When I was a boy, I saw the construction worker at roof heating up the Asphalt block with very bad odour smell. Bituminous asphalt were usually applied in liquid form in row by row with some over-lapping at even interval spacing. Although this materials are proven to be very weather resistance and durable once after curing and set, it is not encouraged to use in new works as per the General Specification (ASD) Clause 12.50. With the advancement of technology , there are now coming with various type of ready-applied roofing felt and some type are even in spraying form.
Nevertheless, the typical defects like blistering of membrane, sagging of membrane, incorrect surface water fall , poor outlet details , lack of backing rod for sealant in expansion, add-on structure impairing the roofing are still prevailing. These are attributed to the poor workmanship, lack of inspection and inadequate design details consideration. Indeed, even though the defects exists , it does not mean we have to end the life of roofing by complete re-roofing. A more sensible way is to carry regular inspection and maintenance than to leave the roof undue long time unattended.