I've been trying to find some sort of diagram and came across this http://www.buildingscience.com/documents/digests/bsd-103-understanding-basements
What do you think of figure 10?

Will this seal my house up so tight that I will need an air exchanger

Nothing is magic, no. You will have to spend a lot of attention to sealing at all stages to get a well sealed home. Framing, sheathing, windows, doors, roof, even penetrations all need treatment to get the place sealed. I doubt that you will be able to get it so well sealed that you have to have a heat recovery ventilator, although they are good to have. Code does allow exhaust only ventilation which is accomplished by good old bathroom and kitchen fans.

Posted By ultimatehomestead on 22 Sep 2013 08:53 PM
With my footings in, I'll have to see if they excavated deep enough for foam underneath.
Should there still be an external house wrap such as tyvek on top of the sheeting? Will this seal my house up so tight that I will need an air exchanger?

You might run into a problem with the footing and slab height if you attempt to put foam under the slab now. Talk to the contractor and see what he says. I am leaning towards him saying "no."

I would also try and get EPS instead of XPS, both in terms of cost and green house gases. XPS requires a lot of nasty gasses to create, EPS is much more friendly. If you have termites, get the EPS treated with termite treatment.

Judging by what you stated about the contractor, the house will NOT be so tight that you will require an ERV or HRV. Unless the contractor is schooled in building tight homes, he/she will not build it that tight. A tight home doesn't happen by accident, it requires very close attention to detail and practices that this builder is NOT knowledgeable in. If he doesn't put foam under slabs and doesn't insulate outer basement walls, then I can confidently state he is not building to passive house standards.

As far as a vapor barrier goes, Tyvek could work but it in and of itself is not a complete air barrier and will not make the house too "tight" that it will require mechanical ventilation.

RE: under slab
Insulate under the slab - You'll regret not insulating long after you get used to the ceiling that's 2" lower. The vapor barrier ideally goes above the foam, directly under the slab, but if you do it the other way, it'll work. And yes, you need a thermal break at the floor/wall/footing. 2" is ideal; 1" is lots better than nothing.

Posted By Alton on 22 Sep 2013 09:37 PM
. . . I think I will need 2" of XPS foam under the slab for an R10. That should be on top of a vapor barrier (poly film) which is on top of gravel?   . . .

You might want to check with Dana1 about the best location for the vapor barrier.  Also, if there is space, using EPS might be better and less expensive.

It doesn't matter where the vapor barrier goes, unless you plan on a finished floor on that slab, in which case it goes on top of the foam. If it's under the foam there will be pockets/bubbles of space between the foam & poly that can trap a significant amount of liquid water- but not permanently. The water WILL come out- but it comes out slowly through 2" of foam, an if you so much as painted the floor in the first couple of years the likelihood is that the paint would blister and fail.  With the poly between the foam & concrete, the concrete compresses out and fills any bubbles when it's poured & vibrated, and the high vapor permeance of concrete means any residual excess moisture of the pour is gone in the first year.

It's generally cheaper and in several ways better to use EPS rather than XPS under slabs.  XPS has a higher R/inch, due to the HFC134a blowing agent that is semi-trapped in it's closed cell structures.  But it loses most of it, and it's R value along with it over a handful of decades, and fully dissipated it's pretty much the same R value as EPS of equivalent thickness & density.   EPS is blown with pentane, a much smaller molecule that is nearly fully dissipated by the time it's at the distributor's yard, and the rated R value is the fully-dissipated value, not some decade long average as is the case with XPS.  (And that's not even getting into the global warming potential of the HFC134a, which is ~1400x CO2, to pentane's ~7x CO2.)   EPS has a higher fraction of closed cells, but interstitial spaces in the macroscopic beads. Under immersion conditions it initially takes on moisture much more quickly than XPS but it stops at ~7%, where it's R-value is about 90% of what it is in it's non-saturated state. When the tide goes out it gives up that moisture just as quickly as it takes it on. XPS takes on moisture more slowly, but hangs onto it much longer (almost permanently, in earth burial situations.)

