Most re-roofing specifications require that the old roofing, gravel and other debris be removed and properly disposed. On multi-storied buildings, chutes or throwing of debris over the side are not possible and, therefore, it may be necessary to lower the debris by hoist or crane. Modern day roofing necessitates the use of machines for scraping up gravel. Some scraping machines have cutter blade attachments so that the roofing and insulation may be cut into square portions of such size that they will easily fit into whatever device is being used for lowering the debris.
Many roofers lower their debris at the same time they hoist their roofing gravel. This is good roofing practice as the counter balancing weights speed up the entire operation and two operations are carried out at the same time.
Roofing materials and debris must not be allowed to accumulate in large piles as there is the possibility of the roof deck collapsing due to overloading or weaknesses in the structure due to previous work or material degradation. The roofer must endeavour to remove debris daily or disperse piles in such a manner that they do not overload the roof deck.
It must also be remembered that a pile of roofing debris (membrane, insulation, old gravel, etc.) may not have overloaded the roof deck, but, should a heavy rain or snow occur, the subsequent soaking up by the roof insulation and inability of the water to drain away may cause roofing debris to increase in weight, causing the deck to collapse.
The ideal method of disposing of old roofing materials and debris is either by hoisting, or throwing it down a chute, having a dump or dump box truck waiting. Good re-roofing practice is to remove all loose gravel, debris, etc. prior to ripping off the roofing membrane. This type of work can be completed on marginal weather days, while waiting for materials, or during any other delays that may occur.
Whenever re-roofing, it is advisable to strip-off the existing roofing system and flashings and replace them with a completely new roofing system, including flashings and sheet metal work. Complete removal of the existing roofing permits a thorough inspection of the deck parapets, etc. so that any decking or structural defects may be corrected.
Where roof decks are known to be sound and the existing roof membrane are in repairable condition, the existing roof system may serve as a satisfactory vapour retarder for new roof insulation, over which a new roofing system can be applied. However, any existing roof membrane that is badly blistered, buckled, or water-soaked, should not be considered a suitable surface on which to install insulation or new roofing. However, roofing over an existing roof is not always possible or desirable. Therefore, each individual situation should be carefully studied.
Old gravel roofs being re-roofed should be thoroughly scraped free of all gravel until a smooth surface is obtained. Particular care should be taken so that no sharp or protruding edges of gravel remain embedded in the membrane. All buckles, blisters, wrinkles, fishmouths, or otherwise deteriorated or wet roofing shall be cut free and the affected area patched and brought to a smooth level surface with at least two plies of felt and bitumen. All loose nails shall be pulled. Under no circumstances should any new roofing be installed over wet or otherwise deteriorated roof insulation. Whenever this condition is found or suspected, the roof shall be removed and replaced with new materials of like thickness.
All old flashings shall be cut out and stripped from walls and curbs, which shall then be cleaned, repaired, or otherwise conditioned to conform with the requirements for new construction.
Any damaged cant strip shall be repaired, replaced, or re-nailed to conform to the requirements for new construction.
The entire roof shall be swept free of all dust, dirt, grime, or other foreign material before proceeding with application of new roof system.