International Code Council

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1 International Code Council ICC edition Standard on the Design and Construction of Log Structures Public Comments Draft #1 The ICC Standard Development Committee on Log Structures (IS-LOG committee) met in November 2010 to consider public and committee proposals that were submitted on the 2007 edition of the ICC 400 Standard in response to two call-for-comment periods (4/13/10-5/26/10 and 6/16/10-7/15/10), which resulted in this first public comments draft. This document is a listing in legislative format (Line through text to be deleted Underlined text to be added) of the actions taken by the IS-LOG committee. Only the text shown in legislative format is subject to public comment at this time. To obtain the ICC go to Page 1 of 11

2 CHAPTER 2 DEFINITIONS PROJECTION FACTOR. The ratio of the overhang width (O W ) to the overhang height (O H ) above the door threshold or window sill (PF=O W /O H ) providing a drip line beyond the lowest exposed wall surface. CHAPTER 3 GENERAL REQUIREMENTS Staff note: For revisions to Tables 302.2(1), 302.2(3) and 302.2(5) see separate document titled Tables 302.2(1), 302.2(3) and 302.2(5) Notches. Notches on the edges of bending members shall not be located in the middle one-third of the span. Notches in the outer thirds of the span shall not exceed one-sixth of the actual member depth and shall not be longer than one-third of the depth of the member. Where notches are made at the supports, they shall not exceed one-fourth the actual log depth. Exception: Where the net section has been designed to be sufficient to bear the anticipated loads Roof overhangs. Roof overhangs shall provide a projection factor of 1/8 to the bottom of the sill log or bottom plate (e.g., minimum 12 overhang to 96 wall height) or to a projection from the exterior of the log wall (e.g., porch roof, balcony, deck, or any individual log joist, purlin or wall-log). Exceptions: Roof overhang projection factor does not apply where 1. Logs within 24 of a lower horizontal surface (e.g., finish grade, bulkhead cover, deck, balcony, roof, etc.) are treated in compliance with section Wood treatments. 2. Roof water discharge is diverted (e.g., by means of a gutter and downspout he sill log or bottom plate log is at least 18 above an adjacent horizontal surface. 3. The roof above the log wall extends beyond lower decks (e.g., porch roof). 4. Decks adjacent to the log wall have structural grating or other means equal in width to the overhang to allow precipitation to pass through the deck to finish grade. Page 2 of 11

3 Calculating slumping. Settling due to slumping shall be calculated using the following formula: SL= H CA N C SL where: (entire formula to remain unchanged except for the last entry for C SL ) C SL can be assumed to be 0.5 when: p =0.375d, MCD = MCFSP, MCS =12%, and S T =8%. p =0.375d, MC D = MC FSP, MC S =12%, and S T =8% Electrical Wires Within Log Walls. The maximum number of electrical wires allowed in an electrical chase bored in a log wall shall be the same as allowed in similarly sized conduit as specified in the applicable electrical code Procedural requirements. Compliance with the requirements of the International Energy Conservation Code or the energy provisions of the International Residential Code shall be determined in accordance with one of the following methods: 1. Section and International Energy Conservation Code Chapter 5, including Table (1), Mass Wall Prescriptive Building Envelope Requirements for Exterior or Integral Insulation. Section Energy compliance program. 3. Performance basis using a certified energy rating system Prescribed method. The R-value of the opaque log wall assembly shall be selected from Table The prescribed method shall be in accordance with Section or U-Factor. The U-Factor (Uw) of the opaque log wall assembly shall be selected from Table Thermal envelope. The thermal envelope shall be compliant with the requirements of Table and this section Climate Zones 5 through 8. In Climate Zones 5 through 8, a minimum heating AFUE of 90% (gas) or 85% (oil) is required. Boilers also need a modulating aquastat or outdoor temperature limit control. Page 3 of 11

4 TABLE R-VALUE OF LOG WALL (R o )BY AVERAGE WIDTH (W L ) AND SPECIFIC GRAVITY Average Width 5 in. 6 in. 7 in. 8 in. 9 in. 10 in. 12 in. 14 in. 16 in For SI: 1 inch = 25.4 mm. Notes to Table : 1. The tabulated values assume MCS to be at 12 percent. 2. Above and left of the bold line, log criteria does not meetiecc requirements for heat capacity for thermal mass credit. The tabulated R-values represent walls with log-to-log contact at all seams inclusive of air films. The u-value, required in energy conservation calculations, is the inverse of the R-value. Page 4 of 11

5 TABLE CLIMATE ZONE TABLE INSULATON AND FENESTRATION REQUIREMENTS BY COMPONENT a LOG WALL, W L h FENESTRATION U-FACTOR b SKYLIGHT U- FACTOR b CEILING R- VALUE WOOD FRAME WALL R- VALUE c FLOOR R- VALUE d, e BASEMENT f / CRAWL WALL R- VALUE SLAB R- VALUE & DEPTH Page 5 of 11 HEATED SLAB R- VALUE g 1 5 min min min or /13 5, 2-ft. 5 4 & MARINE 5 EXCEPT MARINE 5 min. 5 SG 0.50; or /13 10, 2-ft or /19 10, 2-ft. 10

