Firecut joists in masonry

[Don P]

We removed the floor system in the old service station at work the last couple of days. I thought some of you might be interested in some of the details.

When joists are bearing on masonry they need at least 3" of bearing vs the typical 1.5" min bearing on wood. If the masonry continues on up to form bearing walls they also are "firecut". This is done so that if the floor collapses in a fire it doesn't pull the walls and whatever is above down, slowing the collapse and in our case also preserving the fire separation between the room we were in and the room on the other side, containing the fire. These walls run on up through the roof to form parapets above the roof all to divide the building into fire containment areas, technically type 3B construction, nothing combustible exterior, fire separation into containment areas. The B there means unsprinklered, A would be sprinklered. Typically most of us work in VB (5B), combustibles anywhere.

This is a couple of firecut ends and blocking facing up, floor top to the left. Notice the sloped cut to insert into the masonry, and the decay and termite damage, hence the 3" callout. This is from around '46




This is a joist in a joist pocket, notice the termite trails up the walls




More of the fun from in there, this is the underside of some of the diagonal subfloor, multiflora mold under there. No ventilation and damp, this was the "wet" side of the station. Oak flooring and subfloor broke short and brash, the crowbar often breaking thru the subfloor. We'll pour a rat slab in that crawl which will allow conditioning the crawl and will hopefully keep the groundhog out, he had tunneled under the footing and up into that space.





The joists were nice mostly heart pine, predate grading. My partner said this is nice wood, and it mostly was nice looking, till we started grading as we removed. Grading is not a bad thing, it was generally from better trees than I get nowadays but much of it fell below #2 and it was overspanned, I'll be putting in a midspan girder and piers to get us up to modern 100psf commercial loading, it wasn't up to 40psf as built.

The BO should have just gotten to work, annuder day begins

[samandothers]

Interesting, thanks for sharing.  Termites traveled a good ways to get that meal.  Is that distance less than code for wood above grade? 

[Don P]

The short answer is joists closer than 18" and girders closer than 12" to dirt have to be treated, this is actually in the protection from decay section.

We are around 32" above the dirt now that we've leveled the dirt under there. aside, we had asbestos abatement done last week, the friable stuff was on old boiler piping and a good bit had fallen onto the dirt under there. Although it was all done by pros and monitoring, clearance testing etc, I still picked up some as we removed the floor and I know it was on the exposed dirt. With the floor in place he was belly crawling, he did as good as could be done under the circumstances. We stayed in respirators until we had buried all of that soil. I then suited up and went after the old piping, it'll be out by tomorrow. The lab clearance report came back with 1 fiber, allowable would be 5, we're going for 0 if possible by opening and we'll get there.

Back to termites, we've got tunnels up piers in another section 5' above grade before they entered wood so any reasonable height distance isn't going to deter them. The longer read is sections R317 for decay and R318 for termites here, this is the IRC (residential) which I navigate better but the IBC is basically the same here;
https://codes.iccsafe.org/public/document/VRC2012/chapter-3-building-planning

Prior to pouring or final covering the dirt we'll have the soil treated and go play in the woods for a week. If we condition the basement and crawls then I need to insulate the foundation walls, something that concerns me with the termite pressure. We will terminate the foam about 1.5" below the sills leaving an inspection gap which must be monitored. That is another reason for the rat slab, people don't crawl on dirt willingly, make it nice and well lit and they are more likely to check under there. I just bull floated the one under our house and it is a nice dry space but is rough to crawl on, I learned to at least quickly trowel those surfaces smoother.

I kept playing phone tag with the BO so he dropped by on his rounds today and we walked through. I'm about done with the discovery phase and have been coming up with solutions to run by him as we work so we got to talk and adjust those to make everyone happy. The building was built as a IIIB but over the years a wood framed addition and deck were added on one side and a wood truss canopy out front over the pumps. I may add another wood deck at the rear to give seating and remote egress. Those are all combustible exterior elements that violate a 3B so I asked if we could change to a VB which I can due to the fact that we have plenty of room around us. It won't cause any other buildings problems but I also asked him to alert me whenever I am crossing from a 3B to a 5B, I want the building to be easily converted back to a 3B in the future so I won't put elements into the building that would make it hard to do that for a future owner. That all falls under "building type".

Occupancy is another concern in a commercial building that applies to structural requirements, egress, fire areas and sanitary requirements. He will allow us to call it a B, business, max occupant load 50. The size of the building allows it to be an A2, assembly, max occupant load 225, a restaurant or tavern would be examples that apply to this building and would be easy conversions. 95% of businesses fail within 5 years so what's next is something to think about, so is current budget, a fine line to walk, don't break the incoming business but also set it up to grow or change easily. Structurally this building is the same in either but the bathrooms move essentially from 2 to 4 holes and fixtures. Aside from cost it eats up room, if they are sexed bathrooms then each needs an accessible stall which is pretty large, so that is an ongoing discussion.

Mostly TMI but a look at another part of construction.

[nativewolf]

Good stuff, always appreciate the informative threads.