Vented Attic to Unvented Attic conversion

[Brandon Lemen]

I'm currently an annual survivor of terrible summers in the Houston, TX area. I live in a decent 6-7 year old, 2-story production builder home with all the mechanicals located in the hot attic. Recently, I've learned more and more about these unventilated attics with spray foam insulation on the rafters as opposed to blown in insulation on the flat. It blows my mind that homes are so commonly built this way with A/C's having to pump cold air through 120-140 deg F attics for 9 months out the year. I sure wish I knew about this before building this house.

Considering the fact that moving and building a more efficient home is unlikely due to great school districts and not uprooting kids, I was wondering if anyone had any personal experience with retrofitting their attic to a unvented, conditioned space. I've tried searching locally to find an AC or insulation company or contractor that advertises this and haven't seen anything. I also realize this is a large task with all the considerations of gas furnaces, gas water heaters, and various attic penetrations. I'd love to speak with a contractor who has this down to a science with significant experience doing this operation, and seeing if this is even feasible for us. It stresses me out in the summers knowing my AC is running around the clock for the majority of the day and that it's lifespan will likely be shortened because of this extra strain.

Thanks for reading,
Brandon Lemen

[Maurice Mcmurry]

There are several threads about this. How to avoid creating a "hot roof" situation that voids the warrantee and shortens the life span of asphalt shingles is a recurring dilemma.

https://sawmillcreek.org/showthread....ter-contractor

https://sawmillcreek.org/showthread....oof-insulation

[Bill George]

First the AC compressor and condenser are located outside with just the evaporator and blower in the attic, correct? The duct work in the attic should be all insulated, correct? If not please state otherwise. I did this work for well over 30 years and then taught the stuff for 12 more years.

Sure and it would help a lot to have the attic ceiling or your roof spray foamed. It might make your roof shingles or material hotter, find a good roofer and ask. It might be wise to change to a metal roof or lighter color. Down South a lot of unskilled labor in the trades and it shows.

[Ken Combs]

I recently added insulation to my attic, rather an insulating contractor blew some for loose fill fiberglass on top of my existing. We discussed super insulating the ductwork but he, and others I spoke to didn't seem to want to try that.

My theory is that adding foam or other to the ducts would help with loosing the 'coolness' of the air that moves through the system. Trying to get the same benefits of foamed roof underside without the shingle heat issue. But it's hard to do in an existing house. Without the roof in the way it could be fairly simple to spray a coat on the ducts, or create a box around them of a very thin OSB to hold the insulation. Spray on has the advantage of permanently sealing any leaks.

In my feeble mind this seems preferable to the other options.

[Maurice Mcmurry]

Duct loss is for sure a factor when load is calculated. I have the tables in a book somewhere... We also have the web. Lots of good data on the first result of a search "duct loss in unconditioned space".

https://www.dnr.louisiana.gov/assets...%20low%20loss.

[Bill Dufour]

California has required all roof replacements or new roofs to be cool roofs for several years they reflect more solar gain then standard colors. This includes black cool colors.
BilLD

[Kevin Jenness]

Here's an introduction to roof insulation and ventilation https://buildingscience.com/document...of-design/view. Make sure you understand how your attic space is constructed including air/moisture barriers and the ramifications of changing from a cold to a warm roof design in your region before making any changes.

[Bill George]

Well you do not need to put ductwork in the attic. Up here when we build a house 90% of the time it has a basement. Duh with the equipment and ductwork in down in the nice cozy basement, If needed on the second floor we use a chase for the ducts to that level or put inside the insulated wall space. Sure it takes more skill and money but your not dealing with ductwork in a hot attic. Planning ahead and skill plays a big part of saving energy, cheap and fast does not and builder grade is usually both.

Yes and the ACCA Manual J and N have charts for both insulated and non insulated ducts in a unconditioned space.

[Jim Becker]

The Build Show (Matt Reisinger) who is located in Texas has done some very good videos about insulating the envelope to insure that HVAC, ERV and other infrastructure is inside the insulation since in Texas, basements are not a thing and the space available is typically up under the roof. You can find the Build Show on YouTube and then check for specific episodes about this topic. There was one not long ago, as a matter of fact.

[Maurice Mcmurry]

I see several episodes of the build show about metal roofs. I wonder if the roof above the conditioned attic is metal.

attic video
https://buildshownetwork.com/content...-attic?page=17

[Brandon Lemen]

Mr. Risinger’s channel is what really brought this to my attention. It just doesn’t seem that this conversion to a conditioned attic is an offered service at first glance unless a home is being completely gutted and redone.

[Maurice Mcmurry]

It is not an offered service for retrofit in our area. It is non standard. If non standard building techniques are part of a permit application our building department requires an architect and engineer to produce stamped plans. The insulation contractor I have used will only bid on a fairly limited range of standard applications.

[Jim Becker]

Mr. Risinger’s channel is what really brought this to my attention. It just doesn’t seem that this conversion to a conditioned attic is an offered service at first glance unless a home is being completely gutted and redone.

That's probably because so many homeowners don't know it's an issue. But it is. Any qualified insulation contractor should be able to help you with this project.

[John Lifer]

Many of the homes have most of the A/C and heating units in the attic. main condenser outside, but everything else is in the hot (or COLD) attic. Got to believe that you have a 5 to 10% loss in heating and cooling efficiency

[Jim Becker]

Many of the homes have most of the A/C and heating units in the attic. main condenser outside, but everything else is in the hot (or COLD) attic. Got to believe that you have a 5 to 10% loss in heating and cooling efficiency

Yes, that's historically been true. I suspect in many places that 5-10% loss might be optimistic, especially in the cooling season with elevated average seasonal temperatures. But many builders who "get it" (like Reisinger mentioned previously) are starting to move toward ensuring infrastructure is within the conditioned envelop in new construction, especially where it's customary for that infrastructure to be in attic spaces. This, combined with higher efficiency gear and quality ERV systems for ventilation, makes for a great home environment. Retrofit, like the OP asks about, is a little more challenging because of the "where" and the "what's in the way", but it's certainly doable.