Renovating an Unfinished Basement

March 12th 2010
Renovating an Unfinished Basement

Renovating an unfinished basement is a wise investment that will not only create more functional living space for your family, but will also help save on heating bills through insulating walls and floors and ceiling. Whether it's a home theater, games room or a secondary suite this project will transform a dark cold basement into usable space; however, to get the most from your lower level renovation there are some steps to follow to ensure a warm and inviting space that your family will enjoy. If you are planning a basement renovation, you should inspect your basement for possible problems first.The CMHC Canadian Mortgage and Housing Corporation has some helpful tips to follow.

To begin, if your basement isn't high, dry and sound, you should correct these problems before starting renovations.

  • Must you stoop to avoid bumping your head on a beam or duct?
  • Are there intermittent or permanent traces of moisture or mold on the floor or walls?
  • Is there a persistent musty odour in clothing and other objects that are stored in your basement?
  • Are there cracks as wide as a pencil, or that appear to widen or shrink, in the walls or floor?

Check Local Building Codes and Permits:
To begin, you must obtain a building permit if you intend to alter the structure of your house, increase the size of windows or exterior doors, or change the occupancy - for instance, by adding a self-contained apartment suite. The building permit ensures that the changes respect minimum standards of health and safety. To make a good living space, a basement should be high enough to permit ceiling fixtures or fans with space beneath for a 1.8-m (6-ft.) tall person to stand. Most municipalities require a height of 2.1 m (6.8 ft.) from finished floor to ceiling before they will issue a building permit, which is also the minimum height required by most electrical codes for a ceiling light. Ask your building official what minimum heights are required.

Addressing Moisture Issues:
With basement rooms, the most important task is keeping moisture out. There are multiple ways to keep your basement dry. Ensure good drainage off your roof and away from your foundation, provide good ventilation of bathrooms and kitchens to the outside, and don't open windows during humid periods. Another option is to install a subfloor panel system, which creates a moisture barrier. Also a Humidex System is an effective way to remove excess moisture from the basement.

Moisture Sources:
Dampness or leaks in the walls or floor must be corrected, because a damp or wet basement isn't a suitable living space. Moisture problems can ruin even the most expensive renovations and make your basement unlivable. Damp walls and floors result from holes or cracks in the foundation, insufficient dampproofing on the exterior face of walls, poor drainage at walls and footings and site grading that slopes towards the  foundation. Wetness may also be caused by a high water table, which exerts hydrostatic pressure on the walls and floor.

Steps to repair common sources of moisture:

Control Humidity: Humidity is a common source of discomfort in basements and can contribute to odours, staining, mold growth and wood rot. Excessive humidity is caused by leaks; damp materials; improperly installed insulation, air barriers and vapour retarders; weather conditions and building occupants.

Cracks: Although small cracks may be patched on the inside, large cracks and other causes of dampness are best repaired from the outside. This often means using heavy machinery to excavate around the foundation walls to the footings. Once the walls and the top of the footings are exposed, it is possible to patch small holes or cracks with water-resistant grout. If cracks are large or appear to be moving, you should hire a structural engineer to investigate and recommend repairs.

Drainage: Water can seep up through the basement floor, appear at cracks and holes and accumulate at the perimeter where the floor meets the walls. If this occurs frequently or seasonally, it may be the result of an improperly functioning foundation drain. The drainage tile or pipe around the footing may be crushed, plugged or missing, and should be repaired or replaced. The drainage tile should be perforated with holes to collect groundwater, and positioned so that its bottom is below the basement floor.

Ensure that the foundation wall has an uninterrupted coating of bituminous dampproofing, or a waterproof membrane when there is hydrostatic pressure. The coating should extend from finished grade to the top of the footing and seal the joint between the wall and footing. Cover this with a drainage membrane or free-draining fill to provide the drainage zone mentioned above, and slope the backfill so it will carry surface water away from the foundation wall.

Foundation Walls: To prevent heat loss to the surrounding earth, most jurisdictions require exterior basement walls to be insulated for most of their height. Although builders usually place the insulation on the inside face of the foundation wall and cover it with gypsum board, it would be better to place water-resistant insulation on the exterior face where it can keep the foundation warm. If the wall is warm, the dew point, the point at which air vapour condenses as water, occurs on the exterior of the foundation wall where condensation will do no harm.

When insulating the foundation on the inside, you should expect some moisture to condense on the inside face of the foundation wall. Place a moisture barrier, such as vapour-permeable building paper, on the interior face of the foundation from exterior grade to the bottom of the wall to prevent this moisture from wetting the insulation. The top of the wall and the space between the joists should be insulated, because it is here that most of the basement heat loss occurs. Cover the warm face of the insulation with a polyethylene vapour retarder and seal with caulking where the polyethylene meets the floor, walls and ceiling, and at all laps to prevent moisture from getting into the wall. Consult the building code for your jurisdiction for your basement insulation requirements.

Most basement floors start off as a cold concrete slab where dampness and cold can enter the floor from the ground beneath it. Even the best-designed basement may experience a serious leak, spill or flood. It is prudent to install water-resistant or impermeable floor and wall finishes, with ceramic tile, carpet or a luxury vinyl such as Karndean. All are durable choices that are easy to install over concrete. Solid-wood flooring isn't recommended for basement applications because moisture levels can cause buckling and warping, but engineered is a suitable alternative. Building codes require an occupied basement in a new house to have a moisture barrier, such as polyethylene, beneath the slab. The Delta-FL membrane, is a dimpled membrane that allows concrete to breathe and also serves as a vapour barrier, which in the end means a warmer floor. Once the Delta-FL is in place, you install your sub floor on top, and then finish with your flooring. You can purchase this product through Basement Systems.

Create Height:
Suspended Ceilings are great for adding a finished look. They cover ductwork, electrical components, and bare joints from the floor above. But they can lower the ceiling height by about a foot. If you don't want to lose this height, consider using furring strips to drop the ceiling only enough to hide everything but the ductwork. Then install tongue-and-groove planking or standard drywall to finish the ceiling. Decorative moldings also add to the character of the space.

Bring in the Light:
Bringing in natural light is one of the biggest challenges when creating a basement room. Window wells are the most common solution where the window-opening height is below ground level. In case of an emergency, you can climb out the window and up the well. Choose window well locations carefully so you can make them as wide and deep as possible. The wider and deeper the well, the greater the amount of sunlight flowing into the basement. Also, replace unsightly steel basement window wells with a plastic enclosure that can reflect sunlight back into the space. Window wells can collect snow and water, and often contribute to dampness in basements. Install a length of drainage tile filled with crushed stone from the bottom of the well to the foundation drain, to ensure rapid removal of standing water from the well. Installing Low-E glass in the basement windows will also make a very significant difference in their ability to insulate.

Sound Proofing and Noise Control
Whether your lower level is a secondary suite or media room noise can travel throughout the household. Control sound transfer by soundproofing interior walls and ceilings. Insulate interior walls and choose drywall that is soundproof. Dryco's QuietRock drywall is visually indistinguishable from standard drywall, but it's engineered to dampen noise.

Heating a Basement
Heating a basement can be a challenge. Registers in the ceiling push warm air into the room, but that warm air rises to the ceiling. In-floor heating is a good solutions for cold feet. Radiant-heat systems provide inexpensive, even warmth throughout a room and eliminate the cold spots and drafts. Another option would be a convection heating unit such as Convectair.

If a media room is in the plans, it's ideal to address the wiring of the system before the walls and ceiling go up. This is especially helpful in an open concept layout where wall space will be limited.