Insulation and Ventilation

Insulation

As homeowners, you're always looking for ways to save money and make your home more efficient.  By improving both the Insulation and the ventilation of your home, you can do just that!  A well insulated and properly ventilated home will not only cost less to heat and cool, it will also provide a healthier living space by decreasing the amount of dust, allergens and even mold present in the home (yes mold, which is virtually everywhere -see the Mold Information Fact Sheet.) Insulation is also an affective sound barrier, so you can make your home quieter with quality insulation installed correctly and in the correct amounts. Unfortunately, if your house is already built, then you don't have very many options to cost effectively change what is in the exterior walls. However, you can "upgrade" the insulation in the ceiling (attic floor) and in the floors (that is if your raised house has a large enough crawl space). Some of these upgrading projects can be done fairly easy by the homeowner (i.e. adding fiberglass insulation batts to the attic), but many should definitely be left to the pros (i.e. spray foam insulation in the attic). One of the main factors to consider when planning this upgrade is the cost.  The more expensive it is, the longer it may take to re-coup this cost in the form of energy savings.  If your house is fairly new (approximately 10 years old or less), then it might be efficient already.  If it's an older house (approximately 15+ years old), then improving the insulation may be worth considering.  And, if you are building a house, you have a lot of options for insulating the entire "home envelope" (see below). Again, cost will probably be a determining factor, but by properly insulating and ventilating the entire house, you can realize quicker returns on your investment.

 

Most of us are familiar with the term "R-Value" when it comes to insulation, but what does it mean?  R-Value is loosely defined as "the capacity of an insulating material to resist heat flow or heat transfer". The higher the R-Value, the greater the insulating power. However, this can be a little misleading because R-Value only measures one type of heat transfer-conduction. In reality though, heat transfer occurs in 4 ways-conduction, convection, radiation and air infiltration. You can learn more about conduction, convection and radiation by clicking here. Air infiltration occurs when cold air finds its way inside, or infiltrates, during the winter and when warm air gets into your home in the summer. 

There are many ways that you can insulate your home from the elements.  For example, the exterior of your home (bricks, siding, stucco, etc.) is the first form of insulation. Likewise, the interior of your home (wall board, paneling, etc.) is also a form of insulation.  These parts of your home are important and do provide some protection, but they are not very efficient forms of insulation.  To improve on this, the "empty" areas, or cavities, are filled with some type of insulating material.  These cavities are present in the walls, with the exterior wall cavities being the main area of concern, the floors (on a raised home) and in the ceiling (attic area).

One of the most common types of insulating material is fiberglass.  It can be "loose", in "batts", or in rolls. The most recognizable is made by Owens Corning and is pink in color.  There are several other manufacturers and colors of fiberglass insulation.

Fiberglass Insulation Batts

Fiberglass Insulation Batts

Fiberglass Insulation Rolls

Fiberglass Insulation Rolls

Loose Fiberglass Insulation being "Blown" into an attic.

Loose Fiberglass Insulation being "Blown" into an attic.

The fiberglass batts can be faced (a Kraft paper or plastic sheet attached on one side) or they can be unfaced, as seen in the top left picture.  If the batts are faced, the facing is a vapor barrier which will inhibit moisture intrusion. It is generally recommended that the facing of the batts be placed towards the "warm, conditioned part of the house".  The facing is also used to hold the batts in place, usually by stapling them to the wall studs or ceiling/floor joists.

These batts and rolls are available in various thicknesses (thicker=higher R-Value) for use in different locations within the house and for different climates.  In the South, we generally have mild winters and hot summers so the requirements are different than the far North.  Generally speaking though, the attic is going to require 2 to 3 times the amount of insulation (R-30 to R-60) as the walls and floors (R-13 to R-19).  Again, these numbers may change depending on the climate. There are a couple of reasons why the attic usually gets more insulation than the walls or floors. First, simply because in can.  You can only add so much insulation to a 2" x 4" or 2" x 6" wall cavity, but youcan add quite a bit in the attic because it's usually open and its not "living space". Secondly, because warm air rises, it will escape (transfer) through the attic first (bad in the winter) and because the attic can get very hot in the summer (140-160 degrees F down south) the conditioned air will be affected by heat infiltration and by radiant heat from the attic. When talking about fiberglass insulation, the batts and/or rolls are usually used in the walls (and floor cavities in a raised house) and the loose or "blown in" is usually reserved for the attic floor.

The fiberglass, especially the batts or rolls, is good to insulate from conductive heat transfer, but it's not that efficient at insulating against convection, radiation and air infiltration forms of heat transfer.  There are several other forms of insulation that improve the efficiency in those areas.

Fiberglass batts on the left and cellulose on the right.

Fiberglass batts on the left and cellulose on the right.

