Is sill seal required by building code?

Yes. The IRC Section R403.1.6 requires a gasket or sill seal between the concrete foundation and the wood sill plate to create a continuous air barrier. Most local building inspectors will flag missing sill seal during the framing inspection.

What thickness of sill seal should I use?

Standard 1/4-inch foam sill seal is sufficient for most applications on smooth, level foundations. Use 1/2-inch sill seal on foundations with minor surface irregularities or in climates with significant temperature swings where additional compression and sealing are needed.

What width sill seal do I need?

Match the sill seal width to your sill plate width. Use 5.5-inch sill seal for 2x6 sill plates and 7.5-inch for 2x8 sill plates. The seal should cover the full bearing surface without extending past the edges.

How many rolls of sill seal do I need for a house?

Divide your total foundation perimeter by the roll length (typically 50 feet). A 1,500 sq ft house with a 160-foot perimeter needs about 4 rolls. Always buy one extra roll for waste and overlap at seams.

Can I use caulk instead of sill seal?

Caulk alone does not satisfy the code requirement for a gasket between the foundation and sill plate. You can use acoustical sealant in addition to sill seal for an even tighter air barrier, but sill seal is the primary material required.

Does sill seal prevent termites?

Standard foam sill seal does not stop termites. In termite-prone areas (most of the southern US), consider using a borate-treated sill seal or installing a stainless steel termite mesh between the foundation and the sill plate in combination with regular sill seal.

Sill Seal Calculator

Sill seal calculator: Estimate foam gasket rolls by foundation perimeter. Free tool for 90 mm & 140 mm widths — prevents air infiltration.

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Enter Your Measurements

How to Use This Calculator

1Measure your total foundation perimeter in linear feet.
2Enter the roll coverage (most rolls are 50 ft).
3Click Calculate to see how many rolls you need.

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About This Material

Sill seal is a closed-cell polyethylene foam gasket installed between the concrete foundation wall and the pressure-treated sill plate. Its primary purpose is to block air infiltration and prevent moisture from wicking up through the concrete into the wood framing. Standard sill seal comes in 5.5-inch and 7.5-inch widths to match 2x6 and 2x8 sill plates, sold in 50-foot rolls. Thickness options are 1/4-inch for standard applications and 1/2-inch for foundations with minor surface irregularities. Some premium sill seals include a polyethylene moisture barrier bonded to the foam. In termite-prone regions, borate-treated sill seal or stainless steel termite mesh may be required. Sill seal costs approximately $5 to $10 per 50-foot roll, making it one of the least expensive but most important air-sealing materials in the building envelope.

Next Steps:

Pressure Treated Sill Plate Calculator →Anchor Bolt Calculator →

Installation Tips

•Unroll sill seal along the foundation just before placing sill plates.
•Overlap seams by at least 6 inches.
•Use PT-compatible sill seal — some foam degrades with treated lumber chemicals.

Common Mistakes to Avoid

Forgetting to install sill seal — it is a code requirement in most jurisdictions.
Not overlapping seams, leaving gaps for air infiltration.

Sill Seal Calculator

How to Use This Calculator

About This Material

Installation Tips

Common Mistakes to Avoid

Frequently Asked Questions

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