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Improving The Efficiency Of Your Home, Part 1: Insulation & Air Sealing

Energy efficiency can help slow the rate of climate change. Learn about making your home more efficient so you can reduce carbon production and also save money.

One of the ways to slow the advance of climate change is to reduce your personal carbon usage. While we can’t efficiency our way to climate neutrality, we can buy ourselves time by slowing the rate of carbon emissions and conservation, as Negawatts are often the cheapest form of clean energy available (and the least polluting). Also when you have less energy to replace, it’s cheaper to do so (i.e. if you cut your energy use in half, then only half the renewables are needed to make it sustainable).

Our homes can seem like a monolithic entity — they need heat and or cooling, they use water and heated hot water, they consume electricity, and need lighting and plumbing. But the structure plus our actions can alter how much carbon is produced by several orders of magnitude. Two equivalent homes standing side by side could have 5 to 20 times the difference in carbon pollution produced in daily operation. A 100+ year old leaky home with inefficient appliances and high electricity use creating dozens of tons of CO2 a year can stand next to a Passivhaus or Net Zero home, which has very low or even no carbon emissions whatsoever. And there is a huge continuum in between these extremes. Many existing homes that are inefficient can be upgraded to various degrees to reduce their carbon footprints.

This will be a 4-part series:

Part One: Insulation & Air Sealing
Part Two: Heating/Cooling & (Hot) Water
Part Three: Plug Loads
Part Four: Building For Net Zero Or Better

The standard disclaimers apply, all advice is for informational purposes only, CleanTechnica is not responsible for any damages caused by inaccurate information or following any information provided, consult professional expertise before making any modifications to your home, all information is subject to change as our knowledge evolves, and objects in the mirror may be closer then they appear.

This article series is focused on detached and semi-detached homes, but many of the concepts are applicable to all building types.

It is always cheaper to design a house with high amounts of insulation beginning from the conception stage. However, most of us live in pre-existing homes. Adding insulation to existing buildings is more expensive and there are often practical limits to how much can be retrofitted before the costs get out of control. That said, retrofitting insulation and air sealing can often still be cost effective and cut your bills (and carbon) by a large amount.

Your home uses energy in many ways: electricity; heat, which is often provided by electricity, natural gas and or oil; air conditioning, which is electrically powered; and most houses also have running water. Water usage can also be reduced by various means, which saves energy used to create potable water (hence your bills) and saves you heating money for hot water use. Finally, making your home more efficient increases its resiliency in case of a natural disaster that cuts off energy supplies.

Heat moves by 3 mechanisms: conduction, convection, and radiation. Hot chases cold, and any temperature migration requires an energy difference, hot being a higher energy state than cold. This article won’t deep dive into thermodynamics, but enough detail will be presented so you can understand how things work

Air Sealing

Every home has bidirectional air leakage to the outdoors. This is measured by a blower door test. A large purpose-built fan is used to suck air out of the house (or blown in if asbestos or other dangerous insulation is present), the pressure difference is measured and the air leakage rate calculated based on the volume of the home. The test assumes wind is blowing in all 6 directions into the house, which is impossible but helps to determine the total air tightness of the house, which is expressed in air changes at 50 pascals of pressure, or (x)ACH50. There are no typical house values, but at about 5ACH50 or lower you should have mechanical ventilation (an HRV or ERV, which is a device that brings in fresh air and conditions it with air exhausted from your house, recovering most of the heat or coldness in the outgoing air). New homes should aim for 3ACH50 or less, and the very stringent Passivhaus standard requires 0.6ACH50 or less. However, very inefficient homes can have 10-20ACH50 or more! These houses are wasting huge amounts of heat and air conditioning and may in fact be losing more energy to air leakage than they are to uninsulated walls, ceilings, and floors!

