Pressure-Blocked Joists

[Gunnar Alquist]

Does anyone know if pressure-blocking is still allowed? I just ran into a (mostly) nicely constructed home addition in which, much to my surprise, some of the floor joists under an addition were pressure-blocked. I am probably going to recommend the use of hangers, but it got me thinking; I haven't seen these in anything built more recently than the '60s.

I couldn't find any specific code prohibiting, but...

I do have to say that it was neat to see.

[Jerry Peck]

Gunnar,

"pressure-blocking"

That's a new term for me - what is the difference between that and "blocking" between the joists?

Those joists look to be setting on the wood frame foundation wall wall, is uplift resistance required? If not, the gravity load should be addressed by the bearing of the joists on the wall.

We have uplift requirements, not all places do, I would suspect that California would as, when a structure 'bounces up' due to that shaky-earth thing you have, you don't want it to come back down in separate pieces (maybe "uplift" is not the best term, maybe just 'strapping together'?).

[Steve Payson]

"pressure-blocking"

That's a new term for me - what is the difference between that and "blocking" between the joists?


Here's a quick video: https://www.youtube.com/watch?v=TgJvQ3cwQYE

[Jerry Peck]

Here's a quick video: https://www.youtube.com/watch?v=TgJvQ3cwQYE

Interesting ... and when used in floor framing they are just blocks (blocking) according to that person ...

Still doesn't say why he calls them "pressure blocks" for stairs or how they are different than the blocks/blocking which has been used for a few centuries or so.

It's a new term I haven't heard before and was curious about ... now I'm wondering if it is like some other "new" stuff ... fancy "new" name for the same old blocking technique which has been used for eons?

Just curious ... even more curious now.

Seems to me that "pressure" blocks would not to be full height of the stringers ... wouldn't they?

But ... isn't blocking full height anyway?

[ROBERT YOUNG]

Interesting, is like some other "new" stuff ... fancy "new" name?
Here is another, homie.:p

Just pulling your leg.

New term to me as well. Instead of joist hangers it end blocks the joist?
Thanks Gunner.

[Jerry Peck]

Instead of joist hangers it end blocks the joist?
Thanks Gunner.

It may just be me and my eyes, but ... I see joists bearing "on" a plate, no joist hangers needed.

The blocking keeps the joists from rotating, some hangers do not even do that.

The main thing I see are what looks like some USP RT15s in that one photo. The are made for uplift, but will also (obviously) hold things together too.

[ROBERT YOUNG]

It may just be me and my eyes, but ... I see joists bearing "on" a plate, no joist hangers needed.

I can not see the plate.

The blocking keeps the joists from rotating, some hangers do not even do that. As well as keep the joist from cupping. Seen my fair share the past several weeks.


The main thing I see are what looks like some USP RT15s in that one photo. The are made for uplift, but will also (obviously) hold things together too.
Link please.

[Jerry Peck]

I can not see the plate.

See photos below.


Link please.

See photo below and http://www.uspconnectors.com/us/products/connectors/truss-rafter-tiedowns?gclid=Cj0KEQjwjoC6BRDXuvnw4Ym2y8MBEiQACA-jWTok3diglAPSn3J2nurQw7a99y3AtTDT1brcirXQ1ZcaAmI08 P8HAQ

[Mark Reinmiller]

I enlarged the photo and can't tell whether the joist sits on a plate. If not, then I don't see what hold it up.

I also have never heard the term pressure blocking. Much be a regional term.

[ROBERT YOUNG]

See photos below.



See photo below and http://www.uspconnectors.com/us/products/connectors/truss-rafter-tiedowns?gclid=Cj0KEQjwjoC6BRDXuvnw4Ym2y8MBEiQACA-jWTok3diglAPSn3J2nurQw7a99y3AtTDT1brcirXQ1ZcaAmI08 P8HAQ

Much thanks!

[Gunnar Alquist]

Sorry folks, I was out of town this weekend. Maker Faire in San Mateo.

