Cables Stapled To Bottom Edge Of Roof Rafters

[David Tontarski]

I understand that NM cables (of certain gauge) can not be attached to the bottom of floor joists and that more than 2-cables should not be secured with staples, but is there a code issue with NM cables stapled to the underside of roof rafters, as long as they are stapled at least every 4.5'?

[Bill Kriegh]

Code language pertaining to NM-B type cable installation attached to floor joists addresses just that - floor joists. Much of the intent is that by drilling through floor joists the cable is better supported if someone elects to use the cable as a "hanger bar" for clothes and other items and might prevent some possible damage.

Attaching cable to the bottom of roof joists presents another problem in that the temperature is much higher at the top of an attic space than on the ceiling joists at the bottom of the space and it is quite unlikely d-rating for this was taken into account. If you play with an infrared temp tester you can see this is really a big deal.

And, if 2 X 4 trusses are used they can't be drilled anyway.

So no, the drilling versus stapling isn't an issue with roof joists but other things might be/probably are.

[Jerry Peck]

The way they are stapled is incorrect.

As Bill said, derating needs to be applied, both for ambient temperature in the attic and for lack of maintaining spacing.

Trusses of any size are not permitted to be drilled, no engineered trusses or engineered lumber are permitted to be drilled unless specifically addressed by the enginer.

Rafters, floor joists, studs are allowed to be drilled, cut, notched with specified limitations, no restriction is stated about drilling, cutting 2x4 any differently than 2x6, 2x8, etc. - if a 2x4 engineered truss then not allowed to drill anyway (again, regardless of lumber size).

[David Tontarski]

Thanks!

[Mike Kleisch]

is there a code issue with NM cables stapled to the underside of roof rafters?

If there is a permanent stair or ladder to the attic then you need to comply with NEC 334.23 which takes you over to 320.23. Seems like this might be a walk up attic, bunch of "stuff" in there??? If it is, and the cables are within 7 feet of the floor it is wrong. If the access is via scuttle opening then it's only an issue if it's within 6 feet of the scuttle opening.

[Jerry Peck]

If there is a permanent stair or ladder to the attic then you need to comply with NEC 334.23 which takes you over to 320.23. Seems like this might be a walk up attic, bunch of "stuff" in there??? If it is, and the cables are within 7 feet of the floor it is wrong. If the access is via scuttle opening then it's only an issue if it's within 6 feet of the scuttle opening.


As low as the peak is above the ceiling joists, it would have an access opening and only be a problem within 6 feet of the opening.

- 320.23 In Accessible Attics.
- - Type AC cables in accessible attics or roof spaces shall be installed as specified in 320.23(A) and (B).
- - - (A) Where Run Across the Top of Floor Joists. Where run across the top of floor joists, or within 2.1 m (7 ft) of floor or floor joists across the face of rafters or studding, in attics and roof spaces that are accessible, the cable shall be protected by substantial guard strips that are at least as high as the cable. Where this space is not accessible by permanent stairs or ladders, protection shall only be required within 1.8 m (6 ft) of the nearest edge of the scuttle hole or attic entrance.