New, researching, questions on rough plan (ICF), questions on AC and roof systems
Last Post 11 Oct 2020 06:23 PM by Smart Shop. 4 Replies.
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mattgUser is Offline
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06 Aug 2020 12:35 AM
Hello all! Been reading a bit, trying to learn as much as I can, and hope to be starting to make actual plans soon.
Do not plan to build for 2-3 years, but have recently acquired property (electric at the road, no water yet) and hope to start laying out foundational work for the whole project soon, like getting electric ran to the back, a shop build for storage and working out of, figuring out water (well or long tie to water district), driveways back into the property, etc.

I am sure I will leave out some info, but to get started:
Climate Zone 3, North Texas. Tornado concern, but not top priority Rural, on acreage, no building restrictions.

Due to some personal and medical issues, my priorities for the build start with *Quiet*, followed by comfort/ efficiency.

To this end I have been leaning hard toward ICF, but if I should be considering something else, please let me know.

This leads to the first set of questions: I am inherently an "if this is good, overkill is more good, and massive overkill seems better yet".
I have seen a buildingscience paper that says in zone 3 I need R20 walls, but also information that ICF loses much of its thermal mass benefits when there are not wider swings below desired interior temps, and with much of our summers seeing 75+ for overnight temps, and 95-105 highs, I understand the reasoning behind this.

So do I need/see a real benefit of bumping the insulation up a bunch, or will a true Rvalue around 22-23 for the wall keep me happy and comfortable for years to come? I do plan to stick with 6" thick concrete, so considering 8" block with inserts, added foam on the outside, specialty blocks, etc.

I am also torn about roof systems. I plan on a steel roof, and again *quiet*/noise abatement is a priority, but I am not sure that a concrete poured roof is the best option. Am I crazy, or should I consider a more traditional roof with lots of insulation and just a poured concrete roof over part of the master suite/the interior room for the "safe room" in the design?

Lastly (for the initial learning, lol) - is there a rough estimator for AC use by square or cubic feet with an ICF house in climate zones 2 or 3? With our high humidity I am looking into an in-line dehumidifier, but am curious about the need for that along with sizing for the AC. We are currently looking at 2200-2700 sq ft houses as we narrow things down. They will be in in a shaded area, with trees to the north, east, a little ways away on the south and west sides. Because of this we are looking for houses with large porches for the overhang (front toward west) combined with trees in the front yard.
newbostonconstUser is Offline
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06 Aug 2020 10:43 AM
You are correct. If in your climate the temp is always above or below your inside room temp then ICF thermal mass does little to help the R-value. You can increase R-value but is there really a payback?

I am not a HVAC expert but know not to oversize AC because it doesn't pull humidity out if the unit short cycles. Air sealing and vapor barriers are keys to help keep out humidity.

I had a house that I added a wrap around porch once and it made a big difference in keeping heat out of the house and also kept water away from the foundation. It was a old house pretty much in a swamp and that solved the basement water problem for me even though that wasn't the purpose of adding the porch.

"Never argue with an idiot. They will only bring you down to their level and beat you with experience." George Carlins
mattgUser is Offline
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14 Aug 2020 04:37 AM
Thanks NewBoston!

The "need" for insulation is a quandary, as it seems many places spec numbers for northern climates, so the "need" from what I am reading, in zone 3, seems relatively low in terms of return. The AC sizing is one that I am seeing a bit in my house recently (though it was quite a humid spring this year). We were replacing a unit a few years back that was close to 30 years old, and upsized with recommendations from the AC company. That proved to be a good decision over subsequent years, but with a rainy and mild "early" summer, I was seeing higher than expected humidity for a few months longer than I expected.

I will keep digging and reading and see if I can ask some more annoying questions as well.
newbostonconstUser is Offline
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14 Aug 2020 11:16 AM
Up sizing AC units causes the unit to short cycle. Short cycling doesn't give the unit time to get the humidity out. Stay away from companies that try to sell you a bigger unit, usually means they don't know what they are doing.
"Never argue with an idiot. They will only bring you down to their level and beat you with experience." George Carlins
Smart ShopUser is Offline
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11 Oct 2020 06:23 PM
More insulation helps but you get in to diminishing returns after the first couple inches. Solar scales linearly so if you think you want more insulation, more solar might give you a better return.

Personally, I'm going to try to net zero but grid tie so I can add batteries later or not.

I think cellulose insulation has a good reputation for noise reduction. If you have a rain screen under a steel roof, that might decouple the noise of rain from the roof deck a bit. If your solar is over your bedroom, that is going to create all of the rain noise and the solar brackets and rain screen should probably decouple the noise a lot. Lastly, you can hang your ceiling sheet rock from noise reducing brackets and even do two layers with green glue between them if one layer isn't enough.
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