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  1. #1

    Texas coastal home ac & insulation advice

    I'm a new builder (1 yr) on the Texas coast. Our 7th home will be for us and I sure could use some advice.

    On the water
    Two story on pilings
    Large porches
    Radiant barrier roof deck
    2x6 frame
    approx 3,500 sq ft (circa 1,700 ft on top two floors)
    My mom will live full time on 3rd floor
    2nd floor will be isolated 90% of time when we're not there
    Lots of east exposure (under porch) glass including some glass walls
    First floor will have a small cooled tackle room & mud room (400 sq ft total)

    I really really don't want to cringe about turning on the ac as I do with our current home down there. I'd rather thrown down now and do this thing right than save a few bucks now and HATE it when I put the ac on 74.

    What is the best insulation to use for this house?
    What ac system would you recommend?
    Any other thoughts?

    We're currently building 2,000 ft on slab so this is a big step for us.

    Thanks a ton and Fair Winds...

  2. #2
    Join Date
    May 2002
    Location
    Houston Texas
    Posts
    6,325
    An accurate load calculation is your first step after you choose a construction type. There are too many construction options all of which will work if performed correctly.

    Common to all would be adequate fresh air/ventilation most homes here are not that tight but tight is good again if done properly.

    Any brand is a good choice if properly sized and installed. I would recommend 2-stage cooling and heat definitely variable speed blower and a quality (Therma-Stor) whole house dehumidifier.

    When you ask about insulation are you referring to for the walls and attic or for the ducts? For the ducts R-8 is best to avoid sweating even better if the ducts are in a controlled environment.

  3. #3

    Yes to all the above...

    I'd like to turn the house into an igloo cooler (as much as is possible) while obviously still allowing the home to breathe (but not too much given its location and local winds).

    Is foam insulation the way to go for the walls? If so, what type should we use on the interior walls? (big fan of sound insulation as well) What is important for ducting in the attic (all we do now is use as much rigid ducting as is possible).

    This quickly becomes a question of "How the heck do I know if the local guys are designing the right system?" or "How much info do smart folks need to give some specific directions/feedback?"

    Given the hack job that TrendMaker did on my home in Houston and the 20 year old "ac hog" I have on the coast now, I'm simply overwhelmed about how to do this thing right for a change.

  4. #4
    Join Date
    May 2002
    Location
    Houston Texas
    Posts
    6,325
    Where are you building?

    Very few contractors around are knowledgeable about higher forms of home building thus the proper systems to install in them. The reason is they have no reason to because the builders and homeowners will not spend the money so they have no impetus to learn or understand.

    Again what are you looking at for construction type, SIP or insulated masonry blocks or concrete walls? You can build an ICF home with conventional wood skeleton encapsulating the walls and ductwork. Any of these homes will work along the coast as long as proper ventilation and humidity control are factored into the designed. I would stay with either snap lock round pipe or square metal duct and spray ICF over it.

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,467
    You need enough mechanical fresh air to get an air change every 4-5 hours. ASHRAE recommends 7 cfm per person (design) plus 1 cfm per 100 sqft. Provide enough dehumdification to maintain <50%RH during low/no cooling load conditions. This amounts to 90 lbs. of dehumidification per 3,500 sqft. of home. All this minimal fresh air to purge indoor pollutants and renew oxygen. We at Therm-Stor have been developing this concept for 18 years. Make-up air helps exhaust devices work when needed. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  6. #6
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,198
    Just fyi...FEMA has an excellent guide to building in coastal climates..don't know if you are in hurricane area. Also www.buildingscience.com has sereral articles based on their findings in Florida after their two hurricanes in 04. Bs has Builder's Guides for Hot Humid climates..and all areas. I think you can read them online. ( I have 2 copies..one falling apart!)
    Great information. Unbiased, tested.

    If you can locate your ductwork in the conditioned space it would make a big difference on the load calculation, the comfort and the energy savings.

    I wouldn't seal ductwork with foam insulation spray as it is not a duct sealing material.
    Mastics seal duct leakage and are hand applied with some degree of control.
    Foam insulation is a quick install. It sprays on very quickly and expands rapidly.
    It will not fill in all the voids and seams with the same degree of air sealing that mastic materials will.
    I get quite a few calls from homeowners with problems due to foam insulation being used as duct insulation. Too often gaps and voids with in the foam installed next to the duct allows for condensation to build up. Put this in contact with the paper backing on sheetrock and you have moisture and a food source. Not good.

    Where are you in your build?

    Best of luck to you.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  7. #7
    Join Date
    Jun 2001
    Location
    DFW
    Posts
    684
    Put the duct work in conditioned space.
    Air seal the house, and bring in fresh air when and where you want it.
    Shade all the windows in the summer time.

    Either make the attic part of the conditioned space, or check out the air-tight drywall approach.

    Wall insulation is not as critical as you might think for southern climates.
    Use HVAC calc and run some numbers to see how much insulation you need and where.

    It is hard to beat cellulose for sound insulation and cost. Foam is a better air seal and better insulation, but the cost is much higher.

    Quality of insulation install is very important especially in walls. Fiberglass is very hard to do right.

  8. #8
    Join Date
    May 2008
    Location
    North Texas
    Posts
    105
    1. White or light-colored roof. Since you are in high-wind area look at the Texas Dept Insurance roof ratings.

    2. All air ductwork inside the conditioned space. Do not put them in the attic unless you are insulating, sealing, and conditioning the attic space.

    3. Insulation should be termite resistant. Foam insulation may provide a path for termites. They will also use sheetrock for tunneling. My preference would be unfaced fiberglass.

