Know Your Low Slope Roof

It’s important to complete a thorough roof evaluation prior to your project installation. While many roofs look the same from the surface, low slope roofs can vary considerably in their physical properties. It is important to have 100% confidence in the roof composition, attachment method and waterproofing system. If there is a roofer of record, have them install the roof attachments to preserve the roofing warranty. If you cannot contract with the roofer of record, find a roofer who is qualified for the specific type of roof and building you are dealing with. Some roofs will require drilling test holes to analyze the physical properties of the existing layers. This will determine not only the exact underlying structure you are attaching to, but also whether modifying is even possible in the first place. It is very important to inform both the owner of the building and the owner of the solar system (who may be different parties) about the problems and solutions that are roofing related and those that are solar related.

Low Slope Roof Construction Methods

Low slope roof construction methods vary significantly from the decking to insulation to the roof covering. Careful evaluation prior to project quotation is imperative. Common decking materials include plywood or corrugated steel decking. Rafters and purlins may be constructed of wood or steel. Insulation is common and varies in thicknesses and is often tapered to facilitate drainage pathways. These pathways should be preserved to help the roof dry quickly after a rain event. Rigid cover boards over insulation are desirable to avoid insulation compression, especially when ballasted mounting systems are used.

We recommend boring through the insulation and mounting the Quick Mount QBase Low Slope Mount to the deck below the insulation. Typically a structural engineer would evaluate point loads from wind and snow and determine the mount spacing and resulting point loading. It is advisable to connect directly to the wood truss or rafter, but metal deck applications often allow securing directly to the deck.

For concrete decks that use post-tension slab construction it is necessary to perform an x-ray scan of the roof to identify and mark cable locations in the effort to avoid driving a fastener through a support cable. However, if the concrete deck is not post-tension slab, you can position the QBase Low Slope Mount anywhere on the roof plane. Ideally, the engineer of record for the building defines the location spacing of the mounts in conjunction with the racking system designer.

Choosing the Right Flashing

The roofer of record should choose the flashings to insure the warranty is preserved. Single ply membrane roofs (TPO, PVC, EPDM) generally require using flashing boots supplied by the roof membrane manufacturer, or an approved third party flashing boot manufacturer. Single ply membrane boots are either heat welded or chemically adhered. These processes are highly refined and cannot be performed by solar installers. Using a qualified roofer is imperative to preserving the warranty. A built-up roof (BUR) is composed of alternating layers of bitumen and reinforcing fabric and topped off with a layer of aggregate for UV resistance. These roofs range from traditional hot mopped tar and gravel roofs to more sophisticated polymer-modified bitumen membrane cap sheets. Flashings for built-up roofing are typically of the metal cone variety. These are either installed with a new roof, or torched down with tar and reinforcing materials and often finished off with a capsheet cover.

Choosing the proper flashing for any given membrane is critically important, so be sure the roofer of record on the job selects and applies the correct flashing for the job. Quick Mount PV does not sell membrane flashings since TPO, PVC and EPDM manufacturers require you purchase the flashing directly from them or their approved third party supplier. Please call us if you have any questions or uncertainty about membrane roof flashings. For built-up roofs, Quick Mount PV sells aluminum 17"x17" cone flashing in 4-inch and 8-inch height. These flashings are sold separately from the QBase Low Slope Mount.

Choosing the Right Mount

The QBase Low Slope Mount is available in three standard post lengths: 7-inch, 9-inch, and 12-inch. These are intended to address the most common insulation thicknesses and flashing heights. We can make longer posts, but a qualified structural engineer needs to review any project using posts over 12 inches tall. Flashings should be taller than the secondary overflow drain to ensure protection if the roof floods.

Sealants

Any sealant should be validated for compatibility with the roofing membrane, insulation, and EPDM seals used to counterflash the standoff to the cone flashing. Most roofing manufacturers list a recommended, approved sealant in their specifications. In the freeze-thaw zones, it is important to follow the manufacturer’s rules for freeze-thaw conditions. Use the properly rated sealant for each specific application and condition.

Mounting Hardware Contents

Each box includes all necessary mounting hardware, standoff posts and bases, sealing washers, and printed instructions. Due to the many different low slope membrane roof types, our mounting kits do not include flashing.