Below are some frequently asked questions, the answers are the opinions of the directors of Scie Construction Ltd based on 40 years experience in the trade and are not necessarily the opinions of any of our supplying manufacturers.
Q: What are low slope roofs?
A: Roofs that have slopes of 4:12 or less are considered to be low slope roofs. (4:12 means a vertical rise of 4 inches for every 12 inch horizontal run, or 18.4°). Never apply asphalt shingles to slopes that are below 2:12 (9.5°). Shingles applied on low slope slopes do not last as long as shingles on steeper roof pitches, due to the increased exposure to sunlight and other weather conditions. Generally, laminated/architectural shingles are better suited to steep roofs, and do not offer aesthetic benefits when applied on low slopes.
Q. While handling a sample of Mineral Torchon, some chips fall off, will this happen when the roof is on?
A. No, handling ( bending, twisting) a small sample is totally different than when the sheet is laid on a stable substrate, During laying, a few chips will be scuffed loose by the applicators foot traffic, but during the 20+ year life cycle of a quality membrane only 1% chip will be lost and loss will be so uniform that it would not be noticed. The latest manufacturing machines have extra rollers to level out the chips as they are applied to the hot sheet coating as it comes through the line and lately our on site applicators are now requesting bags of matching loose chips, as they are unable to sweep up enough loose chips on completion to do touch up work.
Q. In the summer it gets very hot at our property, do temperatures above 30oC affect a Torchon membrane’s performance?
A. As Torchon membranes are thermoplastic, i.e. they soften with heat and harden with cold, the choice of membrane for your area is important. There are dozens of membrane types available to suit from -20oC up to +50oC. As NZ is a temperate climate without real extremes of temperature almost all APP or SBS modified Torchons will provide excellent performance. Mineral surfaced membranes provide the best protection against UV.
Q. Do Torchon Bitumen membranes make the roof structure “sweat”?
A. On residential flat roofs on plywood substrates, the use of a perforated vent sheet is advised, to allow diffusion of internal moisture out, through roof mounted mushroom breather vents, particularly near or over kitchens, bathrooms, laundry etc.
Even the black plain Torchon membranes fade over time to a Grey colour and this increases the ability to reflect heat.
Mineral surfaced membranes have a larger surface area, due to the angles of the chips, and help with heat reflection and UV resistance.
Q. Why do some Torchon membranes wrinkle at the line of the plywood joints?
A. This is more likely to occur to fully bonded membranes with APP modification. SBS membranes, which have a high degree of “memory”, are less likely to show this wrinkling or ridging even if fully bonded. Spot bonding or using an un-bonded but mechanically fixed underlay or first layer eliminates this problem.
Q. If we use a Torchon membrane on the roof , what is the risk of catching the house on fire while it is being done?
A. On new timber framed construction, the plywood roof deck substrate and the dwangs which may be used to support the upstands are primed with a bitumen primer. As well as aiding the adhesion of the Torchon membrane to the substrate, the primer acts as a fire retardant when dry, and stops scorching of the timber surface.
The Torchon membrane should be applied before the building paper or building wrap is fixed to the walls as these are quite flammable.
Our company uses different sized nozzles for the flame torches or maybe hot air guns where a tight corner or difficult up stand creates a fire hazard.
It is all about keeping the work area clean of saw dust, dirt and debris, and only allowing experienced applicators to lay the material. Fire extinguishers are always on the roof area as an Insurance requirement.
On re roofing work an underlay must be mechanically fixed first and/or self adhesive membrane underlays can be used at upstands to reduce the fire risks.
Q. How long will a Torchon membrane roof last?
A. A good quality, exposed, Mineral surfaced polyester reinforced Torchon membrane will last at least 20 years in NZ.
Uncoated sanded or Talc finished APP Torchon membranes will break down faster than those with a painted finish or those with a mineral finish.
Q. Why should we use 2 layers when 1 would do?
A. Its all about dimensional stability over the plywood joints. On average plywood will expand and contract up to 4mm during each 24-hour period. A 2 layer roof with say a 2.5mm underlay and a 4mm cap sheet forms a 6.5mm thick membrane, which is bigger dimensionally than the gap between the plywood sheets and is less likely to buckle/ripple/ ridge at the joints due to movement.
Also with 2 layers if there is a failure of a joint on the top layer there is less chance of a leak through to the underside of the roof structure as there is a second line of defence, the joints of each layer are 500mm away from the joints in the layer above.
Q. Why are there black lines of bitumen at the edge of the joints?
A. Called “ bleed out” this is a good sign that the membrane has been welded together correctly at the overlapping joint.
