Frequently Asked Questions

Flat Roofing

Q: How often should I be inspecting my roof and how much should this cost?
A: At least twice a year have a professional either roof consultant or roofing contractor inspect your roof both in the spring and fall. The inspector should ensure that all roof drains are working and free of debris. Your roofer or consultant can prepare a bi-annual inspection check list suited to your application. Costs will vary from location and size of building, but generally this should be in the price range of $ 500.00 – $ 1,000.00.
Q: How often should an IR scan be carried out and how much should it cost?

A: An infrared roof scan should be carried out at least once every three to four years depending on age of the building. Buildings less than 15 years can be scanned every three to four years. Older buildings should be scanned every 2nd year or if leaks are occurring more frequently. IR scans of roofs start at $1500 for up to 40,000 sq. ft. and generally, cost $0.02 to $0.03 cent per sq. ft. after 40,000 sq. ft.

Q: How should I decide whether to continue to repair my roof or replace it?
A: We generally use a rule of thumb. If you have wet anomalies or wet areas in the roof system scattered over the complete roof section and the value of the wet insulation is greater than 25% of the total roof area then your choice should be to replace this roof. If you only have one wet area in a concentrated area greater than 30% of the total roof area replace the roof. Above all the age of the roof and general conditions of the roof flashing and membrane system should be considered in the replacement decision.
Q: How does a roof consultant decide on the type of construction to be used on my roof?
A: There are many factors involved in the decision process for the type of roof construction.Some of these factors include but are not limited to the following: cost constraints, life expectancy, warranties, environment, building height, roof access, roof traffic, drainage, existing roof construction and reuse of good materials, construction constraints, access for construction, type of deck, R value of insulation, building codes, qualification of trades in area, aesthetics, etc.
Q: I understand that phenolic insulation can corrode my deck. If this is true, how do I know if I have a problem? Do I have to replace this roof now?
A: Phenolic insulation is no longer used in the roofing industry as a insulating product. Phenolic insulation if wet will generally turn to acid and attacked galvanized and non galvanized steel decks. However, this product is not a problem over concrete or wood decks. Phenolic insulation is also not a problem over gypsum boards sealed with a vapour retarder. If you are unsure whether you have phenolic insulation, contact us, a roofing contractor or another consultant and ask for core cut verification. We suggest that phenolic insulated roofs be scanned at least once every two years. If the roof is dry then there is no need to replace your roof at this time. Some of the previous manufacturers of phenolic insulation provide technical assistance and financial assistance to replace damaged insulation, decking or systems. Some of the previous manufacturers to visit their sites include Koppers and Domtar.
Q: All of the contractors I talk with speak about Factory Mutual wind requirements. What does this mean and how do I contact them if I am not sure?
A: Factory Mutual is an insurance body who assist our industry to provide guidelines to reduce losses caused by fire and wind in the roofing industry. There are three sets of data base on wind pressure which establish how a building roof sub assembly should be secured to the deck, i. e. FM – I – 60, FM – I – 90 and FM I – 120. These three design factors are controlled by wind velocities in the area your building is situated in. Building heights and shape are considered factors in the evaluation. Basically Factory Mutual assists the consultant and contractor in determining the method of mechanically fastening your insulation system down. For more information go to our link with Factory Mutual.
Q: What R value do I need on my roof?
A: We now have new energy codes coming out which will soon become part of the Ontario Building Code. R value will vary for type of occupancy and geographical location. For an example a residential apartment in Toronto area requires R 20. That same apartment building in Timmins may require R24 or higher. An industrial building in Toronto may require R 12 minimum but in Virginia this value may be lower. Several states also have their own building codes. You should always inquire with your local government building department to determine what codes govern your area.
Q: When do I need a vapour retarder?
A: A vapour retarder should be used where there is the possibility for moisture to rise above the deck system. i.e. residential buildings, food processing, restaurants, hospitals, schools,pulp and paper process or any area of high humidity.
Q: How much should a roof replacement cost?
A: Costs will depend on several factors. Height of your building, access for garbage removal and set up, complexity of the design, warranties, familiarity of the contractor with the materials selected by the consultant, time of year, environmental conditions, existing roof material conditions, etc. We have listed some of the general price guidelines for retrofit to roofs in Ontario.

Flat BUR 1 – 5 stories high, R 20 – retrofit $ 7.50 – $ 9.00 per sq. ft.
Flat BUR glass felts for above $ 8.00 per sq. ft. – $ 9.50 per sq. ft.
Add for every 10 stories above 5 stories $ 2.00 per sq. ft.
Two ply modified bur roofing… $ 8.50 -$ 9.50 per sq. ft.
Inverted roofing add $ 2.00 per sq. ft.
PVC roofing loose laid and ballasted – 1 – 5 stores… $ 7.00 per sq. ft.
PVC mechanically fastened… $ 9.50 per sq. ft.
EPDM loose laid ballasted… $ 8.00 per sq. ft.
Retrofit over top existing… $ 4.75 per sq. ft. for buildings less than 4 stories
Add if building has many roof projections $ 2.00 per sq. ft.
Add if building has access problems for construction $ 1.50 per sq. ft.
Add if roof is to be done in winter or in peak of summer $ 2.00 per sq. ft.
Add if union roofing contractors required $ 1.50 per sq. ft.
Add if roof is less than 1000 sq. ft. in size $ 5.00 per sq. ft.


Cost to replace an 20 storey apartment building, 14,000 sq. ft. in size in November, downtown Toronto with poor access. Consultant has selected two ply modified inverted roofing R value 20.

