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Author Topic:   Climate Change Denier comes in from the cold: SCIENCE!!!
Posts: 4041
From: Ontario, Canada
Joined: 12-02-2004

Message 185 of 847 (766696)
08-20-2015 12:04 PM
Reply to: Message 164 by ICANT
08-19-2015 5:02 PM

More area = less ice
I have a cube of ice.
I let it melt.
It makes a puddle.
I chill the puddle from the centre... and only half of it re-freezes

Yet still, even though I have half the amount of ice, the area covered by the frozen half-puddle is still much larger than the area of the original ice cube.

Polar ice caps go through winter and summer cycles.
Parts melt, spread out, and re-freeze.

When talking about the amount of ice decreasing... we need to talk about volume, not area.

A greater area of ice is consistent with both an ice decrease and an ice increase.
What matters is the thickness of the resulting ice that re-freezes.

Did your source leave out the thickness?
If so, and since that is indeed the more important factor for identifying if the amount of ice is increasing or decreasing... why do you think they left it out?

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 Message 164 by ICANT, posted 08-19-2015 5:02 PM ICANT has not yet responded

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Posts: 4041
From: Ontario, Canada
Joined: 12-02-2004

Message 507 of 847 (841666)
10-18-2018 10:12 AM
Reply to: Message 506 by Percy
10-18-2018 9:19 AM

Re: A Sort Of Climate Change Related Question
I have a few answers, maybe a springboard for more searching?

First, a bit on blocking.

First of all, to remove confusion, I believe blocking is not "getting in the way of something" blocking... but more "using a block of wood" to add structural support blocking.

Think of framing a wall.
You have the base 2x4, and the top one.
Then you have the studs going vertically each one spaced by however-much (12" normally? 16"?... whatever it needs to be).
The "blocking" is the horizontal short pieces that go inbetween the studs.

When you have a frame, and you put plywood on the outside of it (think of the building of the exterior walls of a house)... I think this is called "shearing" a wall.

Plywood comes in 4x8 sheets. However, these sheets are not always long enough to go from base-to-top of a framing wall (think of a 9' ceiling or something like that...). Therefore, you end up with "horizontal joints" in-between the plywood that is not located at the base-2x4 or the top-2x4. This "shearing horizontal joint" is in the middle of the wall... only connecting to the studs.

I think the point of the "blocking" is to put in some horizontal support so you can nail in the plywood along these middle-horizontal joints.
Without this... you can have plywood supported more on it's vertical sides (nailed into vertical studs) than it will be supported along it's horizontal top and bottom. This would make the structure weaker.

Now... that's all normal shearing. Normal plywood on a normal frame.

Windstorm plywood (again, I think...) is special plywood that is created long enough to go from the base-2x4 to the top-2x4 of the framing without the need of a middle joint.

Therefore you don't need need the "blocking" to support the "additional hardware" to support the plywood along the middle-horizontal-seam... because there is no middle-horizontal-seam. The only horizontal seams would be along the already existing base-2x4 and top-2x4.

I also found this link helpful:

Windstorm FAQ
-Especially the section under "What is special about Windstorm and why does it work?"

This message is a reply to:
 Message 506 by Percy, posted 10-18-2018 9:19 AM Percy has responded

Replies to this message:
 Message 508 by ringo, posted 10-18-2018 11:58 AM Stile has acknowledged this reply
 Message 509 by Percy, posted 10-18-2018 5:51 PM Stile has responded

Posts: 4041
From: Ontario, Canada
Joined: 12-02-2004

Message 510 of 847 (841689)
10-19-2018 9:47 AM
Reply to: Message 509 by Percy
10-18-2018 5:51 PM

Re: A Sort Of Climate Change Related Question
Disclaimer again - not my area of expertise - but here goes with another possible-explanation.

Percy writes:

But how is "no blocking" stronger than blocking? It seems that blocking done correctly should even stronger since two parallel studs with no horizontal block between them have to be weaker than when there are one or more horizontal blocks.

Yes, you are correct if taken literally.
That is... blocking is better than no blocking if you're not going to add any plywood to the outside of the wall.

However... a wall is not as literally described here. The sheathing (the plywood on the outside) acts just as well as the blocking as far as bracing for lateral movement. In fact, it acts even better because it's larger and connects multiple studs instead of just two specific studs. It also has multiple nails in it per-stud or per-connection... where each blocking only has one point of connection to each stud.

