Lecture 15 - Timber Wall Framing Example Unitec New Zealand Construction Systems 1 Lecture 15 - Timber Wall Framing Example © Unitec New Zealand

Wall Modelling EXERCISE:   Undertake the sizing, layout and fixings for the following modelled example house. The house cross section provided is to be used as a basis for this. The following criteria has been set for the project and are based on the site location and construction decisions already made. Wind zone – Medium Stud height height – 2.4m. Strength grade SG 8. Roof system – light roof with trusses @ 900 crs. Floor joist spacing – 400 crs. © Unitec New Zealand © Unitec New Zealand

Wall Modelling MODEL ANSWER: Step 1   Step 1 The cross-section below provides the information regarding the roof system (roof trusses which spans from outside wall to outside wall), building width (7200 wide), and wall height (2400). No floor plan is necessary, the assumption is that all external walls supporting the roof are loadbearing, and any internal walls are non-loadbearing. © Unitec New Zealand © Unitec New Zealand

Wall Modelling © Unitec New Zealand © Unitec New Zealand

Wall Modelling MODEL ANSWER: Step 2 - Stud Sizes & Spacing (centres) Use NZS 3604:2011, Table 8.2 to find stud size and spacing in loadbearing walls for all wind zones. Before being able to select the correct row, the loaded dimension will have to be ascertained. Go to the loaded dimension tables Figure1.3 and select the roof type used in the project. This is (A) Support Span. For this exercise, this is 7200 / 2 = 3600 or 3.6m. loaded dimension © Unitec New Zealand

Wall Modelling Stud Sizing Continued The row is now determined, the correct column can now be ascertained. The stud height is known (2.4m), there is a need to now select the stud spacing. The alternatives provided are 300, 400 or 600. It must be considered that the sheet sizes attached are typically 1200, and so studs are spaced in the module of the sheet. Stud spacings of 600 are ideal for fixing plasterboard sheets to, and so are the optimum selection.   The row and column have now been determined and the intersection of these gives the stud size. In the exercise, the stud size is 90 x 35. This is the minimum stud size required. In industry, it may be more cost effective, and easier to have supplied, 90 x 45 timber. The final outcome will be 90 x 45 SG 8 studs @ 600 crs. © Unitec New Zealand

Wall Modelling  MODEL ANSWER: © Unitec New Zealand

Wall Modelling MODEL ANSWER:  Step 3 – Stud sizing in non-loadbearing walls Studs in non-loadbearing walls are sized from NZS 3604:2011 Table 8.4 Typically, the roof system spans from outside wall to outside wall, making the two end walls non-loadbearing. In this exercise, these end walls are 2400 high as the truss is above this.  First, determine the row. The wind zone is medium and the length (height) of stud is 2.4.  Now determine the column. The most desirable stud spacing is 600 crs. This could be changed if the resultant stud sized is inappropriate.   © Unitec New Zealand

Wall Modelling MODEL ANSWER: Table 8.4   Table 8.4 The intersection of these is 90 x 35. This is the minimum stud size required in an external non-loadbearing wall for this exercise. Again, if the studs selected in all the other external walls are 90 x 45 (and more readily available or cost effective), then the actual outcome may be 90 x 45 SG 8 studs @ 600 crs for external non-loadbearing walls. © Unitec New Zealand

Wall Modelling MODEL ANSWER: Table 8.4   Table 8.4 While using this table, internal non-loadbearing walls can also be sized. They have their own part at the bottom of Table 8.4. Again, use the criteria for the row and column, and the resultant minimum stud is 70 x 45. This is readily available, and may be selected, however, many designers like to keep all their framing consistent, prefer thicker walls for better sound insulation and durability, and so they will often upspec this to 90 x45 SG 8 studs @ 600 crs for internal non-loadbearing walls. © Unitec New Zealand

Subfloor Modelling MODEL ANSWER: Step 4 – Top Plate sizing   Step 4 – Top Plate sizing Top plates are sized from NZS 3604:2011 Table 8.16 Select ‘Single or top storey’ out of all the tables for top plate sizing. This is a table where the outcome (top plate selection and size) has already been decided, and it is really used just a check to see if it is appropriate to the situation. The most typically used top plate is a combination of a 90 x 45 top plate with a 140 x35 strengthening plate on top. This selection means that the top plate size matches the stud size (both 90 x 45), and the strengthening top plate allows the roof framing to be supported anywhere on this system, and provides support to the edge of the ceiling lining. © Unitec New Zealand

