Will radiant ceilings work in a house with a vented attic?

mtgentry

Hi All,

I'm installing radiant cooling panels in the ceilings of my 1908 craftsman here in Los Angeles. My ceiling panels are based off John Siegenthaler's design (OSB + Pex + foil polyiso).

I'll control the humidity with a whole house dehumidifier and temp/humidity sensors in every room.

One thing I'm to figure out is how the (vented) attic will affect the system. The OSB in the panels is also the floor of the attic:





Seems like the panels are mostly in the thermal envelope of the house below but not totally. I will air seal the gaps and cracks on the attic floor and cover it with insulation but I'm not sure if that's enough.

Should I close all the vents in my attic and run my dehumidifer up there as well?

Alternatively, will insulation be enough to keep heat away from the OSB?

mattmia2

Insulate it well. Is there knob and tube wiring up there that is active? You will have to replace that before you can insulate those parts. You don't want to seal up the attic itself, that will cook the shingles from the inside out.

mtgentry

Nope, all the knob and tube wiring was removed years ago. Thanks for the feedback!

hot_rod

You will want to monitor dew point carefully. In the conditioned space and at those transfer plates.

Those plates will sweat when you hit dew point. No exposed metal surfaces, for sure.

JUGHNE

Knob and tube is often mentioned and warned of before insulating attics, however another danger is old school recessed lighting.
If covered with insulation and incandescent bulbs remain in use, that poses the same fire danger as the K & T.

I have taken down 70's standard surface mount light fixtures that were over lamped (say 3 X 100 watts) and the Romex of that day was cooked. The individual conductors had their insulation cooked off. This heat is partially conducted by the copper wires up into the J-box and then the close proximity of the fixture bulbs themselves....and well insulated on top of it all.

So a recessed can buried in insulation is worse.

Jamie Hall

sverreet said:

You're definitely on the right track with air sealing and insulating the attic floor. I would also recommend closing off the vents in the attic.

Probably not. As others have mentioned, condensation is your enemy, and an unvented but inevitably cold attic is going to be a soggy mess. What you do need to do, though, is air seal as thoroughly as possible any openings between the occupied house and the attic. Attic stairs, for example, are real villains,