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Anderson - Thesis 11-5-02 Page 1 Manual for the Inspection of Residential Wood Decks and Balconies by: Cheryl A. Anderson Thesis submitted to the faculty of Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Biological Systems Engineering APPROVED: __________________________ Frank E. Woeste, Chairman __________________________ Joseph R. Loferski __________________________ John V. Perumpral November 2002 Blacksburg, VA Keywords: inspection, wood, lumber, deck, balcony, residential, decay, rot, railing Page 2 Manual for the Inspection of Residential Wood Decks and Balconies by: Cheryl Anderson Frank E. Woeste, Chair Biological Systems Engineering Abstract Residential deck and balcony failures are preventable if the decks and balconies are maintained and inspected regularly. Inspection of in-service decks or balconies is not common and often is unregulated or building codes do not appear to be widely enforced. With every failure, the need for a comprehensive inspection manual for residential wood decks and balconies becomes more apparent. Research was conducted on inspection techniques, common deck and balcony construction methods, maintenance issues, decay detection and the evolution of the building code regulations on decks and balconies. Eight decks were inspected to find the extent of structural inadequacies and non- conformance with building codes. Using the information gathered from the research and inspections, a Manual for the Inspection of Residential Wood Decks and Balconies was written for professional inspectors and building officials. The manual includes recommended methods to prepare for inspection to preparation of final reports. It contains an appendix with information on the “pick test” for detecting early decay, information on adequate deck attachment, and a sample report for a complete deck inspection. Page 3 Acknowledgements iii Acknowledgements First of all, I would like to thank my parents, Al and Barb Finch, who have always supported me and provided me with the two best role models I could ever have. Thank you to my graduate committee, Dr. Frank Woeste, Dr. Joseph Loferski and Dr. John Perumpral, whose ideas and support made my time as a graduate student one of the most rewarding experiences I have ever had. Without Dr. Loferski, the idea for this unique research may have never come up. I want to especially express my gratitude to Dr. Woeste, whose never-ending enthusiasm, support, stories and good humor were the reason I decided to pursue a graduate degree. Thank you to the entire Biological Systems Engineering Department who created a family-like atmosphere in a hectic college town. Thank you to all those who provided the insights, ideas and criticisms that made this thesis and the inspection manual possible. Thank you to the members of the Blacksburg community who let me crawl all over, pick at, stain and insult their decks and balconies. And, of course, thank you to my friends who have called me from all over to tell me about decks and who have pretended to be fascinated by my constant stories about decks and balconies for the past year. Page 4 iv Table of Contents Acknowledgements.......................................................................................................iii Table of Contents.......................................................................................................... iv List of Figures................................................................................................................ vi List of Tables................................................................................................................... x 1. Introduction..............................................................................................................xvi 1.1 Justification........................................................................................................... 1 2. Objectives.................................................................................................................... 4 3. Literature Review....................................................................................................... 5 3.1 Issues that need to be addressed..................................................................... 5 3.2 Standards/Codes...............................................................................................35 3.3 Do-it-yourself books ..........................................................................................38 3.4 Inspections .........................................................................................................43 3.5 Conclusion..........................................................................................................49 4. Investigations ........................................................................................................... 50 4.1 Fairfax County Typical Deck Details ..............................................................50 4.2 Lag Screw Design Values ................................................................................68 4.3 Deck Attachment Issues...................................................................................74 4.4 The Pick Test .....................................................................................................86 5. Full Inspection of Residential Deck....................................................................92 5.1 Introduction.........................................................................................................92 5.2 Objectives ........................................................................................................... 