from CMHC website
Renovating a full-height basement can be a relatively easy
and cost-effective way to add new living space to your
house.
But is your basement really a good candidate for a
renovation?
If your basement isn’t high, dry and sound, you should
correct these problems before starting renovations.
If you are planning a basement renovation, you should
inspect your basement for possible problems.
- 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?
If the answer to any of these questions is “yes,” you
should include the costs of fixing these problems in your
budget.
Preparing
the groundwork
Building permit
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.
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. 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. Some jurisdictions
permit limited obstructions, such as beams and heating duct
bulkheads, within this space. Ask your building official what
minimum heights are required.
Moisture sources
Dampness or leaks in the walls or floor must be corrected,
because a damp or wet basement isn’t 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 wall, 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. The
following are ways to repair common sources of moisture.
1. 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.
2. 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.
Some builders enclose the
drainage tile with a geotextile “sock” to keep fine soil
material from clogging the tile. The tile and sock should be
covered with at least 100 mm. (4 in.) of clear, crushed stone
extending to a free-draining zone over the face of the
foundation. A length of unobstructed pipe should slope
downwards from the foundation drain to the storm sewer to
carry away any water that collects around the footings.
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. As
an added precaution, create a clay “dam” around the foundation
walls just below the topsoil, to deflect surface water away
from the house. Figure 1 shows a foundation drainage
system.
3. Eavestroughs and downspouts
Eavestroughs collect water from the roof and rainwater
leaders, or downspouts, and carry it to the ground. When the
downspout fails to direct the water away from the foundation,
or the grade doesn’t slope away from the walls, this water may
leak into your basement. A simple solution is to extend the
bottom section of the rainwater leader at least 1,200 mm (4
ft.) away from the foundation, and to adjust the grade around
the foundation so that it slopes away from the house.
4. Window wells
Window wells can collect snow and water, and often
contribute to dampness in basements. The base of a window well
should consist of 150–200 mm (6–8 in.) of free-draining
material, such as crushed stone, and must be at least 150 mm
(6 in.) below the bottom of the window. Window wells are
places where snow and water will naturally collect. 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. As an added
precaution, consider installing a clear Plexiglas cover over
the well if you don’t plan to use the window for ventilation.
If the bottom of the window well is less than 1,800mm (6 ft)
above the footing, consult a geotechnical engineer about
protecting the footing from frost action.
5. Floor drains and sump pumps
Most basement floors in houses built after 1900 are sloped
to a drain that, in turn, slopes to a sewer or dry well. It
became common practice after about 1940 to install a ‘P’ trap
in the drain, to prevent sewer gases from entering the
basement.
If you intend to live in your basement, ensure there is a
proper drain with a trap situated at the low point of the
floor. The trap should be kept full of water to function
properly and should be topped up periodically.
If there is no sanitary sewer in your vicinity, you may
install a sump pit with a pump near the lowest point in the
basement floor. The sump pit should be capped and sealed to
prevent soil gases from entering. The pump should discharge to
a dry well or to a location above ground where the water will
not leak into the basement.
6. Backwater valves
A backwater valve is a device that automatically closes to
prevent sewage in an overloaded sewer line from backing up
into your basement. A properly installed backwater valve
should be located to prevent sewage from coming through any
fixtures in your basement, such as sinks, toilets, showers and
laundry tubs. Installing a backwater valve may be expensive,
but it can protect your basement renovation from serious
damage, such as that which often occurs during periods of
heavy rain.
Preparing the space
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.
Floors
Dampness and cold can enter a basement floor from the
ground beneath it. Building codes require an occupied basement
in a new house to have a moisture barrier, such as
polyethylene, beneath the slab. If you have an older house
with no moisture barrier below the floor, consider placing
polyethylene over the existing floor before installing the
finished flooring. If space and headroom permit, you might
also install water-resistant insulation, such as extruded
polystyrene, beneath the finished flooring to obtain a warmer
floor.
Putting
the systems in place
Canadian houses contain mechanical and plumbing systems
that contribute to our comfort and health. The National
Building Code of Canada (NBCC) sets minimum standards for
water and waste piping in kitchens and bathrooms and for heat
and ventilation in habitable rooms. All new NBCC “Part IX”
residential dwellings and small buildings that are supplied
with electrical power require mechanical ventilation, to
ensure a continuous and adequate fresh air supply. The
ventilation capacity required of exhaust appliances for
kitchens and bathrooms is set out in Section 9.32.3 of the
NBCC.
Air circulation
Excessive humidity and insufficient air movement contribute
to two common problems in basements: mold growth and stale
air.
Once you have repaired sources of water entry, you may put
in heating and air circulation to make the space comfortable.
Electric baseboards supply heat, but provide no circulation.
