TG20:12 – Supplement 1

1 of 16

N A S C

This supplement to TG20:08 is an interim document which has been prepared to take account of thewithdrawal of the wind loading code, BS 6399 part 2:1997 and its subsequent replacement by BS EN 1991-1-4:2005 part of Eurocode 1. The supplement is designed to be read in conjunction with TG20:08 and onlycovers section 2 of volume 1 of TG20:08. A revised edition of TG20:08 is in preparation which will incorporatea full set of changes, provide a full set of new safe height tables and include some additional data.

This supplement also includes a revision to Appendix H which gives the maximum permissible heights forunclad scaffolds, tied to permeable open structures (see pages 14 and 15).

In conjunction with the supplement a set of markers has been provided for insertion into TG20:08 to identifywhere the supplement has made changes. Replacement tables and text are set out in the supplement andare as follows:

Revised versions of the following text:

Clause 4.4.3 Procedure to determine the safe height of a Basic Scaffold.Revised Figure 5 Basic wind velocityRevised Figure 6 Topographical factor TwindTable 2 Safe heights for unclad Basic independent tied scaffoldsTable 3 Safe heights for debris netted Basic independent tied scaffoldsTable 4 Safe heights for sheeted Basic independent tied scaffoldsTable 5 Safe heights for unclad Basic putlog scaffolds

In addition to this the following nomenclature has been changed:

The basic wind velocity, Vb is replaced by the fundamental basic wind velocity Vb,map

The wind factor S is replaced by the wind factor Swind

The topographical factor T is replaced by the topographical factor Twind

The revised text is set out below:

4.4.3 Procedure to determine maximum safe height of a Basic Scaffold

In order to identify the appropriate safe working height of a Basic Scaffold using the summary Tables inSupplement 1, the following procedure should be followed:

a) Choose the fundamental basic wind velocity (Vb,map) from the map at revised Figure 5 (page 3) for thesite on which the scaffold is to be erected. (The range will be from 20m/s to 30m/s)

b) Establish the critical direction from which the wind will affect the scaffold. This is done by calculating themost demanding topographical factor (Twind) from revised Figure 6 (page 4) by considering all possiblewind directions. A knowledge of the site location is required to determine whether the terrain is nominallyflat, moderately steep, or steep. Hills and ridges have different factors to those for cliffs and

INTRODUCTION

TG20:12 Supplement 1The effect of the introduction of the European Wind Code: BS EN 1991-1-4:2005 on Basic Scaffolds and TG20 Appendix H

Rev A January 2012

escarpments. The values for the topography factor Twind for scaffolds erected up to 50m in height onmoderate hills or escarpments up to 20% (1in 5)slope, and for steep hills or escarpments greater than30% (1in 3.3) slope, are shown in Figure 6. Engineering judgement should be used to establish valuesof Twind for intermediate values of slope. (The range is Twind = 1.00 to Twind = 1.26)

c) Establish from information provided by site the altitude A (in metres above sea level) of theground on which the scaffold stands. A can also be obtained from Ordnance Survey maps orvia the internet. (i.e. www.google earth).

d) Calculate Swind, the wind factor, from

Swind = Vb,map Twind (1 + )The value of Swind is sufficient for use in the revised Tables 2, 3, 4 and 5 (pages 5, 6, 7, 8, 9 &13) to determine the minimum safe height.

e) From revised Tables 2, 3, 4 and 5, (pages 5, 6, 7, 8, 9 & 13) determine the maximum safeheight of the scaffold using the value of wind factor Swind, determined above.

Note that this is a simplified version of the procedures set out in BS EN 1991-1-4. For ascaffold on a particular face of a building a less conservative approach is first to consider eachwind direction in turn for that face and calculate the topography factor Twind and thecorresponding wind factor Swind. For each value of Swind and the upwind distance to the seaassociated with it use Appendix A (TG20:08 page 170) to determine a permitted height forthe scaffold on that face of the building.

The lowest of these heights is then taken as the permitted height.

A1000

2 of 16

N A S C

As an example, consider a site in Manchester, 10km from the edge of the city and surrounded bybuildings. The independent tied scaffold faces due south and is slightly more than half way up aridge, which has an average slope of 1 in 18 (0.056). The site altitude is 60m. The scaffold is fullyboarded, five boards wide and with two lightly loaded inside boards, designated 3-5-2 for generalpurpose use (Load Class 3) and will be debris netted with lines of ties at alternate lifts.

