# Running wire in the attic



## wease (Dec 5, 2006)

Hi all,

I posted something like this last winter and now I'm doing the job...finally. My attic is permanently accessible with a ladder.

Some questions:

1. As an example, I have 2 recessed lights that span about 4 joists in the floor of the attic (ceiling of the remodeled space). Is it ok to drill the joists straight across to connect these together? Or is it better to bring it up and run it over the joists? I believe that it's not ok to do the latter per code without 'protection'. But what if I did this close to the edge of the house where the roof comes down on the side walls? Say like 2 feet?

2. Can I run a bunch of wires on the face of joists? I'll have about 40 feet of run for 30 circuits and they will run parallel to the joists. Thought I'd just staple them to the side of the joists. Insulation would eventually cover this wiring. 

Thanks in advance.


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## J. V. (Jun 1, 2007)

No problem drilling through the joist or placing them on top. Drill just a little bigger than the cable. If you run them on top of the joist you will need to notch the joist if you plan to put down plywood ect..
You can run as many cables on the side of the joist as you want. However, do not staple all cables under on one staple. The staple will list the amount of cables allowed to be stacked. Allow some room between the runs of cable as this is called bundling. When you bundle cables you must follow certain NEC rules. So just do a nice neat job, keep cable stacks seperated and use the right staples for the job......Have Fun John


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## ChristopherSprks (Sep 17, 2007)

J. V. said:


> No problem drilling through the joist or placing them on top. Drill just a little bigger than the cable. If you run them on top of the joist you will need to notch the joist if you plan to put down plywood ect..




Avoid notching at all cost; it weakens the integrity of the wood.
Drill into the center of the ceiling rafter, you can drill a multiple 1" holes and pull in the cables loosely (don't over fill the hole).
For multiple runs of cable try these - http://products3.3m.com/catalog/us/en001/utilities_telecom/oem_electrical/node_GSW462SHGGbe/root_GST1T4S9TCgv/vroot_GSHBRQT7DVge/gvel_B9XKSZGDTVgl/command_AbcPageHandler/theme_us_oemeletrical_3_0


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## J. V. (Jun 1, 2007)

Notching is not a violation of the code, as long as you use nail guards. Why would holes be any more concern than notches?


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## Stubbie (Jan 7, 2007)

Notching of ceiling or floor joists have strict rules by the building codes as do bored holes. Very generally notches cannot exceed d/4 and must be made at the end 1/3 of a joist , no notching is allowed in the center 1/3 period.
Bored holes must be no closer than 2" of the face of the joist and the diameter is not to be greater than d/3.

Rafters have different rules, as do studs, as do top plates, .....

Stubbie


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## ChristopherSprks (Sep 17, 2007)

*As Per NEC 2005*
*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.
In accessible attics, Type AC cable installed across the top of floor joists or within 7 ft of the floor or floor joists across the face of rafters or studs must be protected by guard strips. Where the attic is not accessible by a permanent ladder or stairs, guard strips are required only within 6 ft of the scuttle hole or opening.
*(B)* Cable Installed Parallel to Framing Members Where the cable is installed parallel to the sides of rafters, studs, or floor joists, neither guard strips nor running boards shall be required, and the installation shall also comply with *300.4(D).*
*300.4(D)* Cables and Raceways Parallel to Framing Members and Furring Strips In both exposed and concealed locations, where a cable- or raceway-type wiring method is installed parallel to framing members, such as joists, rafters, or studs, or is installed parallel to furring strips, the cable or raceway shall be installed and supported so that the nearest outside surface of the cable or raceway is not less than 32 mm _(1 1/ 4 in.)_ from the nearest edge of the framing member or furring strips where nails or screws are likely to penetrate. Where this distance cannot be maintained, the cable or raceway shall be protected from penetration by nails or screws by a steel plate, sleeve, or equivalent at least 1.6 mm _( 1/ 16 in.)_ thick.
As shown in Exhibit 300.3, NM cables are positioned so as to equal or exceed the minimum clear distance of 1 1/ 4 in. that is required between the furring strip (wood strapping in this case) and the nearest edge of the NM cable as required by *300.4(D).* 

*Exception No. 1:* Steel plates, sleeves, or the equivalent shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.
*Exception No. 2*: For concealed work in finished buildings, or finished panels for prefabricated buildings where such supporting is impracticable, it shall be permissible to fish the cables between access points.
*Exception No. 3*: A listed and marked steel plate less than 1.6 mm ( 1/ 16 in.) thick that provides equal or better protection against nail or screw penetration shall be permitted.

