Weatherization Guide: Insulation

Places to Insulate

Basements & Crawl Space Insulation

Many insulation projects can be found in the basement area. Basement walls, ceilings, ducts, and water heaters are the big heat losers.

Basement Walls

The bright spots along the foundation in this infrared photo indicate the large amount of heat that is being lost through the basement walls and rim joist. In fact, a concrete block wall has about the same R-value as a single pane of glass! If you plan on heating your basement, insulate the walls (from the inside or the outside).

Exterior Wall Insulation

Extruded polystyrene foam is recommended for exterior basement walls. For Michigan frost lines, dig down 42" around the foundation to expose the uninsulated basement wall. Attach foam board with the recommended adhesive. Cover exposed insulation with a protective coating (e.g. paint) to prevent breakdown from exposure to sunlight.

Interior Wall Insulation

Use either fiber glass or extruded polystyrene foam to insulate your inside basement wall.


If moisture is a problem in your basement, start by correcting drainage problems and sealing the wall from potential water leaks with a vapor barrier or vapor retardant paint. Cover the whole wall with insulation. For fiber glass, install 2x4s in order to accommodate 3 1/2" batts or rolls of insulation. The vapor barrier (or paper facing, if any) should be installed next to the wall. If interior foam board is used to insulate basement walls of living areas, it must be covered with 1/2" of drywall or fire-rated gypsum wallboard.

Rim Joists

The rim joist or "band joist" area should be insulated with 6" (R 11-19) fiber glass batts.

Cut the insulation slightly larger than the width of the joist space for a tight fit. Try not to compress the insulation as this will decrease its effectiveness. The faced paper side should be installed toward the inside. The insulation should stay in place by itself, but a staple gun can be used to hold the batts in place if necessary.

Seal the joist space with pressure-fitted polystyrene and caulk around the edges. A further covering of 1/2" drywall or fire-rated gypsum wallboard will reduce fire hazards and is required by code for living areas.

Basement Ceilings

While it is generally best to insulate basement walls and rim joists, for some basements this is impractical. In such cases you may opt to insulate the basement ceiling instead. If you do, then you should also insulate heat ducts, pipes, etc.

Basement ceilings are typically insulated with fiber glass batts or blankets. Install a vapor barrier against the warm side. Use either faced insulation or polyethylene plastic stapled between the floor joists.



Insulation supports or "tiger teeth" are thin metal rods the size of coat hangers which can be used to hold the batts in place without compressing them.

Crawl Spaces

To block water vapor from entering the crawl space, drape a layer polyethylene plastic from the rim joist down the wall and across the entire floor. Lap and tape the seams between the sheets of plastic. Then insulate either the walls and floor or the ceiling of the crawl space.

Coordinate your insulation choice for crawl spaces with the way you handle any connected basement areas. Insulating the ceiling is usually the most difficult and costly of the two choices. If you have ducts or pipes in your crawl space, you should definitely insulate the walls and floor. If it is not clear what the best choice is, consult a specialist.

For wall and floor insulation, attach fiber glass batts to the rim joist area with a staplegun. Extend the insulation two feet out from the wall onto the crawl space floor.

Vents in vented crawl spaces should not be sealed permanently or covered with insulation. The vents should be closed during heating season and open otherwise.

Floors situated over unheated spaces should be insulated. Methods are likely to be specific to the individual site. Consult your insulation supplier or contact Urban Options.


All ductwork should be sealed. Be sure the ducts are clean and dry. Seal the seams of the ducts where air might leak. Use a high quality silicone caulk or aluminum tape.



Warm air ducts which travel through unheated areas should be insulated. These will typically be at the top of a forced-air furnace and feel warm to the touch when the furnace is operating.

Insulate ducts with vinyl-coated fiber glass, foil-coated adhesive-backed foam, or insulated duct board. Use vinyl tape to hold the insulation in place.

Water Heater

Next to the heating system, your water heater is one of the biggest energy users in your home. Most older types lack built-in insulation and thus waste much of the energy used all year long. So it is important to consider whether insulating is appropriate and to take action when it is.

When to Insulate

Newer tanks that have built-in urethane foam insulation should not be further insulated. If your tank is very close to another heating apparatus, a chimney, or is placed tightly in a corner, it may not be appropriate to insulate it. Don't insulate faulty or damaged tanks either - including any tank that is rusty, leaks water, shows deterioration on the top or sides, lacks a flame door or pressure relief valve, or is situated under pipes that are likely to leak onto the tank top. If your tank makes popping or crackling noises, it probably needs replacement and should not be wrapped. If you are in doubt about the condition of your tank, consult a specialist.

How to Insulate

With gas or oil-fired water heaters, don't cover the top or the bottom of the tank. Covering the top may obstruct the venting of exhaust gases or create a fire hazard due to occasional backdrafts from the vent. Covering the bottom blocks the combustion air supply. Insulating blankets should be at least 4" above the floor.

Cut around control panels. For electric models, cut an extra 4" around the control panel to avoid overheating. For all models, keep insulation away from pressure relief valves and drain valves.

Pre-made, water heater insulating blankets are available in a variety of sizes and thicknesses. Choose one that fits your tank or make your own out of faced fiber glass insulation. Fasten the blanket securely to the tank, try not to compress it.


Insulate the first 5 - 10' of hot water pipe starting at your water heater. This pipe will be warm to the touch. Also insulate the first 2 - 3' of the cold water intake pipe for the water heater. Hot water pipes that run through unheated, uninsulated areas should be insulated as well.


If you have a hot water or steam heating system, insulate those pipes too. Heat-resistant insulation (fiber glass or foam) is available for this purpose.

To prevent pipes from freezing that run through unheated areas - basements, crawl spaces, attics - use heat tape. For winter climates that are milder than Michigan's, insulating cold water intake pipes may be sufficient to prevent freezing.





Table Of Contents

MEO's Weatherization Guide Introduction

Air and Insulation Introduction

Air Leakage