To prove this point... think of an Ikea-ish bookshelf. Have you ever put one of these together?
You lay the long sides down, you put the top and bottom on and you add in the shelves.
Here, the shelves act like the blocking would in a framed wall as far as lateral-movement is concerned.
However, if you've ever stood up a shelving unit at this point, you know it's very weak against lateral-movement still. If you push it from one side, the two side-ends (the "studs") push over together and the "blocking" shelves barely do anything to stop this motion. Of course... the shelves aren't nailed into the studs where the blocking would be... but this isn't adding a lot of structure... only the connection point of the single-nails-per-blocking-per-stud. It's still relative-ly weak against lateral movement.

However, there's always that super-flimsy back piece you put on those shelves. Put that on... and the entire shelf suddenly becomes super-rigid. This back piece is the sheathing... the plywood we put on an exterior wall. It's very good at preventing lateral movement because it connects the top and bottom and all the studs together into their "full square shape" with multiple connection points (multiple nails per stud or top/bottom piece.)

A non-windstorm plywood is good... but if it is jointed in the middle it means it's not connecting the top and bottom and studs all together. It's only connecting the top and studs... or maybe just the bottom and studs. This is "good" but connecting all 4 sides... top, bottom and studs... all together with one large-enough windstorm-plywood (or whatever it's made of) is much better for bracing against lateral movement.

Also, there's a step-back view of the whole structure.
Windstorm plywood is larger... so you have less pieces in total. Regular plywood is smaller and would require more smaller pieces to fit together in order to cover all external faces.
When dealing with structural support... larger one-piece things are always stronger than smaller-multiple-pieces-connected-together things. Therefore, even without blocking, the less-pieces-because-they're-bigger idea of the windstorm plywood covering is stronger than the smaller-multiple-pieces-connected-together idea of the non-windstorm plywood.

What is the "gable end hinge point"? Is that the top of the gable? And what is the "bottom chord"?

What is a top chord? Is this the underside of the roof?

Let's go through some pictures:

Basic Truss

Just need to look at the top-most picture on the right side here.

A Truss is one-triangle-piece of a roof support system.
Bottom chord is the base of the triangle.
Top chord is either one of the two top-sides of the triangle.

Examine the blow-up of the overhang. Understand that the "butt cut" is the part of the roof-truss that is exposed to the exterior wall-side, but not covered by the truss's top chord.

Gable End Frame

I believe a "gable" is a bunch of trusses all together to form a roof. As shown in this picture.
Notice how the wind is hitting the flat-face of the end-truss of the gable. This is the gable end frame.

The same wind direction is used in the following pictures:

Gable End Hinge Point

We're now looking at the side of the gable... that's why we no longer see the triangle shape.
Notice here that the wind is bending the structure where the gable meets the base structure (roof meets top of wall.)
Notice how this gable has it's own sheathing and the base structure has it's own. This separation is causing most of the gable end hinge point problem.

Now with a single piece of sheathing going from bottom of base structure to top of gable:

No More Gable End Hinge Point

Here, the wind's force is distributed across the entire face of the windstorm sheathing. (The picture doesn't clarify this very well at all - in fact, it makes it seem like it isn't... but it really is - that's just physics.)
The roof and wall system are now "connected" and the hinge point disappears.

How do plywood sheets that extend all the way up to the roof eliminate the need for hurricane clips or at least something to fasten the roof to the top plate? Do these longer plywood sheets somehow get attached to the roof?

However it is done, how does it prevent "lift and roll over"? How would it "prevent lift" since this whole junction between plywood sheath and roof is covered by the soffit?

I think these questions go back to the first picture again. Remember the "butt cut?"

If the butt cut is not covered by plywood, or covered with it's own plywood and not connected to the wall - because the wall-plywood was not large enough - this would make "lift" a difficult problem. It would only be single-point hurricane clips holding the roof to the wall structure.

Now, add in windstorm sheathing that goes from the bottom of the wall structure up to the top chord of the roof truss - covering the entire butt cut as well.
This, again like the flimsy-back-piece of the Ikea shelves, adds much more structure and many more connection points between the wall structure and the roof structure.

"Lift force" from the wind still exists - this will always exist as long as the overhang exists.
However, going from single-point-connection hurricane clips to mutliple-point-and-single-large-piece windstorm sheathing connections is such a huge gain is structural stability that it reduces it so much some claim it to be "eliminated."

The soffit isn't structural... it doesn't add in to this in any significant way. Any lift force generated because of wind and the overhang (regardless of it going on the soffit or not) will be transferred to the structural connection of the hurricane clips or the windstorm sheathing. The roof will want to come off all together ("rolling") this puts strain on the connection between roof-and-wall/base.

