Wood Joists in Brick Masonry Pockets 1

[bookowski]

In this area typical brownstone/rowhouse construction used 3x dimension lumber pocketed into brick masonry 'party walls', walls that are shared by both neighbors and therefore not exposed. These joists were bricked in tight, no air gap, and had a fire cut at their ends.

When doing joist replacement, new joists into existing pockets, the question has come up about protecting the ends of the joists. My interpretation/understanding about wood in contact with masonry was that this applied to exterior walls or walls likely to get wet. These are essentially interior walls as they are shared by a neighbor. I've had some suggestions to wrap the ends in a membrane - but that seems like a lot of work and I am not confident they'd get it well sealed anyway.

The existing joist ends are typically fine in these conditions and have lasted 100+ yrs, unless there was a specific water leak/issue at a particular location.

Any code reference/guidance on when you are required to use treated wood, or to protect the ends? We could leave the pockets open but I don't like the way that feels - I prefer some connectivity.

 

[EngineeringEric]

I am thinking you may have a fire issue. I believe party walls typically have a 2 hour rating (1 hour at a minimum). Depending on how much brick you have on either end of your joist will dictate what the assembly rating 4"=1hr i think (confirm in IBC)...

 

[woodman88]

Per the 2009 IBC section 2304.11 Wood floor joists would need to be more than 18" from exposed ground to not need PT treatment. Per section 2304.11.2.5 only wood girders ends would need an air gap for ends entering masonry walls.
Not sure if I would allow the use of untreated wood joists in those masonry pockets. But, maybe the calculations for the joists would look good to me.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[bookowski]

Thanks woodman, very helpful. I checked the definitions in IBC and didn't see 'girder' but I assume they are using this in the traditional sense - so wood members supporting other framing (beams, headers etc) would need air gaps but not the typical joist. Any idea why the differentiation?

If it was a new building I wouldn't like the detail - but after seeing them strip out joist after joist with a perfectly sound 100yr old end I'm more confident in it for this application.

 

[SLTA]

Out of curiosity - what triggered the joist replacement? Meaning why strip out old joists if they're working just fine?

 

[bookowski]

Wealthy client bought the building, wanted everything level and new - he had very strict deflection/vibration desires. 100% removal of existing except for the three exterior walls (4th wall was also removed). Pretty typical here. That is why I get to see the old joist ends but there is no problem with them.

 

[woodman88]

I would assume that the fact that girders typically supporting larger floor/roof areas would trigger the added safety factor of the air gaps. But have not looked into it.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[XR250]

I have never seen a problem with wood rot on interior masonry - except in crawlspaces that were not vented properly.

 

[msquared48]

If it worked on an interior party wall where no moisture penetration was possible, I would say to do it again. (If it ain't broke, don't fix it)

However, if the pocket is an exterior masonry wall exposed to the weather, I would provide a 1/2" air gap at the sides, top, and end, and use pressure treated joists for that span. I would also look into providing a small metal bearing plate if it was practical to do so.

Re3membver to provide the thru-the wall ties to the joists if embedded tie straps are not there already.

Mike McCann
MMC Engineering