Manual J:Encapsulated foamed attic vs. traditionally vented/insulated

[ga-hvac-tech]

These foam houses really do not impress me so far. Especially if u need an ERV or even worse a dehumidifier. Seems u just need more equipment to deal with the tightness of the home. Then u got to maintain / repair this additional equipment.

If I built again dont think I would use foam. JMO

Here in the Atlanta area... I know a couple of spec builders.

They do the roof (under the roof) with foam, then use conventional insulation in the walls. The result seems to work out as a good compromise.

[Timber]

Here in the Atlanta area... I know a couple of spec builders.

They do the roof (under the roof) with foam, then use conventional insulation in the walls. The result seems to work out as a good compromise.

Do you still need the ERV's / vetalation / or dehumidifiers ? If not, then I would consider that option.

[ga-hvac-tech]

Do you still need the ERV's / vetalation / or dehumidifiers ? If not, then I would consider that option.

Mostly no. Depends on how tight one builds the house... but generally no.

The main thing about a foamed attic (under the rafters) is not having that 'oven' just above the ceiling of the upper floor.

Hope this helps.

[teddy bear]

These foam houses really do not impress me so far. Especially if u need an ERV or even worse a dehumidifier. Seems u just need more equipment to deal with the tightness of the home. Then u got to maintain / repair this additional equipment.

If I built again dont think I would use foam. JMO

Any well built home needs fresh air ventilation to pruge indoor pollutants and renew oxygen during the calm warm weather. Even worse, supplemental dehumidication is needed in green grass climates if you want the best in comfort and avoid growing mold/dust mites.
ASHRAE, American, Lung ASS, EPA and most modern building codes suggest mechanical fresh air ventilation for the above reasons.
The posters on this site represent traditional opinion not the building research community. Check out the above IAQ experts or researchers like Building Science.com for the state of the art specifications.
It hard to part with tradition when dealing a changing industry.
I have been involved with IAQ for 25 years and find is hard to believe how difficult is has been to get the concept of controlled fresh air ventilation and real humidity control in a modern well built home.
Good luck on getting a quality home to live in.
Regards TB

[tedkidd]

TIPS, I've yet to see load, modeling or any cost/benefit software that can accurately reflect the energy or load impact of foam.

As you may be seeing in these threads, guys talk about going to foam houses on 100f days and the equipment doesn't run once the whole time they are there. That indicates gross oversizing to me, how about you?

Good luck on getting a quality home to live in.
Regards TB

Since you were considerate enough to respond I guess I'll drop in behind you.

I think when people don't do or ask what the numbers are, they're defining their ability to make smart decisions.

Some would rather pay $2 per sf/year for energy than $0.25 per sf/year for energy and $0.50 per sf/year for the increased mortgage for the better home. To me that's living in a crappy home and throwing away $1.25 per sf a year.

The difference between ignorance and stupidity is ignorance doesn't yet know, stupidity doesn't have the capacity to know.

[ga-hvac-tech]

TIPS, I've yet to see load, modeling or any cost/benefit software that can accurately reflect the energy or load impact of foam.

As you may be seeing in these threads, guys talk about going to foam houses on 100f days and the equipment doesn't run once the whole time they are there. That indicates gross oversizing to me, how about you?



Since you were considerate enough to respond I guess I'll drop in behind you.

I think when people don't do or ask what the numbers are, they're defining their ability to make smart decisions.

Some would rather pay $2 per sf/year for energy than $0.25 per sf/year for energy and $0.50 per sf/year for the increased mortgage for the better home. To me that's living in a crappy home and throwing away $1.25 per sf a year.

The difference between ignorance and stupidity is ignorance doesn't yet know, stupidity doesn't have the capacity to know.

Sometimes stupidity knows and does not care... I hate to see that... but it is out there.

I cannot tell you the number of folks that say: Gee, it will not pay back in a year... why bother. Amazing IMO.

[ChaseAir]

The homes we have done were so tight they really needed a dehumidifier to remove moisture. An 85 degree day was simply not enough to cause the units to run with the stat set at 78. Gross oversizing?

Well even 2 stage units are "grossly oversized" on a light load day with a homeowner who doesn't have thermostat set as low as the "design conditions" were determined in the load calc.

Not to mention that big oak tree on the west side of the house that reduces the load by 3/4 ton in some circumstances. Needless to add, the load calc is a great tool, but it does not answer all things.

[teddy bear]

The homes we have done were so tight they really needed a dehumidifier to remove moisture. An 85 degree day was simply not enough to cause the units to run with the stat set at 78. Gross oversizing?

Well even 2 stage units are "grossly oversized" on a light load day with a homeowner who doesn't have thermostat set as low as the "design conditions" were determined in the load calc.

Not to mention that big oak tree on the west side of the house that reduces the load by 3/4 ton in some circumstances. Needless to add, the load calc is a great tool, but it does not answer all things.

