How Much Insulation Should I Have?

Believe it or not, “How much insulation should I have?” is one of the first, and most influential questions that can be asked when starting the design of a new home or renovation.  The answer to that question can affect the usable square footage of your home, the cost of the entire project, and will likely also affect many of the other construction details from the underside of your slab to the top of your roof.  And crucially it will greatly affect the comfort of your residence when construction is complete and you have moved in.

There are basically 3 answers to “How much insulation:”  Code level, upgraded, and super-insulated.  While the legal minimum must comply with code requirements for your area, one can go any amount beyond code minimum as desired.  Let’s take a look at insulation value basics, and then at each “level” of insulation.

Gulf Island Sanctuary © HA Photograhy 2015

There are many ways of measuring, or indicating insulation values.  Some values measure how easily heat can pass through a material (or building assembly).  This is known as the u-value, and is used across much of the world, and in many physics caluclations in thermal modelling.  Essentially in this system, the higher the number, the more easily heat can move through the material.  The lower the number, the more difficult it is for heat energy to pass through the material.  In the metric u-value, for example, a value of “0” means that heat CANNOT move through (which is impossible), and a higher value such as “3” would mean that heat will move with great ease through a material.  The obverse of this type of measurement is R-value, which is the resistance with which heat energy is impeded from transferring through a material or assembly.  In this system, which is most common in North America, the higher the R-value, the more resistant the material is to allowing heat to pass through, and the lower the value the more easily heat will migrate across.  So a very poorly insulated old period home may only have an r-value of about R-6, while a new home might be closer to R-15.  Essentially, every time you double the r-value, you halve the amount of continuous heat loss through that assembly.  (That’s a gross oversimplification, but paints a clear picture of the basic relationship between r-value and heat loss.)

So now, let us look at our 3 basic levels of insulation that one can pursue in a new project or renovation:  code level, upgraded, and super-insulated.

CODE LEVEL:

While the 2012 BC Building code is transitioning to a “Step Code” program, whereby new projects will slowly be expected to have increasingly higher levels of insulation as years go by, the basic levels for our climate (zone 4) are still as such:

Concrete slab on grade: no requirement if below frost line and unheated, or minimum R-12 if heated or above frost line

Basement/below grade wall: minimum R-11

Exterior above grade wall: minimum R-16

Vented roof/attic: minimum R-40

Windows/doors: minimum R-3.2 (min. metric u-value of 1.8)

These prescriptive amounts of insulation are considered the minimum legally permitted to ensure the health and safety of occupants, and to ensure that the structure will remain structurally sound.  For many new homes, these levels are sufficient, and will keep the cost down.  They are, after all, what a vast majority of the population are accustomed to.

UPGRADED INSULATION LEVELS:

Now, if one wanted to slightly improve the energy efficiency of their home, they could choose to increase their insulation levels a bit beyond code.  Conservation of energy (which insulation serves to do) is usually the smartest, most cost effective way to reduce energy costs.  This is because it lasts forever with almost no need for repair or servicing.  Choosing to modestly improve your insulation levels could be easily performed in several ways.

Adding extra insulation beneath a slab on grade can significantly reduce the heating costs for one’s home.  Because concrete has little to no r-value in a 4″ thickness (a typical slab dimension), AND because the earth on which that concrete sits has an unlimited potential to absorb heat from the interior of your home, any amount of insulation one can add under their slab is money well spent.  A suggested minimum for all slabs would be 3″ of Type II EPS, which would provide about R12.

Another great way to stem heat loss through an assembly is to provide a layer of continuous insulation on the exterior face of wood framed walls.  

Because the wood studs run continuous from the interior side of the wall across to the exterior side, that wood is essentially the only insulation for that section of wall.  Wood has an R-value of roughly 1-per-inch.  That means that a 2×6 has an r-value of about R-5.5.  The batts of insulation in a typical house that fit between those studs will have an r-value of around R-20.  So, the wood studs are a real weak point in the assembly, and are considered “thermal bridging,” since they are parts of the assembly that interrupt the nominal insulating value of the wall by conducting heat through a single, poorly insulated material directly from the warm side to the cold side.  By placing a continuous layer of insulation (whether it is a type of rigid foam, a mineral wool, or through some other method), that thermal bridge is broken with a highly insulating layer.  This will dramatically improve the overall r-value of the building, and is very efficacious, meaning it is a great bang for your buck.  Pheasant Hill Homes encourages our clients to use this approach on pretty much every new build and major renovation as a bare minimum.  It is not terrifically expensive to do up-front, and will pay for itself in energy savings for the life of the home.

