Basement renovations, which are typically undertaken to either provide or improve usable space in a home, afford many opportunities to build in features and technologies that will improve the performance of the renovated space.
However, basements can also have significant moisture problems that must be solved before a renovation can proceed. If they cannot, the homeowner should be discouraged from proceeding with the renovation, as the moisture will damage the newly installed materials and finishes, making the renovation all for naught.
Your plan for a green basement renovation should consider the five principles of Healthy Housing™.
Quick Reference: Green Basement Renovations
Occupant health / healthy indoor environments
- Correct moisture problems.
- Prevent moisture and mold problems with moisture control strategies and moisture-resistant materials, finishes and surfaces.
- Test for soil gas (radon, methane, etc.) and mitigate if necessary.
- Reduce material pollutant emissions by using low-emission flooring (ceramic tile, natural stone), cabinets (hardwood, low-emission or sealed particleboard), countertops (solid surface, laminates, sealed particleboard), paints, cements, grouts, sealants and caulking.
- Provide air circulation.
- Improve wall and floor insulation.
- Provide effective air barriers.
- Install high-efficiency appliances and equipment.
- Insulate cold and hot water pipes.
- Utilize low-energy lighting. Provide design of task lighting, optimize available natural light.
- Install energy-efficient windows.
- Inspect, adjust and seal forced-air system ducts.
- Select certified forest products for flooring, cabinetry and millwork; recycled content in tiles and drywall; materials with low embodied energy that are locally sourced and lightly processed.
- Choose materials and products that are durable, resilient and serviceable.
- Design for accessibility / aging in place to extend the amount of time the occupants can easily access and use the basement.
- Plan for future retrofits of green features.
- Plan for renovation waste management, reuse/recycling of fixtures, cabinetry and materials.
- Choose products and materials with low pollutant emissions.
- Avoid expensive rework by identifying and addressing any concerns at the beginning of the job.
- Control maintenance and replacement costs using quality, durable materials.
- Include energy- and water-saving features to reduce operating costs.
- Ensure good, timeless design to extend the life of the finished basement and time between demolitions.
- Design for accessibility / aging in place to allow occupants to stay in the home as they age.
- Insulated cold and hot water pipes
- Higher-efficiency appliances
- Energy-efficient windows (source of natural light)
- Improved wall insulation where feasible
- Low-energy use lighting
- Mold resistance via moisture-resistant materials, finishes and surfaces
- Improved floor insulation where feasible
- Sealed sump pump cover to provide soil gas control (radon, methane, etc.)
Site Conditions and House-as-a-system Considerations
When analyzing the existing conditions of a basement, you must understand issues related to structure, moisture, ventilation, plumbing and durability of materials in order to identify any pre-existing problems and prevent them from recurring after the renovation.
Carefully examine any symptoms of structural problems before beginning any renovation work. Look for signs of previous repairs or renovations that may be hiding problems, and bring them to the attention of the homeowner. Foundation structural problems may include:
- cracks in slabs, walls and footings; if cracking is severe, and for active cracks (ones that may open and close), you may need expert advice to develop a solution tailored to the problem. In an older home, hairline cracks may not represent a significant concern if there is no water leakage and they are not active (though they should be sealed as part of the renovation);
- inadequate support of the main floor system above the foundation; check for joists that have been overextended, cut to allow passage of ducts and pipes or spaced too far apart; lack of bracing; and beams that are too small or inadequately supported;
- spalling concrete (concrete that has broken up, flaked or become pitted) indicating freeze-thaw problems;
- porous or powdery residue on concrete (known as efflorescence) that indicates moisture transfer through the walls or floors;
- expansive aggregates in concrete that can cause concrete to deteriorate;
- expansive aggregates used under concrete slabs that can cause the slabs to uplift and buckle;
- poorly insulated and sealed joist spaces at the top of foundation walls; and
- moisture-damaged wooden beams or joists where they rest on, or within the foundation walls; moisture and temperature conditions in the wall can cause the beam and joist ends to rot.
- If there are leaking fuel tanks or landfill sites nearby, soil gases may be a concern. Soil gases such as petroleum vapours and methane can cause chronic illnesses and even explosions. If you suspect that soil gases coming into the basement contain high levels of methane or other pollutants, the homeowner should contact municipal authorities to determine who can fix this problem.
