RainScreen Siding

4

Rainscreen Siding System; How And Why

A rainscreen style wall is a method of wall construction designed to improve an exterior wall’s ability to manage water.

Rainscreen systems separate the exterior wall cladding from the inner wall by way of a vented airspace. In doing so, a rainscreen wall allows penetrated water to drain while airflow through the wall dries the system.

Rainscreen wall construction originated Norway, in early barn construction.

Today, vented rainscreen systems have gained popularity in the United States and Canada for their ability to keep wall assemblies dry.

The following article discusses and documents my exterior wall rebuild using a vented rainscreen system.

All Walls Leak Water & Trapped Water Rots Walls

Over the last several decades, water-related residential construction problems have been on the rise.

The increased use of synthetic building materials like EIFS (synthetic stucco), vinyl cladding, and polymer house wraps, and a focus on air-tight construction is largely responsible for this rise.

These materials and building practices may encourage water trapping, which can lead to the rotting of building materials.

As a result, many builders now think differently about wall construction. Instead of focusing on keeping water out, many are now more concerned with allowing water to escape.

All walls will leak. Understanding this, our idea of the ideal wall is changing. The best walls are not perfect, but forgiving – walls that drain water and dry quickly.

The Benefits Of A Rainscreen / Vented Wall Design

Vented rainscreen walls are designed to be forgiving.

Rainscreen walls allow penetrated water to drain by way of a ventilated air space or drain plane within the wall design. This airspace or drain plane created, minimizes the effects of water and moisture within the wall structure. Water passed into the wall quickly drains, while airflow through this cavity dries the assembly.

Vented rainscreen wall simple diagram.

A simple vented rainscreen wall; siding – drain plane / airspace – sheathing

In addition to the drainage and drying benefits, a rainscreen system also provides the advantages of separating the siding from the weather-resistant barrier.

Separation of wall layers provides weather barrier redundancy and reduces natural forces that tend to drive water into wall structures.

Separating natural wood siding from the weather resistant barrier within a wall assembly may also improve the performance of these barriers.

Multiple studies have shown the ability of surfactants (soaps, tannin, wood extracts, others) to degrade the performance of house wraps and other weather resistant barriers. A rainscreen wall design helps eliminate surfactant contact with these barriers.

The Many Benefits of A Vented Rainscreen Wall:

  1. Allows drainage of water out of the wall
  2. Allows airflow through wall promoting drying
  3. Provides a “break” in the water path and disrupts capillary movement of water
  4. Creates a redundant weather shield – what gets through the first layer is stopped by the second
  5. Disrupts water vapor movement due to heat and pressure gradients
  6. Separates siding from weather-resistant barrier – limiting effects of tannins and surfactants 

 

Rainscreen Wall Construction – The Layers 

Building a rain screen wall system is fairly simple. It does require a bit of extra planning and work compared to traditional wall construction.

To build a rainscreen wall, simply add space between your siding and your weather-proof barrier covered sheathing.

CONVENTIONAL VS. RAINSCREEN WALL LAYERS (inside to out)

Traditional wall (redundant barrier):
framing | sheathing | weather-resistant barrier | siding

Rainscreen wall (vented rainscreen):
framing | sheathing | weather-resistant barrier |  vented airspace | siding

Rainscreen wall diagram showing the layers of a simple sided rainscreen exterior wall.

The layers of a rainscreen wall. Air and water can readily move throughout the airspace created by the rainscreen mat installed be between the siding and the felt covered sheathing

 

The secret to a rainscreen wall system is the airspace separation between siding and sheathing.

Traditional wall construction consists of an exterior siding (primary barrier) installed over sheathing. Between the siding and the sheathing is a suitable weather resistant barrier (asphalt felt, house wraps). This style of sandwiched wall design is known as a “redundant barrier” system; the siding being the first barrier and the underlying WRB they other.

A rainscreen system improves on the redundant barrier wall by adding a gap or airspace between the two barriers that provides drainage and ventilation for drying.

A rain screen airspace can be created by a variety of methods:

  1. Furring strips – thin strips of wood or other material can be installed horizontally (for vertical siding) or vertically (for horizontal siding) to lift the siding off the weather-resistant barrier covered sheathing. Furring strips can be created using 1/4″ or thicker material cut from sheathing material, strips of treated lumber or one of the many manufactured products.
    Here is a list of available commercial furring strip products for building a vented rainscreen wall:

  2. Rainscreen Spacer Mats – designed to add space between the sheathing and siding of the wall. Several manufactured spacer mats are available to create a rain screen wall using this technique.
    Here is a list of Rainscreen venting mats:

    • DriWall Rainscreen – tangled polymer 3D rainscreen mat by Keene Building Products
    • Home Slicker® – 3D polymer matrix mat by Benajamin Obdyke
    • Cedar Breather® – 3D polymer matrix mat by Benjamin Obdyke
    • Waterway – polymer entangled 3D mat by Stuc-O-Flex International
    • Enkadrain – recycled polymer fused, entangled filament mat by Global Plastic Sheeting
  3. Draining House Wraps – these generally are not sufficient to provide a true vented rainscreen but may enhance water drainage within a wall. Designed with an applied spacer or with a textured or grooved surface, these products create additional space in front of the the wrap designed to create a drain path for water.
    Here is a list of draining house wraps:

What I Used To Build My Vented Rainscreen Wall

To build my vented rainscreen wall, I used a rainscreen mat installed over #30 asphalt-saturated organic felt. For the rainscreen mat, I used the Driwall™ rainscreen mat by Keene Building Products.