If your house has a forced-air heating system, the furnace can
provide heat and air circulation to the basement. Most
furnaces provide circulation by pushing heated air out of
registers and pulling cooler air into return-air grilles. The
supply registers should be close to the floor in all rooms to
allow the room air to mix effectively and should be near cold
surfaces, such as windows. Return-air grilles should also be
located near the floor in all rooms, except the furnace room,
to remove the layer of cooler air that tends to collect there
and ensure proper air circulation.
Providing your basement with a heating and ventilation
system that equals the one in the rest of the house should
improve air quality and comfort during the heating season. But
what about the period when the furnace is off and there is no
air movement?
Mechanical ventilation
It is advisable to run the furnace fan year round, or use a
furnace cycling device to circulate the air throughout the
house. Because fan operation consumes energy, consider
replacing a conventional furnace with one equipped with an
electronically commutated motor (ECM). This will enable you to
select the fan speed to suit your airflow needs and conserve
energy. Opening windows usually increases humidity during the
warm season, because this is the period when the outside air
contains the greatest concentration of moisture. Dehumidifiers
and air conditioners are more effective at drying and cooling
indoor air during the non-cooling months.
A heat recovery ventilator (HRV) is a valuable addition to
a ventilation system, because it can exhaust stale air to the
outside and replace it with fresh exterior air. The fresh air
recovers heat from the exhaust air, then mixes with the house
air and is heated and circulated by the furnace.
The stale air in most of our houses is exhausted by the
kitchen and bathroom fans, and replaced by fresh air leaking
in through cracks and openings. This results in drafts, heat
loss and uncertain air quality. A properly designed and
installed HRV system can correct these problems in the
basement and throughout the house.
Although it is common for occupants to not use, or to
disable noisy bathroom and kitchen fans, this leads to higher
relative humidity and increased concentrations of volatile
organic compounds (VOCs) in the air. Rather than compromise
your air circulation, consider replacing a noisy fan with a
quieter model that produces no more than 1.5 sones of
noise.
In some jurisdictions, the fan can be connected to the
light switch so that it operates when the room is in use. More
information on VOC’s can be obtained from Health Canada.
| Source |
Moisture produced — litres per
day |
| Four occupants |
5 |
| Humidifier |
2-20+ |
| Whirlpool bath |
2-20+ |
| Firewood, by cord |
1-3 |
| Floor washing |
2 |
| Cooking |
1.5 |
| Gas cooking appliance |
1 |
| Plant, each |
0.2 |
| Seasonal release of moisture (autumn) |
3-8+ |
| Total per day |
30 |
| Source:Adapted from G.
Christian |
Table 1: Daily moisture generated by
a family of four
Control of humidity
Humidity is a common source of discomfort in basements and
can contribute to odours, staining, mold growth and wood
decay. High humidity can result in fungal growth progressively
damaging organically based materials, such as wood and
wood-based products, and natural fibres in carpets and
upholstery.
Excessive humidity is caused by leaks, damp materials,
improperly-installed insulation, air barriers and vapour
retarders, weather conditions and building occupants. Table 1 shows how
human activities, such as bathing, can significantly increase
the moisture in air. Conditions of high relative humidity (RH)
permit mold and wood rot to become established. Therefore, it
is important to keep room humidity levels within an acceptable
range to prevent mold growth and ensure occupant health.
If the air circulation provided by the furnace does not
limit excessive humidity, a dehumidifier can be placed in the
damp space or connected to the furnace. If you put a bathroom
or kitchen in your basement, you are introducing a potential
source of moisture. Humidistats can be installed in kitchen
and bathroom fans, to start them automatically when the RH
exceeds a selected level, and shut them off when the humidity
has decreased sufficiently. This measure is relatively
inexpensive and removes some of the humidity at its source. It
also ensures that the fans will run when they are needed most,
when cooking and bathing are taking place.
Keeping it safe
Fire and smoke detection
Smoke alarms are required on all floors of a residence and
near bedrooms. Although most smoke alarms are wired directly
to the electrical panel in newly-constructed houses, some
jurisdictions permit battery-powered alarms in existing
construction. It is prudent to install a carbon monoxide (CO)
detector near a fuel-fired appliance, such as a fireplace or
furnace, and near a doorway to an attached garage.
Electrical outlets and fixtures
The electrical code requires electrical outlets to be
placed at intervals around all finished rooms. They are
usually located no more than 3,600 mm (12 ft.) apart, and from
100 mm (4 in.) to 300 mm (1 ft) above the floor. Kitchen
outlets should be on a separate circuit and provided with
ground fault protection to prevent shocks. Some appliances,
such as stoves, ovens and dryers, require higher voltages with
special outlets. Electrical fixtures and wiring must be
installed and inspected by a certified electrician in most
jurisdictions.