92 5.3 Materials and Methods .....................................................................................92 5.4 Results ................................................................................................................97 5.5 Conclusion........................................................................................................113 5.6 Appendix to Full Deck Report........................................................................115 6. Inspections to Define the Type and Extent of Deficiencies of In-Service Decks and Balconies ..........................................................................................125 6.1 Introduction.......................................................................................................125 6.2 Objectives .........................................................................................................125 Page 5 v 6.3 Deck B ...............................................................................................................125 6.4 Deck C...............................................................................................................134 6.5 Deck D...............................................................................................................146 6.6 Deck E ...............................................................................................................157 6.7 Deck F ...............................................................................................................172 6.8 Balcony G.........................................................................................................183 6.9 Balcony H .........................................................................................................193 6.10 Conclusion......................................................................................................200 7. Summary and Conclusions ................................................................................204 7.1 Summary...........................................................................................................204 7.2 Conclusions ......................................................................................................205 7.3 Recommendations ..........................................................................................205 8. References ..............................................................................................................207 9. Appendix ..................................................................................................................213 9.1 Appendix A: Sample Calculations .................................................................214 9.2 Appendix B: An Inspection Manual for Residential Wood Decks and Balconies...........................................................................................................232 9.3 Appendix C: Supplemental Worksheets for the Inspection of Residential Wood Decks and Balconies ...........................................................................325 Vita.................................................................................................................................338 Page 6 vi List of Figures Figure 3.1. The climate index is a measure of the decay threat. Higher numbers indicate more decay protection is needed (Forest Products Laboratory, 1999). ................................................................. 14 Figure 3.2. A deck detail of the deck-to-house connection shows a lag screw supporting the gravity load from the deck..........................................26 Figure 4.1. A simple joist span is from the center of one bearing to the center of the other. Joist spans with may have a maximum of 3’-0” overhang on each side............................................................................................54 Figure 4.2. The beam spans are shown with the joists stacked on top and the maximum overhang of 2’-0”..................................................................55 Figure 4.3. Spacing of fasteners and edge clearances as required by the Fairfax County Deck Details .................................................................62 Figure 4.4. This typical guardrail detail is required by the Fairfax County Deck Details. The rail cap must withstand a 200 lb concentrated load and the infill must withstand 50 lbs over a 1 ft2 area........................64 Figure 4.5. This free body diagram of a guardrail post shows the reactions in the 1/2 in. diameter thru bolts caused by a 200 lb force applied to the cap rail...............................................................................................65 Figure 4.6. A deck detail of the deck-to-house connection shows a lag screw supporting the gravity load from the deck..........................................76 Figure 4.7. (a) Building codes require decks to be designed to carry a uniformly distributed load over the entire surface. Half of the assumed uniform load is carried by the deck-to-house connection; the other half is carried by the posts. (b) People tend to gather near the railings of the deck, and less load is likely carried by the deck-to- house connection...................................................................................80 Figure 4.8. In this deck detail, wood-to-wood bearing or wood-to-concrete bearing is relied upon for vertical load transfer, rather than connections. The attachment to the house is for lateral support Page 7 vii only. Hollow masonry must be reinforced by rebar and concrete.. ..................................................................................................................84 Figure 4.9. The sound wood broke in a solid piece, and far from the tool. It was difficult to penetrate deeply. One end did not break at all. The wood under the splinter is intact and looks new. ..............................88 Figure 4.10. The decayed wood broke easily; the break is across the grain with no splinters. ............................................................................................. 