Flat (Low Slope) Roof Replacement Systems  
Installation Specifications and Design Considerations

Calgary, Vancouver, Edmonton, Fort McMurray, Lethbridge, Red Deer

Flat Roofing - Flat Roof Solutions

Flat Roof Calgary, Red Deer, Edmonton, Fort McMurray, Lloydminster, Saskatoon, Regina, Medicine Hat, Lethbridge, Canmore, Cranbrook, Kelowna, Vancouver, Whistler, Winnipeg, Mississauga Toronto and points between. Alberta, Saskatchewan, British Columbia, Manitoba, Ontario.

 Problems Residential and Commercial Property Owners Experience

Some of the most common flat roof installation problems we see building owners face are improperly designed or poorly installed systems, poor choices in the particular system given the circumstances, and roof leaks or problems that resemble ones frustration with an electrical problem in a car.

"Ultimately, our job is to bring real solutions forward that eliminate your roof problems all-together."

We have a Lifetime Guarantee on our Workmanship. We found that as soon as we committed our workmanship guarantee in writing that our roofers became more solution focused. This is good for you the client, us the contractor, and even the roofer. He/she now works with an elevated ownership of his/her trade and takes great pride in a job well done.

"Our client list includes Fortune 500 companies, local commercial business owners, and home owners."
SBS, Modified, Torch On, Tar Gravel, Commercial, Replacing, Re-roof, Industrial, Residential, EPDM, TPO, PVC
When the time comes for you to replace your flat roof, there are many things to consider that can improve the performance of a flat roofing system. A number of factors can contribute to poor performance of your roof including the slope of your roof, poor roof drainage design, and structural issues. The use of your commercial or residential building and geographical location will also determine other considerations such as the R Value
, wind uplift, and Fire Classification Requirements.

[The photo to the right is a Flat Roof Replacement Calgary Project] 

Our Project Managers understand cost is also a very important factor when deciding on a roof replacement versus repairing your existing system. We are often able to provide short term solutions for our customers in the form of repairs while also providing forecasts for future roof replacement.

Things to Consider When Replacing a Low Slope System

It is extremely important to understand fundamental "good practices". The following guidelines will help ensure that the flat roofing you select is the correct installation specification for the commercial or residential building on which it is to be installed.


 Slope : Re Sloping Proper Water Shedding
The slope is an important factor when considering how your roof sheds water. One of the biggest problems our roofers encounter with most installations is poor slope.  

 Ponding Water 
The problem with poor slope is that when the roof begins to leak, the leaks are much worse than they would have been on a system that sheds the water properly.

Simply put, your roof should be designed to shed water off it as quickly as possible and not retain water like a pond or a swimming pool.

Incorrect slopes can be corrected with additional tapered ISO insulation (sloped insulation), sloping of the substrate, a new roof-overlay design, or by other design or installation methods.  

 Drainage : Effectively Draining Water Mississauga, Toronto, Ontario, Winnipeg, Manitoba, Alberta

The drainage system with low slope roofing is important. How your roof eliminates water is critical. Slope, or "the shedding of water" and drainage refers to the removal of or "water disposal" from your commercial or industrial roof. If you get the slope right and you get the drainage system right, you are half way to a perfect install. 


 Drains : Internal Drains
Are there sufficient drains installed? Take in to consideration the diameter of the drains and the total area of the roof. Are there correctly designed and installed roofing saddles (or sloped / tapered insulation) positioned between each drain to effectively shed water so there is no "ponding"?


 Scuppers : External Scuppers
Scupper design and installation errors are one of the most common causes of failures. The majority of the commercial and industrial roofing repairs GRS Roofers attend are due to scuppers being improperly installed.


 Gutters and Downspouts : External Gutters & Downspouts
Moving water off your roofing system as quickly as possible is critical. Gutters and downspouts need to work correctly or significant damage can occur. Check to be sure the gutters and downspouts are large enough to handle the water flow and there are enough downspouts installed. An improper installation of drains or downspouts or plugged drains can collapse a building.


If your roof is found to have an insufficient number of internal drains or scuppers we can add more drains or scuppers to the system at point of install.


 R-Value, Insulation, Sloped Insulation (ISO) Medicine Hat, Lloydminster, Canmore, Cranbrook, Whistler, Kelowna, BC, Saskatoon, Regina, Saskatchewan

R value definition. R value is the measure of a roofing materials' resistance to heat transfer. The higher the R value accomplished, the more resistant the roofing material will be to heat transfer. Modern rigid foam roof insulation is a very effective way to add R-value to a roof structure.


Polyisocyanurate insulation (commonly referred to as Poly-ISO or ISO) is widely used and offers an R-value of about 5-6 per inch of thickness and has great anti-compression strength (it resists compression). Poly ISO insulation is available in many thicknesses and can be installed with multiple layers to achieve the desired R value results. When installing layers of Rigid board be sure to off-set the board edges to avoid thermal gaps.

Poly ISO is also available in a pre-formed tapered panel (sloped insulation, ISO). Poly ISO is used by Roofers at GRS to add slope where none or little slope exists now.

You want to consider the existing R-value and how it relates to heating & cooling costs of the building. This allows you to determine if adding R-value makes sense for you. If the slope is inadequate, it is typically more cost effective to increase the slope using tapered insulation than by structurally changing the roof assembly or substrate – and with ISO you get the added benefit of increasing the R-value.

More on R Value Poly-ISO R Values at Wikipedia.


