The facilities of EXISTING BUILDINGS are very sensitive, delicate places – personal residence and other facilities require care, consideration and the utmost design approaches. Conditions can include unique restricted access over multiple additions and roof areas, crowded ground conditions, sensitive occupants and delicate interior operations.

It is an inherently risky activity to remove a roof system from a building – without a roof, a building is severely exposed and all interior operations are threatened. Occupants and staff in a multi-unit residential building are in a sense, captive – reactions to serious changes in their environment often cannot be made quickly, if at all.

Roof replacement on a building that is “Home” or Livelihood to many should be performed as infrequently as is humanly possible.

The roof replacement process for a Residential or Sensitive Building is different than almost all other facilities. All factors that can possibly be integrated into the design, implementation and final outcome must be considered. Roof replacement at a Residence must be carefully scripted, carefully choreographed, carefully watched and be extremely well coordinated by a very competent team.

Roof replacement for Residence and Livelihood facilities requires a very special design process. Roof systems for specialized buildings should be extremely robust and able to withstand mechanical abuse, environmental degradation, significant humidity conditions and severe weather abuse in the very long term. Long, reliable service life is required due to the sensitivity of the interior environment and the demanding requirements of the occupants and staff.

A comprehensive listing of “Roof System Design Criteria” should be established prior to roof system selection. A specific custom designed roof system is necessary – “it is better to design a roof system than to pick one”.



1. Identify facility and determine construction type of building – e.g. masonry cavity construction, structural components – wood or steel joists, deck type, wall constructions and details and all other components and systems as possible.

2. Determine extent and type of problems – leaks where? when? how bad? under what conditions? when started? any other unique or “telling” conditions. Review any other information such as infra-red scans, leak reports, verbal descriptions

3. Determine the composition of the roof system on the subject areas – membrane type, insulation type and thickness, vapour retarder, base flashing assemblies, any unique characteristics or situations. What are client standards, if any? All Proposal requirements will be met.

4. Determine the access to the roof area, height, set-up areas, material storage, power lines, garbage bin location, chute requirement, condition of ground surfaces, access to set-up and garbage bin areas – will re-sodding and landscaping be required? All other conditions and concerns – assess alternate roof systems and different approaches and budget costs.

Note: It is essential to gather all information possible in order to design the best roof system possible for the particular roof areas and avoid making the same mistake twice – “Those who do not know roof history are doomed to repeat the same mistakes” – to liberally paraphrase a well known proverb. Mistakes have been made on roofs at this Residence – it is best not to repeat those mistakes.

Too many times a roof system on a given area is replaced and the same leaks appear right after installation of the new roof system, because some thing or feature, situation or detail has been missed – a lot of money can be wasted by not knowing everything that can be known.

5. Identification of other parties that could be involved in the process:

  • Plumbing contractor to install new roof drains and/or refurbish or replace existing roof drains
  • Structural engineer to validate structural capacities of building structure or to review areas of structural concern or provide information for areas of reinforcement
  • Mechanical contractor to disconnect and/or remove HVAC units and other HVAC activities including gas lines
  • Electrical contractor to disconnect existing wiring or to renew electrical components on the roof
  • Electrical engineer or mechanical engineer as required
  1. Other variables that may be discovered:
  • Discovery of an area of deteriorated deck – could be subject to review by a structural engineer – remove existing bad section and replace to match existing
  • Discovery of deteriorated wall materials e.g. spalling brick – remove back to sound material and then install 
  • plywood facing on wall – install base flashings up the plywood
  • Area of ponded water – review interior drainage system – install new drain and tie-in laterally to existing piping or exit the drainpipe out a wall
  • Discovery of a deteriorated HVAC curb – remove unit if in place – fabricate new curb from either wood or metal components – flash new curb – reinstall unit
  • Discovery of deteriorated perimeter – cut out bad section – install new wood or metal components as required to restore original detail
  • Deteriorated or defective skylights – curb problems. Defective seals and lites, metal cladding, condensation issues


Commentary On Process

The best and most relevant method to evaluate an existing roof system is to view all roof and building conditions from the perspective of a roof replacement project. This perspective provides a more complete process and essentially a check list for all considerations.

Not all considerations listed will be knowable or relevant – but the framework provides an organized system for assessment and evaluation.

An additional added benefit of a very systematic, organized condition assessment can be the discovery of conditions that require immediate repair or remediation.

Roof System Considerations

Specialized Buildings provide a number of challenging variables for roof system consideration. These variables include – but are not limited to:

  • The sensitive nature of a Residence or Livelihood building
  • The significant, potential, negative impact of wind and storm events and exposure of the roof to debris and significant leakage events
  • Significant traffic on the roof to service units, repair systems and review operations
  • The number and types of all units on the roof 
  • The physical orientation of the roof areas, i.e. some levels relatively inaccessible to the work site/set-up area
  • Lack of ease of “normal roofing operations” such a lifting by crane
  • The vulnerability of the occupants and staff and the activities in the Residence affecting those occupants
  • The requirement for a very long service life roof system 
  • The sensitivity to noise, confusion and odours of the Residence environment
  • Flexibility or lack of, of Residence staff to change, redirect or modify HVAC unit/cooling operations
  • Necessity of a redundant waterproofing membrane
  • Consideration of low temperature conditions and higher relative humidity
  • The relatively significant exposure of the roof areas to winds and precipitation
  • Drainage requirements – tapered insulation, additional drains, drain type for replacement, plumbing issues
  • Proper and long term flashing details of larger units such as HVAC units and cooling towers
  • Modifications to piping, electrical conduits and other rooftop accessories that must be changed to facilitate roof replacement
  • Renewal of electrical components on the roof that may not now meet the Electrical Code
  • Detailing of all pipes and projections through the roof deck and roof system
  • Insurance and code provisions – FM requirements and other specific requirements
  • Puncture resistance requirements
  • Lowtemperature flexibility, elongation, water immersion and movement tolerance
  • Fire resistance 
  • Effective and proper surfacing for the roof system
  • Energy efficient and environmentally responsible design
  • Adjacent wall systems, windows and other abutting surfaces that must be watertight and must not compromise the roof system or lead to leakage
  • Renewal of fans, ventilator and other smaller rooftop units and projections that have or will in the near future require replacement
  • Ultra long service life requirements
  • Low maintenance requirements
  • Very low life cycle costs – initial costs are not the only value consideration

Additional Roof System Considerations

  1. Wind Uplift Calculations must be made. All applicable factors including exposure, exposure type, height of roof area, structural components, perimeter type and configuration, wind speeds, precipitation, surrounding topography must be considered and calculations made according to Factory Mutual standards. Factory Mutual standards are generally recognized to be the most stringent in the industry.
  1. Moisture Measurements and Interior Conditions should be assessed. Roof system type and amount of insulation, vapour barrier type and configuration and other roof system factors must act in concert with the interior conditions and requirements at the arena.
  1. Perimeter Details must be constructed to resist wind forces, provide long service life and protection of the roof system flashing system. Full metal coverage and proper securement are required. 
  1. Roof Membrane Construction must be mechanic and Residence friendly and provide redundant waterproofing. The roof system must stay attached to the building and all design criteria must be satisfied before the specification is written. The roof system must be suitable for the roof areas for which it is intended.
  1. Manufacturers must be pre-screened for appropriate roof system components of appropriate quality. All components must be compatible and the manufacturer must provide warranty coverage that means something. If a warranty claim comes, they should be prepared to write a cheque without question or hesitation. This type of manufacturer exists and will also provide good technical support and other services as required.