Was totally sold on this for reducing framing factor, but I've been warned by an architect that I might have wavy walls. He's recommending tried and true 16" OC. This guy designs "green" buildings, so I was taken aback by this recommendation a little. I would think that if 24" OC walls consistently turned out wavy, then it would be a short lived fad. I can imagine it wouldn't be do-able with 1/2" drywall, but 5/8" would probably give adequate strength to horizontal joints. Is it worth me sweating about this? I can add a little more foam to the exterior to make up for it and rest easy with 16" OC. Not sure how much extra PITA (and upcharge) getting a contractor to do 5/8" everywhere would be and if it would be worth it. Thanks....

Its the exterior sheathing that can get wavy, and it does with standard sheathing and your siding will reflect it. I would try a 5/8 exterior sheathing.

Done correctly OVE construction is fine. It takes more thought and less wood. You do have to be more careful where wall cabinets will be placed and add backers so you have something to screw into. I would do this anyway so it is no big deal You also need to think out ahead of time locations for switches, and outlets etc as there will be less places to put them, but this just takes planning. Wavy walls come from using non straight studs, use kiln dried fir studs for the parts that need to be straight. A lot of framers like to just fill spaces with studs.

Also pay close attention to headers. It is common to way oversize headers and end up with a large space over every window and door that is poorly insulated. Often you can use a single thickness of LVL and then a nailer so you have something to attach the drywall to and fill the rest with insulation, or use lvl-xps-lvl for the header.

Ceilings can be dealt with using 5/8 drywall or alternatively strapping perpendicular to the ceiling joists with 1x3 12” OC it you are using cellulose so it does not sag
The one place I think you need to think it through very carefully is in the floor framing. I am a fan of designing the whole floor framing to L/480 deflection. Who knows down the road what flooring materials will be used where. It is a lot harder to change it later then to do the whole floor that way from the start. Plus it feels better under foot.
Cheers,
Eric

There are plenty of wavy walls out there, that is for sure. Some are being built right now.

My home originally was designed as a wood frame home and there was no way my builder or architect would recommend 24" o.c. The builder who was very respected and built many of great homes simply refused to do it at 24" o.c because of the issues he experienced in his 25+year career and what he had seen in the field. In the end the home required 2x6 @ 16" o.c. and even then I was required to have a double-sheared OSB wall on some corners. The header beams were plentiful and I knew that thermal bridging in the home would be huge. The 16" vs 24" oc is more a question of code and strength/engineering and that will always be the final ruling factor. Since then I had the home redesigned as an ICF home.

On important factor that influences OVE is that today's wood is less dense, has more moisture in it and is more prone to experiencing movement than the wood of old due to the trees being harvested for framing are young. They are not chopping down 75 year old trees to frame a home. All your lumber today is young growth.

What is your reasoning for OVE? Is it environmental or because of thermal bridging? If the latter, studies show that energy savings are negligible. Whole wall framing on a OVE might save you R-1 or R-2 in some cases. Just not worth it in my opinion. Also any money saved in lumber will be lost in engineering costs, labor costs and supplies like steel splice plates, drywall clips, header hangers, etc

Posted By Lbear on 07 Sep 2012 02:38 PM
What is your reasoning for OVE? Is it environmental or because of thermal bridging? If the latter, studies show that energy savings are negligible. Whole wall framing on a OVE might save you R-1 or R-2 in some cases. Just not worth it in my opinion. Also any money saved in lumber will be lost in engineering costs, labor costs and supplies like steel splice plates, drywall clips, header hangers, etc

For thermal bridging, definitely. At this point, I'm thinking of maybe doing a hybrid approach with 16" OC studs and double top plates, but with OVE aspects like insulated headers, 2 stud corners, etc. that won't affect drywall or siding appearance. I can always put a little more foam on the outside to make up for the framing factor loss. Thanks for all your replies....

There are many homes being built using OVE andnot having wavy walls. Obviously the design of the home has a lot to do with it.

