Assessment 7 floor framing

Use AS1684.4 Residential timber-framed construction, the BCA and the house plans for Mr & Mrs Walk to complete this assessment. Write your answers on the student assignment worksheet for submission.

Floor framing

  1. 1. Look at the plans provided for Mr & Mrs Walk. Check the scope of AS1684.4 to see whether components of this building can be designed using AS1684.4 Residential timber-framed construction, with respect to:
  2. Wind classification (assume that, from AS4055, the site has been determined to be N2). Give a reason for your answer.
  3. Give a reason for your answer. iii. Number of storeys of timber framing iv. Width. Give a reason for your answer.
  4. Wall height. Give a reason for your answer.
  5. Rafter overhang. Give a reason for your answer. vii. Roof types. Give a reason for your answer.
  6. 2. Can AS1684 be used to design the floor for this building? Give your reason(s).
  7. 3. Referring to the BCA, what would be the minimum depth of the concrete slab thickened edge beam for this brick veneer (masonry veneer) building on a Class S site?
  8. 4. For drainage purposes, what is the minimum height of the slab above the surrounding natural ground level if the dwelling is to be built in a medium intensity rainfall area? Where would you find this information?
  9. 5. From the contour lines on the site plan, and the finished floor level shown, and the requirements as noted in the BCA, will there be any requirement for fill? (Assume that 150mm of topsoil will need to be stripped from the area of the building footprint). Give reason(s) for your answer.
  10. 6. What is the allowable bearing pressure of the soil on which the slab edge beams are to be founded? What is meant by controlled fill and rolled fill? What is kPa a term for, and what does this allowable bearing pressure mean?
  11. 7. Look at the drawings provided of the residential dwelling for Mr & Mrs Walk. With reference to the BCA, which of the figures;,, or would most resemble a detail through the external wall at floor level? Give your reasons.
  12. 8. With reference to definitions in the BCA; what is a DPC and how does it work?
  13. 9. With reference to the definitions in the BCA; what is ‘ flashing’?
  14. 10. Give several examples of where flashing would be installed? Sketch a typical flashing detail.


For this exercise, you are asked to size the timber members for a simple outdoor deck. If you would like to read more about the construction of a deck, you could go to or or use a suitable reference book for home building.

The plan diagram in Figure 1 below shows the layout of the proposed deck, and Figure 2 shows a section through the proposed deck.

You are to indicate the location of timber stumps, bearers, joists and the ledger, on the plan diagram. The posts should be 1800mm apart, and the joists should be spaced at 450mm.

Assessment 7 floor framing image 1

Then size the members in the following table:

AS1684 table used

Timber stress grade

Span mm

Spacing mm

Single or continuous

span used for sizing?


(mm x mm)

Post (note: footing type 2)





Unseasoned F11


Unseasoned F11


You will need to do a little



Spotted gum


Notes: the unseasoned timber has some warp and will need to be crippled.

Wall framing

  1. 12. What is the minimum cavity allowed in a brick veneer building? Where would you expect to find this information?

Fixings are required to all building elements to prevent sections or elements of the building from being ‘lifted off’ in high winds. ‘Bracing’ is required in the walls and roof (and in the sub-floor for framed flooring) to prevent ‘racking’ due to the wind. Section 8.3.2 in AS1684.4 details the procedure for the design of wall bracing. Section 9 deals with fixings and tie downs.

Consider that this dwelling will have Type A bracing units (see Clause 1.7f in AS1684.4) and that a wind classification of N2 applies.

  1. 13. What are the nominal fixing requirements according to AS1684.4 for:
  2. The bottom plate to the slab
  3. The studs to the bottom plate
  4. The studs to the top plate
  5. 14. What are the specific fixing requirements if the building is to have a sheet roof:
  6. Bottom plate to slab (truss span 7830mm; fixings at 600)
  7. Bottom plate to studs
  8. Studs to top plate
  9. 15. For common studs spaced at 450mm, notched to allow for services, what size is required for the studs, given that it is proposed to use radiata pine, stress grade F5, seasoned timber? Q. 16. If MGP10 (machine graded pine) was used, would a smaller size suffice?
  10. 17. Will this size and grade satisfy the requirements for the western gable end wall studs?

(Consider a roof pitch of 30 degrees and that a cathedral roof has been designed for the bedrooms)

If not, suggest a grade and size that will. Show your calculations for the average stud height as per

Figure A6 in AS1684.4. (note: do not try to size the studs that support the ridge beam)

  1. 18. Determine the appropriate house elevation option for each wind direction from Figure 8.3 in AS1684.4

Wind direction


East – west

North – south

  1. 19. From Table 8.2 in AS1684.4, determine the number of Type A bracing units required for each wind direction.

Wind direction

Number of Type A units required

East – west

North – south

  1. 20. From the bracing types for Type A bracing shown in AS1684.4 Table 8.3, complete the following table:

Type of bracing

Minimum length of wall (with no openings)required for installation (mm)

(a) Two diagonally opposed pairs of timber or metal angle braces

(b) Metal straps - tensioned

(c) Timber and metal angle braces

(e) Diagonal timber wall lining or cladding

(g) Plywood

(i) Decorative plywood - nailed

(k) Hardboard

  1. 21. Using the guidelines in AS1684.4 for the distribution of wall bracing, arrange your chosen number of bracing units on a floor plan of the building. Note that you may substitute Type B bracing and nominal bracing as long as you comply with the Rules and allowances in Clause of AS1684.4. Indicate the type of bracing (Type A or B or nominal, and what type from Table 8.3) you have chosen in each location. Assessment 7 floor framing image 2

    Roof framing

    Consider that the roof of Mr & Mrs Walk’s house is to be conventionally framed (pitched on site). Using the plans and AS1684.4 as required, answer the following questions:

    1. Suggest a ceiling joist size for the lounge room that would require one hanging beam at mid-span. Use MGP10 at 450 spacing.
    2. What is the span of your ceiling joist, and should it be single span or continuous?
    3. What will be the span of the hanging beam?
    4. Suggest a size for the hanging beam (use MGP10)
    5. Indicate on a plan view, the location of the hanging beam and the ceiling joists in the lounge room.
  2. If the roof pitch is 30 degrees and the rafter is to be sized to suit the widest part of the building (the western end), determine the following:
    1. the roof span (the horizontal distance that the roof will span between the top plates on the external walls). Express your answer in mm.
    2. the rafter span considering that there is no underpurlin (assume rafter spacing is 900mm)
    3. Using the tables in AS1684.4, determine and state whether an underpurlin is required.
    4. If one underpurlin were to be placed at the mid-span of the rafters, what size of rafter would satisfy this span (MGP10)
    5. If the eave width on the plan has been confirmed to be 450mm (the horizontal dimension from the outside face of the brickwork to the end of the rafter), using Figure 2.10b and the roof pitch, determine the rafter overhang.
    6. Is this overhang compatible with the overhang limit for a rafter with a standard birdsmouth notch?
    7. What type of roof bracing would be required for the gable ends of this building?
    8. If this was a trussed roof, where would you look to find the bracing requirements?
Assessment 7 floor framing image 3