Collar roof:
* When the span increases or when the load is more, the rafter of the couple close roof have the tendency to bend.
* This is avoided by raising the tie beam and fixing it at one-third to one-half of the vertical height from wall plate to the ridge. This raised beam is known as a collar beam or collar tie.
* Suitable for span up to 5 m.
* Primary function of collar beam is to stabilize the rafters by preventing them from spreading outward under the weight of the roof.