The Driwall Rainscreen mat is a three dimensional spacer mat available in several thicknesses which is installed over your weather-resistant barrier (#30 felt for me). The mat creates a space between the builders felt and the siding. Keene offers multiple thickness, I used the thinnest mat, which is 6 mm (0.25 inch) thick.

Rainscreen wall construction using Driwall™ Mat by Keene.

Rainscreen wall construction using Driwall™ Rainscreen 020-1 mat by Keene installed over asphalt felt before installing the board and batten siding

Because this was a remodel project, I first removed the old siding and wall materials prior to building my vented rainscreen exterior wall. Once down to the studs, I replaced the wall cavity insulation with fiberglass bats and replaced the old fiber board sheathing with 3/4″ plywood.

The layers I used to build my exterior wall (from inside to out)
  1. 2×4 studs 16″ oc

  2. R-13 Fibergalss batt insulation 

  3. 3/4 CDX exposure 1 plywood

  4. #30 asphalt-saturated organic felt (tar paper)

  5. Driwall™ Rainscreen mat by Keene

  6. Cedar board and batten siding

 

Rainscreen wall layers for board and batten siding.

The layers of my rainscreen wall with board and batten siding: plywood-tar paper-Keene Driwall rainscreen mat-board and batten siding

Closeup of rainscreen wall profile showing airspace created by Keene Driwall rainscreen mat.

Closeup of rainscreen wall profile showing airspace created between the tarpaper and the siding board by Keene Driwall rainscreen mat

 

A Properly Built Rainscreen Wall Is Vented At The Top And Bottom

To ensure the proper air movement and water drainage of a rainscreen wall system, you will need to vent the airspace at the top and bottom of the wall. There are many ways to do this and some commercial products that can be used too.

Ways To Vent A Rainscreen Wall System:

  1. Three dimensional rainscreen mat – Use a 3D rainscreen mat behind the entire height of wall from skirt board to the eves and allow air to enter below bottom most board (skirt board or other) and exit at top by top gapping topmost board or other method. Here is a list of rainscreen mats (same as above):
    • DriWall Rainscreen – tangled polymer 3D rainscreen mat by Keene Building Products
    • Home Slicker® – 3D polymer matrix mat by Benajamin Obdyke
    • Cedar Breather® – 3D polymer matrix mat by Benjamin Obdyke
    • Waterway – polymer entangled 3D mat by Stuc-O-Flex International
    • Enkadrain – recycled polymer fused, entangled filament mat by Global Plastic Sheeting
  2. Furring Strips + Top and Bottom Vents – Install furring strips in a fashion that allows vertical airflow from top to bottom of the wall. Add vented horizontal furring strips or similarly designed vent strips to allow bottom and top venting. Here is a list of commercially available vented furring strips or vents:

 

If you are using a rainscreen mat like I did, you can vent the wall by simply carrying the mat the entire height of the wall.

Then install the water table, rigid flashing, and siding on top of the mat, leaving a continuous, uninterrupted airspace from the bottom to top of the wall. Vent the airspace at the top and bottom of the wall to allow free airflow within the wall that promotes drying.

Rainscreen wall - airflow through airspace behind siding

Air moves behind siding in a rainscreen wall entering under the skirt board and exiting above top trim piece.

When planning your vents, consider wrapping mesh or screen over the cut end of the rainscreen mat to deter insects from passing into the airspace.

I did this at the top and bottom of the rainscreen mat using flaps of fiberglass screen. Most rainscreen mats have redundant mesh along one side of the mat to serve the same purpose.

Rainscreen mat install showing addition of fiberglass screen over bottom of mat to serve as insect barrier.

Bottom and top of the rainscreen wrapped with fiberglass screen to help prevent insect passage into the rainscreen air space but still allow air to move through the wall

 

 Choosing A Weather-Resistant Barrier

If your project is new construction or remodeling you will need to choose a weather-resistant barrier. This typically means choosing from many different house wraps or asphalt felt (tar paper).

Weather-resistant barriers (WRB) serve three main purposes:

  1. Block water penetration (water resistance)
  2. Release water vapor (water permeability, ability to breathe)
  3. Block the passage of air (air permeance)

House wraps and asphalt felt (tar paper) have different blends of performance within these categories.

The perfect WRB would be impermeable to water yet allow any water behind the barrier to escape. However, like most things, WRBs offer trade-offs. Some are very water resistant but don’t breath or release water well. Others are not as impermeable to water, but breath well allow them to release water and dry quickly.

In addition to traditional WRBs, newer winkled, Textured, grooved and dimpled wraps are available. These house wraps aim to improve water drainage within the wall.

If you do not plan to install a vented rainscreen system, the use of a draining house wrap may be beneficial. While these wraps may not provide the range of benefits of a true vented rainscreen system, they may offer water drainage benefits compared to traditional house wraps.

Modern house wraps are constructed from woven or non-woven polypropylene or polyolefin polymers. Different manufacturing processes create a variety of water resistance and water permeability between wraps.

Some have natural permeability based on their manufacturing process, while some are perforated to provide permeability. Different products may also have differing durability and performance characteristics – resistance to surfactants and tannins for example.

Here is a table comparing properties of common house wraps and asphalt felt and paper.

