User Guide

DESIGN GUIDE
7
Shingle Roofs
All shingle roofs (fiberglass, cedar shake, flat tile or
concrete shingle) can utilize heating cable installed
in a serpentine pattern as detailed in the partial
sketch below. The heating cable may be attached to
the roof and fascia with cable fasteners (Catalog No.
RG-CRF) or similar devices held in place with suitable
fasteners or adhesives. Typically one RG-CRF per
peak and one in each lineal run of cable greater than
0.6 m (24"). Care should be exercised to maintain the
integrity of the roof.
To determine the layout pattern for RGS heating
cable on shingle-style roofs, use Table 3.2.
Recommended moderate and heavy conditions
multipliers have been shaded for each overhang
distance. Should conditions dictate a specific
pitch, multipliers for additional spacings have been
included. Be sure to add sufficient extra cable to
reach the power connection point for each circuit.
To establish the amount of cable required, select the
Gutters and Downspouts
RGS heating cable can be utilized in gutters and
downspouts regardless of whether heating cable
has been installed on the roof. The amount of cable
required is based on the width of the gutters, the
level of protection desired and the linear footage of
gutters and downspouts. A typical layout is shown
below.
As stated in IEEE Standard 515.1, Recommended
Practice for the Testing, Design, Installation, and
Maintenance for Electrical Resistance Heat Tracing
for Commercial Applications, in-line and T-splice
kits should be avoided. This will require that heating
cable in downspouts be looped (also an IEEE 515.1
recommendation) to eliminate splicing the cable.
Additionally, the heating cable end termination
should not be located in the lowest portion of the
downspout.
Select the level of protection required (based on
the size of the gutter) from Table 3.3. Choose the
multiplier which corresponds to the application and
apply this multiplier to the footage of gutters and
the number and footage of downspouts to be heat
traced. Add sufficient heating cable (including a drip
loop) to reach the power connection junction box.
Table 3.3 Gutters and Downspouts
Table 3.2 Shingle Roofs
Heavy Conditions Multipliers
Moderate Conditions Multipliers
Spacing Pitch
Cable in Gutter
Section Detail
RG-CRF
Overhang
Distance
Spacing Pitch
350 mm
(14")
400 mm
(16")
450 mm
(18")
500 mm
(20")
550 mm
(22")
600 mm
(24")
650 mm
(26")
700 mm
(28")
450 mm (18") 3.3 3.0 2.7 2.4 2.3 2.1 NR NR
600 mm (24") 4.2 3.7 3.3 3.0 2.8 2.6 2.4 2.3
750 mm (30") 5.0 4.4 3.9 3.6 3.3 3.0 2.8 2.7
900 mm (36") 5.8 5.1 4.6 4.1 3.8 3.5 3.3 3.1
1050 mm (42") 6.7 5.9 5.2 4.7 4.3 4.0 3.7 3.5
Loop Cable in
Downspout
Gutter
Width
Gutter
Allowance
Downspout
Allowance
≤150 mm (≤6") 1X Gutter Length 1X Downspout Length
150-300 mm
(6-12")
2X Gutter Length 2X Downspout Length
≥300 mm (≥12") Contact a Thermon Factory Representative
row with the corresponding overhang distance and
follow across to the multiplier that matches the level
of protection desired. After selecting a multiplier,
read the corresponding spacing pitch value at the
top of the column. Multiply this number by the
number of linear feet of roof eave to be protected
and add sufficient cable to reach the power supply
junction box.