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Markings on old rules ??

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Forum topic by Joeshop posted 03-22-2011 04:27 AM 2421 views 0 times favorited 17 replies Add to Favorites Watch
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Joeshop

49 posts in 2581 days


03-22-2011 04:27 AM

Topic tags/keywords: question rules

On some “old” rules there are little marks at about every 19.25 inches. A friend had told me that someone had told him what they were used for but he had forgotten their exact meaning. He seemed to think it was similar to joint spacing similar to 16” centers, but these show up every 19.3 inches. Do any of you old-timer carpenter types know what they were for ? I’ve seen them on a Lufkin tape measure and also on an old folding rule.

Thanks for any help on this as it’s making me curious.

-- ~You cannot do a kindness too soon, for you never know how soon it will be too late.~ - Joe


17 replies so far

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bblogna

26 posts in 2128 days


#1 posted 03-22-2011 04:45 AM

They are on alot of tape measures. Lay out marks work out to 8Ft, mostly used for laying out floor joists. My stanley tape has them also.

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Dave

11405 posts in 2304 days


#2 posted 03-24-2011 01:23 AM

I believe in Texas that is the wall joist center.

-- Superdav "No matter where you go - there you are." http://chiselandforge.com

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canadianchips

2350 posts in 2461 days


#3 posted 03-24-2011 01:50 AM

When using LVL you can increase the width and still meet building codes. Contractors can save 1 floor joist in every 8ft.
The so-called diamond mark is actually positioned at exactly 8/5 of a foot (that’s exactly 1.6’ or 19.2 inches, which is indeed pretty close to 19” 3/16 ).

The diamond marks are also called “black truss” markings, because they correspond to the truss layout which is used with 8-foot sheets of plywood (or other material), namely 5 trusses per sheet.
This is to be contrasted with “red stud” markings which appear every 16 inches by showing the corresponding inch number in red instead of black. The black markings and the red markings coincide at 8-foot intervals (96 inches).
That is to say: 5 black intervals or 6 red ones in an 8-foot width.

5/8 = 0.625 is a standard slope for a roof, which may thus be built by measuring horizontally as many diamonds as there are vertical feet.

-- "My mission in life - make everyone smile !"

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GaryL

1094 posts in 2294 days


#4 posted 03-24-2011 02:17 AM

As canadianchips mentioned they are marking for a different “on center” layout for framing. Usually used more for TGI (I-joist) floor systems. It is a way to engineer a floor to save some material if the floor live and dead load ratings could still be met. From a framers stand point, it’s a pain. HVAC contractors hate them. I framed a few with this, but after I would have my supplier send me enough I-joists for 16” centers. That way all floor. wall, and ceiling joist framing can be stacked for strength and mechanical / HVAC / plumbing runs.

-- Gary; Marysville, MI...Involve your children in your projects as much as possible, the return is priceless.

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devann

2201 posts in 2156 days


#5 posted 03-24-2011 02:39 AM

They are for eight foot centers when you’re working for someone that buys massive amounts of lumber doing building on a very large scale. It save them some money, just another way to cut corners and spend less. Least that how it was explained to me years ago.
Sometimes I’ll see an Architect call for that spacing in a floor system, usually with TJI joist systems with an above average span.

-- Darrell, making more sawdust than I know what to do with

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Gregn

1642 posts in 2447 days


#6 posted 03-24-2011 04:31 AM

Never paid attention to those markings before, it was always 16” & 24” centers I had to deal with. Learn something new everyday.

-- I don't make mistakes, I have great learning lessons, Greg

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jusfine

2405 posts in 2390 days


#7 posted 03-24-2011 05:01 AM

Great explanation Canadianchips!

As a former framer for many years, we used this system on a regular basis.

Seemed goofy to start with, but as the engineered trusses span a longer distance and can be spaced farther apart because of their load bearing capacity, it only makes sense.

-- Randy "You are judged as much by the questions you ask as the answers you give..."

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TopamaxSurvivor

17671 posts in 3140 days


#8 posted 03-24-2011 07:55 AM

GaryL Why do HVAC hate them?

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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Edziu

150 posts in 2515 days


#9 posted 03-24-2011 02:01 PM

Where I work, A customer came in to try and stump me as to what those black diamonds were. I told him about the alternative joist/stud/truss spacing and saving material and it all working out to 8ft centers, etc. He seemed very sad that he could not stump the employee that day. He just shrugged and said “yeah whatever” and walked away.

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GaryL

1094 posts in 2294 days


#10 posted 03-24-2011 02:09 PM

Topomax…It limits the number of wall bays that line up with the floor bays for running their warm air supply runs. This is of course if walls are standard 16” O.C. Mainly a pain for bigger two story homes. It just makes it difficult for them to design an efficient system when you have to run 30’ of duct to get 10’ of distance, if that makes sense… It also limits the areas for utilization for cold air returns which is normally framing cavities closed off to form a wood duct so to speak.

-- Gary; Marysville, MI...Involve your children in your projects as much as possible, the return is priceless.

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TopamaxSurvivor

17671 posts in 3140 days


#11 posted 03-24-2011 03:06 PM

OK, yup, I see it. I didn’t think of the interscting wall being way off.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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jusfine

2405 posts in 2390 days


#12 posted 03-24-2011 03:51 PM

Gary, I still don’t get your point.

If a wall is on 19.2 Centers, and he makes a run two joist spaces over, instead of 32” he is at 38” + -. Not that big of a difference, is it?

I have never heard that complaint from any of our subtrades, it has been the standard here for about 25 years.

-- Randy "You are judged as much by the questions you ask as the answers you give..."

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devann

2201 posts in 2156 days


#13 posted 03-24-2011 04:13 PM

justfine, Up north the HVAC guys do it a little different than we do down in Texas. The framing members of a buildind should still stack anyway. Makes for a better building. On houses I generally designate the corner with the two longest walls has the “layout corner”, all layouts for studs, etc come from that point.

-- Darrell, making more sawdust than I know what to do with

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canadianchips

2350 posts in 2461 days


#14 posted 03-24-2011 06:07 PM

Unfortunatly it all comes down to COSTS: The Framer saves money by not having to shoot nails into an extra joist, the contractor saves time & money by not having to buy an extra joist and the HVAC people don’t want to buy extra pipe if they don’t have to. The sub trade people will ALWAYS charge the people MORE money for the “EXTRA’s”, rarely passing on the savings !

-- "My mission in life - make everyone smile !"

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GaryL

1094 posts in 2294 days


#15 posted 03-24-2011 07:49 PM

jusfine…I have never seen walls at 19.2 centers, but that does not mean it’s not done. The problems we had were with larger, 2500 to 4000 sq. ft., houses, with basically no walls that line up from 1st floor to 2nd floor. In this case all HVAC runs need to weave from first floor framing up a wall, then through second floor framing to the proper location of the register. This only leaves one out of three framing cavities to run a typical 3 1/4×12 duct. If you have a large room with lots of windows, you may need to get four of these to that room, especially for AC with the solar gain off the windows (lake front homes, Lake Huron). With limited framing cavities it can be a head scratcher for the HVAC crew. And it kills the efficiency of the system.
Also another point is 3/4 ply or OSB is not sufficiently rated to span the 19.2 centers, but everyone does it anyway. If you go by the book, it should be 7/8” single layer or two layers of 1/2”. I always cringed when I knew there was ceramiic tile going over a 19.2 center floor. To much flex in the subfloor. Old fashion dry pack mud pack with expanded metal lath for those floors!

-- Gary; Marysville, MI...Involve your children in your projects as much as possible, the return is priceless.

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