We have someone challenging that the crawl space under a SFD is not a damp location.
Our supervision says that the NEC definition is to vague to make a ruling on the location.
They are saying that if the crawl space is open or properly ventilated that it would not be considered a damp location by the Florida Building Code.
We did bring up the fact that if mechanical duct work is installed under a house it must be rated for the damp environment encountered.
There are other inspection agencies in our area still allowing NM cable in these areas.
How are you guys looking at this type of installation?

Neal Burdick
City of Tampa
Construction Inspector II

NM cable has always been allowed under residences here,however since 2005 we have not allowed it below the flood plane.

We allowed it also until the 2008 NEC change in 334.12(B)(4).
When we asked our "Buiding" inspectors what type of location (wet, damp, dry) was the crawl space area, they told us that it was considered a damp location. So with the 2008 NEC change NM or NMS could no longer be installed under a house in the crawl space area. Now our supervisor is saying that it is not a damp location, so my question is, do you and your departments consider this a damp location.

Thank you,
Neal Burdick
COT Construction Inspector II

Hey Neal; We allow it in existing buildings only for repair. New circuits or complete rewire to be done IAW 2008 NEC, under the house is as we see it a damp location

If your crawlspace is damp enough to saturate the paper packing in RX (the best explanation of the hazard I have heard), I would be more worried about mold and rotting of the structural floor.

See editor's note for question 60 below (I have underlined it). Apparently it is just "one of those things," and I would tend to agree with your supervisor - unless rain can blow into this area easily. I also agree with the previous comments on flood plane.

International Association of Electrical Inspectors
75th Anniversary Diamond Jubilee Meeting
Coronado Springs Resort – Lake Buena Vista, Florida
September 7-13, 2003

Code Questions

The answers to the code questions are given as they were submitted by the Code Panelist. They do not necessarily reflect the official position or interpretation of the IAEI nor should they be considered as an official interpretation of the Code. An “Editor’s Note” shown in brackets has been provided when additional clarification was necessary, which also is not an official interpretation. An interpretation is only official when expressed from the applicable Authority Having Jurisdiction (AHJ).

60. Is the crawl space of a pier-and-beam dwelling unit considered to be a damp or dry location? If this is a damp location, can Type NM cable be used in this crawl space?

Answer:

The CEC defines “damp location”. Table 19 of the CEC permits use of NMD90 exposed wiring in damp locations. NMWU is allowed to be used for exposed wiring in wet locations

[ Editor’s Note: The determination of whether a specific location is to be considered wet, damp, or dry for the purposes of applying the NEC is the responsibility of the authority having jurisdiction (AHJ). The NEC defines a “damp” location as locations protected from weather and not subject to saturation with water but subject to
moderate degrees of moisture. “Dry” locations are defined as those locations not normally subject to dampness or wetness. There are many crawl spaces under dwelling units considered by the AHJ as a dry location and the use of Type NM cable is permitted by the NEC. Typically the Type NM cable is secured to the underside of the floor joist and not subject to direct contact to the ground under
the dwelling in the event of some unforeseen moisture entering the crawl space. ]

--Dave Clements

I believe that per definition if, "some basements, some barns, and some cold-storage warehouses" may be considered a damp location, then SOME crawspaces would be too.

For the sake of consistent and uniform enforcement, it might be wise to simply consider and declare ALL crawspaces as either a damp location or as a dry location and apply the applicable rules.

I feel this is more of a product use issue rather than a life or property safety matter.

The Canadian Electrical Code gives us the answer??

I would tend to agree with Bryan.


Due to temp changes under the home in the crawl space, I feel that that location would be subject to moisture. My ruling would be that it is a damp location. Even 550.15(H) addresses under-chassis wiring:

Nick,
What is NMD90 and NMWU?
I have only seen NM and NMB being used in our area.
I agree with Bryan and Mike, and feel it is a damp location in most situations.
I also feel we cannot enforce a specific code requirement on a case by case basis.

Neal Burdick
COT Inspector II

I only know what I read on the ECN BB but I gather NMD90 is essentially NM-c and NMWU is UF up in the great white north.

Precisely what that code panel is looking for - is that the decision be made by the local AHJ.

There are other things to consider. If it is considered a damp location, then floor trusses and/or framing might possibly have to be pressure treated. Now we are getting into a cost factor.

I'm not saying that I'm against writing it into the Florida Building Code - that this location be considered a damp one. But I'm not saying that I'm for it, either. I think that you will never get it written into the NEC. Try and see the response you get back from the panel.

Exactly correct Greg, those are the terms for romex and UF in Canada. Nick's response was right out of the Canadian Electrical Code, table 19.

I was merely quoting what someone else said.

After thinking about it over several days, I'm going to change my answer. I do NOT think it would be good if we can blanket all crawl spaces as "damp location." Lets use my house as an example:

Structurally, my house is wooden, not block. But it sits on block piers, poured solid. Around the perimeter of the house, the framing sits on a 3-1/2 foot concrete-block stem wall, that is poured solid. There are no openings, save for the FEMA-required venting, which isn't very much.

I call this crawl space the "black hole" and I can't stand going under there because of the trolls and bogeymen that live down there. If I see one, I may have to kill it, so I'd just as soon avoid the altercation altogether.

HOWEVER -- when I DO embark into the dark depths of the black hole for one reason or another, I can assure you that it is very dry. The floor trusses are dry. The lumber (bracing) is dry. The floor is not poured, it is dirt. The dirt is dry. It is not damp.

Soooooooo, I will have to disagree with those who say that ALL crawlspaces should be damp location, or that the code language should be more specific. I still say it depends whether or not rain can blow in. It depends upon the physical characteristics of the crawl space itself. So I AGREE with the code panel (this is rare) for NOT making the language more specific! I think NEC covers the issue just fine. It is an AHJ call.

PS - Now I will add - that I believe it to also be wrong to blanket-label all crawl spaces as "NOT" being damp location. Like I said, I believe that it depends upon the physical characteristics of the crawl space itself, in my opinion. Other than that all I can say is to please never, EVER, feed the trolls.

Here's just a thought, I normally find that crawl spaces under houses are dry, other than the outer 2ft around the edges where there is no underpinning , no stem walls, just open to the weather

Nick, if your house is truly a stem wall house, why didn't they fill the box with dirt and pour a slab floor? That is the way they build stem wall houses over here.