Vented rainscreens for walls and roofs are are an important part of high performance construction. In our blog post Vented rainscreen: what a high performance building wants, we argue that a rainscreen is a good idea pretty much across the entire USA (and Canada), for the following reasons:
- It keeps the sun and the majority of rain away from the weather resistant barrier (WRB)
- It provides optimum drying potential of the enclosure when it is cold
- It helps maximize the performance and life expectancy of the waterproofing and exterior air barrier
We like to recommend a “fully strapped” rainscreen, usually consisting of 1x vertical wood battens creating an unobstructed 3/4″ air gap between the weather resistant barrier and the siding. However, the high cost of this approach is too often a barrier to its widespread implementation. This is especially true when builders install cedar shingle cladding, for which “double strapping” is required via a second layer of horizontal strapping for each shingle course.
An alternative approach that has gained traction involves the use of geotextile rainscreen mesh that is applied over the WRB. While often quicker and less expensive to install than strapping, it too requires an extra step between the WRB and cladding – resulting in three trips up the staging or cherry picker.
To the rescue comes SOLITEX UM from Pro Clima – a 4-layer, vapor open, waterproof membrane with integrated 3-D mesh. It’s an excellent vented underlayment for metal roofs and a vented WRB for shingled or sided walls – providing superior weather protection for high performance projects. It can be applied over insulation, plywood, OSB and exterior gypsum board. Like other SOLITEX membranes, it has an actively vapor open, monolithic layer of TEEE film that is extremely waterproof – and outperforms vapor closed underlayments both in outward drying potential as well as ease of application. It used to be blue, as pictured in images from this project but is now a dark grey.
Blue fuzzy stuff on your walls
Oakley Smith of Smith & McClain needed a rainscreen for the walls of a new construction house in Lincoln, VT. Having used some airtight membranes and tapes from 475 in the past, he was intrigued to learn about the new product on the block. By divine intervention, our first SOLITEX UM delivery from Germany was 6 rolls – at 404 SF per roll just enough for his exterior walls. The architect, Selin + Selin Architecture of Shelburne VT, had called out 30# building paper with “Benjamin Obdyke Rain Slicker” [sic] under vertical 1×10 shiplap siding. Eager to avoid double strapping and facing a winter building calendar, Oakley liked the promise of fewer steps along with the highest performance weather protection that the SOLITEX membrane would provide.
As New England product consultant for 475 High Performance Building Supply I like to get my hands dirty helping builders learn about our building products and construction techniques that are new to them. So I arranged to join Oakley on the job site – not knowing just how cold my hands would get too. It was indeed surprisingly frosty for early December – but the clear skies and spectacular view over Mt. Ellen made up for the chill. We got right to work. The plywood sheathing and windows were already taped airtight. All that remained between the plywood and shiplap siding was a continuous application of SOLITEX UM.
When installing housewraps like SOLITEX Mento 1000, we like to roll it out across openings, then cut and fold into the rough openings (before adding EXTOSEAL Encors sill tape and windows). Since SOLITEX UM just goes on the sheathing, it’s not a bad idea to wait until windows are installed before applying. The first piece we cut spanned from one corner to a door opening midway down the wall. At 5′ high, this 20 foot length was easy to move into position. Though manageable enough for one person, the unrolled mesh/membrane laminate was easier to handle and maneuver with four hands. Once aligned and stapled into place, we then cut around windows with a utility knife. The 0.27″ thick mesh also cuts easily with scissors. Cuts don’t have to be too precise, since TESCON Vana tape can cover the gaps.
The second course was installed much like the first, but positioned so it overlapped the mesh-free part of the first course. Then the butyl adhesive strip was activated. No additional cutting or taping was needed at the overlap.
- Staple only under overlaps – the best location is above the butyl adhesive strip.
- Make it watertight and windtight by taping all edges and activating adhesive strips at overlaps. Avoid reverse shiplaps! Keep it shingle style at all times for positive drainage
- Apply above 40F for best adhesion of the butyl adhesive strip. (The temperature during our installation was about 20F, so we stapled through the adhesive strip to help it to bond permanently once the wall warmed. This was confirmed afterward.)
- When used with shingle roofing, the roof should be covered with a waterproof sheet in case of rain. As with any underlayment, it’s imperative that the shingle decking be rain-tight. Condensation of water at the backside of the shingles can dry very easily because of the 8mm back-ventilation and the extremely vapor open SOLITEX (~150 perm).
Note: For this project, airtightness was already assured at the exterior with taped plywood seams (and at the interior with INTELLO Plus membrane). Because of this (and the cold), staples were applied somewhat liberally across the field.
Installation under metal roof
Installing SOLITEX UM as vented roof underlayment is comparatively easier. Our SOLITEX UM Application Guide takes you through the steps. When it comes to roofs, proper water protection is essential, so pay close attention to steps 3 and 9:
- Clean substrate/sheathing Remove protruding nails, screws or splinters which can puncture or damage the membrane. Clean the substrate with a broom or shopvac.
- Unroll membrane Roll out membrane perpendicular to the gable, with the 3-D mesh facing out. The membrane can be pulled taut, independent of exterior temperature conditions. Overlap the membrane a minimum of 1.5” (4cm) over adjacent construction elements, so it can be adhered airtightly to them later.
- Attach membrane Fix the membrane to the substrate with heavy duty, galvanized staples. Min 3/8” (10mm) crown and 5/16” (8mm) legs every 4” in area that will be protected by the overlap. To increase waterproofing of the subroof, only staple in area that will be protected by the taped connection.
- Attach second membrane Roll out second membrane parallel to first. The 3-D mesh has been trimmed in the area to be overlapped. Use this to orient and get the proper overlap.
- Adhere membrane overlap Make sure overlapping membrane is dry, clean and free of grease and silicones. Flip up the upper membrane, remove the release paper in sections and press the membrane down into the adhesive strip. Make sure that the adhesion is free of creases and or permanent tensile forces.
- Adhere butt joint overlap In case of a horizontal butt joint – fold back the membrane about 4” (10cm) and cut back the 3-D mesh about 1.5-2” (4-5cm). Apply the membrane and staple down in area that will get covered by the next/covering membrane. Release 3d mesh from membrane on next/covering membrane 1.5-2” (4-5cm). Align the edge of this membrane with the cut back 3d mesh of the already installed layer. Staple only in area that will be covered by tape.
- Tape the butt joints Lift up the 3-D mesh on either side and apply TESCON VANA at the overlap, covering any visible staples. Use the PRESSFIX tool to get high pressure and best adhesion of the solid acrylic tape.
- Connect eave Connect to flashing or overlap at eaves, with DUPLEX or TESCON VANA. Make sure connection is free of creases.
- Attach metal roofing Follow manufacturer’s instructions when applying the metal roof. The strong 3-D mesh can be considered solid decking for this purpose. However, do include a ridge vent to assure proper ventilation of the metal roof. For additional and best practice waterproofing, apply pieces of TESCON NAIDECK under mounting clips to seal those screw connection tight to the membrane.
Note: Solitex UM used to be blue but is now grey.