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New Construction

Our company offers most types of insulation required for new homes and commercial structures. The standard protocol for a new home is to use fiberglass batts in the walls and floor and then use either blown cellulose or the same fiberglass batts in the ceiling. Here are the standards and some variations on this part of the plan.


Blown in InsulationWhile we are not a big believer in the cost effectiveness of floor insulation for our climate zone, many people request it and the Title 24 calculations may require it. Almost 100% of the time fiberglass batts are used for floor insulation. It is installed in two different methods. The first (and in our opinion the best) is to pan the floor joist bays with a nylon netting and then lay in the floor insulation in from the top before the plywood subfloor is installed. This is a superior method because the netting holds much better than using “insulation support rods” as would be used for the other method. Some builders worry about water damage from installing floor insulation too soon, but if you think about it the only place the plywood can leak water is at the long side joint (which is usually a T&G joint) or the short side joint. At the long side the water just can’t make it thru the T&G with enough volume to saturate the insulation. At the butt joints not enough water can get between the pieces and then find it’s way between the bottom of the plywood and the joist. Especially if the plywood is laid with glue on the short side joints. If the builder is really worried just go down and buy the cheapest oil based paint you can find and paint the floors as soon as the plywood goes down. This will help preserve the plywood itself in the event of a large amount of rain. And your chalk lines will show up better.  Another benefit to this type of installation is the netting can be hung lower than the bottom of the joist so a batt thicker than the floor joist could be used, such as an R-30 (10” thick) batt hanging from a 2” x 6” floor joist.

If the fiberglass is installed after the subfloor goes down then a different method is used. The batts are pushed into the joist space from below, from the crawlspace. We use special unfaced batts that are cut wider and are made stiffer than a faced batt. The primary fit then is a friction fit between joists and the secondary support is provided by “Lighting Rods”. These are pieces of springy metal that are a little longer than the distance between the joist, and sharp on each end. They are pushed up between the joists and since they are longer they bow upward. That spring tension then causes the sharp points to dig into the wood and hold them in place. The reason we prefer the first method is because the floor joists are usually 2 x 6 and usually R-19 insulation is used. This means pushing a 5.5” batt into a 5.5” space. So there isn’t really anything for the Rod to bite into. Or, if you push the rod up high enough to cause the rod to find purchase it compresses the insulation which compromises its R-value. Occasionally we hear of people putting plywood across the bottom of the floor joist and filling the space with cellulose. It can be done but the expense makes it not cost effective. Same with spray foam.


Wall Insulation, Foam BoardFor new construction we find fiberglass batts are mainly used. They are of course installed prior to drywall. Typically for exterior walls the plans will call for an R-13 batt in a 2” X 4” wall or an R-19 in a 2” X 6” wall. The newest thing is to frame outside walls at 24” O.C. to lessen the number of studs. Since wood has an R-value of about R-1 per inch, a 2 x 4 is only going to be R-3.5 as opposed to the rest of the wall space at R-13 or R- 19. In some instances a higher R-value is needed and a special high density batt is used. These come in R-15 for a 3.5” wall and R-21 for a 5.5” wall. The Title 24 energy code requires all exterior walls must be insulated to a certain level. Many people also insulate the interior walls as well. Insulating the interior walls means the walls are relatively sound proof, and the home just has a more solid feel when you shut the doors. Many builders just have all walls insulated as a standard procedure and we agree with this approach. 

On occasion a home builder, for whatever reason, may want a different material used in the walls. It’s possible to hang the drywall prior to installing insulation and then drilling 1 ½” holes in every stud bay and blowing cellulose insulation into the empty wall cavity. This amount of pressure is enough to pack the cellulose tightly enough to where the cellulose remains stationary in the wall cavity if the wall covering is removed, but not packed with enough pressure to blow the drywall off the walls. In addition, some builders use a wet spray cellulose or wet spray fiberglass where the insulation is wet and sprayed onto the walls and sticks there. A guy with a screed comes along and smooths everything flat. We are even starting to see spray foam installed this way. By mixing the chemicals at the spray nozzle, when it hits the depression between the studs it expands to fill the space. This can be very touchy as just the correct amount of material must be used and the combination of the mixed chemicals must be exact and a lot depends on weather. We don’t install the foam type spray insulation (although we install rigid foam board products). We just don’t think it’s a wise thing to put into a person home when you must get into a full protective body suit with it’s own outside air source in order to install it. That says to me that those are pretty strong chemicals.


Attic Insulation

In new construction about half the projects are done with a fiberglass batt before the drywall is installed and the other half the time a loose fill product is used. This can be either cellulose or loose fill fiberglass. The price difference isn’t all that much but it does require a separate trip for the loose fill installation crew. The floor is done when the floor joist go down and then the walls are done when the outside wall covering is up. If the attic (roof) is going to be batts it can be installed with the walls. If loose fill, the installer will have to return when the drywall is installed on the ceiling. Some builders prefer batts so if they if they have to repair or go into the attic for any reason the batts tend to be cleaner. The trick however, is to finish everything in the attic before you have the attic insulation installed and then never worry about going up there again.

The ideal way to choreograph this is to do the floors whenever the builder wants them done. Then then come back and do the outside walls when the siding is up. Then have the drywall guys hang the ceiling and just one side of any interior wall that they want insulation in. Then the installers can return and hang the inside walls when there is something to hold the insulation in place and they can also blow loose fill into the attic. Loose fill gets down in all the little spaces that are very hard to fit around with a fiberglass batt. And the batts have a space between them and they have to go around the ceiling joist. The loose fill just covers everything with a blanket. In addition cellulose has a higher R-value per inch which means an R-30 in cellulose is 8.25” thick and with loose fiberglass (or batts) an R-30 is 10” thick. In addition, fiberglass tends to let air flow right through it. That is why it’s used for air filters. We prefer cellulose because it stops air flow. 

Attic R-values have been going up since insulation was first required in the mid 1970’s. It started as R-19 and increased to R-30 and then to R-38. We are now on the verge of the next increase which will be to R-44. These R-value increases keep pace with fossil fuel cost increase since most of our power is generated by burning fossil fuels. 

Some homes may not have an attic. These have a vaulted ceiling where the rafter is also the joist. If the vaulted area has drywall on the bottom of the joist/rafter and roofing on the top, then fiberglass or cellulose can be used in the resulting cavity. If the vaulted ceiling is made up of exposed wood rafters with exposed wood making up the ceiling then it might be that rigid foam board is the only option. If it’s installed on top of the roof it’s usually the roofing contractor that installs it. If the foam ends up going between the beams then it’s a job for the insulation contractor.