Roof and Attic¶
Table of Contents
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 | 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 | 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 | 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 | 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>
Radiant Barrier¶
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.
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"/>
<ExteriorAdjacentTo>attic</ExteriorAdjacentTo>
<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.
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.