Hello all. I have been lurking here for a while now and I just decided to join. I'm about to begin construction on a house and I have some questions I thought some people here could help me with.
I'm building a 2,100 Sq. Ft. two family in Western MA. I'm thinking about building a regular 2x4 frame with another 2x3 frame on the inside to create a 12" cavity for dense pack cellulose with no thermal bridging. The interior frames would just tip up. I plan to use no sheathing, just Tyvek or poly on the outside under Hardi board and perhaps poly on the inside, depending on what goes on the outside. The foundation will be either ICF or just a regular poured foundation with XPS on the outside, whichever is cheaper. Does anyone have any input on my plans?
Also I'm in dire need or recommendations on doors and windows. I'm completely lost in the selection. I really don't have any clue as to where to start. Does anyone have any recommendations on good, affordable windows? I'm thinking 3 pane and filled with some of these high tech gasses from Mars or wherever. But I'm doing all this on a limited budget (who isn't, right?) so nothing too fancy.

Thanks for having me here. This forum is a great source of information.

Colin

S-F;

if there is no sheathing how will you brace the exterior walls structurally?

With the Hardi board. I originally got the idea from this article: http://www.greenhomebuilding.com/articles/larsentruss.htm and then the architect I'm working with suggested it without me mentioning it.

Posted By S-F on 10 Feb 2011 08:06 AM
With the Hardi board. I originally got the idea from this article: http://www.greenhomebuilding.com/articles/larsentruss.htm and then the architect I'm working with suggested it without me mentioning it.

You may still need "let-in" bracing

Right. I just re read that article and saw that. Whatever method is used I'm sure the architect will cover those bases. Honestly I have never tried to frame up anything like this so it will be a learning experience.

What is going to keep the dense pack cellulose from bulging outward? If the Tyvek or poly is pushed up against the Hardi, you will trap moisture in there. It is recommended to have a drainage plane behind fiber-cement siding so it can dry properly after moisture inevitably gets in there. OSB is cheap, and it braces the wall effectively so you don't have to do the let-in bracing. I would sheath it, at least at the corners.

I do plan to use some form of sheathing at the corners. And I have decided to go with shiplap as opposed to Hardi. Hardi seems like a PITA, it's more expensive and I like wood better. Maybe I will sheath the entire house. Not sure. A lot of that depends on cost.

Alside makes an inexpensive triple pane vinyl window I have used. Make sure the opening windows are level and square when installing because the active seals are picky on sealing. Adjust glazing to optimize windows for locations. If you are going to double wall give yourself at least 24 inches of fill space. At that thickness the cellulose is an effective air block. Use Thermalblok on the studs to stop most of the conduction. Cross brace with 2x2s for air gap behind siding. Use a radiant barrier under the cross bracing. Use a raised heel truss with space for 30 inches of cellulose in the ceiling. You should use a radiant metal standing seam roof with a minimum of 16 inch spacing to allow for stick on solar panels on a south facing roof in the future. Have an air gap with a radiant barrier to the inside to the attic heavily vented. This gives you an effective R-100ish wall and an R-120 plus roof, suitable for a zero energy home. Use an in ground insulated heat recovery and tempering system. At this point you will need very little heating and no cooling. If you have solar available and build in adequate internal mass you can eliminate the need for other heating all together.

This design will save you over $100,000 in utility savings over the life of the building. The monthly utility savings will be greater than what you will add to your monthly mortgage. It will be a net positive cash flow from day one.

These are just a couple thoughts.

Brian

If double-studwall (as opposed to Larsen truss, which can be more difficult to build) going with 2x6" 24" on center framing for the structural wall will have the same number of board-feet & structural strength as 2x4" 16" o.c. and less thermal bridging (despite the deeper studs.)

OSB sheathing will be easier to turn into an air-barrier than ship-lap.

Begging to differ a bit with Brian...

