I live in Chicago and am building a home and to be honest am completely confused at this point. I want to build an efficient home but it's hard to get a straight answer in person. I am hoping an internet forum like this will get me some unbiased untempered answers. the back of the home faces E, the front faces W. On the E we have 5 sliders. On the W there is a large curtainwall about 12 feet tall by 6 feet wide. We plan on using very efficient glass on the curtain wall with an interior mechanical sunshade. the lot is wooded on the E and W and minimal windows on the S where there is another home on that side (street runs N/S with 10' setbacks). I would like radiant floor in basement/garage. We will have forced air for cooling in summer. I have been debating the solar thermal hot water with the solar guy who says using it to backup the furnace with a coil that does furnace heat "assist" is the way to go. The solar hot water is expensive. $25k. I would still need to add a boiler to get radiant basement/garage. I don't know what to do. The basement is approx 1500 SF. Garage is 3 car, and I don't need a 72 deg garage. 50-55 deg is fine. Exterior walls will be 2x6 with closed cell plus a layer of foam board for a total of R20. Roof is R38 insulated with metal standing seam roofing planned. any suggestions?

I should mention the metal roof will be light gray to reflect heat, the solar heat system has a 120 gal tank that goes up to 170 degrees. The panels should get direct sun from aroun 10-6pm.

You are going to flail unless you come up with a plan. $25K for solar hot water in Chicago? What's that about?
Are you trying to tie in the solar hot water with the heating system?
And you already did forced air but you want radiant, too?
Do you know what the actual heating and cooling needs of this structure are?

The solar for DHW only should cost $6K for a cheap system to $12k for a really good one (no Chinese components, my bias), installed. If you want to use it for heating to any degree, you are better off spending the money on your insulation and passive solar first, then start thinking about the heating side. Design your heating so that you need the lowest water temp possible to do the job, which would be below 40C (104F).

$25K for solar hot water in Chicago? What's that about?

Agree. The quote is for $28k, after rebates it is around $11k I believe, for 4 4x10 AET collectors in the system. Or $12k, $5.5k after rebates, for two 4x8 panels. Using several heating load calculators online, the home will require approx 45k BTU/hr. (builditsolar.com/borschengineering.com)

Are you trying to tie in the solar hot water with the heating system?

Yes, the solar guy said for $1800 more I can add a coil that fits in the furnace that does furnace assist. That is another $2k though!

And you already did forced air but you want radiant, too?

Home is not built yet.

If you want to use it for heating to any degree, you are better off spending the money on your insulation and passive solar first, then start thinking about the heating side.

S facing wall has a home there and only upstairs bedrooms would get passive solar so it is not that much of an option. West wall has lots of glass but I need to limit solar gain in the summer (Chicago zone 5).

Design your heating so that you need the lowest water temp possible to do the job, which would be below 40C (104F).

Could you please elaborate on what you mean by "design your heating"...?

So, 45K BTU/hr to heat the house and what portion of that is supplied by the assist from the solar collectors? What is the size of the home?

ANY passive solar, when used properly, is the biggest bang for the buck, but aren't your west windows going to cost you more in cooling than you will receive in heating assistance?

Exterior walls will be 2x6 with closed cell plus a layer of foam board for a total of R20. Roof is R38 insulated with metal standing seam roofing planned. any suggestions?

Aren't these bare minimum requirements for your climate zone? Can you get any cost/benefit from improving your insulation? Can you really get away with R38 for your entire roof under 2012 code? Why are you only getting R20 out of your exterior walls and what is the cost of all that closed cell under foam board? Is that 1" or 2" of exterior foam?

So, 45K BTU/hr to heat the house and what portion of that is supplied by the assist from the solar collectors? What is the size of the home?

Perhaps I wasn't clear. The home is not built yet. 3300 SF. Solar PV system quoted is either 5.2kW or 6.1kW I have not decided on any HVAC/Heating/Cooling at this time - this is the whole point of this thread. I am leaning toward a air sourced heat pump with elec assist that the PV system can run for free during the day.

aren't your west windows going to cost you more in cooling than you will receive in heating assistance?

I stated I plan to use low U/SHCG on the West curtainwall with an interior shade already.

"Exterior walls will be 2x6 with closed cell plus a layer of foam board for a total of R20. Roof is R38 insulated with metal standing seam roofing planned. any suggestions? "

Aren't these bare minimum requirements for your climate zone? Can you get any cost/benefit from improving your insulation? Can you really get away with R38 for your entire roof under 2012 code? Why are you only getting R20 out of your exterior walls and what is the cost of all that closed cell under foam board? Is that 1" or 2" of exterior foam?

The wall section calls for R19 batt with R3 zipsheathing over that. I am trying to figure this out now. I am not an expert in every building product available or their combination of uses to achieve best cost benefit. Hence the reason for this post. I appreciate the attention/questions.