I would disagree on both points that energy saving are negligible, and engineering costs, and fasteners eat up cost savings of framing members.

Here is a link to a reasearch project that when studied gives very good objective information: http://www.buildingscience.com/documents/reports/rr-0903-building-america-special-research-project-high-r-walls

Posted By steveusaf on 07 Sep 2012 05:29 PM


For thermal bridging, definitely. At this point, I'm thinking of maybe doing a hybrid approach with 16" OC studs and double top plates, but with OVE aspects like insulated headers, 2 stud corners, etc. that won't affect drywall or siding appearance. I can always put a little more foam on the outside to make up for the framing factor loss. Thanks for all your replies....

I think the best bang-for-buck is going to be to put more foam on the outside of the home. This will give you a much better ROI than trying to frame the home with the bare minimum of wood framing to prevent thermal bridging.

If you put 2" or more EPS on the outside of the home, that will give you a R-8/R-10 value and will cut down most of the thermal bridging issue. It won't eliminate it but it surely will help a lot.

There are better alternatives than OVE. One can go the route of SIPS and eliminate thermal bridging. Plus with SIPS you will get a wall that is 2-3 times stronger than a 2x6 wall 16" oc.

I think you are missing the point. For Stick Framed moderate sized homes OVE construction and principals reduce costs without sacrificing anything. Now you have more money to add exterior insulation. I am a big fan of outsulation, I have it on my house, in conjunction with OVE framing and cellulose insulation. Once you get out of standard building practice and into the realm of very highly insulated structures, there are many options. Sips, straw bale, very thick ICF, Persist, double wall buildings, autoclaved aerated concrete block, earth bermed come to mind. Some of them can be great structures. The best thing you can do for energy efficiency is build small, tight and simple and smart. Everything else is negotiable and there are many ways to get there

"The best thing you can do for energy efficiency is build small, tight and simple and smart. Everything else is negotiable and there are many ways to get there"
Eric - what a great way to put it; agree 100%!

I have no doubt that a house can be framed using full-blown OVE and be strong. My decision to weigh is - is the thermal bridging benefits of 24" OC OVE framing worth the potential pitfalls of wavy siding and drywall, and the associated hassle of getting someone to deal with these problems if they arise? Alternatively, I suppose I could go with 5/8" drywall and thicker sheathing to compensate for 24" OC framing, but there's cost involved in that also. For a few percentage points of insulation value boost, I'm not convinced it's worth the risk at this point. Things like insulated headers and 2-stud corners can be done regardless with no impact on siding and drywall appearance - I will no doubt spec those for the house. Good point about more than one way to get there - I just assumed full-blown OVE was a must for an energy efficient stick built house, but it's only one possible approach.

Either double stud or 4" of exterior insulation effectively prevents thermal bridging. In a DS wall the interior non structural 2x4 wall contains no headers or excess framing so your wall cost is less than the exterior structural walls.

If you can get decent lumber, you're a better man than me. I got so frustrated trying to get usable lumber for my barn, I decided to go ICF on the house, complete with TJI floor joists and metal studs for the internal walls. Even when I carefully selected studs, they went crazy even stored inside. All of the lumber yards around here only carry #2, with anything better being special order- by the truckload. As an example, I had a 2X12 that crowned about 1" after I bought it. I had to snap a line and re-cut it to make it usable.

Posted By jdebree on 08 Sep 2012 05:19 PM
If you can get decent lumber, you're a better man than me. I got so frustrated trying to get usable lumber for my barn, I decided to go ICF on the house, complete with TJI floor joists and metal studs for the internal walls. Even when I carefully selected studs, they went crazy even stored inside. All of the lumber yards around here only carry #2, with anything better being special order- by the truckload. As an example, I had a 2X12 that crowned about 1" after I bought it. I had to snap a line and re-cut it to make it usable.

That is a the point that many seem to be ignoring. Today's lumber is of a lesser quality, lesser density, and has a higher amount of moisture than the lumber of yesteryear. My family out east consists of builders who have been building for 25+ years. If you talk to builders who have been building for 20+ years, they will verify this issue.

