What are the best wall assemblies in Dallas, TX?

With so many different options to build an exterior wall these days it is almost impossible for our clients to figure out themselves what might be best for their specific home. ICF’s (Insulating Concrete Forms), SIP’s (Structural Insulated Panels), Advanced framing techniques and traditional stick framing are the most common wall assemblies.  Anybody reading the building science blogs and websites such as BuildingGreen and GreenbuildingAdvisor might be overwhelmed with the opinions and options out there.

First of, let me start by saying that we build in climate zone 3 and the statements made in this post are my personal opinion based on years of studying building science and studying our own homes we built. Most information out there are strategies for cold climate zones up north, so whenever you read any articles about building envelope performance, make sure you understand which climate zone they are talking about. Why is this important? Delta-T! Delta-T is the temperature difference between indoor and outdoor temperature. While the Delta-T in Texas is between 30-40F, it is more like 70-80F in Maine. One consequence of this fact: Thinner thermal mass and insulation can be used.

So let’s examine the different wall assembly options out there and let me tell you why I think certain ones are better than others for our climate zone – all of that with a cost/performance benefit in mind. After all, if I spend 20% more on a wall assembly, I should get at least “some” performance benefit out that, maybe not 20%, but “some”… right? So let’s take a look:

ICF’s (Insulating Concrete Forms)

Most brands of insulated concrete forms (ICFs) consist of two parallel panels of foam held apart by rigid plastic spacers. Builders stack ICFs like Lego blocks, brace the forms, and fill the forms with concrete delivered by a pumper truck. The ICFs are left in place as a permanent part of the building. ICFs are becoming increasingly common. Among their advantages over conventional wood-frame construction are low air infiltration, high thermal mass, high strength and fire resistance and good sound-deadening qualities. They can be used to form basement walls alone or for an entire wall system, including above-grade walls. According to two articles in Environmental Building News (“Thermal Mass and R-value” and “Thermal Mass”), high mass can enhance energy performance, but only when outdoor temperatures cycle above and below the indoor temperature in a 24-hour period. ICF’s are considerably higher in cost to install vs a traditional wall assembly so the cost/performance benefit should be considered when choosing this assembly.

SIPs (Structural Insulated Panels)

Structural insulated panels (SIPs) consist of an insulating foam core sandwiched between an inner and outer face, typically made of oriented strand board (OSB). SIPs combine structural framing, insulation, and sheathing in a single product, to be used for roofs, walls, or floors. Panels are typically precut and delivered to the site ready for assembly with a crane. Standard thicknesses range from 4 ½ inches to 6 ½ inches, lengths up to 28 feet, and widths up to 9 feet. Some manufacturers also make custom sizes, although these cost more. Interior faces can be made from drywall, sheet metal, or finish lumber. The foam core and exterior facings are typically glued together. SIP construction is more expensive than standard frame construction, even compared to Advanced framing with spray foam insulation and a layer of outsulation.

Standard Stick Framing

Standard stick framing is still today the most common used technique, mostly because of easy accessibility to a labor force that can install this system easily. Traditional stick framing uses 2×4 lumber, installed 16″ O.C (on center) with traditional headers, corners and sheathing material that is most commonly OSB board. It is most definitely the least expensive of the four options listed here, but also the least advanced and efficient solution.

Advanced Framing Techniques with advanced sheathing materials

Our preferred method of constructing our building envelope is to build the structure with 2×6 exterior framing through advanced framing techniques. With this method we are framing the exterior walls 24″ O.C. and therefore, this allows us to install more insulation in our walls than in the standard 16″ O.C installation. In addition we use advanced sheathing products such as DOW’s SIS panels and Huber’s ZIP-R panels which are superior to standard OSB or plywood sheathing. Other details of advanced framing are the use of insulated headers, stack framing and california corners. I am going to spare you the details, but if you’re interested, here’s probably the best source to explain how it all works in detail. This wall assembly then gets insulated with 4.5″ of open spray foam insulation. We have been able to achieve extremely tight houses through this technique and the construction costs are lower than comparabile performing systems such as ICF’s and SIP’s.

So if cost is not an issue, our clients have 3 very good wall assemblies to choose from: Advanced Framing, SIP’s and ICF’s, but if budget considerations come into play, I would certainly argue that an advanced framing assembly gives you the best “bang for your buck”.

To support our own findings I have come across a study conducted comparing several different wall assemblies, “Building America Special Research Project: High-R Walls - Case Study Analysis” Research Report – 0903 March 11, 2009 (rev. 8/7/09) John Straube and Jonathan Smegal

For the geeks of you – here’s the link to the full report: http://www.buildingscience.com/documents/reports/rr-0903-building-america-special-research-project-high-r-walls

In this study the follwoing different wall construction options were tested.
1a 2×6 AF, 24″oc, R19FG + OSB
1aii 2×6, 16″oc, R19FG + OSB
1b 2×4 AF, 24″oc, R13FG + OSB
1bii 2×4, 16″oc, R13FG + OSB
2a 2×6 AF, 24″oc R19FG + 1″ R5 XPS
2b 2×6 AF, 24″oc R19FG + 4″ R20 XPS
3 2×6 AF, 24″oc, 2×3 R19+R8 FG
4 Double stud wall 9.5″ R34 cellulose
5 Truss wall 12″ R43 cellulose
6a SIPs (3.5″ EPS)
6b SIPs (11.25″ EPS)
7a ICF – 8″ foam ICF (4″ EPS)
7b ICF – 15″ foam ICF (5″ EPS)
7c ICF – 14″ cement woodfiber ICF with Rockwool
8a 2×6 AF, 24″ o.c., 5″ 2 pcf R29 SPF, OSB
8b 2×6 AF, 24″ o.c., 5.5″ R21 0.5 pcf SPF, OSB
9 2×6 AF, 24″oc, 2″ SPF and 3.5″ cellulose
10 Double stud with 2″ 2.0 pcf foam, 7.5″ cell.
11 Offset frame wall with ext. spray foam
12 2×6 AF, 24″oc, EIFS – 4″ EPS
*AF – Advanced Framing

They were evaluated in 5 categories; Thermal Control, Durability (wetting/drying), Buildability, Cost and Material Use and then given a Total score.
The study gave the highest marks to 2×6 Advanced Framing assemblies and SIP’s and ICF’s scored somewhere in the middle. So in addition to our own findings on the best wall assemblies, this study clearly supports our assessment and strategy – That is why we build the best wall assemblies for your money in Dallas, TX.

If you would like more information on how we build our homes, please contact us today.

EGC Custom Homes is an innovative builder of energy efficient, green, sustainable structures. New homes and remodeling projects in Dallas, TX.

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