Monday, July 17, 2006

Ventilated vs. Sealed Attics

I have heard conflicting reports regarding attic ventilation. Some say that very good attic ventilation is an absolute requirement in hot climates and some say that sealed attics can actually outperform vented attics. Which is it for hot humid climates like Houston?

Below is some research concerning mostly the energy savings of sealed attics...

_________Via The Florida Solar Energy Center (FSEC)__________

"In hot humid climates the combination of cooler ceiling temperatures meeting with hot humid air can conspire to cause condensation, which in turn can be absorbed into the ceiling materials, according to MHRA. The venting of attics, at least for multisection homes is a HUD Code requirement and required to validate shingle warranties.

In many cases sealed attics can have energy performance advantages over ventilated attics. Air conditioning ducts are most often located in the attic of slab-on-grade homes (most Florida homes). If the insulation for the "lid" of your home is located in the roof instead of in the ceiling, then these ducts remain much cooler. This results in air conditioning energy savings.

Duct leakage is also problematic in many homes, often with much of the air leaking into the return side of the air handler system coming from the attic. A sealed attic will reduce the energy waste associated with these duct leaks. Additionally, on beach-side properties, sealed attic systems can have additional advantages related to keeping wind-blown moisture and salt-laden air out of attics.

In addition combining white shingles or a white metal roof with a sealed attic is likely to produce greater cooling energy savings.

Measurements also have shown that sealed attics and attics with radiant barriers have hotter roofs. This occurs because heat can not readily leave the inboard side of the roof sheathing if it is insulated.

In general, cooling energy savings will be greatest when sealed attic and insulated roof deck construction is used in combination with highly reflective white tile or metal roofing materials."

Things to consider:
+Use thicker sheathing
+consdier roof assembly with ventilated airspace above the insulated decking (a double roof)
+instead of more insulation with a ventilated attic, consider a radiant barrier
(+Indoor air quality?? of which, Indoor Air Quality (IAQ) seems to be unmentioned but definitely something to be considered...the EPA warns that IAQ is one of the top five risks to public health.)

So which is it? Comments?

* Florida Solar Energy Center
* Building Science
* Attic Ventilation Strategies[via]
**Energy efficient and Ventilation via fine home building this one seems to answer a lot of questions. Especially dealing with hot humid climates. ;)
* More info on proper attic ventilation

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