The easiest way to airseal your home is to get a blower door test done and arrange with the auditor beforehand to have the device run for 15-30 minutes while you check every square inch of floor, wall, and ceiling, from the basement floor to the top floor ceiling for air leakage using your hands or a feather. Make a list, or better yet photograph each and every one of these with your phone and then seal them (the sealing method depends on the location). Thermal imaging is an excellent accompaniment to blower door testing if there is a decent temperature difference between outdoors and indoors on testing day. Finally, get a second blower door test done to determine the magnitude of improvement you have achieved.

Pay special attention to the basement vectors elaborated on below and ceiling penetrations and gaps, because put together, these lead to high levels of hot and cold air loss on extreme weather days. This is known as the stack effect — warm air rises, and when it exits your home it takes away energy that you paid money for and the earth paid carbon for. The larger the temperature difference, the faster the rate of heat loss.

There are a few air leakage vectors you likely cannot easily seal — chimneys for example — and sometimes you can’t reach holes in shallow crawlspaces. Some homes may have wood paneling for walls or ceilings which can be loosely fitted and damn near impossible to seal and so on, not to mention dryer vents and kitchen and washroom vents. Do your best and look at installing dampers where appropriate and keep your dryer door closed when it is not in use.

A note of caution: if your house is too airtight and you don’t install mechanical ventilation, you could harm the occupants. Again, seek professional advice before air sealing your home.

Building Temperature Control

Resistance to energy movement (hot and cold) is measured in R value. You want higher R values to keep the warm in when its cold outside and the coolness in when it’s hot outside. The bigger the difference in temperature between inside and outside, the faster they will try to equalize, thanks to thermodynamics. This is a constant you cannot change, but higher R values mean slower equalization across all temperature ranges, and will save you energy and money. The thermal envelope is the barrier between your home and the outside environment and is where you want to have insulation and to airseal. Walls and floors inside your thermal envelope (interior walls) typically do not need insulation unless you are doing so for other reasons, such as soundproofing.

The biggest enemy to any wood-framed building is water. It rots wood, rusts metal, turns drywall into oatmeal, penetrates concrete over time, and it also feeds mold. You need to control water in order to ensure the longevity of your building. So pay attention to flashings, window wells, roofs, and every other exposed surface to control water. Insulation can cause or exacerbate water-induced rot while air sealing typically helps prevent water vapor-induced damage. This is one of the major reasons you must get professional advice before upgrading the insulation and air sealing of your home.

There are many insulation types available. In the past asbestos, vermiculite, and others were used and are toxic. If you have these, consult a professional on how to handle or remove them. Ditto for lead paint. This can get pricey quickly, but it’s far better to protect your health than save a few dollars.

Today the typical insulation materials in use are cellulose (with boron or similar fireproofing), Roxul (spun rock), fiberglass, open cell and closed cell spray foam.

Cellulose: Air permeable. Best for recycling purposes and low toxicity and low climate impacts in production and stable for long lifetime. Install it densely packed and not loose-filled. Be extra careful of this, as loose fill costs less but settles over time, wasting the investment.

Roxul: Air permeable but relatively air movement blocking, relatively safe for air quality.

Fiberglass: Energy intensive to produce, very air permeable, and often poorly installed, reducing its effectiveness when used but is common due to its widespread recognition and low cost. Avoid unless you have no other options.

Open cell spray foam: Air movement retarding if installed properly. A big caveat. Usually uses water as a blowing agent and has a low Global Warming Potential (GWP). Medium cost. Often unnecessary.

Closed cell spray foam: Air retarding if installed properly. A big caveat. Typically uses very high GWP blowing agent. Avoid for use except for interior basement walls or other special circumstances. Newer formulations are coming onto the market with low GWP blowing agents. Insist upon these. Most other uses besides basement walls are a waste of money, despite what sales people tell you (unless there are very special circumstances involved).

Spray foam installers sometimes falsely claim their product performs better than its R value and that you can use fewer Rs of foam to get the same insulating performance. This argument is meant to compensate for the much higher purchase price of their product, and to make it work they conflate air sealing with R values to make these claims. The bottom line is that R20 of cellulose performs exactly the same as R20 of sprayed foam. This is the definition of R value. However, you should ensure any air permeable insulation assembly has the proper air sealing so that you get thermal and air leakage performance up to expectations.

