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Costs and benefits of framing and insulating under new codes

With the adoption of new energy codes, new homes have to be much more airtight and much more insulated. The logical questions builders are asking are:

  • Will this change how to frame a house?

  • How will this affect the cost to build a new house?

Let’s examine that.


Here, we’ll look at different options for meeting code compliance as well as how each option will affect cost, time and home performance. We’ll look at:

  • R-20 cavity insulation

  • R-13+5 insulation

  • Double framing

  • SIPs

  • Alternative framing & insulating options

  • And other things you can do to reduce costs & improve performance

2x6 Framing


The new energy codes (whether its 2012, 2015 or 2018) require either R-20 cavity insulation or R-13 with a R-5 continuous insulation. In order to get to an R-20 cavity insulation, you’re going to have to switch to 2x6 framing lumber.


The great thing about making this switch is that there isn’t much of a learning curve in how to frame it. The biggest change is that you can switch from building 16 inches on center (IOC) to 24 IOC.


This is huge.


We’re talking about having to use about 30% less wood in order to frame the house. Its especially key to keeping the costs down, because you are going to have to pay more for both the 2x6s and the R-20 insulation.


While the cost increase may not be exorbitant, you will probably see cost of materials for framing increase a few hundred dollars.


A few things to cover: first, it is not a given that you’ll be able to switch over to 24 IOC. That depends on the design. In some situations you may have to stick with 16 IOC, at least for the first floor.


Second, although you’re going to see a materials cost increase, this will likely be one of the cheapest options for hitting the new code required insulation values. That’s partly due to being able to increase the spacing between studs and partly due to the fact that there really isn’t going to be too much in terms of extra labor costs. Some of the other options will have higher labor costs.


Pros

  • Very little change to current building practices

  • Can increase spacing to 24 IOC (30% fewer studs)

  • One of the most affordable options

Cons

  • Increased framing lumber cost

  • Increased planning for loads (to determine 16 or 24 IOC)

2x4 Framing


You may decide that you want to stick with 2x4 stick framing. If you’re going to do that, you will need to have at least an R-5 value of continuous insulation.


One great reason to do this is that you went ahead and calculated the total R-value of the wall system. While 13+5 doesn’t add up to more than 20, once you do the math for total R-value (which includes the wood), R-13+5 may be a better insulated wall. That will depend on whether you went 24 IOC or 16 IOC, but it certainly is possible that the R-13+5 route will reduce thermal breaks and increase whole wall R-value.


Additionally, it may do a better job of controlling moisture and vapor inside the wall cavity.

There are many different ways to build this way, with different materials you can use as well as different ways to incorporate them. Each option has its own unique pros and cons.


The Zip System


The Zip System is a unique tool that combines structural sheathing with a water-resistive barrier and continuous foam insulation. It serves as both an air barrier and water barrier. There biggest claim is that it saves a lot of time because you only have to hang a single material, and then tape the seams.


The Zip System R-Sheathing comes with a few different R-value options.


Install it just as you would OSB or plywood around the frame. The only major change is that there is a special Zip System tape that needs to be applied to each and every seam. This step is crucial. It serves the same purpose as taping the seams of your WRB, but this is where some builders have complained about the efficacy of Zip System.


If the tape is not installed correctly, water will absolutely be able to infiltrate the sheathing.


The good news is that the Zip System gives you a surface that you can flash to and nail siding to. It is structural, so once the Zip System is up, you have theoretically done three steps at once.


The Extended Plate and Beam System


The extended plate and beam system is an innovative way of increasing a walls R-value, eliminating thermal breaks & still allowing 2x4 framing.


Basically, the walls are framed with 2x4s, but the top and bottom plates are made with 2x6s. Then you’ll use 2 inch rigid foam boards on the exterior of the frame. Install the OSB or plywood sheathing over the rigid foam boards, and then cover with a WRB as you’ve been doing for years.


There is not a large learning curve here. The only major changes are using 2x6s for the plates & rim joist and then applying the foam board insulation before the OSB or plywood sheathing goes up. Once the insulation is up, it will be the same process as before.


One other consideration is to think about how you are going to do windows. Now that the walls are going to be 6”, you’ll need to put a little extra thought into how you set up, flash and install your windows to properly control moisture.


Rigid Foam as the exterior layer


If your only goal is to make as few changes as possible to what you do, it is possible to install the rigid foam boards over your structural sheathing. This is going to add a layer of complexity, though, and if you don’t think through all the steps and effects carefully, you are taking a big risk on liability.


It’s not that this is an inferior way or a bad way of building. But you now need to consider furring strips to create a drainage plane, whether to use a WRB or use the foam board as the WRB, if you use a WRB where does it go, how are you going to frame and flash the windows and how are they going to drain and a whole lot of other questions.


If you have good answers for all these questions, then by all means go ahead and build this way. It does a great job of preventing thermal bridging, increasing air tightness and improving R-value...but so does using the Zip System or the Extended Plate and Beam System.


Double Framing


A relatively straightforward and common sense way to get to higher levels of insulation is to build a double framed wall. Basically, you frame a house the same as you ever would using 2x4s (the only exception is you can use two-stud corners since you’re only going to hang sheathing on this frame, no drywall).