Posted By Lbear on 23 Sep 2013 01:35 AM

Posted By ultimatehomestead on 22 Sep 2013 08:53 PM
With my footings in, I'll have to see if they excavated deep enough for foam underneath.
Should there still be an external house wrap such as tyvek on top of the sheeting? Will this seal my house up so tight that I will need an air exchanger?

You might run into a problem with the footing and slab height if you attempt to put foam under the slab now. Talk to the contractor and see what he says. I am leaning towards him saying "no."

I would also try and get EPS instead of XPS, both in terms of cost and green house gases. XPS requires a lot of nasty gasses to create, EPS is much more friendly. If you have termites, get the EPS treated with termite treatment.

Judging by what you stated about the contractor, the house will NOT be so tight that you will require an ERV or HRV. Unless the contractor is schooled in building tight homes, he/she will not build it that tight. A tight home doesn't happen by accident, it requires very close attention to detail and practices that this builder is NOT knowledgeable in. If he doesn't put foam under slabs and doesn't insulate outer basement walls, then I can confidently state he is not building to passive house standards.

As far as a vapor barrier goes, Tyvek could work but it in and of itself is not a complete air barrier and will not make the house too "tight" that it will require mechanical ventilation.

All houses need ventilation, even leaky houses, since the locations of the leaks aren't guaranteed to be located where the ventilation is most needed.  All houses built to IRC 2012 tested-tightness of 3ACH/50 max do too, but MOST custom houses already being built in the upper midwest would meet that spec, even if some tract-houses wouldn't.  

An HRV in a new home that size is a ~$1500-2000 cost adder, but takes all the guesswork out of it- air is ducted & exhausted from every room, and YOU get to decide the ventilation rate by how you operate it. There's no real science behind ASHRAE 62.2 ventilation rates, but anything that gets installed should be sized to deliver that much. But there's no law that says you need to operate it at those rates, and in ND that would be excessively drying in winter, as well as energy consumptive.

Tyvek is not a vapor barrier- it has VERY high vapor permeance- much higher than #15felt in fact, but  about 4-5 orders of magnitude (10,000- 100,000x) higher than foil facers on polyiso.  It can be detailed as an AIR barrier, but sealing the structural sheathing as an air barrier and taping the facers on the iso are more important.

With exterior foam you'll still need a weather resistant barrier (WRB), such as housewrap or #15 felt. For thin foam with foil facers it's generally better to use a crinkly type housewrap, and place it between the foam & sheathing, lapping it correctly with the window & door flashing.  With thick exterior foam it's sometimes desirable to mount the windows "outie", with the glass roughly co-planar with the exterior of the foam rather than co-planar with the sheathing, in which case you'd need the WRB on the exterior side of the foam to be able to be continuous with the window flashing details.  (I've seen foam as thick as 6" on the outside of super-insulated buildings in New England, but 3-4" is more common. At 3-4" I've seen both "outie" and "innie" window mounting, but only "innie" at sub-2" foam-overs.)

An HRV in a new home that size is a ~$1500-2000 cost adder

Unfortunately, you need to budget a bit more than that as the unit itself costs about $1200 and then there are the penetrations and the ducting and the outlets cost something if you want anything that looks good or has some function to it.

Good news from the builder. I can still get the 2" of foam under the slab and we will be doing it that way. I hope you all won't flame me too much, but I will be insulating the basement as shown in the building science figure I posted earlier. 2" foam under the foundation and I will have 1" foam on the interior of the basement, followed by 2x4 or 2x6 with batts of some sort. I am looking at it from a good, better, best view and hopefully chose "better".

An additional idea I had today was to have the well drillers for the geothermal drill me an extra well for my house. I will most likely just use it for watering my 2.3 acres, but I like the idea of my own water source if necessary. I'm kind of an emergency preparedness guy and will also have a propane home standby generator. My thought on the well was that I'll already have them out there, water should be somewhere around 25 ft deep, and it will officially be part of the geothermal system and I may be able to get the 45% tax credits on that as well. I'm thinking it will end up being a few hundred bucks more is all, and I can live with that.

