How much insulation is too much in attics and walls?

Home Insulation - how much is too much?

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.

In reality, there is an optimal balance between the up-front cost of insulation and the long-term energy performance and savings you could expect to enjoy. And, it works on a bit of a sliding scale. What we would recommend as the ideal level of insulation to achieve a highly efficient, and often close tozero energy home, is frequently questioned by builders because it often doubles the amounts required by regional building codes. Bear in mind, that building code is theminimum一个房子的标准建造，它从来都不是“理想”的数量。

当大多数人想到家里的隔热层时，他们想到的是寒冷的气候区。但即使在气候温暖的地区，如美国南部各州，那里的房屋主要是制冷而不是取暖，适当的隔热也会为你省钱。

Rule #1 for the right amount of home insulation

Heat always moves from hot areas to cold areas. Heat movement can never be stopped, but it can be slowed down. That's what insulation is for.

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. That is, of course, just a general guide rather than a hard-and-fast rule. Read on and we will explain...

What is the return on investment for home insulation?

投资回报率(ROI)指的是花多长时间还清某件事。In terms of insulation it goes something like this; if you live in a cold climate and currently have a 2x4 wall with fiberglass batt insulation and you plan to add two inches of rigid board insulation, the ROI could be 5 years - to randomly pick a number. That ROI calculation could be arrived at if it cost $2,000 to buy and install the insulation and it will save $400 a year on heating (and/or cooling costs). In 5 years the investment is paid and you will keep an extra $400 a month in your jeans for as long as you live in the home.

That is a simple equation to answer one simple question of when the actual money spent will 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 you plan 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?

It's as simple as this - adding one inch of insulation to a wall that has only one inch of insulation is certainly well worth the investment, in any climate.在大多数气候条件下，在隔热层为5英寸的墙壁上增加1英寸的隔热层是有意义的。在一堵有30英寸绝缘层的墙上增加一英寸绝缘层毫无意义。即使是尤达大师也活不长，无法获得这么多绝缘材料的投资回报，所以这几乎毫无意义。

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. The law of diminishing returns means that there is a point where it's best to stop insulating homes and start planning to add heat, or risk spending money andembodied energy in materialsthat 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 actually better for the environment than buying and installing more insulation. Wierd, but true.

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.

理想的设计和建筑围护结构会因不同的原因而发生巨大的变化，比如纬度、当地的“微气候”、海拔、日照(房屋获得的日照量)、电力来源(可再生/化石燃料)以及当地各种类型的绝缘成本。See here to find your climate zone.

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 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 to span such a range? The only thing building codes consistently provide is a false sense of accomplishment when we meet the performance requirements.

事实是，《建筑规范》的隔热水平并不是由思考隔热“理想”量的伟大头脑决定的。最初的代码R值是根据最常见的绝缘材料(玻璃纤维棒)和螺柱之间的厚度来决定的。

On occasion there are minor improvements made to code requirements, but they are often kept minimal so as not to risk upsetting the building industry and the familiar model of profitability they have established.

一些地方地区，比如不列颠哥伦比亚省温哥华市，认识到改进建筑的好处，并有比国家建筑规范更严格的性能要求。In aspiring to achieve the status ofWorld's Greenest City 20/20, Vancouver promoted Passive House Certification, and the province ofBritish Columbia has recently released the BC Energy Step Code, which demands the highest performance of any provincial code in Canada, in a move towards achieving the province's goals of havingall buildings be Zero Net Energy ready by 2050.

So, whatisthe 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 draw the most sensible conclusions, 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, decor and staying on budget, or energy efficiency, long term investment and the embodied carbon footprint.

多少绝缘是太多?

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 even effective. And sometimes they have to do that in order to meet a certain performance standard.

Case in point - for all that we like about Passive House and their performance targets, that system is not without its flaws. I know of one certified Passive House that had so many windows that in order to get certified they needed an absurd amount (24 inches) of insulation below the slab to meet the overall energy goals. Therefore, due to those windows, the net result of seeking Passive House certification was ahigher carbon footprint,因为大量的绝缘材料远远超过了任何合理的ROI。不管他们的窗户是什么，如果他们只安装8英寸的副板隔热层，在经济上和生态上都会更好。

But we still think thePassive House Standard of construction is better than code. We love it, warts and all, because having all homes built to Passive House standards would be far better than what the industry currently builds by default.

There are many othergreen building certifications and standardsthat should be considered - the best of which, in our opinion, take careful consideration of all factors before dictating the required amounts of insulation for walls, roofs or floors.

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, andhow 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 measureusing a blower door test.

So, follow that logic for a moment – when 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 aZero Energy home.

All that to say, there is rarely one single 'right' answer to how to build the most efficient and greenest home. There are always other variables to consider. And in terms of insulation, it is possible to have too much of a good thing.

Now that you know more abouthow much insulation is too much in a house, find more pages aboutsustainable and resilient green building techniques here: What is the best insulation for a home? 绿色住宅建筑需要多少绝缘材料? The difference between Polyiso, EPS & XPS foam insulation & styrofoam Tips for successfully building affordable eco homes Resilient design features for sustainable new home construction Find more aboutgreen home constructionin the EcoHomeGreen Building Guide pagesor to learn more aboutthe benefits of a free Ecohome Network Membership, see here.