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RE: Insulrock diaphragm

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Tectum was a bit different. Tectum like Fibroplank and Permadeck is structural wood product that was used a lot in gymnasiums to control sound. It also was designed to bear on bulb / truss tees.

The term Insulrock is new to me, but the "rock" portion would indicate that it is a gypsum base product.

I would suggest that you connect with:

Most assemblies (as this one) were UL rated, and UL is product specific. A lot of roof assemblies were FM rated, and FM is another good source, and they might have the diaphragm data.

There was another US Gypsum called "Span-Rock Gypsum Roof Planks". They were factory laminated gypsum board planks that were supported by bulb / truss tee's.

The installers generally hold a gap at the bulb / truss tee's and the space was grouted with gypsum. This was done for Permadeck and Tectum as well. This is how the diaphragm resistance was developed.

Harold Sprague

From: "Joe Grill" <jgrill(--nospam--at)>
Reply-To: <seaint(--nospam--at)>
To: <seaint(--nospam--at)>
Subject: RE: Insulrock diaphragm
Date: Mon, 3 Jan 2005 11:25:39 -0700

Several years ago I looked at an old building with a roof system that was
referred to as (IIRC)a "Tectum" system, which sounds similar to what you are
describing.  But, as Harold stated there were probably a number of
manufacturers.  I seems as though I was able to find some information doing
a search for "Tectum Roofing".  Sorry, but what I had is still with an old
Hope this helps.

Joseph R. Grill, P.E. (Structural)
Shephard - Wesnitzer, Inc.
Civil Engineering and Surveying
1146 W. Hwy 89A Suite B
Sedona, AZ  86340
PHONE (928) 282-1061
FAX (928) 282-2058

-----Original Message-----
From: Will H [mailto:haynewp(--nospam--at)]
Sent: Monday, January 03, 2005 11:17 AM
To: seaint(--nospam--at)
Subject: RE: Insulrock diaphragm

Thanks Harold,

I can't find any mention of the gypsum concrete on the drawings. They are
showing the 2 1/2" form boards with built up roofing directly on top of
them. So it looks like it could not be justified as a diaphragm.

Will Haynes, P.E.

>From: "Harold Sprague" <spraguehope(--nospam--at)>
>Reply-To: <seaint(--nospam--at)>
>To: seaint(--nospam--at)
>Subject: RE: Insulrock diaphragm
>Date: Mon, 03 Jan 2005 17:55:20 +0000
>This appears to be a gypsum roof deck system.  There were many
>manufacturers of gypsum systems in the 1960's. The particular system that
>was used varied region to region.  My advice would be to find an old ICBO
>Research Report on Insulrock.  I have an old US Gypsum Research Report on
>Thermofill and Pyrofill.  Generally the gypsum formboards were just there
>to support the cast in place gypsum, and contributed little to the strength

>of the diaphragm system. What you are referring to were often called "form

>boards".  The sequence of construction for the gypsum structural deck
>consisted of:
>1.  The bulb tee or truss tee's were welded to the structural steel
>2.  The form boards were placed on the bulb / truss tees (The form boards
>were held back from the tees to allow the cast in place gypsum to flow
>around the exposed portion of the tee's)
>3.  Wire mesh was placed on the form board and tee's.
>4.  Gypsum concrete was placed on the deck system.
>The system worked pretty well unless you got a leak in the roofing system.
>Allowable shear loads ranged from 510 to 1200 pounds per lineal foot.
>Harold Sprague
>>From: "Will H" <haynewp(--nospam--at)>
>>Reply-To: <seaint(--nospam--at)>
>>To: seaint(--nospam--at)
>>Subject: Insulrock diaphragm
>>Date: Mon, 03 Jan 2005 10:22:49 -0500
>>I have an existing building from the 1960's that used Insulrock roof
>>panels on bulb tee purlins. I don't see how this can be considered a
>>structural diaphragm, but it is the only thing that has been distributing
>>the lateral loads on the building for 40 years.
>>Does anyone have any experience with this product? By looking at the
>>document below, I think the planks are only resting on the tees and
>>clipped to the main steel beams but the drawings don't specify.
>>thanks for any help
>>Will Haynes, P.E.

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