Nu-lok Design Overview

The Nu-lok fastening system consists of Galvalume battens laid horizontally across a pitched roof, fastened through 1” x 2” counter battens or 3/8-inch rubber shims into a plywood deck. A conventional waterproof membrane such as roofing felt or other proprietary product is used between the plywood deck and the battens. Fasteners are specified as galvanized ring-shank nails into the roof rafters.Battens are installed at 12-inch spacing, with care taken to insure exact spacing and parallel runs.

With battens nailed down, and starting at any row on the roof, Galvalume link channels are positioned at 16-inch centers and locked into the upward-facing flange on the battens. Natural or ceramic slates are then placed into the 316 stainless-steel retaining clip on each link channel to complete a horizontal course. Another course is then started, working up the roof, by locking the next row of link channels into place.

The link channel eliminates the need for horizontal overlap between slates, as each link channel spans the horizontal gap between the two slates it supports, catching water seepage and conducting it onto the next course of slate below. In essence, each link channel contains a 3/4-inch wide, 5/32-inch deep miniature gutter.

The system uses a four-inch vertical overlap and no horizontal overlap with 16-inch slate, for a 75% exposure ratio. Exposure ratio is the amount of slate “showing” on the finished roof divided by the amount of slate required by the fastening system. Traditional nailed-in-place slate has an exposure ratio of 40%, meaning that 2.5 square feet of slate are needed for every one square foot of roof area to be covered. Nu-lok requires only 1.3 square feet of slate per square foot of coverage. The Nu-lok fastening system allows for very efficient use of relatively expensive slate surface materials, which reduces installed weight to less than six pounds per square foot.

The counter batten or shim under the batten creates a space between the waterproof membrane and the batten, which allows drainage of condensation and seepage, if any, down the roof into the main roof gutters. The height of batten and link channel adds another one inch to the airspace between the decking and the underside of the slate. Excellent ventilation of this space is observed; with upwards flow of hot humid air driven by natural convection, facilitated by the approximately 1/8th-inch vertical gap between each course of slate.

The slate colors generally preferred by homeowners are dark with a non-reflective finish, which inevitably attracts and holds solar heat. Studies show that daytime surface temperatures can reach 200 degrees Fahrenheit. The ventilated airspace between the slate and the roof reduces heat transfer to the waterproof membrane, which helps to extend the life of both the plywood deck and the waterproof membrane.

For ventilation of attic spaces through the plywood deck, O’Hagin’s, www.ohaginvent.com has designed a series of ridge vents for use with the Nu-lok system.

An important fundamental advantage of the Nu-lok suspension system is that it allows either natural or ceramic slate to be fastened without nails or screws. A rigid material such as slate is strongest if suspended in a fastening system slightly more flexible than the slate itself. This reduces stress concentration under point loading. When traditionally installed, the most common reason a slate breaks when walked on is stress concentration at a hard point created by the fastening system. The hard point could be contact with a high point on the slate below, or stress concentration at a nail. Nu-lok supports each slate in a frame composed of a link channel on either side, stainless steel clips below, locked in place by the course of slate above. Spot loading is evenly distributed to both sides of each slate.

Experience demonstrates that installers, homeowners, service contractors and inspectors can walk on a Nu-lok roof with no concern of slate breakage, either natural or ceramic. We recommend slate of no less than 1/4th of an inch in thickness from our preferred supplier, Greenstone Slate in Poultney, Vermont, www.greenstoneslate.com. Nu-lok ceramic slate is a standard 5/16th of an inch in thickness. Every Nu-lok roof is walkable without breakage.
A less obvious feature is that the stainless steel clip can be swung sideways allowing individual slates to be removed and replaced from below without disturbing the course above, below or on either side. This allows inspection at any time of the waterproof membrane, installation of vents or other roof penetrations, and replacement of individual slates if any are damaged. This feature also allows the roof to be laid starting from a middle course of slate and working up to the ridge, then completed from the gutter working back up to the first course laid. This installation sequence may be desirable for installation safety or due to design specifics of the roof.

Installation Benefits

Nu-lok design minimizes installation time spent on the roof, increasing safety and reducing worker exposure to hazards. Once the battens are laid in evenly spaced parallel courses, the speed of installation over open roof spans is remarkable. Correctly installing the battens is important and must be well supervised, but is not difficult with a spacing jig.

Installation cost increases with the complexity of the roof, and skilled supervision is required to accomplish details such as closed valleys or interior drains. Purpose-specified components such as valley clips batten shims, fascia flashings, shims and ridge vents; make detail work somewhat faster than for traditional nailed-in-place slate. The overall level of installation complexity is generally less difficult for Nu-lok than for traditional slate installation. Nu-lok ceramic slate can be cut on the roof with a conventional tile cutter, the same type as is used with floor tiles.

We hope this overview addresses most of your questions about the system. However, we are always ready to discuss the design and address any questions you may have. Please feel free to contact us.