# 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 because it is important to know which roof relates to each attic space.

## 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 not translated
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’ cath_ceiling
Attic vented_attic
Other not translated

Note

The attic/roof type cond_attic has been removed from HEScore as of Q1 2022. Homes with conditioned attics should be described in a way that translates to a cathedral ceiling. In HPXML v3, the conditioned attic type is automatically translated to cathedral ceiling. In HPXML v2, the extension workaround to specify a conditioned attic has been removed and the user will need to identify the house as having an attic type that translates to cathedral ceiling to achieve the desired effect.

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.

## Attic and Roof Area¶

Home Energy Score needs to know the area of the thermal boundary between the living space and unconditioned spaces. The areas needed depend on which Attic/Roof Type is selected.

It’s best practice to provide areas for all roof and attic floor surfaces regardless of Attic/Roof type.

### Vented Attic¶

The thermal boundary for a vented attic is at the floor of the attic. In HPXML v2 that area is attached to the Building/BuildingDetails/Enclosure/AtticAndRoof/Attics/Attic element:

                        <Attic>
<SystemIdentifier id="attic1"/>
<AttachedToRoof idref="roof1"/>
<AtticType>vented attic</AtticType>
<AtticFloorInsulation>
<SystemIdentifier id="attic1flrins"/>
<Layer>
<NominalRValue>49</NominalRValue>
</Layer>
</AtticFloorInsulation>
<AtticRoofInsulation>
<SystemIdentifier id="attic1roofins"/>
<Layer>
<NominalRValue>0</NominalRValue>
</Layer>
</AtticRoofInsulation>
<Area>1200</Area>
</Attic>


In HPXML v3 that area is retrieved from a referenced FrameFloor element from the Building/BuildingDetails/Enclosure/Attics/Attic element:

                    <Attic>
<SystemIdentifier id="attic1"/>
<AtticType>
<Attic>
<Vented>true</Vented>
</Attic>
</AtticType>
<AttachedToRoof idref="roof1"/>
<AttachedToFrameFloor idref="framefloor1"/>
</Attic>

                    <FrameFloor>
<SystemIdentifier id="framefloor1"/>
<Area>1200</Area>
<Insulation>
<SystemIdentifier id="attic1flrins"/>
<Layer>
<NominalRValue>49</NominalRValue>
</Layer>
</Insulation>
</FrameFloor>


If there are more than one Roof elements attached to an attic (HPXML v3 since HPXML v2 only allows one roof to be referenced per Attic), you will need to provide an area for each one so that the most common roof color and exterior finishes may be selected.

### Cathedral Ceiling¶

The thermal boundary for a cathedral ceiling is the roof deck, so the area of the roofs attached to the attic are used.

In HPXML v2 a single Roof can be referenced by the Attic and the area of that roof is used.

                <AtticAndRoof>
<Roofs>
<Roof>
<SystemIdentifier id="roof1"/>
<RoofColor>medium</RoofColor>
<RoofType>slate or tile shingles</RoofType>
<RoofArea>679</RoofArea>
</Roof>
</Roofs>
<Attics>
<Attic>
<SystemIdentifier id="attic1"/>
<AttachedToRoof idref="roof1"/>
<AtticType>cathedral ceiling</AtticType>
<AtticRoofInsulation>
<SystemIdentifier id="ceilins1"/>
<Layer>
<NominalRValue>15</NominalRValue>
</Layer>
</AtticRoofInsulation>
</Attic>
</Attics>
</AtticAndRoof>


In HPXML v3 multiple Roof elements can be referenced by the Attic and the sum of those ares is used. The properties of the roofs will be area weighted as described below.

            <Enclosure>
<Attics>
<Attic>
<SystemIdentifier id="attic1"/>
<AtticType>
<CathedralCeiling/>
</AtticType>
<AttachedToRoof idref="roof1"/>
</Attic>
</Attics>
<Roofs>
<Roof>
<SystemIdentifier id="roof1"/>
<Area>679</Area>
<RoofType>slate or tile shingles</RoofType>
<RoofColor>medium</RoofColor>
<Insulation>
<SystemIdentifier id="ceilins1"/>
<Layer>
<NominalRValue>15</NominalRValue>
</Layer>
</Insulation>
</Roof>
</Roofs>
</Enclosure>


## 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 and roof deck insulation R-value is 0, the attic is assumed to have a radiant barrier according to the construction codes available in HEScore. If the Roof/RadiantBarrier element exists and has a “true” value but roof deck insulation R-value greater than 0, the roof will be modeled as a roof with no radiant barrier.

## Roof R-value¶

The roof R-value can be described by using NominalRValue or AssemblyRValue. If a user wishes to use a nominal R-value, NominalRValue elements for all layers need to be provided. Otherwise, AssemblyRValue elements for each layer need to be provided.

If nominal R-value is used, the R-value is summed for all insulation layers. 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. The nearest discrete R-value from the list of possible R-values for that roof type is used to determine an assembly code. Then, the assembly R-value of the corresponding assembly code from the lookup table is used. The lookup table can be found at hescorehpxml\lookups\lu_roof_eff_rvalue.csv.

If assembly R-value is used, the discrete R-value nearest to assembly R-value from the lookup table is used. The lookup table can be found at hescorehpxml\lookups\lu_roof_eff_rvalue.csv.

If the attic has more than one Roof element and/or if multiple attics of the same type and their associated roofs are to be combined, a weighted average assembly R-value is determined by weighting the U-values by area. Then the discrete R-value nearest to the weighted average assembly R-value from the lookup table is used.

\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*}

Then the nearest discrete R-value to the weighted average R-value from the lookup table is used. The lookup table can be found at hescorehpxml\lookups\lu_roof_eff_rvalue.csv.

## Attic R-value¶

Determining the attic floor insulation levels uses the same procedure as Roof R-value except the lookup table is different.

If nominal R-value is used, the attic floor center-of-cavity R-values are each R-0.5 greater than the nominal R-values in the enumeration list.

If assembly R-value is used, the lookup table at hescorehpxml\lookups\lu_ceiling_eff_rvalue.csv is used.

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

## Knee Walls¶

The Home Energy Score Q1 2022 release includes the ability to directly model knee walls. As such, the workaround of adding knee wall area to attic floor area is no longer used. Knee walls are now directly translated and passed to Home Energy Score as follows:

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

In 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>11</NominalRValue>
</Layer>
</Insulation>
</Wall>
<Walls>


The knee walls R-value can be described by nominal R-value or assembly R-value.

If nominal R-value is used, the nearest assembly code by R-value in the code is selected and the assembly R-value is looked up for that code.

If assembly R-value is used, the nearest assembly code by assembly R-value is looked up from that table.

Knee Wall Assembly Codes and R-values
doe2code U-value Eff-R-value
kwwf00 0.346 2.9
kwwf03 0.154 6.5
kwwf07 0.101 9.9
kwwf11 0.083 12.1
kwwf13 0.075 13.4
kwwf15 0.068 14.7
kwwf19 0.055 18.1
kwwf21 0.050 20.1

If an attic has more than one knee wall and/or if multiple attics of the same type need to be combined, the area weighted average assembly effective R-value is calculated from all the associated knee walls. The areas of all the knee walls are summed. The assembly code with the nearest assembly effective R-value is chosed to represent the knee walls.