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Allowable cmu wall height during construction

Allowable cmu wall height during construction

Are there any ACI or other code limitations on how high cmu walls can be built in one day?  Obviously an 8' high wall is not an issue, but what about 10, 15 or even 20'?  Will the mortar have issues?    

RE: Allowable cmu wall height during construction

I don't know if there are any limitations in ACI-530 but in my specifications I do not allow more than 10' to be built per lift.

RE: Allowable cmu wall height during construction

Generally the only height limitations are those imposed by necessary bracing for wind.  It is usually assumed that masons will build horizontally at a much faster rate than vertically, as this is how alignment is maintained.  Given that, the load on the mortar is not substantial, and by the time they work back to the next couple of lifts, the mortar has set sufficiently to support the relatively low dead loads.

This could conceivably be an issue if you have a large crew and a short wall.

RE: Allowable cmu wall height during construction

You can get your temporary/construction design wind loads here:

Link to ASCE/SEI 37-02


RE: Allowable cmu wall height during construction

Who is responsible for bracing the wall during construction?  I would have thought it would be the masonry subcontractor or the general contractor.   


RE: Allowable cmu wall height during construction

There is a code you're looking for is, "Standard Practice for Bracing Masonry Walls under Construction." (BMW)

When you're constructing CMU walls over 8', wind becomes a factor as stated previously.  A masonry block wall can be constructed up to 8' in winds up to 35mph winds during the initial period.  The initial period in the first working day and the intermediate period is any time after the first working day until all structural elements are in place as designed.  Say you were constructing a 21' wall, 8" 125psf CMU's w/ S type mortar.  From BMW, T4.2, the max height is 14' for the initial period, by the end of the day a brace would need to be placed at a height 11'-4," BMW TA1.  This table also states that the max unbraced height is 5'-4," 14'-11'-4" = 2'-8", less than max. ok.  The remainder of the wall could be built the next day.  There also needs to be a restricted zone that must be evacuated when the winds exceed 35mph.  

To answer your last question, a Masonry Contractor w/ some substantial experience could use the BMW.  If it's not stated in the subs contract the they need to have a bracing plan, that it's up to the GC to provide a safe work zone for all that enter the site.

RE: Allowable cmu wall height during construction

fjriii...some states have safety criteria that are more stringent than the "Standard Practice for Bracing Masonry Walls Under Construction".  I believe Michigan and a couple of others have criteria that fall under their construction safety laws.

RE: Allowable cmu wall height during construction

The maximum height of masonry wall construction in the UK is approx 1.5m per day when using cement gauged or hydraulic lime mortar.
This is to safe guard against the squeezing of fresh mortar and minor disturbances when setting which can lead to a rounded profile to the hardened mortar and reduced bond at the ends of the units.


RE: Allowable cmu wall height during construction

I am not worried about the bracing aspect, but rather the vertical loads on the mortar.  Basically I have a residential client under the direction to "build the walls in a day" so would presumably have the crew sized accordingly.  Single story wall heights might get up to the 12' range.

RE: Allowable cmu wall height during construction

No problem with the mortar on a 12' high wall from a strength standpoint if there is temporary bracing until some diaphragms are installed unless it is a cantilever design.

Mortar is not a major factor in the strength of the wall assembly since the major factor is already at 90% to 95% of ultimate.

Here, 9' to 10+' basements are commonly built daily. From an appearance standpoint, you must make sure they do not tool the joints too quickly. It is very similar to grouting where 8" to 11" slump grout is required so the units can absorb the excess water from the mortar quickly, but the load speeds that up and provides stability.


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

RE: Allowable cmu wall height during construction

The other thing to be cautious with is limiting your lift heights. My faith in the average masonry contractor getting the solid grouted cells properly consolidated goes way down above 10' wall heights. So if you end up letting them build up to 12' in a day, I would limit them to using two 6' lifts when they grout, so they can consolidate the cells properly, and maybe even provide a mid-height clean-out for inspection (keep 'em honest).

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