From the wind velocity map, revised Figure 5, Vb,map = 22.5 m/sec

For the slope at 1:18, the location is a moderately steep ridge. More than halfway up the slope at0.5 Lu gives a Topography Factor Twind, from Figure 6 (b) so that, Twind = 1.09

The wind factor Swind = 22.5 1.09 (1 + ) = 22.5 1.09 1.06 = 25.99 = 26In Table 3 (page 6) the minimum safe height is given as 15m using standard duty ties.

601000

Revised Figure 5 Fundamental basic wind velocity Vb,map

0

0 20 40

Statute miles

Kilometres

60 80 100

40 80 120 160

Aberdeen

Inverness

Dundee

Edinburgh

NewcastleCarlisle

Preston Leeds

Nottingham

York Kingstonupon-Hull

Manchester

Stoke

Aberystwyth

Swansea

CardiffBristol

Taunton

Plymouth

Oxford

LONDON

Northampton

Birmingham

Leicester

BedfordIpswich

Norwich

Brighton

Ch l I l d 24 /

Bournemouth

Liverpool

Belfast

Galway Dublin

Limerick

Waterford

Cork

Londonderry

Glasgow

Perth

Oban

Sheffield

25

25

25

24

24

22

22

21.5

23

23

23

26

26

26

27

27

27

28

28

28

2828

2929

29

30

30

30

31

3 of 16

N A S C

Revised Figure 6 Revised Topography factor Twind

(a) Nominally flat terrain, average slope < 1: 20

Wind Factor Twind = 1.00

Wind Factor Twind

Wind Factor Twind

Wind Factor Twind

Wind Factor Twind

(b) Moderately steep terrain, average slope 1: 3 (e) Steep terrain, average slope >1: 3

