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pressue blocking

I learned to pressure block everything, the first metal we saw was Teco clips in the early 50s, when Simpson came out with joist hangers I was one of their first customers at their manufacturing plant by the Oakland Airport in 1957. I didn't really trust the "flimsy tin" as the old guys referred to them, so we pressure blocked and added the joint hangers on top of the blocks. And by the way, I still won't use a rim joist, I solid block everything.

Now that steel construction is threatening to displace wood, Simpson has come out with their own line of bolt-together moment frames, obviously they are seeing so many moment frames in wood buildings that builders are going to think: "If I have a steel crew here welding moment frames together, why not do the whole thing in steel and eliminate the poor quality wood and all the metal connectors required to build a wood house? By providing bolt-together moment frames they can keep the carpenters building the house using their metal.
 
Rio: Legality aside? That does hit the nail on the head when pressure-blocking!

JBI: Options are generally a good thing. Still. I paid for a training seminar recently based on the 2006 IRC advertised as sponsered by our Homebuildes's Association, but Simpson is serving the sandwiches an hour after the instructor is "requiring metal" based on the engineering behind the code. Do you know of any engineering studies that may have been done to research the effectiveness of pressure-blocking? I am not speaking of having a study done for particular elements of a particular project, rather, a study done to determine if prescriptive elements might be codified to allow pressure-blocking in typical wood framed SFHs.

conarb: I wasn't even a gleam in papa's eye in '57! You are gett'in old as dirt! Probably wise and experienced too ... do you know of any studies done to determine if prescriptive elements might be codified to allow pressure-blocking in typical wood framed SFHs? Maybe the guys selling gun nails, (Bostitch, Paslode, Hilti, etc.), might consider funding such a study.
 
Someone said they didn't see a difference in pressure blocking and using a 2x2 ledger strip. It is possible that the code doesn't specifically allow pressure blocking because when you nail the end of the joists into the block, the nail is so close to the end of the joist that the nail would often split the grain, particularly if you are using SYP? When nailing a 2x2 in place it's not likely to split unless you put the 3 required nails a little too close together.
 
The combination of nailing the joist into the pressure block and toenailing into the girder makes for one heck of a hard to impossible connection to disassemble. My experience in the field is that 2x2 ledgers are prone to splitting if nailed securely enough with gun to "feel" secure. What is nailing pattern for ledgers? I can't find it in IRC.

Note: I am not the one to say I don't see the difference; pressure blocking is clearly better, but do agree both practices depend on the shear strength of the nails.
 
Haven't seen pressure blocking in a long long time. I've seen pressure blocking used for support and to keep the joists from twisting.
 
I agree with Mule the main reason for pressure blocking is to prevent rotation or lateral displacement, just check out the WFCM (Wood Frame Construction Manual) page 21 Sections 2.3.1.3 & 2.3.1.4.
 
Due to the moisture of "green" lumber and the, Tangential and radial shrinkage values in the green lumber we cannot rely on just "good" construction and "Pressure blocking". The only way I would rely on "Pressure blocking" is if the lumber is oven dried and the moisture content is verified at the time of installation.

"Pressure blocking" should never be relied on for primary support members, or as a substitution for any steel clips, hangers, excreta.

Should Not be codified

All blocking should be tight fitting, with NO gaps, at the time of framing.
 
Mark: Should not be codified?

I agree with some of your concerns, but believe those same concerns affect other codifed methods. I believe an engineering study could and should be performed, and the results commonly available, before the potential codification of the method of pressure blocking is marginilized.

I have read in the archived ICC posts that forum members commonly experienced this method being engineered into a particular project. It stands to reason that a prescription for codification can likewise be established.

Agreed: All blocking should be tight fitting, with No gaps, at time of framing. Would add to check for nail type and pattern if engineering prescriptions were available.
 
If you want it codified answer this question:

How does wood shrinkage effect "Pressure blocking" and how do you "prescriptively" mitigate the effect?

With "green" lumber Pressure blocking is already marginalized.
 
