board-n-batten rain-screen questions
considering everlast board-n-batten siding.
manufacturer says it acts as a rain-screen, so it can be applied directly to sheathing.
there is about 1/8″ gap behind the product, so sounds legit at a glance.
so couple of questions:
(a) if applying to a thick-wall assembly what are the implications of screwing directly into sheathing?
(a1) would there be a significant thermal bridge with stainless-steel screws?
(a2) is there a concern over penetrating wrb wrap with screws?
(b) if applying over an exterior semi-rigid mineral-wool assembly would standing water on horizontal furring be a concern since the cladding has an 1/8″ clearance and the mineral-wool is semi-permeable?
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Replies
buildzilla,
There is a hierarchy of rain-screens depending on how many of the characteristics of one a system includes. At the top would be a vertical cavity that is vented top and bottom, which is deep enough to to allow drying and a clear capillary break. The other end of the spectrum would be a dimpled WRB. The Everlast siding falls somewhere in the middle, so depending on how important a rain-screen is in your assembly, and how it is installed, it may or may not meet your needs.
a) It is fine fastening it to the sheathing, as long as your sheathing is adequately thick (1/2" or more).
a1) If it is only attached to the sheathing, not penetrating an insulated layer, there will be next to no thermal bridging from the screws. If you are attaching either the siding or battens through a layer of insulation, there will be some, but it is inevitable, and occurs in every assembly with exterior insulation.
a2) Because the siding gets fastened through a point where it is in direct contact with the WRB, the concern is minimal.
b) No, practically you are fine. Here in coastal BC it would not meet our code, but neither would attaching it directly to the sheathing.
If you are considering installing board and batten Everlast siding over external mineral wool, I would consider using 3.5” mineral wool batts. You could rip 3.5” wide strips of 2” foam board and install 2x4s horizontally over the 2” foam strips. Install them 16” apart and you could install 16” mineral wool batts horizontally between the 2x4/2” foam furring. You could then install a sheet wrb over this assembly.
Just an option I have considered to save cost over rigid mineral wool.
that's pretty clever kyle, kind of a spin on a larsen-truss
Yup, same idea. Although on second thought, you would want to space them 18” apart, so that batts for 16” 2x lumber would fit.
i've got a little wrinkle with the everlast tho in that they want the strapping to be 14" oc, always something am i right? :)
Yeah but I think they are assuming a thinner furring strip. With a 3 1/2” wide furring strip I wouldn’t be afraid to put them 18” apart.
+1 I've done this for an over-roof, cheap, simple and works great.
If the 2x is horizontal, there is no need for foam at all. I've done the math on that type of assembly and it is pretty close to the same R value and continuous rigid foam without any thermal break on the exterior studs. The thermal bridge where the interior and exterior studs cross is so small that it barely budges the assembly R value.
I hadn’t thought about that, but good point Akos. Did you install the studs on edge with some clips
kyle brings a good question wrt to your design, which edge of the 2x4 is in contact with the sheathing, the 1.5" edge or the 3.5" edge?
if the 1.5" edge, how do you fasten them?
This was for a roof, so the studs were toe nailed to the rafters bellow and anchored with hurricane clips at the walls.
For a wall, I guess you can do something similar but I would add in blocking to provide racking resistance. Anchoring the 2x down with some long screws or clips would be a good idea. Putting a screw through a 2x4 on edge is not fun but if you predrill even partially or use screws with a drill point it is much easier.