Subfloor Modelling MODEL ANSWER: Step 4 – Top Plate sizing   Step 4 – Top Plate sizing It now requires the table to be used to see if this plate works for the situation: In the row, the top plate is selected, and the truss spacing is at 900 crs. In the column, the roof is light, and the stud spacing is 600. Where they intersect, the maximum loaded dimension can be seen to be 6.0. The actual loaded dimension is 3.6, which is below the max. allowed, so the selected top plate is suitable. The top plate is 90 x 45 SG 8 top plate with a 140 x 35 SG 8 strengthening plate. © Unitec New Zealand

Wall Modelling Step 5 – Bottom Plate sizing Bottom plates are sized from NZS 3604:2011 Table 8.17 Select ‘Single or top storey’ out of all the tables for bottom plate sizing.   This is another table where a desired outcome has already been decided, and the table is now used to confirm if the selection is suitable. As all the wall framing selected is 90 x 45, it seems reasonable to select a bottom plate that matches. Use the table to check that this is correct. For the row, use 90 x 45 and floor joist spacing of 400. For the column, use light roof and stud spacing of 600. © Unitec New Zealand

Wall Modelling Step 5 – Bottom Plate sizing The intersection gives a maximum loaded dimension of 6.0. The actual loaded dimension of the wall supporting the roof (from Figure 1.3) for this exercise is 3.6. Therefore the bottom plate selected falls within the loaded dimension criteria and is suitable.   The bottom plate for this exercise is 90 x 45 SG 8. © Unitec New Zealand

Wall Modelling MODEL ANSWER: Step 6 – Lintel sizing (in loadbearing walls) All the walls have been determined for this exercise, it now needs any openings in these walls to have their various trimmings sized. The first of these is to consider the size of the beams over the top of any openings in loadbearing walls. The beam above any opening in a wall is called a lintel.   As there is no floor plan associated with this exercise, some assumed opening widths have been given so the lintel sizes can be assessed. The following are to be used: Opening widths of 1200, 2600, 3400, and 4000. Lintels are sized from NZS 3604:2011 Table 8.9 © Unitec New Zealand

Wall Modelling MODEL ANSWER: Step 6 – Lintel sizing (in loadbearing walls) © Unitec New Zealand

Wall Modelling MODEL ANSWER: Step 6 – Lintel sizing (in loadbearing walls) Select ‘Lintel supporting roof only’ out of all the tables for lintel sizing. Note that this is the only table for sizing lintels in single storey or upper level of two storey buildings. All the other lintel tables are for sizing lintels in different locations in the lower storey of two storey buildings.   Determine the row required. For this exercise, light roof, and for openings in the loadbearing walls (see the diagram below), a loaded dimension of 3.6. Determine the column required. For the lintel tables, this means applying the lintel span inside the table, then selecting the lintel size directly above. © Unitec New Zealand

Wall Modelling MODEL ANSWER: Step 6 – Lintel sizing (in loadbearing walls) For an opening 1200 wide, the lintel size is 140 x 70. For an opening 2600 wide, the lintel size is 240 x 70. For an opening 3400 wide, the lintel size is 290 x 90. For an opening 4000 wide, the lintel size cannot be selected as it is beyond the scope of the table and either must be specifically designed or an alternative engineered lintel used.   Note that the first two lintels sized, the lintel width is 70. This is not compatible with the thickness of the wall framing (walls are 90 wide), and so would typically upgraded to 90 wide lintels. Remember, the sizings are minimums and can always be made bigger but not smaller. © Unitec New Zealand

Wall Modelling MODEL ANSWER: Step 6 – Lintel sizing (in loadbearing walls) Note also that 70 and 90 thick members can be substituted with built-up members. In this exercise, all three lintels would be substituted as a cost effective exercise. It must be remembered that lintels are fully enclosed and the substituted members are unseen inside walls.   The final lintels would read: 2/140 x 45 SG 8 (for a 1200 wide opening) 2/240 x 45 SG 8 (for a 2600 wide opening) 2/290 x 45 SG 8 (for a 3400 wide opening) © Unitec New Zealand