Air tightness is needed for insulation materials to perform to their rated R values. A 6-sided air barrier is required for all air permeable insulation to prevent heat/cold loss due to air movement. Spray foam, if installed carefully, can be an insulation and air barrier, but operator skill is necessary along with a bit of luck. Do not assume spray foam is an air barrier without proper testing after installation, as it is not guaranteed no matter what a salesperson tells you.

Spray foam is a permanent insulation that typically cannot be removed without destroying the structure it is attached to. Hence you want to be very careful about its installation and choose an installer with a great deal of experience as it can be virtually impossible to fix if screwed up. Also there have been many reports of off-gassing and odors, often due to a screwup in the mixture ratio or bad batches of product. This can make a home uninhabitable and may be a health risk. A very experienced installer can reduce this risk, but the risk cannot be completely eliminated, so bear this in mind if you choose to use spray foam.

There are other types of insulation available, such as denim, Airkrete, and more, and if you’re considering using them, consult a learned professional on their pros and cons. Beware of anyone who says there are no cons, as every insulation type has pros and cons.

Reflective barriers are basically useless in a residential setting — they only work on radiative gains, they need to face an air gap to work (and a small air gap will just lead to conductive gain), they are often expensive, are typically flimsy, and a coating of dust renders them inert. Also, decent R values in the rest of the structure would mean the heat exchange from one side of the assembly to the other would be minimal anyways. Hence don’t waste your money on them. Ditto for scams such as “insulating” paint.

Thermal bridging is a concept you will occasionally hear about in regards to insulation. It means that certain parts of assemblies (wall, floor, ceiling, window, door, etc.) transmits hot/cold at differing rates then the other parts of the assembly. Thermal bridges can be very hard to mitigate. For example a 2×4 wall can be insulated with ~R12.75 in the stud bays with densely packed cellulose, but the wood framing has an R value of about 5, or less than half of that. The only way to get more out of this assembly is to add insulation on the inside or outside of the wood framing/studs. Rigid foam on the outside of the wall will add R value to both the stud bays and the wood framing. For example, R10 rigid foam will raise the insulation values to R22.75/R15 respectively. Whole assembly R value is a calculation that will tell you the performance of the entire wall, taking into account the square footage percentages of framing and studbays multiplied by the R values of each component in the wall/ceiling assembly.

In a retrofit situation, it can be very difficult and expensive to address thermal bridging. If you are insulating on the exterior, this is easier to remedy as you would use continuous insulation, which would handle the problem in most cases. If it is not cost effective to insulate thermal bridges, this can become a hard limit on how much improvement you can make to the structure.

A house contains a number of walls, windows, floors, and ceilings. Each of these are energy loss and gain vectors.

The Basement


Basement floors are often made of dirt or concrete. If it’s dirt, insulating will be difficult, but you should cover the dirt with thick plastic to control radon and moisture. You may decide to install a concrete slab to make a solid basement floor. If you go this route, do install appropriate rigid foam insulation below the slab, 2-3 inches equaling R10 or so is adequate for most climates.

If you have a low height crawlspace and the floor is already concrete, then you can use rigid foam on top of it if there will be no regular foot traffic to damage the foam. It may need covering for fireproofing, so consult your local building permit office. If your crawlspace is dirt-floored, then thick plastic for moisture control is the lowest cost method to reduce vapor drives, but be wary of ever walking on it.

In usable basements, floors are often made from concrete (basement or on grade). Concrete is a excellent conductor of temperature, hence a very poor insulator (R value of 0.1-0.2/inch). Insulation should be added during construction or can be retrofitted later if you will still have enough floor space (low ceiling height basements are very common, especially in older homes). Concrete also is water permeable — if you spray water on it it absorbs it (relatively slowly) and when saturated it will come out the other side eventually. All changes to your home should bear this in mind, and may need to be skipped if water penetration issues cannot be permanently addressed. In a new home you should add 2-3 inches of foam before the concrete slab is poured. Make sure you using the correct type of foam, as there are many types and not all can bear the weight for the lifetime of the home. Consult a professional for proper guidance.