Radiant barrier will buy you NOTHING in western MA (and very little anywhere, with an R40+ wall.) R100+ walls and ceilings are neither necessary nor cost-effective in this climate, but R55-60 can be in a double-studwall or Larsen Truss setup can be (an can even get you to PassiveHouse levels of heating energy use, with the right design). Before doubling the R value of the walls or attic, take a careful look at the heat loss out of the foundation & slab, beef up R values and thermal breaks accordingly. (The PassiveHouse tools are pretty good for this analysis.)

Rainscreened backventilated siding is a good idea, but the 1.5" you'd get out of 2x2s would be overkill. 1x furring (3/4") is already almost twice code requirement for (even cooler climes in) Canada, and 3x8" is "enough" for western MA. With 1.5" of gap you can pretty much guarantee rodents setting up shop in there. Using 1x furring with ample vent area at the bottom and under the eaves (with mesh to keep the critters out) does wonders for the drying capacity of the assembly.

The best way to minimize losses from glazing it to minimize the square footage. Triple glazing can buy you more view area, but decent double-panes optimally sized and typed for the solar gain balance can get you there. Double-hungs have far more air leak potential over time, so try to keep it to awnings & casements for operable windows, and don't presume that if it's a window it needs to open (ever). A lot of good north-side daylighting can be had with few square feet of fixed, well-sealed double glazed window, with lower heat gain/loss than larger, operable, triple-panes. Shrink the glazed area by 1/3 to 1/2 from the best-in-class triple panes, and you're looking at comparable heat transfer rates. With R40+ clear walls, a square foot of even the best triple panes are still worth 5 square feet of wall losses (and that's without the infiltration loss factors) but a better-class double-pane is still worth less than 10 square feet of wall area loss.

In a massive cellulose wall avoid true vapor barrier materials such as poly (or radiant-barrier foils). With a rainscreened siding approach the exterior drying capacity is highly enhanced, and you should be able to get away with ~2perm standard latex on the interior as your only vapor retarder as long as you make the interior gypsum air-tight, which would maximize the drying capacity of this very hygroscopic wall. (Robert Riversong has been successfully doing ~ R40-45 Larsen Truss designs for this climate sans-vapor retarder for quite awhile now, but you DO have to make it air-tight on the interior.) This means going on an air-sealing Jihad with a caulking gun, (and buying stock in Tremco! :-) ) Air seal every stud-plate & cavity as you go. There's no such thing as "too tight".

Great! Thanks for the replies guys. Where to begin?

First of all, I'm not going to build a 2' thick wall. It sounds cool but if I keep going like this I'll end up living in a 100 Sq. Ft. room with tunnels for doors and windows. I think I'm set with 12". Also how would that kind of wall be supported? A 2' thick foundation wall? Much of this plan is inspired by the work of Robert Riversong. He has actually done some work right in the area where I live and some of the locals know him. I have actually spoken to him recently for tips on how to dense pack such walls. The architect I'm working with and I decided on using his Larsen truss method as opposed to tilting up double walls because there will be no issues with insulating the plates. As to making a rain screen, he is not using any sheathing. And I believe that he is using ship lap also. Is he caulking all of the boards as he puts them up? That sounds crazy. What would the added cost be of sheathing with OSB and building a rain screen? In materials only mind. How is Robert Riversong getting away with what he’s doing?
As to windows, last count I think I determined that I would be using about 20 and 2 small bathroom windows. I can’t really shrink that number too much because then I’ll have no light or windows. And the wife wouldn’t move in. Neither would any prospective tenants. Did I mention that there is going to be a rental apartment in this house? I’m not really a fan of casement windows. The house I grew up in has a room filled with 6’ Pella casements and they simply suck. None of them close properly… EVER. Every fall my mother has me go back to her house to set up a ladder and push the damn things closed. I think it’s double hung for me. Could anyone recommend some decent double hung windows?

Thanks again everyone.

The Larsen truss home article says he burns a cord of wood a year. That would not be anywhere close to passive house. His HERS rating is 46. The goal is to get to 0. The last passive house I was involved with was R-120 roof, R-84 in walls and R-60 in the floor. That was in Oregon, a milder climate. The numbers I suggested are not out of line for Western, MA if you are building to zero energy use. I did not take the time to go through the actual calcs. The cost of the extra cellulose is minimal $1 per foot. Cellulose is not an effective air barrier until it is 24 inches thick per the manufacturer.

