Comments and Considerations
Home Design Service
|Over the years I have made some observations about
engineering that may help others, and I wish to pass on to
others. Many of these observations are from firsthand
experiences, or learning the hard way. This is a place
for my general philosophy and comments on design, engineering and
Some of these comments are the ramblings of an engineer and are of interest to only a few home owners/builder.
|1. Find a designer that you are comfortable working
with on all aspects
of the project.
|2. This is a comment on wall thickness and insulation.
I read about an interesting wall design that claimed to be a superior wall insulation design. Everything has trade-offs. Here are a few comments in the briefest of summary. The comparisons are calculated based on a 96 inch standard wall section.
Given all else equal an R11 insulated 2x4 w/16”OC studs wall has an R- value of R-10.3. The studs in the wall lower the R value of the insulation. If you place a 3x4 ft window in the wall the R- value is reduced to R-8.7. The window controls the R- value.
An R19 insulated 2x6 w/16”OC studs wall has an R- value of R-17.8. The studs in the wall lower the R value. Place a 3x4 ft window in the wall and the value is R-14.6.
Based on materials cost a 2x6 wall is about 13% more expensive.
An R?? insulated staggered 2x4 w/staggered 24”OC (or 12’OC) studs wall built on a 2x6 plates should have an R- value of just below R19 because the studs from one side of the wall do not touch the other side. This is about 6% better than the standard 2x6 16”OC insulated wall. If you put a window in the wall the window will drive the R-valve of the wall.
The cost savings in the long run depends upon the ability of the contractor to build the staggered stud wall correctly including putting the insulation in correctly; it is not a standard wall. The insulation will have to be place, cut specially, to get the full R value. This will cost more to build and will offset the materials cost savings. Additionally, to get the same sheer strength from the walls additional sheer structure will be required, some change in wall design will be necessary that will likely increase building cost.
If everything works, the cost savings will be long term energy costs only and be no better than 6%. And the R value of the wall is based on or driven by the window. If it costs an average of $150.00 per month to heat/cool a house you will save at most $108.00 per year.
|3. You have to be careful of window advertised R
high numbers are often just the center of the window, and always are
for new clean windows.
|4. The R value of a single pane window is less than
R-1. The R value of a double pane window is about R-2, which
is still a 100% improvement, but still only R-2. The R value
of supper windows, expensive gas filled, supper E etc windows after 10
years is still about R-2. They start at a little higher.