flexiblefullpage - default
Currently Reading

Essential Details for Warm, Dry Basements in Cold Climates

billboard - default
Quality Matters

Essential Details for Warm, Dry Basements in Cold Climates

For a warm, dry finished basement, pay attention to these details—getting it right goes beyond damp-proofing and exterior drains

By Graham Davis March 6, 2018
Construction details for a dry basement
Best practices that will help ensure a dry finished basement. (Illustration: IBACOS)
This article first appeared in the March 2018 issue of Pro Builder.

Many builders in cold climates choose to build on basement foundations. If you have no intention of finishing the basement space, the typical damp-proofing and exterior drain system are usually sufficient. But for a warm, dry, comfortable finished basement, additional details must be considered.

The drawing below shows best-practice details. These start at the roof (with a wide overhang) and extend down to the footing (with a good drainage system). They include surface drainage to keep water away from the foundation and subsurface drainage to ensure that any water that reaches the foundation won’t stay there long enough to be absorbed. (Click to download the PDF at the end of the article to better see the illustration.)


Construction details to ensure a warm, dry finished basement

Illustration: courtesy IBACOS


Above grade. The basics here include gutters and downspouts to manage roof runoff, and positive grade that’s sloped away from the house. Avoid garden plantings against the foundation. Every wall assembly must have a properly installed weather resistive barrier (WRB) that is integrated in weatherboard fashion with all the flashing components and laps over the foundation by at least 1 inch.

Foundation damp-proofing vs. waterproofing. A thin layer (about 10 mils) of asphalt coating on the foundation will reduce moisture absorption from damp soil but won’t stop liquid water under hydrostatic pressure. In wet soils, waterproofing is best done by applying a thick (40+ mils) coating of rubberized asphalt, which doesn’t get brittle when cold and can span cracks up to 1/16 of an inch.

As part of waterproofing the foundation wall, apply a thick bead of sealant around pipe penetrations and at the intersection of the foundation wall and footing. Tool the sealant into place to ensure complete coverage and good adhesion.


Drainable backfill. Letting water sit against the foundation is, obviously, a bad idea. To avoid the potential for hydrostatic pressure against the foundation, install a drain mat or board over the waterproof coating, then backfill with clean sand. 

Perimeter drains. Setting the drain tile on the inside and outside of the footing will provide ultimate protection for the slab against high water tables and water seeping into the soil from rain and snow. In regions with low rainfall (below 20 inches per year) and low water tables, installing just an exterior drain tile is sufficient. 

Slab protection. In addition to keeping the foundation walls dry, you’ll need to keep the floor slab dry. Best practice here is to place a 4-inch-thick layer of gravel (1/2-inch stones or larger), followed by a robust vapor barrier. Seal this to the top of the footing, and seal all penetrations through it. This not only protects the slab from moisture but can also serve as one of the critical components for a radon mitigation system.

MORE INFO: Do Concrete Slabs Really Need Welded Wire Mesh?

Insulation. When finishing a basement, rigid board (polyiso or XPS) performs better than fiberglass batts. Install a sufficient thickness to meet or exceed code requirements. The rim joist can be insulated using a flash-and-batt method: Apply 2  inches of closed-cell spray foam to the rim joist to reduce the potential for condensation, followed by fiberglass batts.

Mechanicals. Besides properly detailing the foundation, the best thing you can do to keep that below-grade space (and the rest of the home) comfortable is to properly size the HVAC. An oversized unit won’t run long enough to fully dry the air in humid climates, a problem that’s most noticeable in the basement. 

The most comfortable heating technology for basements is hydronic radiant heating in the slab. This is ideal for climates where cooling isn’t considered necessary. When doing in-slab radiant heating, it’s important to install at least 2 inches of XPS foam insulation under the heating lines, below the slab, and on top of the vapor barrier. This helps to drive the heat toward the conditioned space. 

Graham Davis drives quality and performance in home building as a building performance specialist of the Perform Builder Solutions team at IBACOS.


leaderboard2 - default

Related Stories

Quality Matters

5 Ways to Silence Squeaky Floors

Take these tips to heart to deliver quiet floors and satisfied homeowners

Quality Matters

Tips for Placing HVAC Ducts in Conditioned Space

See how putting HVAC ducts inside conditioned space in a home benefits both the builder and the homeowner

Quality Matters

Don't Underestimate the Importance of Roofing Underlayment

Regardless of which product you choose to use, installing a roofing underlayment will help ensure the roof system withstands the elements and the home stays dry

boombox1 -
native1 - default
halfpage2 -

More in Category

Home builders can maximize efficiencies gained through simplification and standardization by automating both on-site and back-office operations 

Delaware-based Schell Brothers, our 2023 Builder of the Year, brings a refreshing approach to delivering homes and measuring success with an overriding mission of happiness

NAHB Chairman's Message: In a challenging business environment for home builders, and with higher housing costs for families, the National Association of Home Builders is working to help home builders better meet the nation's housing needs

native2 - default
halfpage1 -

Create an account

By creating an account, you agree to Pro Builder's terms of service and privacy policy.

Daily Feed Newsletter

Get Pro Builder in your inbox

Each day, Pro Builder's editors assemble the latest breaking industry news, hottest trends, and most relevant research, delivered to your inbox.

Save the stories you care about

Lorem ipsum dolor sit amet lorem ipsum dolor sit amet lorem ipsum dolor sit amet.

The bookmark icon allows you to save any story to your account to read it later
Tap it once to save, and tap it again to unsave

It looks like you’re using an ad-blocker!

Pro Builder is an advertisting supported site and we noticed you have ad-blocking enabled in your browser. There are two ways you can keep reading:

Disable your ad-blocker
Disable now
Subscribe to Pro Builder
Already a member? Sign in
Become a Member

Subscribe to Pro Builder for unlimited access

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.