How Much Does a Flat Roof Replacement Cost?

Flat roof replacement cost is a question commonly asked by our clients throughout the GTA.

Whether you have commercial, industrial flat roofing assets or a residential flat roof on your home; the following information can help simplify what can be a complex question. When initially speaking with a client over the phone. They will often ask” how much per square foot do you charge”?

The honest answer is that the cost can vary considerably based on a number of factors and job site conditions.

In general terms, there are some basics to be determined which relate to every type of flat roof and its ultimate relationship to price. A primary consideration is the working access and number of stories the structure is, which relates to the labour involved to get materials onto the flat roof, handling the tons of debris to come off the roof, and the actions required to secure pedestrian walkways, entrances, traffic flow, and hydro wires.

These are among the first things the project estimator must assess.

Once on the roof; the estimator must obtain accurate measurements and document all the unique details of that particular flat roof. In other words, you can have two different flat roofs, both of similar size, but end up with two completely different price points for each specific job.

The details are a great determiner ultimately of price. The more complicated the details, the price will obviously increase.

In very specific terms; the number of layers of flat roofing materials that must be removed to expose the bare substrate becomes one of the most influential factors as it has a direct bearing on the amount of labour hours needed for the removal and the subsequent handling of the garbage. An example is that if there are four layers on a downtown residential flat roof, with each layer of tar & gravel weighing 750 lbs./per 100 square ft.; that translates into 3,000 lbs. for a 10’x10’ section of a flat roof.

A typical downtown residential flat roof having a common 400 sq. ft. size can weigh six tons. Now think about taking that down to the ground from three stories in the air. Then having to remove such debris between two homes, where a wheelbarrow barely fits. Imagine in this instance that the homeowners expect no damage to their home and especially their neighbour’s home.

It is then easy to deduce when thinking of such an example; why there could be a considerable difference in the cost of a flat roof replacement on such a project, when compared to a 400 sq. ft. flat roof which is located one storey off the ground, and where the debris may be discarded in a dump trailer in the front driveway.

Other residential perils include having to bag the debris and do a “triple drop” from different elevations to the ground level, steep slopes which lead up to the flat roof, hydro line coverage, and the list goes on.

After consideration of access and debris handling and property protection, comes the determination of specifications of the replacement flat roof assembly. This plays a key factor in the cost of a new flat roof replacement.

As an example; most older homes in the GTA were not built to today’s building code standards. When retrofitting such flat roofs; they will typically require the installation of a vapour retarder layer and thermal (polyisocyanurate) insulation to be installed.

The building owner must also decide whether they will spend to have the flat roof structurally sloped to improve drainage. As many older flat roof structures settle or develop bows from snow and water load over time; it is often prudent to create a minimum two percent grade (as with modern building code requirements).

Structural repairs involving the replacement of rotted roof boards or rotted roof sheeting are a common requirement when dealing with older multi-layered flat roofs. In the case of commercial and industrial flat roofing projects; corroded steel pan decking panels may require replacement as a typical practice during retrofit.

On commercial and industrial buildings, it is almost always assured that there will be a need to disconnect and re-connect HVAC equipment on the roof and the associated gas line piping.

Appliances on a flat roof such as skylights, pipe protrusions, internal or external roof drains and heat stacks are all examples of items which influence both the material and labour requirements which influence the cost of a flat roof replacement project.

On residential flat roofs, we often run into projects where there are entry doors leading onto the flat roof. In some instances, such doors need to be removed and re-installed or completely replaced to accommodate proper waterproofing details required beneath the sill of the door.

Similarly roof lounge decks, railings, and divider walls on semi-detached homes contribute to the required costs of flat roof replacement. Details such as the amount of sheet metal work necessary to cap the tops of parapet walls, roof to wall junctions and flat roof perimeters contribute to the final flat roof project costs as well.

Where flat roofs adjoin shingle slopes, sided or stucco walls; it is often necessary to restore or tie-in to such adjacent surfaces in order to achieve water-tight sealing of a flat roof assembly.

As there are a variety of flat roof waterproofing choices; each one has its’ merits, and the amount of labour time involved can vary with each type of system.

