Hello I posted in another section of the forum but think this is the better place for it. I am building a large house 6100 sq ft living 7000 total in the Florida Panhandle on a bay. Site orientation is South-West and I am in the high velocity zone 130-140 mph winds during hurricane season so impact resistant glass is a must. House is a 2 story with attached 3+ car garage and media/ gym above the garage. ICF is planned for the entire vertical envelope using Nudura with 6" concrete walls. Roof will be conventional stick and thinking insulation on the 2nd floor ceiling would be better than foaming the underside of the roof (cost plays a factor too). A lot of windows facing South-West on both floors to take advantage of the bay views (why buy a bay lot if you don't take advantage of the views?). Currently researching windows and doors as this is my biggest solar gain for the house, east-north-west windows and doors are minimum. Geothermal to provide HVAC needs. First question. Kitchen, 1st floor bathroom, 2nd floor master bathroom (over the kitchen family room area) and 2nd floor bathroom which is above the 1st floor bathroom are planned to be radiant heated and all floors will be some tile on top of concrete. Does using radiant heat provided by the geothermal system with the rest being forced air make sense? I think comfort would be better and that having those zoned areas will cost more but not significantly more. Currently have not discussed what insulation should be in the floor for the main part of the house but the house sits on sand. Will still need HVAC in the summer for those areas too but thinking the comfort might be worth the added cost. No experience with living with radiant heat so your input is helpful. Also planning to use a 10KW solar PV system with two inverters grid tie system. Roof to be concrete tiles (no choice this is an HOA requirement). We are not going crazy on being green but think if we can do these things (minus what the solar gain is from the windows) we should have a pretty comfortable house. Main energy use is running AC from mid May to mid Oct where I live so unlike many our issue is too much heat. Winter temps hardly touch 20F and then for usually a day or two and typically we are mid 40's for lows to mid 60's for highs. No plans to live here in the summer months and plan to keep the HVAC at 83-4F to keep out mold. 2nd question. Not sure yet if my architect is going to run a manual J or not seems variable in this area but almost every contractor I know doing HVAC over sizes the systems and they short cycle often. Had two out of two experiences with this and debated with the HVAC contractors that system is over sized. Does a good ACCA manual J software program exist or is it too expensive for a one time use? I know that whatever manual J is run I plan to sit down and go through each and every detail to get this right. I do understand why the HVAC people do this because under sizing an AC system where I live is bad because where I live summers are sweltering and sweat soaked so better too big then sweating... I think getting the windows right with correct overhangs is key to this house being comfortable. Planning to begin building in DEC so any input is appreciated as to things I should watch or watch out for. Thanks

Sweat soaked and sweltering is exactly why the AC should not be oversized. An oversized AC system will not handle the latent load (humidity) properly.

Think of it this way. The AC will turn on and blow only long enough to tell the thermostat that it has brought the temp down. If it has too much cooling power (oversized) then it won't run for very long and won't have adequate time to remove the moisture from the air. It will be humid and sticky in the house.

Properly sized is best, but erring on the side of undersizing is better than erring on the side of oversizing. If it is undersized then it will run longer to bring the temp down and have more time to handle the latent load.

I'm in Wheezy-Anna, so I know about sweat

Even a properly sized AC will short cycle when the weather is mild. Better to select AC with a multi or variable speed compressor/fan and a stand alone dehumidifier (for when you don't need any cooling at all).

Current system short cycles on the hottest days we have thus the reason my focus is on manual J for the new house.
Should be interesting reading on what I get for manual J calculations once I get a little more data on windows...

"Not sure yet if my architect is going to run a manual J or not..."

Seriously- if your architect won't run a Manual-J (or hire someone to do that), get a different architect! A greener architect would do one better, and run an energy use simulation tool (at least BeOpt, which is a freebie download tool that's fairly easy to use) for tweaking in some of the parameters.

It doesn't take rocket scientist to project that  SW facing windows probably boost the peak cooling loads by more than 50%.  Operable exterior shades are probably going to be "worth it"- no need to keep the bay view during periods when you're not there, but it does mean you have to actually operate those shades. Keep the view, but think about it before making it floor-to-ceilng-end-to-end glass. You can't much enjoy the view from inside the solar collector, even with the AC blowing in your face.