These types are usually sprayed in, although some can be blown in just like the loose fiberglass. One type is cellulose, which is made up of ground up, recycled news print.  It is treated with a fire retardant so that it won't propagate fire within the home.  It is usually applied (sprayed) damp to promote adhesion in wall cavities and will fill most voids more completely than fiberglass which provides better convection transfer properties.  Likewise, because it is sprayed, it is more dense which offers better radiation and air infiltration properties.

Loose cellulose Insulation

Loose cellulose Insulation

Cellulose being applied to wall cavity.

Cellulose being applied to wall cavity.

Cellulose being blown into an attic.

Cellulose being blown into an attic.

Excess cellulose being removed with a "Stud Scrubber".

Excess cellulose being removed with a "Stud Scrubber".

Another type of insulation is cotton/denim.  It is ground up cotton and blue jean material that is recycled from textile factories.  It is can be applied in a similar manner as cellulose or it can be inserted in wall cavities in batts.  Denim/cotton provides similar heat transfer properties to
cellulose.

Batts of denim insulation.

Batts of denim insulation.

One of the most popular (and effective) "new" insulation materials is Spray Polyurethane Foam (SPF).  It has excellent insulation properties and can be used in a variety of ways.  SPF comes in two basic forms-light weight, open cell foam or mid weight, closed cell foam.  These foams are used for a variety of insulating purposes.  They are used to insulate refrigerators and freezers, as the main insulation in the popular new "roto molded" types of ice chests, and of course to insulate homes. When compared with the more traditional types of insulation (fiberglass, cellulose, etc.), both types of SPF are more expensive.  When compared to each other, close cell is more expensive than open cell.  Each one of these SPF's has advantages and disadvantages. Let's take a look at a few:

CLOSED CELL

Pros

  • Higher R-value (Approximately 6.0-7.0 per 1")
  • Less susceptible to water degradation.
  • Considered a "vapor retarder" (Vapor Semi-Impermeable)
  • Strong

Cons

  • More expensive than open cell foam
  • Contains more plastics/chemicals which translates to a more negative effect on the environment (Sometimes is applied using Hydrofluorocarbons-HFC's)
  • Does not expand when applied like open cell foam
  • Does not offer much of a sound barrier

OPEN CELL

Pros

  • Less expensive than closed cell foam
  • Will expand to fill hard to reach voids
  • Offers a good sound barrier
  • Contains less plastics/chemicals than closed cell foam and can sometimes be applied with water (less environmental effect)

Cons

  • Lower R-Value than closed cell foam (Approximately 3.0-4.0 per 1")
  • Will degrade in water
  • Not as good of a vapor retarder as closed cell foam (Vapor Semi-Permeable)
Applying SPF.

Applying SPF.

SPF in wall cavities.

SPF in wall cavities.

SPF in attic.

SPF in attic.

SPF in crawl space.

SPF in crawl space.

With all of these things in mind, you must choose carefully and base your decision on your particular situation. For instance, if insulating a crawl space (under flooring), it is almost always recommended to use closed cell foam because of its vapor retarding and moisture resistive attributes. In walls and attics, both open and closed cell foam are used, with open cell being a little more common because of its expanding capabilities.  As with other insulations, and no matter where it will be used, it is very important to have a reliable professional do the installation.  The foam is a mixture of chemicals and must be applied with special equipment.  The equipment heats the chemicals to the proper temperature and keeps it heated during the spraying process.  Improper temperature and/or mixing can result in foam that will shrink, causing gaps or a foam that will not adhere properly. However, when installed (sprayed) properly, SPF is an excellent form of insulation, even if it is the most expensive! There are a few other things to think about when considering spray foam insulation and we will talk more about them in the next section on ventilation.

Ventilation

In certain parts of the house, ventilation is just as important as insulation.  On a raised house (crawl space), proper ventilation is required both under the house and in the attic., especially in a climate like ours (HUMID!) Good air flow under the house is necessary to help keep it dry. Unfortunately, this air flow can also lead to heating and cooling loss.  This is why good insulation and good ventilation are needed.  Because of the high moisture level here in Southern Louisiana, it is often necessary to put a moisture barrier (visqueen or other plastic sheeting) on the ground under a raised house to keep the moisture to a minimum. This barrier, along with good ventilation, will help prevent moisture build up.  This type of barrier is also placed on the ground before pouring a concrete slab (especially if the slab will not have any other flooring added to it, such as in a garage) to prevent the slab from "sweating" (moisture permeating through the concrete). If moisture under a house is a persistent problem, then spraying the underside with a closed cell foam (see picture above) may be a good way to prevent the moisture from getting into the home. In the attic, the summer time temperatures can often exceed 150 degrees F.  This means higher cooling costs due to all of the types of heat transfer discussed in the insulation section.  By incorporating good ventilation, you can lower that temperature significantly, saving you $$$.  Proper ventilation can be achieved with proper soffit vents (they can't be blocked by insulation-see the picture with the rafter (soffit) baffles), continuous ridge vents, gable vents, dormer vents, turbine (wind powered) vents and even electric power vents that can be thermostatically controlled.  However it is attained, good ventilation is necessary to remove the heat during the summer and to keep the attic dry. Proper attic ventilation will also prevent "ice damming", but because it rarely, if ever, happens here, we won't discuss it (see picture).