(c) Moderately steep terrain, average slope

5 of 16

Lines of ties at alternate liftsPart Boarded Fully Boarded

Load Class Swind

1 - 3 - 0 20 - 28323640

2 - 4 - 0 20 - 40

3 - 5 - 0 20 - 40

3 - 5 - 0S 20 - 40

3 - 4 - 1 20 - 40

3 - 4 - 1S 20 - 40

3 - 4 - 2 20 - 40

3 - 4 - 2S 20 - 40

3 - 5 - 1 20 - 40

3 - 5 - 1S 20 - 40

3 - 5 - 2 20 - 40

3 - 5 - 2S 20 - 40

4 - 5 - 0 20 - 40

4 - 4 - 1 20 - 40

4 - 4 - 2 20 - 40

4 - 5 - 1 20 - 40

4 - 5 - 2 20 - 40

safe height m Tie duty/kN

47 light46 light44 light42 light

41 light

41 light

47 light

43 light

49 light

37 light

43 light

38 light

44 light

33 light

39 light

39 light

42 light

37 light

36 light

31 light

Load Class Swind

1 - 3 - 0 20 - 28323640

2 - 4 - 0 20 - 40

3 - 5 - 0 20 - 40

3 - 5 - 0S 20 - 40

3 - 4 - 1 20 - 40

3 - 4 - 1S 20 - 40

3 - 4 - 2 20 - 40

3 - 4 - 2S 20 - 40

3 - 5 - 1 20 - 40

3 - 5 - 1S 20 - 40

3 - 5 - 2 20 - 40

3 - 5 - 2S 20 - 40

4 - 5 - 0 20 - 40

4 - 4 - 1 20 - 40

4 - 4 - 2 20 - 40

4 - 5 - 1 20 - 40

4 - 5 - 2 20 - 40



21 light

20 light

24 light

23 light

27 light

18 light

21 light

19 light

23 light

16 light

19 light

20 light

23 light

19 light

20 light

16 light

Lines of ties at every liftPart Boarded Fully Boarded

Load Class Swind

1 - 3 - 0 20 - 28323640

2 - 4 - 0 20 - 3640

3 - 5 - 0 20 - 40

3 - 5 - 0S 20 - 40

3 - 4 - 1 20 - 40

3 - 4 - 1S 20 - 40

3 - 4 - 2 20 - 40

3 - 4 - 2S 20 - 40

3 - 5 - 1 20 - 40

3 - 5 - 1S 20 - 40

3 - 5 - 2 20 - 40

3 - 5 - 2S 20 - 40

4 - 5 - 0 20 - 40

4 - 4 - 1 20 - 40

4 - 4 - 2 20 - 40

4 - 5 - 1 20 - 40

4 - 5 - 2 20 - 40



47 light44 light

50 light

50 light

50 light

50 light

50 light

50 light

50 light

50 light

49 light

50 light

50 light

50 light

50 light

50 light

50 light

Load Class Swind

1 - 3 - 0 20 - 2428323640

2 - 4 - 0 20 - 323640

3 - 5 - 0 20 - 3640

3 - 5 - 0S 20 - 3640

3 - 4 - 1 20 - 3640

3 - 4 - 1S 20 - 3640

3 - 4 - 2 20 - 40

3 - 4 - 2S 20 - 40

3 - 5 - 1 20 - 40

3 - 5 - 1S 20 - 3640

3 - 5 - 2 20 - 40

3 - 5 - 2S 20 - 40

4 - 5 - 0 20 - 3640

4 - 4 - 1 20 - 3640

4 - 4 - 2 20 - 40

4 - 5 - 1 20 - 40

4 - 5 - 2 20 - 40


24 light23 light22 light21 light19 light

24 light23 light22 light

28 light26 light

36 light34 light

31 light30 light

40 light38 light

25 light

33 light

27 light

36 light35 light

22 light

30 light

32 light31 light

37 light36 light

30 light

32 light

27 light

table 2 Safe heights for UNCLAD Basic independent tied scaffolds,FULLY ledger braced with LIGHTLY loaded inside boards

Notes: 1. Tie densities are defined in Clause 4.4.2. It is not permissible to reduce the tie density by inserting a fewer number of ties of aduty heavier than that specified in the safe height tables.

2. For the tie pattern in figure 9(c) and 9(f) tie duties shall be determined by reference to the appropiate table in Appendix A (page 170 Volume 2) and doubling the tie duty listed.

3. The presence of the suffix S denotes a class 3 scaffold with a bay length no greater than 1.8m.

6 of 16


Load Class Swind

1 - 3 - 0 20 - 24283236

40

2 - 4 - 0 20 - 283236

40

3 - 5 - 0 2024 - 2832 - 36

40

3 - 5 - 0S 20 - 2428 - 3236 - 40

3 - 4 - 1 2024 - 2832 - 36

40

3 - 4 - 1S 20 - 2428 - 32

36

40

3 - 4 - 2 2024 - 2832 - 40

3 - 4 - 2S 20 - 2428 - 3236 - 40

3 - 5 - 1 2024 - 2832 - 36

40

3 - 5 - 1S 20 - 2428 - 32

36

40

3 - 5 - 2 2024 - 2832 - 40

3 - 5 - 2S 20 - 2428 - 3236 - 40

4 - 5 - 0 20 - 2428 - 3236 - 40

4 - 4 - 1 20 - 2428 - 32

36

40

4 - 4 - 2 20 - 2428 - 32

36 - 40

4 - 5 - 1 20 - 2428 - 3236 - 40

4 - 5 - 2 20 - 2428 - 3236 - 40


40 standard39 heavy35 heavy31 heavy

26 12.3

36 standard36 heavy33 heavy

28 heavy

36 light36 standard36 heavy35 heavy

42 light42 standard42 heavy

41 light41 standard41 heavy3 6 heavy


43 heavy





41 heavy





39 heavy

36 Light36 standard

36 heavy

34 Light34 standard34 heavy


Load Class Swind

1 - 3 - 0 20 - 24283236

40

2 - 4 - 0 20 - 283236

40

3 - 5 - 0 2024 - 2832 - 36

40

3 - 5 - 0S 20 - 2428 - 3236 - 40

3 - 4 - 1 20 - 2428 - 32

3640

3 - 4 - 1S 20 - 2428 - 32

36

40

3 - 4 - 2 20 - 2428 - 3236 - 40

3 - 4 - 2S 20 - 2428 - 3236 - 40

3 - 5 - 1 20 - 2428 - 3236 - 40

3 - 5 - 1S 20 - 2428 - 3236 - 40

3 - 5 - 2 20 - 2428 - 3236 - 40

3 - 5 - 2S 20 - 2428 - 3236 - 40

4 - 5 - 0 20 - 2428 - 3236 - 40

4 - 4 - 1 20 - 2428 - 3236 - 40

4 - 4 - 2 20 - 2428 - 32

36 - 40

4 - 5 - 1 20 - 2428 - 3236 - 40

4 - 5 - 2 20 - 2428 - 3236 - 40



14 heavy


15 heavy





25 heavy









18 Light18 standard

18 heavy



table 3 Safe heights for DEBRIS NETTED Basic independent tied scaffolds,FULLY ledger braced with LIGHTLY loaded inside boards

Notes: 1. Where a figure appears in the Tie duty column, the tie duty exceeds that for a heavy duty tie. The number given is the tensile tieforce in kN which must be resisted by the tie assembly

2. Tie densities are defined in Clause 4.4.2. It is not permissible to reduce the tie density by inserting a fewer number of tiesof a duty heavier than that specified in the safe height tables.