Building with a decent amount of interior side thermal mass in the rooms with the SW facing windows is something to consider too, since that can moderate the peaks by quite a bit.  Concrete-slab floors, and masonry walls (granite counters, marble staircases & fountains :-) ) all add usable thermal mass for moderating cooling loads.  If you can peel back a ton or three on peak loads by trimming windows add adding thermal mass it saves quite a bit on system cost on the geothermal, as well as some on the operational cost. This is the sort of situation where SCIP beats ICF performance with margin, at almost any R-value. The thermal mass of a SCIP is accessible for moderating window-gains, whereas with ICF it's isolated.

For floor insulation in slab on grade construction in US climate zone 2 you don't need much (if anything) for an ICF where the footing is below grade- R4-R6 at the slab edge (or would be useful otherwise.  By earth-coupling the slab you gain the mass benefit of the ~70F deep subsoil temperatures:



Heating with radiant floors would require at least ~R4-R8  (1-2" of EPS) under the slab in those zones,  but that would reduce the thermal mass benefit during the cooling season.  While it's fine to do radiant heating for the second floor, limiting it on the first floor to only those rooms with low summertime solar gain is probably the best compromise. Radiant ceilings can still be used with good effect on those high solar gain rooms.

If you're not already 1001% committed to an ICF solution, you may want to flip through this guy's blog on eventually building with a SCIP approach in Panama City FL, even though he originally considered ICF was the cat's pajamas for building in hurricane zones.

Are you sure you want 'conventional stick construction' in a hurricane-prone area? The FL panhandle is prone to hurricanes- it's not a matter of 'if', but 'when'. If I were building in FL, I would look at stronger roof systems, such as concrete.

A steel SIPs roof is a nice hurricane resistant marriage to ICF walls and much more affordable than a concrete roof.

Update:
Dana
All good information and no insulation under the foundation (except hydronic) make a lot of sense. I am meeting with my HVAC guy next week to work some things out. My architect did run manual J's and actually helped the county he is in develop a program that they use. I have run a couple manual J estimates (estimates since I have no locked in U-factors yet but using what I think I will end up with) and plan to hire out an expert to run one too after seeing what I get back. I have followed the Panama City blog and admire the fortitude of the owner given the house is not done after 3 years. I am not going SCIP but looked at them hard.

Stick construction is what I am going with for the roof. I would prefer SIP but cost is a factor too. My architect is familiar with SIP and can accommodate them. I am concerned about the strength of a stick built roof and I will be onsite the entire time to be sure that it has all the required straps and bracing required. 2 foot overhangs on a 6/12 roof helps for both solar gain into the windows for the 2nd floor and I have two large patios on the 2nd floor that cover 66% of the 1st floor so everything we can do to help reduce solar load in the summer is on my mind.

No house is perfect and we live in a world of compromises. I appreciate all the input and it is taken with careful consideration. I have discussed some of these suggestions with the architect firm and my general contractor as well.

Again your comments good and bad all help and hopefully stop me from making a large mistake regarding some system for this home...

fun2drive I would encourage you to look more into steel SIPs for your roof. They're much stronger but lighter, so no crane needed. And you're in Florida which is a major market for steel SIPs. I bet the cost won't be that far off of stick-built once you consider framing/trusses, sheathing, hurricane straps and spray foam.

Jelly
I think you are right. I just have not seen anyone in this area that has much experience with SIP. My architect is all for them but my builder is not familiar. I meet with him next week and will discuss again as the truss design is not started. 4/12 roof pitch is what I am stuck with since the height of the house cannot exceed 35ft. How are the steel SIP panels supported? Beam from the gables and the panels laid on the beam?

The entire area under the SIPs then becomes conditioned space correct?

My start date is going to be delayed simply because of the approval process from Dec 14 to Feb 15. That's life!!

Ask about steel SIP's on the SIP sub-forum. Cmkavala will help you- he is a steel SIP dealer in FL. We were going to build our house with them, but I'm one person, working alone, so I went ICF instead. Yes, the entire space below the SIP is conditioned space. They come in a wide variety of thicknesses and lengths.

Posted By fun2drive on 12 Nov 2014 05:50 PM
...How are the steel SIP panels supported? Beam from the gables and the panels laid on the beam?

The entire area under the SIPs then becomes conditioned space correct?

Yes like jdebree said the entire area under the SIPs is conditioned space, and that is best for the hot/humid Florida climate.

There are a number of ways to design a SIP roof, but in general they go together like you said. Ridge beams made out of steel C-joists and track are light enough to go up with scissor lifts, or even be built in place with the aid of ladders. Glu-lam beams would require a crane.

Of course you can also design a hip roof, anything you like.