Tips to Correctly Estimate Materials for your EPDM Job - Rubber Flat Roof

Top Tips To Correctly Estimate Materials For Your EPDM Rubber Roofing Job

Here at Rubber Flat Roof, we’ve complied some tips on how best to estimate the materials you will need for your EPDM rubber roofing job.

1. EPDM Membrane
EPDM Rubber Roofing Membrane 1.5mm – Rubber Flat Roofs

EPDM Rubber Roofing Membrane 1.5mm – Rubber Flat Roof

  • To estimate how much material you need you will have to calculate the area of the rubber required. You can use the following formula:

(length of roof + overhang) x (width of roof + overhang) = square meters of membrane needed.

(Note: We recommend an average of 200mm overhang on all sides for most roof installations. Also the EPDM rubber comes in fixed widths and the closest width will be recommended for the project)


2. Bonding Adhesives
  • Water based: this is a type of glue used to adhere the EPDM membrane to your flat roof boards – we recommend this for the main roof area also known as the field area. We stock a range of adhesives in a variety of sizes up to 20L. To calculate how much water based adhesive you will need you can use this formula:

(length x width of roof surface) divided by 4 = kg of adhesive needed.

  • Solvent based: we recommend the use of solvent / contact adhesives for the perimeter of the roof area (approx. last 100mm) and also for any upstands. Contact adhesives need to be applied to both mating surfaces i.e. roof deck and rubber to create a quick curing bond.
    The formula for the amount of contact adhesive required is as follows:

    (length of roof + width of roof) x 0.4 = litres of adhesive required.

    (Assuming 200mm allowed for perimeters and upstands)

  • Solvent based only: if you’re using one of our solvent-based adhesives for the complete roof area then follow this formula instead:


(length x width of roof surface – including overlap) divided by 2 = Litres of adhesive needed.

Quickbond Water Based Bonding - Rubber Flat Roofs

Quickbond Water Based Bonding Adhesive – Rubber Flat Roof

3. Seam Tape
  • Seam Tape is a waterproof tape used to join your EPDM rubber roof, ensuring any seams are completely waterproofed.
  • We offer 75mm x 7.62m seam tape.To calculate how much seam tape you will require, follow this formula:

Total length of seams divided by 7.62 or 30.48 (depending on which size you use) = number of rolls needed.

Seam Tape - Rubber Flat Roof

Seam Tape – Rubber Flat Roof

4. Seam Tape Primer
  • Seam tape primer is designed to clean and prime the EPDM membrane to prepare it for proper seaming or taping. We provide this in 500ml or 3.78 litre sizes.
  • To estimate how much primer you need for your job keep in mind that 3.78L will cover 10m², both sides of the rubber.
Rubberall Seam Tape Primer - Rubber Flat Roofs

Rubberall Seam Tape Primer – Rubber Flat Roof

5. Uncured Flashing Tape
  • We have these available in widths of 6”, 9” and 12”. These are designed to form seamlessly around awkward features (pipes, penetrations, drain outlets, etc.) where the ability to stretch and form the material is required to create a watertight seal. Use this formula to estimate how much you will need:

Number of upstand external corners (i.e. wall, roof light, under tiles, step etc) x 0.3L/m of flashing tape

Note: you can also use flashing tape for pipe / drain details or other penetrations on the roof surface. Please contact Rubber Flat Roofs for further advice.

6. Peel and Stick Pipe Boot
  • These are used for weather-proofing around drainage access points. We provide Peel and Stick Pipe Boots that will fit various pipes up to 6″. To calculate how many you will need use this formula:

Number of cylindrical penetrations = number of pipe boots

7. Water Cut-Off Mastic
  • These are used as a sealing for adjacent roofs, top of pipe boots or upstands, and we have them available in 325ml tubes. To estimate how much you need remember that one tube will cover approximately 3.05 linear metres in a large bead.
8. Lap Caulk
  • This is specifically designed to ensure a watertight seal while seaming two EPDM liners or while weather-proofing. We have these available in 325ml sealant tubes. To estimate how much caulk you’ll require, remember that one tube will cover approximately 6.10 metres of your roofing surface.
Lap Caulk - Rubber Flat Roof

Lap Caulk – Rubber Flat Roof

9. Rubber-to-Rubber Adhesive
  • This is used to adhere EPDM, membrane to membrane. We have these available in 3.78L tins, each allowing you to cover approximately 3m².
10. Termination Bar
  • These are used in conjunction with Water Cut-off Mastic & Lap Caulk to create a waterproof junction on up-stands or where EPDM membrane joins into existing roofing materials such as felt. We have them available in 3.1 metre sections. To calculate how much you will need use this formula:

    (length of perimeter + length of parapet) divided by 3.1 = number of Termination Bars.

    Note: on many upstands a metal flashing detail or lead may be used in place of a termination bar.

11. Scrub Pad
  • This is used to apply your seam tape primer. Typically you will only need one per day of construction.
12. Quicktrim
  • This is used to secure the EPDM membrane around the perimeter of the flat roof and to improve appearance.
  • Quicktrim Check kerb (upstand) trim is used as an edge detail to stop water running off of the side
  • Quicktrim Drip (gutter) edge trim is used on the side where a gutter will be installed to allow water to run off the flat roof into the gutter.
  • Solid corners are available for both Check and Drip Trims and for internal or external corner details. These should be installed first and trims installed between the corners.
  • Use this formula to calculate how much you will need:

Roof perimeter (in metres) divided by 2.5 meters = trim lengths required.

As you can see, we stock all the above products and can cater for all of your EPDM rubber roofing needs, please browse our website to view our full range. For more information on how to estimate your materials, get in touch with us today or see our roof quote tool.