Once you’ve framed the house, you then build a second frame inside the home with enough of a gap for however much insulation you’re going to put in. You can use whatever board you want for this frame (2x4, 2x3, whatever) because this will not be load bearing. You could even move the studs on the interior frame to 24 IOC, again, this is not a load bearing wall.


A couple considerations:

  • This will take more time. After all, you’re building a second (albeit smaller) frame.

  • This will take more wood. Same reason. But you get to stick with 2x4s, and you can get highly insulated walls.

  • Moisture management and air sealing becomes especially critical here. Because of the super insulated walls, condensation could be a real concern. Air seal, use a vapor barrier where required...in general, just be diligent.

Pros

  • Performance potential

  • Limited learning curve

Cons

  • Increased material costs

  • Increased labor costs

  • Increased build time

  • More difficult with elaborate designs (works best with simple homes)

SIPs


SIPs (Structural Insulated Panels) are two rigid sheathing materials sandwiching a foam insulating material. Most commonly, SIPs are OSB over EPS (expanded polystyrene) or XPS (extruded polystyrene).


A house made from SIPs is a completely different kind of build. You won’t be framing and sheathing traditionally because the SIPs join together sort of like building blocks, so if you’re going to transition to SIPs you should expect a longer build time on the first couple homes until your crews get the hang of it. (You can install SIPs over a traditionally stick framed house if you want, but it is still a different build.)


Once your team is good to go with SIPs, it should make the build much quicker. SIPs are built to specification at a factory and delivered ready to go. That means you aren’t doing all the framing on site. You’re framing, sheathing and insulating in one step; you just have to connect all the SIPs (which are labeled exactly for which connects to which).


SIPs (if installed correctly) may offer some performance benefits. According to WBDG, a room made from SIPs compared to an identical room of 2x6s with drywall, the SIP room had 90% less air leaks than the 2x6 framed room. That is a huge performance jump.


The downside of SIPs is that if they are installed incorrectly, they can quickly rot and deteriorate. Moisture management, air sealing, and diligent work are absolutely critical. Also, because the SIP is structural, if there is damage to one of the panels, it can be costly to repair or replace.


According to SIPs.org (obviously a proponent of building with SIPs) you can save money on jobsite waste disposal costs. They also report that an R.S. Means study found a 55% labor savings when using SIPs instead of conventional wood framing.


Pros

  • Performance potential

  • Reduce build time

  • Reduce jobsite waste

  • Customized packages for your home (also pre-done designs)

Cons

  • May require equipment to lift

  • New technique/product to learn

ThermoBuilt Energy Envelope


An option you may not have heard of is ThermoBuilt. ThermoBuilt is a Zero Energy Ready Home Innovation Partner.


They have an innovative product that is reminiscent of a SIP, but works a bit differently. With their patented design, ThermoBuilt panels are installed over traditional stick framing (you can use 2x4s or 2x6s). If installed correctly, you’ll still get the great air tightness of a SIP, but these panels are different.


They don’t come in huge or heavy sections, which means that the pieces don’t need to me moved by a crane or forklift on the job site. It also means that damage to a section won’t be quite as invasive to repair.


ThermoBuilt wall panels are insulated to R-32 standard, seriously exceeding the current code requirements in Tennessee. The roof system is a standard R-50.


Again, the ThermoBuilt Energy Envelope will be the 2x6 wall framing with headers, insulation, sheathing and all structural connectors for your standard framed house. Once your team has gotten a couple reps at it, they estimate that you’ll be able to frame and put up a ThermoBuilt shell in just 3-4 days (obviously depending on the size of the project and the team).


Pricing here also comes in at a very competitive $19 per square foot. Remember, that’s the sheathing, insulation, framing lumber, and the adhesives & sealants you need.


Pros

  • Cost & value

  • Performance potential

  • Reduce build time

  • Reduce jobsite waste

  • Customized packages for your home (also pre-done designs)

  • Zero Energy Ready Home partner

Cons

  • New technique/product to learn

Summary


Where you go from here is up to you. The bottom line is that, across Tennessee and the southeast, building codes are changing. With some of the new science, new products & options, it’s time to increase the insulation and give your customers higher performing homes.


As more and more people move to Tennessee from the north and the west, energy efficient features and design is only going to grow in importance. The National Association of Home Builders listed green features as one of the top things buyers are looking for now.


There are all sorts of techniques out there, and this guide is just an overview of some of the more common, easy and affordable ones. This is an opportunity to differentiate yourself in a very competitive market that will only get tighter if the economy slows at all.


Once you start building to the new code, you will already be building to a standard that would earn a good HERS rating, which is a great way to prove the quality of your homes and to be able to justify a higher sales price.




References:

https://www.apawood.org/advanced-framing

https://www.greenbuildingadvisor.com/article/the-case-for-continuous-insulation

Extended Plate and Beam System

Practical High-R Walls

https://www.enercept.com/blog/five-key-tips-for-building-with-sips

https://www.wbdg.org/resources/structural-insulated-panels-sips

https://www.sips.org/about/frequently-asked-questions-faqs-regarding-structural-insulated-panels-sips#b

https://www.thermobuilt.com/interactive-cutaway/

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