ALSO-
*330.23* In Accessible Attics
The installation of Type MC cable in accessible attics or roof spaces shall also comply with *320.23*.
In accessible attics, Type MC cable installed across the top of floor joists or within 7 ft of the floor or floor joists across the face of rafters or studs must be protected by guard strips. Where the attic is not accessible by a permanent ladder or stairs, guard strips are required only within 6 ft of the scuttle hole or opening.
Exception: In buildings completed before the wiring is installed, attic and roof spaces that are not accessible by stairway or permanent ladder and have headroom at all points less than 900 mm _(3 ft),_ the wiring shall be permitted to be installed on the edges of rafters or joists facing the attic or roof space.

*Read this through, if you don't understand (and I don't expect u 2) please feel free to ask.*


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## DuncanB (Sep 18, 2007)

I'll second Stubbies post. 
Most inspectors prefer to see holes within the last foot or so from the walls. They can be out 1/3 of the joist span by code, though. The center 2/3 is the ABSOLUTE forbidden zone. This is only for conventional lumber.

Engineered joists (the type with vertical waferwood and a top and bottom chord of 2X3 or 2X4 lumber) have different characteristics, and you need to consult the manufacturer's recommendations for drilling. Often they will want the holes in the center of the span.


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## wease (Dec 5, 2006)

First of all, thanks for not telling me to get an electrician. Thought for sure I'd receive one or two comments like that. Excellent, informative posts instead.

Thanks for the code quote, that helps somewhat. I'll try to get some understanding there.

Not sure what the 'forbidden zone' comment means. Are you saying you shouldn't drill a hole in the middle third of a joist span? Seems odd that this would be a problem. Most codes refer to not drilling within a couple feet of the end of a joist span...not the middle.


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## DuncanB (Sep 18, 2007)

Sorry, Yes the "forbidden zone" (my comment) is the area in the center third of the span. You cannot drill or notch in this area. Only the outer 1/3 of the span.
I don't know what kind of Code you have seen that recommends or even allows this. Please cite it if you can.


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## Stubbie (Jan 7, 2007)

The forbidden zone is for notching, this is the middle 1/3 of the joist. 

Duncan... I believe you are allowed bored holes. I'll try to find some documentations and post.

I should make one correction the notch can not be more than d/6 if it occurs anywhere but the very end which is d/4 so notching is allowed out to the beginning of the center 1/3... ie ... if my joist is 9 feet I can notch for the first 3 feet on either end. I cannot notch in the center 3 feet. 

You say your running 30 circuits?


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## wease (Dec 5, 2006)

Yes, a little less than 30 circuits. Most of them will be in the kitchen which is a much shorter run of about 35 feet.


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## dmaceld (Jul 4, 2007)

J. V. said:


> Notching is not a violation of the code, as long as you use nail guards. Why would holes be any more concern than notches?


It's a physics issue, not a code issue per se. Think of the joist as a whole bunch of fibers, or strands, layered one above the other. When you put a load on the joist that bends it downward, the fibers on the top get compressed and fibers at the bottom get tensioned. The fibers right in the center don't go into compression or tension. If you notch the joist on either the top or bottom you are cutting away fibers that are carrying the load. Because the middle fibers have little or no tension and compression you can drill through them and not materially affect the strength of the joist. The bending stress in the joist is greatest at the middle (in a simple beam situation) and drops to zero at the ends. That's why the code allows some notches at the ends but not toward the middle.


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## DuncanB (Sep 18, 2007)

*Not a Code issue per se:*

From the International Building Code - 
_________________________________________________________________
2308.8.2* Framing Details
*Notches on the ends of joists shall not exceed one-fourth the joist depth. Holes bored in joists shall not be within 2 inches (51mm) of the top or bottom of the joist, and the diameter of any such hole shall not exceed one-third the depth of the joist. Notches in the top or bottom of the joists shall not exceed one-sixth the depth and shall not be located in the middle third of the span.
*__________________________________________________________

*Keep in mind that this is an absolute, and does not take into consideration any structural concerns. Joist spans, both dead and live loading requirements, etc., are taken into consideration when designing structures.