You are incorrect about the radiant barrier. It only costs about 10 cents per foot and will make a difference in cold winters and will help in the summer. It makes a bigger difference in hot areas but is still worthwhile.

In a standard home double pane windows account for 40% of the heat loss. Going to triple pane cuts that in half. In a zero energy home it is a bigger deal by far. In the last house I built the additional cost of the triple pane windows was only 50 cents a foot. So the additional cost or the suggestions is $1.60 a foot to go from a 50% energy hog to a zero energy building, easily justifiable.

I have been doing zero energy buildings since the late 70s. I have developed better more cost effective methods of getting to zero energy buildings that I now use. I did not mention the foundation stuff here and agree there are a lot of other things you can do. If you plan on building a double stud wall and if the goal is cost effective zero energy my suggestion are on the money.

By the way, how many zero energy homes have you built?

Brian

Don't shrink the number, of windows, just the size. (I usually opt for narrowing them before making them shorter in height.) You can get a remarkable amount of daylighting out of down-sized windows, but it can impinge on the view. On the sunny side you may want to UP size the glazed area for passive gains, but it pays dividends to model it correctly ahead of time to get the right balance (the PassiveHouse package is pretty cheap, built on spreadsheet software. It's a PITA to fill out every line, but it can save SO much money up front, and boost the performance/$ enough that it's a worthwhile exercise, even if you're not taking it to PassiveHouse levels overall. http://www.passivehouse.us/passiveHouse/DesignTools.html )

Riversong "gets away" with what he's doing by paying close attention to air-sealing details, particularly on the interior finish of exterior walls, making that the primary air-barrier. (He's a Tremco Acoustic Sealant devotee.) It's not every board, but every critical junction. He starts by balloon framing the interior chord of the truss with full-dimension rough sawn 2x4s, (the structural chord is the interior, not exterior as you had been proposing), and installs & seals the interior walls before insulating. (There are several features that differentiate Larsen Truss from double-studwall designs.) By making the interior chord structural the band-joists are all thermally broken, inside the bulk of the insulation, boosting it's relative performance over a double-studwall. He makes the exterior siding structural by using 3/4" drop siding over the housewrap, but there is some risk to this approach when compared to a sheathing & rainscreen approach. You can think of that as an insurance expense- it doesn't take much of an issue down the road to overshoot the material cost of sheathing & rainscreen furring. The extra inch of wall thickness is well worth it. A bunch of details & pics of Riversong's approach can be found here: http://www.builditsolar.com/Projects/SolarHomes/LarsenTruss/LarsenTruss.htm

Ship lap is great structurally, but it's more expensive than OSB. (At ~$7-7.50/sheet for 4x8s of 7/16" goods you're talking less than 25 cents/square foot- you're talking well under a grand in material cost for a typical 2100' building- probably less than $600.) And since you can make it into a pretty-good exterior air-barrier with some detailing, you can TEST & remediate the air sealing of the structure before insulating by installing the windows & doors and running a blower door test. Get it under 2ACH/50 on the empty shell, before the interior gypsum goes up- under 1ACH/50 if you can. Air-sealing is the single most cost-effective performance enhancement.

I know what you mean about larger casements' ability to close & seal correctly, but think SMALL, or at least narrow with casements and the forces on the mechanisms go down significantly, and reliablity goes up. If they NEVER opened or closed properly it's likely they were mis-installed. The types of mechanisms differ in action & quality too. Awning windows have fewer issues getting to close properly than casements, (and FIXED windows have none.) Double-hungs (particularly lower cost versions are the performance dogs of the window world- it's just too hard to get a reliable air-seal. But poorly installed none of them are worth much- they'll all leak air/water.

