# Presentation: 721626

## Thermal Performance of Log Structures

**Acceptance of Traditional, but “Alternative”, Materials and Methods of Assembly**

- Copyright 2006 © RobPickett &Associates

- 2006 National Workshop on State Buildng  Energy Codes

**Notes:**
Good morning
Introductions
Audience Poll – built a log home? Affilitated with a log home company? Design professional? Student? Other?
Format – Intro to LHC, Codes and Log Building, AF&PA’s participation, Design & Construction elements, Q&A
Announcements – Make sure your card is swiped so we can send more information to you.  Handouts in the back of the room.

## Historic Perspective

**Ancient settlements date to 700 BC**
**Use of indigenous materials**
**Relatively simple, often one room**

**1785 hewn log cabin**

**Post Office, MN**

- 2006 National Workshop on State Buildng  Energy Codes

## Early Log Structures

**Full length logs extended at corners to delay the effect of decay**
**Mud, straw, moss, and other materials used to seal between logs**

- 2006 National Workshop on State Buildng  Energy Codes

**Notes:**
Definition: 
[n]  loose hemp or jute fiber obtained by unravelling old ropes; when impregnated with tar it was used to caulk seams and pack joints in wooden ships 

Webster's 1913 Dictionary 

Definition: 
\Oak"um\, n. [AS. [=a]cumba; pref. ? (cf.G. er-, Goth. us-, orig. meaning, out) + cemban to comb, camb comb. See {Comb}.] 1. The material obtained by untwisting and picking into loose fiber old hemp ropes; -- used for calking the seams of ships, stopping leaks, etc. 2. The coarse portion separated from flax or hemp in nackling. --Knight. {White oakum}, that made from untarred rope. 

## Evolution of Technology

**Organic finishes from local ingredients**
**1920 -- Pre-cut log home “kits”**
**Proprietary solutions to seal out air & moisture**

***Source: REAL LOG HOMES******®***

- 2006 National Workshop on State Buildng  Energy Codes

## Modern Log Structures

**Offer variety of corner & log styles**
**Incorporate sophisticated custom design & engineering**
**Use modern methods & techniques – finishes, pre-cast foundations, insulation, etc.**

- 2006 National Workshop on State Buildng  Energy Codes

## Principles of Construction

**Same as conventional:**
**Project planning & preparation**
**Design loads and deflection criteria**
**Plumb, square and level construction**
**Receiving, handling, and protecting materials**

***Detail courtesy of Southland Log Homes Inc.***

- 2006 National Workshop on State Buildng  Energy Codes

## Tradition Mixes with Convention

**Conventionally built systems except for log walls and log framing members...**
**Foundations, subfloors, partition walls, windows, doors, roofing**
**Plumbing, electrical, mechanical**

*There’s only one right way to build a log home...*
*Per the blueprints, details, and instructions (construction manual) provided with the log package.*

- 2006 National Workshop on State Buildng  Energy Codes

## Building System Variations

**Wall-Logs: Species, size, shape, treatments, MC**
**Extent of processing: Lineal length, pre-cut, handcrafted**
**Joinery: Corners, butt joints, openings, sealants**
**Connections and fastening patterns**
**Accommodating movement: Compaction and shrinkage**

**Settlement allowance over openings is a function of the building system.**

- 2006 National Workshop on State Buildng  Energy Codes

**Notes:**
Most often, high performance windows are sold in log packages
for thermal value
Provide fire protection – higher thermal perf. Resists heat transfer from fire side to combustibles on the other side
Double glazing allows outer pane to be sacrificed while inner pane remains intact – use tempered glass for even more protection.

## The Log Home Industry

**Annual stats taken from industry publications:**
**Over 25,000 log homes built from North American producers**

| Types of Producers | # of Co.s | Annual Production |
| --- | --- | --- |
| Handcrafters | 200-300 | Up to 100 units/year; 85% < 25/yr. |
| Manufacturers of milled products | 270-325 | Up to 1000 units/year; 90% < 200/yr. |

- 2006 National Workshop on State Buildng  Energy Codes

**Notes:**
About 325 milled log home producers manufacture from 20 to 1000 units

## A Market Snapshot

**Over 400,000 log homes exist in North America. **
**7% of custom-built housing market**
**$1.4 billion market**
**Annual production of log home packages increased 41% from 1988 to 1995 and 46% since.**** **

