Economy of PEMB

[rholder98]

This has come up again in my office--at what point to metal buildings lose their economic advantage over conventional construction? I contend that PEMB is better for simple, rectangular buildings with few frills, but when you start introducing plan irregularities and multiple roof heights, you're better off going with conventional. What are your opinions?

 

[archeng59]

this is a relatively old thread, but I'd like to offer an opinion anyway. I agree with you on the point that the engineered metal buildings are economical if you buy the "standard off-the-shelf" building. when there are design requirements that are different than what the metal building manufacturer considers his/her "bread and butter" components, the cost goes up. that's been my experience anyway.

 

[DJYork]

In general, a metal building is cheaper if you just need a building, and that is it. If you desire many changes than a convential system is more economical.

The design of metal buildings are goverened by the Metal Building Association, and they find every loop hole to get past the IBC. They have seperate codes for metal buildings. They use there own loads, and seperate the loads when possible. The dead load, is just the structure themselves, and collateral load is everything else that is a dead load. If you do not tell them everything they will use a collateral load of 0. Then they always reduce the live load on the roof. Why does that matter, well if you only have the minimum dead load, and reduced live load, there is no extra for anything else. Take where I'm from, Texas, the last big snow fall we had several metal buildings collapsed from the excess load, but no convential structures. Why would they do this, the simple answer is to get the job. Every additional 5psf adds an additional $1 per square foot. That might not sound a lot, but if it only cost $4-5 to build one, it becomes a big deal.

Metal buildings do not have any redundancy (a safety factor that convential buildings have).

Metal buildings are not required to be designed for drift. Granted a lot utilize it to some aspects, but some still do not. What does that mean, no brick.

Basically, little or no cost advantage if standard items are not used.

 

[bjb]

I used to live in Buffalo, NY, and after every winter my firm could count on projects to investigate PEMB that had very large deflections, distress to partitions, etc. Even though these buildings were designed (in theory) for snow load, they still had problems. Often they were designed to 105% of allowable. When we would spec one we would often get into battles because we required a heavier collateral load and didn't let them go to 105% of allowable. None of our spec'd PEMB ever had a problem with Buffalo winters.

To anwer your question, I basically agree with you. I also think that if you need more stiffness in a building, maybe you have cladding other than metal panels, or you have interior partitions that you don't want distressed by lateral or snow loads, conventional is the way to go. I usually see them used as utility or manufacturing buildings.

 

[rholder98]

Thanks everyone. That seems to be the general consensus, as I suspected. In this particular case, the decision was not mine to make, so my argument went unheeded. I do plan on being pretty strict on the specs; we'll see how it works out. Thanks!

 

[jike]

I would like to comment also.

One winter, when our state received more than the design snow loads, I was told that there were 25 buildings that collapsed in our state. All were PEMB's.

I examined one and measured the snow and it was right at the specified LL plus safety factor. Men were on the roof shoveling at the time the building shuddered, lurch and came down. They all jumped onto another roof and were OK.

Many in our state were designed and built with no allowance for sprinklers, lights, ductwork, etc.

Unless specified differently and enforced, the PEMB will be built with extremely large deflections and sway that basically ignores the deflection compatibility limits of other materials on the building such as masonry, brick, drywall, piping, etc. This reduces the initial cost but ultimately adds to the overall maintenace cost and performance problems in the years ahead.

There is always an associated cost with whatever building type you choose to go with. The cheapest building will have much higher overall maintenance costs! If you go with the lowest cost up front, beware of future costs!