I will have a cathedral ceiling on this property and was looking for ways to upgrade my insulation there now as well. Any recommendations that may fit my "good, better, best" approach?

Posted By ICFHybrid on 23 Sep 2013 08:21 PM

An HRV in a new home that size is a ~$1500-2000 cost adder

Unfortunately, you need to budget a bit more than that as the unit itself costs about $1200 and then there are the penetrations and the ducting and the outlets cost something if you want anything that looks good or has some function to it.

In his case volume is small, the layout is dead simple & fairly open, and it's reasonable to not have dedicated supplies & returns for every room.  In this instances it'll work fine to HRV just the bigger common area (one supply, one return), and duty-cycle the geothermal system's air handler for distribution to the other rooms as-needed.  It would be hard to get it as low as $1500 with union-scale labor, but pretty easy as a DIY.

Posted By ultimatehomestead on 24 Sep 2013 01:12 PM
Good news from the builder. I can still get the 2" of foam under the slab and we will be doing it that way. I hope you all won't flame me too much, but I will be insulating the basement as shown in the building science figure I posted earlier. 2" foam under the foundation and I will have 1" foam on the interior of the basement, followed by 2x4 or 2x6 with batts of some sort. I am looking at it from a good, better, best view and hopefully chose "better".

An additional idea I had today was to have the well drillers for the geothermal drill me an extra well for my house. I will most likely just use it for watering my 2.3 acres, but I like the idea of my own water source if necessary. I'm kind of an emergency preparedness guy and will also have a propane home standby generator. My thought on the well was that I'll already have them out there, water should be somewhere around 25 ft deep, and it will officially be part of the geothermal system and I may be able to get the 45% tax credits on that as well. I'm thinking it will end up being a few hundred bucks more is all, and I can live with that.

I will have a cathedral ceiling on this property and was looking for ways to upgrade my insulation there now as well. Any recommendations that may fit my "good, better, best" approach?

For the basement wall foam in your climate zone you need 2" of polyiso if going with 2x6 & batts, 1.5" if 2x4. You're in climate zone 6, the-cold edge of zone 6. http://publicecodes.cyberregs.com/i...par025.htm

Cathedral ceiling work best if you have at least part of the code-R on the EXTERIOR of the roof deck and  go un-vented, which can be expensive.  In zone 6 you need at least R25 ( 4" of polyiso, or 6" of EPS ) above the roof deck for an unvented approach to work, but you could then finish out the R on the inside with unfaced R25-R30 batts or open cell foam to hit R50-55. To attach the shingles you need to add a 1/2" OSB or plywood nailer deck above the foam, through-screwed to the rafters 24" o.c. with pancake head timber screws (FastenMaster HeadLok or similar. Box stores carry some lengths of HeadLoks.)   See: http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_8_sec006.htm

The approach is sound, and eliminates mold/rot potential at the roof deck, and can be made very air-tight.  But it doesn't fall under "...inexpensive ways to go green".  It's a big cost uptick on an attic floor high-R cellulose solution with a vented attic.

A vented cathedral ceiling requires 1.5" minimum air gap between the interior of the roof deck & insulation (2" is better) and continuous soffit & ridge venting to keep the roof deck dry, but that also promotes stack effect infiltration pulling conditioned air through the ceiling. It also makes for a VERY thick roof assembly.  Best you can do with 2x12 rafters is high density R38s and an interior side poly vapor barrier.

Then there's the cheaters approach, which works too but doesn't meet the letter of code: Spray 2" of closed cell foam on the underside of the roof deck (~R12), and stuff the other 9-1/2" with unfaced high density batts, or damp sprayed cellulose (or damp sprayed Certainteed Spider), with no interior side vapor retarder.   That gets up to the requisite R50ish center-cavity R value, and the vapor retardency of the 2" of foam is sufficient to limit moisture loading of the roof deck during the winter, but still vapor open enough to dry seasonally. The Building Science guys did a whole series of very good simulations of different unvented stackups using different climate data, and 2" of close cell +  high density fiber works everywhere. See Table 3 in this document.

