Hi all,
I’ve read some excellent threads on rain-screen siding installation, but still have a few questions. I plan to cut 1.5″ x 3/16″ cedar furring strips to run vertically beneath the cedar bevel siding.
– Bevelled cedar siding is easily available, but not Dolly Varden (bevel w/ shiplap edge). Is it worth hunting down the latter?
– The siding needs furring strips at the ends (probably wider than 1.5″), so these furring strips would run beneath the trim as well, but it would seem that the trim would not then be vented (if one wide strip is used), or the vent channel would be very small (if one narrow strip is used beneath each edge of the trim), since the trim piece is not much wider than the furring strip. Is there a better way to do this?
– What is used to keep bigger bugs and very tiny bats out of the space between the sheathing and siding? I would think something like roof ridge vent material would work, though it is a little too thick.
– Should the siding be run up under the inside edge of the soffit so that the top of the vent space is protected from the same bugs (and very tiny bats) kept out by the ridge vent stuff at the bottom?
– Should any flashing be used at the bottom edge of the sheathing to prevent wetting from ground splash?
Thanks ever so much,
Scott
Replies
I'll take a stab at a few of these. First off - 1/2" treated plywood ripped into strips makes for a cheap and effective rain-screen furring strip.
1. If you're buying enough, most yards will mill whatever profile you want. Dolly Varden isn't necessary for a rain-proof beveled treatment, but if you want a flatter look without going to T&G, it's a nice alternative. If you don't care, regular square edged bevel is going to be a bit cheaper.
2. Furring strips should all run vertical, but they aren't limited to running along the studs. Add an extra strip on either side of windows for the trim. There should already be a strip that is running along the king trimmer for the butt of the siding run. As long as the distance between vertical furring strips is more than a 1/2" or so, water will have no problem traveling down it as a channel.
You can cut very short (e.g. 2" wide X width of the course) shims to slip behind butt joints that don't fall on a furring course.
3. Cor-a-vent makes a bottom channel screen, although it's pretty easy to just staple a length of 6" wire mesh along the base of the wall (about 3" up from the where the base of the furring strips will go) BEFORE you nail up the furring strips. After the mesh is up, nail the furring strips in place and roll the mesh up and staple it over the front face of the furring strips. Done.
4. Your call - some folks run it up flush to the soffit to keep bugs out, and some folks go with a second screen and opening, which creates a "pressure equalized rain screen" system. I cannot speak to the relative effectiveness of the two.
5. You should have enough clearance from the ground to where you don't need any additional flashing. Anything short of 6" clearance to wood siding is asking for trouble.
Westcoast sent me a very nice pdf guide to rain screen standards for BC, you should be able to search it out on this forum.
By the way, steelhead fasteners makes collated SS nails, which are expensive, but well worth the insurance - especially on stained cedar siding.
-t
I forgot the most important question.
Is a rain-screen siding installation necessary/worthwhile/excessive for the Chicago area? This is a bump-out containing a breakfast area and closet for the house. It faces west, the source of most of the storms. The west exposure is 11' w x 13' h. The north exposure width is about 6' and the south exposure is about 3'.
If that's all you are doing and where you are doing it I wouldn't bother with rainscreen. Carefully wrap and detail any joints or openings with paper, tape and peel and stick, make sure to back-coat your cedar. Doing a good job of conventional siding installation makes rainscreen in most climates un-neccessary. You'll notice all the replies so far have come from those of us who live in coastal BC where using rainscreen isn't optional.
Scott,
check out Benjamin Obdyke's Home Slicker, designed for creating a rain screen on sidewalls, they have a similar product for wood roof shingles as well, also available with Typar integrated into the rainscreen.
Geoff
What is used to keep bigger bugs and very tiny bats out of the space between the sheathing and siding? I would think something like roof ridge vent material would work, though it is a little too thick.
I use leftover corregated ridge vent material with great success.
I use doubled strips of 30# felt as the firring strips. Cheap, easy to handle, durable and no sawdust.
A La Carte Government funding... the real democracy.
All the literature I've seen has the cavity at 1/2" minimum to be effective. Less than that and you end up with bridging between the siding and paper as well no air space for drying.
In a humid climate you want more air space for drying. In a relatively dry climate you just need a capilary break. 1/32" is enough in that case--like Chicago (Op's location) or New England.
I'm curious as to where you get the 1/32". I've never seen any rainscreen system published with anything close to that as an airspace. Unless you were using one of the sheathing systems that do not require paper or wrap there is no way you could avoid bridging and capillary action. The main cost component to adding rainscreen to a job is the labor. Why spend the time installing an in-effective product?
My mistake, should have said 1/16". From a Joe Lstiburek seminar summarized here: http://www.buildingscience.com/documents/information-sheets/3-water-management-and-vapor-control/drainage-plane-water-resistive-barrier/?searchterm=drain screen
Right, but we are are talking about two different things. Drainage planes, which already exist behind beveled siding, can be as simple as providing two layers of building paper (which for us us is the code minimum). The elements in this assembly are all touching each other at least intermittently so capillary action is still present in wind driven conditions, and I don't see how adding intermittent strips of #30 building paper would add significantly to its effectiveness.
Rainscreen are another animal altogether. There is a significant literature around their construction which goes back some 25 years and has accelerated in volume recently. While I don't pretend to be an expert, I have spent quite a bit of time exploring it and as I say have never seen anything suggesting they can be effective with less than a 1/2" gap.
Good point regarding the proper terminology. A proper rain screen does allow space for air movement and drying. In your location I wouldn't skimp on such a detail.
For those of us in locations where it's relatively dry as often as it is wet, while a rain screen is still the best way to build, it's usually considered overkill. Homeslicker does have some popularity, and we've been using Tyvek's "drainwrap" lately for a similar effect. You'd be surprised how much difference a tiny gap can make in letting the siding dry out.
I'm no great defender of rainscreens. As I said in my first post I wouldn't think of using them anywhere but here, and even in the PNW there was no widespread building envelope failures that couldn't be accounted for by shoddy design and poor building techniques. Properly detailed conventional walls work perfectly well - and properly detailed walls include drainage planes.
My rather repetitive posts have tied to make the point that if you are going to the time and expense of building a rainscreen you might as well include the elements, such as a sufficient gap, that distinguish it from a properly built conventional wall.
OK... do it their way.
I would too if I were in the rainforests of the PNW.
But I ain't, so I won't.A La Carte Government funding... the real democracy.
Fair enough, but my point was why do it at all? Rainscreen is a building technique developed to combat building envelope problems related to water infiltration in extreme climates. If it isn't necessary, why do it? If it is necessary, why do half the job?
"If it isn't necessary, why do it? If it is necessary, why do half the job?"
It makes the siding run more true over any sheathing imperfections, and...
in my climate, it is far MORE than the full job expected of the codes
and building standards in this area.A La Carte Government funding... the real democracy.
Benjamin Obdyke's "HomeSlicker" mesh product comes in 7 and 10 mm thicknesses (about 1/4 and 3/8"), the latter being to satisfy the Canadian requirement. Somewhere a study was done on how well a cavity would dry as a function of thickness, and somewhere along the line the Canadians settled on 10 mm as minimum for wherever a rainscreen was required. From my reading, most actual implementations are much thicker.