Renerabbitt

CRC compliance for wall assembly U-Factors

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I do drafting for a slew of contractors that use the big box stores for their materials. That being said, the prescriptive requirements of U-factor 0.51 for new exterior 2x4 wall assemblies specify cavity insulation of R-15 and continuous R-8. Welp, R-8 isn't all that readily available, so I downloaded an assembly calculator sanctioned by energy.gov that calc'd R-15 with continuous R-6 as meeting the maximum U-factor. Has this been anyone's experience, is R-6 meeting the mark for you California folks? 

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Additionally, has anyone incorporated the rigid insulation with a braced wall panel at the exterior side of framing?

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I never use any r-6 exterior wrap, just r-15 cavity wall insul.. If you use a computer program for compliance , you can trade off values to get it to work.

There is a Chief guy here that prepares title 24  energy calc's at a really good price. Barry Hanes-- I use to do my own but I now would rather spend my time drawing. His  e-mail is 
 barry.hanes@hanesconstruction.com    .  

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BTW--Your area could be much different than mine by climate zone so you may have to include exterior rigid insulation.

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51 minutes ago, DRAWZILLA said:

BTW--Your area could be much different than mine by climate zone so you may have to include exterior rigid insulation.

It's my understanding that all exterior wall assemblies going forward in climate zones 1-5 and 8-16 will require some form of rigid insulation greater than r-4 for a 2x4 exterior wall, and even in zones 6,7 will still require rigid to meet the u-factor 0.065

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8 minutes ago, Renerabbitt said:

It's my understanding that all exterior wall assemblies going forward in climate zones 1-5 and 8-16 will require some form of rigid insulation greater than r-4 for a 2x4 exterior wall, and even in zones 6,7 will still require rigid to meet the u-factor 0.065

Not for me, but if you use a computer program , you can trade off less in the walls for beefing up other areas of the project, this method has no defaults like the prescriptive methods. Here we have climate zones from 4 to 12 and I have never had to put anything other than r-15 in the walls.

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Personally, I think if you can show that you used a CEC-approved program to get to the U<=.051, then why not? (Although this does seem to be in conflict with the J4 table, so you might get some pushback from the building department.)  Regarding the structural panels over the top of the insulation, this does create some detailing issues, but apparently not a big deal structurally, and may actually be an advantage. https://neea.org/docs/default-source/reports/thermal-break-shear-wall-a-case-study-of-rigid-foam-insulation-between-frame-and-sheating.pdf?sfvrsn=4  However, I don't know if the nailing patterns would need to be adjusted, and what other code issues you may need to deal with.

 

Personally, I'm using a lot more sprayed-on foam these days.

 

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1 hour ago, Renerabbitt said:

Additionally, has anyone incorporated the rigid insulation with a braced wall panel at the exterior side of framing?

We dont have the energy requirements that you guys deal with, but regarding rigid foam in a braced wall, Huber has a neat product.   They sandwich foam on inside so no lath or siding nailers required.   They have engineered the sheer requirements to allow the foam in the inside.  Pretty cool stuff.   I am a fan of Zip system as well.   This takes it a step further.

 

Was going to use this on a recent project, but went with a staggered stud and spray foam application instead.   I still used Zip on outside which was probably overkill, but the material itself is much better than standard OSB.   Much greater water resistance in how it is made. (not just an exterior coating)

 

http://www.huberwood.com/zipsystem/products/zip-system-rsheathing

 

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8 minutes ago, VisualDandD said:

Thank you for the resource, and how AWESOME is it that you can get water/vapor barrier assembly out of this

25 minutes ago, Richard_Morrison said:

 

Personally, I'm using a lot more sprayed-on foam these days.

 

Any problems you've run into using the spray foam. I wonder if the trade off is there for hiring a sub to spray or in-house install of rigid and a thicker wall assembly.

Considering doing the performance method as Perry mentioned

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29 minutes ago, Renerabbitt said:

Thank you for the resource, and how AWESOME is it that you can get water/vapor barrier assembly out of this

Any problems you've run into using the spray foam. I wonder if the trade off is there for hiring a sub to spray or in-house install of rigid and a thicker wall assembly.

Considering doing the performance method as Perry mentioned

I chose to use spray foam because of it's air sealing properties.   It is amazing really, but you do  have to make extra precautions such as fresh air provisions as the home become too tight.   I used an ERV.


I did a full sealed envelope.  I just finished the project in Dec, and we did a blower door pre-drywall and were less than .5ach BEFORE drywall.  HSF is 8800 sqft.   My HVAC guy sized it conventional and said I needed 13ton if I buit the home "normal".    I used a 2x8 plate stagger stud with 4" of foam (any more was a diminishing return and there was a LOT of wall).  In retrospect, I could have used a 2x6 plate and got the same effect.   The fact that they dont have to "shave" the foam actually makes it more efficient.  The skin yeilds greater performance that is not factored into normal calculations.

 

I spec'd andersen 100 series windows, which have decent performance.   I hired an energy consultant to do a detailed long form manual J and ductwork modeling.   The entire home sized out for 2.9 ton on a 95 deg design temp day.   Total utility bill (home is all electric) for Feb was $160.