88 Figure 4.11. This example is a block of virgin Douglas Fir with no decay. It shows a splintered break that begins far from the penetration.......90 Figure 4.12. On the surface, this 50-year-old Douglas Fir purlin looked sound, however with the pick test, decay is indicated by a brittle cross grain break directly over the tool. The entire break is less than one inch long..................................................................................................90 Figure 5.1. Section views of the rail post attachment to the deck: (a) Connection type A is two 1/4”x3” lag screws and one 16d annular threaded nail (b) Connection type B is one two nails and one lag screw........................................................................................................99 Figure 5.2. The nail removed from a rail post (a) before it was removed and (b) when it was measured. .......................................................................100 Figure 5.3. The lag screw that was removed from the rail post. There is noticeable discoloration at the screw head and the interface between the post and the perimeter joist. ........................................101 Figure 5.4. (a) The kerf on railpost #12 (b) The split in railpost #14 and the lag screw added by the homeowner........................................................102 Figure 5.5. The rail analysis unit was two typical infill posts. ............................104 Figure 5.6. Sapwood decay was present at the end-grain of deck boards.....106 Figure 5.7. One half of joist No.30 was supported by the beam, which was probably a construction error and not intended. .............................107 Figure 5.8. Carriage bolts, which are not recognized by the NDS rusted around the edges and crushed the wood around them...............................108 Page 8 viii Figure 5.9. Digging 6 in. below the ground surface and using the pick test showed no evidence of decay on Post No. 5..................................109 Figure 5.10. Material between the ledger and the band joist was observed at a vent. From right to left the materials are the band joist, 1/2” insulation, ledger and 2x2 support for joists. ...................................111 Figure 5.11. (a) The ledger screw (nominal 1/2”x4”) was long enough for the pointed end to stick out of the band joist. (b) The shiny area on the ledger screw is where it penetrated the insulation..........................112 Figure 5.12. (a) Plan view of deck including beam and post numbering...........115 Figure 5.13. Typical section of railing......................................................................117 Figure 5.14. Side view of stairway. ..........................................................................117 Figure 6.1. Plan view of Deck B showing the locations of joists, beams, rail posts and deck posts...........................................................................127 Figure 6.2. (a) A typical railing section. The 2x6 infill pickets were staggered on either side of a 2x4 cap rail. (b) A typical 4x4 rail post. .................127 Figure 6.3. (a) The longest section of deck railing leans outward 4 inches. (b). The side section of railing curves inward. ........................................129 Figure 6.4. The plan view of deck C showing the joists, posts, beams, ledger and cross-bracing. ...............................................................................135 Figure 6.5. (a) A typical section of the railing. (b) A typical railing picket........135 Figure 6.6. A deck post, running from the ground to the top of the railing......136 Figure 6.7. The addition of a scab with four 1/2”x5” lag screws would support the design load.....................................................................................145 Figure 6.8. The plan view of Deck D, showing the steel posts, steel beams, and joists. ......................................................................................................147 Figure 6.9. (a) A typical railing section on Deck D (b) a typical rail post and (c) a typical infill post .................................................................................148 Figure 6.10. A side view of the stairs on Deck D. .................................................148 Figure 6.11. The plan view of Deck E, showing joists, posts and railing posts. Posts P1, P2 and P3 are 4x4 posts detailed in Figure 6.13. Posts P4 and P5 are 2x4 railing posts shown in Figure 6.14. .................159 Page 9 ix Figure 6.12. Deck E was two stories. The 4x4 deck posts were continuous up to the bottom of the top deck..................................................................160 Figure 6.13. A side view of posts P1, P2 and P3 on deck E showing notches and where the railings were attached.......................................................161 Figure 6.14. (a) The typical railing on Deck E. (b) A side view of rail posts P4 and P5 on the deck located next to the exterior house wall. ........162 Figure 6.15. The notch for the 2-2x10beams on posts P1, P2 