R19 batts are about the crummiest thing you could do for cavity insulation, and your stackup barely meets IRC code for US climate zone 5 (Chicago):

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_11_sec002.htm

R19 batts are only R18 after compression to 5.5", and with the thermal bridging factored, with standard ZIP sheathing the whole-wall R comes in at about R13, with the R3 R-ZIP you're at about R15, R15.5.

If you're going to build with 2x6 framing and heat it with solar (passive or active) the LOWEST whole-wall R you should be condering is R30, and R35-40 isn't insane. A common and easy-to-build way hit R30+ with 2x6 framing would be use standard OSB or plywood sheathing, and add 3-4" of rigid polyiso foam on the exterior, held in place with 1x furring through-screwed to the studs 24" o.c. with pancake-head timber screws (eg. FastenMaster HeadLok) to minimize the thermal bridging through the screws. More:

http://www.buildingscience.com/documents/guides-and-manuals/gm-guide-insulating-sheathing

http://www.greenbuildingadvisor.com/blogs/dept/musings/how-install-rigid-foam-sheathing

Use of closed cell foam between studs is a total waste of good foam and imparts a fairly heavy greenhouse gas hit from the HFC245fa blowing agent used. The difference in whole-wall value between 5" of closed cell foam (the max you can really do in 2x6, since it's not easily trimmable) and a full-fill of 5.5" of open cell foam (which is water-blown, low greenhouse gas issue) or damp sprayed cellulose is about R2. Adding an half-inch to the thickness of the exterior polyiso would be both higher performance and less environmental impact. Polyiso is blow with pentane, with less than 1% of the lifecycle global warming impact of HFC245fa. XPS (pink, blue, green) is even worse that closed cell polyurethane, due the heavy portion of HFC134a blowing agent (40% more damaging than HFC245fa.)

To reap the thermal performance of the insuration, the place needs to be as air-tight as possible- glue or caulk the framing to the sheathing, caulk between doubled-up top headers, and between the bottom plates & subfloor, subfloor & band-joist, band-joist & foundation sill, and use a bead of expanding foam between the sill-gasket and foundation sill to guarantee air tightness at the concrete/wood interface. Define the primary air barrier in the plans, and the details of how it connects on all sides of the cube, from the vapor barrier under the slab, up the foundation walls to the foundation sill & above grade wall, to the attic floor plane, and make sure that it is continuous, with no ill-defined offsets. Window & door flashing air sealing detials must be continuous with the air-barrier.

Even a 55F basement adds 10,000BTU/hr or more to your heating system sizing requirements in a zone-5 climate. Build the foundation using R20-R22 insulating concrete forms (ICF), and put 3" of EPS (not XPS) under the slab if not radiant, 4" if radiant. Insulating and air sealing the basement is far more effective than anything you could ever do to the basement ceiling/first-floor floor boundary, which is damned near impossible to air seal adequately, and insulating it only makes the basement a few degrees cooler during the humid summer, increasing the mold hazard for everything stored there, and isolating the boiler's distribution loss heat from the rest of the house, truly losing/wasting that heat. Insuatating both the slab walls (floating the slabs for no thermal bridging at the walls) is the right way to go. If not ICF, put 2" of EPS against the foundation wall that extends down to slab-foam, and build a non-structural 2x4 studwall insulated with R15 rock wool and NO VAPOR BARRIER trapping the foam to the wall, and use spray foam to insulate & air seal the band joist & foundation sill.

With better windows, attention to all thermal bridging, an R60+ attic, and rigorous air-sealing on all 6 sides of the cube you should be able to reduce the heat load at Chicago's ~ 0F 99% outside design temp to well under 30,000BTU/hr, and probably under 25,000BTU/hr.

FWIW: Sliders are fairly air-leaky compared to swinging patio doors that have better weatherstripping options. Be sure not to over-glaze a high-R home your you'll cook yourself out, even in winter.

Solar PV system quoted is either 5.2kW or 6.1kW

There's a PV system, too?

How set are you on radiant garage/basement? What is the layout of the rest of the house? Main floor with bedrooms on a second floor?

What are your goals with this home? Minimal usage of grid energy? Minimal environmental impact? Self-sufficiency? "Wow" factor? Comfort?

I have radiant in my walk-out basement/drive-under garage, 30 X 40 basement area, 30 X 24 garage. Ranch is 30 X 64.

Glad your researching before you build so you won't make the same mistakes (not really wrong but could have done better) I made.

I am using a ground source HP to heat my radiant water. Most efficient below 100*F, same with solar.

DIY'ed the 1/2" pex-al-pex tubing in the slab. Was told that 12" on center for the tubing would work. 1200 sq. ft. 4 tubes at 300' ea. is what I was sold. If I knew then... I would have done more runs of shorter lengths.
Like 8 tubes at 200', more tubing means lower temp water can be used.

