor plumbing and HVAC can begin before or after the floor system is framed. It is generally best to have the plumbers and HVAC put in after the stem wall is poured. At this stage each trade installs the main drain lines and trunk lines. After the floor and the rest of the house is framed, they can return to complete the rough-in.

Radiant floor Heating
Where slab floor are used, radiant floor heating is a popular heating system. Pipes carrying hot water run through the slab. The heat is transferred to the slab which radiates through the home. Radiant floor heat is a comfortable and efficient heating system. It costs more than a typical forced air system but many people believe that it is worth it.
When installing a radiant floor system the plumbing is installed first. Rigid insulation board is laid on top of the ground, followed by the radiant floor pipe. The system is tested and then covered with the concrete floor slab. Most installers recommend that the pipes remain under pressure during the slab pour so that damage to pipes can be detected and repaired.

Notes to the owner-builder
It is critical that placement of the under slab plumbing and heating is accurate. It is possible to make changes by cutting the concrete but that is expensive. If radiant floor heating is used, it would be difficult to change the sub-rough plumbing below with out major expense to the in floor heating system. It takes about a day each for the sub-rough plumbing and heating.


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