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RE: Connecting to Existing Metal Roof Deck

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David,

I have seen a couple of systems that appear to be what you are describing.  
*	One was the "Load Master" deck system.  
*	The other was a hybrid which consisted of conventional metal form
deck, a leveling course of "Elastizell" concrete (35 pcf), polystyrene
insulation board with holes in it, and then a topping of about 2 inches of
more Elastizell.  Had a problem with adhered membranes, but mechanical
fastened membranes (like used in Dade County) are O.K.
If it is the Load Master, it will be difficult to match profiles.  Forcing
you to a butt joint.  If it is conventional metal deck that you can match
profile, match it and lap the joint.

I believe that your concern may be reflecting a joint in the roofing
material, if you are forced into a butt joint.  If the roofing is a modified
bitumen, tar & gravel, or other somewhat rigid system; your concern is
justified.  You should provide about a 2' strip of 20 ga steel flat strip,
lapped over the joint, and screwed to the top of the flutes.  That provides
a degree of continuity from one deck to the other. Use an insulation board
(like polystyrene) that can be pushed down on the screw heads.

Roofing materials that are single ply membranes like EPDM, Carlisle, etc.
don't have the same tendency to reflect joints.  These roofs should not be a
problem, and you should not have a problem with butt joints.

Regards,
Harold Sprague

> -----Original Message-----
> From:	PEC - Lake City [SMTP:pec(--nospam--at)isgroup.net]
> Sent:	Friday, January 14, 2000 8:22 AM
> To:	Seaint; StrucTX
> Subject:	Connecting to Existing Metal Roof Deck
> 
> I looking at a small addition to a local mall.  The existing roof is metal
> deck with insulation board and light weight concrete.  The roof on the
> addition will match it.
> 
> At the connection between new and existing, I anticipate cutting back the
> existing roof to the centerline of the supporting joist.  The new deck
> will
> be attached to that joist (probably with puddle welds).
> 
> How is the connection between the new and existing roof systems normally
> detailed?  Is is just a "butt" joint or is there some attempt to provide
> some kind of positive connection between the roof systems other than both
> are attached to the joist?
> 
> The project is located in North Florida:  high winds, low seismic.
> 
> 
> David Finley, P.E.
>