What translates on paper to what happens on the field are sometimes two different animals. When you specify 24" o.c. sitting at a desk and then your builder out in the field experiences issues with movement and achieving a square wall, the builder must resort to special plates or more framing. There are too many variables at play when dealing with modern lumber. The paper theory assumes that the lumber is straight and true and will not deviate in the field. HA! Time to remove the shirt & tie and put on a tool belt.

You or your builder are going to have a hard time getting and keeping a straight wall with 24" o.c. and 7/16 OSB. That's a fact. You can step up to 1/2" OSB and 5/8" drywall and it should help keeping it square. At 24" o.c, if you have kitchen cabinets on an exterior facing wall, you will need to plan for that.

Depending on your codes and the related natural phenomena you might experience (seismic, winds, etc), you need to always keep a continuous load path from the roof to the foundation. When you space the framing to 24" o.c, this will require special ties and plates, and a more experienced builder and engineering.

Can it be done? Sure. Does it make sense to me? NO. There are better ways to go about getting an energy efficient wall without compromising strength.

Remember OVE "Optimum Value Engineering" was developed by HUD back in the 70's. It was developed to reduce costs of lumber and labor. It was NOT developed as a technique to reduce thermal bridging. Since then it kind of changed into what you and I would call Advance Framing. It's original purpose also changed, it's seen more as a way to reduce thermal bridging.

As mentioned, I don't see the benefits of going OVE, especially with the newer and better energy building techniques and alternatives out there. Depending on your house size a 16" o.c. home vs. 24" o.c home might see a 5%-10% reduction in thermal bridging.

If you are truly set on this method, drop the OVE approach as it is 40 years behind the times. Embrace the Advanced Framing technique that's out there and use something like a modified Larsen Truss system or other AF systems. It's like trying to get a 1975 Buick that weighs 4,500 LBS to get better gas mileage by tweaking the engine to run lean. While it's much easier and less costly to just buy a 2012 vehicle that gets 40MPG or higher. There are newer and better alternatives out there than OVE. SIPS would give you an air tight home, virtually no thermal bridging, and 2-3 times the strength of a 2x6 home.

In the end you will also have to deal with local code enforcement that might baulk at your approach. The 2006 IRC only recognizes some of the OVE/AF techniques. All of which will go out the window if you live in a high wind area or a seismic area. Many of the OVE/AF techniques will go away when your local code enforcement looks at your plans.

When you build using a technique that skates on the thin line of building to the bare minimal structural code, then you, your code enforcement and your builder will have to deal with these issues that will present themselves.

Posted By steveusaf on 08 Sep 2012 02:41 PM
I have no doubt that a house can be framed using full-blown OVE and be strong. My decision to weigh is - is the thermal bridging benefits of 24" OC OVE framing worth the potential pitfalls of wavy siding and drywall, and the associated hassle of getting someone to deal with these problems if they arise? Alternatively, I suppose I could go with 5/8" drywall and thicker sheathing to compensate for 24" OC framing, but there's cost involved in that also. For a few percentage points of insulation value boost, I'm not convinced it's worth the risk at this point. Things like insulated headers and 2-stud corners can be done regardless with no impact on siding and drywall appearance - I will no doubt spec those for the house. Good point about more than one way to get there - I just assumed full-blown OVE was a must for an energy efficient stick built house, but it's only one possible approach.

The difference in whole-wall R between an OVE framed 2x6 wall with a 15% framing fraction (rare, but sometimes possible) and a "who cares" 2x6 wall 16" o.c. with a 25% framing fraction, both with ~R20 cellulose fill is R15 instead of R13.

That's a difference that can be made up with an additional 1/2" of EPS or iso sheathing thickness for about 20-30 cents per square foot, installed.

For the same wall thickness as a no-foam 2x6 wall you could put up 2x4 wall 16"o.c. 25% framing-fraction wall with R13 cellulose (~ R9) and put 2" of exterior iso (R12) and get whole-wall R of R21, beating the no-foam OVE 2x6 wall.

