I. PURPOSE: This Exhibit prescribes thermal performance construction standards to be used in all housing loan and grant programs. These requirements shall supersede the thermal performance requirements in any of the development standards in § 1924.4(h) of this subpart.
II. POLICY: All loan or grant applications involving new construction (except for new Single Family Housing (SFH)) and all applications for conditional commitments (except for new SFH) shall have drawings and specifications prepared to comply with paragraphs IV A or C and IV D of this Exhibit. All new SFH construction shall have drawing and specifications prepared to comply with paragraph IV F of this Exhibit.
A. British thermal unit (Btu) means the quantity of heat required to raise the temperature of one pound (.4535 KM.) of water by one degree Fahrenheit (F). For example, one Btu is the amount of heat needed
to raise the temperature of one pound of water from 59 degrees F to 60 degrees F.
B. Glazing is the material set into a sash or door when used as a natural light source and/or for occupant's views of the outdoors.
C. “R” value, thermal resistance, is a unit of measure of the ability to resist heat flow. The higher the R value, the higher the insulating ability.
D. “U” value is the overall coefficient of heat transmission and is the combined thermal value of all the materials in a building section. U is the reciprocal of R. Thus U = 1/R or R = 1/U or 1/C where C is the thermal conductance and is the unit of measure of the rate of heat flow for the actual thickness of a material one square foot in area at a temperature of one degree Fahrenheit. The lower the U value, the higher the insulating ability.
E. Winter degree-day is a unit based on temperature difference
and time. For any one day, when the mean temperature is less than
65 degrees F (18.3 degrees Celsius), there are as many degree-days as the number of degrees difference between the mean temperature for the day and 65 degrees F. The daily mean temperature is computed as half the total of the daily maximum and daily minimum temperatures.
(12-19-07) PN 416
RD Instruction 1924-A
F. CABO MODEL ENERGY CODE, 1992 EDITION (MEC-92) - This code sets forth the minimum energy/thermal requirements for the design of new buildings and structures or portions thereof and additions to existing buildings. The MEC is maintained by the Council of American Building Officials (CABO).
IV. MINIMUM REQUIREMENTS
A. All multifamily dwellings to be constructed with Rural Development loan and/or grant funds and all repair, remodeling, or renovation work performed on single family and multifamily dwellings with Rural Development loan and/or grant funds shall be in conformance with the following, except as provided in paragraphs IV C 3 and IV D of this Exhibit:
MAXIMUM U VALUES FOR CEILING, WALL, AND FLOOR
SECTION OF VARIOUS CONSTRUCTION
Days Ceilings Walls Floors Glazing Doors
(Note 1) (Note 2) (Note 3) (Note 4) (Note 5)
less .05 .08 .08 1.13 ----
2500 .04 .07 .07 .69 ----
2501 Storm door if
to hollow core door 4500 .03 .05 .05 .69 if over 25% glass _________________________________________________________________________
6000 .03 .05 .05 .47 Storm Door
more .026 .05 .05 .47 Storm Door
(U values are not adjusted for framing. Values calculated for components may be rounded. For example, a total R Value of 18.88 converts to a U value of .0529 rounded to .05)
RD Instruction 1924-A
Note 1. Winter degree-days may be obtained from the ASHRAE Handbook; the "NAHB insulation Manual for Homes/Apartments"; local utilities; and the National Climatic Center, Federal Building, Asheville, NC. Manuals are available from NAHB RF, Rockville, MD 20850, or NMWIA, 382 Springfield Avenue, Summit, NJ 07901. Other sources of degree day data may be used if available from a recognized authority.
Note 2. Insulation must be continuous (i.e. no gaps) above all ceiling joists. In pitched roof construction, compression of insulation at the outside building walls is permitted to allow a 1" ventilation space under the roof sheathing. For any loose fill insulation, a baffle must be provided. Raised trusses are not required.
Note 3. For floors of heated spaces over unheated basements, unheated garages or unheated crawl spaces, the U value of floor section shall not exceed the value shown. A basement, crawl space, or garage shall be considered unheated unless it is provided with a positive heat supply to maintain a minimum temperature of 50 degrees F. Positive heat supply is defined by ASHRAE as heat supplied to a space by design or by heat losses occurring from energy-consuming systems or components associated with that space."
Where the walls of an unheated basement or crawl space are insulated in lieu of floor insulation, the total heat loss attributed to the floor from the heated area shall not exceed the heat loss calculated for floors with required insulation.
Insulation may be omitted from floors over heated basement areas or heated crawl spaces if foundation walls are insulated. The U value of foundation wall sections shall not exceed the value shown. This requirement shall include all foundation wall area, including header joist (band joist), to a point 50 percent of the distance from a finish grade to the basement floor level. Equivalent Uo configurations are acceptable.