Common House Wraps, Felt and Paper –  Properties and Tests

ProductMfg.MaterialVapor PermWater ResistanceWater ResistanceAir Perm
   (ASTM E96)
(perms)
(ASTM D779)
“Boat Test” (>mins)
(AATCC 127-1995)
“Water Column” (cm)
(ASTM E1278)
(mL/s/m2)
Tyvek®DuPontnon-woven, non-perforated, spunbonded polyolefin5810210 
TyparPGInon-woven, spunbonded polyolefin with perforated coating 11.7108653.2
Weathermate PlusDownon-woven, non-perforated polyolefin 75>5520
R-Wrap®Barricadenon-woven, non-perforated polyolefin595>220 
FlatWrap®HPBenjamin Obdyke tri-laminate – top and botton non-woven polypropylene with middle micro-perforated film36 556.2
Pinkwrap®Owens Corning perforated woven polyolefin7.76012 
GreenGuard® Classic Wrap (Amowrap)Kingspan cross-woven polyolefin with perforated coating1560  
GreenGuard® MaxKingspan cross-woven polyolefin with coating16120>6000
CertaWrapCertainTeedwoven polypropylene with perforated coating11.7108653.2
WeatherSmart®Fortifibernon-woven, non-perforated polyolefin with single side coating810>602.5
Two-Ply Super Jumbo Tex® 60 MinuteFortifiber®Two-ply asphalt-saturated kraft paper. 12 lbs/100 sq ft10 (dry)150   
#15 Asphalt Felt (tar paper)Multiple asphalt-saturated organic felt 5 (dry) 60 (wet) ~50 
Asphalt Kraft Paper (Grade D Paper)Multiple asphalt saturated kraft paper 5   

Water Resistance (ASTM D779, “Boat Test”)* = boat shaped piece of material floated on water, time to water passage through material into “boat” recorded in minutes. The higher the value, the longer it takes for water to “leak” through the WRB boat-shaped testing bowl. Higher value = more water resistant material. (* note: that some highly permeable materials (Tyvek) may falsely test low for water resistance using this test. This test uses a indicator power that changes color with water vapor and therefore can give an artificially low value (meaning low water resistance) for highly permeable materials that will quickly pass water vapor and trigger an indicator color change even though they are highly resistant to liquid water passage and have not yet passed liquid water.)

Water Resistance (AATCC 127-1995, “Water Column Penetration Test”) = Hydro-static pressure resistance test. Measures height of water column in cm need to penetrate material. Higher numbers mean more water pressure is required to “push” water through the WRB tested. Higher value = more water resistant material.

Permeability Rating (Perm Rating) (ASTM E96) = measure of water vapor passage in a 24 hour period stated in perms. Also known as the Water Vapor Transmission. Higer numbers mean more permeability. Higher value = more breathable material. Permeability categories: ≤ 1 perm = impermeable, 1 – 10 perm = semi-permeable, > 10 perm = permeable.

Air Permeance (ASTM E2178, “Air Permeance of Building Materials”)= Determines the volume of air in liters (L)* that passes through a flexible or rigid piece of 1 meter x 1 meter material in 1 second. Lower value = less air through material (better air barrier). *Note: values below recorded in milliliters for easier comparison.

 

 The beauty of Old School Asphalt Saturated Felt

After considering the many choices for a weather-resistant barrier, including the multitude of house wraps, I decided to use good old fashioned asphalt saturated builders felt (or what my dad called tar paper).

Not only has asphalt felt been successfully used for the last 100 years, it is still chosen by some of the leading building scientists. Paul Fisette, Professor of Buidling & Construction Technology at the University of Massachusettss, Amherst, in his article Housewraps, Felt Paper and Weath Penetration Barriers (bct.eco.umass.edu. 2001), endorses asphalt saturated felt as a weather-resistant barrier. He also notes that he has felt on his own home and if he had to choose again he would choose felt. He continues to explain that house wraps can trap water that finds its way behind the weather-resistant barrier as they only are permeable to water vapor, not liquid water. Asphalt saturated felt, in comparison, can absorb liquid water and dry quicker than house wraps.

Felt is unique in that it can absorb liquid water, and once wet, dry faster due to its’ unique quality of increased water vapor permeability when wet.

Long ago, asphalt felt was made from recycled cotton rags saturated with asphalt. It was used as an inexpensive and quick water resistant roofing material. Today the “felt” is no longer made from cloth, but from asphalt saturated recycled cardboard and sawdust.

Asphalt felt is available in #15 felt (Type I) or #30 felt (Type II). These numbers refer to the original weight of the product per 100 sq ft (a roofer’s square). As the cost of petroleum increased the amount of asphalt added to these products decreased, and today many of these products weight only half of the originals. With this change, the names where changes to “pound” to “number” – today referred to as number 15 (#15 or No. 15) and number 30 (#30 or No. 30) felt.

The ASTM (American Society for Testing and Materials) has two standards for asphalt felts – a standard ASTM D 4869 and a more demanding ASTM D 226. With these standards, minimum weights for Type I (#15) and Type II (#30) asphalt felts are published. In general, rated, heavier weight felts suggest better quality and more asphalt used in manufacturing the product. Unrated, typically lighter felts, are also readily available.

Asphalt Saturated Felt Minimum Weights for ASTM Standards*

StandardNo. 15 Felt (Type I)No. 30 Felt (Type II)
 weight (lbs.) / 100 sq ftweight (lbs.) / 100 sq ft
Not ASTM Ratedless than 8less than 13
ASTM D 4869813
ASTM D 226 “ASTM Grade”11.526

*(ASTM D226/D226M − 09 and ASTM D4869/D4869M − 05)

 

Asphalt Felt vs. Grade “D” Builders Paper

The is a fair amount of confusion and when speaking of asphalt saturated weather-resistant barriers. With this confusion, it is good idea to briefly discuss the differences between asphalt-saturated felt (Roofing Felt) and asphalt-impregnated kraft paper (ASK).