6 6 SG> or /19 15, 4-ft & or /19 15, 4-ft. 15 For SI: 1 foot = mm. Notes to Table a. R-values are minimums. U-factors are maximums. R-19 batts compressed into a nominal 2 6 framing cavity such that the R-value is reduced by R-1 or more shall be marked with the compressed batt R-value in addition to the full thickness R-value. b. The fenestration U-factor column excludes skylights. The glazed fenestration solar heat gain coefficient (SHGC) applies to all glazing (0.30 in Climate Zones 1-3; not required in Climate Zones 4-8). Glazing area shall be limited to a maximum fenestration area of 20 percent of the gross conditioned floor area. Glazing area includes window and skylight opening area, plus actual glazed area of glass in doors. Sunrooms are exempt from this requirement. c means R-13 cavity insulation plus R-5 continuous insulation. If structural sheathing covers 25 percent or less of the exterior, insulating sheathing is not required where structural sheathing is used. If structural sheathing covers more than 25 percent of exterior, structural sheathing shall be supplemented with insulated sheathing of at least R-2. d. Or insulation sufficient to fill the framing cavity, with R-19 as the absolute minimum in Climate Zones 5-8. e. Insulate perimeter of floor system to match floor R-value requirement with basement/crawl foundations. f. 15/19 means R-15 continuous insulation on the interior or exterior of the home or R-19 cavity insulation at the interior of the basement wall. 15/19 shall be permitted to be met with R-13 cavity insulation on the interior of the basement wall plus R-10 continuous insulation on the interior or exterior of the home. g. The required insulation shall be installed beneath the entire slab for heated slabs. h. W L is the average wall-log width. Nominal callouts will be larger (e.g., a 5 log would be 6x or 7 diameter; a 7 would be 8x or 9 diameter). SG = specific gravity Thermal mass effect of log walls. Log walls having a mass greater than or equal to 20 lb/ft 2 (98 kg/m 2 ) of exterior wall area shall be deemed to have heat capacities equal to or exceeding 6 Btu/ft 2 [KJ(m 2 +K)] The thermal mass benefit of log walls shall be determined in accordance with this section Establishing thermal mass. Thermal Mass shall be established using one of the methods described in the following sections Prescribed method. Log walls shall be evaluated as mass walls in accordance with Section of the International Energy Conservation Code. The thermal mass of the opaque log wall assembly shall be established from Table Test method. Physical testing of the thermal mass shall be in accordance with ASTM C 976. Page 6 of 11

7 Calculation method for computer modeling Weight of wall. Either c Calculate the weight of the wall in pounds per square foot (psf) using the density equation in Section Heat capacity. or determine Calculate the heat capacity for the thermal mass provision using the following. HC= w c where: HC = Heat capacity of the exterior wall, Btu/ft 2 F [kj/(m 2 K)] of exterior wall area. w = Mass of the exterior wall, lb/ft 2 (kg/m 2 ) of exterior wall area is the density of the exterior wall material, lb/ft 3 (kg/m 3 ) multiplied by the thickness of the exterior wall calculated in accordance with section c = Specific heat of the exterior wall material, Btu/lb F [kj/(kg K)] of exterior wall area as determined from Table The moisture content references in Table shall be selected to be less than or equal to MC S Applying the thermal mass effect. When the wall assembly is determined to have sufficient thermal mass, the wall shall be deemed to comply with the code and is permitted to be further evaluated as a mass wall with integral insulation Determine the required U w. Using the gross wall calculation and the required U-values in accordance with the International Energy Conservation Code, determine the required U-value for the opaque wall area using the equation: U w = (A o U o ) [(U g A g )+(Ud Ad)] A w where: U w = The thermal transmittance value for the compliant insulated frame wall. A o = Gross wall area. U o The allowable overall U for the gross wall. Page 7 of 11

8 A g = Window area. U g = The actual value for windows. Ad = Door area. Ud = The actual value for doors. A w = The area of the opaque wall. Where there are more than one door or window in the wall, the equation shall sum the UA for each window and door Determine the mass U w. Referring to IECC Table (3), select the column by matching the U w determined in Section to those heading the columns. Select the row according to the design heating degree days. Where the column and row cross provides the U w with thermal mass effect. 306 INFILTRATION Log Walls. Log walls shall comply with this Section Air Leakage. The building thermal envelope shall comply with Sections 304, and Sections through Thermal envelope. Joint design and any applied sealants shall be capable of maintaining the weather seal at penetrations of the thermal envelope. Such penetrations shall include, but not be limited to, components passing through or over exterior log walls Patterned Sheathing and/or decking penetrating or passing over log walls. Methods shall be employed to restrict air flow between interior and exterior where patterned sheathing/decking (e.g., tongue and groove decking with v-groove pattern exposed to view) connections penetrate to the exterior of the building envelope Patterned sheathing and/or decking seams at ceiling areas. Methods shall be employed to restrict air flow and moisture migration through the joined edges of patterned sheathing/decking Structural components passing over or through log walls. Where structural roof or floor members pass beyond the weather protection provided by the joint design, the penetration shall be capable of maintaining the weather seal Page 8 of 11