**-- **_**Log Home Living Institute**_** survey, 2001**

**Building Systems Magazine’s 2001 Excellence in Model Home Design – **
**Appalachian Log Structures, Inc.**

- 2006 National Workshop on State Buildng  Energy Codes

**Notes:**
With an industry this big, why would code acceptance be an issue?

## 1977: The LHC First Meets

**22 Charter Members form the Log Homes Council to respond to code issues**

**Develop and promulgate standards of quality and safety throughout the log home industry**
**Disseminate information about developments in the log home industry to regulatory bodies, governmental agencies, the press, and the general public**

***Photo courtesy of Kuhns Bros. Log Homes***

- 2006 National Workshop on State Buildng  Energy Codes

## Today’s Log Homes Council

**60+ LHC Members**
**Subscribe to the Code of Ethics**
**Represent about 20% of all North American log home producers****	****BUT**
**Produce 50% or more of new log home construction**

- 2006 National Workshop on State Buildng  Energy Codes

**Notes:**
Education seminars
Potential testing that will benefit the industry
Support of local organizations that promote log building and its heritage

## LHC Milestones:  Log Grading

**1980: ASTM D3957 Standard Methods for Establishing Stress Grades for Structural Members Used in Log Buildings**
**1981: NES QA-154: Accredited LHC as a rules-writing grading agency**
**1984: Mandatory Log Grading implemented**
**2006: Code requirement published **
** ****IBC (2303.1.10) / IRC (R602.1.3, R802.1.5)**

- 2006 National Workshop on State Buildng  Energy Codes

**Notes:**
D-3957 -- Sponsored by the LHC – effort began in the late 1970’s
             -- first published consensus standard relating to log construction.

## LHC Milestones:  Energy Codes

**1983: Thermal Testing**
**National Bureau of Standards tests 6-20’x20’ buildings w/90” walls:**
**2x4 insulated R-12**
**2x4 without insulation R-4**
**masonry internally insulated R-14**
**un-insulated masonry R-5**
**7” solid square log R-10**
**masonry externally insulated R-12**
**1989: MEC 502.2.1.1.2 Mass Walls**
**Thermal mass credit when density ******** 20 lb/ft2**
**2005: ORNL Whole Wall Test Program**

- 2006 National Workshop on State Buildng  Energy Codes

## LHC Milestones:  Fire Codes

**1997: Urban-Wildland Interface Code**
**“****Log Wall Construction” defined and recognized as a one-hour-rated fire-resistive exterior wall**
**“...****where the smallest horizontal dimension of each solid wood member is at least 6” (152mm).”**

***Test report photos at the 60-minute mark, courtesy of Honka Homes USA, Inc.***

- 2006 National Workshop on State Buildng  Energy Codes

## LHC Milestones:  Construction Standards

**1995: LHC Guide for Construction Manuals**
**Response to HUD for guidance in the review and acceptance of Structural Engineering Bulletins to aid Federally-insured mortgage programs**
**2002: ICC-400 Standard for the Design & Construction of Log Structures**
**Response to ICC and industry request for a standard**

- 2006 National Workshop on State Buildng  Energy Codes

**Notes:**
Hold up a copy of the book.

## Log grading & moisture content
Design values and section properties
Fire-resistance ratings

**Design values and section properties**
**Fire-resistance ratings**

**Settling provisions**

**ICC-400 Log Properties**

- 2006 National Workshop on State Buildng  Energy Codes

**Notes:**
The LHC paper, Fire Performance of Log Walls, uses an old ICBO Standard (7.7) and NER-250 (AITC) to show that a log wall that has a 4” minimum thickness and is 8-feet high will meet a one-hour fire-resistive rating.  These calculations are supported by testing provided by Honka Homes USA, Inc. and Lincoln Logs, Ltd.
AF&PA fire engineers have added Ch 16 to the NDS to calculate the fire resistive rating based on the remaining sound wood beneath the char from a fire.  They do not agree with the approach taken in the LHC paper.
The IS-LOG committee adopted the language of the ICC Urban Wildland Interface Code of a minimum 6” thickness for a one-hour rated wall.  Beyond 1-hr, testing is required.
Total SETTLING = Slumping + Compaction + Shrinkage or a prescribed allowance of 6% or more of the involved height.
 Options for a prescribed minimum, a calculation method, formal engineering analysis, or full scale testing are permitted for each mode of settling.
 NDS 3.10 sets the requirements for bearing to eliminate compaction. Here, compaction is permitted as a technique in sealing log to log.
 Calculating shrinkage – the difference between the design and certified MC and the Service MC as indicated on the following map

## Moisture Content by Climate Zone

- 8-13% MC, avg. 10 %

- 12-15% MC, avg. 13 %

- 13-15% MC,
-  avg. 14 %

- Marine =
- 13-17% MC,
-   avg. 15 %

- 2006 National Workshop on State Buildng  Energy Codes

**Notes:**
While no information is available for zone 9, it is clear that there is very little correlation between HDD regions and EMC.  The designation of humidity zones on the zone map, does however correlate well to the EMC data.  Therefore, the humidity zones are used in the Final Presentation.