Both asphalt felt and asphalt paper are used as weather resistant barriers. Asphalt felt had it’s origin as a roofing underlayment that became popular as a wall underlayment as well. Asphalt kraft paper started as a wall underlayment and is still used as such, especially for stucco.

Asphalt kraft paper is generally made from thinner, new paper stock rather than thicker, recycled material used to make felt. Asphalt paper is typically more pliable than felt and promoted as easier to bend around corners.

Asphalt paper is often called Grade “D” builders paper referring grade of water resistance required for this product according to UBC Standard 14-1. Despite this minimum water resistance rating of 10 minutes, many building paper makers manufacture higher performing papers rating for 60 minutes or more of water resistance.

In general, asphalt felt is considered to be more durable and less prone to rot. This may not be true for some higher quality paper products like Fortifiber’s Tex line of asphalt papers.

Asphalt saturated kraft paper - Fortifiber Two-Ply Super Jumbo Tex 60.

High quality asphalt saturated kraft paper by Fortifiber

 

Asphalt Felt or Paper?

Considering the differences of asphalt felt or paper, which one should you use? Well, like most questions, it depends.

In most cases, felt is probably better. That assumes equal quality products. I would much rather use a 60 minute asphalt kraft paper of high quality (like the Fortifiber Two-Ply Tex pictured above), than some unrated crappy lumber yard felt.

  Asphalt Saturated Felt vs. Asphalt Impregnated Kraft Paper

 #15 or #30 Asphalt FeltGrade “D” Asphalt Paper
 Made fromrecycled cardboard / sawdustnew kraft paper
Benefits more durable, thickermore pliable, thinner
 Common Useroofing, exterior wall underlaymentexterior wall underlayment (stucco)

For my siding project, I used a quality #30 felt. I chose the #30 instead of a #15 felt as modern product has a similar asphalt weight as the older, heavier #15 used for more than 100 years in domestic construction.

Pick a Sheathing Material

If this is new construction or you plan to replace your sheathing, you will need to decide which type of sheathing material to use. For structural sheathing, you basically have two choices; OSB (oriented strand board) or plywood.

Oriented Strand Board or OSB

OSB or oriented strand board is a manufactured wood panel made from layers of oriented wood strands compressed and bonded with heat and glued to form a sheet. OSB panels, similar to plywood, are made up of several layers, typically with alternating wood strand orientation. This is unlike waferboard, which is made up of randomly oriented wood strands in a single layer.

OSB performs similar to plywood and is essentially interchangeable with plywood. There are some exceptions. Both OSB and plywood are building code approved wood structural panels for sheathing roofs, walls and floors. Both have similar strength, fastener holding and weight. OSB performs better under shear force, and is commonly used for manufactured trusses. Despite their similarities, they do have a few important differences.

For one, OSB and plywood handle water differently, and this may be the biggest negative of OSB products. OSB is more water resistant and less water permeable than plywood. This may sound like a positive, but with these characteristics, once OSB gets wet it is much slower to dry and tends to swell, especially at the edges.

This tendency of OSB to expand at the edges can lead to telegraphed panel borders known as “ghost lines” that can show through roofing and wall finishes. For this reason, some product manufacturers and associations advise against the use of OSB under their products, especially for flooring (Tile, Vinyl) and roofing materials.

In attempt to panel edge swelling, OSB manufacturers now seal panel edges with wax or paint. This obviously does little to prevent swelling at cut panel edges unless those are sealed after cutting. If you are considering OSB, check the recommendations of the finishing product you will be using over it to ensure compatibility and warranty compliance.

The second difference between OSB and plywood is price. OSB is typically much cheaper than plywood, often by a difference of up to 50%.

Plywood

Plywood is a manufactured wood panel made from multiple thin sheets of wood compressed and bonded with heat and glue to form a panel. The wood plies used to made plywood are thin veneers of wood stripped from rotating logs. These plies are assembled with alternating grain directions to improve strength and dimensional stability.

Plywood as noted above tends to handle water better. Wet panels tend to dry quicker and retain the panel dimensions, assuming exterior grade products. Some perceive benefits with fastener holding, but tests suggest similar performance compared to OSB.

Approved for all wood structural panel applications, plywood is commonly used as sheathing for roofing, walls and floors.

For my project, I used plywood.

 Plywood vs. OSB

 

 PlywoodOSB
 Made fromglued layers of cross-oriented wood veneersglued layers of oriented wood strand
 Cost$20 (19/32″ ext 4’x8′)$11 (19/32″ ext 4’x8′)
Usestructural panel – roof decks, walls, subfloors structural panel – roof decks*, walls, subfloors*
*Use exceptions 

roof decks with some products
roof decks in Dade County, FL
subfloors with tile, vinyl, laminates

Positives water handling, perceived qualityshear strength, lower cost
Negatives higher cost, slightly heavierwater handling / panel swelling

 

 

Rainscreen Siding – Overview

Preparation and Materials

Project Overview

  • Level: Intermediate
  • Time: Days to Weeks
  • Cost:  Standard material costs plus $0.5 – $3 per sq ft for rainscreen materials

Project Big Picture

  1. Prep wall (remove old siding, etc.).
  2. Install sheathing.
  3. Install weather-resistant barrier.
  4. Install rainscreen system.
  5. Install siding.
Materials – Vented Rainscreen Exterior Wall Build
ItemWhat I usedCost
Insulation$60 / 105 sf
Sheathing 23/32 Exterior Plywood$25 / 4′ x 8′
Weather-resistant barrier$30 / 216 sf
Rainscreen Mat$150 / 150 sf
Flashing Tape$25 / 100′ roll
Cap Nails$24 / 2000
Rainscreen Siding – Tools / Supplies
ItemWhat I usedCost
Framing Nailer$225
Framing Nails$65 / 3600
Compressor$150
Circular Saw$175
Saw Blade$15
T-Square$20
Stapler$50
Galvanized Staples$8 / box
Level$35
Hammer$30
Chalkline$10
Utility Knife$10
Scaffold Tower$750

Rainscreen Siding Exterior Wall Build – Step by Step

    1. Order Materials and Supplies, Organize Tools.

      Plan for and order the necessary materials and supplies. Diagram and measure your exterior walls to generate a bill of materials. Remember to order 10% or extra for waste. For my cabin exterior wall rebuild, I measured the square footage of wall surface and came up with an estimate of around 1,100 sq ft.