BUR (Built Up Roofing); aka tar and gravel roofs tend to be very labour intensive as one requires a kettle operator on the ground, and at least three to four technicians on the roof to complete preparation work, mop felts in hot asphalt, and complete the hot asphalt pour and final gravel process.

On very large commercial and industrial BUR projects; the economy of scale changes as mechanized processes can be used to achieve large daily square footage replacement.

Two-ply assemblies such as modified bitumen tend to be a bit less labour intensive when discussing application of the waterproofing membrane itself. Materials for this type of system tend to be more expensive than BUR materials.

Single-ply assemblies such as TPO or EPDM, tend to be most labour cost-effective due to the nature of large field sheets being employed; but the material costs are also greater than BUR or Modified Bitumen assemblies.

When receiving an estimate for flat roof replacement, a consumer can wonder why there may be vast differences in prices obtained from soliciting various vendors.

When evaluating the cost of such proposals, it is first important to consider the differences and similarities in relationship to the specifications being detailed, and to understand how the project will be executed. As an example, if one vendor was setting up scaffold to protect over a busy sidewalk, and the opposing vendor was not doing so; there could be literally thousands of dollars difference in the bids.

Once the client has checked that the materials being used and methods being employed are the same; the only variables affecting price can be overhead costs and profit.

When bid scopes look similar, but prices vary greatly (over 10% from one another); there can only be three primary reasons for a dramatic difference in price. They are:

  • Correct Calculation of Overhead Costs (both direct and indirect)
  • Profit
  • Calculation Errors

When considering the correct calculation of overhead costs, one must consider the structure and heritage of the bidding construction firms.

Among well-established vendors, labour costs tend to be similar including the payroll tax obligations associated with paying their workforce.

Some less established firms may not account for or actually pay such costs, so the consumer should check this point for their own protection.

Established and experienced firms will account in their bid pricing for overhead items such as:

  • Proper liability insurance coverage
  • Auto insurance coverage
  • Current WSIB clearance
  • Health & Safety training & compliance
  • Permanent place of business
  • Advertising
  • Sales Costs
  • Warranty Costs
  • Accounting & Taxation
  • Vehicles (Purchase, repairs, maintenance, etc.)
  • Tools & Equipment

The list of such items goes on.

The point is that in-experienced businesses often do not account for the real costs of doing business and remaining in business. An industry study demonstrated that the majority of roofing contractors across North America reported sales of less than two million dollars annually and that the failure rate for such businesses was eighty percent within the first five years.

The primary reason for the business closing or becoming bankrupt, was that the businesses were not accounting for and generating enough revenue to cover their true operational costs.

While this can be true for a number of industries; it certainly explains why consumers can often receive flat roof replacement bids which are thirty to fifty percent less than what may appear to be their highest quote.

Profit is necessary for every business to remain in business. In the construction industry, a business needs to achieve at least a 32%-40% gross profit after hard project costs are accounted for. Hard costs being materials, labour and disposal.

The gross profit is what the indirect costs of running a business get paid from. In other words the overhead costs, staff taxation, etc. The reality is that after accounting for all operational costs a successful contracting business may only net about 10% of their gross sales in a good year.

Compare that to the margin on a cup of coffee at a favourite retailer.

The idea for both the consumer or the budding construction entrepreneur is that one needs to pay and charge respectively, the correct price for flat roof replacement or any roofing /construction services for that matter.

Most business people will readily understand this requirement. Those obtaining bids for flat roofing replacement or other services now understand that it is unwise to pay too much, but it is very unwise to pay too little.

As of the date of this writing; in the GTA, the average cost of flat roof replacement can range as follows:

Residential Flat Roofing: $15-40 per square ft.

 Large Commercial/ Industrial Flat Roofing:  $11-30 per square ft.

The range in pricing accounts for the most common configurations, with historic annual increases of about 10% annually for materials and 2-5% annually for labour costs. The information supplied is only a guide, and those interested to obtain actual pricing specific to their particular project requirements should contact their preferred roofing vendor for their particular city, or if in the GTA visit; or view us on YouTube™