Home Insulation - how much is too much?
Who says that it's possible to have too much insulation in homes? We do! A House can definitely be under-insulated (millions of homes throughout the United States and Canada have this very problem), but can a home have too much insulation? In short, yes it can!
The point being that there's an optimal balance between cost and performance that works on a sliding scale. What we would recommend as optimal insulation levels to achieve a highly efficient (and often close to zero energy homes) is frequently questioned by average builders as to whether it is too much insulation because it's always more than code - bearing in mind that building code is the minimum standard a home can be built with!
The other thing is that when most people think of insulation in homes they think of cold-climate zones, but even in warm climates such as the southern US states - where homes are primarily cooled rather than heated - insulation will reduce energy costs, just probably not as much. Part of that reason is that in hot weather in areas that have big seasonal swings many people react by flinging windows and doors open to ventilate homes in hot weather - without realizing that the net result is letting the hot air in! If a home is built to high performance standards, then in hot weather as well as cold it's far better to keep them closed so the internal environment (or conditioned space) is kept sealed, and to rely on efficient HRV or ERV ventilation systems for the fresh air part.
What well-specified, well chosen and carefully installed insulation can do is to improve the comfort levels in homes - and this is also very true in a hot climate where controlling excessive radiant solar gain is a priority. So, getting the right level of insulation is a balancing act.
Rule #1 for the right amount of home insulation
Heat always moves from hot areas to cold areas - and heat can’t be stopped from moving, but it can be slowed down. Thats where insulation comes in - it puts the brakes on heat movement!
In summer, exterior heat will flow toward the cooler interior of a home. In winter, interior heat will flow toward the exterior. The role of insulation is to slow this heat flow and in general, thicker insulation is more effective than thinner insulation though this depends on the type of insulation as some simply works better - just like the brakes on a new Corvette tend to be better than those on a fifteen year old station wagon for example.
Many high performance home builders in the USA have proposed the following rule of thumb: The R-value of insulation installed in a green building should be about twice the code minimum for optimum performance to cost balance. This is, of course, a general guide as a "rule of thumb" rather than a hard-and-fast rule. Read on and we will explain...
What is the return on investment for home insulation?
The return on investment (ROI) refers to how long it will take to pay something off. With insulation it goes something like this; if living in a cold climate, currently have a 2x4 wall with fiberglass insulation and are wondering if adding two inches of rigid board insulation is a good idea, the ROI could be 5 years - to randomly pick a number. So that means if it costs $2,000 to buy and install that insulation and it will save $400 a year on heating (and/or cooling costs), then the ROI is 5 years.
That is a simple equation to know one basic variable; when will the actual money spent be back in the bank? Beyond that, a well-insulated house is, for many reasons, usually more durable and more valuable in terms of resale. It also means that if planning on occupying that house for the next 50 years, then it's possible to save $20,000 for a $2,000 investment. But there's more to it than this simple calculation of ROI.
What does ‘diminishing returns’ for insulation mean?
Adding an inch of insulation to a wall that has only one inch of insulation is certainly well worth the investment, in any climate. Adding an inch of insulation to a wall that has 5 inches of insulation makes sense in most climates. Adding an inch of insulation to a wall that has 30 inches of insulation makes sense nowhere. Even Yoda won’t live long enough to get a return on investment for that much insulation, so it’s pretty much pointless.
The term ‘diminishing returns’, when speaking of insulation, refers to the reduced value that could be expected in terms of cost-effectiveness and energy savings if continuing to add insulation after a certain R value has been achieved.
The first inch of insulation in a wall is far more valuable than the 30th inch in terms of insulation performance, as the cost of purchase may never be recovered through energy savings for that last inch of insulation.
Houses should be built with their specific climate in mind, and there is a 'sweet spot' of performance for any given geographical region, meaning an estimated ideal level of insulation given. The laws of diminishing returns means that there is a point where it best to stop insulating homes and start planning to add heat, or risk spending money and embodied energy in materials that simply will not be recouped in a reasonable time period or over the life of the house.
That is to say, there is a balancing point where generating heat is more sensible than adding more insulation - but in terms of net result - the way the energy is produced and the type of energy used for heat can change everything. Probably the easiest energy type to clean up in terms of environmental impact is electricity - but then depending on the state or province, electric prices may make heating with electric cost prohibitive - unless of course the home is well insulated and needs less heat or cooling! See the problem yet for giving a simple answer?
Build right for your climate zone
Building codes span entire States and Provinces, and often, certainly with Canadian provinces, they will have vastly differing climate conditions from North to South and even East to West.
The ideal design and building envelope will change dramatically from place to place, and for a variety of reasons such as latitude, local 'micro-climates', elevation, insolation (how much sun exposure a home gets,) source of power (renewable / fossil fuel), as well as the local cost of various types of insulation. See here to find which climate zone to insulate for.
So, it is important to view the National Building Code for what it really is – the bottom rung of performance that must be achieved when building or renovating a home. In other words, it’s the worst house any builder is legally allowed to build. How’s’ that for some perspective on what building to code really means?
Is insulating a building to code good enough?