Cost = $ 8.50 per sq. ft. + $ 2.00 for inverted + $ 1.50 for access + $ 2.00 for winter + $ 2.25 for height = $ 16.25 per sq. ft.

Total Cost = $ 227,500 + engineering + G.S.T. + contingency allowance.

Q: What are the obligations of the roof consultant once hired?
A: The roofing consultant like a professional engineer has a duty to protect you the client and the public. For more details on consultant responsibilities visit our RCI web link. For responsibilities of the roofing contractor visit the NRCA web link.
Q: What are the safety requirements required for my site?
A: The Occupational Health Act and Construction Codes of your state or provincial area will direct you to the requirements for safety on site. In general any worker working closer than 2.4 meters from the roof edge should be tied off. Tie off points do not include ladders on walls, vents, etc.. They do include fall restraint or fall arrest anchor systems. It is the responsibility of not only the worker and contractor to ensure safety but the owner and his representatives on site. Safety barriers or warning lines are also mandatory on all construction sites greater than one storey.
Q: If I have a fall restraint or fall arrest system how often do I need to have it inspected and who can carry out this inspection?
A: A fall restraint or fall arrest system should be inspected by a professional engineer or qualified person at least once every year.
Q: What types of inspections are available during construction?
A: Thermaco offers full time inspection or part time inspection. Full time means will be on site just after completion of the tear off and will leave with the roofer at the end of the day when the building roof is water tight. Part time inspection is based on 2 – 3 hours of inspection at strategic times of the day.
Q: How critical is drainage to maintaining my roof over the long term? How expensive is it to add more drains if I need them?
A: Good drainage is one of the key factors in maintaining a good roof. We try to incorporate in our design at least one roof drain for every 3 – 4,000 sq. ft. of roof area. A general rule is the roof should be dry 48 hours after a rainfall to have good drainage. Drains can be added for about $ 500.00 – $ 850.00 each including plumbing.
Q: I have experienced deck corrosion in the past. The roofing contractor treated my rust with asphalt primer he had on site. Will this protect me?
A: No. Asphalt primer is not a protective coating for rust. Corrosion once the process has started will continue if not properly treated with a rust inhibitor paint applied in accordance with the manufacturer’s recommendations. If the deck is corroded, we suggest that a roof consultant or structural engineer be contacted to determine if the structure is now sound.


Q: When should an IR roof survey be carried out and under what conditions?
A: An IR roof survey should be carried out first after a high solar loaded day and at least 1 – 2 hours after sundown to allow the roof to cool off. The roof surface must be totally dry at least 6 – 8 hours prior sundown to allow sufficient heat absorption into the roof assembly.
Q: Can an inverted roof or loose laid ballasted roof system be scanned?
A: The inverted roof cannot be scanned. A loose laid ballasted roof can only be scanned under specific environmental and temperature conditions and should not be tried by inexperienced thermographers.
Q: Is verification required by the thermographer during the IR scan?
A: Yes. A thermographer should verify during the scan with electrical capacitance or moisture meters. Further destructive testing is required i.e. moisture probe verification with a Delmhorst moisture meter or core cut tests are required to verify the presence of moisture.
Q: Can PVC roofing be scanned if it is mechanically fastened?
A: Yes. However the experienced thermographer will look for specific conditions. Hot temperatures in the day time and cold temperatures at night generally will cause the PVC surface to sweat which is detrimental to the scan. Thermaco has found it most effective to scan these types of roofs where the temperature at night is within 8 – 10 C of the day time temperature. Once you can see your foot print in the membrane at night it is time to stop.
Q: Can buildings be scanned effectively if they are surrounded by higher buildings in a down town core?
A: Yes to a point. The window for thermal gain in protected areas will be small. The scan will be limited in time for the thermal window to be open.
Q: How often should I have my electrical system scanned in my plant ? What should I scan as part of the survey?
A: If you plant is controlled by ISO 9000 or insurance requirements at least once every year. Scan the complete electrical system including your switch gear, motor control centres, bus duct work, distribution panels, equipment panels and emergency systems.
Q: How often should I have my apartment building electrical system checked? How often for any commercial buildings in my portfolio?
A: Generally if no problems arise once every two year for your commercial building and once every three years for a residential building.
Q: We are a public utility. How often should we scan our system and what equipment should we look at?
A: We recommend to our utility customers to scan the high voltage distribution system at least once every year or second year depending on the site of the utility. Larger utilities scan twice a year. Depending on your budget you should at least scan the three phase system, all your substation equipment, all major underground switch gears and all major vaults servicing downtown customers.
Q: How much should an IR electrical scan or utility scan cost?
A: Prices will vary from consultant but generally electrical scans cost about $ 700 – $ 1,000 for buildings and $ 550.00 – $ 650.00 per day for utility scans.
Q: How effective are IR building envelope scans. Will the information be useful? When should they be done?
A: Building IR scans require specific conditions to be carried out effectively. Generally we try to place the building under positive air pressure. The scan is completed at night during the fall, winter or spring when temperature differentials between the building interior and exterior temperature reach at least 20 oC. The scan should cover all sides of the building and some interior shots as well. Some buildings even under positive air pressure unless perfectly balanced will have some areas with negative air pressure. The information should be placed not only in thermogram/ real image format but should be identified on elevation drawings. A good thermographer will obtain the basic construction design information prior to carrying out the survey and should be able to see if design or construction flaws exist which may require remedial measures. An IR survey building audit should be carried out upon completion of construction but before hand over of the building.
If you have any additional questions not answered on this page, please contact us