Purchasing a replacement roof system is a major expenditure and is a major business decision – decisions require information to ensure that the new roof system meets all of the requirement of the building and building operations and to ensure that value for money is obtained – energy considerations, longevity of service life, suitability for the building and many other technical considerations such as wind uplift resistance and long term, ongoing maintenance. (please see roof design criteria from previous information message for a complete listing of considerations)
Following is a discussion and commentary on the basics of flat roof systems – the knowledge of which will assist in a proper evaluation of the roof systems proposed and the differences and effects of those differences on price, service life, performance, maintenance requirements, energy requirements.
Three thoughts About Roof Systems
- It is always better to design a roof system – than to just pick one.
- There are three components required for a high quality, problem free, long service life roof system – good design, good materials and good labour – miss any one those three and the roof system will fail.
- Roof warranties – “the only way a roof warranty is going to keep water out of a building is by smearing a patch of roofing compound on the surface of the roof and pasting that roof warranty paper right in the centre of the smear.” (Paraphrased from – Dick Fricklas – scientist, researcher, author, speaker, teacher, consultant and magazine editor – A True Giant Of The Roofing Industry).
Warranties for roof systems are selling tools and they benefit only the Manufacturer. Roof system warranties include exclusions – “act of God”, “regular maintenance not performed”, “work by an unauthorized contractor” and many more. The warranties contain “out clauses” – clauses that allow the Manufacturer to opt out of paying money for a roof problem.
Some warranties are sold hard and taken very lightly. The fact of the matter is that a Building Owner is buying a roof system – not a warranty – but often the roof materials salesperson mentions the warranty as a predominate element of the decision – it is not predominate element – paying for an extended roof warranty is a contribution to the manufacturer with little or no benefit to the Building Owner.
Please refer to Point # 2 above – there is no mention of a warranty in the components for a high quality, problem free, long service life roof system.
Roof System Materials
- Asphalt – provides the waterproofing component of the roof membrane
There are two types of asphalt used in roofing systems:
- Oxidized or pre-aged – delineated by Type I, Type II or Type III
- Rubberized asphalt or otherwise referred to as Kettle modified
- Reinforcement – provides the strength for the roof membrane
There are five major types of reinforcement used in roofing systems:
- Organic or #15 paper felt – essentially blotter paper saturated with asphalt
- Fibreglass – non-woven filament, asphalt saturated – Type IV or Type VI
- Fibreglass – non-woven, filament, coated glass mat – typical weights 80, 90 100 gms per square meter
- Polyester – non woven, spun bonded, asphalt coated – different weights per textile standards – weight per square meter – most common – 80, 90, 100, 180, 250
- Composite – fiberglass and polyester reinforcements combined
- Insulation – provides the thermal resistance and performance of the roof system
There are three major types of insulation used in roof systems in 2019:
- Polyisocyanurate – a plastic foam insulation is the most used insulation with R value of approximately 6 per inch
- Rockwool or stone wool – expanded rock to form a relatively soft rigid insulation – R value approximately 4 per inch – this is a relatively newer insulation to be used in flat roof systems
- Fibreboard insulation – wood particles or cane fibers formed into rigid insulation boards with an R value of approximately 3 per inch – this is the oldest insulation type used
- A fourth type of insulation – rigid fiberglass is essentially no longer used in flat roof systems – the use of rigid fibreglass was severely diminished by the introduction of the plastic foam insulation to the marketplace – higher R values, easier to handle and install
- Vapour barrier or vapour retarder – provides some vapour control to moderate moisture diffusion – depending on the type – can act as a redundant waterproofing layer
There two types of vapour retarder/barrier used in modern roof systems :
- Kraft paper – a light duty vapour retarder composed of a lightweight reinforcing mesh coated with asphalt and sandwiched between two layers of brown kraft paper (like the post office paper) – this is not a redundant waterproofing membrane
- Self-Adhesive, rubberized vapour barrier – a woven polypropylene mesh coated on once side with a barrier film and on the other side with a layer of rubberized asphalt – this is a “peel and stick” product – remove the release paper and adhere
to a primed surface – this medium duty vapour barrier – not just a retarder – functions as a redundant waterproofing membrane.
