Rain/ventilation batten thickness Cora-vent vs strapping
I am having problems with my fiberglass frame window and door trim details with a 3/4″ thick batten rain/vent screen. Here in New England 1×3 “strapping” is usually only about 11/16+ thick and WAS my original choice, however:
1. I am concerned about the “strapping” getting moldy in mountain climate (originally I was going to stain or prime all the strapping). EVERYthing gets moldy around here.
2. Strapping is not wide enough to meet the warranty specs for LP Smartside. They do not have a detail for battens over plywood sheathing (only 1×4 battens over rigid foam) and therefore probably will not be warrantee (least of my concerns).
3. MY biggest concern is the window and door trim details using the thicker battens. A 3/8″ Cora-vent Sturdi-Strip/SV-3 would work better.
I have 2 questions which I cannot seem to figure out despite searches.
A) is the 3/8 gap enough drying potential for PGH style double stud wall with COMMERCIAL tyvek (seems to lie much flatter once fastened).
B) Who has used the Cora-vent system? did you just add extra strips where needed at siding joints?
c) Do plywood battens hold up over time?
I am in Climate zone 6 NH
10.5″ deep cavity with dense pack cellulose,
Rain/vent screen ? thickness with top and bottom vents.
Commercial Tyvek (awesome product, lies flatter)
1/2 cdx sheathing (air barrier detailed),
double stud wall, drywall
Fiber-tec OR Alpen fiberglass windows
Thanks for any advice from those who have used the Coravent system especially
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Replies
Hi,
I used Coravent SV-3 and Sturdi-strips on my NH build 3 years ago. Installed over 15# felt and SIP panels, vented high and low. Easy to work with, I fastened in place with 1" staples, then cedar clapboards over with 2" stainless RS nails. Easy to use and my windows/trim detail accomodated the extra 3/8" with no problem. Worked great- but not cheap and was a PIA sourcing locally. Building a barn now with verticle pine cladding and I'm using horizontal 1x3 strapping- cheaper, faster, and perfectly fine for the purpose, same windows (Marvin) are furred out.
I can only answer question A, quoting Building Science Corporation:
"Small gaps (1/8” or 3 mm) can allow a small and potentially beneficial amount of ventilation flow, but larger gaps (over 3/8” or 10 mm) are usually required to ensure significant ventilation."
Source: https://buildingscience.com/documents/digests/bsd-013-rain-control-in-buildings
dirkgently,
- Plywood furring works well. We include a cavity because it is a good space to dry things, and that includes the furring. If you have doubts, you can use PT strips.
- When you measure the depth required for attachment over foam, you just use the thickness of the furring. When you measure that same depth on plywood, you add the two thicknesses together. If that still isn't enough, you can locate the furring over the studs behind. Practically, the cladding just needs the furring and studs for attachment.
- 1/2" or 3/4" is ideal, but 3/8" gives you most of the important benefits of a rain-screen, and functions well.
- I would reserve Cor-a-Vent for the bottom of the cavity, although even there I prefer perforated flashing like this: https://www.menzies-metal.com/metal-flashings/perforated-j-channel-rain-screen-low-back/
I found this thread from 37th search engine try. It is excellent and has lots of great input from Malcom. Wish I found it earlier. https://www.greenbuildingadvisor.com/question/longevity-of-battens-for-rain-screen
Thanks for the replies.
I have done the math on costs for a linear foot in 2024.
.51 cent/foot Coravent sturdi strip (pro: no mold, con: 1.5" wide)
.33 cent/foot 1x3 strapping (pro: wide siding nailing, Con: mold factory?
.15 cent/foot 2" wide strip 1/2" cdx (pro: use up scraps, Con: mold factory + durability?+ below
.20 cent/foot 2.5" wide strip 1/2 cdx (same as above + Con: need to rip strips.)
My current thinking is to try 1/2 cdx on 1 wall and see if it has any obvious problems.
I wish there was 1/2" Sturdi strips for xtra drying potential.
Since the backside of LP siding is bare wood.....I suppose my mold concerns on furring strips is kinda dumb...ha ha.
Thanks for the replies again.
I hope others find the info useful
dirkgently,
"I suppose my mold concerns on furring strips is kinda dumb..."
No it's understandable. We get mold and moss on our siding here too - and sometimes on the underside of roof sheathing. Surprisingly the one place I've never found it is in rain-screen cavities.
Home Depot has 1x2x8ft furring strips at $1.26 in bulk by me. Saves having to rip plywood down. For reference - 1x3 are $1.89.