If you’re retrofitting, the correct procedure is 2-3 inches of properly weight-rated foam on top of the concrete, covered by plywood, properly anchored, and then your preferred flooring installed on top. Aim for ~R10 of foam, which is enough to bring your new floor to about room temperature and prevent dew point mold formation. Make sure bulk water is well controlled before making this upgrade. If water pools under the foam it can migrate upward, soaking your plywood and leading to mold formation and an expensive repair. Avoid low R value products — some are sold as interlocking flat panels with insulation already attached, but not enough insulation as they often don’t have enough R value for dew point mold control. Also, in basements try to avoid carpet and wood-based flooring. Tile is a durable and mold resistant permanent floor covering. Rugs typically work fine as they are not attached and do not take up the entire floor area (and can be removed and/or replaced easily).


Basement walls are typically made of concrete, brick, stone, wood, or dirt. All of these are very poor insulators. In many locations once you get ~5ft below ground the earth is a constant temperature, often trending towards 10ºC, although this varies by geography. In theory all basement wall types can be insulated to save energy in cold climates. However, the method of insulating them is very dependent on their construction.

Bear in mind that if you’re adding insulation to the walls or floor, you want to avoid having water pipes, drain pipes, HVAC piping, or electrical wiring and breaker boxes hidden away behind the insulation. This may require some extra advance work to move them away from the walls, but is typically well worth it to maintain future access and prevent frozen pipes that may be caused by cutting off the interior heat flow to these chases.

Basement wood walls are rare, but if you have them it’s likely a good idea to leave them uninsulated, as the moisture flow to inside will be cut off if you cover and insulate them and they could rot, threatening the structural integrity of your home. If cost-effective, consider insulating basement wood walls on the exterior (if it won’t threaten the structural integrity of your home — get an assessment from an appropriate engineer).

Stone and dirt walls can also be problematic to insulate. You may decide to install an interior concrete or cinder block supports for the house then insulate these appropriately. This can be very costly, but if your foundation is already looking worse for wear, hire a structural engineer to evaluate it. On occasion closed cell spray foam can work well and add structural integrity, but installer skill is paramount. If they screw it up, your house may collapse in the future. Only attempt this if you can find someone with experience in this niche area of spray foam installation and with a strong written warranty, and ensure they have the proper insurance in case of problems caused by the foam.

Brick walls can be susceptible to moisture lock and freeze/thaw crumbling so interior insulation should also be approached cautiously. This is not a well known concept so even professionals may inappropriately advise to insulate it, but it can actually be a bad idea. You may consider also leaving these walls uninsulated. Exterior insulation will mitigate this problem but is exceedingly expensive and you may be better off spending that money on solar panels than insulation. This can be calculated by a learned professional and don’t be surprised if solar does cost less.

Cinder block and concrete basement walls are the best candidates for insulation. Avoid fiberglass or Roxul insulation below grade and aim for rigid foam or closed cell spray foam. Choose a low GWP foam since the closed cell spray foam blowing agents can have a GWP of over 1000 in many cases, which could undo all the CO2 mitigation your new insulation will accomplish. More information here.

Open cell foam is a bad idea for basement insulation, since it is vapor-permeable and the earth contains a lot of water. Also avoid using cellulose, Roxul, or fiberglass insulation in a basement. An alternative to closed cell spray foam is rigid foam. This can be a bit more troublesome as water can pool behind it. If you need to do exterior foundation repair work, then this is a good opportunity to use rigid foam and insulate your basement walls on the outside, which is generally a very safe thing to do (but expensive unless you’re digging up the foundation anyway).

These articles at Green Building Advisor contain plenty of useful information if you have a membership to view them.