 

I put in a lennox variable speed OUTDOOR unit which can actually change it relative size depending on demand and ensure proper run time.  I used a 4 ton unit which can effectively run down to 1.5 ton if it needs it.   I used a separate 2 ton unit for the walk-out basement as load is almost nothing.  That area we added a dehumidifier in case the unit does not run long enough.

 

Modeled in chief and built last year.

 

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2 hours ago, Renerabbitt said:

Any problems you've run into using the spray foam. I wonder if the trade off is there for hiring a sub to spray or in-house install of rigid and a thicker wall assembly.

Considering doing the performance method as Perry mentioned

No real problems (except maybe with troglodyte contractors) and a lot of benefits. As Zero Net Energy approaches in 2020, I  think we'll be seeing a lot more of it.

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5 hours ago, DRAWZILLA said:

Not for me, but if you use a computer program , you can trade off less in the walls for beefing up other areas of the project, this method has no defaults like the prescriptive methods. Here we have climate zones from 4 to 12 and I have never had to put anything other than r-15 in the walls.

It's a shame that REScheck isn't compliant in Cali

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As Perry mentioned, the walls CAN be changed/modified depending on the Title 24 Part 6 calculations.

 

I know as I also do performance calcs.

 

Andy.

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13 hours ago, AndyGump said:

As Perry mentioned, the walls CAN be changed/modified depending on the Title 24 Part 6 calculations.

 

I know as I also do performance calcs.

 

Andy.

I’m in complete agreement that the performance approach can get you around mandatory measures, mkennedy2000 is helping me get through some res software so I can get on your level of self performing the calcs.

Still, I consistently find information that contradicts this approach. See attached:

739555C1-95A7-4A69-9D5C-0D130D49E17A.thumb.jpeg.04ba9df503c5c15423c6022a4b0121c3.jpeg

 

Exceptions may apply is never spelled out in this document. I would conclude that if you can reasonably show an overall performance package that satisfies the intent of the code, then the plan checker can get on board with it.

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1 hour ago, Renerabbitt said:

Still, I consistently find information that contradicts this approach.

No, you can never get around the mandatory measures, even if the performance approach shows that you will still be under the energy budget. Think of these measures as the absolute minimum you must do, regardless. Even if you design a super-efficient box that is WAY under the energy budget, you can never use less than R-15 in a 2x4 framed wall, for example. (BTW, 2x4 framing in an exterior wall is now only allowed where an existing 2x4 wall is being extended. 2x6's must be used otherwise in an exterior wall.) If you use a performance approach, you can add other energy-saving measures to maybe allow you to use just a regular ol' 2x4 wall with R-15. If you use the prescriptive approach, unless you are doing an addition where the code cuts you some slack, you are looking at a U<= 0.051 factor for exterior walls, which almost certainly will be batts plus continuous insulation, or sprayed-on foam. In the prescriptive approach, you also need to be very careful about which windows are spec'd, too. Only a small percentage of windows meets the prescriptive requirements.

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8 minutes ago, Richard_Morrison said:

No, you can never get around the mandatory measures, even if the performance approach shows that you will still be under the energy budget. Think of these measures as the absolute minimum you must do, regardless. Even if you design a super-efficient box that is WAY under the energy budget, you can never use less than R-15 in a 2x4 framed wall, for example. (BTW, 2x4 framing in an exterior wall is now only allowed where an existing 2x4 wall is being extended. 2x6's must be used otherwise in an exterior wall.) If you use a performance approach, you can add other energy-saving measures to maybe allow you to use just a regular ol' 2x4 wall with R-15. If you use the prescriptive approach, you are looking at a U<= 0.051 factor for exterior walls, which almost certainly will be batts plus continuous insulation, or sprayed-on foam. In the prescriptive approach, you also need to be very careful about which windows are spec'd, too. Only a small percentage of windows meets the prescriptive requirements.

This is news to me, do you have a reference? I did know that you could continue a wall and just put r-15 but hadn’t run into problems using 2x4 assembly. I’ve read through so much new code in the last couple days my head is spinning. I suppose I should collect my resources before I contribute more to the conversation.

What I keep finding contradictory info on is that the min mandatory is up towards u-factor of .102, and then I find it at .051...what a huge difference, and both point toward apendix j04 with dated documents only months apart in the first quarter of 2017. So if performance methods must meet minimums of .102 then it’s feasible that you could use just r-15 in new assemblies, but if the min is .51, the performance approach technically would not be acceptable unless there is some exception that I can’t seem to find.

I understand that people ARE using the performance approach and avoiding continuous insulation, but does this actually meet code requirements and can anybody explain why this would be allowable.

this is table 150 from the energy code:

F2FB3C29-FF5F-4E44-AD93-FE62A568A6B4.thumb.png.db27183f569e424eec4f6470f6eab1e6.png

 

I like to go to battle with overwhelming amounts of irrefutable hard data, and I feel as if I have a bag of hear-say and conjecture which is my own lack of clarity and experience as I typically only deal with remodels and frankly, just can’t seem to find a timeline of unbroken data.

This forum is amazing btw, such a talent pool.

