Flashing Single Wythe CMU Walls

[fm2000]

First Post! Thanks for any reply's!

Structure:
~ single-wythe 12" ACMU to 20' w/ 8" ACMU parapet to 24'. (ACMU ~ being split face block) 12" are load bearing walls, 75% of which are shear walls, top 6 feet or so, including parapet is grouted solid.

~Bond beam at top of 12" cmu and 8" cmu parapet.

Architect is requesting thru-wall flashing, within the 12" ACMU at RHC locations (grouted solid), thus a 4" ACMU with an 8" CMU on the inside. Some of which is within the bond beam.

Architect is requesting thru-wall flashing, within the 8" ACMU parapet (grouted solid), thus a 6" ACMU and a 2" Soap on the inside. This flashing is in some cases is 1 course below the parapet cap flashing!

Am I crazy for being opposed to this? In a solid filled wall, I have never have thru-wall flashing detailed. I know NCMA recommends against this.

Any thoughts?

 

[shobroco]

What is the purpose of the flashing? It only has a purpose in a two wythe wall or at the top of the parapet, below a masonry cap if there is one.

 

[concretemasonry]

shobroco -

Flashing at the base of a hollow CMU wall (6" or 8") is valuable when the narrower CMU is on a bond beam or a wider block that is grouted solid and it provides an exit for any moisture from above.

One of the befits is that a hollow, ungrouted CMU can function similarly to the classic cavity wall. That is one of the reasons for not arbitrarily grouting all cores, which is reflected in the NCMA suggestions. Any grouted cores do cause some interruptions, so they should be minimized, although some areas and designers allow the practice in the interest of speed and economy for the contractor.

Even in a cavity wall, it is assumed the outer wythe can allow moisture, but the cavity provides drainage and prevents the situation where wind pressures are negated by the gap, but a hollow ungrouted CMU provides a similar, but lesser benefit.

Of course, using parapet walls quadruples future problems.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[shobroco]

dik;

I agree with your scenario of moisture in hollow blocks, but that's not what the OP describes. The parapet is 8" & the flashing faces a soap with a 6" split-faced over it in the 8" thickness. Which side is the exterior? The last time I looked at a parapet, both sides were exposed.