When it comes to windows in your home, use triple glazing with a low-e coating.  Basic, double-glazed windows have an r-value of about 2.5.  They are an abysmal way to keep the heat in your home, and a large number of complaints about the discomfort of a building are directly related to poor quality glazed units.  They simply “feel” like having a giant hole in the insulation of your wall, and effectively, they are.  There is absolutely no reason to stick with double-glazing.  On an average home, it will cost you about $1500 to upgrade to triple glazing with a low-e coating, and you will literally feel the difference instantly.  We simply refuse to build a house without triple glazing anymore because it’s such a clear improvement in quality, comfort, and energy use reduction.

Assuming you have a typical vented attic (most homes do), the last really easy way to upgrade your home’s insulation level is to blow more cellulose insulation into that attic space.  Whether you have batt insulation between your rafters or trusses, or already have some level of blow-in insulation in your attic, blowing more insulation into this space is fast, easy, and inexpensive.  You can either rent a blower unit and purchase the insulation yourself from a box store, or if you’d rather not crawl around in your dusty, cramped attic yourself, you can hire an insulating contractor to do the work for you.  Since hot air rises, the top levels of a building are often the warmest, which means they have increased heat loss.  Adding some extra insulation to your attic space will make a big difference.  We generally aim for about R-50, which is a depth of about 14″.

SUPER-INSULATED PROJECTS:

Oceanside Craftsman

Lastly, one can go for the gusto and choose to build a “super-insulated” house.  If you choose to do this, you are probably an energy efficiency fanatic, and have consumed large quantities of the “building science Kool-aid.”  The good news is that by improving the insulation levels of your home to such great degrees, you will end up with a home that is superbly comfortable (no drafts or radiant heat loss “cold spots”), is very soundproof, and has extremely low energy bills.  While going with a super-insulated design means that your architect or builder will need to know this from day one to craft the design and construction details to suit such a stringent criteria, there are some “rules of thumb.”  In general, these are the starting points for r-values one would expect in super-insulated home:

Concrete slab on grade: minimum R-10

Basement below grade walls: minimum R-20

Exterior above grade walls: minimum R-40

Vented roof/attic: minimum R-60

Windows/doors: minimum R-5

This is pretty easy to remember, as it is the “5-10-20-40-60” guide.  The trick is that those are “effective” insulation values.  A house of this level will be using extensive computer modelling (which can be performed by certified energy advisors, or by certified Passive House consultants) to determine the specific heat losses of building assemblies and the home as a whole.  This modelling will take into account any thermal bridging from studs, floor joists, roof framing members, the style of window installation, etc.  To avoid getting too complicated, it probably means that those building assemblies will also have to be either thermal bridge free, or they will have to have around 20% higher r-value in the actual insulating material to hit those “effective” r-values listed above.  To comply with the world’s most stringent energy efficiency program, the Passive House standard, going well beyond these measures may also be required.

It is a significant investment to take one’s home from code level to super-insulated.  It will likely be in the neighbourhood of about a 12% premium over your basic construction cost, and the energy savings will likely take about 15 years to pay for themselves.  However, it is possible, if one designs very wisely and has a very well-educated builder and architect, than the increased cost of the mortgage to build a super-insulated house will actually be less than the energy savings one would realize each month.  In that instance, it is possible that a super-insulated house will begin saving you money from the very day you occupy it.  But this approach will require that you have a very strict design that will demand that you make concessions on things like floor to ceiling glazing, 12′ ceilings, and a 4,000sq. ft. home to spread out in.

Now that we have reviewed some simple categories of “How much insulation should I have,” it’s important to note that, like anything, the real world is more complex than first glance would suggest.  Building a home is complicated.  It can take well over a year from the day you start designing to the day you move in.  There are thousands and thousands of large and small decisions that need to be made to have it all come together correctly, and successfully.  But one of the first things clients should think about is “How much insulation should we have?”  With the information above, hopefully you can come to builders and architects a bit more prepared to know just how far you want to go towards achieving a comfortable, energy efficient home.

Pheasant Hill Homes encourages all of our clients to go as far as their budgets will allow, because after years of building everything from basic code to nearly meeting the most energy efficient building standard in the world, we have seen the difference that upgrading the insulation of a building can make.  It improves the quality of life for our clients in their homes and renovations, it reduces their energy costs, and it helps use the resources of our planet in a sparing and wise way.  There are few other ways in which we can “get it right” so easily in a project.

Contact Pheasant Hill Homes to find out how we can help you craft your project with exactly the insulation levels to suit your needs.

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