January 23, 2017

Vented High Performance Standing Seam Metal Roof

SOLITEX UM Project Spotlight in Waltham MA

A metal roof and a vented underlayment with SOLITEX UM go hand in hand

SOLITEX UM from Pro Clima is  a 4-layer, vapor open and waterproof membrane with integrated 3-D mesh.  Like other SOLITEX membranes, it has an actively vapor open, monolithic layer of TEEE film that is extremely waterproof (see The SOLITEX MENTO Difference)– and outperforms vapor closed underlayments both in outward drying potential as well as ease of application. With the addition of a sturdy 3/8″ high geotextile mesh, SOLITEX UM becomes an all-in-one rainscreen – and a perfect underlayment for metal roofs. An added benefit of the mesh is acoustical dampening of rain and hail noise.

In a previous post, Project Spotlight: Lincoln, VT Shows Off SOLITEX UM, we showed how UM’s integrated membrane and mesh goes up easily on walls – a time- and cost-saver under cedar shakes, vertical cladding and other situations where strapping might not be practical or cost-effective.

p_solitex_um_connect_ret_15x10cm_cmykSOLITEX is also a high performance waterproof “sarking membrane” designed for the much more demanding conditions at the roof. Unlike micro-porous housewraps, SOLITEX provides reliable outward drying while keeping the roof protected from the weather on roof pitches 3:12 or higher. (For pitches below 3:12, Weldano provides an even more robust permeable underlayment).

In this post, we show how SOLITEX UM goes on a pitched metal roof – providing superior weather protection and vented performance. Aurora Custom Builders, led by architect and Passive House certified builder Nathaniel May, is a Metro Boston residential design/build company with more than 20 years of experience integrating new technologies. We feature Nat’s own home retrofit that includes many of 475’s high performance enclosure products from Proclima, as well as our Lunos e2 and eGO ductless heat recovery ventilation systems. To turn the existing one-story bungalow into an efficient and comfortable two-story home for his family of four, he removed the old roof, added a second floor with a new scissor truss roof, and is upgrading the entire enclosure guided by Passive House performance metrics.

A Vented Roof that Goes Up Fast

Mokema1a

Project includes a new roof with SOLITEX UM, walls with SOLITEX over mineral wool, and robust interior airtightness and vapor control with INTELLO Plus smart vapor retarder

A plywood sub-roof over a super-insulated enclosure can be risky. To keep moisture levels within safe limits, airtight and smart vapor retarding INTELLO Plus is specified on the warm side of the enclosure. But a vented roof is always best practice in roofs that are insulated with dense-pack cellulose or other fibrous insulation. Hence the desire for a vented rainscreen above the plywood to optimize outward drying. (Also see this recent “belt & suspenders” detail for a sheathed roof). Metal roofs that skip the venting risk not only a wetter sub-roof but also faster degradation of the metal by anaerobic corrosion from below.

On this roof installation (as on much of his project), the owner did much of the work himself in order to learn about the new high performance products. In fact, installing this vented underlayment is straighforward enough for first time installers. The key goal is keeping the underlayment watertight. If a separate mesh product is added on, sequentially, after an underlayment, it’s pretty much impossible to seal all the fastener/staple holes. With SOLITEX UM, the mesh is already “welded” in place right on the roll for a watertight product right out of the box. The job of the installer is to make sure that the fastening points are protected under shiplaps.

Here’s a condensed version of the SOLITEX UM instructions:

All-in-one: Rainscreen mesh pre-attached to monolithic membrane makes for a watertight metal roof underlayment in one step.

  • Rolls are 59.5″ (1.50m) wide and 82.’6″ (25m) long. After preparing the sheathing surface to be clean and free of fasteners and splinters that could damage the membrane, unroll horizontally and cut to width.
  • Line up membrane to bottom of roof, and use markings 59″ from edge to make the top and bottom parallel.
  • Stretch the membrane taut to remove wrinkles in both directions during application.
  • Fold out mesh-free flap at top, and fasten with galvanized T50 staples (5/16″ legs min) every 4″-6″ along the top of the membrane. ONLY fasten in the area that will be covered by the shiplap – ie above the “connect” zone – for best protection against leaks.
  • Roll out the next layer and overlap the mesh-free zone, using the mesh as a guide for correct alignment.
  • After assuring the materials are dry and free of dust, silicones and grease, “connect” the overlap, by removing release paper from the butyl adhesive strip, and pressing down firmly. Make sure to pressurize the entire joint and verify that it is free of tension and creases. Note: Butyl “connect” strips must be installed above 40F.
  • At ridge, fold membrane over ridge onto other pitch, then “connect” with adhesive strip. (If necessary, trim membrane/mesh and release 4” (10cm) of 3d mesh from lower membrane and tape with TESCON Vana, and use PRESSFIX to pressurize tape properly and easily.)
  • At roof edges and vertical butt joints, peel back mesh, tape with TESCON Vana and pressurize with PRESSFIX.
  • At valleys, first install a continous layer of SOLITEX MENTO – before shiplapping and taping SOLITEX UM over it.

Added Bonus: Temporary Roofing

SOLITEX-MENTO-active-vapor-open-TEEE-membrane

Left: SOLITEX is actively vapor open, preventing bulk water movement through the non-porous TEEE membrane. Right: Microscopic image of monolithic TEEE membrane

SOLITEX UM is very waterproof – resisting 8 feet of water column – so with the right detailing it will serve not only as a secondary waterproof under-layer, but also as a temporary waterproof roof for any unanticipated storms. As it happened, Nat’s roof schedule hit some bumps in the road, and he will attest to the fact that the UM kept his project dry over several months. (SOLITEX UM is rated for 3 months UV exposure).

A word of caution: unlike many roof underlayments, SOLITEX is not an asphaltic conconction designed to self-seal around penetrations. Nevertheless, it’s very resilient, with protective fleece layers on either side of the active waterproof  layer. The  mesh provides an additional buffer against hard boots.  To be on the safe side, tread lightly and be vigilant about taping over holes outside the shiplaps. If you follow these steps, your project will be protected until the metal is ready to go on. Do watch out for high wind events and take additional measures (temp strapping) to secure SOLITEX UM on roof.

Venting Details Are Essential

A key part of vented rainscreens – you guessed it – is venting. For a vented roof rainscreen, you need airflow entering at the eave and exiting at the ridge. It also helps to have unimpeded airflow in between – fortunately not a problem on this simple gable roof.

If this were a roof with wood strapping, it would be easy to add a 3/4″ Cor-A-Vent strip vent or similar between the strapping to allow air in at the soffit. For this roof, Nat instead placed a narrower 3/8″ strip vent vertically along the soffit trim board. This helped him avoid a messier install on or around the mesh, while also avoiding any holes in the roof plane.

 

Left: Vent strip attached over the vertical soffit board. Right: Roofing drip edge covers vent strip, nailed through mesh and awaiting standing seam

Ridge Vent

At the ridge, getting it vented and watertight is pretty straightforward

Sealing Clips with double sided TESCON NAIDECK Butyl Tape

ClipThe final detail for a watertight metal roof installation is sealing the roof clips. For this roof, over 600 clips were used. Each pair of screws (left) was sealed at to the  membrane with TESCON Naideck double-sided butyl tape. The butyl rubber in this tape is fluid and will penetrate into the spunbound structure of the SOLITEX underlayment below and permanently seal the screw (or nail) penetrations. To install, apply TESCON Naideck to the back of the clip – remove the releasepaper and screw into the roof, right over the mesh.

 

 

 

 

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