Brian;

point us to your website

note that I am proofing a new multi page site that will be up in the next week or so. my site is
http://www.zehtalk.com/

Brian

My plan is to have the interior chord be structural.
So Dana, what you're suggesting is that I shoot OSB to the outer chord, wrap is as usual and then create a rain screen with fur strips and then the ship lap?And caulk the hell out of the seams in the OSB? What about a vapor barrier?

And back to windows; Have you seen any of these casement windows you are speaking of after 10 + years in use? My mothers windows were probably fine for the first decade. Now after 20 + years she would tear them out and put double hung in if it wouldn't cost thousands upon thousands of dollars. When she put them in they were supposed to be the best and they are essentially disposable. If things have honestly changed then I'll look into them but otherwise I'll just buy the extra 1/2 cord of wood a year and know that my windows close and open when I want them to.

I need to get this all ironed out pretty soon or the architect will start getting tired of the changes in plans.

Posted By zehboss on 14 Feb 2011 08:43 PM
note that I am proofing a new multi page site that will be up in the next week or so. my site is
http://www.zehtalk.com/

Brian

You are a member of the USGBC ?.

Posted By Dana1 on 14 Feb 2011 05:47 PM
.... I know what you mean about larger casements' ability to close & seal correctly, but think SMALL, or at least narrow with casements and the forces on the mechanisms go down significantly, and reliablity goes up. If they NEVER opened or closed properly it's likely they were mis-installed. The types of mechanisms differ in action & quality too. Awning windows have fewer issues getting to close properly than casements, (and FIXED windows have none.) Double-hungs (particularly lower cost versions are the performance dogs of the window world- it's just too hard to get a reliable air-seal. But poorly installed none of them are worth much- they'll all leak air/water.

I too have a question on the casement windows, if I may. Would anyone want to venture some opinions on dimensions to the "think SMALL" of casements. I am especially in interested in this for south side windows (which could be larger for passive solar) and must be large enough to meet egress (bedrooms) - but I wonder about the long-term operation of the hardware. Having lived with DH windows all my life, I have no feel for this and would appreciate additional input.
Thanks!

My Parents house has (12) 24"X 72" Pella casements from 1969 that still open and close just fine. A couple of windows have the roll up insect screens busted. On one window the glass is fogged, but that was replacement glass by a local glass shop ( I put a rock through the original one as a 10 year old with a bad aim).

Casements that are built well and installed correctly, should not be an issue. If you want realy high quality windows, look for the german tilt and turn windows.

The other thing to remember is that if you actually open your windows, a casement has twice the opening as a double hung, or a slider.

Good Luck
Eric

Posted By S-F on 14 Feb 2011 09:17 PM
My plan is to have the interior chord be structural.
So Dana, what you're suggesting is that I shoot OSB to the outer chord, wrap is as usual and then create a rain screen with fur strips and then the ship lap?And caulk the hell out of the seams in the OSB? What about a vapor barrier?

And back to windows; Have you seen any of these casement windows you are speaking of after 10 + years in use? My mothers windows were probably fine for the first decade. Now after 20 + years she would tear them out and put double hung in if it wouldn't cost thousands upon thousands of dollars. When she put them in they were supposed to be the best and they are essentially disposable. If things have honestly changed then I'll look into them but otherwise I'll just buy the extra 1/2 cord of wood a year and know that my windows close and open when I want them to.

I need to get this all ironed out pretty soon or the architect will start getting tired of the changes in plans.

The air-sealing obsessed will caulk under the stud-plates, caulk the interior perimeter of each stud bay to the OSB, caulk the interior gypsum to the interior studs/plates. In a densed-packed truss wall with exterior OSB, caulking the stud plates and caulking the perimeter of the OSB to the framing as you go is step 1, then paint the exterior seams 2" each side of the crack with a quality acrylic latex paint as a bonding surface, then apply housewrap tape.  Similarly, caulk the interior gypsum as you go, and foam seal all electrical & plumbing penetrations.

Siding can be mounted directly to the furring, as long as the furring is properly through screwed to the outer chord studs, and not just hanging on the OSB.  OSB is structural(if you use the right stuff, not the thinnest & cheapest goods in the lot) and you don't need exterior shiplap to handle racking forces.  A Tyvek or similar high-perm exterior housewrap makes a highly permeable (more permeable than #15 felt) drain plane, which should be flat up against the OSB, not the siding.