A 3 – 5mm bleed out is normal and some manufacturers even require this bleed out to be visible and consistent throughout the roof area before a Guarantee is issued. Sprinkling the hot bleed out with loose chips during application or by reheating on completion can easily hide the black lines if required.
Welding the laps with hot air guns enables the joints to be lapped together with less of a bleed out 1-2mm, which gives a neater appearance.
Q. Should my bitumen surfaced roof be painted to protect from UV attack?
A. If the membrane does not have a mineral chip top surface, especially SBS modified membranes, the answer is yes. Some APP membranes finished with a sanded or talc surface can be left exposed to the elements without major breakdown for approx 5-10 years. Then the decision of whether to paint or overlay needs to be made.
Oxidised bitumen roof membranes require either a painted finish, or a layer of gravel or chips for protection.
Once a bitumen roof is painted, there are difficulties thereafter of obtaining a good bond between the original roof membrane and any new layer of the same type of material being applied over it, or if repairs are required.
Bituminous Aluminium Paint provides the best reflective qualities and bonds very well to most bitumen surfaces, however the only product which will bond to a roof membrane painted with Bituminous Aluminium Paint is Bituminous Aluminium Paint!. Once it is on you are stuck with that finish.
Repairs become expensive as the coating has to be removed to obtain a bond to the bitumen underneath.
If the roof is to be overlayed with a new membrane, the choices are, to burn and scrape off the Bituminous Aluminium Paint, or lay an isolating underlay mechanically fixed through the old roof membrane, or, remove the old membrane down to the substrate and start again.
Q. Can the PVC Deck membranes be laid over existing rubber or bitumen deck membranes?
A. No, not without a seperating layer of plywood or cement sheet mechanically fixed over the existing. Rubber and Bitumen are not compatible with PVC and the adhesives used for PVC will not bond to rubber or bitumen. The thermoplastic properties of the 3 membranes mentioned are totally different and even if they could be bonded together, there would be different amounts of expansion and contraction between the two, causing wrinkling, bubbling and delamination.
If the existing substrate under a rubber membrane meets the criteria for a substrate for PVC membranes, then it is sometimes possible to remove the membrane and sand off the residue adhesive from the substrate and lay the PVC to the prepared surface.
The same applies to laying rubber over bitumen or bitumen over rubber .back to list
Q. Does a longer warranty mean a better product?
A. Since it is probable that defects, should any be present, will appear during the first three to five years of the life of the roof, a longer warranty does not necessarily mean as much as it would appear to. An applicable warranty term for any product, is based on many factors, including price, composition, regional usage recommendations, etc
Q. What is a drip edge and how is it applied?
A. Drip edges are used for watershedding at the eaves and rakes and for preventing wood materials from rotting. It is important that the drip edge is made of a corrosive-resistant material that extends approximately three inches (75mm) back from the roof edges and bends downward over them.
The drip edge should be applied beneath the underlayment or eave protection along the eaves and over the underlayment on the rakes back to list
Q. How are asphalt shingles made?
A. Shingles are made in a continuous web process. Large rolls of felt are fed into a dry looper, which serves as an accumulator. The felt then goes to the saturator tank. In the saturator tank, the felt is impregnated with saturant asphalt. From the saturator tank, the felt moves to the wet looper, where the saturant is drawn into the felt as it cools. This allows the felt to attain a high degree of saturation and dries the surface of the sheet. The saturated organic felt or the glass mat (glass mat shingles do not require the saturation process) moves to the coater. At the coater, coating (asphalt with air blown through it) is applied to the top and bottom surfaces of the sheet. Mineral stabilizers are added to the coating which improve the shingle’s fire resistance and weatherability. Next, granules are applied to the top surface of coating. Granules are ceramically colored crushed rock; the granules give the shingle its color, but more importantly protect the coating from ultraviolet light. Backsurfacing is then applied to the sheet to prevent it from sticking to the machine and to other shingles when packaged. The release tape is also applied to the back of the sheet to prevent the sealant buttons from sticking to the next shingle in the package. The granules are then pressed into the topcoating. Once the sheet is cooled, sealant buttons are applied. The sealant buttons allow one shingle to bond to the overlying shingle on a roof, to prevent wind uplift. The roofing sheet is then measured and cut into shingles. At this stage, the two pieces of laminated shingles are adhered together. The shingles are wrapped into bundles and stored in the warehouse until they are ready to be shipped to the appropriate location. back to list
Q. What is the algae (or fungus) found on roofs?
A. In certain moist areas, algae can grow on mineral surfaced flat roofing and asphalt shingles. Although the algae has no proven effect on membrane or shingle life, it does stain or discolor the surface. Commonly (and usually incorrectly) called fungus, this algae staining can be unattractive. The algae-containing stains can be dramatically reduced by the use of special copper granules.
