Blog About Stuff That's In Your Home | Appliances and Stuff

12 Nov 11 Buiding a conditioned attic in a hot & humid climate the right way!

My name is Matt Risinger of Risinger Homes and welcome to my Video Blog on Green Building and Building Science topics. Check out our latest creation. This is a tour of a spray foam insulated attic in Austin, TX. I’ll show you the why & the how of conditioned attics.
Video Rating: 5 / 5

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Video Rating: 4 / 5

Tags: Attic, Buiding, Climate, conditioned, humid, right

Reader's Comments

  1. |

    @amusingisthedawn Good point about the radiant barrier. This house has a very reflective Galvalume metal roof so the radiant barrier is on the top side of the roof. Also, you could not effectively insulate this particular attic at the roof line with batt insulation. The foam forms a total seal and insulation barrier over ALL the framing which batts couldn’t accomplish. Thanks for commenting. Matt Risinger

  2. |

    Im my opinion, adding a radiant barrier like a foil – with a small air gap between the foil and the roof deck – and THEN spraying the foam would be much more efficient. The foam has better air sealing abilities…but it isn’t much different than laying batt insulation.

  3. |

    @MattRisinger There have been a few applications when I was hanging fiberglass insulation and in some of them we had to use card board batting for an airspace,I have watched quiet a few foam spraying videos learning about this and thought if they had an inch of space stapling up cardboard between the rafters and then spraying the foam it would seem the singled roof would then get its airflow that way without overheating the shingles and still have the insulation?

  4. |

    @Artoconnell I can tell you from experience that a conditioned attic with temps in the low 80’s on a 100 degree Austin TX day are much more manageable to be in compared to a typical Austin attic that’s 130 degrees when it’s 100 outside. Think about how much more efficiently this equipment will run when the environment around it is 50 degrees cooler than a neighbor’s house. Seems to me that anyone working in a hot attic would be tempted to hurry with their job at hand. -Matt Risinger

  5. |

    @aaronoftexass This was not a pretty install. This particular crew was fairly new at spraying foam. I highly recommend using a coat hanger to do a depth poke test. Just wrap a piece of tape around the 5.5″ mark on a coat hanger and you can ensure that it’s meeting that min depth. That’s one of the beauties of using foam in that a rookie crew can still do very well performing install even if it’s not pretty. Using traditional insulation requires expert crews and even then it’s not as good.

  6. |

    @tappakeggaday1 GREAT QUESTION> Conventional wisdom has been that shingles need to be vented underneith or they will cook. In this house we used a metal roof so that issue doesn’t translate to metal. However, the latest building science talk is that shingle temp only rises by 2-3 degrees without venting underneith. Building Science expert Joe Lstiburek talked about that issue in the latest issue of Fine Homebuilding. I wouldn’t hesitate to foam under a shingle roof and have done it before.

  7. |

    I have a question about this myself,I live in North west Florida and when I was younger and doing roofing I was inside a roof and had asked why dont they put insulation up here as well? The answer I got back was the shingles get hot enough on top of the roof and if the insulation was under them they would bake off of the roof so i never thought anymore about this video are you under a metal roof or a shingled one?I can see metal holding up with the foam but not sure about shingles.

  8. |

    @Artoconnell Are you saying you would do a worse job of serviceing a hard to get to a/c to the point it would only last half as long? And they are designed for that “extreme” envionment arent they? I just saw an a/c from 1960 still working in an attic……………….please tell us a/c pro how this stuff makes a/c’s last longer and why, but come up with something better than saying a/c guys do crap work until they get into an attic that the homeowner cools all year. extra btu load=more a/c run

  9. |

    Would LOVE to work in that attic…the equipment life is basically doubled from being more serviceable, and also not being in such an extremely hot environment. NIce JOB

  10. |

    I have been trying to use my thermal camera to come up with real world heat gain comparisons. This may seem crazy, but it looks like a thin layer of radiant barrier foil will emit less heat than the underside of a foamed roof deck. Your dislike of the r-value system comes straight from our climate where conductive heat is only important in our smaller heating season. But your like for foam is odd, it does as little for radiant and conductive heat as installing r-19 batts on the roof deck.

  11. |

    @MattRisinger Can you guarantee 100% that the house will always get .35ach? I take it you do the pop a hole run a duct from the outside to the return plenum and pressurize the house? How can you use that system to guarantee proper fresh air. What if they don’t run the hvac much? I guess my question is, how exactly can you guarantee .35 ach without an erv, or tested natural airflow of .35?

