The one difference is that we need to calculate the roof rise using the pitch. For calculations based on the roof pitch: The formula used to calculate rafter length from roof pitch is, in fact, the same as the one above. (basically take a hole saw, saw in about 1/2 inch, and put about a 7/8 inch long section of pipe/like in that hole saw cut). In order for the metal sheets to be easily fixed to the purlins they should be at least 50mm wide. For calculations based on the roof rise: rise + run rafter length, meaning that: rafter length (rise + run). Not saying your not pushing the modern limits of construction, but if you have enough 2圆's one could double up a few one on each side of the existing rafter, or as far as shear, if your concerned, could consider a split ring type of attachment,

It will eventually be enclosed but will not have ceiling or insulation. The slope of valleys in such roofs shall not be less than.

Length will be 54' long and as wide as I can make it in the space we have. 4.2.2.1 Roofs shall be provided with a pitch of not less than that given in tables 1 and 2, provided that sheeted roofs without hips and valleys in category 1 buildings may have a roof slope of 5 subject to all end laps in such sheeting being sealed and having a minimum lap of 250 mm. The new roof will slide under the existing metal. How many lengths is a bundle of batten The number of lengths in a bundle of battens can vary depending on the supplier and the length of each batten. To keep things simple, I'm planning on sliding the new rafters alongside the chords and resting them on the top row of banding. Common spacing ranges from 12 inches to 24 inches. I have buildings with 2x4 on 24 spanning 12 foot, slight sag after 90 years,Īnother building 2x4 24 on center spanning 10', no seeable sag, 70 years,īarn lean to sheds, 2圆 24 oc, 15 foot, span slight sag it is 105 years old, (all lumber is Douglas fir)Īll have approximately the same slope as your drawing, all of my buildings are 1x sheeted and have been shingled, with asphalt shingles, the barn is sheeted but tinned now, Unevenly spaced or misaligned rafters can lead to issues down the line, including uneven weight distribution and potential sagging of the metal roofing panels. The spacing for roof battens in metal roofing applications depends on the specific metal roofing system and local building codes.

Metal roof rafter spacing