Looking for advice. I have a passive solar cottage in south louisiana.1150 sq feet with 108 sq ft southern glazing Serious Windows 900 series. It is metal framed with ferocement skin as exterior substrate.

Our wall system is R-39(six inch steel stud bumped out with 2x2 horizontal furring--mooney wall--and we used two, 1/4" Thermablok aerogel squares at each point of attachment) 2 inches closed cell sprayfoam and 6 inches sprayed fiberglass.

We have a tightly sealed envelope and a Fantech  SE704 ERV.

The roof is a white standing seam metal roof double fold with 5 inches closed cell sprayfoam directly on underside of roof and flashed over rafters.

We have had a colder than normal winter and  morning interior temps drop to 60 when it is 25-30 outside. We do not have thermal shades installed yet nor a small direct vent propane faux wood stove as we had orginally planned.

I would like to install a radiant barrier before summer heat but i also think I need to supplement insulation for a more comfortable winter next year. Can put in ceiling insulation by laying in fiberglass batts or blown in for ceiling insulation in combination with the existing spayfoam on the underside of the roof?

Thanks

I take it then that you have an attic.  If so, I think the choices for insulation should be between spraying in more foam under the rafters or blowing dry cellulose on the attic floor.  I think these two choices are much more effective than fiberglass. 

I think radiant barriers work reasonably well until dust settles on the foil.  I do not know if radiant barriers will ever pay for themselves.

Have you done a blower door test?  Are you sure you do not have infiltration problems?  I will gladly defer to Dana1.

Thanks Alton.
I tend to agree cellulose for the ceiling is the better option. No, I have not had a blower door test but I am fairly confident I have the doors and windows sealed very good and as I mentioned we have 2" closed cell on walls and gable walls and 5" closed cell on the underside of roof so we are sprayed in slab to ridge.

I am noticing one possible mistake I made was using steel doors(for security) but the conductive transfer may be more than we modeled for(I used Energy10 for design simulations). That decision seems to be contradictory considering the lenghts we went to mitigating thermal bridging in the wall assembly.

Dear Bleu,

Fancy seeing you here! By the way, your innovative combination of Mooney wall & aerogel thermal breaks has served two houses (VA & FL) quite well over this winter.

Some thoughts:

• 60F inside when it's below freezing outside is nothing to be ashamed of, especially if your structure is a standard standalone (not earth bermed/sheltered)
• Ceiling cellulose will definitely help, and is relatively low-cost
• If I recall correctly, your floor is polished concrete? Try carpeting or a radiant floor. The radiant floor doesn't even need to be active; the floor's radiant barrier insulation should affect your perception of coldness
• An all metal door will definitely leak energy; it has a lot of surface area, few thermal breaks. One solution is a fiberglass or wood door, or interior insulation for the door (see below)
• Your southern large windows, while great for accepting energy during the day, have a large surface area and will leak energy during the cold night

When I designed my earth-bermed Solar Arcade series of houses during the 70's/80's (the articles should still be up on Mother Earth News), I always specified window quilts for the large solar openings. While low-tech, they might be the least expensive, lowest-hanging fruit for your cold window & door issue:
http://www.windowquilt.com/products/full_broch.htm

Good luck!
Angus Architect