      I was replacing the existing insulation with fiberglass batts, replacing the existing sheathing with 23/32″ plywood, covering this plywood with #30 asphalt roofing felt (tar paper), and installing a 3D rainscreen membrane (Keene Drywall). Therefore my bill of materials included enough of each of these to cover 1,100 sq ft plus waste;

      – Fiberglass batts
      – Plywood sheathing
      – #30 Felt
      – Peel and stick flashing tape
      – Rainscreen mat 

      In addition to the materials, I was planning on using my framing nailer and 2 1/2 ring shank nails for the sheathing, galvanized staples for the roofing felt and cap nails for the rainscreen mat. So, before starting any demo, I ordered and organized everything I would need once the wall was pulled apart.

      Exterior wall construction - delivery of plywood and fiberglass insulation

      Plywood and fiberglass insulation ordered and delivered prior to beginning project

    2. Demo Existing Wall.

      With materials on site and everything organized, start to remove the existing wall siding, sheathing and insulation. Our cabin walls were constructed in the 1950’s and sheathed with a wood fiber board – Temlok by Armstrong. Wall cavities were insulated with a wood fiber insulation “Balsam Wool”. These panels do not contain asbestos. Confirm the product you are working on does not contain asbestos prior to removing it.

      Exterior wall demo prior to rebuilding a vented rainscreen wall.

      Demo of existing cabin exterior wall. Old Balsam Wool insulation, Temlok sheathing and redwood siding removed

      Rainscreen wall rebuild - wall cavity thoroughly cleaned and vacuumed prior to rebuild.

      Wall cavity thoroughly cleaned and vacuumed prior to rebuild

    3. Replace Wall Cavity Insulation.

      After removing the old wall cavity insulation, I replaced it with fiberglass batts. I realize there are other, better wall insulation products available, but given my interest in inexpensive, reasonable performance insulation I went with fiberglass batts. The R-13 fiberglass batts I installed were a significant improvement compared to the existing R-3 wood fiber batts from the 1950s.

      I also wanted to maintain the ability to run additional wires and possibly pipes through the walls cavity as needed, somewhat ruling out spray foam wall cavity insulation.

      Rainscreen wall rebuild - replacing the wall cavity insulation.

      Old “Balsam Wool” wood fiber insulation (R-3ish) replaced with R-13 fiberglass batts.

    4. Install Plywood Sheathing.

      After replacing the wall cavity insulation, re-install the wall sheathing.

      Rainscreen vented wall rebuild - measuring plywood sheathing.

      Dave measures new plywood sheathing

      I decided to use plywood sheathing for my new exterior walls. I chose plywood over OSB mainly for the moisture forgiveness of plywood. I also decided to use thicker plywood and beef up the exterior walls.

      I really like the easy structural gain for the building simply by adding thicker (23/32″ in my case) plywood. It is an easy relatively inexpensive way to fortify the exterior walls.

      When installing plywood sheathing, cut so the panels start and end on a stud. Panels should be carried the entire height of the wall – from rim joist to top plate if possible. This will tie together and reinforce the entire wall frame. Start the bottom of the plywood panel just above the bottom edge of the rim joist and above the block to help prevent water wicking from below.

      Prior to fastening sheathing, locate and protect and wiring and plumbing passing through framing members or within the wall cavity with the appropriate shields and nailing plates. In addition, I like to take several pictures of the wall cavity prior to installing the sheathing as a reference while nailing the panels. 

      Rainscreen wall rebuild - protect wires and pipes with nail plates prior to nailing sheathing in place.

      Prior to installing the sheathing, protect wiring and plumbing with nailing plates.

      When fastening the plywood panels to the wall frame, use appropriate fasteners and an appropriate spacing schedule. Local building codes may require certain fastener size, style and schedule – this is especially true in Florida and other hurricane or earthquake prone locations. In general wood panel sheathing should be fastened with 8d – 10d equivalent nails spaced 6″ at the edges and 8 – 12″ in the field.

      Re-sheathing vented rainscreen wall with span rated plywood.

      Walls re-sheathed with span rated plywood. Notice spacing of panels for expansion and extension of plywood over rim joist for added wall strength.

      When driving fasteners, it is important to not over-drive the head of the fastener. Nails and screws with heads that penetrate the sheathing panel are known to loose significant holding power. Just set the head flush to the sheathing surface when fastening sheathing.

      Coated, galvanized, ring shank, spiral shank and other specialized nail designs typically have better holding characteristics compared to plain smooth shank nails. I used 2 1/2″ galvanized ring shank nails to fasten the plywood with 6″ edge spacing and 8″ field spacing. I did not use adhesives or caulk between the panels and framing.

