Is there equipment available or testing methodology for calculating the R values of walls and ceilings in the field.

Tags: Calc, Field, R, Values

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Yes and no!

There is one instrument that sticks a couple of thermocouples against a surface and then calculates an r-value and then there are the surface temperature graph which yield another r-value number.  I use a graph when necessary, but that is only part of the observation.  An IR scan then gives me more insight as to what is happening behind the surface.  The type of insulation helps me judge how it is performing.  Is the solar exposure affecting those IR readings?  Is the orientation, horizontal vs vertical, makeing a difference.  Encapsulated on 6 sides or exposed to air flow.  Plywood sheathing or old boards on the outside?  And then the big question.  What number would the next technician use and is this truing for fuel consumption or just a model?

If you get carried away with accuracy you stand alone with results that no one else will arrive at.  It makes you feel good, but everyone else will say you are wrong.  I arrived at that conclusion when a potential HERS provider warned me (I guess they didn't want to support someone way up in Maine) if I varied more than 10% off of their QA results I would be placed on probation and possibly suspended.  The choice boils down to accuracy vs consistency.  Following the prescribed path to identify any insulation, measure its thickness and look up that r-value in a table keeps one out of trouble.  But I still refer to my surface temperature charts and yes, I'm often in trouble (different opinions at least).

I can find the instrument mentioned above if needed and I designed my own, but decided it would be too controversial to market.

Now, what did you have in mind?


I agree with you on the visual inspection and IR analysis. But every once in a while a customer asks what is the R rating of my Ceiling/Walls now. I perform rudimentary calculations and tell them what I can. But I really don't know what's in the walls or  even a vaulted ceiling. I found this site just yesterday and it will come in handy. 

Best one I have found to date. I would imagine the surface temperature procedure requires the inside of the house to be unconditioned, or does it take into consideration the base temperature?? 

Thanks for the response. Tony

Here's another, easier, calculator:

If you want to look fancy, and the tool has other uses, check this one out:  Testo 435 HVAC Performance Test Kits

The r/u value measurement requires this probe:

Here's a link for the meter:

Both of these approaches will require mother nature to cooperate with a delta T so the house needs to be conditioned.

Careful with the clay they use as it might stain the surface.  A painters tape might work instead.

If you have an IR camera you will find it makes a great impression and provides the temperature numbers required.  I agree, areas like a vaulted ceiling can be impossible to inspect and often subject to air flow affecting the performance value.  But, solar issues and radiant heat loss make temperature measurements questionable.  But still, it can help.




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