4" CMU at Wood Porch

[T_Bat]

Hey everyone,

I've got a wood amenities center I'm designing with a wrap around wood porch. Normally I would provide a CMU pedastal to support the porch posts then span a wood girder between to catch the porch framing. The owner and architect want a stone facade below the porch and are using some lick and stick veneer. We've discussed provided a 4" CMU wall around the porch to a) provide a substrate for the veneer to attach to and b) support the porch framing. I envision laying a PT 2x4 on top of the 4" CMU wall for the porch framing to bear on. I'm not concerned about strength of the CMU wall, more detailing and any issues I may not foresee in construction. Has anyone used 4" cmu in this way? I need a way to anchor the 2x4 sill down to the wall. Do I grout the wall solid or can you make a 4" bond beam? The wall may be 2'-3' feet tall above the foundation and probably a maximum of 2' above grade.

 

[jayrod12]

ugh, 4" cmu just seems so piddly. I'd be arguing for 6" CMU at a minimum so you can actually grout it and get a nailer fastened to it. Provided there's no uplift, you could just use tapcon screws or the like into a grouted bond beam (if you went 6" CMU)

 

[T_Bat]

That's a good thought. I agree they are piddly but everyone is pushing for cheap. Let me see if I can get them to change. I can't imagine the cost will be that much different, although my sense is that they will already be surprised we need CMU at all...

 

[jayrod12]

You could do a PWF (PT) stud wall as your backup. Then all you'd need is a strip footing, which you need for the CMU anyway.

 

[T_Bat]

Would that be an issue since part of this wall will be below grade? I know wood foundation systems exist and have a friend who built his house almost 30 years ago on one... He mentioned the wood required a special treatment. Would typical PT take care of this?

 

[jayrod12]

No that's why I mentioned PWF. Look into PWF foundation walls.

Alternatively, pour a concrete upstand on your foodting to t.o. grade.

 

[BridgeSmith]

If you opt to frame it with PT lumber, consider using cement board (durock, wonderboard, etc.) as sheathing attached to the framing. Possibly embed the CMU blocks below grade, with PT framing from the grade line to the porch, and face the CMU and PT framing with the cement board. With the cement board attached to both the CMU blocks and the framing, attaching the framing to the CMU becomes unnecessary.

 

[T_Bat]

Sorry Jayrod - wasn't aware PWF stood for permanent wood foundation. Broke a cardinal rule in not understanding before trying to be understood. I'll also bring up the PWF. How common are these in the Southeast US (Middle TN to be exact)?

 

[jayrod12]

How common are these in the Southeast US (Middle TN to be exact)?

I'm north of the 49, so unfortunately no idea. Around here they're common enough.

 

[T_Bat]

Gotya - just spoke with the architect. PWF is a no go. He isn't comfortable with it and since I have never personally done it I'm not prepared to die on that hill. I'll let you know what happens with the CMU.

 

[hokie66]

4" CMU is not a structural material. Use 6" if masonry is the way you decide to go.

 

[jayrod12]

To me that's unbelievable. It's a "WOOD amenities centre" why not showcase what wood can do for you.

Anyway, not my monkey not my circus. Good luck.

 

[T_Bat]

Now we are going to span girders between the pilasters to support the porch framing with a slight overhang. We are going to use the 4" masonry as a backup only under the overhang.

 

[masonrygeek]

While 4" CMU "could" be used in this application, most 4" CMU units are near solid and can't really be vertically reinforced or grouted solid. So bolting into the unit could be tricky or not possible. See the Q&A from NCMA's website about this topic:

http://www.ncma-community.org/topic/80-grouting-4-in-cmu/.

And how about a split face block unit instead of adhered veneer? Split face could give the owner the look they want and maybe make the wall thinner than a 6" block with 2" adhered veneer.

 

[dik]

jayrod... somedays you just have to shake the sawdust out...

Nie mój cyrk, nie moje małpy

Dik