- Structural Decks – this is the building component to which the roof system is attached and serves as the support for the roof system.
There are many types of roof decks – for the purposes of this information – only two types will be mentioned:
- Concrete – cast-in-place or pre-cast
- Metal or steel – ribbed steel sheeting – most common is the Type “B” deck with 1 ½ inch high steel ribs (also called a “Q” deck)
- Attachment of the roof system to the steel deck – the roof system must be secured to the structural roof deck – permanently and be able to resist all wind uplift forces to which the roof system will be subjected. Wind uplift forces are comprised of two forces – uplift from under the deck and suction from above the roof membrane.
The wind uplift forces vary in strength according to location on the roof areas of the building – typically the forces approximate to: one time force for the field or centre of the roof area, two times force along the edges of the roof area and three times force at the corners of the roof area. Any type of securement of the roof system to the building structure must be designed to accommodate the increased uplift forces at the edges and the corners.
There are three types of non-mechanical securement to the steel roof deck:
- Loose laid – not an actual method of securement – but this process is still used in some areas – it is not a goof practice – wind blow-off of roof system have occurred many times – this practice is cheap
- Mopping – sprinkle or solid mop with hot asphalt – this is a very unpredictable process – how much asphalt is actually applied is highly variable and the asphalt will not adhere if it cools or is cold – there is no consideration for the additional forces at the edges and corners – highly unreliable and unpredictable – this practice is very old and outmoded and does not account for the physics of wind uplift forces.
- Cold adhesive – somewhat better than hot asphalt because the adhesive will remain tacky longer – but the extreme variable is how much adhesive is actually applied – typically, the cold adhesive is dispensed by drips from the end of a corn broom, a hole punched in
the bottom of a 20 litre pail that is allowed to drip out onto the roof deck – sometimes an adhesive spreader is used – but the dispensing holes in the spreader plug up and impede dispensing of the adhesive. Again, a highly unreliable and unpredictable practice – this practice does not account for the physics of wind uplift forces
- Notes: The jeopardy of failure of attachment of the roof system and the disastrous departure of the roof system from the building is further exacerbated by the introduction of a kraft paper vapour retarder to the roof deck under the insulation layer. The kraft paper vapour retarder is a very flimsy material which tears easily and it must be adhered to the steel deck – well adhered, in fact.
Then the insulation layer must be adhered to the kraft paper – a two stage process – both layers must be secure – the kraft paper to the steel deck and the insulation to the kraft paper – both adhesive attachments must be essentially perfect.
If the kraft paper is not well adhered and the insulation is well adhered to the kraft paper, the entire roof system will be loose laid. If the kraft paper is well adhered to the steel deck, but the insulation is not well adhered to the kraft paper – the entire roof system will be loose laid.
Essentially, the only uplift resistance that a loose laid roof system possesses is the weight of the pea gravel surfacing – about 6 lbs. per square foot – over all areas of the roof area.
The typical wind uplift forces (actual calculations will be provided) for a building of a given size, height and location would be on the order of:
- Field of roof area– 20 lbs per square foot
- Edges of roof area – 2 times 20 lbs = 40 lbs per square foot
- Corners of roof area – 3 times 20 lbs = 60 lbs per square foot
Obviously, 6 lbs per square foot will not hold the roof system on the building – the risk of departure is a very real. There is in fact, no way of being able to verify the uplift resistance with raft paper and adhered insulation – either asphalt or adhesive.
A further very important consideration – the quality of the labour installing the kraft paper and insulation with asphalt or adhesive – a poor quality contractor will invariably perform very poorly when adhering the kraft paper and insulation.
- Mechanically fastened – attach the insulation with or without the kraft paper with screws and large plate washers to the steel deck – the number of fasteners can be increased in the edges and corners to account for the increases in wind uplift forces. Fasteners can be counted from below – so verification of attachment is possible and relatively easy.
