Thursday, March 24, 2011

More on Building Costs

Here are some construction cost numbers that can be found on the energetech web site. They also provide detail as to how these numbers were generated. I do think the cost of the 2x6 walls could be lower and the R-value higher if they used 24” centers.

Wall Construction                                     R-Value                 Cost/S.F.                 Cost/R-value/SF

Standard 2x6 @ 16" O.C.                          13.70                      3.72                         0.27
2x6 @ 16" O.C., 2" XPS                             25.00                      6.56                         0.26
2x8 staggered stud, 1.5" XPS                    30.00                      6.45                         0.22
Double 2x4 wall, 12" total thickness          36.50                      6.96                         0.19

By searching the web, I came across some SIPs numbers that appear to be an average, but no sure how accurate they really are.

6.5” SIP w/5.5” EPS                                 21.00                     6.50                          0.31

This is with $4.25 per sq ft for material and $2.25 per sq ft for installation of SIP panels. I am assuming the $4.25 price is for SIPs is ready to install including all window and door cutouts. Also, the $2.25 per sq ft cost for installation seems a little high, but I did find similar numbers on several web sites.

It does seem that SIPs appear to be the higher cost in relation to R-value per sq ft.

One item that is not taken into account with these numbers is air infiltration. With proper installation, the SIPs walls should have a lower rate of air infiltration than the stick framed options. But the higher cost stick framed options should have very low air infiltration rates compared to standard construction.

So I am not sure there is a good answer in the information here. While most of the stick framed walls have higher R-values, they will probably suffer slightly higher air infiltration. And though the SIPs wall has a lower R-value, it would typically be considered a structurally stronger wall than the other options. If I find more or better information on this subject, I will post it.

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