Fixing a Wet Basement

How to Insulate a Basement Wall

Mold formation is often a basement concern in many climates. It forms when the humidity exceeds 65% and there is a lack of sunlight to neutralize it. Many basements get above this magic number and mold starts to grow on walls, floors, ceilings, and contents. Many homeowners have dehumidifiers to keep the humidity below 65%, but these suck down a lot of energy. Even the newest Energy Star-rated units are not particularly miserly on power. The best way to reduce or eliminate the need for a dehumidifier is to determine why you have a moisture problem and then solve it. Sometimes this is not completely possible, and you may have to live with some dehumidifier use, but in many cases there are bulk sources you can handle, ranging from dirt floors (cover with thick plastic and seal the edges to the walls carefully), covering any large surface area drains as long as you’re not compromising drainage, waterproofing walls appropriately, sealing any air leakage from outside if you’re in a humid climate (if inappropriately vented due to incorrect knowledge of yesteryear, seal the vents). You may have a hidden water leak raising your humidity or your drains may be clogged or overflowing, your water pipes may have a hidden leak, your washing machine may be leaking, as might any sinks or showers (which may have insufficient ventilation), and so forth. Sometimes it takes professional assistance to find and fix the source of water ingress.

You can also reduce your dehumidifier’s electricity use by setting it to 60%. Going lower uses exponentially more energy and is not needed for mold prevention, though you might choose to use lower percentages for comfort if you spend a great deal of time in your basement. It can be worth comparing the usage at 60% and your preferred percentage to measure the extra energy penalty. Using an appropriate wattage meter, test at 60% for a week and at your preferred percentage for a week. Repeat both tests again for a week each. If you get similar numbers for both 60% weeks and your preferred humidity weeks then consider them usable numbers and make your decision forthwith. Feel free to run this test several more times for more data to confirm your decision, as outdoor humidity varies daily in many areas and by season (aim to do these tests in the wettest season if applicable).

Typically, you would not insulate a basement ceiling since it is inside your thermal envelope. If you wish to do so for soundproofing purposes for example, there is no harm, but it won’t save you much energy. Roxul and densely packed cellulose are commonly used for soundproofing, although soundproofing is a system and you often need to go far beyond just stuffing empty rafter bays for good noise isolation. Resilient Channel, Green Glue, Quietrock, and more are often combined to achieve good soundproofing.

As mentioned earlier, air leakage ingress often comes from basement vectors such as the mudsill (where the concrete ends and the wood frame begins), gaps between walls and floor and window openings, utility chases, water drain pipes, the dryer vent, HVAC penetrations, hot water tank and furnace venting, and so forth. Not to mention gaps in other foundation types or sometimes vents to outside that were absurdly used decades ago before building science understood dew point considerations.

Finally, test all basements for Radon before and after any work is done, as it is a colorless, odorless gas and exposure to it over time can lead to cancer. It’s the second leading cause of lung cancer behind cigarettes. If there is no basement, then test the first floor. You want to test the lowest portion of the home that is frequently occupied. The 3-month test done during the coldest season with windows closed is the more accurate test, though if not possible, shorter tests are better than nothing. Radon mitigation can be cheap or very pricey but it’s worth knowing what the levels are. Also, air sealing can raise Radon levels, since the ventilation rate of the house is being lowered.

Above Grade


Some homes don’t have basements, so the building starts at grade. The insulation and air sealing concerns here are at the walls, windows, and ceilings.

Wall composition from inside to out is typically made of drywall or plaster-lath, sometimes vapor barrier, studs (wood or metal), exterior sheathing, water resistive barrier (housewrap), and exterior facade — common ones are wood/metal/vinyl siding or brick. Sometimes the order of these can be mixed up, with the sheathing being behind the plaster/lath, for example. Older homes will often have empty stud bays if no one decided to fill them during its lifetime, and houses built in the 1970s or later often have some form of insulation in them, such as fiberglass, cellulose, vermiculite, etc.. The necessity of vapor barrier in cold locations is in dispute and it is not a settled question either way.

Very few homes will have walls made from insulated concrete forms. This is hard to add insulation to after construction, but should be decently insulated already. Also rare are Structural Insulated Panel walls, which are a foam/rockwool core with wood or metal laminated to the inside and/or outside. These are also difficult to insulate after construction but also are usually sufficient already. For both, try to determine what the insulating value currently is.

