How to determine the cost savings of ins
I am going to be doing a small job at the end the month installing Hardiepanel on the second floor of a house. I will be removing the T-111 and may replace the fg if old and/or moisture has been a problem.
The second floor is cantilevered 20″ and we will install Hardiepanel under the cantilever. If there is no insulation in the cantilevered floor, it will be added.
I am also considering adding 1/2″ rigid foam, seams taped, to the exterior wall (R2.5) and the cantilever. i can’t put anything thicker because the house has no eaves.
Is there a site I can reference to determine the cost savings of adding the foam? The homeowner wants to know if the $400 – $500 investment is worth it.
Dave Otto — Otto Construction — Pittsburgh, PA
Edited 10/1/2007 10:38 pm ET by DOtto
Replies
To be perfectly honest, adding 1/2" of foam to the exterior wall won't hurt, but the total energy saving for the whole house will probably amount to squat. Considering that the house has T-111 siding, my assumption (which is probably wrong) is that the windows were installed for economy as well. I'd consider upgrading those first.
Dave Otto,
Henry Redford is mistaken. Replacing existing windows with new windows will almost never yield enough energy savings to justify the cost of window replacement. However, installing 1/2 inch of exterior foam may be justifiable, although the calculation is complicated. In addition to providing additional R-value to the wall, the 1/2-inch foam will probably improve the wall's airtightness, which is good. There are too many variables to easily calculate the energy savings from adding the foam. But if it was my house, I'd add the foam.
Me too, except that I'd use one inch instead of half.And I am not sure that I'd tear the T1-11 off unless there is some compelling reason to based on existing conditions.If this was built as I suspect, that T1-11 may also be the sheathing, part of the structural strength of the wall which would then be compromised unless he goes carefully only replacing a couple sheets at a time.But all that brings up the Q of how he will detail around the windows, so they may need to come out and be reset anyways.....There is just enough info to tease here...
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As has been mentioned, there are a ton of details and variables, but just for purposes of consideration as they kick this idea around...
With a bunch of SWAG and generic rules of thumb....
if you add one inch of foam, that might feasably increase the R-value of the wall by 50% .
If about one third of their heat loss is through the walls, and they are spending $100/month on heating, they are losing $33/month through the walls.
The previous assumption means that the wall heat loss would then be reduced to $22/month, for a savings of eleven bucks in those thirty days.
IF
all those assumptions are close to correct, then it would take four yeas to pay back 500.
In the past, the general rule of thumb has been that it takes about three years to earn payback on insulation added.
With energy costs going up as fast as they are, I'm thinking that is at least true.
In addition, they gain physical comfort in the home and some minor potential that in the long run, working the heat plant less hard could increase its lifespan...
And you could appeal to their conscience - it is just the right thing to do.
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
I have attached a picture of the wall that includes the window. (I resized so I hope it is ok, sorry I don't have the best camera). The window is a Pella and was installed about three years ago. There is a matching window on the other end of the wall.
Any time I do a job around a window or door, I always consider the fact that the window/door will need an "upgrade" in flashing and/or air sealing. I have to change the aluminum trim to a different color anyway, so I will inspect.
As for 1" foam: The picture shows the lack of overhang detail, so that limits me to 1/2". With that said, there will be a new roof and gutters installed after I am done, but I don't believe that the homeowner is interested in rebuilding the overhang.
I will be replacing part of the T-111 at a time. I agree that it is probably serving a structual purpose. I am removing it to keep the overall wall thickness down to allow for the foam.
The Hardiepanel will be the new structural sheathing. Nailed according to J Hardies instructions.
I appreciate the response and agree with both you and Martin that foam is worth adding. The homeowner complains about the rooms being cold in the winter and hot in the summer. Hopefully some added insulation, better sealing at the end of the walls and the cantilever will help.
Dave Otto -- Otto Construction -- PA