Factory Mutual (FM) is a large U.S. insurance operating on global basis – in 1983, FM had grown tired of writing big cheques for losses due to wind blow-off of roof assemblies – those assemblies were loose laid, adhered (poorly) with asphalt or adhered (poorly) with cold adhesive – the wind blow-off losses totaled hundreds of millions of dollars – so this was no small problem.
FM declared that all roof systems had to be mechanically fastened in conformance with a very strict set of requirements – the FM Bulletins were very clear on the requirements for fasteners and all aspects of the roof system.
In addition, components were not recognized as an Approved system – a roof system specifier could not use one type of insulation with another type of membrane and various other pieces. FM Approved roof system had to be tested as a complete system with all of the required components – no substitutions were required to an Approved system. An Approved system was assigned an Approval
number and then that system was quite assured of success when installed.
The volume of wind blow-offs dropped dramatically to virtually zero. FM roof system design requirements are the most stringent, they work and they are an excellent design standard.
- Self-adhered vapour barriers and Urethane foam adhesives are now a very recognized combination for attachment of a roof system to a building. The steel roof deck is primed – a visible and verifiable process – the primer is not spot applied, or sprinkled – every top flange of the steel is coated with a roller application of primer. The self-adhesive vapour is applied in a continuous manner to the primed steel deck. The surface of the vapour retarder is rolled to ensure complete adhesion – after this application process, the vapour barrier is fully adhered and will provide wind uplift resistance in the 100 lbs per square foot range.
The insulation boards are adhered in a urethane foam adhesive, that has exceptional adhesion to virtually all substrates – and adheres tenaciously to the surface of the fully adhered vapour barrier. The urethane foam rises to grab onto the insulation board and provide secure adhesion that will conform to the substrate.
Note: cold adhesives or asphalt do not rise – they are thin film adhesive that do not make continuous or assured contact with the insulation board placed over the adhesive or asphalt – in fact, the insulation may bridge over the asphalt or adhesive and never make contact negating any possibility of adhesion.
The combination of fully adhered, self-adhered, vapour barrier and urethane foam adhesives to secure the insulation boards to the vapour barrier substrate is recognized by Factory Mutual and approved assemblies are numerous.
The application of the urethane foam is metered by well designed dispensing equipment and the amount of urethane adhesive can be increased at the edges and corners to conform to wind uplift resistance requirements.
This is a very different, sophisticated process and so very different than the adhesive drips off the corn broom or the hole in the pail.
A Roof System For An Important Building
The existing roof system on the roof areas at XXXX is a four ply or layers of organic felt laid up shingle style, over as reported, 2 inches of rigid fiberglass insulation – probably over a kraft paper vapour retarder on a Type B steel deck. The surfacing on the membrane is a floodcoat of asphalt with embedded gravel surfacing.
There are areas of roof system at XXXX that are in poor condition – hence the need for roof replacement.
The typical course of deterioration and mode of failure for this type of organic felt roof system is weathering away of the top floodcoat of asphalt, exposure of the organic or paper felts to moisture, saturation, freeze-thaw cycling and the eventual rotting of the paper reinforcement.
The rotting and deterioration of the reinforcement results in a loss of strength of the membrane and ultimately the waterproofing starts to exhibit splitting, blistering and membrane defects that result in leakage.
Once the membrane has lost strength and leakage is occurring – the insulation will retain moisture, lose R value, the steel deck can rust and the only solution is replacement of the roof system.
The Question, of course, is replace the roof system with what???
Information On Roofing Asphalt
The asphalt fraction of crude oil is called straight run asphalt as it is distilled or moved from the fractionating columns at the refinery. The softening pint of this raw asphalt is about 125oF – too low to be used for roof systems – if used with a softening pint in this range – the roof system would be a gooey mess for much of the year.
For asphalt to be useful for roofing, the softening point has to be in the 180 to 200oF range. In order to increase the softening point of the asphalt – it is necessary to take advantage of the physical attributes of asphalt – the primary attribute is the fact that as asphalt ages, the softening point increases as the various intrinsic oils that help to maintain flexibility and water resistance are degraded, boiled off or emulsified.