There are several parts of OVE that can and should be used in any studwall where performance is a factor, such as the outside corner detailing that delivers cavity-fill into the corner, spacing windows to minimize extra studs, designing wall lengths to work out evenly at the chosen stud spacing, etc, even if you still used 16" o.c. spacing and need doubled top plates.  It doesn't take a rocket scientist of a designer to get that framing fraction down to 20% for a "free" R1 or so using less lumber & labor.  I tend to use 20% framing fraction and R14 for 2x6 wall estimation (R10  if 2x4) where there is some flexibility in the design to make these relatively minor adjustments.

With a 20% framing fraction the cost-adder to the foam to make it equivalent to OVE is about 10-15 cents per square foot of wall, and avoids most of the "...potential pitfalls...".

From a dew point/moisture loading control point of view in cooler climates I personally prefer 2x4 framing + 2" of foam to 2x6 framing + 1" of foam to hit the equivalent whole-wall R, since it puts the sheathing in a warmer layer in the stackup.  A 2x4" wall with 3" of foam hits the mid or high 20s for whole-wall R at the same wall thickness as a 2x6 wall with 1" of foam at R20-ish whole-wall R.

Posted By Dana1 on 19 Sep 2012 05:02 PM

For the same wall thickness as a no-foam 2x6 wall you could put up 2x4 wall 16"o.c. 25% framing-fraction wall with R13 cellulose (~ R9) and put 2" of exterior iso (R12) and get whole-wall R of R21, beating the no-foam OVE 2x6 wall.

ISO loses its R-Value over time and is assigning it R6 per 1" a little overzealous?

The DOE reports that due to to thermal drift, the R-value of polyiso may drop dramatically by 1/2 a point within just 180 days of manufacturing. So what will the R-Value be in 10 years?

Research from the Oak Ridge National Laboratory set R-value deterioration for permeable-faced polyiso at 15%.  The Research Council of Canada found that permeable-faced polyiso insulation R-value degrades approximately 20% over 5 years.

ISO is not dimensionally stable like that of EPS.

Posted By Dana1 on 19 Sep 2012 05:02 PM

There are several parts of OVE that can and should be used in any studwall where performance is a factor, such as the outside corner detailing that delivers cavity-fill into the corner, spacing windows to minimize extra studs, designing wall lengths to work out evenly at the chosen stud spacing, etc, even if you still used 16" o.c. spacing and need doubled top plates.  It doesn't take a rocket scientist of a designer to get that framing fraction down to 20% for a "free" R1 or so using less lumber & labor.  I tend to use 20% framing fraction and R14 for 2x6 wall estimation (R10  if 2x4) where there is some flexibility in the design to make these relatively minor adjustments.

With a 20% framing fraction the cost-adder to the foam to make it equivalent to OVE is about 10-15 cents per square foot of wall, and avoids most of the "...potential pitfalls...".

From a dew point/moisture loading control point of view in cooler climates I personally prefer 2x4 framing + 2" of foam to 2x6 framing + 1" of foam to hit the equivalent whole-wall R, since it puts the sheathing in a warmer layer in the stackup.  A 2x4" wall with 3" of foam hits the mid or high 20s for whole-wall R at the same wall thickness as a 2x6 wall with 1" of foam at R20-ish whole-wall R.

ORNL Study

Building Science Study

In the end one would have to calculate the amount of windows & doors of the home because they are the areas where framing becomes heavy. The number of windows & doors can and usually does effect the thermal bridging factor more than the stud spacing (16" vs 24" oc).

When I use the ORNL R-Value Calculator it requests the amounts of DOORS and WINDOWS in the home and uses some type of algorithm to compute a total wall R-Value.

From my research, window and doors play as big or bigger role than stud spacing. Look at the framing that goes around a 4x3 window, you have a header and then they will nail 4 or more 2x4's around the sides and bottom of the window frame.





In the end the code and engineering will dictate how much framing is needed. In high wind or seismic areas, code & engineering overrules OVE.

