Running LV conduit through attic - what do I need to know?
NEC Article 362

I've copied the NEC portions that cover corrugated HDPE (High Density Polyethylene) conduit for your reading pleasure. The NEC differentiates between corrugated and non corrugated HDPE conduits by referring to corrugated HDPE as ENT and non corrugated as just HDPE. Non corrugated HDPE is not allowed at all in any buildings, whereas corrugated is.

Also, the NEC doesn't specifically differentiate orange corrugated HDPE from blue corrugated HDPE but instead simply refers to Optical Fiber Cable conduit as "Innerduct".

770.12 Innerduct for Optical Fiber Cables.


  Listed plenum communications raceway, listed riser communications
  raceway, and listed general-purpose communications raceway selected
  in accordance with the provisions of Table 800.154(b) shall be
  permitted to be installed as innerduct in any type of listed raceway
  permitted in Chapter 3.


Also interesting is Carlon, the maker of Riser-gard refers to "Innerduct" when comparing their different Riser-gard products. See here.
I think it is safe, in general, to compare innerduct to the safety regulations required for ENT installations.

The most important parts for you will be 362.12 Uses Not Permitted, 362.30 Securing and Supporting A-B, and 362.26 Bends.

Notably Securing and Supporting(B) addresses your horizontal attic runs which permits the rafters to support the ENT if they are not greater than 3' apart and provided you secure the ENT within 3' of every pull/junction box.

Also interesting is 362.10 which only permits buildings not exceeding three floors for exposed work.

And anything over 122°F ambient temperature is not permitted unless listed otherwise.  This may be a problem for hot summer attics without proper ventilation.

As for drilling into attics that is more a building code issue.  This answer addresses the codes for that.


  II. Installation 362.10 Uses Permitted.
  
  The use of ENT and fittings shall be permitted in the following:
  
  (1) In any building not exceeding three floors above grade as follows: 
  
  a. For exposed work, where not prohibited by 362.12 
  
  b. Concealed within walls, floors, and ceilings 
  
  (2) In any building exceeding three floors above grade, ENT shall be concealed within walls, floors, and ceilings where the walls, floors, and ceilings provide a thermal barrier of material that has at least a 15-minute finish rating as identified in listings of fire-rated assemblies. The 15-minute-finish-rated thermal barrier shall be permitted to be used for combustible or noncombustible walls, floors, and ceilings. 
  
  Exception to (2): Where a fire sprinkler system(s) is in stalled in accordance with NFPA 13-2013, Standard for the Installation of Sprinkler Systems, on all floors, ENT shall be permitted to be used within walls, floors, and ceilings, exposed or concealed, in buildings exceeding three floors above grade. Informational Note: A finish rating is established for assemblies containing combustible (wood) supports. The finish rating is defined as the time at which the wood stud or wood joist reaches an average temperature rise of 121°C (250°F) or an individual temperature of 16.3°C (325°F) as measured on the plane of the wood nearest the fire. A finish rating is not in tended to represent a rating for a membrane ceiling. 
  
  (3) In locations subject to severe corrosive influences as covered in 300.6 and where subject to chemicals for which the materials are specifically approved. 
  
  (4) In concealed, dry, and damp locations not prohibited by 362.12. 
  
  (5) Above suspended ceilings where the suspended ceilings provide a thermal barrier of material that has at least a 15-minute finish rating as identified in listings of fire-rated assemblies, except as permitted in 362.10(1)(a). 
  
  Exception to (5): ENT shall be permitted to be used above suspended ceilings in buildings exceeding three floors above grade where the building is protected throughout by a fire sprinkler system installed in accordance with NFPA 13-2013, Standard for the Installation of Sprinkler Systems. 
  
  (6) Encased in poured concrete, or embedded in a concrete slab on grade where ENT is placed on sand or ap proved screenings, provided fittings identified for this purpose are used for connections. 
  
  (7) For wet locations indoors as permitted in this section or in a concrete slab on or belowgrade, with fittings listed for the purpose. 
  
  (8) Metric designator 16 through 27 (trade size 1/2" through 1) as listed manufactured prewired assembly. Informational Note: Extreme cold may cause some types of nonmetallic conduits to become brittle and therefore more susceptible to damage from physical contact. 
  
