Below-grade walls come in several common forms:
Cinder Block foundation (with or without filled cores)
Poured concrete foundation
Brick or stone foundation
Insulated Concrete Form (ICF)
Each construction transfers heat to the surrounding soil at a different rate, and the depth of the wall below grade changes the load further. Getting the Below Grade Walls settings right is essential to accurate basement load calculations.
This article walks through every setting on the Below Grade Walls screen.
Always verify construction details and assumptions in the home. Confirm the foundation material, check for any interior framing or board insulation, and confirm how much of the wall is actually below grade. A flashlight and a tape measure go a long way here.
Note about Is Below Grade toggle: It tells Amply to treat the wall as below grade and enables different construction options, different temperature assumptions, and following the manual J standard, zeros out cooling load for below grade surfaces. Turn it off and the sidebar reverts to standard above-grade wall materials. Just like above grade walls, Is Exterior it determines whether the wall counts toward the load calc at all.
Both toggles can be found in the upper right of the sidebar when a wall is selected.
Edit below-grade wall assumptions
To make changes to a below-grade wall, tap on the wall in the 3D model, and the sidebar will appear where you can edit the assumptions, like whether or not it's below grade and all the details about the wall construction.
Then tap on the existing assumptions menu to make changes.
Shortcut for full basements: If the entire story is below grade, set the story to Below grade and Amply automatically switches every wall in that story to below-grade materials and changes the floor to a slab below grade. See How to model floors for details on the slab below-grade settings.
Construction type
Construction type describes what the foundation wall is built from — for example, block (with or without filled cores), poured concrete, brick or stone, or ICF. Pick the option that matches what is actually there. Each construction has its own Manual J U-values that Amply uses together with the wall's depth below-grade to compute the heat-transfer rate.
Frame wall on interior
Turn on Frame wall on interior if there is a framed wall built against the inside face of the foundation wall — typically wood or metal studs holding cavity (batt) insulation. Manual J Table 4A treats a foundation wall with an interior frame-and-cavity assembly as a different construction from the bare foundation wall, so this toggle changes which U-value Amply uses.
Leave it off for foundation walls that are exposed on the interior, or that have board insulation only.
Board insulation
Board insulation is the R-value of rigid foam or similar board insulation applied to the foundation wall, typically running from the sill plate down. If there is no board insulation, set this to None. Otherwise, pick the value that matches what is actually installed.
Why board insulation is its own field: Manual J treats board insulation on the foundation wall separately from any cavity insulation behind interior framing. The two stack — a poured concrete wall with R10 board and a 2x4 stud wall holding R13 batts is a different construction from either insulation alone — and Amply uses both fields together to look up the right overall wall assembly U-value.
Walk-out basements or partially below-grade spaces
Not every basement wall is fully below grade. Daylight basements often have one fully exposed walk-out wall, a fully below-grade back wall, and side walls that go from grade down to the basement floor. Amply makes mixed cases easy to model, wall by wall.
If a wall is completely above grade — like the walk-out side of a daylight basement — turn off
Is Below Gradeon just that wall. The sidebar switches to standard above-grade wall materials and you can configure it like any other exterior wall.If a wall is partially below grade — like the side walls of a daylight basement — leave
Is Below Gradeon and use the average below-grade depth to set the assumption. Manual J's procedure uses average depth when the grade line varies along a wall.
Set your changes as the default
Once the wall matches what's around the below-grade story, turn on the default toggle for that wall type. Amply then applies the same settings to every other below-grade wall in that story. Override it for individual walls that are built differently — for example, a section with framed and insulated interior that the rest of the basement doesn't have.