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Home efficiency (Attic venting)

Old 01-14-2010, 11:17 AM
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Default Home efficiency (Attic venting)

Has anyone changed from a vented attic to a unvented attic ? I have started seeing this on DIY and building shows that propose this will save on overall HAVC cost ? Just seeing if anyone has went through this..... Plus i'm bored so looking up new projects
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Old 01-14-2010, 11:43 AM
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Unvented meaning a fan" that goes on only when temperatures are needed? - or insulating the attic itself? Guess I don't know what you mean. You don't wanna be plugging the vents unless you are making other provisions for moisture removal.

Either way you have to be careful of temperature differences and associated moisture building up.
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Old 01-14-2010, 11:47 AM
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Whole-house exhaust fans make a HUGE difference at least for cooling a house in the summer.
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Old 01-14-2010, 11:54 AM
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Currently I have a vented attic, 1 exhaust fan and 2 roof vents. I have seen where where they remove the fan, close the vents. Sprayfoam the attic cieling. Obviously this has not been around long enough, just poking around.



http://www.builderonline.com/codes-a...tic-vents.aspx



http://oikos.com/esb/30/atticvent.html
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Old 01-14-2010, 11:55 AM
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Advantages of Conditioned Attics:

Energy Savings

Ductwork and HVAC equipment in conditioned space
System leakage to conditioned space
Reduced conductive gains or losses
Reduction of infiltration through ceiling
Elimination of blown attic insulation which settles, compacts, scatters, etc...
Improved Health Conditions

When ducts are located in conditioned space, less dirt and contaminants
Other Benefits

Usable Storage Space
Better conditions for servicing mechanical equipment
Increased life expectancy of mechanical equipment due to less harsh environment
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Old 01-14-2010, 12:34 PM
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You better be real careful of insulating the underside of the roof. This is called a hot roof and if your shingles were not designed for it they will curl right off the building.

This was a problem when I was designing and building my house in Maine 4 years ago.
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Old 01-15-2010, 11:07 AM
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One case study: http://www.icynene.com/assets/docume...ol1602-HBA.pdf

My home is all foam insulated and will be 10 years old this May.

Not many homes here have shingle roofs but it can be either a non issue or you can install the shingles with an air gap.

The pluses for this type of insulation for outway any take aways.

Insulate tight, ventilate right.

Two test houses were constructed and monitored in Las Vegas with unvented-cathedralized
attics. Results showed that the unvented attic houses yielded both cooling and heating energy
consumption savings over the conventional 1:150 vented attic house. The 3oF maximum tile top
temperature difference agreed well with the simulated prediction. The maximum measured plywood
roof sheathing temperature increase of 21oF for the unvented attics was less than the temperature
variation that would be expected by changing from tile to asphalt shingles of any available color. The
maximum measured roof sheathing temperature of 154oF for the unvented attics was well within
acceptable temperature limits. These results set into motion the construction of entire subdivisions with
unvented-cathedralized attics. Long-term monitoring was also conducted on ten unvented attic houses
compared to conventional vented attic houses; that analysis is on-going.

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Old 01-16-2010, 06:39 AM
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If you can turn over the attic air 6-7 times an hour you can keep it at ambiant temp and thus reducing the run time of an AC or even Heater. Also proper insulation will aid in this. I'm going with these fans this spring, since they are solar powered it is a win win all around.

My plan is to install just the fans in my turbins so I do not need to add extra items on my roof.

http://www.atticbreeze.net/

Click to Zoom Model AB-256 Features high-efficiency 25 watt remote mounted solar panel with 15 feet of shielded wiring and low profile mounting brackets. Unit comes standard with corrosion resistant zincalume alloy vent housing, flush mounted louvers, ultra-quiet 14 inch fan, and rodent guard. Fan is rated for 1550 CFM maximum airflow and can effectively ventilate an open area space of up to 32,250 cubic feet (equivalent to an open area of 1800 sqft with 18' high ceiling). Product is ideal for workshop, garage, or warehouse ventilation applications. Unit can also be used for residential attic ventilation applications where a wall mounted unit is desired. AB-256 Price: $629.99
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Old 01-16-2010, 07:01 AM
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Powered attic ventilators, already suspected of using more energy than they save, can also create excess moisture, structural problems, discomfort, and combustion safety problems for home occupants, according to a recent study. John Tooley of Natural Florida Retrofit, and Bruce Davis of Alternative Energy Corporation's Applied Building Science Center in North Carolina, presented "The Unplanned Impacts on Houses by Powered Attic Ventilators" at the 1995 meeting of the Energy Efficient Building Association

