Wrap and strap cement board strapping
My timber frame wrap and strap has 2 1/2″ of xps on the exterior and I’m beginning the 4″ strapping soon. Being built on a slab-on-grade I won’t be starting my wood siding at grade, but 24″ above. That 24″ space from grade to siding will get a 10″ stone veneer. With masonry and moisture considerations in mind I won’t be running the wood strapping down to grade, but will terminate it at the 24″ above grade mark. I was thinking I’d either rip cement board down and use it as the strapping behind the stone work (with diamond lath attached for backer), or use the cement board as a continuous 24″ backer.
I’d greatly appreciate your thoughts and input. Thanks
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Replies
Daniel,
Does your slab-on-grade foundation have vertical rigid foam at the perimeter? If so, is the foundation perimeter insulation also 2.5 inches of XPS, just like the exterior insulation on the timber frame?
The usual detail is to include metal Z-flashing at the horizontal seam between the siding and the foundation.
The perimeter xps on the slab footing and the xps on the wall frame match up evenly. That seam is sealed and taped. That seam will then be behind the veneer wall.
Daniel,
Why do you need strapping behind the stone veneer?
How thick is the stone?
Is the stone self-supporting, sitting on a footing? Or is it somehow adhered to the foam or the concrete behind the foam?
The strapping is to fasten the foam tightly to the insulation frame behind it. It's a wrap and strap enclosure and I'm not comfortable relying on the plastic capped nails alone to hold the foam to the frame. There's no concrete behind the foam. The foam is installed on the exterior of my insulation frame which is to the exterior of the timber frame. The foam gets 1"×4" vertical strapping at each stud. I'm not comfortable with wood behind the stone wall (which is self supporting on it's own footing) so at the point where the stone wall terminates I'd like to substitute the 1x4 wood strapping with cement board either ripped to 4" like the strapping or continuous.
Daniel,
Maybe I'm being dense, but I could use a sketch.
I understand your timber frame, I think. What I don't understand is the stone veneer (which, as I understand the situation, is adjacent to your concrete slab-on-grade foundation). If the stone veneer is self-supporting on its own foundation, why do you need the strapping again? Isn't the foam attached to the concrete slab with TapCons and big washers?
The stone wall extends 24" above the slab footing, which only extends 4" above grade. As a slab on grade the foundation is almost entirely below grade, save for the 4". The stone wall is primarily to bridge the space from where I'm comfortable beginning my wood siding- I don't want to run the siding right down to grade, and without a proper foundation wall abive grade the stone veneer will offer that higher level of resistance to rot. I'm familiar with exterior masonry issues in cold damp climates like mine (my original design was a complete stone veneer on the house exterior) but the trade off for a couple feet of stone seems worthwhile to wood running down to grade... or maybe it's not. I don't know. Will the masonry absorb moisture and dry to the exterior with no issues. Is it a good idea to use 4" cement board strapping so that there's an airspace behind the masonry.
Daniel,
Is it a stemwall-plus-slab foundation or a thickened-edge slab foundation?
With most slabs, you can lower the grade more than 4 inches below the top of the slab.
It's a thickened-edge. I could lower the grade a bit more but I'd only gain a few more inches at best and the siding would still be too close to ground for my comfort level. I'm just wondering if there's moisture issues with my plan that I'm not seeing.
Daniel,
The stone veneer will tend to be damp if it is in contact with the soil. I would probably use pressure-treated furring rather than ripped cement board. Horizontal Z-flashing is needed, of course, as a capillary break to separate the damp stone veneer from the wood siding above. Otherwise, your plan should work.
Why the pressure treated instead of cement board? The cement board's life will likely be easily as long as the treated, and it probably wouldn't absorb as much water as the wood. As a stone mason by trade I'm always a little more than hesitant to use any wood, treated of not, directly behind masonry where moisture might be high.
"Maybe I'm a little dense, but I could use a sketch."
I have this thought often. When people post their questions, it's often regarding an issue that they've thought about for a while, so the situation is clear in their mind. For others considering the problem/situation for the first time, it takes a little longer to wrap their head around it. Perhaps it's just me. A sketch can be extremely useful. I also find that even simple conceptual sketches (no CAD required) help in both explaining and gaining understanding. It'd be nice if we could encourage posters to do this if possible, even if their drawing skills are basic.
This is intended to be a general comment, in no way a criticism of this thread's OP.
Daniel,
It's your house, so you should use what you want. Here are my thoughts: There are a variety of manufacturers of products called "cement board." Some may allow contact of their product with soil, but most don't. You can check.
If you use pressure-treated lumber for your furring strips, then you can fasten something to the furring strip with a screw if necessary. You can't do that with cement board.
Another alternative might be plastic strips of something like Trex.