Copper-containing granules are mixed with colored granules during the manufacturing process. The effect is to produce an environmentally safe cuprous oxide wash which is dispersed by rain or other moisture. The wash inhibits growth of algae and the resulting stains. back to list
Q. Is fungus the same as moss?
A. Moss is not fungus. Moss is the green spongy stuff that grows on the south side of trees and on the ground in shaded, damp areas. And, in some areas it also grows on roof membranes and shingles.
Mosses reproduce via airborne spores. If a roof is covered with moist organic matter or soil, and if there are minerals and fixed nitrogen present in the dirt on the roof, mosses can grow from the spores that are carried there. It is obvious that if there is no dirt on the shingles, moss cannot take root. But, even when dirt is present, it is possible that the copper used in most fungus-resistant shingles today will prevent moss development in its early stages back to list
Q. How do I get rid of the algae growth on my roof?
A. There are several ways to reduce the discoloration:
* For a new roof, install a zinc or galvanized type metal near the ridge of the roof. As the metal ions are oxidized and erode off of the metal strip, they wash down the roof inhibiting cellular algae growth.
* A dilute solution of chlorine bleach, trisodium phosphate and water can be applied – one part chlorine bleach to three parts water with a quarter cup of trisodium phosphate. Note: Trisodium phosphate should be available at any paint supply store. Gently spray the solution on the roof membrane or asphalt shingles. For stains that are hard to remove, scrub mildly. Scrubbing too harshly will remove granules. Rinse the shingles thoroughly with water. In the past, this has been a temporary solution and usually needs to be repeated every couple of years. Apply this solution carefully to avoid damaging other parts of the building or the shrubbery below and wear rubber gloves and protective glasses.
* Due to the increase in algae discolored roofs, asphalt shingles are now available with small quantities of zinc or copper granules embedded in the mineral surfaced granule coating. These particles inhibit the algae growth through some of the life of the asphalt roof.
Q. Re-roofing? What to can we expect during the process?.
A. In preparation for the roofing process, following are some items to consider;
Once you have approved the proposal and price for your re roofing project, and the terms and conditions form (contract) has been signed and returned, one of our Directors will contact you to arrange a start date, and will be the one you need to talk to regarding any concerns or questions you may have. They are highly skilled and qualified in every aspect of roofing. Our Supervisor/Tradesperson undertaking the roofing work will introduce themselves the first day on the job, and give you a brief description of what we will be doing, and arrange any facilities that may be necessary to carry out the work, e.g. access to power supply, moving vehicles or garden furniture for access to the roof by ladder etc . If you are at work and no one is at home during the day, we will ask you for a contact phone number, is case there are any unexpected problems, e.g. finding rotten substrate that was not expected. We will explain the extent of work required and any extra costs that may be involved, for your approval, prior to undertaking any repair which was not in the original contract. We will normally digitally photograph such repair work if you are unable to inspect it yourself at the time.
When your old roof is being torn off, we will be placing a rubbish skip, or rubbish trailer as close to your home as possible to minimize debris falling in your yard. We may also have several company vehicles near your home, we will do our best to keep your access open to your driveway. This may mean that we will have to park one or more trucks in front of your neighbors home. If you are concerned that your neighbors will feel inconvenienced, you may want to notify them of the work being done so they are prepared.
During the roofing process, as with any construction project, there will be noise inside the house and out, that you are not accustomed to. We may be using electric and pneumatic powered tools, along with some hand tools.
While work is in progress, we will be loading and moving material, and other operations that will cause vibrations to the interior walls and ceiling of your home. We are very careful and respectful of your property, but total elimination of vibrations is impossible. If you feel that this vibration would cause any disturbance of pictures, or light fixtures such as ceiling fans or chandeliers, you should remove those items from the walls / ceiling to prevent damage.
There will be some debris from any construction project, most debris comes from a tear off. We try very hard to make sure that all debris is removed from the area the day we tear off, and again when we are finished with the project. We ask that you take precautions while we are there and stay clear of the debris until we have had a chance to remove it. Once we have left, we recommend you inspect your yard for any small nails or wood prior to mowing.
As mentioned before, when we tear off an old roof, some debris may fall to the ground, this could include flower beds, shrubs, bushes, if close to your house. We will make every attempt to protect the landscaping you have worked so hard on. We ask that you assist us in this process, by informing us of any particularly delicate items, and suggest or put in place the adequate protection.