    5. Apply Weather Proof Barrier Over Sheathing.

      With the wood sheathing is in place, install a weather resistant barrier (WRB) over this sheathing. You have many choices with regard to the specific WRB you decide to use. I discuss the options in some detail in the beginning of this article.

      For this project I chose #30 Asphalt Roof Felt as my WRB.

      No matter which WRB you use, always install it horizontally from the bottom to the top of the wall. Horizontal seems should overlap by several inches and vertical seams by 8 – 12 inches or more. Use a level and chalk line to help install the WRB sheets level.

      Roofing felt used as weather-resistant barrier for rainscreen wall build.

      #30 roofing felt installed bottom to top over plywood as weather resistant barrier. Install felt starting just under the rim joist. Carry felt around corners and up tight to windows and doors.

      Fasten the barrier with approved fasteners (galvanized staples for my roofing felt). Continue the WRB around wall corners and overlap the adjacent wall barrier by 8 – 12″. If the barrier you are using tends to crack when folded over corners, use flexible peel and stick flashing tape to reinforce and seal corners.

       

    6. Install Flashing, Seal Windows.

      Reseal windows and doors to the weather-resistant barrier (WRB) using flexible flashing tape and other recommended rigid flashing.

      For this project, on my single story cabin with generous roof overhangs, I used only peel-and-stick flashing tape and did not add rigid flashing above my windows or doorways.

      If you have windows and door openings that will likely see water from above, consider adding rigid flashing above these openings. One consideration when installing rigid flashing is the position of this flashing in regard to any rainscreen plane of the wall.

      Traditional rigid flashing is tucked under the WRB. Flashing tucked under the WRB will interrupt the rainscreen drain plane if you are using one. When installing rigid flashing in a wall with a rainscreen layer, some recommend installing the flashing above the rainscreen mat or layer. This way, water will tend to stay above the rainscreen and keep the drain plane cavity un-interrupted.

      For my project, I re-sealed the windows to the WRB using peel-and-stick flashing tape.

      Peel-and-stick flashing tapes are, in general, one of two types; asphalt-based or butyl-based. Certain flashing tapes will work best with certain WRB or house wraps. Typically, using products from the same manufacturer is a good idea, as they are often designed to work together (Dupont flashing tape with Tyvek, for example). Check with the manufacturer of the WRB you plan to use to determine if certain flashing tapes are recommended.

      As you can see, I am using asphalt roofing felt as a WRB and found that both Dupont flashing tape (butyl rubber tape) and WindowWrap (rubberized asphalt tape) worked well. I did find that the WindowWrap tape seemed to have a better initial stick to the asphalt felt, which may make sense as it is also an asphalt-based product.

      To seal a window using peel-and-stick flashing tape, apply strips of flashing tape to the sides and top of the window in a layered, shingle-style fashion. The bottom of the window should not be sealed with flashing or caulk to allow for water escape the bottom of the window and drain above the WRB.

      Install window flashing tape to sides and top of window.

      Flash windows with peel-and-stick window flashing tape applied to sides and top.

      If you are installing new windows, wrap the house wrap or WRB inside and through the window rough opening per the recommendations of the window manufacturer.

      Then flash the sill rough opening with 9″ flashing tape or one of the pre-made window sill flashing products. Run this sill flashing up the sides of the bottom of the window opening 6″ – 12″. If possible, slope the sill pan toward the outside of the home to encourage drainage in that direction.

      Once the sill is flashed, you may also apply a strip of flashing tape at the bottom of the window rough opening, overlapping the sill flashing prior to installing the window. Next, install the window, with the side and bottom nailing fins above the WRB or as directed by the manufacturer.

      If you are sealing existing windows to a new WRB (like I am with this project), you will not have access to the rough opening to flash the rough sill. Instead, allow the bottom window nailing fin to be above the WRB barrier if possible. No flashing tape should be applied to this bottom nailing fin for existing windows.

      Tuck weather-resistant barrier under side and bottom nailing fins of existing windows if possible.

      When installing weather-resistant barrier around existing windows, tuck barrier under bottom and side nailing fins of window if possible.

      Next, for both new and existing windows, apply a strip of flashing tape on both sides of the window, taping over the nailing fin and WRB. These strips should extend several inches beyond the bottom and top of the window.

      Flash windows with peel and stick flashing tape starting at the sides.

      Start window flashing tape with strips down both sides of the window. Overlap the top and bottom of the window. In general, you do not want to install a strip of flashing tape along the bottom of the window to allow water drainage.

      Then apply a strip of flashing tape to the top of the window, again covering the nailing fin and underlying WRB. This top piece will layer over the side flashing and should extend beyond both sides covering the side flashing strips.

      Window flashing showing top strip application.

      After applying side flashing strips, apply a wide, overlapping strip of flashing to the top of the window.

      Finally, add reinforcement “bow-tie” pieces to the top corners.

      Window flashing tape install - top corner bow ties.

      Top detail of window flashing showing “bow tie” corners. Notice how peel and stick flashing tape is stuck directly to window frame and pressed smoothly into corner between window and the WRB.

      Prior to installing flashing tape, take some time to thoroughly clean the outside frame of the window were you will apply the flashing tape. Remove old caulk with a utility knife. Use denatured alcohol or similar to create a clean surface to help create a permanent water tight seal between the window and the flashing tape.

      Use utility knife to remove old caulking prior to applying flashing tape to window frame.

      Use sharp utility knife held at a sharp angle to remove old caulk from window frame prior to applying flashing tape

      Alcohol used to clean window frame prior to applying peel and stick flashing tape.

      Use denatured alcohol to clean window frame prior to applying peel and stick flashing to ensure a permanent bond.