Thank you for your responses. Very helpful. I should not have posted the second photo. Support for those joists was on the top plate of the wall. The first and third photos had the pressure-blocking

In the first and third photos, the joists are not supported from below. They are supported by nailing into one side of the joist, through the thickness of the joist and into the blocking on the other side of the joist. The blocking is then nailed to the original exterior wall framing on the other side (actually, the blocking is installed first, but you get the idea). The only real difference between pressure-blocking and joist hangers is there is no direct support under the joist (well, that an the number of nails used). The support for the joist is being provided by the shear value of the nails.

This was pretty common in home construction (at least out here in the wild west) in the early 1960s and prior. Metal hardware came along and most current carpenters have never heard of pressure-blocking. The term is a misnomer because pressure is not really used, just the shear value of the nails into the joists. I mostly see it in ceilings when the joist runs change direction, but ceilings do not need the same level of support that floors do.

I'm not sure about anyone else, but I will occasionally see something done so nicely that I begin to second-guess myself. "Well, it sure LOOKS professionally done..."

Anyway, here is a video about pressure-blocking on ceilings. Like I said, more common with ceilings. I feel better recommending corrections now that I have had the "what the heck is pressure-blocking?" feedback from most of you.

https://www.youtube.com/watch?v=RTCZeC6VmZA

[Mark Reinmiller]

Sorry folks, I was out of town this weekend. Maker Faire in San Mateo.

Thank you for your responses. Very helpful. I should not have posted the second photo. Support for those joists was on the top plate of the wall. The first and third photos had the pressure-blocking

In the first and third photos, the joists are not supported from below. They are supported by nailing into one side of the joist, through the thickness of the joist and into the blocking on the other side of the joist. The blocking is then nailed to the original exterior wall framing on the other side (actually, the blocking is installed first, but you get the idea). The only real difference between pressure-blocking and joist hangers is there is no direct support under the joist (well, that an the number of nails used). The support for the joist is being provided by the shear value of the nails.

This was pretty common in home construction (at least out here in the wild west) in the early 1960s and prior. Metal hardware came along and most current carpenters have never heard of pressure-blocking. The term is a misnomer because pressure is not really used, just the shear value of the nails into the joists. I mostly see it in ceilings when the joist runs change direction, but ceilings do not need the same level of support that floors do.

I'm not sure about anyone else, but I will occasionally see something done so nicely that I begin to second-guess myself. "Well, it sure LOOKS professionally done..."

Anyway, here is a video about pressure-blocking on ceilings. Like I said, more common with ceilings. I feel better recommending corrections now that I have had the "what the heck is pressure-blocking?" feedback from most of you.

https://www.youtube.com/watch?v=RTCZeC6VmZA

Apparently a west coast thing. They do so many different things with framing than on the east coast. Before joist hangers the standard practice here was to nail a continuous ledger to the wall and then toenail the joists into the ledger. This almost always included a 2"x 2" strip attached to the face of the ledger at the bottom and then the joists were notched to bear on that strip. In the old days the strip was often a 1x.

[ROBERT YOUNG]

Sorry folks, I was out of town this weekend. Maker Faire in San Mateo.

Thank you for your responses. Very helpful. I should not have posted the second photo. Support for those joists was on the top plate of the wall. The first and third photos had the pressure-blocking


Gunner,
No need to be sorry although I was scratching my head looking for supports and seeing joist fasteners in another image.

Hope you had an enjoyable time.

Regards.

[Jerry Peck]

Apparently a west coast thing. They do so many different things with framing than on the east coast. Before joist hangers the standard practice here was to nail a continuous ledger to the wall and then toenail the joists into the ledger. This almost always included a 2"x 2" strip attached to the face of the ledger at the bottom and then the joists were notched to bear on that strip. In the old days the strip was often a 1x.

That, or for a narrow hallway as shown in the first parts of the video - just toe-nail the 3 foot joists to the ledger ... but the main thing would be to cut out the drywall first (during construction, just nail the ledger up first) - all it has is the drywall load on those ceiling joists ... probably stronger with a 2x4 / 2x6 toe-nailed than the modern equivalent of metal framing studs installed horizontally as is done for a dropped hallway ceiling in metal framing.