The US states are for the most part, small enough that there aren't generally great differences in climate from one corner to another, so let’s take the Canadian province of Ontario as a more extreme example; building code requirements for home insulation remain constant from the vineyards in the southern-most region of Niagara, to the Arctic shores of Hudson Bay. This makes no sense whatsoever.
One person in Ontario could be working up a sweat picking grapes at the exact same moment that another Ontarian is being chased by a polar bear across the frozen tundra. And in order to meet building code standards, they are both required to build a house the same way despite those homes needing to perform in dramatically different climates.
None of us would think there is a single 'ideal' outfit that would protect from sunburn, let sweat evaporate AND protect from frostbite and polar bears, so why would we expect there to be one 'ideal' home design? The only thing building codes consistently provide through their entire range, is a false sense of accomplishment when we build to the bare minimum performance requirements.
Meeting building code thermal performance will not earn any home an 'A' grade; it’s more like a 'D', meaning it barely passed muster. Getting a 'D' on a test score is not something many people set out to acheive or run home to tell their parents about, yet the vast majority of homes are built with that equivalent grade as a target as if it were arrived at by great minds pondering the 'ideal' amount of insulation.
Nope. It was usually chosen because that's what fits between the studs. And on occasion, they make code a 'little' bit better, but not 'too' much better to risk upsetting the building industry and the familiar model of profitability they have established.
Bear in mind that building code continually changes and never in the direction of reducing the amount of insulation required; it’s always to increase it. Some local regions like the city of Vancouver, British Columbia, for example, recognize the benefits of improved buildings and have much more stringent performance demands than the National Building Code. In aspiring to acheive the status of World's Greenest City 20/20, Vancouver has promoted Passive House Certification, and the province of British Columbia has recently released the BC Energy Step Code, which demands the highest performance of any provincial code in Canada, in a move towards the province's goals of having all buildings be Zero Net Energy ready by 2050.
So, what is the right amount of insulation in a home?
The right amount of insulation in a home - be that attic, walls or floor, will of course vary by region. To get the best idea, designers should conduct specific energy modelling and make key decisions based on balancing performance. Homeowners when having a home built or when renovating need to decide what is most important to them – home size and staying on budget, energy efficiency and carbon footprint, or building an off-grid or resilient home that can stay warm or cool during power outages because it's design is high performance and efficient.
In fact - we think that's a great way to answer that question of "How much insulation is enough in a home?" - Enough to make it efficient, in the true sense of the word, that's the right amount...
How much insulation is too much?
This is, oddly enough, a question that needs to be addressed also - is it even possible to install too much insulation in a home? Sometimes people can get a little over ambitious and install far more insulation than is necessary or to use our new word - efficient. And sometimes they have to do that in order to meet a certain performance standard. For all that we like about the Passive House Certification and performance targets, that system is not without its' flaws.
In order to meet an overall energy performance target - (that was set somewhat arbitrarily in Germany in the case of the Passive House Institute or PHI) - builders may need to use utterly ridiculous amounts of insulation in certain areas to compensate for things like large windows all around a home, despite that provision has been made by shading, placement or specification to balance the homes' performance. But we still think the Passive House Standard of construction is better than code. We love it, warts and all, because if a home is built to Passive House standard then it's going to perform very well. Under our new definition though - depending on many other design elements and considerations - it may not be what we would consider efficient - as its' net footprint may not be optimal.
There are many other building certifications and standards for Green or Sustainable homes that should be considered - the best of which, in our opinion, take careful consideration of all factors before dictating what is the perfect amount of insulation for walls, roofs or floors. The very best specifications for insulation though are those that keep families comfortable - and that don't break the bank. (which is why we consider that rigid foam insulation has it's place in Green and Sustainable construction, read more here)
The best return on investment for home construction & insulation:
All cold-climate homes need some source of heat to maintain a livable temperature in winter. How much heat is required depends on how fast a house loses heat. How fast it loses heat depends on how well insulated it is, and how well-sealed a home is against air leakage - which in terms of a high performance homes' efficiency and durability is another hugely important factor to consider, build to and to measure using a blower door test.
So follow that logic for a moment – if homes lose less heat, they need to ADD less heat. And sometimes…not all the time but sometimes… that can also mean reduced costs in heating and cooling infrastructure. What that in effect means, is that rather than buying a big furnace to heat a poorly insulated house, it's possible to buy a small furnace to heat a well-insulated house - or even, if designed and built very carefully, to end up with a Zero Energy home.
I, for one, would prefer my money to go into the best home possible rather than to evaporate into energy bills - and if that also results in a lower carbon footprint for my family and a healthier home, great! Achieving this for the forseeable future means careful planning, building and renovating better than code, and striking a balance between cost, performance and in a careful choice of non-toxic building materials - this is why Ecohome exists - to help homeowners to make informed choices, to build better, renovate better and to live better... Please leave comments below!
Now we know more about how much insulation is too much in a house, find more pages about sustainable and resilient green building techniques here :
Find more about green home construction in the EcoHome Green Building Guide pages or to learn more about the benefits of a free Ecohome Network Membership, see here.