Foundation Insulation

Determining the primary foundation

HEScore permits the specification of two foundations. A Foundation element for each foundation in the house is required in HPXML. The two foundations that cover the largest area are selected. This is determined by summing up the area of the FrameFloor (v2 or v3), Floor (v4), or Slab elements (depending on what kind of foundation it is). Area elements are required for all foundations unless there is only one foundation, then it is assumed to be the footprint area of the building. If there are more than two foundations, the areas of the largest two are scaled up to encompass the area of the remaining foundations while maintaining their respective area fractions relative to each other.

Foundation Type

Once a foundation is selected, the HEScore foundation type is selected from HPXML according to the following table.

HPXML to HEScore foundation type mapping

HPXML Foundation Type		HEScore Foundation Type
Basement	Conditioned=”true”	cond_basement
	Conditioned=”false” or omitted	uncond_basement
Crawlspace	Vented=”true”	vented_crawl
	Vented=”false” or omitted	unvented_crawl
SlabOnGrade		slab_on_grade
Garage		unvented_crawl
AboveApartment		above_other_unit
Combination		not translated
Ambient		vented_crawl
RubbleStone		not translated
BellyAndWing [1]		belly_and_wing
Other		not translated

[1]

BellyAndWing is first available in HPXML v4. It can be specified in earlier versions using FoundationType/Other/extension/BellyAndWing element.

Warning

For foundation types that are not translated the translation will return an error.

Foundation wall insulation R-value

If the foundation type is a basement or crawlspace, a FoundationWall is required to be referenced via the Foundation/AttachedtoFoundationWall element. For each foundation wall R-value can be described by using nominal R-value or assembly R-value. If a user wishes to use a nominal R-value, nominal R-value for all layers need to be provided. Otherwise, assembly R-values for the whole foundation wall needs to be provided. Preference is given to assembly R-values.

If nominal R-value is specified, the R-value is the sum of the FoundationWall/Insulation/Layer/NominalRValue element values for each foundation wall. For each foundation wall, an assembly R-value for that wall is looked up based on the nearest R-value in the following table.

Basement and crawlspace wall effective R-values

Insulation Level	Effective R-value
R-0	4
R-11	11.6
R-19	16.9

When more than one HPXML FoundationWall element must be combined into one foundation wall construction for HEScore, an area weighted average R-value is calculated for the foundation walls. The area is obtained from the Area element, if present, or calculated from the Length and Height elements. The weighted average R-value is calculated by weighting the U-values by area.

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

Finally, the nearest nominal insulation level is selected from Basement and crawlspace wall effective R-values.

Slab insulation R-value

If the foundation type is a slab on grade, an area weighted average R-value is calculated using the value of ExposedPerimeter as the area. (The units work out, the depth in the area drops out of the equation.) The R-value is the sum of the Slab/PerimeterInsulation/Layer/NominalRValue element values for each foundation wall. For each slab, an effective R-value is looked up based on the nearest R-value in the following table.

Slab insulation effective R-values

Insulation Level	Effective R-value
R-0	4
R-5	7.9

Then a weighted average R-value 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 effective R-value of the R-0 insulation level is then subtracted.

\[R = R_{eff,avg} - 4.0\]

Finally, the nearest insulation level is selected from the enumeration list.

Floor insulation above basement, crawlspace, or belly and wing

Warning

In HPXML v2 and v3, the FrameFloor element is used to describe the floor. In HPXML v4, the Floor element is used. The translation logic is the same between versions of HPXML, in the documentation we will use Floor, but if you are using HPXML v2 or v3, you should replace with FrameFloor.

If the foundation type is an unconditioned basement, crawlspace, or manufactured home belly and wing, a Floor element is required to be referenced via the Foundation/AttachedToFloor element. For each floor above the foundation, a weighted average using the floor area and R-value are calculated. The area is obtained from the Area element.

The floor R-value can be described by using NominalRValue or AssemblyEffectiveRValue. If a user wishes to use a nominal R-value, NominalRValue elements for all layers need to be provided. Otherwise, AssemblyEffectiveRValue element is required.

Nominal R-value

If NominalRValue is used, the nominal R-value of each layer is summed for the floor: sum(Floor/Insulation/Layer/NominalRValue). The nearest assembly code to that nominal R-value is selected from the lookup table. For example, the following Floor in xml:

<Floor>
      <Insulation>
         <Layer>
            <NominalRValue>10</NominalRValue>
         </Layer>
         <Layer>
            <NominalRValue>8</NominalRValue>
         </Layer>
      </Insulation>
</Floor>

Has a summed nominal R-value of 18, which corresponds to the closest assembly code efwf19ca and an assembly effective R-value of 22.2.

Assembly Effective R-value

If AssemblyEffectiveRValue is used, the nominal R-value nearest to assembly effective R-value from the lookup table is used.

Combining Multiple Floors

When more than one HPXML Floor element must be combined into one floor construction for HEScore, a weighted average assembly R-value is determined by weighting the U-values by area.

\begin{align*} U_i &= \frac{1}{R_{eff,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 assembly code nearest to the weighted average assembly R-value from the lookup table is selected.

Lookup table for floor effective R-values

doe2code	U-value	Eff-R-value
efwf00ca	0.169	5.9
efwf03ca	0.113	8.8
efwf07ca	0.083	12.1
efwf11ca	0.064	15.6
efwf13ca	0.058	17.2
efwf15ca	0.054	18.5
efwf19ca	0.045	22.2
efwf21ca	0.042	23.8
efwf25ca	0.037	27.0
efwf30ca	0.032	31.3
efwf35ca	0.028	35.1
efwf38ca	0.027	37.0
efbw00	0.152	6.6
efbw11	0.058	17.4
efbw13	0.052	19.3
efbw19	0.040	25.1
efbw22	0.036	28.0
efbw30	0.028	35.8

Manufactured home belly and wing assemblies

Todo

This should be moved to an engineering documentation section.

For the assembly R-value and U-value of the belly and wing foundation, we made assumptions as follows:

• All floor joists are 2x6 16 inches o.c.

• In the outer portion of the floor, the loose insulation is compressed against the frame. So, there is no air space between the frame and loose insulation.

• 10% frame fraction and 10% outer portion of the floor.

• The subfloor is 5/8” plywood.

• The interior floor covering is R-2 carpet.

• To determine the assembly R-value, the floor is divided into four heat transfer paths:

  • Framing area on the outer portion where the loose insulation is compressed against the frame.

  • Framing area in the center where the insulation is not compressed.

  • Non-framing area on the outer portion where the loose insulation is compressed against the frame.

  • Non-framing area in the center where the insulation is not compressed.

• A rectangular belly with a depth of 14 inches because the duct diameter for a manufactured home is commonly limited to 14 inches.

• The loose insulation has larger area compared to the floor area, but when modeling the floor, it is necessary to model it using the floor area. Therefore, the R-value of the loose insulation is modified based on the ratio of the loose insulation area to the floor area, with an assumed ratio of 1.04.