Your home is a chemical wasteland when you add up the contaminants from personal care products, cleaning products, smoke and odors from cooking, deodorants and other aerosol products as well fumes that are emitted from hardwood and paint from your flooring and walls respectively. And that’s just a start.
While you might be tempted to use certain paints inside your home, you need to understand why some coatings are only meant to be used outdoors.
Exterior paint should only be used outside the home and on items that will be used outdoors. Exterior paints use stronger additives and resins than interior paints to offer better protection for outdoor elements and exposure to them may be higher than is recommended given gases that they release.
Exterior vs interior paint chemical composition and ingredients
Exterior paints are designed and formulated to take into account the potentially extreme cold and hot temperatures they must withstand outdoors. As a result, exterior paints tend to incorporate additives and resins that are harsher and potentially more dangerous for humans to be exposed to in closed quarters ie. inside the house.
In that regard, exterior paints should generally only be used for external use outside the home or on items that will be used outside the home such as wooden fences, outdoor furniture and things of that nature.
| Exterior paint | Interior paint | |
| Durability | Exterior paint is tougher so that it can withstand harsh weather, mildew, fading, chipping and cracking. The focus is on the paint being weather resistant for temperature and other outdoor extremes. | Interior paint lacks chemicals that exterior paint has since it is only meant to be used indoors where people will breathe in gases that it gives off. The focus is on the paint being scrubbable and washable. |
| Resins | Exterior paint resins are softer to offer outside protection from various weather elements, fluctuating temperatures and moisture. | Vinyl acrylic resins are used that are rigid to allow for scrubbing, cleaning and to resist stains from day to day use. |
| Additives | Stronger and more potent than interior paint additives for durability. As a result it makes exterior paint inappropriate for indoor use. | Lacks the weather-specific additives than gives exterior paint its extra durability. Designed for indoor use only. |
| Other | Often contains UV protection, mildewcides and fungicides which are most often not approved for indoor use. | You can add mildewcides and other additives to indoor paint to make them more room-specific (ie. bathroom) and many indoor paints are designed with specific rooms in mind. |
VOC levels in paints
VOC refers to volatile organic compounds which are solvents that get released into the air as a paint or other coating dries. Over time, governments have required paint and coating manufacturers to reduce the amount of VOCs in their products for environmental reasons.
The biggest source of VOCs are from cars and paint and paint-products are the second biggest. When you paint or use paint strippers inside the house, the level of VOCs climbs to unhealthy levels, as much as 1,000 times
higher than outdoor levels. Using exterior paint and coatings inside the house potentially exposes you to chemicals that were not approved for indoor use due to their VOC levels.
Traditionally before the environment was as much of a concern, paint and coating manufacturers used many additives and chemicals that made their products more durable but that contributed to greater levels of pollution. As more stringent pollution requirements were introduced, manufacturers were required to lower the VOC levels in their products which in many cases reduced the effectiveness and quality of them since the high VOCs were often what made them what they were in the first place.
Check your old home for lead-based paints
While the US government banned the use of lead-based paints used for home building in 1977, you might be surprised to know that most houses were built with paint containing lead for many decades leading up to this time. According to the EPA, lead-based paints were used in the following decades up the ban which came into place from 1978 onwards:
| Years home were built | % of homes built with lead paint |
| Before 1940 | 87% |
| Between 1940 and 1959 | 69% |
| Between 1960 and 1977 | 24% |
If you live in an old house as defined by the year ranges shown above, it’s possible it still contains some lead paint if you have wooden windows & sills, wooden stairs, railings, banisters & porches and wooden doors & door frames.
If you suspect you might have lead paint in your home, contact a certified lead professional before stripping old paint, painting over it or attempting any sort of related renovation to be safe.
Low VOC paints
Over time, VOC content in paints and coatings have been reduced by manufacturers to adhere to local and national regulations. It’s important to remember that even low VOC paints have dangerous and harmful chemicals. They just don’t emit as much gas as their predecessors.
Higher levels of VOCs were used to keep the wet edge of a coating, to help it remain wet longer and slow the drying process as it was being applied.
So what does low VOC actually mean?
By the late 2000s, federal government regulations capped VOC content of flat paints at 280 g/L and 380 g/L for other finishes. Since then, VOC levels have come down.
While there aren’t generally any specific standards stipulating specific levels for non-industrial coatings, products that have less than 50 g/L (grams per liter) of VOCs are considered low VOC according to guidelines published by the EPA and WHO.
Pre-1980s, you could buy oil-based house paint that was 30% – 50% VOC content by weight. Currently, it’s not uncommon to see paints with 1% – 5% VOC content and even less.
Most low VOC paints are now latex-based (water) rather than oil based as before.
Choosing low VOC paints
- Low VOC exterior paint generally has no more than 50 g/L of VOCs.
- Low VOC interior paint generally has no more than 10 g/L of VOCs.
- You might find some paint manufacturers that choose to produce products with even lower levels of VOCs.
- A paint with < 5 grams/liter VOC can be considered Zero-VOC even though it does have some VOC content.
- If you see Green Seal stamped on a can of paint, it means it has no more than 50 g/L VOC for flat paint and no more than 150 g/L VOC for higher-grade paints.
To ensure the air you breathe is clean, change your furnace filter regularly according to the recommended schedule. Higher quality HVAC filters can help to filter out VOCs and other toxins inside the house.