7 of 16


3 continued Safe heights for DEBRIS NETTED Basic independent tied scaffolds,FULLY ledger braced with LIGHTLY loaded inside boardsLoad Class Swind

1 - 3 - 0 20 - 24283236

40

2 - 4 - 0 20 - 283236

40

3 - 5 - 0 2024 - 28

32 36

40

3 - 5 - 0S 20 - 2428 - 3236 - 40

3 - 4 - 1 2024 - 28

3236

40

3 - 4 - 1S 20 - 2428

32 - 40

3 - 4 - 2 2024 - 28

3236

40

3 - 4 - 2S 20 - 2428

32 - 40

3 - 5 - 1 2024 - 28

3236

40

3 - 5 - 1S 20 - 2428 - 3236 - 40

3 - 5 - 2 2024 - 28

3236

40

3 - 5 - 2S 20 - 2428 - 3236 - 40

4 - 5 - 0 20 - 2428 - 3236 - 40

4 - 4 - 1 20 - 2428 - 3236 - 40

4 - 4 - 2 20 - 2428 - 32

36 - 40

4 - 5 - 1 20 - 2428 - 3236 - 40

4 - 5 - 2 20 - 2428 - 32

36

40



20 heavy


28 heavy


41 heavy



43 heavy



42 heavy



41 heavy



40 heavy



5 0 light50 standard50 heavy

50 Light50 standard

50 heavy



49 heavy

Load Class Swind

1 - 3 - 0 20 - 24283236

40

2 - 4 - 0 20 - 283236

40

3 - 5 - 0 20 - 2428 - 32

3640

3 - 5 - 0S 20 - 2428 - 32

36

40

3 - 4 - 1 2024 - 28

3236

40

3 - 4 - 1S 20 - 2428 - 32

36

40

3 - 4 - 2 20 - 2428 - 3236 - 40

3 - 4 - 2S 20 - 2428 - 32

36

40

3 - 5 - 1 20 - 24283236

40

3 - 5 - 1S 20 - 2428 - 32

36

40

3 - 5 - 2 20 - 2428 - 32

3640

3 - 5 - 2S 20 - 2428 - 32

36

40

4 - 5 - 0 20 - 2428 - 32

36

40

4 - 4 - 1 20 - 2428 - 32

36

40

4 - 4 - 2 20 - 2428 - 32

36 - 40

4 - 5 - 1 20 - 2428 - 32

36

40

4 - 5 - 2 20 - 2428 - 3236 - 40


21 standard20 standard18 heavy16 heavy

13 heavy


16 heavy



28 heavy


23 heavy


32 heavy



32 heavy


22 heavy


29 heavy



29 heavy


26 heavy


30 heavy

30 Light30 standard

30 heavy


27 heavy


Notes: 3. For the tie pattern in Figure 9(c) and 9(f) tie duties shall be determined by reference to the appropriate table in Appendix A(page 170 - Volume 2) and doubling the tie duty listed.

4. ns means not stated as calculation indicates the stress exceeds the allowable limit on the scaffold.5 . The presence of the suffix S denotes a class 3 scaffold with a bay length no greater than 1.8m.