  12. |

    @MattRisinger Like adding up the extra cost of insulation, then the extra cost of and air exchanger, then the extra cost of a high efficiency furnace, than applying an 8% mortgage to those costs, then realizing that annually you lose money by using that system. Send 5$/month to the bank in interest to send 1 less dollar/month to austin energy? I though I also heard that if you figure in manufacturing waste, petro used, biodegradeability and intallation waste that foam was on of the least “green

  13. |

    @MattRisinger Why not be fooled by r-value, is that what ashrae would say? As energy professionals do we calculate loads with hearsay?

  14. |

    @clintsmith96 Good question. I believe it’s just shy of R-4 per inch. This assembly is technically R-19 in total but don’t be fooled by R value totals. I’ll take R-19 at the Roof Deck over R-42 blown any day. We’ve totally sealed out any air leaks from penetrations (ie Ceiling Cans), we’ve run our ducts through a hospitable environment, and we’ve lowered the tonage of our AC system. Perfect for a hot/humid climate. Since this video I’ve gone to adding rigid foam on the roof deck too. -Matt

  15. |

    What R value do you get with 1 inch of open cell foam? Do you ever use the closed cell foam?

  16. |

    @Dutchy1965 It’s a gas burning unit but the sealed combustion chamber makes it completely safe. I’ve been building homes with gas furnaces for 15 years and never heard of any fire issues. The foamed/sealed attic does mean that you can’t use a traditional flue pipe nor rely on the combustion air coming from the attic however. Not using a sealed combustion unit with air from the outside would be VERY unsafe. Houses are complex and we need to use good Building Science judgement when building.

  17. |

    fire hazard?

  18. |

    Nice video, Check out my videos about Home Wind and Solar system intalling on the Rooftop. On Earth Day I won a green design contest for my home energy system the RoofMill. Have a look at my home wind turbine videos of installing and running Hybrid Energy Systems. Friends and Subscribers Wanted. Have a good day , Thanks, Sam

  19. |

    @MattRisinger Thanks Matt for the opinion as well as mentioning Mr. Holladay. I had not come across his blog before now and I’m glad you brought it to my attention. Thanks again.

  20. |

    @Artsee77 I’ve not done an ERV yet. I think it’s a great idea but I’ve just paid the energy penalty for bringing in unconditioned air. I think a better option would be a dehumidifier that had a fresh air input so it would be mechanically dehumidified. I read Martin Holiday’s post this month on ERV’s and he think they move very little moisture. It’s really HOT in Texas but we’re never more than +-25 degrees from 75 (inside temp). I think HRV’s are more impt for cold climates with 50+ deltas

  21. |

    Matt, have you ever used a HRV/ERV in any of your projects. I’m not familiar enough with your climate down there, but it seems like an ERV would prosper within the humid weather areas. However, doesn’t the ERV require an additional dehumidifier to be set up since it is not considered a dehumidifier itself?

  22. |

    @benpie12 What? Are you referring to the fresh air system not functioning? We don’t have a single combustion appliance in this house. All furnaces are power vented and sealed combustion, tankless water heaters are mounted on the exterior. The fresh air system is purely for indoor air quality issues. It’s meant to remove general pollutants from the indoor air and replace that stale air with outdoor air at a prescribed rate. We follow ASHRAE 62.2 standards for how much fresh air is needed.

  23. |

    @MattRisinger death

  24. |

    @MattRisinger I too live in TX and see alot of HVAC’s in closets, so I still don’t understand from a RESdesign perspective, even if you fill in the duct system as being w/in the envelope, it still doens’t seem to trump the increased conditioned space, the increased evelope sqft., and the r-30 ish foam setup, compared with the up to r-60 loose fill. Those three items seem to increase the btu gain beyond the saved btu gains of bringing the ducts into the envelope.

  25. |

    @MattRisinger I meant the fresh air system for the occupants…..if it stops working, the house is now dangerous for the occupants, I was wondering if there is any way for the homeowner to know if the fresh air system has stopped working? And what about covering the ducts with insulation, 10{” over the duct with fiberglass would make R-34 or so on top of the duct and R-60 for the sides and bottom. And if the btu’s are being removed from the attic, aren’t you paying to do so?

  26. |

    is it better than the regular air condition

  27. |

    We had the Unico High Velocity air conditioning system installed in our home last summer(2009). It out performs the conventional air conditioning system that we had in our old home in every respect – quickly decreases the humidity, cools the hours, quiet and efficient. This is an excellent system and makes a lot of sense for installation in older homes as well as in new construction.