- Radon gas comes from uranium deposits in the soil and is a factor in increased levels of lung cancer. Before renovating a basement, test for the presence of radon using a home test kit that is available from home improvement stores, mail-order services or through the Yellow Pages™ under “air quality services.” It is advisable to conduct the test over a three-month period in late fall or winter to get a long-term average. Shorter test periods may not provide a result that is representative of typical conditions. If the test confirms radon is present at levels that exceed Health Canada guidelines, a radon mitigation system can be planned as part of the basement renovation.
Look for signs of moisture problems from inside and around the foundation and conditions that can lead to moisture problems. These may include:
- moisture staining on foundation floors and walls;
- moldy odours in the basement;
- visible mold on wood framing, drywalls and finishes;
- grading around the house that slopes towards the foundation;
- evidence of previous flooding incidents such as water marks on walls and floors;
- gaps between concrete floor slab and foundation walls;
- eavestroughing that deposits roof water at or around the foundation;
- poorly drained window wells; and
- wet insulation, condensation on wall-mounted polyethylene air/vapour barriers, moldy framing.
Moisture problems can be the result of excessive water vapour in the air (high humidity), capillary water that wicks through concrete and/or bulk water that leaks into the basement.
Problems From Water Vapour (High Humidity)
When the amount of water vapour in the air gets too high, it can condense on cool surfaces. This can lead to mold growth, moisture-related damage and wood decay and reduce the thermal resistance of some types of insulation. The presence of condensation on cold water pipes, exposed concrete surfaces or structural steel members generally indicates that the relative humidity of the air in the basement is too high, or the surfaces that are too cold. Symptoms of high humidity include:
- condensation on windows, cold water pipes and other fixtures;
- condensation on or behind the wall and joist space vapour barrier;
- damp spots or mold on walls and floors; and
- moldy or musty smells.
Problems from Capillary Water
Water can move through porous materials, including masonry, stone rubble and concrete via capillary action. This movement results from a suction pressure exerted by small tube-like pores in the material. The concrete slab and foundation walls can wick water into the basement from the surrounding soil unless moisture protection has been provided (for example, exterior dampproofing on the basement wall, sheet polyethylene under the floor slab). Symptoms of capillary water moving into the foundation are found both on the interior and exterior of the house and include:
- damp walls and floors;
- musty or damp carpets;
- wood window sill and buck decay;
- wet or decaying wood in contact with the foundation walls or slab;
- stuffy or damp smells;
- white powdery stains (efflorescence) on exposed concrete walls and floors (interior or exterior); and
- presence of mold.
Problems from Bulk Water
Free water that interacts with the house as a measurable volume of liquid is called bulk water. Groundwater, precipitation, and plumbing leaks are common sources of bulk water. Water leaking through basement walls or collecting in window wells is often due to poorly diverted rainwater and snow melt water. This is often due to incorrectly installed rain-shedding details and systems, improper grading and the presence of a crack or hole in the foundation walls or floor that provides a path into the house. Moisture problems are sometimes the result of a high water table, a situation that can prove difficult, if not impossible, to solve. Bulk water symptoms include:
- stuffy or damp smells;
- wet insulation;
- concrete cracks with water leakage or staining;
- standing water in the basement;
- decaying interior basement frame wall sill plate;
- presence of mold; and
- visible water leaks in basement (this could include conditions the occupants may have observed but are not evident to you as you perform your inspection).
A Simple Test for Capillary Moisture Problems
To find out if a foundation floor or wall is wicking moisture into the house, try this test: attach a square of polyethylene film (300 x 300 mm) to a dry section of wall or floor and seal the edges with tape. Leave it for a day or two. If moisture appears on the underside of the sheet, it is migrating through the concrete. This test is not exact but can usually reveal a problem if it exists.
This test is worthwhile even if there are no reported and no visible signs of moisture before undertaking a basement finishing project. Moisture may have been evaporating through the floor and walls without obvious signs. If undetected, this may become a serious problem after the surfaces have been covered with new finishes that might trap the moisture and cause it to accumulate to the point where it becomes a problem.
- Mold is a sign that there are moisture problems in the basement that must be corrected before the renovation proceeds. Identify any mold issues or evidence of hidden mold early to ensure they do not continue to be problems after the basement is refinished.
- Consult the homeowner about signs of mold growth and about past or seasonal wetting incidents.
- If a significant amount of mold is present, precautions will have to be taken to safely demolish and dispose of the affected materials.
Ventilation and Air Circulation
- Ventilation of the basement will help control moisture, odour and contaminants. Air circulation can help prevent odour buildup and will help keep air temperatures more consistent and relative humidity conditions in an acceptable range.
