Roof Rafter Spread

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Roof rafter spread.

Roof spread can be dangerous for a house and very damaging for a roof. When considering what to do about sags in a roof start by noticing if the sag is in sheathing between rafters page top photo0 or sagging along the length of the rafters. N modern cut timber roofs pre 1970 constructed on site this force is normally resisted by joining the bottom of each pair of rafters see fig. 2 with ceiling joists.

Roof spread affects a roof that begins to move after it is installed. If looking for the obvious and common cause of roof spread then this particular issue could so easily have been missed especially when limited to a head and shoulders inspection from the loft hatch. Roof rafter decking sagging. This ties them together and prevents any outward movement.

It also leaves a void the loft which can be used for storage or the placing of water tanks etc. This article describes a diy repair project using a site built spreader to straighten sagged roof rafters and decking. Factors that cause the situation include bad construction improper materials and water and rot problems. Split ridge board causing rafter instability and subsequent applied horizontal thrust to the wall plates.

So fixing the problem as soon as possible is vital. Roof spread occurs when the principal rafters of the roof are not adequately supported causing them to open in a scissor like pattern. Therefore the first signs of roof spread are often cracking bulging or leaning at the head of the masonry causing bowed walls. Something else to look for in regards to roof spread is sag.