With an exterior rainscreen, air-tight methods on the interior, and 12" of  cellulose to buffer winter moisture you don't really need anything more vapor retardent than standard latex as an interior vapor retarder.  If the code inspectors balk, use vapor-retardent latex primer (one coat, not two).  Under NO circumstances should you be using anything as vapor retardent as poly or foil on a 12" thick cellulose wall.  Cellulose that thick can buffer a heluva lot of water, but it also takes time to release moisture, and if you severely hamper the drying capacity to either side you're asking for A: Higher rates of settling in the cellulose (even dense-packed, unless you're going for 4lbs/ft3 in your climate), and B: higher moisture content in the structural wood (==higher rot potential).  IF you were to install a poly or foil vapor barrier, it should be between the chords (more than 35% of the distance from either the interior or exterior), not on the interior edge of the insulation the way you would in a thinner studwall.  (With cellulose even 2x6 studwall construction works better without poly on the interior, especially when there's an exterior rainscreen maximizing drying to the exterior.)

I have four 32" x 60" middle-of the-road Pella casements in a family room addition that are a bit over a dozen years old, still working fine.  But narrower ones would close tighter/quicker.  If I had it to do over again I would opt for narrower (and shorter), since it's the highest heat-loss room in the house due to total glazed area.  I've seen ~18" wide Andersens 3+ decades old that work GREAT!  Mis-installation, or settling/frost-heaving foundations can mess up any window- don't let your mother's experience drive this decision.  Awing windows tend to work somewhat better than casements, since you don't have a moment-arm & gravity working against the hinge- gravity is working in your favor rather than at cross-angles, and the hinge is loaded evenly.

Riversong uses 14-16" wide copper flashing as a both a capillary break and termite shield between the foundation and a very-wide single foundation sill for the trusses, a practice well worth considering.  even if you split the foundation sill(s) between inner & outer chord, a full width METAL capillary break caulked/foamed in place is preferable to foamy sill gasket materials when looking at a 12" thick hygroscopic insulation layer.

Also, whether ICF or insulated from the exterior, put a 10mil poly capillary break between the footing and foundation wall, and float the slab with at least 1.5" of XPS between the slab edge and foundation wall as a capillary break.  This will minimize the moisture in foundation wall mitigating mold issues.  DO insulate the slab as well.  There's a good economic rationale for R16 if you use Type-II EPS rather than more expensive XPS.  (IIRC, R10 under slabs is code-min now in Maine, but R20 isn't unreasonable if you go with lower-cost goods.) In your climate and subsoil temps, going with something like half or higher of whatever your clear-wall R is for the above grade walls is the ballpark you should be shooting for.  On the foundation walls you'll want to split the difference, at least down to the frost line, which may be 2/3 of the way down to the footing in your neighborhood. (FWIW: I retrofitted R19-R20 to the interior of my foundation walls in Worcester 2x4 stick-built antique, resulting in a ~15-18% cut in heating fuel use for the whole structure.  The slab is on my list, but it's down there a ways- as a retrofit it's a much bigger job than in new construction.  If I had the headroom I'd insulate above the slab, but I don't.) 

Also see:  http://www.buildingscience.com/documents/reports/rr-1003-building-america-high-r-foundations-case-study-analysis    (Look carefully at the details & discussion for Case 11 if you're going with exterior- foam only,  Case 13 if ICF. Note the locations of all capillary breaks.)

OK. Well, after a couple harrowing weeks I think I'm ready to give my building plans the all systems go stamp. Interest rates have gone up and then back down so it's been difficult to ascertain whether or not I will have the $ to build. Any way, wile looking through the Building Science paper on Walls I noticed that they have a Larsen truss analysis. Interestingly the outer chord in their design hangs below the bottom plate. Before I have the final meeting with the architect on Wednesday, what is keeping the outer chord from sagging over time? Does it simply rely on the trusses?