Services for Building Professionals
Thermal Analysis of Building Elements
Thermal analysis of building constructions helps to minimize the energy a particular construction in
your building leaks heat.
These are losses due to the materials and position of those materials in the construction.
In the example below we see a window detail. The left edge of the window is the inside, right the
outside. What we are looking for here is the construction that allows for the isotherms (the bands of
color) to return to parallel in the wall the fastest (over the shortest distance).
We can see that the standard window on the outside of the envelope takes the longest for the lines to
return to parallel in the wall. The rightmost example has insulation in front of the frame to the
outside. This is the most energy efficient install for the window.
To be useful an analysis should be done on all
sides of the window (left and right if the
materials the window sits in differs, like say with
So you ask, what is the savings for this type of
detailing? Is it worth it?
Here are the numbers on this anaysis:
U-whole Psi-install Relative Energy Cost
+0.57 kBtu/sqft yr*
+0.39 kBtu/sqft yr
-1.42 kBtu/sqft yr
*These numbers are relative based on a particular wall construction,
type of window and the number of windows. The Relative Energy Cost
are based on +/- from a Psi-install of 0.00. A Psi-install of 0.00 in this
instance would not increase nor decrease the Relative Energy Cost.
An analysis of proposed construction details can be optimized so that with little added
cost a sizable savings in energy can be realized.
We are developing a database of construction details which we can use to help aid in
design decisions and can consult on these options with the Therm outputs as a guide.
Each house and project is different. We have design advice for thermal bridge free construction to
cut down on the need for thermal bridge calculations.
Just think of your plans. Every time the geometry of a wall changes (changes in plane) or there is
a penetration (door, window, skylight, etc.) there is the possibilty a thermal bridge exists.
Common places for thermal bridging:
- Foundation to slab/under slab reinforcement
- Foundation to wall
- Wall to roof/ceiling
- Between floor to wall
- All windows, doors, skylights and other thermal envelope penetrations
Eco Houses of Vermont, LLC
Copyright 2013 Eco Houses of Vermont, LLC
Chris West is a Certified Passive House Consultant
Affiliated with the PHIUS and PHI 2013