If there are no or fewer stud to plate connectors and floor to floor connector straps, doesn't that just mean using more nails? I'm still not getting how it's possible to ever eliminate hardware. Are nails not considered hardware?

I think this is more of a laymans vs. expert terminology thing.
I really don't know, because I'm very much a layman here as well.

My guess is that nails are technically "hardware" in the sense that you will find them in the hardware section of any hardware store.
However... they are considered so much fundamental hardware that they are sometimes not included when discussing "using hardware" especially when the context is around using other-connection-things that are not nails/screws/bolts... like hurricane clips or plate-connectors or straps or anything else like that.

So I think this is a definitional/contextual confusion issue more than anything else.

Maybe if you're talking about "getting nails" you can say you're getting hardware for the job.
However, if you're talking about all-the-other-connection-types... and you mention dealing with "the hardware" you would be referring to everything-that-connects-stuff but not really including the nails (because nails are so fundamental and obviously required).

Is wall air leakage a significant contributor to exerting destructive force on a structure during high winds?

This one... I'm really not sure.
Maybe? Or maybe something else entirely like R-Value of the wall in general (nothing to do with hurricanes or winds?).

As far as high winds are concerned... my initial thought is that gaps/seams would help (assuming all other structure aspects are equalized somehow)... because wind blowing through something causes a lot less force than wind getting trapped by something. That why I think this might have something to do with non-hurricane-winds benefits.

But maybe it's touching on the idea of more-seams = more-little-pieces-connected-together-instead-of-solid-one-piece-things... which would also imply that the structure is weaker against wind forces (more joints = more possible bending/weakening locations).

This message is a reply to:
 Message 509 by Percy, posted 10-18-2018 5:51 PM Percy has responded

Replies to this message:
 Message 511 by Percy, posted 10-21-2018 8:51 AM Stile has responded

Posts: 4041
From: Ontario, Canada
Joined: 12-02-2004

Message 512 of 847 (841807)
10-22-2018 9:28 AM
Reply to: Message 511 by Percy
10-21-2018 8:51 AM

Re: A Sort Of Climate Change Related Question
Percy writes:

Doh! Yes, of course, I see now. Blocking in the shape of an 'X' would be far more effective than a horizontal block, but only structurally. It would be useless for providing a connection point where two pieces of plywood join.


On which side of the gable would one install hurricane clips, the end where the arrow is, or on the sides?

I'm not really sure.
My guess is either "on the sides" or "everywhere."

If the answer is both then how would windstorm plywood eliminate the need for hurricane clips on the side. Or if you don't need hurricane clips on the side then why not? Isn't lift generated here, too? In fact, isn't the danger of rollover from the sides, not the gable ends?

I think there are two different problems.

The hinge point at the gable-end-frame is one problem. I think we understand that one now, and how windstorm sheathing prevents it.

The other problem is the whole lift-issue and danger of rollover.
And I think you're right - these are a problem more on the sides, not the gable-end faces.

Therefore, the wind would have to change direction from those pictures and come from one of the sides in order to cause this second issue.

In my previous post - the section talking about the "butt-cut" and using windstorm sheathing from the bottom-of-the-wall to meet up with the bottom-of-the-top-chord-of-the-roof (covering the "butt-cut") is about protecting these sides and helping to greatly reduce lift along the sides. The windstorm sheathing connects the wall section to the roof section better (apparently) than hurricane clips.

I don't really know what a hurricane clip is... but I'm guessing some sort of single-point connector spaced out every 12" or so along the roof-wall connection line.

With no windstorm sheathing (and either a narrow piece of plywood covering the butt-cut or nothing covering the butt-cut at all...) these hurricane clips would be the only thing holding the roof onto the wall section. Perhaps there are some nails... but these would be vertical (from the roof down into the wall) - these vertical nails wouldn't do much in stopping the vertical lift from winds.

With the windstorm sheathing, we now continue the "flimsy-Ikea-backpiece-greatly-increasing-structural-stability" idea up from the wall section and onto the butt-cut area of the roof section. The horizontal nails holding the windstorm sheathing to the roof butt-cut section would be a great deterrent against vertical lift. As well, there would be many more nails in each windstorm-sheathing piece then there would be hurricane clips (I would guess).

Thanks for the effort it took to explain all this.

No problem. It was interesting for me too.

This message is a reply to:
 Message 511 by Percy, posted 10-21-2018 8:51 AM Percy has acknowledged this reply

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