The shed designer priced two coats of paint or solid stain for the siding, at 350 sq ft a gallon. The trim boards around it are all bought primed: the 1x6 fascia, the rake boards, and the corner boards and casings. Primer is not a finish, and nothing on the list paid for painting them. Anyone painting a shed to match their house would have come up a can short.
What the tool now counts. It adds up the face of every trim board it buys and prices two coats of exterior semi-gloss at the same 350 sq ft a gallon:
- 5-1/2" for each foot of fascia;
- 3-1/2" for each foot of rake, corner board and casing.
It buys quarts until a gallon is cheaper:
| Design | Trim face | Buys |
|---|---|---|
| 8x8 lean-to | 37 sq ft | 1 quart, $25.98 |
| 8x10, 8x12 | 44 sq ft | 1 gallon, $48.98 (two quarts would be $51.96) |
| 12x16 | 57 sq ft | 1 gallon |
Prices are Behr Premium Plus exterior semi-gloss paint-and-primer at Home Depot, from search results read on 2026-10-30. The quart (model 505004) was $25.98. The gallon was $39.72 to $48.98 depending on the colour, so the tool uses $48.98. Lowe's lists HGTV Home by Sherwin-Williams quarts from $28.98.
Why there is no primer line. The lap siding, LP panels, HardieTrim, LP 540 and pine trim the tool lists all come factory primed. The paint is a paint-and-primer, which Behr says can prime coated or uncoated surfaces; it recommends a separate primer only for woods that bleed tannin, such as cedar or redwood. LP and James Hardie ask that cut ends be sealed or touched up, and the paint does that. A shed in bare cedar would need a primer, but the tool doesn't build one.
What it does to the totals. The default 8x12 goes from $3,169.67 to $3,218.65. The "8x12 classic" preset goes from $3,193.03 to $3,242.01. Like the sloped rafter hangers earlier today, this is a cost the list had been leaving out, not an upgrade. Leave the siding "unfinished" and the trim paint goes too, as the siding paint does.
Every price links its source and can be edited. The tool is a planning aid, not an engineered or code-checked design.