That's what Mike was talking about when he said "Design your heating so that you need the lowest water temp possible to do the job".

We did the insulation under the slab ourselves also. Did the perimeter of the slab cutting the tops of the rigid foam to 45*. But forgot about door openings. Cement guys put up boards to hold back cement at doors, I should have put foam strips maybe 5" in from the form boards.
Especially at the garage doors, floors of garages extend out under overhead doors. That cement should have a thermal break(rigid insulation) from the slab being heated.

ChrisJ

I would convert all the options to ROI.

For air sealing, I'd avoid dependence on caulk, glues, films and spray foams and use tapes, gaskets and solid boards (Zip sheathing is nice). And of course test the results.

There's a PV system, too?

How set are you on radiant garage/basement? What is the layout of the rest of the house? Main floor with bedrooms on a second floor?

What are your goals with this home? Minimal usage of grid energy? Minimal environmental impact? Self-sufficiency? "Wow" factor? Comfort?

Layout has one bedroom on main floor. Three bedrooms up above. Greatroom vaulted ceiling in center. I want a combo of all you are posting: less energy, some self sufficiency, of course wow (won't build an ugly house) and I don't want to be uncomfortable... There is likely a PV and solar system. Heat loads using other calculators were 25k-40k (Dana commented on another thread the calculators I used were not optimal).

We did the insulation under the slab ourselves also. Did the perimeter of the slab cutting the tops of the rigid foam to 45*. But forgot about door openings. Cement guys put up boards to hold back cement at doors, I should have put foam strips maybe 5" in from the form boards.
Especially at the garage doors, floors of garages extend out under overhead doors. That cement should have a thermal break(rigid insulation) from the slab being heated.

ChrisJ

What do you mean by cutting at 45deg? Also are you saying to put the foam break on the outside of the garage or inside where the door would close?

Dana Im reviewing your articles. I notice the first references the thermal break using zipsheathing which is what I am doing. The question is the thickness of the foam.

"What do you mean by cutting at 45deg? Also are you saying to put the foam break on the outside of the garage or inside where the door would close?"

Cutting at 45*, I have a traditional poured concrete foundation. Foam under the slab and around the perimeter. The pieces around the edges were attached to the walls at the finished floor height with the tops cut at an angle. Keeps the slab from touching the walls, heat transfers to cold. If your doing ICF walls disregard.

Inside where the door would close. That way the part of the garage floor that is always outside can be outdoor temp.

Posted By Surfsup on 20 Aug 2013 09:10 PM
Dana Im reviewing your articles. I notice the first references the thermal break using zipsheathing which is what I am doing. The question is the thickness of the foam.

Which is indeed the question.

In your climate R3 sheathing isn't even sufficient exterior-R to avoid wintertime moisture accumulation inside the wall cavity without an interior side vapor barrier (or at least a class-II vapor retarder).  The total whole-wall R is also on the very skimpy side (barely code-min) for a building with real performance requirements, and a high performance building enclosure is what you need if you're going to be offsetting any significant fraction of your primary energy with either passive solar or PV/active-solar.

Design your heating so that you need the lowest water temp possible to do the job, which would be below 40C (104F).

Could you please elaborate on what you mean by "design your heating"...?

For example, if you have 12" tube spacing you may need 110F entering water temps but if you had a 6" spacing you may only need 90F and when designing for any solar thermal, the lower the supply temps needed, the more use you will get from the system and the less backup you will need. I know a guy in Ireland that puts the tube at 4-6" and he is running off heat pumps and solar with very high COPs. 

All this being said, if the controls are not up to the task, you won't get the efficiency you need which mean a control that measures all the temps in the right places and someone who is knowledgeable enough to program it.

In your climate R3 sheathing isn't even sufficient exterior-R to avoid wintertime moisture accumulation inside the wall cavity without an interior side vapor barrier (or at least a class-II vapor retarder). The total whole-wall R is also on the very skimpy side (barely code-min) for a building with real performance requirements, and a high performance building enclosure is what you need if you're going to be offsetting any significant fraction of your primary energy with either passive solar or PV/active-solar.

Okay so since I am asking and we are discussing how can I develop a 2x6 wall section that is R25 without breaking the bank?

Mikesolar, could i use larger diameter tube? Such as 3/4" rather than 1/2" at a 12" spacing for the garage and basement? I don't need perfect heat in eaither of these slabs. Garage will only be set to 55 anyway. Basement maybe 65 or 68?

The large tube should provide less resistance and better thermal footprint in contact with the concrete to transfer heat. The circumference of a 3/4 vs 1/2 tube is 50% greater which is 50% more conduction. The larger tube also provides less pump pressure.