After-the-fact remodeling (for instance, 2 recessed lights that span across 4 joists) can only serve to weaken the structure without properly resupporting or bracing them.


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## Stubbie (Jan 7, 2007)

Good morning Duncan

I found this which supports what you have posted.... page 3

http://www.ladbs.org/faq/info bulletins/building code/IB-P-BC 2002-007 Wood cutting notching.pdf


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## ChristopherSprks (Sep 17, 2007)

wease said:


> First of all, thanks for not telling me to get an electrician.


Would you have listened?
The way I look at it  is, you obviously think you can do this and you're going to do this one way or another.
So we might as well give you all the guidance we can and after all that ... maybe then you'll come to your senses...:wink:

Good Luck on your project :thumbsup:


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## beer_geek (Feb 19, 2007)

DuncanB,
Just looking for clarification here. 
You state "You cannot *drill *or notch in this area. Only the outer 1/3 of the span." However, the passage you quoted only talks about notches and not holes. I can't find anything that says you can't drill. Can you provide supporting documentation that addresses being unable to drill in the middle third of a joist?
Thanks


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## Stubbie (Jan 7, 2007)

I think Duncan is referring to engineered joists, without an engineering stamp on the bored hole design you wouldn't be able to bore the center of this type joist. You are allowed to bore the center one third of a dimensional lumber joist. If a 2x10 your max. hole would be a hole 3 1/16" in diameter. Note that a 2x10 actual is 9 1/4". In the link I posted earlier note that under the heading it states that unless altered by an engineering drawing with signed and approved stamp. As an example here is a joist span that is bored right thru the center with a 4 inch hole on 2x10 dimensional. This was in violation of IRC rules. However the design has an engineering approval based on the sister joists and use of adhesive so it was acceptable. (taken from the NACHI Website)


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## J. V. (Jun 1, 2007)

It's great that we all try to give sound and NEC required advice to the DIY'ers. But sometimes I think we get a little to carried away. Probabaly even confuse someone.


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## Stubbie (Jan 7, 2007)

J.V.

The last 5 or 6 replies aren't even geared towards the original poster. They are a result of other inquiries, probably should have suggested a new thread. I asked Wease about 30 circuits because I don't think you should try to take 30 circuits thru bored holes in ceiling joists. He is wanting to run parallel and then at times branch off perpendicular like the can lights. he was inquiring about a situation like this where he was thinking he could run perpendicular on the face of the joists in a permenently accessed attic if he was back close to the rafters.









by code you could not but I do believe an inspector may allow what he was asking by exception. In this photo and stating that the longest joist shown is the middle joist and it is showing exactly 1/3 of the span. then anywhere in that picture I can bore or notch acorrding to IRC rules. You could also have running boards. I think I would just do running boards from plywood and or 1x2 if running perpendicular. If parallel I would staple those 30 circuits to two or three joists using the face and stay up from the drywall face a couple inches even though not required.

But I agree J.V. we got way out in left field beyond what wease was asking.

Stubbie


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## ChristopherSprks (Sep 17, 2007)

J. V. said:


> It's great that we all try to give sound and NEC required advice to the DIY'ers. But sometimes I think we get a little to carried away. Probabaly even confuse someone.


 
Well now, isn't that just to bad.......


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## wease (Dec 5, 2006)

Stubbie said:


> J.V.
> 
> The last 5 or 6 replies aren't even geared towards the original poster. They are a result of other inquiries, probably should have suggested a new thread. I asked Wease about 30 circuits because I don't think you should try to take 30 circuits thru bored holes in ceiling joists. He is wanting to run parallel and then at times branch off perpendicular like the can lights. he was inquiring about a situation like this where he was thinking he could run perpendicular on the face of the joists in a permenently accessed attic if he was back close to the rafters.
> 
> ...


That's what I'm going to do. I have a catwalk setup in the attic and I think I will raise it with 2x4's and run the wires under that.

Thanks for the excellent help all.


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