  (9) Conductors or cables rated at a temperature higher than the listed temperature rating of ENT shall be permitted to be installed in ENT, if the conductors or cables are not operated at a temperature higher than the listed temperature rating of the ENT. 
  
  362.12 Uses Not Permitted.
  
  ENT shall not be used in the following: 
  
  (1) In any hazardous (classified) location, except as permitted by other articles in this Code 
  
  (2) For the support of luminaires and other equipment 
  
  (3) Where subject to ambient temperatures in excess of 50°C (122°F) unless listed otherwise 
  
  (4) For direct earth burial 
  
  (5) Where the voltage is over 600 volts 
  
  (6) In exposed locations, except as permitted by 362.10(1), 362.10(5), and 362.10(7) 
  
  (7) In theaters and similar locations, except as provided in 518.4 and 520.5 
  
  (8) Where exposed to the direct rays of the sun, unless identified as sunlight resistant 
  
  (9) Where subject to physical damage 
  
  362.20 Size. 
  
  (A) Minimum. ENT smaller than metric designator 16 (trade size 1/2") shall not be used. 
  
  (B) Maximum. ENT larger than metric designator 53 (trade size 2) shall not be used. Informational Note: See 300.1
  
  362.26 Bends – Number in One Run. 
  There shall not be more than the equivalent of four quarter bends (360 degrees total) between pull points, for example, conduit bodies and boxes. 
  
  362.28 Trimming. 
  
  All cut ends shall be trimmed inside and outside to remove rough edges. 
  
  362.30 Securing and Supporting.
  
  ENT shall be installed as a complete system in accordance with 300.18 and shall be securely fastened in place and supported in accordance with 362.30(A) and (B). 
  
  (A) Securely Fastened.
  
  ENT shall be securely fastened at intervals not exceeding 900 mm (3 ft). In addition, ENT shall be securely fastened in place within 900 mm (3 ft) of each outlet box, device box, junction box, cabinet, or fitting where it terminates.
  
  Exception No. 1: Lengths not exceeding a distance of 1.8 m (6 ft) from a luminaire terminal connection for tap connections to lighting luminarie shall be permitted without being secured. 
  
  Exception No. 2: Lengths not exceeding 1.8 m (6 ft) from the last point where the raceway is securely fastened for connections within an accessible ceiling to luminaire(s) or other equipment. 
  
  Exception No. 3: For concealed work in finished buildings or prefinished wall panels where such securing is impracticable, unbroken lengths (without coupling) of ENT shall be permitted to be fished. 
  
  (B) Supports. 
  Horizontal runs of ENT supported by openings in framing members at intervals not exceeding 900 mm (3 ft) and securely fastened within 900 mm (3 ft) of termination points shall be permitted. 
  
  362.46 Bushings. Where a tubing enters a box, fitting, or other enclosure, a bushing or adapter shall be provided to protect the wire from abrasion unless the box, fitting, or enclosure design provides equivalent protection.
  
  362.48 Joints. 
  
  All joints between lengths of tubing and between tubing and couplings, fittings, and boxes shall be by an approved method. 
  
  362.56 Splices and Taps. 
  
  Splices and taps shall be made only in accordance with 300. 15. Informational Note: See Article 314 for rules on the installation and use of boxes and conduit bodies. 
  
  362.60 Grounding. Where equipment grounding is required, a separate equipment grounding conductor shall be installed in the raceway in compliance with Article 250, Part VI. III. Construction Specifications 
  
  362.100 Construction. ENT shall be made of material that does not exceed the ignitibility, flammability, smoke gen eration, and toxicity characteristics of rigid (nonplasticized) polyvinyl chloride. ENT, as a prewired manufactured assembly, shall be provided in continuous lengths capable of being shipped in a coil, reel, or carton without damage. 
  
  362.120 Marking. (This is usually done by the manufacturer)
  
  ENT shall be clearly and durably marked at least every 3 m (10 ft) as required in the first sentence of 110.21(A). The type of material shall also be included in the marking. Marking for limited smoke shall be permitted on the tubing that has limited smoke producing characteristics. The type, size, and quantity of conductors used in prewired manufactured assemblies shall be identified by means of a printed tag or label attached to each end of the manufactured assembly and either the carton, coil, or reel. The enclosed conductors shall be marked in accordance with 3.10.120.  (This is usually done by the manufacturer)