The softening point increase process is termed to be “blowing the asphalt” – oxygen is percolated up through a vertical tank of warmed asphalt – as the oxygen reacts with the components of the asphalt and
over a time 20 plus hours, the asphalt is pre-aged and the softening point is increased dramatically. There are three common types of asphalt based on softening point: type I softening point of about 180oF, type II softening point of about 200oF and type III about 220oF.
Note: the blown asphalt is pre-aged – some or much of the service life and qualities that are suitable for roof systems is in effect boiled off. The increase in softening point is necessary to make the asphalt useful for roof systems – but it important to use the asphalt that is the least pre-aged for the roof system design.
Type I asphalt is softer with longer service life but for most roof systems of the type in discussion – it is too soft and will flow in the heat. A typical roof system in our climate will approach about 180oF in summer temperatures.
Type III asphalt is very hard, almost brittle – the service life has been significantly shortened – but a softening pint of about 220oF is too high for our climate.
Type II asphalt retains significantly more service life and is very usable in our climate – there is no reason to use type III for a roof system – the maximum service available is required.
“It is always better to design a roof than to pick one” – the Manufacturers typically devise the roof system that is the best bet for all areas, name the system, put it in a catalogue and let the salespersons sell that system by picking it out of the catalogue.
What About Reinforcement of Roof Systems?
The various reinforcing fabrics come if different weights – from very light and flimsy to heavy and strong. Base sheets range from very light.
A good quality, strong base sheet for a roof system should be minimum of 180 gms total reinforcement and the coating should be rubberized asphalt. Rubberized asphalt is not pre-aged – the softening point of the straight run, virgin asphalt is increased by adding rubber and other ingredients to the asphalt, thus maintaining the flexibility and longer service life of the asphalt.
Note: Oxidized asphalt and rubberized asphalt are not compatible – the interface between the two materials can react badly leaving an inconsistent, poor waterproofing compound. So, while the attempt to introduce a better quality material was a noble attempt – the design of the roof system with non-compatible materials is a failure.
Intermediate and Cap Plies
Good quality, strong intermediate and cap sheets for a roof system should be minimum of 180 grams total reinforcement and the coating should be rubberized asphalt. Rubberized asphalt is not pre-aged – the softening point of the straight run, virgin asphalt is increased by adding rubber and other ingredients to the asphalt, thus maintaining the flexibility and longer service life of the asphalt.
The XXXX building requires a new roof system that meets all of the essential needs of the building, with the required service life and the ability to reliably stay
attached to the building. All of the components should function, be compatible and be included in a good design.
And finally, high quality labour must install the new roof system. The introduction of low quality labour in an attempt to get a low ball price – so that the “sale” can be made is a very poor approach to keeping water out of a sophisticated facility.
Some Additional Information Regarding Rubberized Asphalt
- Tremco – in the early 1990s Tremco commissioned a research study on rubberized asphalt and additionally, conducted in house research on the performance of rubberized asphalts.
The research study was conducted at the University of Western Ontario at Division called Surface Science Western. Some of the findings of that research study and the other Tremco research included:
- Rubberized asphalts are vastly superior to pre-aged, oxidized roofing asphalts in terms of longevity of surface life – the rubberized asphalts essentially do not degrade even after the equivalent of 40 years’ weathering cycles.
- In addition, the rubberized asphalts present absolutely superior low temperature flexibility – flexible to -20 C. and lower. Regular asphalt turns brittle and glass like at about +50 F (about 12 C.)
- Rubberized asphalts are not compatible with oxidized asphalts – the rubberized asphalts contain significant quantities of oils and substances that migrate into the relatively “drier” oxidized asphalt effectively replacing some of the components that have been “boiled” off during the pre-aging process – the result is a very much softened oxidized asphalt that does not have the stability of rubberized asphalt. The interface of the two materials is not stable and can perform poorly as a waterproofing material.
The inter-ply moppings of a multi-ply roof system actually age to a significant degree – by heat aging, oil migration and other processes – this was a surprise – it was expected that because the inter-ply moppings were not exposed to the ambient conditions and ultraviolet – aging would not occur.