Rafter (soffit) baffles to prevent insulation from falling into the soffits.

Rafter (soffit) baffles to prevent insulation from falling into the soffits.

Mold and mildew on inside of roof sheathing (in attic) caused by poor attic ventilation.

Mold and mildew on inside of roof sheathing (in attic) caused by poor attic ventilation.

Soffit Vents

Soffit Vents

Ridge Vent

Ridge Vent

Ridge vent detail.

Ridge vent detail.

Gable vent.

Gable vent.

Turbine style vent.

Turbine style vent.

Power style vent.

Power style vent.

Ice damming caused by improper attic ventilation and poor insulation.

Ice damming caused by improper attic ventilation and poor insulation.

When talking about proper ventilation, especially in the attic, there is an exception to the rule of "good air flow". That is, when you have a "conditioned attic".  This is when the attic is included in the "whole home envelope". In other words, the attic is allowed to be heated and/or cooled to the same condition as the interior of the house (or close to the same condition).  A conditioned attic can be realized in a several ways, but it is usually for one main reason!

So why would you want a conditioned attic? The main reason is probably because your heating and cooling ducts are located in the attic and you want to lower those utility costs. Almost all ducts have some leaks and most of them are poorly insulated.  Think about this. You insulate your house to certain R-Value levels, then put the ducts that carry the conditioned air in an unconditioned location and insulate them with much less insulation than the rest of your house has! And the temperature difference between the air in the ducts and the air in the unconditioned attic is much greater than the temperature difference between the air outside your home and the air inside your home! By conditioning the attic, you will help your heating and cooling system work more efficiently. Of course, a pre-construction design change that moves the ducts into the conditioned area (fur downs, interior soffits, etc.) probably makes more sense.  That's why many homes in Northern climates have the HVAC equipment in the basement with ducts run in the conditioned (basement) crawl space! 

To achieve this conditioned space, the insulation is completely removed from the floor of the attic and the underside of the roof is then insulated, thus allowing the attic to become "conditioned". Sometimes a heating/cooling register and a return air duct may even be added to the attic area. This may be necessary if moisture is a concern, for instance if you insulated the inside of the roof with open cell foam instead of closed cell foam.  The exception to the "good air flow" rule is due to the fact that most of the time, all air flow is sealed off from the outside (much like it would be for any other interior part of the house). The insulation used can be rigid foam blocks or spray foam (SPF).  It is applied directly to the underside of the roof sheathing and the soffits, ridge vent and any other vents are removed or sealed off. In far north climates, it is recommended that an air gap of 1.5" to 2" be created between the roof sheathing and the insulation and that air flow be allowed to continue between the soffit vents and the ridge vents, in each rafter bay, to facilitate the drying of the roof sheathing.  In the southern climates, because the temperature fluctuations aren't as drastic, the air gap is usually not necessary. However, some experts say there should always be an air gap because the sheathing will get damp and with the felt paper and shingles on the exterior and the foam insulation on the interior, this dampness may be slow to dry and could cause wood rot and structural damage. 

A few other factors to think about when considering a conditioned attic. With spray foam, it is much harder to locate any roof leaks.  When you do find a roof leak, it can be much harder to repair or replace damaged roof sheathing that has been sprayed. Also, as mentioned above, if roof sheathing does become damp due to condensation or humidity, it will always dry faster in a well ventilated, unconditioned attic than it will in a conditioned attic.

 

Well, as you can see, there are a lot of things to consider when it comes to insulation and ventilation.  With a variety of material choices and price ranges, there is bound to be a way to increase the efficiency of your home.  So remember, proper insulation and/or ventilation can keep your house comfortable year round and save money in the process!

 

Sources:

Open and closed cell foam: Energsmart.com http://www.energsmart.com/spray-foam-insulation/open-vs-closed-cell-foam.html

Insulation types: Houselogic.com https://www.houselogic.com/organize-maintain/home-maintenance-tips/insulation-types/

Types of Insulation: Cellulose.org http://www.cellulose.org/HomeOwners/WhatTypesInsulationAvailable.php

Creating a conditioned attic: Green Building Advisor.com http://www.greenbuildingadvisor.com/blogs/dept/musings/creating-conditioned-attic

Open Cell vs. Closed Cell Foam: Sprayfoam.com http://sprayfoam.com/content/spray-foam-closed-cell-vs-open-cell/26

Recommended Home Insulation R-Values: Energystar.gov https://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table

Heat Transfer-Conduction, Convection and Radiation PDF: http://alkisites.vansd.org/dgray/Assignments/conduction_convection_radiation_reading.pdf