This discussion has focused on wall framing. Isn't floor and roof framing much more significant in material costs? Floor trusses on 24" centers and roof trusses on 24" centers use less material and installation labor than solid wood joists and rafters. With 24" OC floor and roof framing 24" OC walls just make more sense. As to window and door framing, anything beyond advanced framing is wasted material there only because the framers were ignorant of modern techniques.

>Research from the Oak Ridge National Laboratory set R-value deterioration for permeable-faced polyiso at 15%
>The Research Council of Canada found that permeable-faced polyiso insulation R-value degrades approximately 20% over 5 years.

True, but get the initial R value right- it matters!

Factory-fresh iso typically starts out at about R7.5-R8 per inch when tested within the ASTM C 518 test temperature range, and nowadays falls to under R7 inch in under a year as the blowing agents outgas. But it's not a linear progression down to zero (or crossing over into negative-R :-) ), it's logarithmic curve approaching a non-zero asymptote.

Using the Oak Ridge 15% degradation, on a (lower than fresh) initial R7.0/inch comes in at (0.85 x R7.0=) R6 .

Using the Research Council's 20% number on a (fresher) R7.5 you also get (0.80 x R7.5=) R6.

They're both in the right range- R6 is the asymptote.

Iso that's been on a roof for 30 years still tests at R6/inch, independent of which blowing agents were used. Back in the day they used HCFCs and HFCs with even higher initial Rs and much longer outgassing time constants, which prompted some to argue for using higher "average" performance numbers based on some presumed lifecycle. But these days it's almost all blown with pentane which outgasses comparatively quickly, and you're looking at something pretty close to R6/inch within a very few years. But it's still about R6/inch after multiple decades, not just 10 years.

The values that they're allowed to label are fully aged values, not initial values. So no, R6/inch isn't overzealous. Labeling at the still-steaming initial R8/inch sure would be! The day has long since passed when R7-R7.5-ish kinds of numbers were being used, (even with an asterisk next to them) but 30 years ago some designers did.

The FTC makes an attempt to use fair numbers for most insulation products- the initial depth and R-value of blown cellulose in an attic app are also significantly higher than the fully-settled density depth, but they're still only allowed to label at the settled density & depth. Many would argue (as would I) that they fail when it comes to low-density fiberglass in an open-blown attic application.

The bigger design issue with iso comes in cold/very cold climates (climate zones 6 & 7) where iso needs to be derated to about R5.4-R5.6/inch in an insulating sheathing application. The low-temp performance of iso outside the ASTM range falls with with falling temp. At an average temp within the insulation of +25F (say, +40F at the structural sheathing, +10F outdoors) it performs at about R5.6/inch (fully aged). But that's not an average winter outdoor temp seen for most US climate zones. At 0F average temp through the material there isn't much difference between iso and XPS or EPS, since the the polystyrenes increase in R at lower temp. But for most climates, R6/inch is a pretty good estimator of long term average performance in a wall app, and it's a somewhat more stable R over temperature (lower slope to the derating curves) than you get with polystyrene.

So if you live in Fargo or International Falls, call it R5.6/inch if it's the outer layer.

The BSC whole-wall R values use 16% framing fraction for OVE framing (they call it "AF" for "advanced framing") and 25% for 16 o.c. "typical" framing. (See Table 3 in Lbear's refereced document.) The OVE/AF approach spaces the studs such that the trusses or rafters are directly over the studs, eliminating the need for a doubled top plate, and to get to 15-16% framing fraction requires only narrow windows to allow But yes, wide windows needing oversized headers, window & door placement can make a HUGE difference in the actual framing fraction, more so than mere stud spacing.

Posted By Lbear on 19 Sep 2012 08:30 PM

Posted By Dana1 on 19 Sep 2012 05:02 PM

For the same wall thickness as a no-foam 2x6 wall you could put up 2x4 wall 16"o.c. 25% framing-fraction wall with R13 cellulose (~ R9) and put 2" of exterior iso (R12) and get whole-wall R of R21, beating the no-foam OVE 2x6 wall.

