Roof and Attic

HPXML allows the specification of multiple Attic elements, each of which relates to a Roof element. That relation is optional in HPXML, but is required for HEScore when there is more than one Attic or Roof because it is important to know which roof relates to each attic space. An area is required for each Attic element if there is more than one Attic element. If there is only one Attic element, the footprint area of the building is assumed.

Attic/Roof Type

Each Attic is considered and the AtticType is mapped into a HEScore roof type according to the following mapping.

HPXML Attic Type to HEScore Roof type mapping
HPXML HEScore
cape cod cath_ceiling
cathedral ceiling cath_ceiling
flat roof cath_ceiling
unvented attic vented_attic
vented attic vented_attic
venting unknown attic vented_attic
other not translated

Warning

There is no way to get a HEScore cond_attic.

Note

Items that are not translated will result in a translation error.

HEScore can accept up to two attic/roof constructions. If there are more than two specified in HPXML, the properties of the Attic elements with the same roof type are combined. For variables with a discrete selection the value that covers the greatest combined area is used. For R-values a calculation is performed to determine the equivalent overall R-value for the attic. This is discussed in more detail in Roof R-value.

Roof Color

Roof color in HEScore is mapped from the HPXML Roof/RoofColor element according to the following mapping.

HPXML to HEScore roof color mapping
HPXML HEScore
light light
medium medium
dark dark
reflective white

Note

HEScore allows for more detailed roof color descriptions than HPXML. There is no way in HPXML to specify the following HEScore roof colors:

  • medium_dark
  • cool_color (along with the absorptivity, which is also missing an HPXML element.)

Exterior Finish

HPXML stores the exterior finish information in the Roof/RoofType element. This is translated into the HEScore exterior finish variable according to the following mapping.

HPXML Roof Type to HEScore Exterior Finish mapping
HPXML HEScore
shingles composition shingles
slate or tile shingles concrete tile
wood shingles or shakes wood shakes
asphalt or fiberglass shingles composition shingles
metal surfacing composition shingles
expanded polystyrene sheathing not translated
plastic/rubber/synthetic sheeting tar and gravel
concrete concrete tile
cool roof not translated
green roof not translated
no one major type not translated
other not translated

Note

Items where the HEScore translation indicates not translated above will result in a translation error.

Rigid Foam Sheathing

If the AtticRoofInsulation element has a Layer with the “continuous” InstallationType, InsulationMaterial/Rigid, and a NominalRValue greater than zero, the roof is determined to have rigid foam sheathing and one of the construction codes is selected accordingly. Otherwise one of the standard wood frame construction codes is selected.

<Attic>
    <SystemIdentifier id="attic5"/>
    <AttachedToRoof idref="roof3"/>
    <AtticType>cathedral ceiling</AtticType>
    <AtticRoofInsulation>
        <SystemIdentifier id="attic5roofins"/>
        <Layer>
            <InstallationType>continuous</InstallationType>
            <InsulationMaterial>
                <Rigid>eps</Rigid>
            </InsulationMaterial>
            <NominalRValue>10</NominalRValue>
        </Layer>
    </AtticRoofInsulation>
    <Area>2500</Area>
</Attic>

Radiant Barrier

If the Roof/RadiantBarrier element exists and has a “true” value, the attic is assumed to have a radiant barrier and no roof deck insulation is assumed according to the construction codes available in HEScore.

Roof R-value

R-values for the roof deck are added up by summing the values of the Layer/NominalRValue. If the roof construction was determined to have Rigid Foam Sheathing, an R-value of 5 is subtracted from the roof R-value sum to account for the R-value of the sheathing in the HEScore construction. If the house has more than one Attic element with roof insulation, the insulation values are combined by first selecting the nearest roof center-of-cavity R-value for each roof area from the table below.

Roof Center-of-Cavity Effective R-values
Exterior Composition or Metal Wood Shakes Clay Tile Concrete Tile Tar and Gravel
R-value Effective R-value
Standard
R-0 2.7 3.2 2.2 2.3 2.3
R-11 13.6 14.1 13.2 13.2 13.2
R-13 15.6 16.1 15.2 15.2 15.2
R-15 17.6 18.1 17.2 17.2 17.2
R-19 21.6 22.1 21.2 21.2 21.2
R-21 23.6 24.1 23.2 23.2 23.2
R-27 29.6 30.1 29.2 29.2 29.2
R-30 32.6 33.1 32.2 32.2 32.2
w/ Radiant Barrier
R-0 5 5.5 4.5 4.6 4.6
w/ foam sheeting
R-0 6.8 7.3 6.4 6.4 6.4
R-11 17.8 18.3 17.4 17.4 17.4
R-13 19.8 20.3 19.4 19.4 19.4
R-15 21.8 22.3 21.4 21.4 21.4
R-19 25.8 26.3 25.4 25.4 25.4
R-21 27.8 28.3 27.4 27.4 27.4

Then a weighted average is calculated by weighting the U-values by area.

\begin{align*}
U_i &= \frac{1}{R_i} \\
U_{eff,avg} &= \frac{\sum_i{U_i A_i}}{\sum_i A_i} \\
R_{eff,avg} &= \frac{1}{U_{eff,avg}} \\
\end{align*}

The R-0 effective center-of-cavity R-value (R_{offset}) is selected for the highest weighted roof construction type represented in the calculation and is subtracted from R_{eff,avg}.

R = R_{eff,avg} - R_{offset}

Finally the R-value is rounded to the nearest insulation level in the enumeration choices for the highest weighted roof construction type included in the calculation.

Attic R-value

Determining the attic floor insulation levels uses the same procedure as Roof R-value except the lookup table is different. The attic floor center-of-cavity R-values are each R-0.5 greater than the nominal R-values in the enumeration list.

If the primary roof type is determined to be a cathedral ceiling, then an attic R-value is not calculated.