9 between wall and structural members as the logs reach equilibrium moisture content Wall Openings. Rough openings in walls shall be designed and constructed to protect the opening from air and water infiltration as well as accommodate settling. Window and door units installed in the wall rough opening shall meet or exceed the installation and sealing requirements of the manufacturer s instructions Moisture Protection. The exterior water plane shall effectively shed water from precipitation Water plane. The exterior water plane is formed by the contiguous log surfaces on which a water film may form extending to the point of weather protection provided by joint design in accordance with Section Water collection. Wall surfaces shall be designed and constructed to promote positive drain of water to exterior to eliminate potential for collection of moisture on or in the log wall Seams and joints. Seams and joints occurring in the log surface shall not interupt the water plane Wall penetrations. All penetrations of the log wall shall be protected by roof projection, flashing or other method to move water away from the seams, joints and bottom edges of the penetration Protective treatments. Wood treatment shall be applied to log surfaces in accordance with manufacturer s instructions specific to the condition of the logs (e.g., green, dry, weathered). Treatments shall be selected and applied to insure that moisture drawn from within the log to the log surface will not be trapped against an impervious film. CHAPTER 4 STRUCTURAL PROVISIONS SECTION 403 ENGINEERED PROVISIONS Applicability. If the building geometry, or loads related to the log structure, exceed any of the following limitations, then the building shall be designed using the provisions of Sections 403 through 407. If portions of building geometry, or loads related to those portions, exceed any of the following limitations, then the Page 9 of 11

10 affected portions shall be designed using the provisions of Sections 403 through 407. The limitations are: 1. Loads: a. Greater than 40-psf (1916 N/m 2 ) live load on floors. b. Greater than 70-psf (3353 N/m 2 ) ground snow load. c. Greater than 90mph (39.6 m/s) wind speed (3 second gust). d. Greater than Wind Exposure Category B. e. Greater than Seismic Design Category B. Exception: Detached one- and two-family dwellings located in Seismic Design Category C. 2. Building dimensions a. Greater than three stories or a mean roof height of 33 feet, (100.6 m) measured from average grade to average roof elevation. b. The building aspect ratio (L/W) less than 1:4 or greater than 4:1. c. The building dimension, length (L) or width (W), greater than 80 feet (243.8 m). d. Floor to floor story height greater than 10 feet (3.0 m). 3. Log floor systems a. Single spans of log floor framing members greater than 26 feet (79.2 m). b. Spacing of logs used as floor framing members greater than 48 inches (1219 mm) on center. c. Cantilever lengths of logs used as cantilevered floor framing members supporting load bearing walls or shear walls greater than the depth, d, of the log joists. d. Log floor joist cantilevers supporting nonload-bearing walls which are not shear walls greater than one-quarter of the span, L/4. e. Setbacks of load bearing walls or shear walls on log floor joist systems greater than the depth, d, of the log joists. Log floor joists shall be located directly over structural elements when used in setback conditions supporting load bearing walls. f. Vertical log floor offsets greater than the log floor depth, (including log floor framing members and floor sheathing). g. Log floor diaphragm aspect ratios greater than limits from Table h. Log floor diaphragm openings greater than 12 feet (36.6 m) or 50 percent of the building, whichever is less. 4. Log walls Page 10 of 11

11 a. Load bearing and nonload-bearing log walls greater than 20 feet (61 m) in unsupported height. b. Offsets in a log shear wall line within a story greater than 4 feet (1219 m). c. Upper story log shear wall segments offset from lower story log shear wall segments by more than the depth, d, of the log floor framing members. d. Log shear wall segment aspect ratios greater than 1:1. e. Log shear wall lines oriented to resist loads in two orthogonal directions. 5. Log roof systems a. Single spans (horizontal projection) of log roof framing members greater than 26 feet (79.2 m). b. Roof framing member spacing greater than 48 inches on center. c. Log rafter overhang lengths greater than one-third of the rafter span or 7 feet ( mm) 4 feet (1219 mm), whichever is less. Rake overhangs greater than one-third half of the purlin length or 7 feet ( mm) 4 feet (1219 mm), whichever is less. Notching at the bearing shall be in compliance with Section d. Roof slope greater than 12:12. For purposes of determining uplift, gravity loads, and lateral bracing requirements, the attic shall be considered an additional story when the roof slope is 7:12 or greater. e. Roof diaphragm aspect ratios greater than values from Table Page 11 of 11