Building America Industrialized Housing Partnership (BAIHP)
TRIP REPORT
Southern Mississippi
Problem Home Inspection, Testing and Possible Solutions

DATE
August 9, 2001

PURPOSE

• Assist service and engineering staff in determining the source or probable cause of moisture-related problems and aid in repairs.
• Provide confirmation, if possible, that moisture related problems would not reappear.

INTRODUCTION

• Moisture problems included some discoloring of wallboard and staining of ceiling trim at various transitions.  Also, a section of wallboard near the front door had deteriorated from water intrusion.
• Previously damaged wallboard had been replaced once already by service personnel.  Repairs included replacing with damage drywall with a similar product, repairing supply duct system leakage and sealing wall-ceiling penetrations.

DESCRIPTION

• 3 bedroom-2 bath 1330 ft² singlewide with fireplace.
• Open crawlspace without skirting
• 3 ½ ton split system AC and electric strip heat furnace with an in-line metal floor duct system with metal risers.

OBSERVATIONS

• Thermostat was set at 75F
• Repairs previously made included wallboard replacement, duct sealing (with mastic), and sealing of various ceiling transitions.
• Blend-Air II ventilation system installed.  The attic ventilation fan had been disconnected.
• Homeowner reported that the electric bill for the summer decreased by $40 after the repairs were made.
• All bedroom doors usually closed at night and open during the day.
• Occupants include 2 adults, 2 teenagers and 4 pets (2-cats and 2 dogs).

TESTING

Blower door test

A blower door test was done to determine the airtightness of the building envelope.  A series of building pressures and associated airflows was recorded.  This provides the necessary inputs to determine the CFM50 of the house.  As a general rule of thumb, typical values of building airtightness range between 0.75 and 1 CFM50 per square foot of conditioned floor area.  This house has a floor area of 1216 ft² and a CFM50 of 1855 or 0.7 CFM50 per square foot – a tighter home.

The values of C and n can be used as inputs for the house airflow equation, Q=C* ^pn.  Thus, for any given pressure difference,  P, the airflow crossing the building’s envelope can be determined.

Duct test

A duct system airtightness test was also completed.  A duct tester was attached to the air handler unit.  The supply registers were temporarily sealed off and the system was then depressurized to 25 pascals.  The total and outside leakage flow components were measured.  An airtight duct system would have zero leakage or both the CFM25_total and CFM25_out would be 0.

Duct System Airtightness

CFM25total  = 47 CFM25out  = 32

Pressure diagnostic testing

Pressure differential measurements were completed to determine a magnitude and direction of flow across the envelope when the air handler fan operates.  Interior door closure effect was also measured when the air handler fan operated. 

The pressure difference was also measured across each closed door when the air handler fan was operating (all supply registers were open and exhaust was off).

EFFECTS

• Return air path to AHU is hindered when bedroom doors are closed – especially the master suite door.
• Flow imbalances cause the master bedroom to be overcooled before the other bedrooms are cooled.  This overcooling causes the exterior vinyl covered walls to drop to the ambient air dewpoint temperature or below.
• Duct leakage, on the supply side, causes the entire building to operate at a negative pressure.  Any pathway from the exterior to the interior – such as electrical penetrations- provides a pathway for ambient air to reach interior surfaces.  One such area is at the light fixture mounted on the wall of the master bath.

RECOMMENDATIONS

• Keep thermostat set at 78 F or above.
• The flow imbalances (especially the excessive air in the master suite) should be corrected.
• All duct leaks should be repaired with mastic.  The supply plenum and all risers should be checked and repaired as needed.  The refrigerant line penetration through the air handler cabinet should also be sealed.  The duct leakage should not exceed 3% of floor area or CFM25 less than 40.
• The 3-inch reducer in the supply plenum should be removed.
• A separate return direct to the AHU is needed (through the wall or jump duct) from the master suite.
• Sufficient return air pathways should be installed in the rest of the bedrooms.
• All belly penetrations should be sealed with a permanent, long-lasting seal. No duct tape.
• In general, vinyl covered exterior drywall should not be used in hot and humid climates.

PICTURES

Outside air duct to furnace top	Furnace fan removed to inspect plenum
Electric furnace with 3-row AC coil	AC nameplate
Ceiling transition repair being made	Inspecting wall moisture content