Have to wonder how all our old buildings survived before joist hangers were invented, even Teco clips for that matter? The only building failures I've had in over a half century of building are the failures of the gang-nail plates in lightweight roof trusses, my homes with lightweight roof trusses with glued/nailed plywood gussets from the 50s are all doing fine, but several failures with the gang-nail plates popping off in my homes of the 60s and 70s, since I've always guaranteed my buildings for my life, I've rebuilt several roofs by now. Now I read that Australia is having an epidemic of gang-nail truss failures. I've had no pressure block failures, of course started adding Tecos and Joist hangers in the 50s. I've remodeled a lot of old Victorians and mansions in Piedmont and the pressure blocks are fine, all were built with green lumber.
 
mark handler said:
If you want it codified answer this question: How does wood shrinkage effect "Pressure blocking" and how do you "prescriptively" mitigate the effect?

With "green" lumber Pressure blocking is already marginalized.
Click to expand...
The purpose of a study would be to answer the question you pose.

Can you give me a definition of "green lumber".
 
Jobsaver said:
Can you give me a definition of "green lumber".
Click to expand...
Unseasoned or green lumber has a moisture content greater than 20 percent, shrinks and may warp as it dries.

Dry lumber has 19 percent, or less, moisture content

Dry lumber can cost 1/3 rd more over green lumber and needs to be protected on site to prevent the reintroduction of moisture.

And a side note, green lumber is a major cause of mold in buildings.
 
conarb said:
Have to wonder how all our old buildings survived before joist hangers were invented, even Teco clips for that matter? The only building failures I've had in over a half century of building are the failures of the gang-nail plates in lightweight roof trusses, my homes with lightweight roof trusses with glued/nailed plywood gussets from the 50s are all doing fine, but several failures with the gang-nail plates popping off in my homes of the 60s and 70s, since I've always guaranteed my buildings for my life, I've rebuilt several roofs by now. Now I read that Australia is having an epidemic of gang-nail truss failures. I've had no pressure block failures, of course started adding Tecos and Joist hangers in the 50s. I've remodeled a lot of old Victorians and mansions in Piedmont and the pressure blocks are fine, all were built with green lumber.
Click to expand...
Yeah "Pressure blocking" and green lumber helped this old building....

eq-CA-central-12.jpg
 
Thanks, that is the same thing we call "green lumber" here. I thought we might have been talking about something else.

We don't have any around here that is grade stamped. Our yards carry primarily kiln dried, and some sun dried studs.

I never like to see a pile of wood or a frame exposed to the elements for too long, but believe all existing prescriptive codes must account for a measure of exposure, as would any proposed ones. Wood framing and framing connections depend on dimensional stability inherent to allowable lumber species.
 
Jobsaver said:
Came from a geotech site.
Click to expand...
No, it came from Western Washington University, Yes it is earthquake related, central California, in response to Dicks comments on old buildings, not based on your comments.
 
Would it have been any different with joist hangers?

To me it look's like a positive connection failure.
 
The reality is that the better a building is tied together the better it will survive earthquakes, hurricanes, or tornados. This often means doing things that the contractors haven't done before.

Apparently on the East Coast where they have hurricanes they install steel rods that tie the roof framing to the foundation. This the roof on and keeps the building from lifting off of the foundation.

The first step is to enforce the code. Do not allow local trade practices when they are in conflict with the code. The code provision may have been added in response to problems resulting from these trade practices.

We also need to recognize that when the IRC allows houses to be built without engineering that there will be a greater likelyhood of problems in extreme events. I believe that the IRC is often applied to structures that differ from the idealized structure around which the provisions were written. This has the potential of poor performance.
 
I thought I remembered 3 nails being specified somewhere (because I had put that in my file notes related to using 2x2s for bearing) but now I can't find it in the IRC and what I do find calls for 2. R502.6 states the end of floor joists must bear on not less than 1.5" of wood and R802.6 states the same requirement for ceiling joists. Both chapter 5 on floors and chapter 8 refer to the structural member fastening schedule in chapter 6 on walls, Table R602.3(1). That table specifies for 2" planks that you must have 2-16d nails at each bearing. I assume a 2" plank is the same thing as what I call a 2" ledger since it refers to bearing.

As to pressure blocking, I believe it is prohibited for floor joists by R502.6 where it states it shall have bearing unless using approved hangers. Pressure blocking, no matter how good it might be, doesn't meet either of these requirements. Right below it in R502.6.2 where it describesf framing into the side of a girder it again states you must have a ledger or an approved anchor.
 
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