Drywall and plaster-lath are poor insulators, but you don’t typically add much insulation to them directly. If your house has vapor barrier, it can affect your insulation decisions. If your stud bays are full, then typically you leave them alone. If you have fiberglass insulation, it’s very air permeable and typically won’t perform to its full rated R value, but fixing the problem is seldom cost effective. But you can ensure air-tightness to get the most effect from the insulation present. If the studbays of your home are empty, you can fill them, and the most cost effective and eco-friendly is typically densely packed cellulose. If you have loose fill cellulose, then it has likely settled over the years and can be upgraded to dense pack with some difficulty. Never choose to insulate your walls with loose fill cellulose. The method used to insulate empty stud bays is to drill a hole in each studbay (typically from inside unless you’re doing siding repairs), fill the studbays, then patch the holes with appropriate plaster. You can check out YouTube for many videos on this process, and if hiring someone to do this work, ensure you get dense-packed written in the contract and by watching them do the work.

Many companies market spray foam for existing unopened walls. It’s a poor solution and fraught with failures and risk (though no one likes to talk about these except to say that it never happens to them). The idea is that a hole is drilled in each stud bay and foam is injected. If done skillfully and you get lucky in each bay, the foam will expand and fill the entire bay without voids and without causing any buckling to the house structure. This is hard to consistently achieve given the number of stud bays in your home, and if there is buckling caused by the pressure of the foam that threatens the structural integrity of the house, the only option is to tear down that part of your house and rebuild it. Also, even if successful, the entire assembly R value is not much better than densely packed cellulose because of thermal bridging. Hence, avoid foam injected into wood frame walls.

Insulation on the exterior of a home can be done and is great for eliminating thermal bridging, but it can be expensive. If you’re replacing worn out siding, then it’s a great opportunity to add R10-20 of rigid foam before installing the new siding and the extra cost above just replacing the siding is far more manageable.

If your house is brick framed or brick veneer, you have to consider if the brick can handle being insulated on the inside. Nobody knew of this phenomenon many decades ago, but the heat leaking out from indoors was helping to keep the bricks from falling apart. Brick is a water reservoir cladding — when it rains or is in contact with dirt, it absorbs water, which can freeze inside it, which can then shatter the brick in winter. Get professional advice before insulating any brick building, but a professional knowledgeable in this area may be hard to find and many will tell you they never had a problem so don’t worry about it, which is the wrong response. In short, any brick building insulated on the inside is taking a risk, though some brick is high risk and some is very low risk. That said, some choose to insulate brick on the exterior (typically with rigid foam of R10 or greater) to sidestep the water issue. Then simply install an appropriate facade, strapping and vinyl siding, stucco, etc..

Air sealing walls can be simple or very tricky depending on the situation. In the construction stage you would want to have the exterior sheathing as the primary air barrier, then airseal all penetrations. You would ideally do a blower door test pre-drywall/insulation and another post-drywall/insulation. Bearing in mind that air permeable insulation materials work best with a 6-sided air barrier. For existing homes, during a blower door test you will likely find air leakage coming from outlets and light fixtures, but you can buy foam gaskets for these. However, the stack effect (hot air rises) typically causes cold air to come in from the basement and vent out the ceiling/attic. A concept called the neutral pressure plane means that most wall penetrations cause little air leakage except when the wind blows directly at the wall at high speed.

If you do have gaps in your walls due to cracked corners, wainscoting, baseboards, crown molding, door frames, interlocked wood, or any other reason, try to seal it with weather stripping, plaster, caulking, or another solid substance (as appropriate), while doing your best not to ruin the aesthetics of your home. Paintable stretch caulking can work well for corner cracks.


