ROOF SYSTEM CHARACTERISTICS – COMPARE AND CONTRAST THREE DIFFERENT FLAT ROOF SYSTEMS

Notes: 

  1. Please see roof system schematics following for the sequencing and materials of the roof system components. 
  2. Please review the Comparison Chart – comparing and contrasting the characteristics – of the Three Roof Systems.

THREE POSSIBLE ROOF SYSTEMS FOR A NEW BUILDING PROJECT – ACTUAL SELECTION MUST BE BASED ON ALL CONSIDERATIONS AND INFORMATION

ROOF SYSTEM 1 – BASIC 

SINGLE PLY, LOOSE LAID, 45 MIL EPDM ROOF SYSTEM

¾ -1 ½ inch, round river stone ballast OOOOOOOOOOOOOOOOOOOOOO

applied at 15 lbs per square foot

One layer of 45 mil, EPDM rubber ______________________________

sheet, loose laid under the stone ballast

Top course of insulation – 2.1” ______________________________

polyisocyanurate insulation – _  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

adhered with urethane adhesive ______________________________

Bottom course of insulation – 2.1” ______________________________

polyisocyanurate insulation – _  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

adhered with urethane adhesive ______________________________

One ply kraft paper vapour retarder

With adhered, sealed seams ______________________________

ROOF SYSTEM 2 – BETTER

2 PLY MODIFIED BITUMEN ROOF SYSTEM

Granule surfacing embedded on cap ply ***** *************************

Cap ply of 4.0 mm, 250 gram granulated  ______________________________

polyester ply sheet embedded in a 

solid mopping of hot type II asphalt

1 ply of 180 gram polyester base sheet ______________________________

embedded in a solid mopping of hot 

type II asphalt 

Top course of insulation – 1/2” asphalt ______________________________ 

saturated fibreboard adhered in a solid ______________________________

application of hot type II asphalt

Tapered fibreboard as designated

Intermediate course of insulation – ______________________________

2.0 “ polyisocyanurate insulation – _  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

fully adhered in a solid application ______________________________

of hot type II asphalt

Bottom course of insulation – 2.0” ______________________________

polyisocyanurate insulation – _  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

mechanically fastened to FM 1-90 ______________________________

One ply kraft paper vapour retarder

With adhered, sealed seams ______________________________

ROOF SYSTEM 3 – SUPERIOR

4 PLY HYBRID BUILT-UP ROOF SYSTEM

Gravel surfacing embedded in a heavy OOOOOOOOOOOOOOOOOOOOOO

floodcoat of hot type II asphalt

1 ply of type IV fibreglass ply sheet ______________________________

embedded in a solid mopping of hot 

type II asphalt 

1 ply of type IV fibreglass ply sheet ______________________________

embedded in a solid mopping of hot 

type II asphalt 

1 ply of type IV fibreglass ply sheet ______________________________

embedded in a solid mopping of hot 

type II asphalt 

1 ply of 180 gram polyester base sheet ______________________________

embedded in a solid mopping of hot 

type II asphalt 

Top course of insulation – 1/2” asphalt ______________________________ 

saturated fibreboard adhered in a solid ______________________________

application of hot type II asphalt

Tapered fibreboard as designated

Intermediate course of insulation – ______________________________

2.0 “ polyisocyanurate insulation – _  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

fully adhered in a solid application ______________________________

of hot type II asphalt

Bottom course of insulation – 2.0” ______________________________

polyisocyanurate insulation – _  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

mechanically fastened to FM 1-90 ______________________________

One ply kraft paper vapour retarder

With adhered, sealed seams ______________________________

Comparison Chart For Three Roof Systems – BASIC, BETTER, SUPERIOR

ComparatorSystem 1 – BASIC – 45 Mil EPDM Rubber Sheet Single Ply Roof SystemSystem 2 BETTER –2 Ply Modified Bitumen Roof SystemSystem 3SUPERIOR  – 4 Ply Rubberized Base Sheet And 3 Ply Fibreglass Felt Asphalt Built-up Roof System
SubstrateMetal Deck Metal DeckMetal Deck 
Vapour RetarderOne layer of Kraft Paper With Adhesive Sealed SeamsOne layer of Kraft Paper With Adhesive Sealed SeamsOne layer of Kraft Paper With Adhesive Sealed Seams
Base Insulation2.1 inch polyiso insulation, loose laid over the kraft paper vapour retarder2.0 inch polyiso insulation mechanically fastened min. FM1-90
2.0 inch polyiso insulation mechanically fastened min. FM1-90
Intermediate Insulation2.1 inch polyiso insulation, loose laid over the base course – Total R value = 242.0 inch polyiso adhered in a solid mopping of hot asphalt
2.0 inch polyiso adhered in a solid mopping of hot asphalt 
Top Course of InsulationN/A – none½” asphalt saturated fibreboard adhered in a solid mopping of hot asphalt – Total R value = 24½” asphalt saturated  fibreboard adhered in a solid mopping of hot asphalt – total R value = 24
Base Ply Of Membrane1 layer of 45 mil EPDM Rubber
Sheet with adhered Seams – loose laid
1 ply of 2.2 mm, 180 gram polyester reinforced base ply in a solid mopping of hot asphalt1 ply of 2.2 mm, 180 gram polyester reinforced base ply in a solid mopping of hot type II premium asphalt
2nd Ply of  Roof MembraneN/A none1 ply of 4.5mm, 250 gram polyester reinforced cap ply in a solid mopping of hot asphalt1 ply of type IV fibreglass felt adhered in a solid mopping of hot premium asphalt – shingle style
3rd ply of MembraneN/A noneN/A none1 ply of type IV fibreglass felt adhered in a solid mopping of hot premium asphalt – shingle style
4th ply of MembraneN/A noneN/A none1 ply of type IV fibreglass felt adhered in a solid mopping of hot premium asphalt – shingle style
Membrane AdhesiveN/A none – loose laidType II roof asphalt applied hotPremium type II asphalt applied hot
Surface FinishLarge – 3/4 to 1/1/2 inch round, river stone – loose laidGranulated surface of cap ply is finished surfaceGravel surfacing embedded into a heavy floodcoat of premium asphalt
Renewal of Surface Required During Service Life of System?No, large stone is in place for the life of the rubber  membraneYes, granulated surface will deteriorate in approximately 15 years – must be overlaid with another cap plyNo, gravel and floodcoat are essentially permanent
Top Floodcoat Material – WeightNone – weight of system – 15 lbs per square footN/A none – surface material on cap ply – minimal Hot applied,premium asphalt with exceptional weathering resistance applied at a rate of 70 lbs. per 100 sq. ft.