 Energy Efficiency
As above, the roofers at GRS can increase energy efficiency by either increasing R-value or by applying insulation in a more efficient way. Installation of double layers of insulation board with seams (or edges) staggered to mitigate thermal loss is one technique. This greatly lowers heat loss at the edge of the insulation boards because the heat cannot escape between the Rigid boards.

Another energy efficient installation technique you can utilize is a "screw and mop" application. It requires at minimum two layers of insulation board installed with the board seams staggered (as explained above). Your initial layer of insulation needs to be fastened to the deck by mechanical means and the second layer of insulation board is then fully adhered by way of hot tar mopping (using a kettle) to the initial layer of roof board insulation. This will mitigate heat loss considerably.


 Structural Loads

Another important consideration when establishing your scope of work is the structural weight load to your roof.

Structural weight load definition. Structural weight load is defined as the accumulated weight placed on a building. Weight load is typically expressed in PSF (or pounds per square foot).

When a building is designed they are engineered to handle projected wind and snow loads based on historical data tables. 

Building code typically (almost always) allows for a maximum of two systems to be installed on any building. Be careful when specifying a roof recovery - be sure there are no more than one existing system in place. 

You should consult with a structural engineer if there is any doubt concerning how much weight the building you are going to be working on can handle safely - especially in snow load areas like Edmonton, Red Deer, Fort McMurray, Saskatoon, Whistler, and central and northern Saskatchewan.

 Structural Deficiencies 

Structural deficiencies in the roof deck are another important category of consideration when replacing or retro-fitting over-top of an existing roof.

Structural deficiencies in a roof deck are deficiencies in the roof assembly or decking. For example, a wood framed assembly might have wood joists bowing in the middle from many years of constant load. This is common in snow loaded areas like Edmonton, Fort McMurray, Whistler, Northern BC, Norther Alberta, Saskatoon, and Northern Saskatchewan).

The wood joist bowing will very likely cause the water to pond. The roof assembly and construction may also have deck sheathing elevation changes resulting from remodeling or some form of construction in the past.  

When installing a roof recovery (retro-fit), if the existing roof has deflecting or slope deficiencies the new roof will mirror the existing deficiencies unless they are resolved by way of re-sloping (ISO). Alternatively, if the existing system is being completely removed to the deck sheathing then you will have a better opportunity to have correct slope and drainage when complete. I should not here that even with an engineered sloped insulation system that is installed on bare sheathing that there can still be issue if the building itself is not level. 

 Wind Uplift

Wind resistance or the wind speed that a roof is designed to resist is also an important consideration at time of planning the scope of work.

Wind resistance, or FM code (Factory Mutual testing agency) is the rating of the roof membrane wind uplift resistance (resistance to positive air pressure in PSF).

As a roof experiences positive uplift force (due to wind passing across) a suction effect is created. The suction exerts a force of lift to the system pulling the roof assembly away from the building. A poorly installed system anchored to an inadequate structure can experience a complete system failure or a partial or complete lifting of the system from the building itself.

Repair vs. Replacing a Complete System Liquid Rubber, Spray Foam, SPF, Slope, Drainage, R Value, Insulation, Wind Uplift, Ponding, Structural

Cost is obviously an important factor when choosing flat roof repair, roof recover, or complete roof replacement.

Most building owners and facility / property managers establish building / roof maintenance expenditures in terms of life cycle costs - the life cycle cost then becomes a part of the operating budget. An examination of repair estimates, recovery costs, or complete re-roofs can prove to be challenging for the novice. 

 Complete Tear-off vs. Retro Fit / Overlay (Sustainable Solutions)

The decision to completely tear off, re-cover (retro-fit), or repair can be difficult. We suggest you consider these options with your roofing contractor. 

Sometimes the options are limited because a recovery system simply won't work. If the roof system is saturated with moisture, has more than one roof installed already, or has considerable structural issues then the answer is simple - a full tear is the only answer.

Remember, the new system you install over an existing system is only as good as the roof assembly and building structure that it is installed over. 


Which is right for my building?

The staff at GRS will help you with options that suit you best. In summary, here are your options;

Multi-ply (Tar and Gravel), 2 Ply (Torch on or cold apply), Single Ply (TPO, PVC, EPDM), or a Spray on System (SPF or Liquid Rubber) are the main categories. Click here for a review of membranes available.

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To connect with our staff in your area please call +1.877.497.3528 today.

Related Links:

Systems Available  |  Design Considerations  |  Roof Repair  |  Maintenance  |  Rooftop Decks  |  Green Roofing  |  Drains  |  Commercial Re-Roof Considerations  |  EPDM  |  TPO  |  PVC  |  Tar and Gravel  |  Torch on SBS Modified  |  DecTec  |  Spray Foam  |  Liquid Rubber  |  Coatings  

Article Topics: Flat Roof Replacement Calgary, Red Deer, Edmonton, Fort McMurray, Lloydminster, AB, Saskatoon, Regina, SK, Medicine Hat, Lethbridge, Canmore, Cranbrook, Kelowna, Vancouver, Whistler, BC, Winnipeg, Mississauga, Toronto and points between. Alberta, Saskatchewan, British Columbia, Manitoba, Ontario. EPDM, TPO, PVC, Tar and Gravel, Torch On, Liquid Rubber, Spray Foam, SPF, Single Ply, Slope, Drainage, Drains, R Value, Insulation, Wind Uplift, Ponding, Structural, Overlay 

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