and P3 in Deck E. The length, depth, and location of this notch are not allowed by the NDS-01..................................................................................................166 Figure 6.16. The erosion of a post in Deck E, possibly caused by surface water runoff. .....................................................................................................171 Figure 6.17. The plan view of Deck F, showing the joists, ledgers and the single post.........................................................................................................174 Figure 6.18. (a) A typical section of the railing on Deck F and (b) A typical picket from the railing on Deck F. .................................................................174 Figure 6.19. The post was not continuous through Deck F. It was toenailed to the deck boards. Another deck was under Deck F. Three separate posts created a column from the ground to the roof of the building…. .............................................................................................175 Figure 6.20. The top rail of Deck F was attached (a) to the building with six Tapcon screws and (b) to the post with four screws......................178 Figure 6.21. The plan view of Balcony G, showing the two ledgers and joists.185 Figure 6.22. (a) The railing of Balcony G. The pickets were 2x4’s (actual size) placed 6 in. on-center. (b) A typical picket from the railing..........185 Figure 6.23. The fastener pattern of the ledger board of Balcony G. ................190 Figure 6.24. The ledger board bowed out ΕΎ” away from the building in one corner.....................................................................................................192 Figure 6.25. The stamp visible on the lumber used on Balcony H.....................194 Figure 6.26. The plan view of Balcony H showing the joists, ledgers and the rim joist. ........................................................................................................195 Page 10 x Figure 6.27. (a) A typical railing section of the metal railing on Balcony H. (b) A view of the railing post in the center of the railing...........................195 Figure 6.28. One of the ledger boards on Balcony C showing the spacing of the 1/2 in. thru bolts used to hold the ledger onto the building...........199 Figure 9.1. Free body diagram of 50 lb/ft load on cap rail. The load is horizontal and outwards from the deck. With the infill pickets spaced 8 in. on center, each picket carries 34 lb........................................................224 Figure 9.2. Free body diagram of infill picket. The 34 lb load is the reaction from the 50 lb/ft on the cap rail. The top connection (a lag screw or nail) must carry 252 lb in withdrawal.................................................224 Figure 9.3. Free body diagram of the 50 lb/ft2 on the infill picket of the railing. It is possible for the entire load to be carried by one picket. The distance, a, varies with the placement on the 50 lb/ft2 over the picket......................................................................................................225 Figure C.1. A typical grade stamp found on a deck element. This stamp is for No. 1 Western Red Cedar, surfaced green………………………..239 Figure C.2. This sample of Southern Pine was tested for copper using Chrome Azurol S. The result was positive, indicating the sample was pressure preservative treated……………………………………….240 Figure C.3. Areas with high climate indexes have higher threats of decay. Index values of 35 – 70 are considered to have moderate threats of decay. Values greater than 70 are severe threats……………….245 Figure G.1. The sound wood broke in a solid piece, and far from the tool. It was difficult to penetrate deeply. One end did not break at all. The wood under the splinter is intact and looks new…………………..262 Figure G.2. The decayed wood broke easily; the break is across the grain with no splinters……………………………………………………………262 Figure G.3. This example is a block of virgin Douglas Fir with no decay. It shows a splintered break that begins far from the penetration….264 Figure G.4. On the surface, this 50-year-old Douglas Fir purlin looked sound, however with the pick test, decay is indicated by a brittle cross Page 11 xi grain break directly over the tool. The entire break is less than one inch long……………………………………………………………….264 Figure G.5. A deck detail of the deck-to-house connection shows a lag screw supporting the gravity load from the deck…………………………267 Figure G.6. (a) Building codes require decks to be designed to carry a uniformly distributed load over the entire surface. Half of the assumed uniform load is carried by the deck-to-house connection; the other half is carried by the posts. (b) People tend to gather near the railings of the deck, and less load is likely carried by the deck-to- house connection…………………………………………………..271 Figure G.7. In this deck detail, wood-to-wood bearing or wood-to-concrete bearing is relied upon for vertical load transfer, rather than connections. The attachment to the house is for lateral support only. Hollow masonry must be reinforced by rebar and concrete………………………………………………………………275 Figure G.8. Section views of the rail post attachment to the deck: (a) Connection type A is two 1/4”x3” lag screws and one 16d annular threaded nail (b) Connection type B is one two nails and one lag screw. ………………………………………………………………….283 Figure G.9. The nail removed from a rail post (a) before it was removed and (b) when it was measured……………………………………………….284 Figure G.10. The lag screw that was removed from the rail post. There is noticeable discoloration