A Solstice update on the insulation scheme

Those few, those happy few, who have followed this blog from inception might be curious what all that crazy stuff I did when rebuilding the addition is doing.

The summer solstice was a nice clear sunny day. This was the highest solar insolation of the year, so it was a good time to see what all that work was worth.

While the day wasn't particularly hot, the sun was certainly clear and sharp.



Folks might recall the exterior walls on the addition are double studded. A wall inside a wall, with no mechanical connection between the interior wall, and the exterior wall. This was intended to cut down on the thermal bridging effect of the wall studs carrying the energy from the outside through the wall studs to the inside, and vice versa.



After the exterior stud cavities were caulked and sealed. Unfaced R19 fiberglass batts were added to the exterior wall cavities. Then the interior stud cavities were closed with 2" XPS R10 foam boards. Then the wall was closed with drywall, blah blah blah.
So, let's see how that worked



This within a few minutes of true solar noon, so the sun is hitting the exterior siding at a pretty steep angle, so the insolation is low. But the siding temp is pretty telling.



And right on the other side of the wall? Not too shabby.



For comparison, this is an interior partition wall, not exposed on either side to the outside. Almost exactly the same temp. (well, as far as my thermal probe will say). So, I'd say the thermal barrier is working, at least from a conduction perspective. The inside temp, absent any energy forcing, will equalize with the exterior. But what it's not doing, is adding much temp.
Okay, now for the big stuff.



Folks might recall this major headache. The roof is a standard 3/12 pitch asphalt shingle over decking truss roof with ridge vents. I added 1/2 foil faced polyiso to the ceiling cavities leaving a 1" gap between the underside of the roof and the reflective face of the polyiso. The idea was to trap the radiant heat from the underside of the deck, and create a convection current that would carry that energy from the under eve soffits to the ridge vent, without heating up the low attic space. A radiant barrier.




From there, along the low wall edge, added 2 layers of 2" XPS for R20 right over the wall, then adding unfaced batts as space permitted. Going from R20 to R40 in very short order.



Then to R38 unfaced. Then I closed the ceiling with paper faced R12. I'm hoping for R40/R50 on average across the ceiling/roof. So, let's see what we got.



With 20 minutes of high noon, this is the temp of the roof.




There's a small section of roof that is still shaded by the nice shagbark hickory. Now I know that cleaning gutters is kinda a pain the neck, but for those folks who think that having trees over the house is a bad thing.
Anyway, moving along, ,



This is the temp under the lip of the ridge vent. This is as close to measuring the temp of the air coming out of the attic as I could measure.




This is the underside of the ridge vent. The color of the ridge vent itself is adding some energy. In the winter, this extra heat should help force the convection.



This is the temp of a roof truss above the radiant barrier. This should be pretty close to the ambient attic air minus the radiant aspect.



And this is the temp of that same roof truss below the radiant barrier. All in all, I'd say that thin little piece of polyiso was well worth the time, money and effort.



And this is the temp of the ceiling below the area measured above. This incorporates the effect of the insulation batts. All in all, I'd call it a success.

Again, I'l stress that insulation merely insulates, the inside and outside temps will equalize given enough time. But I'm not adding much heat from the structure itself, and I'm slowing down the heat of the day by a pretty fair amount.

It works.