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All I know is the cities around here accept my calc.s using  2x4 with r-15, at least the last 100 projects without any problems. Maybe they don't know yet and the calres program approves it and Calcerts also approves it.

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1 hour ago, Renerabbitt said:

This is news to me, do you have a reference? I did know that you could continue a wall and just put r-15 but hadn’t run into problems using 2x4 assembly. I’ve read through so much new code in the last couple days my head is spinning. I suppose I should collect my resources before I contribute more to the conversation.

 

The CEC Residential Compliance Manual is huge, and not something you can master in a day. www.energycodeace.com is a helpful website. Anyway, I'll try to explain.

If you are using the PRESCRIPTIVE approach, you can extend existing 2x4 walls with R-15. No problem. However, any OTHER new walls must meet U<=0.051. (except for climate zones 6 & 7) You cannot realistically achieve this with a 2x4 wall without R-8 additional, probably 2" thick, so why not just use a 2x6 wall with spray foam? See JA-4 table.

 

You get more flexibility with the PERFORMANCE approach, but the energy budget is still based on a U<=0.051 exterior wall. If you are using 2x4 walls with R-15 insulation throughout, then you are taking a huge hit in the compliance and must compensate with higher insulation values for roofs/ceilings, higher efficiency mechanical units, HERS inspections, etc.

 

One loophole for additions, if you want to call it that, is using an Existing + Addition compliance approach with HERS existing condition verifications. Unlike the last code cycle, this code cycle you don't get credit for existing conditions that are being upgraded, UNLESS you have obtained the HERS verification and certification before the energy calc's are submitted.

 

I have a hard time believing that 2x4 walls with R-15 are going to comply on a computer based approach as a matter of course without either really massive energy upgrades elsewhere, or something else going on. This just sounds a little hinky to me. I have an architect friend who recently did a new house in the Bay Area and was told by the energy consultant that 2x4 exterior walls were going to be fine. I suggested he look at this more carefully, and somehow he found that all his exterior walls were now required to be 2x6's. I don't know what's going on with these consultants.

 

One nice feature of the EnergyPro software is that you enter in your building and can choose either Prescriptive or Performance, and it will spit out the correct forms. Given the last minute adjustments and fine-tunings to the design that are sometimes required for compliance, it's hard for me to see farming this energy compliance out to someone else.

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Besides that, for almost all new construction today we are using 10' ceiling heights and 2x4 studs just don't work.  I use 2x6's for all exterior and bearing walls.  The walls are much stiffer and getting the extra insulation (even fiberglass batts) provides the necessary U value.

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Also some cities just don't understand the energy codes enough to apply them yet, even though I've been doing them for 30 years. It used to be a lot simpler back in the day.

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I generally use 2x6 exterior with batts or spray foam.  2" rigid with nailers on 2x4 renos.  My question is, what spacing do you use on staggered studs and how does that affect drywall application and rigidity?

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On 3/31/2018 at 12:57 PM, Joe_Carrick said:

Besides that, for almost all new construction today we are using 10' ceiling heights and 2x4 studs just don't work.  I use 2x6's for all exterior and bearing walls.  The walls are much stiffer and getting the extra insulation (even fiberglass batts) provides the necessary U value.

 

On 4/1/2018 at 9:17 AM, DRAWZILLA said:

Also some cities just don't understand the energy codes enough to apply them yet, even though I've been doing them for 30 years. It used to be a lot simpler back in the day.

Joe, I'm in line with Perry on this, some plan checkers may just not be up to speed. New energy code requires new framed assemblies meet a U-factor greater than batt cavity fill can achieve on its own. 

This is a Screenshot from Energy Code Ace:

5acbc15ca3ae3_UFACTORFACTSHEET.thumb.PNG.f3e7cda925bd6261a16c5e0038fbfb88.PNG

Richard was right on the money in his post. These requirements will be commonplace soon enough for new construction if they aren't already. CA energy commission is tackling the thermal envelope this bout.

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Slight off topic rant...so ridiculous the over regulation in this industry at this point.

Now we have to build houses so tight to save "energy" but you then have to put a big hole in the house in the form of  makeup/outside air ventilation so humans can actually breathe without passing out....

 

Eric

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That's why we in Cali. have to install Always on fans to create a negative air pressure , so everyone won't get sick.. every time you open a front door or window, fresh air from the outside is suppose to rush in.. Well--at least you hope it's fresh air..

 

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There is some misinformation here that should be corrected. OF COURSE, we all need fresh air in our houses. The problem is that during extremes of heat or cold, when we WANT the windows shut to save on heating or cooling costs, just opening a window or having a leaky house causes us to spend FAR more to get that fresh air in energy costs. We pay a huge premium for fresh air in temperature extremes by using the "open window" method. By using an HRV or ERV system, we can get the same fresh air for much reduced energy cost, as well as giving us more control over the humidity. Hot fresh air or cold fresh air is not cheap.

 

In general, we want neutral or slightly positive pressure in our houses. Negative air pressure causes backdrafts and problems with gas appliance starvation. Hence the need for adequate makeup air. Negative air pressure (even slight) is unhealthy, and may even kill us in some circumstances. 

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