Warranty
Standard – typically 10 years – more can be purchased – see NotesModerate – typically 15 years – more can be purchased – see NotesPremium – typically 20 years – more can be purchased – see Notes
Estimated Service Life of System10-15 years plus 15 years, then resurfacing required – then another 15 years35 years, plus – a very long term roof system
Resistance To LeakagePoor to Fair – only one layer of rubber sheeting with adhered seams – water can migrate below the membraneGood –two heavy, rubberized polyester plies -essentially seamlessExcellent – the multi-layer membrane features redundant waterproofing, exceptional toughness and resistance to puncture – essentially seamless
Resistance to Traffic Poor to Fair – the membrane can be damaged by foot and other traffic Good – 2 plies of polyester reinforcement provides good resistance to traffic – the granulated surface does not provide much protection from traffic and damageExcellent – the membrane is extremely tough and robust and the adhered gravel surfacing provides excellent protection from traffic and damage
Ease of Leak Source IdentificationVery Poor – punctures great enough to cause leaks will allow water to migrate and flow under the loose laid membrane and over and through the insulation layersGood – punctures great enough to cause leaks will be apparent – 2 ply membrane is tough and well adhered – both layers are fully adheredExcellent – the multi-layer membrane is extremely  tough, all layers are completely adhered together – holes in the membrane are extremely unlikely. If a hole is made by great force – water will not be able to migrate and the hole will be obvious
Low Temperature Flexibility
Good – rubber sheetVery Good – 2 polyester reinforced plies of base sheet are rubberized Very Good – entire system tough and rugged 
Resistance to Thermal ShockGood – roof membrane is flexibleVery Good – roof membrane plies are rubberized both layers are solidly adheredExcellent – entire system is  movement tolerant, rugged and solidly adhered
Elongation and RecoveryVery Good – rubber roof membrane is very flexibleGood –both polyester sheet plies are rubberized and flexibleGood – elongation with  recovery – robust system
Puncture resistanceVery Poor – thin rubber sheet punctures  easily – single ply – no redundancy  – leaks very damaging  if roof surface is floodedVery Good – rubberized plies and polyester reinforcement combined– provide a tough, puncture resistant roof membraneExcellent – the roof membrane is composed of a polyester, flexible base sheet and three extremely durable, fibreglass ply sheets that are very resistant to puncture – in addition the  asphalt provides “bulk thickness” puncture resistance
Perimeter Base Flashing SystemFair – one layer of 45 mil rubber sheet Very Good – base ply of high strength, solid, rubberized flexible, polyester reinforced flashing sheet is covered with a solid cap ply of flexible, rugged polyester cap sheet – both layers solidly adhered in hot asphaltExcellent – base ply of high strength, solid, rubberized flexible, polyester reinforced flashing sheet is covered with a solid cap ply of flexible, rugged polyester cap sheet – both layers adhered in and coated with premium asphalt which provides movement tolerance
Resistance To Ponding WaterGood – the system is non-rotting – but ponding water will attract and promote sharp particles and debris – seams can separateFair – the top surfacing  is only moderately  resistant to the effects of moderate ponding – granule separation from the cap ply is accelerated in ponding conditionsExcellent – the top floodcoat of premium asphalt and gravel surfacing are resistant to the effects of ponding – entire system is non-rotting – full system is resistant to ponding conditions
Resistance to Ultraviolet and Heat agingGood – thestone surfacing resists the effects of ultraviolet and heat agingGood – the top coating of granules will resist the effects of ultraviolet and heat aging while still adhered to the cap plyExcellent – the floodcoat of premium asphalt is resistant to heat aging and the thick coat of asphalt and gravel surfacing that is system integral is highly resistant to ultraviolet attack
Controlled Quality of AsphaltN/A noneNo – commodity grade roofing asphalt – non rubberizedYes – premiumasphalt  whose characteristics and performance is predictable and whose service life is extremely long
Quality of AsphaltN/A noneType II asphalt is pre-aged to raise the softening point to enable use on the roof Type II asphalt is pre-aged to raise the softening point to enable use on the roof

Most Prominent Fault or Weakness of System


Very Poor Puncture Resistance and Loose Laid, Single Ply Membrane Allows Water Migration Under the MembraneGranule Surfacing Will Degrade and Fracture Away From The Surface Of The Cap Ply Allowing Ultraviolet Attack and Deterioration Essentially None – The Entire System Is Seamless, Tough, Robust and Provides A Very Long  Service Life

Notes: Extended Warranties – extended warranties are sold by the manufacturers as a marketing tool – purchasing an extended warranty typically does not necessarily provide more significant protection than the standard, typical warranty – the cost of an extended warranty is significant and in the case of a claim – the warranty document does provide exclusion clauses and other “out” conditions that can allow the manufacturer to not honour the warranty in spite of the extra cost. The best assurance for a good roof system is “good design, good materials and good labour”.