RAFTER SPAN CALCULATOR PLUS

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).

RAFTER SPAN CALCULATOR PLUS

You could also be benefiting from 'real 2x4's', not today's 1.5'x3.5', and the greater strength of old growth lumber, but I can't imagine 2x4's spanning 15' that are unsupported by other framing structure.įor reference, look at Fine Homebuilding's video on YouTube where a Shaker shed that is only 12' in width is built using 2圆 roof rafters plus they used collar ties every 4', that are not shown in the video.TO USE TABLE 10.1 for a building, you need to know: If you could post a picture showing how your house is framed, that would be very interesting. I don't know how your roof is constructed to have 2x4's spanning more than 15' on 24' centers, but there would have to be additional framing supporting the roof that effectively reduces the distance that is spanned. snow load, the 2x4 roof rafter span drops to 8'5' and 9'0' for Douglas Fir-Larch and Southern Pine respectively.įor the 10 on 12 pitch you're talking about, the span is more like 15'7' depending on details, such as the ridge board and wall thicknesses, so 2x8's should work at 12' on-center. for Douglas Fir-Larch #2 or Southern Pine #2 for 10 Lb. Just basically need to know if my spacing should be 12, 16 or 24 inches.Ī 2x4 roof rafter span is limited to 10'10' with 12' on-center spacing. Again I would prefer to use 2×4’s but can go with 2×6’s if I can’t get away with 2×4’s. I plan on putting on a metal roof so just furring strips + 28 ga metal for live load weight. My building will be 24ft wide with each rafter side being 17′ 6″ long if I calculated it correctly based on a 10/12 pitch with an 18″ overhang. So it would be the standard KD WW that the big box stores carry. I would like to frame with 2×4’s now that the price of lumber has come back down. Being in the southern part and based off recent history I would lean more towards the 15. First I live in south central Kansas so my snow load is 15 – 25 psf. Here are some of my details that I hope someone can help me figure out what i need. They still have the one by furring + decking + asphalt shingles and it doesn’t seem to budge an inch when is snows because it doesn’t hold much snow with that pitch. Our home roof is 2×4 (probably SYP) that is spaced at 24″ or more. I am wanting to put up a carraige house to match our Victorian home that has a 12/12 pitch roof(s). I don’t want to under build nor do I want to overbuild. I can’t help but think that the requirements would be different for a 10/12 or 12/12 pitch roof. I know there are a ton of rafter span calculators online that either give you info for under 3/12 pitch or over 3/12 pitch. I did a quick search on here but coulnd’t find a thread that fit my situation.

Rafter span calculator