What type of insulation do I choose for my renovation or new home? Whether you are a home owner or builder, this question can be very difficult to answer. The question is difficult even for an expert in the industry. The best answer really depends on the situation. Where is the insulation going, what part of the country or world is the home located and what are the goals of the product you are choosing.
Here in Michigan we are in a cold climate for the United States. This means insulation is a very important part of the building process. Here are the main types of insulation that we come across on new and existing homes.
- Fiberglass batts
- Dense packed fiberglass
- Blown in fiberglass
- Mineral wool batts
- Mineral wool board
- Blown loose fill cellulose
- Dense packed cellulose
- Wet sprayed cellulose
- Cellulose batts
- Cellulose blanket or boards
- Polyisocyanurate (Polyiso) rigid board
- Polyurethane spray foam (rigid & soft foam)
- Polystyrene foam board (EPS or XPS)
- ICF (insulated concrete forms)
Yes, that is a lot of choices and that is just what we come across here in Michigan. So how do I choose? Well again, it really depends on the situation and where you are putting the insulation.
Foundation, basements and crawlspaces
These are areas where you are going to have moisture. This means you want to choose a type of insulation that does well with moisture. Foam board handles moisture well. You see this commonly used to insulate slabs, footings and the inside or outside of foundation walls. The downside to foam board is it does not hold up to sun exposure. Also many of the foam board products out there need to be covered with a fire barrier, such as drywall, to meet code. Dow claims their foam board does not need to be covered with a fire barrier, which means it can be left exposed. There is a product called ECOcell board that we see used a lot in lower level foundation walls. This type is suppose to hold up well with moisture and does not need to be covered by a fire barrier. Fiberglass and most cellulose products are not recommended for foundation walls based on the fact that once they get wet they are useless and can cause huge problems.
Above grade exterior walls
Fiberglass batt insulation is the cheapest way to insulate a wall and pretty much anyone can install this type. The downside is it rarely gets installed correctly, which means the quality usually suffers. Blown cellulose or blown fiberglass is a cost effective way to have a professional company install insulation for you. The downside is this type of insulation can settle in the wall cavity and leave you with a void at the top of the wall over time. Wet sprayed cellulose offers a good R-value and reduces the chance of settling at the top of the wall cavity (see picture). NuWool produces a really good wet sprayed cellulose product. Polyurethane low density soft spray foam is becoming very popular option for builders looking for some of the qualities of foam, but at a lower cost than rigid foam. It offers the sealing qualities of foam and a good R-value per inch. Polyurethane high density rigid spray foam is the Cadillac of insulation. It has a high R-value per inch, air barrier, vapor barrier and thermal barrier all in one. It is the most expensive and requires some skill to install. You will also see builders use a combination of different types of insulation together. Such as a procedure called Flash and Blow. This is where they spray rigid foam (typically 1 or 2 inches) inside the wall cavity and then blow insulation to fill rest of the cavity. This is a good way to get the air sealing qualities of the foam at a lower cost and insulate the rest with a more cost effective product to get up to a higher R-value. We recommend, especially in colder climates, doing 2 inches of spray foam for a Flash and blow application. You really want to make sure the dew point is not being reached within that wall cavity and 1 inch is taking a chance. You also see builders using a combination of foam board on the exterior of the home and a blown in product in the inside wall cavities. This is a good way to get a continuous amount of insulation on the above grade exterior walls.
Rim and band joists
Rim joists are often forgotten about when we think of insulation. Whether it be new construction or existing, this is a very important part of the insulation plan. For this area we highly recommend using either a soft or rigid spray foam. Rim joists are hard to insulate and a spray foam is easily sprayed in and will seal and insulate that cavity. The rim joist is one of the leakiest areas of a home. We also see products like fiberglass batts and blown in products in these areas, but your best bet is to go with a spray foam. This picture is showing a rim joist that is insulated with a rigid foam. Notice how nice the foam fills the cavity. This can also be done will with a soft foam. The R-value per inch will not be as good but it will fill the cavity really well. This process works really nice on existing homes as well.
In my opinion the attic is the most important area of a home to insulate, especially here in a cold climate. If the attic is not insulated properly, you have the potential of ice damming, which can cause a bunch of other problems (Ice damming is cause by more than just inadequate insulation). Blown cellulose is the best and most cost effective product for insulating most attics. It settles really nice into all the joist cavities. Cellulose will settle so make sure the insulation contractor is installing a couple inches over the proposed R-value to account for settling. For example, if you are installing 14 inches to get an R-50, make sure they install at least 15 to 16 inches to allow for that settling. We also see blown fiberglass used in attics. I don’t like this as much as cellulose because it is not as dense and does not compact as well. Make sure their is continuous soffit venting, baffles and either roof vents or ridge vents to allow that attic to vent properly. You also want to make sure the attic is air sealed. A good way to do this is use a combination of spray foam and blown insulation. Install 1 or 2 inches of rigid foam to the joist cavities and blown in cellulose on top of that to the desired R-value. If you have any ductwork or HVAC equipment in the attic, we recommend creating a sealed attic. This means the thermal barrier becomes underneath the roof deck verses above the attic floor in a traditional attic. A sealed attic usually has the underside of the roof deck insulated with a rigid or soft spray foam. This type of application is much more expensive and why we don’t recommend it unless you have ductwork or HVAC equipment in the attic.
There is no reason to insulate interior walls other than for sound proofing. The best and most cost effective product for this is a mineral wool batt. This can be installed in the wall and ceiling cavities to help reduce sound from room to room.
There are a ton of insulation products out there and it can be very confusing and misleading. Our recommendation is whenever you are building a home or doing a renovation that calls for insulation to be installed, make sure you consult with more than one professional. Get at least 3 quotes and ask a lot of questions. Do research on your own as well. And don’t forget to call in an building science professional like us to help you make the right decision and navigate the current energy code.