Sealed Attics

[AbbyNormal]

I am having good results with a sealed attic in the tropics.

Roof is externally insulated about R7, and utilizes white metal above insulation to reflect the heat away. Gable walls internally insulated.

Attic is unconditioned, however it is separated from the conditioned space by a mere layer of dry wall. So there is some sensible heat transfer still as there are a few degrees of temperature differential, and mositure is passing through the ceiling as well to the dry air below.

Attic is behaving like a plenum space in a commercial building with a roof deck and no ventilation.

If I keep my conditioned space at 75F, RH is down to a pretty solid 40%, attic above averages 81F @51%RH, makes ASHRAE's comfort zone.

I shut system off for several hours via a high day time temperature set back. Ambient air held steady with a dewpoint of about 78.8 over this time frame and after four hours time, the rise in indoor RH was minimal, suggesting low, low natural infiltration rate.

Minimal insulation, keeping the heat out in the first place, sealed attic seems to be blowing the doors off of a hot sauna above a thick layer of fibreglass. Bring on the pot lights now.



Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[NCDesign]

Good to see. I have always felt that keeping the load out of the space was the best thing you could ever do for a building. It drives me crazy whenever I see a metal building going up for offices and they don't insulate the roof and then put insulation on the top of the lay-in ceiling.

I have always understood that the reason attics in houses where constructed with no insulation at the roof and then insulation at the ceiling was because of the shingles. If you put the insulation at the roof it would cause the shingles to "burn up". Any truth to this?

As a side note the worst design mistake I have ever seen was when an architect and an engineer got together and thought having open louvers into a plenum space was a good idea. They insulated at the roof deck and the walls without any insulation over the lay-in ceiling. Then they used the plenum for the return and also located the units there. Small problem, architect thought he needed to treat this school like a house and open it up like an attic. The engineer went right along and thought that the openings would just magically balance the plenum space with regards to outside air intake. They even put the units in the plenum space with some of the returns (which where wide open to the plenum) within 5 feet of multiple open louvers while at the same time put in separate outside air intakes utilizing architectural elements on the peak of the roof. It was a bad, bad mistake. They had to spend a lot of money to fix that one. Covering up louver openings with insulated panels is pretty expensive when you have to do it through lay-in ceilings on nights and weekends.

 

[AbbyNormal]

I have seen arguements that radiant barriers make the roof sheathing and the shingles hotter. I got around this by insulating on the outside and putting a metal roof above the insulation.

Attic venting is to stop ice dams and winter condensation. It does not snow here.

I really hate popping a t-bar tile and seeing trusses with fiberglass batts

Take the "V" out of HVAC and you are left with a HAC(k) job.