# Roof and Attic¶

HPXML allows the specification of multiple Attic elements, each of which relates to one (HPXML v2) or more (HPXML v3) Roof elements. 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 if there is more than one Attic element.

• In HPXML v2, areas can be specified directly by Attic/AtticArea.
• In HPXML v3, translator first searches all the Area of FrameFloor whose id is the same as what referred in Attic/AttachedToFrameFloor, and sums all areas up. Otherwise, the Area of Roof whose id is the same as what referred in Attic/AttachedToRoof will be searched and summed for each attic.

If there is only one Attic element, the footprint area of the building is assumed. If there’s only one roof in HPXML, it will be automatically attached to attic.

## 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 v2)
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 see note below
HPXML Attic Type to HEScore Roof type mapping (HPXML v3)
HPXML HEScore
CathedralCeiling cath_ceiling
FlatRoof cath_ceiling
Attic/CapeCod = ‘true’ cath_ceiling
Attic/Conditioned = ‘true’ cond_attic
Attic vented_attic
Other not translated

Note

Prior to HPXML v3, there’s no existing HPXML element capturing a conditioned attic. The only way to model a HEScore cond_attic is to specify HPXML Attic Type to be other with an extra element Attic/extension/Conditioned to be true.

Otherwise, HPXML Attic Type other will not be translated and 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.

Note

Starting from HPXML v3, HPXML allows multiple floors/roofs attached to a single attic. The properties of the floors/roofs attached to the same attic are combined into a single one.

## 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
medium dark medium_dark
dark dark
reflective white

If the Roof/SolarAbsorptance element is present, the HEScore roof color is set to “cool_color” and the recorded absorptance will be sent to HEScore under the “roof_absorptance” element.

Note

Starting from HPXML v3, if there’re more than one roof attached to the same attic, the roof color of that covers greatest area will be selected.

## 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.

### HPXML v2¶

<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>


### HPXML v3¶

<Atics>
<Attic>
<SystemIdentifier id="attic5"/>
<AtticType>
<CathedralCeiling/>
</AtticType>
<AttachedToRoof idref="roof3"/>
</Attic>
</Attics>
<Roofs>
<Roof>
<SystemIdentifier id="roof3"/>
<Area>2500</Area>
<Insulation>
<SystemIdentifier id="attic5roofins"/>
<Layer>
<InstallationType>continuous</InstallationType>
<InsulationMaterial>
<Rigid>eps</Rigid>
</InsulationMaterial>
<NominalRValue>10</NominalRValue>
</Layer>
</Insulation>
</Roof>
<Roofs>


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.

Starting from HPXML v3, multiple roofs are allowed to be attached to the same attic, if the attic has more than one Roof 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
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. This averaged Center-of-Cavity Effective R value is combined from all roofs attached to the same attic. The highest weighted roof construction type is selected to represent properties of the attic.

\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*}

If the house has more than two attics specified, the attics of the same roof types are combined. Therefore, the same weighted average calculation is performed (taking roof-level averaged R as $$R_{i}$$ and attic area determined in attic area as $$A_{i}$$) to combine multiple attics.

Then the R-0 effective center-of-cavity R-value ($$R_{offset}$$) is selected for highest weighted roof construction type for the attic 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 for the attic is 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.

## Knee Walls¶

In HPXML v2, knee walls are specified via the Attic/AtticKneeWall element.

Starting from HPXML v3, knee walls are specified via wall attachment in Attic/AttachedToWall. The attached wall must have AtticWallType of “knee wall”. See below an example:

<Attics>
<Attic>
<SystemIdentifier id="attic5"/>
<AtticType>
<Attic>
<Vented>true</Vented>
</Attic>
</AtticType>
<AttachedToRoof idref="roof3"/>
<AttachedToWall idref="kneewall"/>
<AttachedToFrameFloor idref="framefloor"/>
</Attic>
</Attics>
<Walls>
<Wall>
<SystemIdentifier id="kneewall"/>
<AtticWallType>knee wall</AtticWallType>
<WallType>
<WoodStud/>
</WallType>
<Area>200</Area>
<Insulation>
<SystemIdentifier id="kneewallins"/>
<Layer>
<InstallationType>cavity</InstallationType>
<NominalRValue>10</NominalRValue>
</Layer>
</Insulation>
</Wall>
<Walls>


If an attic has knee walls specified, the area of the knee walls will be added to the attic floor area. The knee walls center-of-cavity R-value is R-1.8 greater than the nominal R-value. The knee walls center-of-cavity R-value will be reflected in the area weighted center-of-cavity effective R-value of the attic floor. This averaged center-of-cavity effective R value is combined from all knee walls and attic floors attached to the same attic. The highest weighted attic floor construction type is selected.