There is significant data that reaches this conclusion here's one that the above was copied from.
http://www.homeenergy.org/archive/he...95/951103.html



PAVs are mostly worthless.
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Old 01-16-2010, 07:40 AM
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The op is asking about sealing / insulatig the attic. You would not use a powered vent going this route. You will need to provide mechanical ventilation to the home to remove excess living moisture and contaminants. This type ofventilation generally has an exchange mechanism to warm the air coming in ustilizingthe warm air going out. Vice versa in the summer. If you already have AC/heating ductwork it can be (usually) retrofitted to include the ventillation requirements.

I am going this route with an addition I am planning and will also close up the exhisting attic. a portion of the home has cathedral ceilings where i will leave them be. Considering a substantial amount of heat loss occurs through the ceilings/roof, this will help remediate that. While the cost is substantially higher, there are some offsets, particularly in reduced heating and cooling costs as well as the ability to skip the vapor barrier step as the foam also serves these requirements.

This is not to say that a proper barriered and insulated home is inferior but few are. Especially if you have high hats or other recessed lighting in the ceiling that was not properly sealed. These all provide conduits for heat loss and air exchange.

You also have the benefit of moving conditioning units to the now conditioned attic spaceo free up basement space. Homes with second floor bathrooms can also benefit from having the water heater in the conditioned attic, where piping runs are much shorter. Of course, proper care must be taken to provide an adequate catch basin with drainage should the unit fail. Otherwise you could have some significant damage on your hands. No different that having a second floor washing machine.
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Old 01-18-2010, 04:23 AM
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Very good Backto the sea, Let me know how your project goes. I'd be interested in first hand info.

Thanks

Jim
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Old 01-18-2010, 07:51 PM
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Originally Posted by jerseysportfisher View Post
Has anyone changed from a vented attic to a unvented attic ? I have started seeing this on DIY and building shows that propose this will save on overall HAVC cost ? Just seeing if anyone has went through this..... Plus i'm bored so looking up new projects
Been there, done that, love the results. Lower energy costs, improved quality of air, very comfortable attic space ..... high upfront costs.



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Old 01-19-2010, 04:25 AM
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Tireless, Being you are in GA, It does get quite hot down there. Have you had any problems with shingles ?

Did you have to re-roof and put a vapor barrier between the shingles and the ply ?

Thanks

Jim
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Old 01-19-2010, 04:41 AM
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Originally Posted by jerseysportfisher View Post
Tireless, Being you are in GA, It does get quite hot down there. Have you had any problems with shingles ?

Did you have to re-roof and put a vapor barrier between the shingles and the ply ?

Thanks

Jim

We had open cell foam applied directly to the underside of the the roof, no vapor barrier. The shingles have been fine. It's my understanding the closed cell foam traps too much heat and melts the shingles. On summer days when the outdoor temps exceed 90, the attic space in those pictures stays in the low 80's vs. 120 degrees it used to hit before we added the foam.
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Old 01-19-2010, 05:05 AM
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Closed cell foam provides a higher R value per inch than open cell foam. The weight per cubic ft of closed cell is much greater than open thus lending to structural strength. The research I have done effectively points to open cell being the equivalent of fiberglass insulation; however, it fills all voids leading to overall better insulating over conventional insulation.

open cell foam is not an approved vapor barrier, meaning you would need to add a vapor barrier in the application. Closed cell is more expensive.

Open cell foam should not be used below grade where moisture can be an issue. Closed cell is the preferred foam for roofing applications. Presumably because of its properties with water.

This is based on my limited research. I would love to hear from some experts with actual experience using these products.
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