8 of 16


Load Class Swind

1 - 3 - 0 20 - 242832

36 - 40

2 - 4 - 0 2024 - 28

323640

3 - 5 - 0 2024 - 28

323640

3 - 5 - 0S 2024 - 32

3640

3 - 4 - 1 2024 - 28

323640

3 - 4 - 1S 2024 - 28

323640

3 - 4 - 2 2024 - 28

323640

3 - 4 - 2S 2024 - 28

323640

3 - 5 - 1 2024 - 28

323640

3 - 5 - 1S 2024 - 32

3640

3 - 5 - 2 2024 - 28

323640

3 - 5 - 2S 2024-28

323640

4 - 5 - 0 20 - 2428 - 32

3640

4 - 4 - 1 2024 - 32

3640

4 - 4 - 2 2024- 28

323640

4 - 5 - 1 20 - 2428 - 32

3640

4 - 5 - 2 20 - 2428 - 32

3640


32 heavy26 heavy12 13.9ns ns

29 standard29 heavy20 13.59 14.7ns ns

29 standard29 heavy29 12.514 14.08 15.4

36 standard36 heavy30 13.714 14.8

34 standard34 heavy30 12.616 14.38 15.6

41 standard41 heavy38 heavy31 13.816 15.1

33 standard33 heavy30 12.616 14.48 15.7


29 standard29 heavy29 12.515 14.18 15.5

36 standard36 heavy29 13.614 14.9

28 standard28 heavy28 12.515 14.18 15.5


29 standard29 heavy23 13.110 14.0

34 standard34 heavy27 13.512 14.4


29 standard29 heavy24 13.211 14.1

29 standard29 heavy24 13.211 14.1

Load Class Swind

1 - 3 - 0 20 - 242832

36 - 40

2 - 4 - 0 2024 - 28

323640

3 - 5 - 0 2024 - 32

36 40

3 - 5 - 0S 20 - 2428 - 32

3640

3 - 4 - 1 2024 - 28

323640

3 - 4 - 1S 2024 - 28

323640

3 - 4 - 2 2024 - 32

3640

3 - 4 - 2S 20 - 2428 - 32

3640

3 - 5 - 1 2024 - 32

3640

3 - 5 - 1S 20 - 2428 - 32

3640

3 - 5 - 2 2024 - 32

3640

3 - 5 - 2S 20 - 2428 - 32

3640

4 - 5 - 0 20 - 2428 - 32

3640

4 - 4 - 1 20 - 2428 - 32

3640

4 - 4 - 2 20 - 2428 - 32

3640

4 - 5 - 1 20 - 2428 - 32

3640

4 - 5 - 2 20 - 2428 - 32

3640



16 standard16 heavy12 12.49 14.6ns ns

15 standard15 heavy12 13.58 15.4

19 standard19 heavy16 12.313 14.5




20 standard20 heavy18 12.615 14.9


20 standard20 heavy17 12.413 14.6


18 standard18 heavy17 12.413 14.6

16 standard16 heavy14 heavy10 13.9

20 standard20 heavy16 12.312 14.4

17 standard17 heavy16 12.312 14.5



table 4 Safe heights for SHEETED Basic independent tied scaffolds,FULLY ledger braced with LIGHTLY loaded inside boards

Notes: 1. Where a figure appears in the Tie duty column, the tie duty exceeds that for a heavy duty tie The number given is the tensile tie force in kN which must be resisted by the tie assembly

2. Tie densities are defined in Clause 4.4.2. It is not permissible to reduce the tie density by inserting a fewer number of tiesof a duty heavier than that specified in the safe height tables.

9 of 16


4 continued Safe heights for SHEETED Basic independent tied scaffolds,FULLY ledger braced with LIGHTLY loaded inside boardsLoad Class Swind

1 - 3 - 0 20 - 242832

36 - 40

2 - 4 - 0 20242832

36 - 40

3 - 5 - 0 2024 - 28

323640

3 - 5 - 0S 2024 - 28

323640

3 - 4 - 1 202428323640

3 - 4 - 1S 2024 - 28

323640

3 - 4 - 2 202428323640

3 - 4 - 2S 2024 - 28

323640

3 - 5 - 1 2024 - 28

323640

3 - 5 - 1S 2024 - 28

323640

3 - 5 - 2 2024 - 28

323640

3 - 5 - 2S 2024 - 28

323640

4 - 5 - 0 2024 - 28

323640

4 - 4 - 1 2024 - 28

323640

4 - 4 - 2 2024 - 28

323640

4 - 5 - 1 2024 - 28

323640

4 - 5 - 2 2024 - 28

323640



31 standard31 heavy29 heavy13 12.4ns ns



44 standard44 heavy43 heavy25 12.310 13.2ns ns


45 standard45 heavy43 heavy26 12.310 13.2ns ns











Load Class Swind

1 - 3 - 0 20242832

36 - 40

2 - 4 - 0 20242832

36 - 40

3 - 5 - 0 2024 - 28

323640

3 - 5 - 0S 20 - 2428323640

3 - 4 - 1 2024 - 28

323640

3 - 4 - 1S 202428323640

3 - 4 - 2 2024 - 28

323640

3 - 4 - 2S 2024 - 28

323640

3 - 5 - 1 2024 - 28

323640

3 - 5 - 1S 20 - 2428323640

3 - 5 - 2 2024 - 28

323640

3 - 5 - 2S 20 - 2428323640

4 - 5 - 0 20 - 2428323640

4 - 4 - 1 20 - 2428323640

4 - 4 - 2 20 - 2428323640

4 - 5 - 1 20 - 2428323640

4 - 5 - 2 20 - 2428323640







33 standard33 heavy32 heavy27 heavy21 12.910 13.9












Notes: 3. For the tie pattern in Figure 9(c) and 9(f) tie duties shall be determined by reference to the appropriate table in Appendix A(page 170 - Volume 2) and doubling the tie duty listed.