Whatever you do, DON'T put any recessed lights into a cathedral ceiling (or even into a vented attic floor for that matter), as those become 24/365 convection chimneys sucking heated/conditioned air out of your house, and create localized melting of snow to generate ice dams, etc. 

Thank you for the correction on the basement foam. I misread that as only applicable on an exterior wall so I'll get that corrected.

4 to 6" is a LOT of exterior foam! It seems like that will not only be expensive in itself, but the trimming around it seems cost prohibitive as well. Sadly, it looks like I'll be doing some high density batts. I liked the 2" of spray foam + high density fiber but (if I'm reading it right) does not meet code.

I do have 8 recessed lights bid out in the cathedral ceiling and will likely have to get approval from the Mrs. to pull them from the design. Are the recessed light insulating covers worth anything?

I came up with around $10,000 to do upgrades and it looks like it will be split between foam in the basement (for me) and a fireplace upstairs for her. Oh the joys of compromise.

I also wanted to take another opportunity to thank everyone for the advice. This may not be a high performance home, but it will definitely end up much more efficient thanks to you guys.

Posted By Dana1 on 23 Sep 2013 03:19 PM

It doesn't matter where the vapor barrier goes, unless you plan on a finished floor on that slab, in which case it goes on top of the foam. If it's under the foam there will be pockets/bubbles of space between the foam & poly that can trap a significant amount of liquid water- but not permanently. The water WILL come out- but it comes out slowly through 2" of foam, an if you so much as painted the floor in the first couple of years the likelihood is that the paint would blister and fail.  With the poly between the foam & concrete, the concrete compresses out and fills any bubbles when it's poured & vibrated, and the high vapor permeance of concrete means any residual excess moisture of the pour is gone in the first year.

If one wanted to paint the concrete floor with epoxy, your advise would be to put the vapor barrier on top of the EPS foam? How long (months or years) does one have to wait before the concrete slab can be painted with a coating?

I would assume that InsulDeck (2nd floor) would dry via the top of the unfinished slab.

I came up with around $10,000 to do upgrades and it looks like it will be split between foam in the basement (for me) and a fireplace upstairs for her. Oh the joys of compromise.

Wait a minute. Since the foam in the basement is "your" upgrade, do you also get the amount of money saved each month by the reduced energy requirement to be your "mad" money?

And, who is really going to be cutting and schlepping the wood for HER fireplace? This doesn't sound equitable to me at all.

Haha, yes it will be my "mad" money. It will be a gas fireplace, so I can't complain too much! Plus, no one would listen if I did.

I went out to the job site and they have the forms up for the cement walls and they have hauled in around 1200 yards of dirt. It is looking pretty good.

That's 100 truckloads. Is that for floodplain elevation?

Nope, just bringing a large portion of the lot up a couple of feet so I wouldn't be the low lot in the area. It is partially aesthetic, but I also like the drainage to be away from my lot and towards what will be the trees around the perimeter.

Posted By ultimatehomestead on 24 Sep 2013 05:24 PM
Thank you for the correction on the basement foam. I misread that as only applicable on an exterior wall so I'll get that corrected.

4 to 6" is a LOT of exterior foam! It seems like that will not only be expensive in itself, but the trimming around it seems cost prohibitive as well. Sadly, it looks like I'll be doing some high density batts. I liked the 2" of spray foam + high density fiber but (if I'm reading it right) does not meet code.

I do have 8 recessed lights bid out in the cathedral ceiling and will likely have to get approval from the Mrs. to pull them from the design. Are the recessed light insulating covers worth anything?

I came up with around $10,000 to do upgrades and it looks like it will be split between foam in the basement (for me) and a fireplace upstairs for her. Oh the joys of compromise.

I also wanted to take another opportunity to thank everyone for the advice. This may not be a high performance home, but it will definitely end up much more efficient thanks to you guys.

