Rd instruction 1924-a table of Contents




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MAXIMUM U VALUES OF THE FOUNDATION WALL Sections OF HEATED BASEMENT NOT

CONTAINING HABITABLE LIVING AREA OR HEATED CRAWL SPACE

__________________________________________________________________________

Winter Degree Days Maximum U Value Glazing*

(65 F Base)

__________________________________________________________________________

2500 or less No requirement 1.13

__________________________________________________________________________

2501 to 4500 0.17 1.13

__________________________________________________________________________

4501 or more 0.10 0.69

_______________________________________________________________________
(12-19-07) PN 416

RD Instruction 1924-A

Exhibit D

Page 4

*Glazing in heated basement shall be limited to 5 percent of floor area

unless alternative Uo combination is documented.


Note 4. Sliding glass doors are considered as glazing. The glazing value is for glass only. Glazing shall be limited to 15 percent of the gross area of all exterior walls enclosing heated space, except when demonstrated that the winter daily solar heat gain exceeds the heat loss and the glass area is properly screened from summer solar heat gain.
Note 5. 1-3/4 inch metal-faced door systems with rigid insulation core and durable weatherstripping providing a "U" value equivalent to a wood door with storm door and an infiltration rate no greater than .50 cfm per foot of crack length tested according to ASTM E-283 at 1.567 psf of air pressure, may be substituted for a conventional door and storm door. All doors shall be weatherstripped. Any glazed areas must be double-glazed.


MINIMUM R VALUES OF PERIMETER INSULATION FOR SLABS-ON-GRADE

__________________________________________________________________________

Winter Degree-Days Minimum R Values*

(65 F Base) Heated Slab Unheated Slab

__________________________________________________________________________

500 or less 2.8 ----

1000 3.5 ----

2000 4.0 2.5

3000 4.8 2.8

4000 5.5 3.5

5000 6.3 4.2

6000 7.0 4.8

7000 7.8 5.5

8000 8.5 6.2

9000 9.2 6.8

10000 or greater 10.0 7.5

__________________________________________________________________________

*For increments between degree days shown, R values may be interpolated.

RD Instruction 1924-A

Exhibit D

Page 5

B. [Reserved]


C. Optional Standards. Housing design not in compliance with the requirements of paragraph IV A of this Exhibit may be approved in accordance with the provisions of this paragraph. Requests for acceptance proposed under paragraph C 1 below, must be approved by the State Director. Requests for acceptance of site-built housing proposed under paragraph C 2 must be approved by the Administrator. Requests for acceptance of manufactured housing proposed under paragraph C 2 may be approved by the State Director. All submissions of proposed options to the State Director or Administrator shall contain complete descriptions of materials, engineering data, test data (when U values claimed are lower than the ASHRAE Handbook of Fundamentals), and calculations to document the validity of the proposal. All data and calculations will be based upon the current edition of the ASHRAE Handbook of Fundamentals or other universally accepted data sources.
1. Overall "U" values for envelope components. The following requirements shall be used in determining acceptable options to the requirements of paragraph IV A of this Exhibit.
a. Uo (gross wall) - Total exterior wall area (opaque wall and window and door) shall have a combined thermal transmittance value (Uo value) not to exceed the values shown in Attachment 1 to this Exhibit D (available in any Rural Development office). Equation 1 in Attachment 1 in shall be used to determine acceptable combinations to meet the requirements.
b. Uo (gross ceiling) - Total ceiling area (opaque ceiling and skylights) shall have a combined thermal transmittance value (Uo value) not to exceed the values shown in Attachment 2 to this Exhibit D (available in any Rural Development office). Equation 2 in Attachment 2 shall be used to determine acceptable combinations to meet the requirements.
2. Overall structure performance. The following requirements shall be used in determining acceptable options to the requirements of paragraph IV A of this Exhibit.
a. The methodology must be cost effective to the energy user, and must not adversely affect the structural capacity, durability or safety aspects of the structure.
b. All data and calculations must show valid performance comparisons between the proposed option and a structure

(12-19-07) PN 416

RD Instruction 1924-A

Exhibit D

Page 6

comparable in size, configuration, orientation and occupant usage designed in accordance with paragraph IV A. Structures may be considered for Rural Development loan consideration

which can be shown by accepted engineering practice to have energy consumption equal to or less than those which would be attained in a representative structure utilizing the requirements of paragraph IV A.
3. Special consideration for seasonally occupied farm labor housing. The following sets forth the minimum acceptable options to the requirements of paragraph IV A of this Exhibit for seasonally occupied housing serving as security for farm labor housing loans and grants.
a. When the period of occupancy does not encounter 500 or more heating degree-days (HDD) as determined by an average of the previous 10 years based upon local climatological data published by the National Oceanic and Atmospheric Administration, Environmental Data Service, the standards of paragraph IV A will not apply.
b. When the period of use exceeds 500 HDD, the 10-year average value for the period of occupancy shall be used to determine the degree to which the thermal insulation requirements of paragraph IV A shall apply.
c. If mechanical cooling is provided and the period of occupancy encounters more than 700 cooling degree-days (CDD), as determined by an average of the previous 8 years based upon local climatological data published by the same source cited in paragraph IV C 3 a above, the thermal insulation requirements for 1,000 and less degree-days as stated in paragraph IV A shall apply.

D. Energy efficient construction practices. This section prescribes those items of design and quality control which are necessary to guarantee the energy efficiency of homes built according to the standards of this Exhibit. Also included are recommendations for extra energy efficiency in dwellings. This section does not apply to new SFH construction.