4. ns means not stated as calculation indicates the stress exceeds the allowable limit on the scaffold.5. The presence of the suffix S denotes a class 3 scaffold with a bay length no greater than 1.8m.

4.5 Freestanding house building scaffolds

Freestanding scaffolds may be built up to 6m high provided they are built to the following limiting specification:

1. Not more than 6m to the top-working platform.

2. The scaffold is not fitted with sheeting or debris netting.

3. Lift heights do not exceed 2m.

4. Bay length no more than 2.1m.

5. Only one lift is boarded.

6. Scaffold width is either four boards plus one or five boards wide. When fitted, the inside board is forlight duty (0.75kN/m2) loading only.

7. Alternate pairs of standards are fully ledger braced.

8. Single un-jointed tubes are used for the standards and rakers.

9. Faade bracing is fitted from the top of the scaffold to the base every five bays.

10. Maximum imposed working load of 2 kN/m2 is on one level only. This equates to general building work including brickwork, window and mullion fixing, rendering andplastering. It does NOT allow for the storage of palleted material.

11. A maximum wind factor Swind = 26. See revised Clause 4.4.3

The foundations of freestanding scaffolds must not permit settlement of the scaffold.

When such scaffolds are more than 4m high, provision should be made to prevent overturning due to theeffects of wind or other horizontal forces. (Note that a freestanding scaffold four boards wide and 6m high hasa height to width ratio of about 6:1. This is well in excess of the limits for freestanding towers recommendedin Clauses 24.11 to 24.14 (TG20:08 page 82-84). This may be done by the use of rakers to alternate pairsof standards, ties to the faade or to some other stable structure, suitably braced returns around the cornersof the building or kentledge. Combinations of these methods may also be appropriate.

An example of a house building scaffold three lifts high with rakers is shown at Figure 18 (TG20:08 page 45).

When checking for overturning, the ratio of the righting moment to the overturning moment, should be not lessthan 1.5

4.6 Standard Putlog Scaffolds

A standard putlog scaffold consists of a single row of standards parallel to the face of the building and set asfar away from it as is necessary to accommodate a platform of three to five boards with the inner edge of theplatform as close to the wall as is practicable. An example is shown in Figure 8 (TG20:08 page 33).

The standards are connected with a ledger fixed with right angle couplers and the putlogs may be fixed to theledgers with right angle or putlog couplers.

The blade end of the putlog tube or putlog adaptor is normally placed horizontally on the brickwork being built.However, where putlog scaffolds are erected against an existing brick wall for repointing, the old putlog holesmay be reused or others raked out. In this case the putlog blades may be inserted vertically.

Base plates, and where necessary sole plates should be placed under each standard. See also Clauses 7.1to 7.7 (TG20:08 page 50-51). Tying recommendations are detailed in Clauses 5.1 to 5.4 (TG20:08 page35-41) with special attention needed for Through ties. Refer to Clause 5.4.4.2 (TG20:08 page 40).

To ensure the stability of the scaffold is maintained, it is recommended that:

a) At the base lift a foot tie, attached to the standards using right-angle couplers, is installed 150mm abovethe base plates.

10 of 16

N A S C

b) At the first lift an under slung bridle tube should be installed approximately 100mm from the wall/brickwork with right-angle couplers.

c) Ledger braces, connecting the bridle tube to the foot tie, should be installed at every second standard.

Where a putlog is required for a board support and it is opposite an opening in the building such as a windowor doorway, the inside end of the putlog should be supported on an under slung bridle tube spacing betweenadjacent putlogs, as shown in Figure 13 (TG20:08 page 40), which also shows a method of tying throughthese openings.

Longitudinal bracing (also called faade bracing) is required every six bays and extending to the full height ofthe scaffold, fitted either across two bays, or in a continuous line. Ledger bracing is not required in the finishedstructure.

Single lift putlog scaffolds may be in use for bricklaying when the wall has not reached sufficient height to givean effective tie point. In this case, the scaffold should be stabilized by rakers and foot ties, until ties can beinserted in the wall.

A Putlog fitting is not a tie. On walls without openings, single bricks should be left out to accept ties (TG20:08 page 33)

Figure 8 Typical putlog scaffold (TG20:08 page 33)

Notes

1. This drawing should be read in conjunction with the text.

2. Some transoms have been omitted for clarity. See Clause 10 (TG20:08 page 51).

The lift height for brickwork is normally between 1.35 m and 1.50m, although for certain types of masonry alower lift height may be necessary. Putlog scaffolds are not normally sheeted.