Good post but there is some confusion. During high dew point summer weather, extremely air tight homes have less moisture moisture infiltration than the excessively leaky homes. The sources of moisture in all homes is the infiltration/ventilation of outside fresh air and the occupants.
Well insulated air tight homes need mechanical fresh air ventilation when occupied. Yes the a/c will not run enough to remove the mositure from the minimal fresh air ventilation and the occupants. This is usually 2-4 lbs. of dehumidification moisture per hour. Let the a/c run as much as needed to maintain the desire temperature and use a high efficiency dehumidifier to remove the enough of the remaining moisture to maintain <50%RH. When the home is unoccupied, the t-stat can be raised to avoid any cooling. The dehu will maintain <50%RH at a fraction of the cost of trying to cool to <50%RH.
Sorry about picking on a small point, but there is a lot of confusion about these issues. Thanks for the support.
REgards TB

[tipsrfine]

Good post but there is some confusion. During high dew point summer weather, extremely air tight homes have less moisture moisture infiltration than the excessively leaky homes. The sources of moisture in all homes is the infiltration/ventilation of outside fresh air and the occupants.
Well insulated air tight homes need mechanical fresh air ventilation when occupied. Yes the a/c will not run enough to remove the mositure from the minimal fresh air ventilation and the occupants. This is usually 2-4 lbs. of dehumidification moisture per hour. Let the a/c run as much as needed to maintain the desire temperature and use a high efficiency dehumidifier to remove the enough of the remaining moisture to maintain <50%RH. When the home is unoccupied, the t-stat can be raised to avoid any cooling. The dehu will maintain <50%RH at a fraction of the cost of trying to cool to <50%RH.
Sorry about picking on a small point, but there is a lot of confusion about these issues. Thanks for the support.
REgards TB

How does having one of your de-humidifier included in the design of one of these "tight" homes affect the manual j load, and for that matter the manual S calc?

[ChaseAir]

We used the dh90 from Honeywell. Yes ALWAYS have fresh air. The offgassing of that foam has to be toxic as you can smell it years later. On one home we pulled the air out of the attic. I would think the systems would last longer as they hardly run and do not cycle back on rapidly. Great for warranty service. Dh90 is Probly not big enough for these areas but man that 180 is expensive. Is there a better one?

[teddy bear]

How does having one of your de-humidifier included in the design of one of these "tight" homes affect the manual j load, and for that matter the manual S calc?

Good question. The dehumidifier will not have any effect on your manual J calc. The dehumidifier will not run during high cooling loads because the a/c removes more than enough mositure to maintain <50%RH. If the a/c is not maintaining <50%RH during peak cooling load, slow the air flow to get a colder a/c cooling coil. The a/c coil should be 25^F cooler than the desired temp in the home to remove enough moisture.
As the cooling load declines during the evening hours or on a rainy day, the indoor RH will exceed 50%RH. The dehumidifier will be activated by the dehumidistat removing the excess moisture keeping the home at <50%RH.
The Honeywell dehumidifier is a good dehumidifier. A 90 dehu will handle large air home with 70-90 cfm of fresh air ventilation and 4 occupants.
The best dehumidifier is the Ultra-Aire with DEH 3000 controller for scheduled fresh air ventilation. Certianly the Honeywell is ok. There are others that work I am sure.
Regards TB

[rickboggs]

Could one of the pro's do a quick comparison test with their manual j calcs to answer a question I have? Take any house that you have a manual j done on and leave everything the same except for the attic (with no ducts or air handler in attic) and see what happens to the load when you change from a vented attic with traditional insulation levels of fiberglass or cellulose on the attic floor(whatever the R-level is for your area) to an attic spray foamed at the roof with 3 inches of foam (closed cell and/or open cell). Which method results in a higher cooling load? Remember, no ducts in attic. Thanks to anyone willing to do this.

2668 sq ft home
R38 Ceiling
R13 Walls
Total 22506
Sensible 18025
Latent 4479

R25 Foam Encapsulated
R13 Walls
Total 20720
Sensible 17494
Latent 3226

Add duct in the attic

R38 Ceiling
Total 33307
Sensible 26707
Latent 6600

R25 Foam Encapsulated
Total 26620
Sensible 21476
Latent 5144

[ga-hvac-tech]

2668 sq ft home
R38 Ceiling
R13 Walls
Total 22506
Sensible 18025
Latent 4479

R25 Foam Encapsulated
R13 Walls
Total 20720
Sensible 17494
Latent 3226

Add duct in the attic

R38 Ceiling
Total 33307
Sensible 26707
Latent 6600

R25 Foam Encapsulated
Total 26620
Sensible 21476
Latent 5144

It would appear the BIG advantage is if the system (equipment and ducts) is in the attic. Logical for the style of construction down here... probably not that big a deal in areas where equipment and ducts are in conditioned space.