The whole reason John Straube et al  did the simulations in RR-1001 was to point out that the IRC has it wrong when applying the same R-value minimums to interior applied high density/low permeance foam as is required for an above-the deck approach.  The tool they used was WUFI, which is an extremely well-vetted & verified moisture migration modeling tool developed by the Fraunhofer Institute in Germany, but widely used by building scientists and performance builders in the US, and is the tool of choice for building scientists within the US D.O.E.  It's available as a freebie download from the Oak Ridge National Laboratory website if you want to really get into it, but be forewarned, it's not a 'building science for dummies" kind of tool- garbage in WILL reliably deliver garbage out.  But I trust the likes of Straube to get it right.

You can also split the difference, putting 2.5-3" of foam on the exterior and 2" of closed cell foam on the interior, with the rest as fiber, which looks a bit more like the code recommendation, but has the vapor-retardency protection of the interior foam as in the R-1001 document's approach.

Recessed lights in a cathedral ceiling are an energy disaster, especially if you're pulling back to R38 HD batts.  Using gasketed air-tight insulation contact fixtures helps, but you're creating a thin spot in the insulation at the point where you're applying the heat. There's no avoiding the snow-melt issue.  Best you can do is find the lowest-profile LED fixture that you can, which lowers the heat output, but it's still a problem, even at 10 watts.

An open hearth fireplace is an efficiency disaster sucking air out of your house 24/365, with sub-20% efficiency while burning. Gas/propane burning stove can hit the 70s on efficiency but rarely are sealed combustion, which is important in a tight house from a backdrafting risk point of view. A nice woodstove with a ducted combustion air option and a big glass viewing window delivers most of the ambience of  fireplace, with low backdrafting potential and much higher wood-burning efficiency.  (I'm partial to the little Hearthstone soapstone stoves myself, but there are others.) With a sub-3-ton heat load it's easy to oversize wood-burners- look at the BTU firing rates, not the "heats xxxx square feet" numbers.  A 35,000 BTU/hr wood stove could heat your whole house on design day, but a 150,000BTU/hr fireplace would turn the place into a sauna. 

I can, and sometimes do heat my sub-code-R but tighter than average ~2400' house with a ~50,000 BTU/hr woodstove, which is about 1.5x oversized for my design condition load.  She loves it, but she's not the one cutting splitting & stacking the wood. (S'pose I gotta earn my keep somehoaw, eh?  :-) )

Posted By Dana1 on 26 Sep 2013 05:21 PM

Recessed lights in a cathedral ceiling are an energy disaster, especially if you're pulling back to R38 HD batts.  Using gasketed air-tight insulation contact fixtures helps, but you're creating a thin spot in the insulation at the point where you're applying the heat. There's no avoiding the snow-melt issue.  Best you can do is find the lowest-profile LED fixture that you can, which lowers the heat output, but it's still a problem, even at 10 watts.

An open hearth fireplace is an efficiency disaster sucking air out of your house 24/365, with sub-20% efficiency while burning.

Recessed lights are of the devil. It's an old building method that won't go away. Bad habits die hard. On a cathedral ceiling it will be a huge energy penalty like Dana mentioned.

An open hearth fireplace immediately fails you if you are trying to achieve Passive House standards. It's an automatic fail. I've had homes with such fireplaces and they would just funnel air & money right out the chimney. I made my electric company rich paying high electric bills.

I'm at the airport headed to Vegas but thought I would quick check in with ya'll. I have basement walls poured and realized I needed a drain added to the basement for my wet bar. The fireplace I'm planning on will be propane so I can get the dual fuel rate from the utility. Still trying to come up with my plan for ceiling/roof insulation.

I'm using a number of recessed LED cans (horrors!) I have a test model in my barn that stays on 24/7, and it is only slightly warm- you can barely feel it. Here in SC, the climate is so mild I don't think they will be an issue. Snow is rare, and melts in a matter of hours anyway. I used 'air-tight, insulation contact' cans, but they aren't very tight. It appears that the only real seal is the gasket on the bezel. I plan to built boxes out of foil-lined foam to go over each can to reduce the effect of thin spots in the insulation. Does anyone know if I can safely seal the cans themselves? There is a pretty big gap in places that could be sealed with aluminum tape. Or can you spray foam on them when the ceiling is flashed prior to cellulose?