      When installing flashing tape start at one edge and smooth the flashing tape into the corner between the window frame and the wall without rounding off this corner. If you round the corner, the flashing tape may be higher than the wall surface, lifting the edge of siding installed over it and possibly pulling the flashing tape loose.

      Installing peel and stick flashing tape to window frame.

      Install flashing tape by pressing firmly and smoothing out air or gaps. Use firm pressure or a roller.

    7. Install Rainscreen Mat or Furring Strips.

      With the WRB is installed and all windows and wall penetrations are properly sealed with flashing tape, it is now time to create the vented airspace of the rainscreen wall.

      As mentioned above there are many ways to create the air space drain plane between the WRB and the siding of a rainscreen wall. A variety of commercial products are available including dimpled house wraps, 3D rainscreen mats and natural wood or synthetic furring strips. Not matter what system you use, the goal is the same; create a space between your siding and WRB.

      To create my drain plane, I used the Driwall Rainscreen 020-1 mat by Keene Building Products. This product is rolled onto the exterior wall over the weather-resistant barrier (#30 felt in our case). Once in place the sliding is simply installed over this mat. The mat creates a breathable air space under the siding, between the #30 felt and the back of the siding boards.

      Keene driwall rainscreen mat closeup showing 3D character at cut edge of material.

      Rainscreen mat closeup at corner and around window. Notice the three dimensional nature of the rainscreen mat at the cut edge at the corner of the building.

      Before we install the rainscreen mat, we need plan for bottom and top venting of our rainscreen wall and consider installing insect screens at the bottom and top edges of these vents over the bottom and top edges of the rainscreen mat.

      The Keene Driwall mat is covered with a fine, insect proof mesh that is overhung on one edge of the mat. This mesh is overlapped at adjacent rows, but also can be wrapped over the top and bottom edges of the mat to serve as an insect screen. In addition, many will add additional screen at the top and bottom edges of the drain plan for better insect protection.

      I did add extra insect protection by wrapping the bottom and top edges of the rainscreen mat with fiberglass screen. I installed the back edge of this screen to the WRB before installing the rainscreen mat. Then once the mat is installed, I simple wrapped the screen around the rainscreen mat and fastened it to the front of the mat using cap nails.

      Fiberglass screen installed prior to rainscreen mat as an insect screen.

      Prior to rolling on the rainscreen mat, install a double layer flap of fiberglass screen at the top and bottom of the wall that can be wrapped around the rainscreen mat to prevent insect penetration into the rainscreen drain plane.

      Cap nails used to secure bottom rainscreen mat insect screen.

      Wrap pre-installed double layer of fiberglass screen around bottom edge of rainscreen mat and fasten with cap nails.

      Installation of insect screen at the bottom of the rainscreen mat.

      Insect screen protection for the bottom edge of the vented rainscreen mat. Notice free edge of mesh of rainscreen mat wrapped around and behind bottom edge of the mat. Also notice the additional flap of black fiberglass screen stapled to the roofing felt behind the bottom edge of the mat and wrapped around to the front of the mat and secured with cap nails.

      Once the fiberglass screen flap is stapled to the top and bottom of the WRB, install the rainscreen mat.

      To install themat, simply roll the mat onto the wall over your WRB. Do not overlap the 3D portion of the mat. Use plastic cap nails to hold the mat in place prior to installing your siding. Most mat products will have a finer mesh skin that can overlap adjacent rows (see above photo showing mesh from top row overlaped and nailed to lower row).

      Roll on rainscreen mat and attach to wall with plastic cap nails.

      Install rainscreen mat by rolling on over weather-resistant barrier. Do not overlap at seems as the thickness of the mat would cause high spots at these overlaps. Fasten using plastic cap nails. Do not over drive the cap nails or you can over flatten the mat and loose the drain plane.

      Fasten the rainscreen mat to the wall over the WRB using plastic cap nails. Use care not to over drive the cap nails, as you do not want to crush the mat and loose the drain plane gap the mat creates.

      Keene rainscreen mat installation complete.

      Rainscreen mat with insect screen – installation complete.

       

    8. Install Water Table Board and Drip Flashing.

      For the water table around the base of the wall, I will use the same material I will be using for the boards of the board and batten siding – 10″ x 1″ cedar. I did order some longer 16′ boards and will try and use these to limit the seams along the water table.

      Prior to installing the water table board, I used a router to cut a drip angle along the bottom of the board.

      Water table board prior to installing to rainscreen wall.

      I used the same 10″ x 1″ x 16′ cedar boards for the water table as I planned to use for the siding. Prior to installing, I used a 45 degree router bit to angle the bottom edge of the water table to help shed water.

      After routing to create bottom drip angle, I primed and repainted the cut edge. Then I installed the board at the base of the wall as the water table, aligning the bottom back edge of the board with the bottom of the insect screen wrapped rainscreen mat which was just covering and positioned at the bottom edge of the rim joist.

      Water table board install for rainscreen wall.

      10″ x 1″ board installed over rainscreen mat at level of rim joist as water table board. Bottom of board has angled edge encouraging water to run away from the wall.

      When installing the water table over the rainscreen mat use care to not overdrive fasteners and crush the rainscreen mat below. If properly installed, the water table board should allow continuation of the rainscreen airspace and drain plane behind the water table allowing ventilation and draining from behind, entering below the water table.

      With the water table board installed, next install a drip edge flashing piece above the water table top edge. This flashing piece should be installed above the rainscreen mat and not under the WRB as is traditionally done with non-rainscreen wall construction.

      Drip flashing installed over rainscreen mat.

