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  1. #1
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    Default Pressure-Blocked Joists

    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.


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    Default Re: Pressure-Blocked Joists

    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'?).

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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by Jerry Peck View Post
    "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

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  4. #4
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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by Steve Payson View Post
    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?

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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by Jerry Peck View Post
    Interesting, is like some other "new" stuff ... fancy "new" name?
    Here is another, homie.

    Just pulling your leg.

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

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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by ROBERT YOUNG View Post
    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.

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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by Jerry Peck View Post
    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.
    Quote Originally Posted by Jerry Peck View Post
    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.

    Quote Originally Posted by Jerry Peck View Post
    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.

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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by ROBERT YOUNG View Post
    I can not see the plate.
    See photos below.

    Link please.
    See photo below and http://www.uspconnectors.com/us/prod...1ZcaAmI08P8HAQ

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    Default Re: Pressure-Blocked Joists

    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.


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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by Jerry Peck View Post
    See photos below.



    See photo below and http://www.uspconnectors.com/us/prod...1ZcaAmI08P8HAQ
    Much thanks!

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    Default Re: Pressure-Blocked Joists

    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

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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by Gunnar Alquist View Post
    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.


  13. #13
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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by Gunnar Alquist View Post
    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.

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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by Mark Reinmiller View Post
    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).

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    Default Re: Pressure-Blocked Joists

    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.
    stair nailer block.JPG

    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.

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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by Jerry Peck View Post
    (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.

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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by Gunnar Alquist View Post
    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.


  18. #18
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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by Gunnar Alquist View Post
    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.
    Quote Originally Posted by Mark Reinmiller View Post
    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)?

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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by Jerry Peck View Post
    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.


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    Default Re: Pressure-Blocked Joists

    Jerry & Mark,

    Thanks so much. This was an interesting little venture.

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    Default Re: Pressure-Blocked Joists

    Quote Originally Posted by Jerry Peck View Post
    See photos below.



    See photo below and http://www.uspconnectors.com/us/prod...1ZcaAmI08P8HAQ
    No fair. You were wearing your glasses.

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