Windows are typically not worth replacing for energy efficiency unless the glass is broken or the frames have disintegrated and for some reason cannot be rebuilt (wood frames often can, vinyl windows not so much). If your windows are very hard to open, then a palm sander, some low friction wood treatment/lubrication and weatherstripping will take care of it if done very carefully. Replacement is an expensive yet popular energy saving upgrade, but the payback is typically over 100 years. No joke. You can get much more bang for your buck elsewhere even though window replacement is “sexy.” Put the savings towards an EV 😉

If you have single-pane windows, then installing storm windows can get you relatively close to window replacement performance for much cheaper then new high end windows. If your windows are leaking air (not insanely likely when it’s not very windy, as they are in the neutral pressure plane) then you can seal them with removable caulking or in cold climates by installing seasonal plastic window film. If you are still invested in spending the money on windows instead of cheaper solar, then shop around carefully and take your time. Typically windows rated as R5 (U 0.2) are sufficient, the extra cost for higher R values are typically not worth the extra energy savings. Run the numbers for your situation just to be sure.

If you still choose to buy new windows, consider the available options and coatings. Low E and SHGC should be tailored for your climate. In a predominately warm climate, you want low SHGC windows to reduce air conditioning costs. In predominantly cold climates, you want high SHGC windows to maximize solar heat gain. In mixed climates, you should run the numbers to see which is more advantageous (likely trending towards high SHGC because summer heat is easier to offset with solar). Avoid rules of thumb and be precise with your numbers.

Finally you can install awnings outdoors above windows to reduce heat gain in the summer, and if sized and positioned carefully they can allow the sun to enter in winter when the sun is lower in the sky. If you go this route, run some numbers to see if the savings are cost effective.


Roof insulation can be easier or even more tricky than above-grade wall insulation, depending on the house. If you have a conventional attic (high roof height, often triangle, insulation on the floor, and well vented) you can insulate it with cellulose to a high R value (R50 is often quoted). This will reduce energy flow by a huge percentage. However, you need the height to do it, as if your attic height is insufficient for 15-20 inches of insulation, then you might have to make do with less (or in some rare situations none at all). If your attic or top floor has knee walls, they can be tricky to insulate and can require some creativity. Other ceiling types such as cathedral or vaulted or other types can present huge challenges in insulating them and should be evaluated by a learned professional. Insulation options for these can include unvented or purpose-installed ventilation channels.

Air leakage from ceilings often comes from heating appliances (wood/gas fireplaces), chimneys for low/mid efficiency furnaces and hot water heaters, light fixtures, plumbing stacks, electrical wires going into the ceiling, ventilation for kitchen/bathroom fans, and so forth. Most can be air sealed, but you must do it correctly to prevent future fire risk. Seek professional advice on how to seal air leakage vectors. Don’t install spray foam on top of a light fixture box or install insulation on top of it unless it’s insulation contact-rated and spray foam encapsulation-rated. LED lights especially may be designed to shed heat from the top of the can. Also, many newer light fixtures claim to be airtight. Don’t take that claim at face value, as this rating is often enough incorrect.

Drywall or plaster/lath is the most common ceiling material, but wood paneling (sometimes tongue and groove) is not uncommon and can leak like a colander if there is nothing backing it. Air sealing this can be a nightmare, but doing so could save copious amounts of energy if you can find a way. If wood filler or colored stretch caulking is insufficient to seal all of the leaks, you may have to consider removing it, installing drywall, and reinstalling it. However, hundreds or thousands of nails could recreate the air leakage you sought to seal. And glue may or may not be sufficient to hold it up in lieu of nails.

If you have HVAC equipment in the attic, then be extremely careful about insulating and consult professional advice. Often relocating it is not doable, but try. And don’t try to insulate beneath it, this is typically a fools errand, as leaky ductwork can cause depressurization of your home, raising your bills, sometimes astronomically. It is typically a better plan to insulate the roof and bring HVAC equipment that cannot be moved elsewhere to inside the home’s thermal envelope. Consult multiple professionals if necessary.