## Log grading & moisture content
Design values and section properties
Fire-resistance ratings
Settling provisions
Thermal envelope

**Design values and section properties**
**Fire-resistance ratings**
**Settling provisions**
**Thermal envelope**

**ICC-400 Log Properties**

- 2006 National Workshop on State Buildng  Energy Codes

**Notes:**
The extent of settling now estimated, the standard calls out several areas that need to be detailed to provide allowance for the movement.
Settling gap
Sliding joint
Abutments
Settling devices
Staircases
Counter flashing
Connections
Electrical, mechanical, and plumbing systems
The LHC Construction Manual Guidelines also discuss these needs.

FINALLY, CH.3 addresses the Thermal Envelope

## Slide 20

- 2006 National Workshop on State Buildng  Energy Codes

## Note the inverse relationship of mass  and R-value across a range of specific gravities.

- 2006 National Workshop on State Buildng  Energy Codes

## ICC 400 Log Wall Thickness

**ICC 400 Log Wall Thickness**

- 2006 National Workshop on State Buildng  Energy Codes

## ICC 400 Prescriptive R-values 

**ICC 400 Prescriptive R-values**

**Calculated at 12% EMC, including air films**

- 2006 National Workshop on State Buildng  Energy Codes

**Notes:**
ICC400 Prescriptive R-values calculated at 12% EMC, including air films.

Based on the work done for the LHC and presented to the developers of REScheck, this table was created.

This table is a quick reference option for determining the R-value of the wall assembly.
It assumes a 12% MCs, which we now know is slightly low for most of the country.  However, lower MC = higher R-value.
Above and left of the bold line, the log does not satisfy the heat capacity requirements of the code to achieve thermal mass.
The tabulated R-values are for a square sawn log wall with full contact from log to log.  If a log wall is designed with a chinking/insulation gap, the R-value would be the weighted average of wall are that is solid wood wall (from above) and the chink gap R-value. 
Another table, not shown, was also developed to show the what the specific gravity of the wood needs to be for various shapes and sizes of log.  It shows that a 10” thick square sawn log will satisfy the thermal mass criteria with any wood species while a 5” version will need to be Southern Pine (G=0.55) or denser.

## ICC 400 Structural

**Prescriptive vs. Engineered**
**WFCM as model**
**Lateral loading on log walls**
**Diaphragm and shear wall analysis**

**Building Systems Magazine’s 2002 Excellence in Model Home Design – **
**Heritage Log Homes, Inc.**

- 2006 National Workshop on State Buildng  Energy Codes

**Notes:**
The shear wall aspect ratio is an on-going question due to a lack of adequate fundamental knowledge of log wall systems in controlled conditions.

Prescriptive text:
“Log structures not requiring engineering design in accordance with Section 403 shall be permitted to use prescriptive provisions as approved by the building official.”
This may mean that the IRC standards or the WFCM provisions are acceptable without engineering analysis.
Engineered Provisions
 >40-psf floor loads
 >70-psf snow loads
 >90 mph wind speed in open exposures (>B)
 >seismic category C
 >3 stories in height
 >80’ wall length in any direction
 >10’ between floors (story height)
 building aspect ratio (L/W) <1:4 or >4:1
 and other limits taken from the WFCM – back to DENNIS

## Questions?

**To contact Rob Pickett:**
**RobPickett &Associates**
**P.O. Box 490, Hartland, VT 05048**
**802-436-1325**
**robpickett@vermontel.net**
**www.robpickettandassoc.com**

**For more information:**
**Log Homes Council**
**1-800-368-5242 x8577**
**www.loghomes.org**

- 2006 National Workshop on State Buildng  Energy Codes

**Notes:**
How will ICC 400 affect your business and that of your competitors?

Clearly identifies each aspect of log structures that must be addressed and documented in the building system
Sets the MINIMUM requirements for performance of those aspects
Identifies the extent of conditions beyond which engineering analysis is required – will allow building officials to become more comfortable in the permit and inspection process.  This may alleviate current calls for stamped plans in 70% of the country were seismic, wind and snow loading are not severe.
Will become a major advantage to the industry by setting a base level of quality and performance, it will level the playing field