Tips for Making Your Basement Warmer (Continued)

The Better (and Cheaper) Solutions

Virtually all the coldness in a basement originates in air drafts and heat loss taking place up high—at or above ground level.

Ground-level cold is the real culprit. It cascades into your basement through windows, ducts, vents, pipes, spaces around intrusions, the rim joist, header joist, and non-conditioned rooms. If you fix these on-grade sources of cold and you will address most of the cold-air entry points into your basement—all without ripping out floors or walls.

Locate Cold Spots With a Cheap Thermal Camera

If you are finishing your basement, viewing the interior with a thermal image camera or thermal detector is not just recommended—it is practically required. Thermal imaging cameras are no longer just for house inspectors and energy auditors. Cheap but very effective cameras can be purchased for less than $200—a modest investment since this tool will have lots of applications around the house. Or, you can lease a camera from a tool rental center. With a thermal camera, simply standing in the center of a room and viewing the various areas through the viewfinder will pinpoint where your energy losses are occurring. There are also even cheaper thermal detectors available. These require a little more moving around the room in order to detect spots where energy loss is occurring, but they are quite effective.

This makes fall and winter the best times to finish your basement, at least from an energy-control standpoint. This is the time when temperature spikes are at their greatest and are more visible on the thermal camera.

Insulate Rim Joists and Headers

Your house's non-insulated rim joists and headers are probably the biggest offenders. The headers and rim joists are the outer framing members of the floor platform that rests on the concrete foundation. While the vertical walls that sit atop the flooring are themselves insulated, the spaces below the walls are not, and where these rim joists and headers are exposed to the outside air, enormous heat loss can occur. In older homes, these basement joist spaces are left "as is" and are rarely insulated.

To insulate these spaces, you can cut 1 1/2-inch-thick pieces of extruded foam insulation, insert them into the joist spaces against the outer rim joists and headers, and seal the gaps around the foam with a spray foam sealant, such as Great Stuff. Alternately, pieces of fiberglass batt insulation can be loosely rolled up and stuffed into the joist cavities against the header.

Insulate Ducts Leaving the Basement

Ducts are unimpeded "freeways" that shoot cold air straight into your basement. Dryer and bathroom fan ducts are little more than tubes of thin aluminum or paper-thin plastic, and they provide zero insulation from the cold. Replace such ducts with an inexpensive insulated duct or wrap your existing metal duct with insulation.

Install Better Vent Flaps

Most vents (the flap-like fitting where the duct leaves the house) are terrible at preventing cold air from migrating into your house. Little more than a thin plastic door, these vents let cold air pour into the duct, and thus into your house. Replace your cheap, ineffective vent flap with an energy saving "floating shuttle" type of vent flap.

Insulate Above-Grade Basement Walls

Exterior basement walls that have earth mounded up against them do a fairly good job of preventing cold from coming into the basement. Earth, after all, is a good natural insulator. But basement walls that are not protected by earth—such as those found in walk-out basements—are just as susceptible to cold migration as walls elsewhere in the house. 

Exposed concrete walls should be insulated with extruded foam. Wood-framed basement walls can be insulated with fiberglass batt insulation.

Make Sure First-Story Walls Are Insulated

If you remember your basic science, you will know that cold air descends. If they are not insulated, the walls on the first story above the basement can act as conduits for cold air to move down towards the basement. Insulating an entire level's worth of walls just to cure basement cold is probably not cost-efficient, though it might well pay off when you consider the overall energy costs and comfort of your home. But if you are looking to identify where cold air is entering your basement, remember that the cause may not be in the basement at all.

Confine Utilities in an Unheated Space

Rare is the basement that has no functional services, such as a furnace, water heater, and washer and dryer. Unless you have a special need for these items to be heated, it is relatively easy to erect insulated interior walls that block them off, preserving heat for the basement areas that are inhabited. Make sure to allow for the necessary ventilation space when enclosing utilities. Some high-efficiency furnaces draw their combustion air from the room space surrounding the furnace, and it's important not to impede this air source. Generally, though, if you can confine the furnace, water heater, washer and dryer in a single unheated room, it makes it easier to control the temperature in other parts of the basement.

Insulate Basement Ceilings Below Unheated Spaces

Rooms on the ground level that are not heated will compromise your efforts to heat your basement. This is not a common scenario, but some homes may have basement spaces below unheated porches or garages. Insulating the basement ceiling below these spaces will hold in the heat, preventing it from migrating to the unheated space above.

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