Wall Modelling MODEL ANSWER: Step 7 –Head and Sill trimmers in non-loadbearing walls. If a wall is non-loadbearing, it does not require a lintel above. Instead, it is trimmed with a head and sill trimmer and this can be sized from NZS 3604:2011 Table 8.15. © Unitec New Zealand

Wall Modelling MODEL ANSWER:  Step 7 – Head and Sill trimmers in non-loadbearing walls. The head and sill trimmer size can vary depending on the width of the opening. For the three options given (1200, 2600, 3400 wide), the head trimmer size will be the same width as the studs, and the thickness as given in the table above.   For a 1200 wide opening - 90 x 35 SG 8 head trimmer (use 90 x 45) For a 2600 wide opening – 2/90 x 45 SG 8 head trimmer For a 3400 wide opening – 3/90 x 45 SG 8 head trimmer If the opening goes to the floor (such as with a door), then no sill trimmer is required. © Unitec New Zealand

Wall Modelling Step 9 – Trimming stud sizing (in loadbearing walls) Sides of openings both trim the opening, and if a lintel is used, will transfer its loads to the floor. These studs are known as trimming studs (can vary with the relation between the lintel and the top plate). The wall/lintel/top plate scenario is shown is for the exercise house (from Figure 8.5). © Unitec New Zealand

Wall Modelling Step 9 – Trimming stud sizing (in loadbearing walls) Trimming studs are sized from NZS 3604:2011 Table 8.5 Trimming studs shall have the same width as the studs in the wall and thickness as given in Table 8.5   For the three opening widths for this exercise, the trimming studs required are: 1200 wide opening – 90 x 45 2600 wide opening – 90 x 70 3400 wide opening – 90 x 70 ( 2/90 x 35 probably substituted by 2/90 x 45) © Unitec New Zealand

Wall Modelling MODEL ANSWER: Step 10 – Fixings   Step 10 – Fixings All the framing members in the wall framing for the exercise house have been sized. The other important component is how they are fixed together. Some are simply connections between members and others are to prevent uplift from wind. © Unitec New Zealand

Wall Modelling Connection of plates to studs There is a requirement to fix top plates that support roof members (loadbearing walls) to wall studs (or lintels if that situation occurs). Use NZS 3604:2011 Table 8.18 for selecting the fixings © Unitec New Zealand

Wall Modelling MODEL ANSWER:   For the example house, the row criteria is a loaded dimension of 3.6, and the column criteria are light roof, roof member spacing of 900, and a medium wind zone. From this the fixing type is determined. This is a Type B connection. The final solution would therefore be 2/90 x 3.15 end nails + 2 wire dogs fixing the top plate to studs. However, note that also in Table 8.18, it also gives provision for an alternative fixing with a minimum capacity of 4.7 kN. This is commonly also noted so that the builder can use a different proprietary fixing for the same purpose (as long as it has a 4.7kN capacity). © Unitec New Zealand

Wall Modelling Uplift fixings Lintels supporting rafters or trusses require to be secured against uplift as per table 8.14, and if not required under this table, be fixed as per table 8.19. If uplift fixings are required, then the connection of the lintel is to both the trimming stud and the floor. Figure 8.12 illustrates this, and use Table 8.14 to determine fixing requirements and type. See below for table and solution. © Unitec New Zealand

Wall Modelling For this exercise, determine the row and column requirements. For the row, use Light roof, medium wind zone, and loaded dimension of lintel as 3.6. For the column, it can be seen that: For lintel spans of up to 1.4m, no uplift fixings are required (use fixings from table 8.19). For lintel spans over 1.4m and up to 5.0m, uplift fixings are required (use fixings from 8.6.1.8).  Over 5.0m. span, fixings must be S.E.D. See figure 8.12 for fixings to prevent uplift. For the exercise house they will be:  For lintels with spans between 1.4m and 5.0m. Lintel to trimming stud – 25 x 1mm strap with 6/30 x 2.5mm nails into both lintel and stud, or a 7.5 kN connection. Trimming stud to floor – 25 x 1mm strap with 6/30 x 2.5mm nails into both blocking and stud, or a 7.5 kN connection. (for a timber floor system) © Unitec New Zealand

Wall Modelling Use table 8.19 where uplift fixings aren’t required. For the exercise house they will be: For lintels with spans up to 1.4m. Refer to Table 8.19 for other fixing requirements of the various components that make up a Timber Framed Wall. © Unitec New Zealand

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