Poured in Place Gypsum Roof 1

[LPPE]

I have a poured in place gypsum roof deck. It appears to be poured on fiberboard panels. There are steel bulb-tees at 24" oc that support the fiberboard panel edges.

Does anyone have any ideas on how to successfully cut openings in this deck for RTU's, etc? How do you support the cut edge of the gypsum deck, and what would be a good way to attach new support steel framing to the opening edges?

 

[Ron]

Generally an angle frame is used frame out the openings in pour gypsum decks. Any opening larger than about 1 foot square needs framing.

 

[LPPE]

Thanks, Ron.

I have exhause fans and new RTUs going up, and have to cut many openings larger than 12". I'm not even sure how to sit the RTU curb on the edge of the cut gypsum opening and actually securing the curb. Maybe frame out the opening underneath, cut back the gypsum and sit the curb directly on the new steel instead of the gypsum, then pour gypsum back.

Also, what about the steel bulb tees? Should I weld them to my new steel supports? I'm a little concerned about starting a fire with the fiberboard formpanels.

 

[Ron]

I would cut back the gypsum from the top and weld the frame to the top of the bulb tees. You can use a sheet metal shield to protect the fiberboard, although it wouldn't hurt to dampen it a bit (just don't saturate it or the gypsum).

 

[LPPE]

Thanks again, Ron.

Any ideas on how to mate new metal roof deck up to the existing gypsum deck? In some areas, the gypsum deck is in poor condition, and in some areas, it will probably be easier to reframe the small bay where the RTU is located.

 

[Ron]

To mate new metal decking to existing gypsum, I would weld a flat plate to bottom of bulb tee to extend for the metal deck to rest on. Weld the deck to the plate. Fill with lightweight insulating concrete or gypsum. If gypsum is used, don't forget to reinforce it with "chicken wire".