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CMU Flashing at Floor Lines


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Yes. The pictures are split face but I am using those only as an illustration for my question. The building I will inspect is a 2 yr old smooth face CMU but is having severe moisture intrusion per my client. I suspect it is single wythe.

I have read that wall flashings are needed at the outside bearing floor joists but I'm wondering if a continuous flashing at the floors is doing more harm than good for wall drainage.

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This is a tremendously misunderstood area. The codes are both right and wrong. Chicago masonry code doesn't say anything substantive. The generally agreed on "code" derives from MIA and BIA with interpretive allowances depending on all sorts of stuff.

We know that floor flashing both helps and hurts various aspects of wall performance.

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Even when flashing is present, we find inadequate laps, no end dams, no back dams, or the flashing is so full of water ponds it's bellied downward in the block cores.

Installers terminate the platform flashing shy of the block face because they think it's ugly, but extend it all the way to the interior face....and neglect the back dam. They collect water and funnel it to the interior.

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Only one's that we've done. There are no flashing diagrams anywhere for this because it would take military drill team micro precision of the entire process with multiple trades all working as a team so they were assembled and flashing correctly. Doesn't happen. Can't happen.

None of these things have expansion joints, none of the mortar is compatible with the block, none of the flashing is done correctly because there isn't a once size fits all methodology for this stuff, and it's all very bad.

Single wythe CMU multi floor wood platform construction is inherently a mess. This particular diagram comes as close as anything I've found for how one might do it, but there are also problems with this method.

The 2nd page beam pocket detail outlines the problems. It's fraught with problems.

I think the better way is forgo beam pockets altogether and hang the joists on a ledger or similar support. That way, flashing can be installed with necessary dams to prevent interior migration, the top can be vented and the wall dried out, and the wood isolated from the masonry with a capillary break.

Problem is, there's about 15,000-20,000 of these suckers already built.

Download Attachment: icon_adobe.gif CMU Flashing Diagrams - Masonry Urbanus.PDF

1431.31?KB

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Only one's that we've done. There are no flashing diagrams anywhere for this because it would take military drill team micro precision of the entire process with multiple trades all working as a team so they were assembled and flashing correctly. Doesn't happen. Can't happen.

None of these things have expansion joints, none of the mortar is compatible with the block, none of the flashing is done correctly because there isn't a once size fits all methodology for this stuff, and it's all very bad.

Single wythe CMU multi floor wood platform construction is inherently a mess. This particular diagram comes as close as anything I've found for how one might do it, but there are also problems with this method.

The 2nd page beam pocket detail outlines the problems. It's fraught with problems.

I think the better way is forgo beam pockets altogether and hang the joists on a ledger or similar support. That way, flashing can be installed with necessary dams to prevent interior migration, the top can be vented and the wall dried out, and the wood isolated from the masonry with a capillary break.

Problem is, there's about 15,000-20,000 of these suckers already built.

Download Attachment: icon_adobe.gif CMU Flashing Diagrams - Masonry Urbanus.PDF

1431.31?KB

Question: Is composite wall the same as cavity wall except cavity wall has an open space between block and brick?

Marc

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Ok, right.... I never look at those.....I was referencing the 2nd page with the single wythe CMU assemblies.

Yes, composite wall is a "grouted cavity wall". I've never seen one and don't know why anyone would build one.

Like Mike, we've all been trying to find references for single wythe multi floor wood platform construction. This is one of the few references we've ever found.

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If there isn't a code for these things, and no uniform set of standards, then isn't the engineer that stamped the plans responsible for those details?

http://chicago-il.elaws.us/code/coor/co ... c13-40-135

In my entire career, I, nor anyone I've ever known, has seen the details that this portion of the Chicago Building Code requires. Never.

There is no prescriptive code. It's all conjecture and interpretations by the broad assembly of trades, unions, CCBD, architects, and engineers. On the big stuff downtown, it's pretty good. In the residential end of it, down in the weeds where I live, it's a complete and total can of worms.

Steve Hier and I went down years ago and tried to get the codes written intelligibly. It went nowhere over several months time.

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This was a 2 yr old flat face single wythe CMU. Flashings were visible where I expected them and this is a rare time I have seen visible end dams and expansion joints, although some of the end dams were confusing. See photos.

The building was leaking inside but all the leaks I believe were from water penetration at the back deck ledger bolts, and water running down the walls from poorly installed parapet coping.

And there were a bunch of roof leaks beneath a whole roof deck sitting directly on the roof.

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Those ledger bolts are a hole straight through the wall. There should be a horse collar or some kind of flashing to seal the bolt hole, but there never is. Any time you see those steel ledgers and bolts, expect leaks.

Coping is always screwed up and leaking.

The roof deck leaks aren't hard to figure out. Take up the deck and you'll find them.

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