When using Putlog scaffolds it is important to ensure that the supporting structure can resist the forcesgenerated by the scaffold. In cases where the brickwork is green, or there is any doubt about its adequacy tosupport the blade end of the putlog, then an independent scaffold should be considered.

Basic Putlog Scaffolds require no further design, provided the conditions set out in Clause 4.6.1 are satisfied.

4.6.1 Conditions for Basic Putlog Scaffolds

Basic Putlog Scaffolds may be constructed to the safe heights shown in this Guide, provided they areconstructed in accordance with the recommendations set out below:

1. It is a Standard Putlog Scaffold.

2. Loading classes, maximum bay lengths and scaffold widths conform to Table 1 (TG20:08 page 21). (Note that Putlog scaffolds do not have inside boards)

3. There are only two working lifts in use, one fully loaded and one no more than 50% loaded.

4. The lift height is not greater than 2.0m, except that the first lift may be up to 2.7m high.

5. If the bottom lift is more than 2.0m high, the scaffold must be tied at the first lift, or alternativearrangements made, see Clause 6.2.2 (TG20:08 page 46).

6. The scaffold is not subjected to the loading of materials, by mechanical means such as by rough terrainforklift trucks. Loading bays should be specially designed, see Clauses 20.1 to 20.7 (TG20:08 page68-70).

7. The wind loading factor Swind, defined in revised Clause 4.4.3, is not greater than 40.

8. Load Classes 1, 2, 3 and 4 may be considered.

9. The scaffold is unclad, and not fitted with debris netting/sheeting.

11 of 16

N A S C

10. Faade bracing is either continuous or fitted over two bays in every six bays. See Figures 20 (i) and(ii) (TG20:08 page 48).

11. Alternate standards are tied to the building faade.

12. Lines of ties are at alternate lifts as shown in Figure 9(a) (TG20:08 page 36).

Safe heights for unclad Basic Putlog Scaffolds are given in Table 5 for lift heights of 1.5m and 2.0m. Tie dutiesare also specified.

4.6.2 Procedure to determine maximum safe height of a Basic Putlog Scaffold

In order to identify the appropriate safe working height, the procedure in 4.4.3, steps a) to d) should befollowed to obtain the wind factor Swind for use in Table 5.

12 of 16

N A S C

13 of 16

Part Boarded Fully Boarded

2.0m lift height, faade bracing 2 bays in 6 2.0m lift height, faade bracing 2 bays in 6

Load Class Swind safe height m Tie duty/kN Load Class Swind safe height m Tie duty/kN

1 20 2428323640

2 20242832

36 - 40

3 202428

32 - 40

4 202428

32 - 40

1 20 2428323640

2 202428323640

3 20242832

36 - 40

4 202428

32 - 40

20 light16 light13 light11 light9 lightns ns

18 light14 light11 light9 lightns ns

15 light12 light10 lightns ns


1 20 - 36 40

2 20 - 36 40

3 20 - 40

4 20 - 40

11 light10 light

9 light8 light

ns ns

ns ns

20 light18 light15 light12 light10 light9 light

20 light15 light12 light10 light8 lightns ns

17 light13 light10 light8 lightns ns


1 20 - 323640

2 20 - 28323640

3 20 - 28323640

4 20 - 242832

36 - 40





table 5 Safe heights for UNCLAD Basic PUTLOG scaffoldswith lines of ties alternate lifts

1.5m lift height, faade bracing 2 bays in 6 1.5m lift height, faade bracing 2 bays in 6

1 20 - 3640

2 20 - 323640

3 20 - 3640

4 20 - 32364 0

20 light17 light


15 light13 light


1 20 - 3640

2 20 - 40

3 20 - 40

4 20 - 40

11 light10 light

9 light

ns ns

ns ns

2.0m lift height, continuous faade bracing 2.0m lift height, continuous faade bracing

1 20 - 40

2 20 - 323640

3 20 - 28323640

4 20 - 2832364 0

20 light




1 20 - 40

2 20 - 40

3 20 - 40

4 20 - 40

16 light

15 light

14 light

15 light

1.5m lift height, continuous faade bracing 1.5m lift height, continuous faade bracing

Notes: 1. ns means not stated as calculation indicates the stress exceeds the allowable limit on the scaffold.

