Question: I am adding a screened room to my guest cottage at a 1.5/12 slope near Winnipeg Beach. The size is eight feet by 20 feet. Would a metal roof be an option for me? Or do you have any other roofing material suggestions?
Any product would have to meet code, as we are in the Red River Planning District’s jurisdiction. Please let me know.
— Randy McMahon
Answer: Choosing materials for a new roofing installation, or upgrade, has become more difficult in recent years with more options becoming available and cost-effective. Using metal roofing on your low-pitch screen room addition will depend on the specifics of the materials more than local building code requirements.
There are numerous types of metal roofing available for residential and commercial purposes. These may range from typical overlapping styles of corrugated roofing, to interlocking textured and patterned styles. Each of these will have specific methods of installation, many with neoprene ringed fasteners used to secure the roofing to the sheathing. This fastening method of the roofing may be one of the major determining factors on whether it is possible for your project.
Low-slope roofs present one major challenge that may not apply to steeper-pitched roofs. While water almost always drains downward due to gravity, it may periodically run uphill if the right circumstances are present. Strong winds can blow rain and melted snow upwards on a roof, depending on the slope. Steep roofs, above a 6/12 pitch, may not be susceptible to such problems, but lower-slope ones, like your proposed addition, will be a very good candidate for such issues. Compounding that is the problem of wicking of moisture upwards through some roofing material or underlayment, or by capillary action. Any of these phenomenon may cause water to leak through any small gaps, seams, holes or overlaps of some types of metal roofing.
What may cause potential leakage in any form or roofing, especially metal ones, are changes in the material with changing environmental conditions. Bitumen-based roofing materials, commonly known as asphalt, may be the least problematic in this regard due to their flexibility and elasticity. The individual components of this type of roofing are normally bound together with bitumen sealers, which resist coming apart even under extreme changes in temperature. That is why they are the most widely used type in our area. Metal roofs, on the other extreme, are very susceptible to temperature changes and may expand and contract significantly. For this reason, joints and overlaps will be more likely to develop slight gaps that can be a good route for water infiltration. Also, metal-roofing fasteners are more likely to fail, and normally are surface mounted, potentially leaving more openings for leakage. If the slope of the roof is steep enough, these factors may not be much of an issue, but on a relatively flat surface like yours, it could be disastrous.
One type of metal roofing, standing-seam roofing, has several properties that may allow installation on more difficult roof situations. This roofing is normally directly fastened to the roof sheathing only at the bottom, near the eaves. The top of the roofing is held in place by the roof cap, which is secured directly to the sheathing with fasteners that are later covered by the roofing. The individual panels are not overlapped and screwed down, but crimped together at the seams, which rise above the flat-roof deck. That is where the name "standing seam" comes from. Because the individual panels are not directly fastened at the top, expansion and contraction can occur without major stress on the fasteners or the roofing panels, preventing gaps and buckling.
Many people misinterpret the fact that building codes do not specifically address what type of materials can and cannot be constructed on a home, in all situations. They also don’t understand that home inspectors, like myself, are not code specialists, as we do performance-based inspections. It is the municipal building officials who are the authorities in that regard and the ones that should be consulted in relation to what is allowed in your area. While they should easily be able to tell you what type of roofing materials, if any, are not allowed, they may not be able to elaborate on whether the metal roofing you are proposing is possible for use on your low-slope addition. That information may only be available by picking a specific product and consulting the manufacturer’s specifications.
If you plan to install this roofing yourself, you must do extensive research ahead of time to ensure that any metal products are approved for low-slope applications. I would suspect that most metal roofing available to homeowners at building centres would not be usable for your situation. Standing-seam roofing may only be available through commercial application specialists, who can be consulted ahead of time for application restrictions. They may also be able to quote you on application of single-ply membranes, like modified bitumen roofing, which will certainly be more suitable for your low-slope application.
Metal roofing may be an ideal choice for seasonal buildings in harsh environments, like your cottage, but they may not be adaptable to your low-slope application. Contacting the local building officials for requirements is necessary, but only the manufacturers of specific types of roofing may be able to tell you whether their product will work for your low-slope application.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.
trainedeye@iname.com
