Crawl Space Ventilation 1

[ssn61]

I am a mechanical engineer working on HVAC renovation of a 50 year-old private (6-12 grade) school. Part of the duct work and most of the Hot/Chilled water piping is in the crawl space. The owner wants to ventilate the crawl space. One, is this part of an architect's job to calculate the ventilation requirement or the mechanical engineer. Two, what is the process and what are the code requirements?

 

[jkauwale]

1) Ventilation requirements are the responsibility of the mechanical engineer.
2) Code requirements for ventilation are typically based on occupancy (reducing CO2) in the space or they are based on limiting some other contaminant concentration (like noxious fumes, flammable gases, etc.). However, for your situation I believe the code requirement is based on moisture concerns in the crawl space. I believe you can check your building code for the requirement. If your local building code references the International Building Code, then look at Chapter 12 Interior Environment.

Justin K, P.E.

http://www.engproguides.com

 

[ssn61]

Thanks for the info . Part of my question is that who is the responsible to determine whether the ventilation is needed or not. If it's code requirement, then who does the code research and make that determination?

 

[urgross]

I would have guessed from the IBC that you would be required to provide 0.02 CFM/SF and maintain humidity below 60%.

 

[MTES93]

I would think both mechanical engineer and architect would review and determine.

Adhering to the international code (IBC, IMC) I believe the crawl space has to be ventilated if it is unconditioned. As mentioned by jkauwale, if you are only ventilating for humidity and not any bad stuff (radon or what have you) the requirements are outlined in IBC and IMC. If these are your governing codes...

If naturally ventilated the architect would typically take care of it.

If mechanically ventilated the mechanical engineer would take care of it. The rate and RH limit is outlined in Chapter 4 of the IMC.

I imagine other codes (uniform) are similar.

Watch your freeze conditions if the fan is running, you have water lines in the crawl and the outside air is cold...

 

[msquared48]

As I undserstand it, the natural ventilation is the responsibility of the Architect, and any FORCED ventilation would be the responsibility of the Mechanical.

Unvented crawlspaces are a problem waiting to happen, and it should have had natural ventilation when it was originally constructed, regardless of location.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[berkshire]

Depending on the location, it may be required to put in a vapour barrier, if the humidity levels are too high.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[ssn61]

Thank you everyone for your input. I was told by a colleague that we can supply the air from an interior space that has excess outside air to the crawl space from one side and exhaust it from opposite side of the crawl space. This way we can ensure the 60% RH mentioned in IMC is covered. I also heard that IBC does not allow this since a communication path between an occupied space and a crawl space is unacceptable. Any opinion on that? It might be helpful to mention this building is an old school in Dallas, Texas.

 

[willard3]

A fire/smoke path from outside the building to inside the building isn't a matter of opinion, it's a bad idea.

 

[cdxx139]

Try providing a louver and damper on one end, and fan on the other. When H is above 60%, damper shall open and fan shall enerize.

knowledge is power

 

[ssn61]

There are existing vents around perimeter of crawl space. I am going to to put an exhaust fan in the middle of the roof area and route the duct down to crawl space and draw air thru existing vents. Any thoughts on that?
Also, anyone knows any OSHA related rules? I think OSHA asks for lighting of crawl spaces.

 

[berkshire]

If you have perimeter vents on the crawl space, you should not need additional ventilation.
It sounds like it already has natural ventilation.
If your relative humidities are still above 60% then you need to look at the crawlspace floor for rising damp.
Adding a ventilation fan in a situation like that is curing the symptoms not solving the problem.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[cry22]

when you sumbit your plans for code review, who reviews the ventilation requirements? the mechanical reviewer of course, and he will be looking for ventilation per IMC for each room.

So make it yours. your title carries a "V" in HVAC engineer.

 

[Esteves]

Berkshire is right - in a 50 yr old building the source of humidity is either coming from the occupied space above, from condensation on poorly insulated cold water pipes, or leaky pipes (or all of the above). If you're only treating the symptom, you basically have to figure out the volume of the crawl space and figure out air changes per hr of air movement through the crawl space. There is no code guidance on this, this is engineering judgement.

One way to do this would be to install a inline exhaust fans at the existing vents on one side of the building (closest to power source and entry to space for service), and draw make-up air from the opposite side. This worked for me in WI, they had mold in the crawl space and they also had vents.

This is Dallas so there are no issues with freezing pipes in the crawl space right?