Finally you need to ensure your roof is sufficiently vented if it’s a conventional roof. As mentioned earlier, water is the great enemy of building longevity. Insufficient venting can lead to rafter and sheathing rot as accumulated moisture rots wood over time. Ensure the proper venting is in place, but do not use powered or unpowered air extractors. They are unnecessary if you have sufficient vent sizing, and by extracting air they put the house under negative pressure, sucking air out of your home that you paid money to heat or cool since no wood framed building is completely air tight.


Bonus rooms (rooms above garages) can be very difficult to insulate because the floor is connected to a cold/hot zone and the thermal bridging severely reduces the effectiveness of floor rafter insulation if there is even any present. You may need to add rigid foam beneath the insulation to mitigate the thermal bridging before installing an air barrier/firebreak. Or consider adding rigid foam between the sub floor and the floor cladding if you have the height to do so.

Garages can be near impossible to insulate, as the floor is concrete or asphalt, which are poor insulators (and not easy to remedy). Garage doors leak air like a colander and most are uninsulated (and even if they are insulated, the thermal bridging and the air leakage is typically greater than the insulating value), the exterior walls often lack insulation, and the roof is often uninsulated and sometimes even made of metal, which is a conductor, not an insulator.

It is typically best to treat garages as being outside the building envelope and to insulate the shared walls and connections between attached garages and the house instead.

Final Thoughts

In many countries, energy efficiency experts and energy audits are available for new and existing homes. In Canada and the US, energy auditors have developed a system where you can hire them to evaluate your home. They check its age and insulation levels, and conduct a blower door test. Often they give you a report with annual energy usage calculations, expected peak heating/cooling load and a list of recommended upgrades. This is highly recommended as despite the cost, you get a starting point, a blower door test (don’t forget to arrange to leave it running so you can find the leakage vectors), load numbers you can use for furnace/central air equipment sizing/efficiency determinations, and often a follow-up test to test the home after you have completed the upgrades.

Outside North America, it is up to you to determine what residential energy efficiency analysis and upgrade services are available, in many European countries there are also many resources that rival or even surpass what is found in North America.

Typically this process involves modelling your home in software to determine its energy usage and map the effect of upgrades. Before hiring someone, arrange to get a copy of the raw data after completion. If you are handy with computers, you can use this data to virtually test theoretical upgrades before making upgrade decisions and it can give you new ideas on what is possible for your home. In many cases, auditors use software that is freely available for consumers to download and work with. Common ones include HOT2000 and Building Energy Optimization Tool amongst others. Also available is the Passive House Planning Package of which many countries have their own institutes and implementations.

Home efficiency self-audit

Free home efficiency self-audit available here

You may require permits for energy saving upgrades, and if so it’s in your best interest to spend the few dollars and get the permits. They exist to make sure the work is done to a minimum code requirement, which includes safety of the occupants and a minimum quality of the work (and are not governments wasting time and money as many people choose to believe).

Many locations have incentives and subsidies available for energy audits or upgrade work. These vary by country, state, city, energy provider, and income level. Look into any that are available in your area and take advantage of them.

Heritage homes often have many restrictions on what you can and cannot do to the structure, and if you own one of these homes it can put a damper on your insulation/air sealing options. This is worth bearing in mind, although often you can get away with air sealing if you approach it strategically, and maybe adding some insulation.

In conclusion, everything mentioned in this article series is a starting point. While every attempt has been made to assure accuracy and completeness in the information provided, this cannot be guaranteed. Hence do not consider any of it as gospel but as background knowledge for speaking with professional(s) whom you should consult to analyze and recommend upgrades for your home.

Resources to assist you in this endeavor are available in most countries, and there is a great deal of low-hanging fruit in the pursuit of building heating and cooling efficiency.

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I've had an interest in renewable energy and EVs since the days of deep cycle lead acid conversions and repurposed drive motors (and $10/watt solar panels). How things have changed. Also I have an interest in systems thinking (or first principles as some call it), digging into how things work from the ground up. Did you know that 97% of all Wikipedia articles link to Philosophy? A very small percentage link to Pragmatism. And in order to put my money where my mouth is I own one (3x split) Tesla share.   A link to all my articles


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