1. Infiltration.
a. Requirements: All construction shall be performed in such a manner as to provide a building envelope free of excessive infiltration.

RD Instruction 1924-A

Exhibit D

Page 7

(i) Caulking and sealants. Exterior joints around windows and door frames, between wall cavities and window or door frames, between wall and foundation, between wall and roof, between wall panels, at penetrations of utility

services through walls, floors and roofs, and all other openings in the exterior envelope shall be caulked,

gasketed, weatherstripped, or otherwise sealed. Caulking shall be silicone rubber base or butyl rubber base, conforming to Federal Specifications TT-S-1543 and TT-S-1657 respectively, or materials demonstrating equivalent performance in resilience and durability.
(ii) Windows shall comply with ANSI 134.1, NWMA 15-2; the air infiltration rate shall not exceed 0.5 ft 3/min per ft. of sash crack.
(iii) Sliding glass doors shall comply with ANSI 134.2, NWMA 15-3; the air infiltration rate shall not exceed .5 ft 3/min per square ft. of door area.
(iv) All insulation placed in open cavity walls shall be installed so that all space behind electrical switches and receptacles, plumbing, ductwork and other obstructions in the cavity are insulated as completely as possible. Insulation shall be omitted on the side facing the conditioned area; however, the vapor barrier in walls must not be cut or destroyed.

b. Recommendations:


(i) Wrap outside corners of wall sheathing with
15 lb. Asphalt impregnated building felt before siding application.
(ii) Utilize vestibules for entry doors, especially those facing into the direction of winter wind.
(iii) Install plumbing, mechanical and electrical components in interior partitions as much as possible. All water piping should be insulated from freezing temperatures.

(12-19-07) PN 416

RD Instruction 1924-A

Exhibit D

Page 8

2. Heating and/or Cooling Equipment.


a. Requirements: All mechanical equipment for heating and/or cooling habitable space shall be designed to provide economy of operation.
(i) All space heating equipment (including fireplaces) requiring combustion air shall be sealed combustion types, or be located in a nonconditioned area (such as heated basements) or adequate combustion air must be provided from outside the conditioned space.
(ii) All ductwork shall be designed and installed to minimize leakage. All metal to metal connections shall be mechanically joined and taped.
b. Recommendations:
(i) Whenever possible, locate ductwork inside of conditioned areas in dropped ceilings, interior partitions or other similar areas.
(ii) Locate outside cooling units in areas not subject to direct sunlight or heat buildup.
3. Vapor Barrier.
a. Requirements: Adequate vapor barriers must be provided adjacent to the interior finish material of the wall or other closed envelope components which do not have ventilation space on the nonconditioned side of the insulation.
(i) A vapor barrier at the inside of the wall or other closed envelope component must have a permeability (perm) rating less than that of any other material in that component and in no case have a perm rating greater than one. All vapor barriers must be sealed around all openings in the interior surface. Vapor barriers are not required in ceilings and floors. Continuous vapor barriers on ceilings, walls, and floors require adequate moisture vapor control in the conditioned space.
(ii) All vapor producing or exhaust equipment shall be ducted to the outside and equipped with dampers. This equipment includes rangehoods, bathroom exhaust fans, and clothes dryers. If a dwelling design proposes the use of windows to satisfy the kitchen and/or bathroom ventilation

RD Instruction 1924-A

Exhibit D

Page 9

requirements of the development standards, the incorporation of dehumidification equipment should be considered in accordance with paragraph IV D 3 b. Exhaust of any equipment shall not terminate in an attic or crawl space.
b. Recommendation: Forced air heating/cooling systems should include humidification/dehumidification systems where conditions indicate.
E. [Reserved]
F. New SFH construction. New SFH construction shall meet the requirements of CABO Model Energy Code, 1992 Edition (MEC-92).
G. New Manufactured Housing. The Uo Value Zone indicated on the “Heating Certificate” for comfort heating shall be equal to or greater than the HUD Zone listed in the following table:


RHS Climate Zones

(winter degree days)

FMHCSS (HUD Code)

Uo Value Zones


0 - 1000

1

1001 - 2500

2

2501 - 4500

2

4501 - 6000

3

> 6000

3


EXAMPLE: If a manufactured home is to be located in a geographic area having between 2501 and 4500 RHS winter degree days, the Agency will accept a Uo value Zone 2 unit or Zone 3 unit constructed to the HUD Federal Manufactured Home Construction and Safety Standard (FMHCSS).
If a central air conditioning system is provided by the home manufacturer a “Comfort Cooling Certificate” must be permanently affixed to an interior surface of the unit that is readily visible. This certificate may be combined with the heating certificate on the data plate.

(12-19-07) PN 416

RD Instruction 1924-A

Exhibit D

Page 10

V. GENERAL DESIGN RECOMMENDATIONS:


A. Orient homes with greatest glass area facing south with adequate overhangs to control solar gain during non-heating periods. Examples of proper roof overhangs are given in Attachment 3 to this Exhibit D (available in any Rural Development office).
B. Arrange plantings with evergreen wind buffers on north side and deciduous trees on south.
C. Whenever possible, orient entry door away from winter winds.
D. Design house with simple shape to minimize exterior wall area.
E. Minimize glass areas within constraints of required light and ventilation, applicable safety codes, and other appropriate consideration.
F. Minimize the amount of paved surface adjacent to the structure where heat gain is not desirable.
VI. STATE SUPPLEMENTS: State supplements or policy will not be issued or
adopted to either supplement or set requirements different from those of
this Exhibit without the prior written approval of the National Office.


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