Thick foam board exterior insulation attachment
I live at the intersection of climate zones 5A and 6A in New Hampshire. I would like to add 8″ of reclaimed XPS insulation to the outside of a 2×4 wall with 1/2″ CDX sheathing. I plan to air and vapor seal the sheathing with a self adhering vapor barrier before applying two layers of 4″ insulation, w/ staggered seams. I have three questions:
1) Which is more preferable: a vapor permeable self adhered house wrap (such as Henry VP100, or Delta Vent SA) or an impermeable rubberized asphalt membrane w/ self healing properties for screw penetrations (such as Grace Vycor or Henry Blueskin SA), underneath the insulation? I am hoping as well to use a fluid applied weather barrier for the window bucks, and the ones I’ve looked into seem to be permeable for the most part. Please note the answer to this question may also be impacted by my final question regarding permeability of the house wrap water control layer on the exterior of the insulation, under the siding.
2) I recently saw a video from a Youtube channel “Ecohome”. Here is a link to the video:
At the 7 minute mark the presenter details their strapping method, and I’m wondering if this approach is viable when using layers of XPS insulation, as opposed to rockwool. Their approach is to strap the 1st layer of insulation horizontally, securing the strapping with screws through the rockwool insulation to the structural framing of the wall. The 2nd layer of insulation is then applied and strapped, but in this case the strapping is secured with screws to the 1st layer of strapping and not to the structural wall framing. I should add that I will be using nominal 1″ white cedar ship lap siding. Also the walls are open on the inside, so I could add studs at 12″ on center if I wish (they are 24″ on center as built).
3) Once I’ve applied both layers of insulation I would like to add Tyvek house wrap or commercial wrap to the exterior as the water control layer/ drainage plane. I am contemplating using two layers, with the outside layer being a sacrificial layer for UV since I’ll be doing this work 100% on my own. I had planned to tape the outermost layer as well. I actually have two questions, one regarding placement of the house wrap in the sequence of layers and the second regarding permeability. I don’t know if it makes more sense to apply this layer behind the strapping the siding will attach to, or outside of it. It would certainly be easier to attach it on top of the strapping instead of under, but I know that defeats the rainscreen benefit I would get otherwise. Perhaps I could help that by using a drainage style stucco wrap? I am also unsure what level of permeability this water control layer should exhibit, and I realize if I double up the house wrap, I’ll decrease the permeability.
Thank you everyone for any help you can give me. This web site with it’s members and administrators has been invaluable to me in my self-education.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part