Best Rainscreens for Siding: Side-by-Side Specs

Specification	Mortairvent 202	Mortairvent 203	DELTA-DRY
Manufacturer	Advanced Building Products	Advanced Building Products	Dörken
Cavity thickness	0.25 in. (6 mm)	0.40 in. (10 mm)	10.5 mm
Construction	Polypropylene mesh core + heat-bonded filter fabric	Polypropylene mesh core + heat-bonded filter fabric	HDPE dimpled membrane, two-sided drainage
Roll size / coverage	39 in. × 61.5 ft. / 200 sq. ft.	39 in. × 40 ft. / 130 sq. ft.	3.3 ft. × 50 ft. / 162.5 sq. ft.
Skid coverage	18 rolls / 3,600 sq. ft.	18 rolls / 2,340 sq. ft.	24 rolls / 3,900 sq. ft.
Roll weight	14 lbs.	16 lbs.	N/A
Open space (porosity)	93.8%	95.3%	N/A
Drainage (ASTM D4716)	4.22 gpm/ft. width	7.01 gpm/ft. width	N/A
Air flow (ASTM D4716, mod.)	15.8 cfm/ft. width	54.5 cfm/ft. width	N/A
Fire rating (ASTM E84)	Class A	Class A	N/A
Max UV exposure	30 days	30 days	N/A
Insect screen	Built in (fabric flap)	Built in (fabric flap)	Separate DELTA-BUG SCREEN
ASTM E2925 tested	Yes	Yes	Yes
Best fit	Fiber cement and wood lap siding	Wood siding needing more drying, high-exposure walls	Stucco, stone veneer, other absorptive claddings

Why Fiber Cement and Wood Siding Need a Rainscreen Gap

Siding is not watertight. Wind-driven rain gets behind lap joints, butt joints, and trim. When siding is nailed tight to the water-resistive barrier (WRB), that water has nowhere to go, and the back of the siding and the sheathing stay wet. A rainscreen mat holds the siding off the WRB so water can drain down and out, and air can move through the gap to dry the assembly. Advanced Building Products calls this "Drain, Not Remain."

The manufacturer also notes that the 2021 and 2024 IRC and IBC require a capillary break behind absorptive claddings, and recommends products tested to ASTM E2925. Both Mortairvent products are tested to that standard. Confirm with your local building official how your cladding is classified.

Siding-Specific Details to Plan Before You Order

• Fastener length. The rainscreen adds 1/4 in. (202) or 0.40 in. (203) between the siding and the WRB. Size siding fasteners so they still meet the siding manufacturer's required penetration into framing or sheathing.
  
  
• Siding manufacturer's instructions. Fiber cement and wood siding manufacturers publish their own requirements for installation over a rainscreen gap. Check them before ordering, since they can affect which thickness you choose.
  
  
• Trim and window returns. A thinner cavity means a smaller build-out at window, door, and corner trim. That is one reason 6 mm is the practical default for lap siding.
  
  
• Top and bottom of the wall. Mortairvent's fabric flap folds behind the mesh at the bottom and top courses to form a built-in insect screen, so no separate bug screen is needed.
  
  
• Siding schedule. Mortairvent is rated for a maximum of 30 days of UV exposure. Plan siding installation within that window.

How to Install Mortairvent 202 Behind Siding

1. Install the WRB first. Apply a weather-resistive barrier over the sheathing, and flash windows and doors with Spycorbuilding.com's flashing products.
   
   
2. Start at the bottom. Unroll right to left with the fabric flap at the bottom, the blue mesh against the WRB, and the fabric facing out. Staple or nail about every 3 sq. ft.
   
   
3. Run the courses. Butt the blue mesh tightly without overlapping, and lap each fabric flap over the course below, shingle style.
   
   
4. Close the top and bottom. Tuck the fabric flap behind the mesh on the first and last courses to form the insect screen.
   
   
5. Install siding with the siding manufacturer's recommended fasteners and spacing.

For the full step-by-step with every course detail, see our Mortairvent installation instructions.