14 of 16

N A S C

Appendix H

Tying to permeable open structures

This Appendix has also been revised to take account of the requirements of the new European Wind Code BS EN 1991-1-4:2005 which is part of Eurocode 1.

In TG20:08 it is assumed that the scaffold is tied to a building facade that is impermeable and only has a small number ofopenings. For scaffolds tied to open frameworks or facades where there are a high percentage of openings, the scaffoldwill be subjected to a higher wind load and should therefore be specifically designed.

The safe heights for unclad scaffolds are given in Table 2 of TG20:08, but the tie duties given in that table apply only toscaffolds attached to impermeable facades which shield them from the wind. For unclad scaffolds tied to permeable openstructures, the correct tie duty is obtained using Tables A to C below, the wind factor Swind, the bay length in metres andthe safe height for the scaffold given in Table 2.

MAXIMUM PERMISSIBLE HEIGHTS FOR UNCLAD SCAFFOLDS TIED TO PERMEABLE OPEN STRUCTURES

Table A Table B

Table C Notes:

Swind

Maximum permissible height in metresfor scaffolds with Heavy Duty ties

Bay length in metres

1.8 2.1 2.4 2.7

20 50 50 50 50

24 50 50 50 50

28 50 50 50 50

32 50 50 50 50

36 50 50 29 15

40 41 17 9

1. These tables apply to unclad scaffolds tied topermeable open structures only

2. These tables apply only to scaffolds with lift heights of2m or less

3. These tables apply only to scaffolds with tie patternsdetailed in Fig.9 (a), (b), (d) & (e) and comply with therequirements of clause 5.2

4. When the height of the scaffold exceeds thepermissible height given in any of the tables above, aheavier duty tie should be used

5. When a heavy duty tie is not adequate, the tie densitymust be doubled, and heavy duty ties used

Swind

Maximum permissible height in metresfor scaffolds with Standard Duty ties


1.8 2.1 2.4 2.7

20 50 50 50 50

24 50 50 50 31

28 46 20 10

32 10

36

40

Swind

Maximum permissible height in metresfor scaffolds with Light Duty ties


1.8 2.1 2.4 2.7

20 50 40 19 10

24 11

28

32

36

40

Rev A

15 of 16

N A S C

EXAMPLES: USING TABLE 2 (VOL. 1) LINES OF TIES AT ALTERNATE LIFTS PART BOARDED

Example 1 Scaffold designation 3-5-0S with an Swind Factor of 24 (Bay Length 1.8m)

Example 2 Scaffold designation 3-5-1 with an Swind Factor of 28 (Bay Length 2.1m)




1. Using scaffold designation 3-5-0S, Table 1 gives a bay length of 1.8m and Table 2, with an Swind factor of 24, gives asafe height of 47m using Light Duty Ties.

For Scaffolds attached to permeable open structures

In Table A max height using Light Duty ties is 11m LIGHT DUTY TIES CANNOT BE USED

In Table B max height using Standard Duty ties is 50m USE STANDARD DUTY TIES

2. Using scaffold designation 3-5-1, Table 1 gives a bay length of 2.1m and Table 2, with an Swind factor of 28, gives asafe height of 38m using Light Duty Ties.


In Table A max height using Light Duty ties is undefined LIGHT DUTY TIES CANNOT BE USED

In Table B max height using Standard Duty ties is 20m STANDARD DUTY TIES CANNOT BE USED

In Table C max height using Heavy Duty ties is 50m USE HEAVY DUTY TIES




In Table B max height using Standard Duty ties is undefined STANDARD DUTY TIES CANNOT BE USED

In Table C max height using Heavy Duty ties is 50m USE HEAVY DUTY TIES




In Table B max height using Standard Duty ties is undefined STANDARD DUTY TIES CANNOT BE USED

In Table C max height using Heavy Duty Ties is 17m HEAVY DUTY TIES ARE NOT ADEQUATE THE TIEDENSITY MUST BE DOUBLED AND HEAVY DUTY TIES USED.



In Table A max height using Light Duty ties is 50m USE LIGHT DUTY TIES

N A S C NASC, 4TH FLOOR, 12 BRIDEWELL PLACE, LONDON EC4V 6AP TEL: 020 7822 7400 FAX: 020 7822 [email protected] www.nasc.org.uk

Whilst every effort has been made to provide reliable and accurate information, we would welcome any corrections to information provided by the Writer whichmay not be entirely accurate, therefore and for this reason, the NASC or indeed the Writer, cannot accept responsibility for any misinformation posted.

NOTES

Documents

TG20:12 – Supplement 1