- If you are adding a new basement kitchen or a bathroom, plan on equipping each with an outside-vented exhaust fan.
- If the basement is connected to a forced-air heating system, achieving good air circulation will be relatively straightforward with good duct design and installation. Plan on including a mechanical contractor in the renovation work.
- For houses with baseboard heating (no central forced-air system), an air circulation system can be installed to move air from the first storey of the house to the basement. Each room in the finished basement should have some means of having air supplied to it or drawn from it or both.
Lead and Asbestos
Sources of lead include old house paint, plumbing pipes and the service connection into homes (before the 1950s), and solder used to join water pipes and within fixtures.
- Have old paint lab-tested for lead content, especially before major renovations in older homes.
- Sources of asbestos may include vinyl asbestos floor tiles and adhesive, appliance wiring, vermiculite insulation, pipe and boiler coverings.
- For both lead and asbestos, take appropriate steps to protect workers and the occupants in accordance with provincial workplace safety requirements and applicable building codes, regulations and bylaws.
Basement Green Features, Considerations and Options
Green features and options that you can consider for the various components that may be involved in the renovation are covered in this section. It discusses moisture problems and soil gas problems, insulation and air sealing options and green solutions for flooring, ceiling and wall finishes, lighting, ventilation, etc.
Correcting moisture problems
- Check to see that water from the roof drains well away from the foundation. Ensure that the eavestroughing drains properly (it does not overflow where it is not supposed to) and downspouts discharge water well away from the house.
- Ensure that the grading around the house, as well as driveways, walkways, decks and other adjacent surfaces, are sloped so water runs away from the basement walls. While a 2 per cent slope away from foundation walls is commonly specified, a 10 per cent slope away from the wall for the first 2 m is recommended for landscaped surfaces to ensure good drainage.
- For more serious moisture problems, the foundation walls may have to be excavated to replace or repair their moisture protection system. Once the basement walls have been exposed, footing drainage tiles can be replaced (or installed), if needed. Any cracks or other damage can be repaired and the wall moisture proofed. A plastic or rubber waterproofing membrane or a surface bonding material can provide even more protection. Various materials such as membrane products are available to cover irregular, uneven surfaces. Adding exterior insulation to the foundation wall before the foundation is backfilled is an effective way to reduce basement heat loss.
- A far more serious problem is water leaking into the basement because of a high water table. Unless this issue is resolved, the basement should not be refinished.
- Protect wood framing members in contact with the concrete floor and walls with a moisture impermeable material to prevent moisture wicking through the concrete from coming in contact with adjacent wood framing members.
- Carpets, furnishings and other objects laid directly on the slab are also likely to experience moisture damage. Contact with unprotected concrete should always be avoided.
- Install a vapour diffusion retarder and an air barrier over the exterior walls. A combined air-vapour barrier such as sealed polyethylene can be used over frame wall assemblies to prevent moisture in the basement air from coming in contact with the colder foundation walls. Be aware that poorly installed air and vapour barriers can result in condensation, water damage and mold growth within the new wall assembly. Polyurethane foam insulation sprayed directly on the foundation wall can effectively provide an air and moisture seal with high insulation values.
- Provide exhaust fans that vent outdoors in basement bathrooms.
- Ensure provisions are provided to vent clothes dryers to the outdoors.
- Reduce the risks of condensation on cold surfaces in and around the basement by insulating cold water pipes, upgrading to energy-efficient windows and insulating basement walls and floors. Ensure steel beams are insulated 600 mm back from the exterior walls.
- Disposing of moldy materials may raise a cloud of spores that represent a health risk to workers and the occupants. For protection during demolition, use a powerful fan to vent the basement directly outdoors, seal off the basement from the rest of the house, and carefully bag and seal moldy materials and then remove them from the house. Workers should wear appropriate rubber gloves and a respirator. Three suitable types can be used, depending on how severe the contamination is. For mild problems, a comfort mask may be adequate; for more serious jobs, a half-face dust-mask respirator may be needed; for severe problems, use a full-face respirator or have a professional cleaner do the job.
- If the mold is growing in carpets, they should be removed. For mild problems, a thorough cleaning with an outdoor-vented vacuum or one with a high-efficiency particulate air (HEPA) filter may be effective or dry steam cleaning if the carpet can be completely dried within a few hours. Be aware of some anti-fungal treatments, which can be as harmful as the mold. Ensure the carpets are thoroughly cleaned before bringing them back into the renovated basement.
- Upholstered furniture should be discarded if it is very moldy.