How Much Rainscreen Do You Need? Coverage Table

Mortairvent 202 covers 200 sq. ft. per roll and up to 3,600 sq. ft. per 18-roll skid. The figures below use gross wall area. Add your usual waste allowance for openings, cuts, and corners. Project sizes vary, so use your own takeoff.

Wall area to cover	Example project	Mortairvent 202 needed	Mortairvent 203 needed
1,500 sq. ft.	ADU or home addition	8 rolls	12 rolls
2,500 sq. ft.	Smaller single-family home	13 rolls	20 rolls (1 skid + 2 rolls)
3,600 sq. ft.	Larger single-family home	1 skid (18 rolls)	28 rolls (1 skid + 10 rolls)
5,000 sq. ft.	Custom home	1 skid + 7 rolls	39 rolls (2 skids + 3 rolls)
7,200 sq. ft.	Luxury custom home or multi-home phase	2 skids (36 rolls)	56 rolls (3 skids + 2 rolls)

At the same wall area, Mortairvent 202 needs about a third fewer rolls than 203 because each roll covers 200 sq. ft. instead of 130 sq. ft. That means fewer rolls to handle and fewer seams on the wall.

Shop Mortairvent 202 – 18-Roll Skid (3,600 sq. ft.)

Which Rainscreen Should You Buy?

Buyer / project	Recommended product	Why
Residential general contractors and home builders running fiber cement lap siding	Mortairvent 202 skid	Up to 3,600 sq. ft. of wall per skid. The 1/4 in. gap keeps trim and window build-outs small
Custom and luxury home builders using cedar or other wood siding	Mortairvent 202, or 203 on high-exposure walls	203 moves about 3.4 times more air (54.5 vs. 15.8 cfm/ft.) to help wood siding dry from the back
Design-build firms doing ADUs, additions, and remodels	Mortairvent 202 rolls	Buy by the roll for smaller wall areas, with the same performance as the skid
Projects mixing siding with stucco or stone veneer	Mortairvent 202 for siding; DELTA-DRY STUCCO & STONE or DELTA-DRY & LATH for stucco and stone	Dörken designs DELTA-DRY products for absorptive claddings. See our stucco and stone veneer rainscreen guide

Bottom line: for fiber cement and wood lap siding, the Mortairvent 202 skid (3,600 sq. ft.) is the most efficient choice for larger jobs, and the Mortairvent 202 roll (200 sq. ft.) covers smaller additions and remodels.

Choose the Mortairvent 203 skid or 203 roll when wood siding needs more drying.

For stucco and stone sections, see DELTA-DRY STUCCO & STONE and DELTA-DRY & LATH, or compare everything on the Rainscreen category page. Ordering for multiple homes or a development phase?

Contact Spycor Building Products for volume quotes and lead times.

Frequently Asked Questions

Do you need a rainscreen behind fiber cement siding?

A rainscreen gap lets water that gets behind fiber cement siding drain out and lets the wall dry. Whether your jurisdiction requires one depends on local code and how your cladding is classified. Also check the siding manufacturer's installation instructions for requirements when installing over a rainscreen.

Is 6 mm thick enough for a siding rainscreen?

For most lap siding, yes. Mortairvent 202's 6 mm (1/4 in.) gap is tested to ASTM E2925 and drains 4.22 gpm per foot of width. Choose the 10 mm Mortairvent 203 when you want more drainage (7.01 gpm/ft.) and airflow (54.5 cfm/ft.).

How many square feet does a skid of Mortairvent 202 cover?

One skid holds 18 rolls at 200 sq. ft. each, for up to 3,600 sq. ft. of gross wall area before waste.

Does Mortairvent need a separate insect screen?

No. Its fabric flap tucks behind the mesh at the bottom and top courses to form a built-in insect screen.

How long can Mortairvent be left exposed before siding goes on?

The manufacturer rates Mortairvent for a maximum of 30 days of UV exposure. Schedule siding installation within that window.