    4. Take out of the design as many west windows as you can get away with.

    5. Windows need low-e coating.

    6. Outside exposed walls need a drainage plane.

    7. Air barrier and vapor barrier are two different animals. Use latex-painted gypsum board as your vapor retarder. Do not use a vapor barrier.

    8. Consider overlapping two layers of subfloor to reduce air infiltration.

    9. A blocked condensate line will spread mold through the house like crazy. Make sure the double pan is installed, and the overflow cutoff switch works.

    10. Use a hardstart kit on the condensor/compressor. When trying to run from your storm generator, the compressor will draw on start 12x the normal current. (Yes, I know motors are supposed to be 6x, but get a really good data logging meter and try it)

    11. Put shade over that expanse of glass. (You will also have to make sure your shear wall passes muster, and that the glass is impact resistant or can be protected)

    12. Get a copy of International Energy Conservation Code Commentary for more ideas. Energy Code is Texas state law anyway.

  9. #9
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,467
    Quote Originally Posted by sparksandfan View Post
    1.
    7. Air barrier and vapor barrier are two different animals. Use latex-painted gypsum board as your vapor retarder. Do not use a vapor barrier.

    way.
    I have been cautioned on using any kind of vapor retarder on the inside of hot humid climate home?? The point was to have a vapor retarder on the outside of wall not the inside. Any moisture that penetrates the exterior should be allowed to diffuse out of the insulation into the home. You opinions, please. Don't forget mechanical fresh air ventilation and supplemental dehumidification for rainy, cool, weather. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  10. #10
    Join Date
    May 2008
    Location
    North Texas
    Posts
    105
    Texas has over 600 miles of coast. In the East around Port Arthur, it is heavy rainfall. To the south, less rainfall. But all hot and humid. Wind is southerly in summer, so drawing moisture.

    Very challenging to prevent condensation. In summer, where is the condensation point due to cooling by A/C? In winter, where is the condensation point on those rare cold days?

    A heavy rain area like Galveston needs a drainage plane to prevent water from getting into the wall assembly. That's less load for the air conditioing, and less moisture to turn wood into termite food. It also helps to prevent sheetrock cracking from wood swell and shrinkage.

    Drying of the wall assembly should be to the outside. Interior is conditioned space. Latex paint on the sheetrock will retard, not stop, vapor flow. Extremely important to seal sheetrock and all penetrations at the interior plane.

    Removing moisture and latent heat requires energy. Required air changes will add to that load. But don't need to waste energy $.

    Several years ago the TV shows were showing plastic sheeting as vapor barrier and how important a vapor barrier was to your home. Builders and builders badgered by home buyers were adding plastic sheeting here. Really bad idea for this climate. Some walls torn apart to remove it later.

    Moisture and wood equal mildew and mold. All wood products here arrive with mold and mildew, or soon will have.

    Can't speak for rainy, cool weather. On the coast, the weather is 95-95; 95 degrees, 95 percent humidity.

    Just my opinion. 50 years ago this was not a problem. There was no air conditioning, just boiler/radiator heating. It's a work in progress.

  11. #11
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    >>On the coast, the weather is 95-95; 95 degrees, 95 percent humidity.

    A little quibble, if you use a psychrometric calculator (e.g. http://www.envirochex.com/psychro.htm ) then you will see that is a dewpoint of 93 degrees! 244 grains/lb moisture load. Our Texas climate is adverse but not like this<g>.

    For Galveston, the airport weather station ought to be one of the more reliable. You can see from the history the past month had a max dewpoint of 78F and an average of 74:
    http://www.wunderground.com/history/...lyHistory.html

    Seems to me the overnight low temperature has a strong effect on the dewpoint throughout the following day. There may be exceptions but it seems the air is nearly saturated overnight, and the *absolute* humidity does not change all that much during the day. The *relative* humidity changes a lot with the temperature. The result can be some RH numbers 60-65&#37; at mid-day but there is still a whale of a lot of latent load for the AC to remove.

    The above is just a quibble with one thing you said. But you said a lot more and there is a lot to admire in your overall message.

  12. #12
    Join Date
    May 2008
    Location
    North Texas
    Posts
    105
    LOL. I knew I'd catch some grief for that!

  13. #13
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,467
    Quote Originally Posted by sparksandfan View Post

    Very challenging to prevent condensation. In summer, where is the condensation point due to cooling by A/C? In winter, where is the condensation point on those rare cold days?

    A heavy rain area like Galveston needs a drainage plane to prevent water from getting into the wall assembly. That's less load for the air conditioing, and less moisture to turn wood into termite food. It also helps to prevent sheetrock cracking from wood swell and shrinkage.

    Drying of the wall assembly should be to the outside. Interior is conditioned space. Latex paint on the sheetrock will retard, not stop, vapor flow. Extremely important to seal sheetrock and all penetrations at the interior plane.

    Removing moisture and latent heat requires energy. Required air changes will add to that load. But don't need to waste energy $.

    Several years ago the TV shows were showing plastic sheeting as vapor barrier and how important a vapor barrier was to your home. Builders and builders badgered by home buyers were adding plastic sheeting here. Really bad idea for this climate. Some walls torn apart to remove it later.

    Moisture and wood equal mildew and mold. All wood products here arrive with mold and mildew, or soon will have.

    Can't speak for rainy, cool weather. On the coast, the weather is 95-95; 95 degrees, 95 percent humidity.

    Just my opinion. 50 years ago this was not a problem. There was no air conditioning, just boiler/radiator heating. It's a work in progress.
    My point was that there not be any vapor retarder at the inside surface. Moister in an exterior wall should be able to dry to the inside. The drywall is below the dew point of the outside air. The moisture moves to the cool temperature. A sun heated wall will drive the moisture to the inside. If not allowed to move into the home, moisture will condense at the cool surface. Any paint should have a high perm rate. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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