Soil Gas and Radon Remediation
- A complete air barrier is the first line of defence against soil gas infiltration. Therefore the renovation should include a continuous air barrier extending from the first floor joist area, down the basement walls and across the basement floor. Any cracks or holes in the foundation must be sealed, including those around plumbing pipes and electrical wires where they enter the basement.
- Spray applied foam is effective at air sealing and insulating foundation walls. Sheet polyethylene installed over the basement wall framing can also provide a good air barrier, if it is properly sealed. Sealing the wall air barrier system to the basement floor will complete the system. Install a self-priming drain or gas trap to stop air from coming up through the floor drain. Purchase or site-build a sealable cover for sumps.
- In homes with high gas concentrations, a basement sub-slab depressurization system may be required. This typically includes a 75 mm – 100 mm pipe to be installed through the basement floor slab into the gravel layer under the slab. A fan is connected to the pipe which vents air from under the slab outdoors. You should consult a soil gas expert or specialist radon remediation contractor to design and install the depressurization system.
- When a house with a radon problem is served by a well, the water from the well may represent a source of gas. The well water should be tested and may require a treatment system.
- After the remediation measures have been taken and implemented, the homeowner should be advised to conduct a second follow-up test to determine if the remediation system is working.
Basement walls may be insulated on the inside or outside. The choice will depend on whether or not the foundation is being excavated for other reasons (for example, to correct a moisture or structural problem), thereby presenting an opportunity to insulate the foundation while the walls are exposed. More often than not, if there are no moisture concerns, the basement walls are insulated on the inside.
When insulating on the inside, it is important to ensure that a vapour retarder fully covers the insulation on the walls and in the first floor joist spaces. An air barrier is also required to prevent heat loss through the wall system and to stop moisture from seeping into the renovated wall. Options for insulating foundation walls are presented below. In all cases, full-height basement wall insulation helps minimize heat losses.
- If the basement walls are to excavated, take advantage of the opportunity to insulate the basement on the outside. In fact, foundation walls made of stone or rubble may be insulated this way because the integrity of these foundation types can be affected by the installation of interior insulation. Exterior insulation does not intrude on the interior space and keeps the foundation walls warmer and drier, which helps protect them from moisture problems.
- Rigid or semi-rigid insulation panels and spray-applied foam insulation are common exterior insulation materials. Semi-rigid board insulation also serves to direct any water around the foundation downward to the drainage tiles, relieving water pressure on the wall. However, they can only be used where there is a functioning drain tile and should be installed to their full depth with no horizontal seams. Spray-applied foam insulation can provide moisture protection air leakage control and thermal insulation in one continuous blanket of insulation. Exterior insulation should be at least 51 mm (2 in.) thick, although 100 mm (4 in.) offers higher performance.
- The insulation panels can be installed over a dampproofing coating applied directly to the foundation wall. A corrugated or dimpled drainage mat can be put over the insulation to drain water away.
- The top of the foundation insulation must be protected with flashings, and the exposed surface of the insulation panels must be covered with an outer coating of parging, pressure-treated plywood or other suitable covering to prevent damage.
- Consider air-sealing the sill plate and header joist to the sub-floor from outside, if it is exposed during the renovation work. This can stop a lot of air leakage, and make the house more comfortable for very little extra cost.
Once any moisture problems have been corrected, insulating from the inside is a less disruptive and more effective way of increasing comfort and reducing heat loss in the renovated basement. There are a number of options available:
- Framed walls: This involves building standard wood stud walls against the basement walls and using batt insulation. Before the wall is built, an interior dampproofing barrier may be applied to the foundation wall from grade level down to the slab. An air/vapour barrier system is also required, which is typically provided by caulked and sealed sheet polyethylene that is applied over the framed and insulated walls. Ensure that the air barrier is continuous. Electric outlets must be joined to the air/vapour barrier, either by wrapping them with a piece of polyethylene or by installing them in airtight plastic boxes.
- Compact walls: If you have not insulated outside and the space is too tight to use stud frames, you can install rigid board or spray foam insulation (51 mm minimum for energy performance) against the inside of the foundation walls. Battens are then installed over the insulation and are fastened through the insulation to the foundation wall. This provides a space for electrical services and support for the gypsum board. Since this system uses no moisture barrier against the wall, all cracks and penetrations in the wall must be well sealed, and so must all the joints in the finish wall covering. The spaces between the joists must also be insulated and covered with an air and vapour barrier.
