The best method for building homes
July 15th, 2009 by Matthew Leonard
Because of our experience in building extremely energy efficient homes, we’re often asked what materials and methods are best for building the exterior shell. The three types of construction most commonly asked about are structural insulated panels (SIPs), insulated concrete forms (ICFs) or stick framed with cavities filled with foam.
We have experience building with all three methods as well as others and depending on your goals and budget, we can guide you in the best direction. I’ll break down each system and how we have found they work best for our customers.
Insulated Concrete Forms (ICFs)
We have been building using ICFs from the first home we built nearly 15 years ago. ICFs are simple in concept but easy to do incorrectly if you don’t understand their idiosyncrasies. Whenever we build with ICFs, Steve personally sets them up and manages every aspect of the pour. Without experience and care, walls can easily be warped both vertically and horizontally. Too loose of mixture and/or too much vibration can blow out the forms and too stiff of mixture and/or too little vibration can result in voids that will comprimise the structure and never be discovered because they are hidden behind the foam. On the positive side, ICFs are extremely strong and if you more concerned about strength only then they are fabulous. They do have good insulating qualities but there is no proof the claims of ICF companies on the R-value they add for concrete, which is a conductor of heat not an insulator. They also do not provide for thermal mass to retain heat in the house because there is a layer of insulation between the interior volumes and the concrete mass. Also if you want to save money on the initial building process and put more money into the main part of the house, ICFs force you to have to fire-stop the foam in the basement with drywall and if you’re going to drywall it, you should run the electrical so you’ll have to allocate funds for finishing the basement instead of the main living areas. They are more difficult to hang drywall and siding on and they are not flexible to field changes (i.e., moving a window over 1 foot or repositioning other openings which has happened on walk-throughs) ICFs are more expensive then the other systems coming in at approximately $10 to $11 per sq ft of wall surface area. We have had many home owners with ICF designed plans come to us who end up building with SIPs instead. The concrete association is very large and strong and has done a better job at promoting ICFs.
Stick framing with spray foam
We use this method of building but mostly with remodeling projects and almost always when adding a second floor. The reason for this is that in most cases, the existing structure is not square or level and SIPs are an engineered product which means they are extremely straight and square; ICFs are also too heavy for second story additions. Adapting an engineered product to a lesser built existing stick framed structure involves a lot of extra work. So in these cases we can be more flexible with stick framing because it’s not as precise and allows us to make things “work”.
There are two main choices for foams used to fill the wall cavities. Icynene, a waterbased open cell foam, is slightly more expensive but similar in R-value to EPS foam, which is used in SIPs. Urethane closed cell foams are about 25% better performing than EPS or Icynene after off-gassing but cost twice as much.
There are legislative measures underway to remove urethane foam’s VOC (Volatile Organic Compounds) off-gassing which will make them healthier but will drop their R-Values to the same as EPS and Icynene. We don’t recommend stick framing with foam filled cavities for new construction because this type of construction costs about the same or more than SIPs and the effective R-value of the wall is significantly less than SIPs because the wood studs are a poor insulator and de-rate the overall wall’s R-value. There’s also more job-site waste, more dimensional lumber and extra dumpster costs with stick framing. There’s no easy way to add outlets or other wiring in the future because the walls are filled with no chases. The cost is around $6 per sq ft. of wall surface area.
Structural Insulated Panels
Builders are an interesting bunch. They typically get stuck in a rut on how to do things and sometimes it’s true that methods have been refined over the years which keep costs down by doing things a certain way. That’s true for us too. But that can also lead to a blindness to better ways of doing things either out of fear, pride or stubbornness. They’ll justify what they do over other methods because they just don’t want to change. This is best described with roof trusses. Years ago all builders rafter framed the roofs and truss companies developed engineered truss systems using 2×4s nailed together with plates. Builders resisted trusses for years claiming they were dangerous and not as strong and they’d have to change their processes to adapt to the them. Now you can hardly find a home that doesn’t use trusses and only in specific areas that are very complex do you find rafter framing. The only other method that’s commonly used for roofing systems other than trusses are SIPs. Where there are vaulted areas we typically use SIPs because they provide a more dramatic vault than scissors trusses. Sometimes because of span lengths we’ll use trusses or rafter framing with spray foam. Where there are trays in the ceiling or flat ceilings, we use trusses then spray a thin layer of Icynene over the drywall to seal the home from air infiltration then blow in lower cost cellulose over the top. This is a great hybrid system we developed to keep air sealing at a high level but keep the costs down. We also use Icynene at the box sills and the roof heels. See drawing at the following link http://peabuilders.com/features.php SIPs are better at insulating than either stick with foam or ICFs. SIPs are easily field adapted to changes. SIPs are 2 to 3 times stronger than stick framing and have proven to be safe in tornados, hurricanes and earth quakes. They are not as strong as ICFs but they also don’t cost near as much. The cost for SIPs is $5 to $6 per sq ft of wall surface area and the return on investment is about 3 to 4 years.
We know of a competitor that’s building an “energy producing home”. They’re using stick framing with foam. It’s an 1,800 sq ft house and requires a 6 ton geothermal HVAC system and 80 solar panels to be an energy producing home. We built a 1,600 sq ft home with 1,000 sq ft of finished basement. That was only a 4” thick SIP home and has an overkill 4 ton geothermal HVAC system and 24 solar panels. The home owner called us to tell us they made $50 versus paying WE Energies last month. Another home we’re building in New Berlin is 3,400 sq ft has a 2 ton geothermal HVAC system and will only require about 8 solar panels to be energy producing. That house has a lot of extras and is only $161 per sq ft to build.
We have a lot of experience in building with all methods of construction (Steve even built many stick framed homes while working as a project manager for another company before building homes himself) and we’ll use the system that maximizes the energy efficiency of your home based on your budget and meeting your goals. People that have large enough budgets and want strength over energy efficiency will prefer ICFs. People that want to maximize energy efficiency, maximize amenities, keep costs down and still have a very safe strong home will choose SIPs.
This entry was posted on Wednesday, July 15th, 2009 at 5:44 pm and is filed under Green, Save Money, Structure, Uncategorized.