at the screw head and the interface between the post and the perimeter joist………………………… 284 Figure G.11. (a) The kerf on railpost #12 (b) The split in railpost #14 and the lag screw added by the homeowner……………………………………286 Figure G.12. The rail analysis unit was two typical infill posts………………….288 Figure G.13. Sapwood decay was present at the end-grain of deck boards….290 Figure G.14. One half of joist No.30 was supported by the beam, which was probably a construction error and not intended…………………...291 Page 12 xii Figure G.15. Carriage bolts, which are not recognized by the NDS rusted around the edges and crushed the wood around them…………………...293 Figure G.16. Digging 6 in. below the ground surface and using the pick test showed no evidence of decay on Post No.5………………………295 Figure G.17. Material between the ledger and the band joist was observed at a vent. From right to left the materials are the band joist, 1/2” insulation, ledger and 2x2 support for joists……………………….297 Figure G.18. (a) The ledger screw (nominal 1/2”x4”) was long enough for the pointed end to stick out of the band joist. (b) The shiny area on the ledger screw is where it penetrated the insulation………………..298 Figure G.19. Freebody diagram of 50 lb/ft load on cap rail. The load is horizontal and outwards from the deck. With the infill pickets spaced 8.in on center, each picket carries 34 lb……………………………………304 Figure G.20. Free body diagram of infill picket. The 34.lb load is the reaction from the 50 lb/ft on the cap rail. The top connection (a lag screw or nail) must carry 252 lb in withdrawal……………………………….304 Figure G.21. Free body diagram of the 50 lb/ft2 on the infill picket of the railing. It is possible for the entire load to be carried by one picket. The distance, a, varies with the placement on the 50 lb/ft2 over the picket…………………………………………………………………..305 Figure G.22a. Plan view of deck including beam and post numbering ….312 Figure G.23. Typical section of railing……………………………………………..314 Figure G.24. Side view of stairway………………………………………………...315 Page 13 xiii List of Tables Table 3.1. Summary of strength losses caused by brown-rot fungi in softwoods from a review of literature by Wilcox (1978). Losses are expressed as a percentage of the expected value in non-decayed wood.........................................................................................................17 Table 3.2. Load and other requirements for residential (one and two family) decks from the 1976 Southern Building Code, the 1992 and 1995 CABO codes, the 1995 ASCE Minimum Design Loads, the 1998 Fairfax County Deck Details and the 1998 and 2000 International Code Council. ......................................................................................... 36 Table 3.3. Load and other requirements for balconies from the 1995 ASCE Minimum Design Loads, 1996 BOCA, ASTM E985-00e1, the 1997 Southern Building Code and the 2000 International Building Code. ..................................................................................................................37 Table 4.1. Maximum joist spans and beam sizes as recommended by the Fairfax County Deck Details (Table 1, Fairfax County, 1998) ........51 Table 4.2. The tabulated bending, shear and compression perpendicular to grain design values for sizes of No. 2 Southern Pine dimension lumber. ..................................................................................................... 53 Table 4.3. Maximum spans of No. 2 Southern Pine joists .................................60 Table 4.4. Beam sizes for No. 2 Southern Pine beams with simple span joists and overhanging joists. .........................................................................61 Table 4.5. Spacing of fasteners at the ledger board as shown in Figure 4 and the resulting load per fastener for tabulated spans..........................63 Table 4.6. Dimensions of lag screws as described in ASME B18.2.1-1996 ...72 Table 4.7. Lateral design values of lag screws with main member as shown and side member 2x_ southern pine (G = 0.55) ...............................72 Table 4.8. Required spacing of 1/2”x3.5” lag screw connecting SP ledger to SPF band joist for residential deck joist spans (loaded by 40 psf live plus 10 psf dead load). ..........................................................................78 Page 14 xiv Table 5.1. Size and condition of railing posts and the deck-post connection…… .....................................................................................118 Table 5.2. Condition of railing infill .......................................................................119 Table 5.3. Size, span and condition of joists and joist fasteners. ...................120 Table 5.4. Size, span, and condition of beams and beam fasteners. ............123 Table 5.5. Size and condition of deck posts. ......................................................124 Table 5.6. The condition of stairway risers, listed from bottom to top............124 Table 5.7. The condition of stairway stringers....................................................124 Table 6.1. The actual and allowable design values for the joists in Deck B as determined by using the methods in the NDS-01...........................131 Table 6.2. The actual and allowable design values for the beams in Deck B as determined by using the methods in the NDS-01...........................132 Table 6.3. The actual and allowable compression stress parallel-to-grain design values for the deck posts in Deck B as determined by using the methods in the NDS-01................................................................133 Table 6.4. The