RAFTER DESIGN HOW TO

This example is in a high wind zone, so the ‘High and Very High’ multiplier of 1.1 can be used.īack to top Step 3 – Continuous rafter 10% increase? The most likely choice here would be for 600 mm spacing or less, to accommodate ceiling battens and sheet linings (see Figure 4).īack to top Step 2 – Rafter span multipliers This is a skillion roof, so consider roof cladding, how it will be fixed, whether it is to purlins, battens or sarking, and the proposed ceiling lining requirements. This is a heavy roof, so the 1200 mm column on the right side of the table is excluded – it only applies to light roofs. We’re changing the parameters in this second example to:Ĭhoose rafter spacing from Table 10.1 – the options are 480, 600 or 900 mm. (Provided by Standards New Zealand under licence 001094.) Example 2 Read off the fixing type in the same row, in this case Type E (2/90 × 3.15 mm skew nails + 2 wire dogs) or an alternative fixing of 4.7 kN.įigure 2 Example 1 using NZS 3604:2011 Table 10.1. This indicates a 140 × 45 mm rafter size. Read the rafter size in the left column of Table 10.1 for the 2.2 m span chosen. This is more than the span in Figure 1, so a 2.2 m rafter span is suitable. Look at the values in the span column for 1200 mm rafter spacing.Īpply the additional 10% permitted in Note 1:Ģ.86 + 10% (0.286) = 3.146. This rafter extends over two spans, so the 10% increase can also be used to select the most economic rafter.īack to top Step 4 – Work out rafter span Table 10.1 Note 1 also allows rafter spans to be increased by 10% where rafters are continuous over two or more spans, and are not birdsmouth seated. This example is a light roof in a low wind zone, so the Low and Medium multiplier of 1.3 can be used.īack to top Step 3 – Continuous rafter 10% increase Table 10.1 has span length multipliers for ‘Low and Medium’ and ‘High and Very High’ wind zones.

Is 1200 mm rafter spacing appropriate?īack to top Step 2 – Rafter span multiplier When choosing the rafter spacing, also consider the proposed roof type and the support it requires – battens, purlins or sarking. The rafter span is 3.000 m, and because this is a light roof, the far right column of NZS 3604:2011 Table 10.1 Rafters for all wind zones (see Figure 2) can be used for rafter spacings at 1200 mm (see Note 4 in Table 10.1). rafter span 3.000 m continuous over two spans.In the first example, the building’s parameters are: single span or continuous over two spans (without birdsmouth over mid support).rafter span, taken along the pitch line of the rafter (see Figure 1).🪵 Define timber material properties $(k_$.įor a residential house which is classified as Service class 1 according to EN 2.3.1.3 we extract the following load durations for the different loads.TO USE TABLE 10.1 for a building, you need to know: ⬇️ Calculate all characteristic loads (dead, snow, wind, live load, etc.) Here's a quick summary of what we cover in this article

RAFTER DESIGN HOW TO

In this article we'll show exactly, step-by step, how to dimension and design the elements of the rafter roof according to the Timber Eurocode EN :2004. Another day, another design article about timber roofs.🤗 After we have covered the structural designs of the collar beam roof and the purlin roof - it is now time to look at the timber rafter roof and design it.🕵️

Rafter design