ISO loses its R-Value over time and is assigning it R6 per 1" a little overzealous?

The DOE reports that due to to thermal drift, the R-value of polyiso may drop dramatically by 1/2 a point within just 180 days of manufacturing. So what will the R-Value be in 10 years?

Research from the Oak Ridge National Laboratory set R-value deterioration for permeable-faced polyiso at 15%.  The Research Council of Canada found that permeable-faced polyiso insulation R-value degrades approximately 20% over 5 years.

ISO is not dimensionally stable like that of EPS.

Posted By Dana1 on 19 Sep 2012 05:02 PM

There are several parts of OVE that can and should be used in any studwall where performance is a factor, such as the outside corner detailing that delivers cavity-fill into the corner, spacing windows to minimize extra studs, designing wall lengths to work out evenly at the chosen stud spacing, etc, even if you still used 16" o.c. spacing and need doubled top plates.  It doesn't take a rocket scientist of a designer to get that framing fraction down to 20% for a "free" R1 or so using less lumber & labor.  I tend to use 20% framing fraction and R14 for 2x6 wall estimation (R10  if 2x4) where there is some flexibility in the design to make these relatively minor adjustments.

With a 20% framing fraction the cost-adder to the foam to make it equivalent to OVE is about 10-15 cents per square foot of wall, and avoids most of the "...potential pitfalls...".

From a dew point/moisture loading control point of view in cooler climates I personally prefer 2x4 framing + 2" of foam to 2x6 framing + 1" of foam to hit the equivalent whole-wall R, since it puts the sheathing in a warmer layer in the stackup.  A 2x4" wall with 3" of foam hits the mid or high 20s for whole-wall R at the same wall thickness as a 2x6 wall with 1" of foam at R20-ish whole-wall R.

ORNL Study

Building Science Study

In the end one would have to calculate the amount of windows & doors of the home because they are the areas where framing becomes heavy. The number of windows & doors can and usually does effect the thermal bridging factor more than the stud spacing (16" vs 24" oc).

When I use the ORNL R-Value Calculator it requests the amounts of DOORS and WINDOWS in the home and uses some type of algorithm to compute a total wall R-Value.

From my research, window and doors play as big or bigger role than stud spacing. Look at the framing that goes around a 4x3 window, you have a header and then they will nail 4 or more 2x4's around the sides and bottom of the window frame.





In the end the code and engineering will dictate how much framing is needed. In high wind or seismic areas, code & engineering overrules OVE.

Lbear, you are sounding like the EPS reps that come into my office! We know XPS and Iso off gas and drop r value over time, but aged values are still typically higher then EPS depending on the density. However when I am spec'ing roofing insulation, the standard as been Iso but I have since switched to EPS. Downside is I need to have more thickness for initial energy code compliance, but upfront cost is a lot lower then iso. Biggest problem I see with EPS vs iso and XPS is the air sealing abilities and therm properties for wall sheathing applications. I also see nothing wrong with OVE or AF methods in code allowed locations. You focus too much on your general location rather than trying to be more broad with the answer to the question. The answer is check with your codes, correct. However if done correctly, you can still yeild a strong, efficient home.

Posted By Liebler on 20 Sep 2012 11:07 AM
As to window and door framing, anything beyond advanced framing is wasted material there only because the framers were ignorant of modern techniques.

I've seen builders do very light framing around doors and windows and sometimes it's OK and other times you get problems. Doors shifting and sagging, windows get out of square, glazing cracking, window frames buckling, and a host of other issues.

It comes down to code, engineering and what works in the field. Claiming that, "anything beyond advanced framing is wasted material" is not a valid statement. Trust me, if builders could skimp on framing and labor costs, THEY WILL. If they could get away with nailing one 2x4 around a window or door frame, they would. Anytime you remove a wall section and place a window or door there, that area must be reinforced. Whether its concrete lintels in ICF homes or headers with multiple framing members in wood homes, it's not done out of ignorance, it's done out of code and engineering necessity.