Windows
Windows serve three purposes in the building code:
ventilation, natural light and emergency escape.
Unless mechanical ventilation is provided, the natural
ventilation requirements for new dwellings in existing houses
must comply with the applicable building code. The NBCC
requires that all bedrooms have at least 0.28 m2 (3 sq.ft.) of
operable window area. To provide adequate natural light, it is
recommended that the unobstructed area of glass in a window be
at least five per cent of the floor area of each room or
combination of rooms.
Where a window is required to be a means of escape, it must
be large enough and easily reached from the living space, and
provide safe access to grade level. It might be necessary to
replace or enlarge your existing windows to meet these
requirements. Windows near grade might be subject to forcible
entry and require special locks or protective bars. Consult
the building code for your jurisdiction for specific
requirements for windows.
Windows are susceptible to condensation in cold weather
because the glass and frame are usually colder than the
surrounding walls. If the window is deeply recessed in the
wall, heated room air may not reach the glass surface to
remove the condensation and moisture damage might occur around
the frame and sill.
An insulated window should be positioned so the air space
between the glass panes does not extend outside the insulation
on the surrounding wall. Where possible, install the windows
near the inside face of the wall to prevent condensation on
the glass. Be sure to seal the perimeter of the window where
it meets the exterior wall and slope the exterior sill down
and out beyond the wall face, to prevent leaks. Most building
codes require the bottom of a window to be at least 150 mm (6
in.) above ground.
Means of egress
The occupants in all parts of the house, including a
finished basement, should have a safe means of egress, or exit
path, to the outside. The NBCC regulates the size of the
components that make up the exit path.
Doors as a means of egress must be at least 810 mm (32 in.)
wide and 2,030 mm (80 in.) high. Corridors must be at least
900 mm (35 inches) wide. The stair must be at least 860 mm (34
in.) wide between wall faces and have at least 1,950 mm (77
in.) head room. You may also need a handrail and a protective
guard on the open side of the stair. If you are converting an
unfinished basement into living space, the rise, run and tread
depth of the stairs may have to be modified to conform to the
building code in your jurisdiction.
Enclosure of mechanical room
Your furnace and hot water heater are powered by
electricity or fossil fuels, such as oil, propane or natural
gas. Fossil fuel-fired appliances will exhaust through
chimneys or vents to the outside. High-efficiency furnaces are
equipped with combustion air intakes that conduct fresh air
from the exterior to the burners. Medium- and low-efficiency
furnaces use room air for combustion and should have an
unrestricted supply of air. If you have a medium- or
low-efficiency furnace enclosed in a small room, it is
critical to ensure that the furnace is supplied with adequate
air. Consider installing a louvre in the door or wall between
the furnace room and the living space. This ensures the
appliance has adequate combustion air and is less likely to
pull gases down the chimney. As an added precaution, it is
wise to install a CO (carbon monoxide) detector in the living
space near the furnace.
Additional
requirements for multiple occupancies
If you convert part of your basement into a separate
apartment, the NBCC requires you to provide additional fire
safety measures that include the following:
- Apartments must be separated by smoke-tight construction
that will resist the spread of fire from one apartment to
another for at least 45 minutes.
Structural elements,
such as bearing walls, beams and columns that support one
apartment above another must be protected for at least 45
minutes against collapse from exposure to fire.
- The heating, ventilation system and plumbing must be
separate for each apartment and enclosed to prevent the
spread of fire and smoke between apartments.
Each
apartment must have its own entry that is separate from the
other and protected from fire and smoke.
- The floor and wall assemblies that separate apartments
from one another must be constructed to resist the
transmission of noise. The NBCC requires a sound
transmission class (STC) of 50 or more between apartments.
- The requirements for multiple occupancies aren’t the
same in each province and territory. Refer to your building
code for a comprehensive description of the requirements
that govern construction in your jurisdiction.
Finishes
and coverings
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, such as vinyl flooring
and ceramic tile, to lessen the likelihood of damage and make
cleanup easier.
If carpet and underpad are used, they should contain no
organic materials that may promote mold. Area rugs can be
removed and cleaned or disposed of in the event of a flood.
Furniture should have legs that keep upholstery above the
level of the flood water. Refer to the CMHC Research
Highlight: “Renovating your basement—Avoiding basement
flooding” for advice about protecting your basement from
floods.
Most drywall and fibreglass batt insulation must be removed
and discarded if they become wet from flooding. Cement board
and polystyrene insulation are less risky alternatives because
they are almost unsusceptible to water damage. Refer to the
CMHC Research Highlight: “Basement walls that dry quickly” for
advice on the construction of walls that might be damaged by
water.