Nothing 'pressure' about that blocking he is calling 'pressure blocking' - just a nailer block nailed to the the ledger and then the joists end nailed into the nailer block (the weakest nailing is end nailing into the end of the grain).

Would have been better to have just toe-nailed in 3-4 nails (two nail each side or two and one)

But I would never expect to see that for a floor.

As Mark said, a common way (at least that I've seen) is the 2x2 ledger nailed to a main ledger (which carriers the load to the wall framing) with the joists bearing on the 2x2 ledger and then toe-nail the joists to the main ledger.

Interesting use of a term which does not describe what it actually does, not sure why whoever came up with that term called it that ... but I (and others) learned a new term and a different way to do things (do things harder and likely end up with less load bearing capacity because of the end grain nailing aspect, and the fact that there are not very many nails visible in the blocking which actually holds those hallway ceiling joists in place).

[ROBERT YOUNG]

I did not look at the video but I bet the raised wood deck nailer block for the deck stairs from last week will not be as strong.
32715

The contractor, and self admitted engineer at 65 said verbatim, "been using him on all my high end home's for 20 years. I will never let him go."
I told him the deck was amatuer.
Makes you wonder about those high end homes, dosen't it.
You think he meant, "sanitary engineer?"

I added a better view.
Look closely at the stringer deck attachment. Like a jigsaw puzzle & art all in one.
Lovely to look at before you go inside. Puts a smile on your face as they tell you about the master carpenter.
Sets up a real, what am I going to not see behind the drywall hypothesis.
I bet there wasn't much scrap wood left on that job to remove.;)

[Gunnar Alquist]

(the weakest nailing is end nailing into the end of the grain).

Jerry,

I was under the impression that this referred to nail withdrawal. In this particular case, the forces on the nailing are primarily shear. Each joist is held in by the next block, so withdrawal is unlikely to occur.

Not saying pressure-blocking is OK, just curious about the weakest nailing in this particular case.

[Mark Reinmiller]

Jerry,

I was under the impression that this referred to nail withdrawal. In this particular case, the forces on the nailing are primarily shear. Each joist is held in by the next block, so withdrawal is unlikely to occur.

Not saying pressure-blocking is OK, just curious about the weakest nailing in this particular case.

Nails are not permitted to be used in end grain for tension loads. For shear loads the allowable strength is reduced by one-third.

[Jerry Peck]

Jerry,

I was under the impression that this referred to nail withdrawal. In this particular case, the forces on the nailing are primarily shear. Each joist is held in by the next block, so withdrawal is unlikely to occur.

Not saying pressure-blocking is OK, just curious about the weakest nailing in this particular case.


Nails are not permitted to be used in end grain for tension loads. For shear loads the allowable strength is reduced by one-third.

Mark put a number on it, my explanation was just going to be that face nailing puts the nails 'supported by' the grain, with each grain trying to hold the nail up, the shear capacity of the nail is the limiting factor; however, with end grain nailing, the nail is driven in between the grain, the shear load on the nail is trying to pull the nail down through the grain, separating the wood grain as the nail is pulled down.

Think of how you split wood - drive a wedge into the end grain - similar effect.

For Mark - Does the species of wood affect the shear reduction load of the nail? I would think that weaker wood (such as SPF) would be reduced even more than stronger wood (such as SYP)?

[Mark Reinmiller]

Mark put a number on it, my explanation was just going to be that face nailing puts the nails 'supported by' the grain, with each grain trying to hold the nail up, the shear capacity of the nail is the limiting factor; however, with end grain nailing, the nail is driven in between the grain, the shear load on the nail is trying to pull the nail down through the grain, separating the wood grain as the nail is pulled down.

For Mark - Does the species of wood affect the shear reduction load of the nail? I would think that weaker wood (such as SPF) would be reduced even more than stronger wood (such as SYP)?

No (and yes). Fastener design is based on the National Design Specification for Wood Construction (NDS). The end grain factor for shear is 0.67. The yes part is that all nail capacities are based on the Specific Gravity of wood. As an example, if you nailed two 2x members together the shear rating for a 10d common nail in the SYP would be 128 pounds and in the SPF would be 100 pounds. If you use what what is sold ad White Wood, I think that would be 87 pounds (it may be less). All of those numbers are side grain values, not reduced for end nailing.