- Proprietary water/moisture-resistant subfloor systems that can prevent occasional bulk water and capillary water from damaging floor finishes are available. The systems also allow any water that gets under the subfloors to drain freely to a floor drain.
- Hard surface finishes are generally healthier choices because they have little or no off-gassing. Options include ceramic tile, pre-finished wood, laminate flooring and linoleum.
- If ceiling to floor clearance permits, a new floor structure can be installed that includes a moisture barrier, air barrier and insulation. This assembly can provide a warm, dry surface to apply a variety of coverings.
- Vinyl flooring may gradually release pollutants. Hard vinyl tiles emit fewer gases than flexible sheet vinyl flooring. Pre-glued vinyl tiles with lower emissions and low-toxicity, water-based adhesives are available.
- Ceramic, linoleum or stone floors are water-resistant and have few pollutant emissions. Low-toxicity adhesives, sealers and grouts are available.
- Unless the foundation is very dry, carpeting is not often suitable for basements. Carpet fibres trap and hold moisture, provide a good place for mold to grow, and it is difficult to get all the dirt and mold out of them even with regular vacuuming. Area rugs can be used if desired as they can be removed for cleaning.
- If possible, obtain materials from nearby sources to reduce transportation-related energy use and pollutant emissions.
Wall and Ceiling Finishes
- Drywall provides the simplest and most versatile surface, but it is not suitable in damp basements.
- Sealed wood paneling and paperless drywall are moisture-resistant alternatives to conventional drywall.
- Use pressure-treated wood for wall base plates. Provide a moisture break between the wood and concrete floor for extra protection.
There are several other choices for a basement ceiling:
- Acoustic tiles and panels — Urea and phenol formaldehyde resins that may be used to bind the fibres together in the panels can give off emissions.
- If drywall is used, ensure hatches are provided to allow access to plumbing valves, duct dampers and other elements that require periodic inspection and adjustment.
Finishes and Sealants
- Choose finishes that are low-odour and low in chemical emissions. This includes low-VOC paints and water-based urethane coating for wood, which are readily available from many suppliers.
- Choose low-odour and low-emission cements, caulking and sealants.
- Plant- or mineral-based paints and coatings as well as natural clay and lime plasters are available and may be used where occupants are very sensitive to emissions.
Cabinetry and Shelving
- Solid hardwood can offer a low-emission, durable option for cabinets and shelves.
- Particleboard and medium-density fibreboard (MDF) used to make modular cabinets may contain urea formaldehyde glue, which emits formaldehyde and other pollutants which can adversely affect IAQ. In most cases, the material is sealed in with a plastic skin, which brings the emissions down. However, all surfaces — including the holes for the adjustable shelving and the edges of site cut boards — can be coated with a suitable sealer such as waterborne urethane or low-toxicity acrylic sealer to reduce off-gassing.
- Formaldehyde-free MDF, exterior-grade plywood and formaldehyde-free hardwood plywood are other options to minimize pollutant off-gassing.
- Wood products can be FSC-, CSA- or SFI-certified, which provides assurance they come from sustainably managed forests.
- Insulate cold water pipes to prevent condensation and prevent mold growth. Insulate accessible hot water pipes to save energy.
You can improve energy efficiency in a basement by installing efficient lighting and making effective use of what natural light may be available.
- Select ENERGY STAR®-rated fixtures for efficiency.
- Good lighting design ensures that the right number and type of fixtures be installed to reduce lighting energy costs and minimize the number of fixtures required. A lighting store or lighting designer can advise you on the lighting plan.
- Dimmers can create a more intimate sitting area and also save electricity. Make sure to that dimmable fluorescent bulbs are selected.
- Wiring lights to different switches allows you to illuminate one part of the basement, as needed.
- Added windows and light-coloured paint on walls and ceilings can increase the availability of natural light. Window wells can be enlarged to more fully expose below grade windows to sunlight.
- Install an “all-off” electrical switch that allows equipment continuously drawing electricity to be shut off.
Ventilation and Air Circulation
- In houses with forced-air systems, new supply and return air diffusers can be located throughout the basement space and connected to the existing forced-air system to achieve good air circulation.
- Continuous furnace fan operation can help maintain better indoor air quality and comfort in the basement.
- Air returns should not be located in or near closed rooms with unsealed combustion appliances (for example, furnaces, hot water tanks) to avoid backdrafting problems.
- Provide bathroom fans vented to the outdoors.
- Dehumidifiers (ENERGY STAR®) can be provided to help control moisture conditions in the basement. However, they should not be relied upon to correct moisture problems as