# Prerocking



## NSolano (Dec 16, 2004)

We've had to do this at many of our commercial jobs in VA and MD. General Contractors usually require it of subs. We always do it at electrical boxes and outlets, risers, some plumbing pipes, and mechanical ducts before the fire marshal passes inspection. This varies from job to job because some of them require more "prerocking" than others.

I was wondering, what is the point of this prerocking if drywall is going to be hung in those areas anyways? I never thought to ask, we just do the work. 
Anyone here have any input as to how much prerocking you've had to do before, any specific areas, any nightmare stories? 

The only problems we run into is when the plumbers, electricians, or HVAC guys make mistakes and they break our pre-hung drywall and then we have to do it again. Big pain in the ass and sometimes we have to backcharge this. Share stories or tell what the actual point is, or who started this way of working?


----------



## Tim0282 (Dec 11, 2007)

I'm guessing it is for fire blocking. We just did a nursing home that had 864 sheets in the attic and behind furnaces and such. We had to fire tape all of it. And anywhere we missed in the beginning I had to go after everything was installed. Wow that was nasty to tape. Is that what you are talking about when you say pre rock?


----------



## Brockster (Aug 24, 2007)

Tim0282 said:


> We just did a nursing home that had 864 sheets in the attic and behind furnaces and such. We had to fire tape all of it. And anywhere we missed in the beginning I had to go after everything was installed. Wow that was nasty to tape. Is that what you are talking about when you say pre rock?


:laughing:Sounds like a great time Tim.:laughing:

I've also had to prerock so the insulators can do their job.


----------



## kgphoto (May 9, 2006)

Fire rated assemblies require a certain number of layers of drywall to reach their measured performance. Typically, two layers. 

When you put in a recessed light you cut a big whole in one of the layers. So you build a box out of drywall and install it in the bay, behind the device to make up for the penetration through the REQUIRED layer of drywall.


----------



## Tim0282 (Dec 11, 2007)

Or the electrician can buy the fire rated can light...


----------



## kgphoto (May 9, 2006)

This applies to all penetrations of the fire rated envelope, like ducts, pipes, framing, as well as wires and cans. They don't make fire rated wire, just plenum rated insulation.


----------

