The following document was provided by one of the roofing contractors who did an estimate for the roofing project here at Kenthill Townhomes. The article is entitled, " Condominium Roofing: Replacement or Recovery - Defining the Difference".
Roof replacement.
A roof replacement project involves complete removal of all existing roofing materials down to the structural deck. The deck should then be inspected and repaired, if necessary. Finally at a complete new roof system is installed. The new system generally consists of an insulation bed, a waterproof membrane, and some type of surfacing.
Roof recovery.
In a roof recovery project, the existing roof assembly is left in place and the new roof system is installed directly over it. Although there are rare instances when this approach makes sense; in general, it is poor roofing practice to recover an existing roof.
Condominium associations most often decide to recover roofs instead of replacing them, because of that initial savings in cash outlay. However, just because an option cost less front does not mean that it is financially wise. For a number of reasons, recovering a roof can end up costing an Association much more over the long term than the complete roof replacement.
New roof over existing.
First, the Association must remember why they need a new roof. The roof that is in place has likely failed. It is no longer capable of providing the building “envelope protection” that is required of a roof system. If leaks have been occurring, then there is probably moisture trapped within the installation bed. Installing a new roof system over an existing roof assembly with wet insulation will result in a shortened life for the new roof. The trapped moisture will cause premature deterioration of the new roof system by attacking it from below.
Roof deck deterioration.
Secondly, if leaks have been experienced, not only is the insulation likely to be wet, but the structural roof deck may also be deteriorated. [This is particularly true if the deck is manufactured from steel or wood]. The only way to confirm the condition of the deck is to completely remove the existing roof assembly. Recovering a roof may be covering up a serious structural problem
[Editor’s note: Roof recovery appears to be the method that was used on Building J. Note that no roof vents are visible].
