MEP Dead Load Allowances 2

[vmirat]

I have a project to install solar panels on the roof of an existing municipal swimming pool building. The as-built drawings of the pool indicate that the dead load used for design of the roof OWSJ's was 20 psf.

Based on the construction of the roof system, I come up with a dead load of 12.3 psf for the roof construction. This means the EOR used an MEP allowance of about 7 psf.

This seems to be a bit too much for this building. There is ductwork, electrical (lights), and fire sprinkler system hanging from the joists. There is no ceiling (open to roof deck).

If this were an office building, I would typically use 10 psf for MEP. However, there is very little hanging from the roof, so I am inclined to use something around 3 to 5 psf for MEP.

I searched high and low for some kind of guidelines for MEP allowance but found nothing, other than references to 10 psf for office buildings. Anyone have rules of thumb that they use?

 

[BAretired]

What is MEP?...Mechanical, Electrical & Paint?

BA

 

[vmirat]

BAretired,
Sorry. I assumed this was known. Mechanical, electrical, plumbing.

 

[a2mfk]

P= plumbing

 

[a2mfk]

Don't have it handy, but I seem to remember ASCE 7 has charts of suggested dead loads. 20 total DL for a commerical roof is pretty standard/common from my experience.

I have an old SBC 97, Appendix A Dead Load table:
mech duct allowance= 4psf

If you know exactly where the existing sprinklers, lights, etc. are located and what exactly they are, than you can calc their weight and reactions pretty precisely. Then you can probably treat this as a more exact point load analysis when it comes to the racks for the solar panels, rather than doing everything in terms of uniform PSF. Actual weights are allowed to be used in most building codes rather than pre-construction uniform dead load allowances..

HTH,
Andrew Kester, PE
Florida

 

[vmirat]

a2mfk,

Actually, you're right. For this particular project, I can figure out what the actual dead load is. It turns out to be about 3 psf for the MEP.

However, this project got me thinking about the design process and why the EOR used 20 psf for this building. So, my question is probably more of a general nature versus my specific project.

 

[nutte]

Why did the EOR use 20 psf in the first place, instead of 15.3? Because it's quick, easy, and not overly conservative. I doubt this "over"-design increased the cost of the building much.

Besides, somebody may come along one day and try to put solar panels on the roof.

 

[a2mfk]

I have done several hospital projects for new equipment on an existing floor where this is the method I have used. I got all the actual equipment weight to the nearest pound and put notes on my drawings to cover myself in case the customer modified them without my knowledge. There are times when you can safely and easily assume conservative dead loads (new construction) and then cases like these where you must be precise if you want a positive result for the client that is still safe and to code...

15-20 psf for roof dead load allowance on commercial buildings is common in my experience (mostly in Florida and SE), I'd like to know what others are using too...

HTH,
Andrew Kester, PE
Florida

 

[msquared48]

15 - 20 psf including one re-roof normally, depending on the framing system, with 2-3 psf allowance for Mech, Elect. If there are sprinklers, I add an additional 2 psf.

I do not put toilets on the roof, so, no plumbing loads.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[BAretired]

IMO, 20 psf seems imminently reasonable for the dead load of a swimming pool roof. To use less would save peanuts and would jeopardize the possibility of adding anything in the way of mechanical, electrical and plumbing.

In my neck of the woods, engineers are adding considerably more than that to include ballast on roofs with insulation not fully secured to the deck. It does not pay to be nigardly about the assessment of dead load because the money saved is peanuts compared to the money required to rectify the design in the event of some unexpected additional load in the future.

For a swimming pool, an allowance of 30 psf dead load is not unreasonable, considering the possibility of additional mechanical requirements in the future.

BA

 

[a2mfk]

Mike, nice one But roofs may support interior roof drains and sprinklers, not just toilets! (They did put a toilet on a roof in a Scrubs episode, I digress....)