actual and allowable design values for the 50 lb/ft2 design load on the railings of Deck C as determined by using the methods in the NDS-01. ..........................................................................................138 Table 6.5. The actual and allowable design values for the pickets in Deck C as determined by using the methods in the NDS-01...........................139 Table 6.6. The actual and allowable design values for the posts in Deck C as determined by using the methods in the NDS-01...........................140 Table 6.7. The actual and allowable design values for the joists in Deck C as determined by using the methods in the NDS-01...........................141 Table 6.8. The actual and allowable design values for the beams in Deck C as determined by using the methods in the NDS-01...........................142 Table 6.9. The actual and allowable design values for the 50 lb/ft2 design load on the infill pickets of Deck D as determined by using the methods in the NDS-01. ......................................................................................150 Page 15 xv Table 6.10. The actual and allowable design values for the 50 lb/ft distributed load on the infill pickets of Deck D as determined by using the methods in the NDS-01.......................................................................151 Table 6.11. The actual and allowable design values for the 200 lb load applied horizontally on the rail posts of Deck D as determined by using the methods in the NDS-01.......................................................................152 Table 6.12. The actual and allowable design values for the joists in Deck D as determined by using the methods in the NDS-01...........................154 Table 6.13. The actual and allowable design values for the 50 lb/ft2 design load on the railings of Deck E as determined by using the methods in the NDS-01..................................................................................................164 Table 6.14. The actual and allowable design values for the 2x4 rail posts in Deck E as determined by using the methods in the NDS-01. ......165 Table 6.15. The actual and allowable notch sizes for the 4x4 post used in Deck E based on the NDS-01, Section 4.4.3.............................................166 Table 6.16. The actual and allowable design values for the posts in Deck E when the 200 lb load required by building codes was applied outward and the post supported the required gravity loads..........167 Table 6.17. The actual and allowable design values for the joists in Deck E as determined by using the methods in the NDS-01...........................168 Table 6.18. The actual and allowable design values for the beams in Deck E as determined by using the methods in the NDS-01...........................170 Table 6.19. The actual and allowable design values for the 50 lb/ft2 design load on the railings of Deck F as determined by using the methods in the NDS-01..................................................................................................176 Table 6.20. The actual and allowable design values for the pickets in Deck F as determined by using the methods in the NDS-01...........................177 Table 6.21. The actual and allowable design values for the top post in Deck F when the 200 lb load required by building codes is applied outward and the roof load is applied as determined by using the methods in the NDS-01. ..........................................................................................180 Page 16 xvi Table 6.22. The actual and allowable design values for the joists in Deck C as determined by using the methods in the NDS-01...........................181 Table 6.23. The actual and allowable design values for the railing pickets in Balcony G as determined by using the methods in the NDS-01..188 Table 6.24. The actual and allowable design values for the railing infill in Balcony G as determined by using the methods in the NDS-01..188 Table 6.25. The actual and allowable design values for the joists in Balcony G as determined by using the methods in the NDS-01......................189 Table 6.26. The actual and allowable design values for the fasteners in Balcony B as determined by using the methods in the NDS-01..................191 Table 6.27. The actual and allowable design values for the joists in Balcony H as determined by using the methods in the NDS-01......................198 Table 6.28. A summary of deficiencies found in all decks and balconies inspected. ..............................................................................................202 Table A.1. Load and other requirements for residential (one and two family) decks and balconies from the 1995 CABO code, the 1995 ASCE Minimum Design Loads, the 1998 Fairfax County Deck Details and the 1998 and 2000 International Code Council…………………...234 Table G.1. Required spacing* of 1/2”x3.5” lag screw connecting SP ledger to SPF band joist for residential deck joist spans (loaded by 40 psf live plus 10 psf dead load)……………………………………………….269 Table G.2. Size and condition of railing posts and the deck-post connection…………………………………………………………….316 Table G.3. Condition of railing infill………………………………………………317 Table G.4. Size, span and condition of joists and joist fasteners…………….318 Table G.5. Size, span, and condition of beams and beam fasteners………..321 Table G.6. Size and condition of deck posts…………………………………...322 Table G.7. The condition of stairway risers, listed from bottom to top………322 Table G.8. The condition of stairway stringers……………………………………322
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