[Gunnar Alquist]

Jerry & Mark,

Thanks so much. This was an interesting little venture.

[ROBERT YOUNG]

See photos below.



See photo below and http://www.uspconnectors.com/us/products/connectors/truss-rafter-tiedowns?gclid=Cj0KEQjwjoC6BRDXuvnw4Ym2y8MBEiQACA-jWTok3diglAPSn3J2nurQw7a99y3AtTDT1brcirXQ1ZcaAmI08 P8HAQ

No fair. You were wearing your glasses.

[Gunnar Alquist]

Old thread, but I figured that since it was me that started it, I could exhume it.

Pressure blocking came up again the other day and I did some more research and found this in a code forum. I figured Jerry might be interested.

https://www.thebuildingcodeforum.com/forum/threads/pressue-blocking.2515/

Spoiler alert: Pressure blocking is not addressed in the Wood-Frame Construction Manual and I could not find mention anywhere on the AF&PA site either.

[ROBERT YOUNG]

Blocking, bridging, strapping. All acceptable methods to stiffen framing.

Lateral force, pressure must be limited/measurable. Added force can affect members in the environment.

[ROBERT YOUNG]

http://www.inspectionnews.net/home_inspection/attachment.php?attachmentid=34083&stc=1

Appears to be a structural masonry century building.
Bridging/strapping were common.

Lack of bridging, blocking, strapping.
Defer to licensed general contractor.

[Jerry Peck]

The term pressure blocking is actually a misnomer as "pressure" blocking does not require any "pressure".

It is a solid block nailed to a beam (or other similar support) to which a joist is installed next to and nailed to the blocking, then another solid blocking on the other side of that joist, then another joist on the other side of that block.

The idea of cutting blocking too large and having to hammer it into place apparently (I presume) came into practice because of the word "pressure" - how else to get "pressure" there? "Pressure" is not needed.

It should just be called "solid blocking", but I prefer hangers as there is actually support under the joists/trusses provided by the hangers, they are not just nailed through the sides to the blocking.

To me, the reason for cutting the blocking a little large and hammering it into place would be to compensate for shrinkage of the blocking (which would mostly be shrinkage in height of the blocking) and shrinkage of the joists (which would mostly be in width and height of the joists, and it would be that shrinkage in width of the joists which 'wedging the blocking in place by making it too large and having to hammer it into place' would help cancel out.

[Gunnar Alquist]

I have never heard of this cutting a block too large and bashing it into place (except in those cases when I accidentally cut something too long and had to bash it into place). Pressure blocking was used before joist hangers were around (or at least commonplace). Prior to the pics of the floor framing that I posted, I had only seen them in ceiling joist framing, and those were homes built in the 1950s. They are generally difficult to see now because they are often covered with insulation.

As far as it being a misnomer, while I agree that pressure isn't really involved, I don't know if it's any less accurate than "toenail" (in Australia, it's called "skew-nailed", which is a better description), "king stud" (not a monarch), trimmer stud (not trim), lintel (no lint involved) or subfloor (no submarines).

:cool:

[Jerry Peck]

"toenail" (in Australia, it's called "skew-nailed", which is a better description)

I've pondered ponderables most of my life, and, having pondered "toenail" a few times in years and decades past, I ponder whether (with a wink and a nod) that came from the top of the stud being called the "head" and the bottom of the stud being called the "foot" (along the lines of "knee wall" being "knee high" and tubs having a "head" and a "foot", but I digress ... ) and, with "skewed-nails" into the "foot" of the stud, maybe someone pondered ... those must be the "toe nails" ...

:cool:

:peep:

:thumb:

:welcome:

The "Ponderer", hummed to the tune of "The Wanderer" ... https://www.youtube.com/watch?v=IkoidwsLXCg

[Gunnar Alquist]

Oh, crap! Now I'm humming that tune.

Around around around...