      Drip edge flashing installed over rainscreen mat to allow an un-interrupted drain plane behind the siding.

      The drip edge flashing is installed in this manner to prevent interruption of the drain plane behind the rainscreen mat. Flashing material passing through the rainscreen mat would block the up and down flow of water and air that an un-interrupted drain plane airspace would allow.

      Siding, water board and the drip flashing installed on top of the rainscreen mat.

      Siding boards, water table and drip flashing all installed above the rainscreen mat to allow for a continuous drain plane behind the siding. With this drain plane, water can easily drain down wall behind siding an exit behind the water table board.

    9. Consider and Install Venting at Bottom and Top of Wall.

      Ideally, a vented rainscreen wall will be vented at the bottom and top of the wall. Installing the siding, water table and drip flashing above (on top of) the rainscreen mat, I was able to vent the bottom of the wall through the entire bottom edge of the wall water table. Air can easily enter behind the back bottom edge of the water table and flow up through the rainscreen air space.

      Bottom venting of rainscreen wall behind water table.

      Venting at bottom of rainscreen wall via continuous airspace behind water table.

      At the top of the wall, I used a gap between the top trim piece of the siding and the rake board as a top vent. There are many different ways to vent the top of the wall. I decided to keep it simple and simply leave a 1/4″ or so gap between the top horizontal trim piece of the board and batten siding and the eves face board. Each siding system and home will have considerations when deciding on a method for venting the top of a rainscreen wall.

      Homes with less protected walls will likely need a method that will prevent water enter, like a spaced over lapping trim piece.

      Continuous airflow behind siding in rainscreen wall build.

      Air flows behind siding in continuous airspace of rainscreen drain plane. Air enters behind water table and exits through gap above top trim piece.

      Top rainscreen wall vent above siding trim piece.

      Top of rainscreen wall vented through gap above top siding trim piece.

    10. Use the Vented Rainscreen Concepts to Create Your Own Rainscreen Wall.

      There are many ways to create a rainscreen wall. The above documents a simple way to build a vented rainscreen exterior wall finished with vertical wood siding (board and batten — for details read more here). I used a rainscreen mat installed over #30 roofing felt. I then sided the walls with prestained (Michigan PreStain) red cedar boards installed in the traditional board and batten style. This wall system and siding has been in service now for nearly 3 seasons.

      The performance of this simple wall has been flawless. The home is warm and comfortable and feels incredibly solid. The siding has shown no evidence of warping, deterioration or excess moisture. Prior to the rebuilding of our walls as above, the old siding routinely showed dampness and evidence of trapped moisture on the exterior and interior of the walls.

      This was the first rainscreen wall I have built and I’m glad I did. If you are building or remodeling exterior walls, I highly recommend taking the extra time and spending a bit extra to build a rainscreen style wall. Now that I understand the concepts and have seen the results, I see why some building jurisdictions are moving toward requiring rainscreen style wall builds. Time will ultimately tell, but so far I am totally impressed.

 

Rainscreen Siding System Image Gallery

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Originally published December 22, 2014 by Cabin DIY

4 comments

  • Rich Paul May 29, 2016   Reply →

    I am having trouble with how to trim around windows with the rainscreen adding to the thickness of the wall and stopping water. Very fine explainations and pictures. The window trim/rain screen detail is perplexing. Can you help?

  • Mark Sheehan August 12, 2017   Reply →

    I am re-siding my old garage. It was originally Board and Batten and I plan to maintain the look. The original cedar siding was bad but underneath I discovered heavy builders felt and under that sheathing of 3/4″ x 6″ siding boards in remarkably good shape. I’m thinking of prepping the existing sheathing by putting 3/8″ exterior plywood over it to smooth the surface, seal air holes and add strength. It seems like a waste to toss all that old sheathing. What do you think?

    • Cabin DIY August 12, 2017   Reply →
      Cabin DIY

      Hi Mark,

      Interesting that you should ask as I just finished re-siding our boathouse at the cabin.

      Our boathouse was build similar to you garage with 3/4″ pine sheathing and asphalt felt as a weather resistant barrier.

      After I removed the old siding, I planned to keep the 3/4″ pine sheathing and whatever builders felt that was still in good condition. I simply attached a new layer of 30# asphalt felt over the old. I did not add plywood or other sheathing.

      On top of the builders felt, I installed a rain screen mat – Keene’s Driwall 020 1/4″ mat. This is the same rain screen mat I used on our main cabin.

      On top of the rain screen I installed 10″ cedar boards and 3″ cedar battens.

      For your project I would not bother with the additional plywood. Just use screws to attach you siding. One of the nice side benefits of the driwall mat is that it will give you a bit of padding to make up for surface irregularities of the sheathing boards.

      Here are a few pics:
      Boathouse re-siding showing asphalt felt.
      Boathouse - Keene driwall rainscreen mat under board and batten cedar siding.
      Board and batten siding on lake boathouse.

      Thanks for sharing and let me know if you have any other questions,

      Gary

  • Dave October 20, 2017   Reply →

    This is an amazingly detailed and helpful article. Was going to bookmark it, but decided to print it.

    Your effort to document your project is greatly appreciated. It helped me in cedar BnB for a rear extension wall. Was surprised that you would paint the cedar black, as I appreciate the natural color and grain of the wood, but your boat house does look nice!
    I was going to use a drainage layer, but it was too far to drive to get it, and I simply bought Pressure treated Lattice, disassembled it and used the pieces to create a horizontal layer under the cedar siding that would allow air circulation and water drainage. Also coated the cedar with an oil semi transparent stain to keep the look of the wood. Brand is Wolman.

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