Rotted Roof Decking

[SteelPE]

Our client is a tenant who is renovating the building for their business. Unfortunately for the tenant, the lease requires them to make any repairs to the existing building at no cost to the building owner. The existing building has steel decking supported by open web steel joists. Unfortunately the steel decking has deteriorated quite a bit due to lack of maintenance from the owner. The deterioration is at random locations throughout the building. The existing roof in question is approximately 3,600 square feet.

So, during our visit (owner and architect), we recommended removing and replacing the existing steel decking (as the area is small and the deterioration isn't isolated to a specific area). This will also allow them to solve the water intrusion problem and help with energy code issues. This proposal was rejected by the GC (who was not onsite at the time of visit).

The GC is proposing to repair the deck from the underside without removing the existing roofing. I can think of 10 reasons why this is a bad idea (nesting of new deck to existing, support of the new decking, anchorage of the new decking etc). We asked the GC to provide a detail for their proposal which they refused to provide because they have never attempted such a repair before.

Has anyone ever tried to replace steel decking from the inside of a steel building before?

To make matters worse, we need to keep the new materials to under 5% of the existing otherwise we will begin to trigger code required upgrades.

 

[BAretired]

Unless the GC can provide a rough sketch or description of how he intends to carry out the job from the underside, it would seem reasonable to assume it must be carried out from the top side.

BA

 

[SteelPE]

I think it might come down to getting everyone onsite for a meeting and some direct confrontation with the GC over their proposal.

 

[dhengr]

SteelPE:
What caused the deteriorated deck in the first place? What guarantee does the GC offer that he has solved that problem for the life of the new roof deck system? Or, is he just providing a new catchment system which will need draining after every rain? If he can’t generally explain the construction steps and details, you have no idea what he might do, and neither does he, and I’d tell him to go fly his kite elsewhere. Does your clients lease contract suggest anything about a reasonably weather tight building? My goodness, why not lease an open field and put up a tent, and be done with it? Which approach costs the least, not just allows the GC to work in the dry. Most of the cost of the roof replacement, if not all, should be chalked up to significant maintenance effort. And, as such, it should not be (is not usually) counted against the magical 5% improvements/additions which normally trigger stricter code compliance.

 

[SteelPE]

So this morning at 3:00 am I had a thought on how to maybe attempt the process. The detail I came up with is attached. Does this detail seem feasible? I was even considering having them weld the unistrut to the tip of the joist chord.

I received an email from the architect asking to make a site visit to determine the extent of the damage. They continue to push for doing this from the underside. Hopefully we can end the madness soon.

 

[JAE]

I'm not sure I'd consider using plywood as a fix for a metal deck.

I would think the following would be my approach
1. Survey the entire building to understand the extent and variable severity of the deterioration.
2. If the deterioration is everywhere and severe, removing and replacing the entire deck would be necessary.
3. If the deterioration is in localized areas but severe, again perhaps remove/replace would be cheaper but my solution below might be a possible answer.
4. You must review the deck to determine what level of diaphragm capacity/stiffness is lost and whether this forces you to create a solution that works not only for gravity but for lateral diaphragm behavior as well.
5. If a local issue, or if diaphragm capacity isn't compromised, then I would:

a) install new decking below the existing​

b) Attach the new decking to the existing by screwing the top flange of the new deck to the bottom flange of the old deck​

c) At the deck edges near the joists I might be inclined to do nothing as the two decks would tend to work together. You could possibly try to build an angle or plate shelf of some kind but expensive and probably not necessary assuming the shear capacity of the existing deck isn't too severely compromised.​

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