Vented roof eave blocking for blown-in insulation, need R49 for code

[Gopherboy6956]

Since won't be doing fascia and soffit until next spring / summer and because i'll likely be doing my insulation over the winter, it's become immediately apparent to me that I need to do something about my wide open eaves before winter.

I'll likely cut osb strips to close off the bottom of the eaves for winter regardless, but that made me think ahead to insulation and i'm struggling with what I should use to hold back the insulation.

I've seen some of those attic vent baffles and that all makes sense to me, but the thing i'm concerned about is my slope. The bottom chord of my truss is a 10/12 pitch and the top is a 16/12 pitch, and I am planning to use blown in insulation as I don't want to spend the money on spray foam and i'm not sure batt insulation wont get me to the required R49 I need to hit.

Im worried that the blown in will just pile up at the bottom of the truss and I wont be able to keep the thickness at the top. With blown in, I need at least 15" of depth to get R49, which I wont even have the space for until about 2ft up the bottom chord. Each cavity that needs to be insulated is 34 linear feet wall to wall, that's a total of 680 linear feet of insulation total.

Some pics and my truss engineering drawing added for reference.

Thank you!

 

[Uncle murph]

Since won't be doing fascia and soffit until next spring / summer and because i'll likely be doing my insulation over the winter, it's become immediately apparent to me that I need to do something about my wide open eaves before winter.

I'll likely cut osb strips to close off the bottom of the eaves for winter regardless, but that made me think ahead to insulation and i'm struggling with what I should use to hold back the insulation.

I've seen some of those attic vent baffles and that all makes sense to me, but the thing i'm concerned about is my slope. The bottom chord of my truss is a 10/12 pitch and the top is a 16/12 pitch, and I am planning to use blown in insulation as I don't want to spend the money on spray foam and i'm not sure batt insulation wont get me to the required R49 I need to hit.

Im worried that the blown in will just pile up at the bottom of the truss and I wont be able to keep the thickness at the top. With blown in, I need at least 15" of depth to get R49, which I wont even have the space for until about 2ft up the bottom chord. Each cavity that needs to be insulated is 34 linear feet wall to wall, that's a total of 680 linear feet of insulation total.

Some pics and my truss engineering drawing added for reference.

Thank you!

I don’t see blown in insulation working in those trusses,probably time for plan B.

 

[larry4406]

Agreed with @Uncle murph .

Wrong application for blow in.

Batts and baffles are the solution here short of spray foam.

 

[Dagny]

I don't think you have enough room to get R49 in there.

 

[PCustoms]

I don't think you have enough room to get R49 in there.

Certainly not at the soffit area, unless maybe if he did a hot deck and filled with foam, even then looks tight.

@Gopherboy6956 is your ridge vented?

 

[billconner]

Just a comment on the code required R49. The code anticipates your condition of compressed or reduced insulation at the eaves, and offers this if you actually achieve insulation to the eave.

"Where Section N1102.1.3 requires R-49 insulation in the ceiling or attic, installing R-38 insulation over 100 percent of the ceiling or attic area requiring insulation shall satisfy the requirement for R-49 insulation wherever the full height of uncompressed R-38 insulation extends over the wall top plate at the eaves."

I addressed it by building a soffit so I could get 20" of insulation plus vent space to the wall sheathing.

You might look at using rigid insulation at the eaves for both more insulation and forming the vent baffle.

I agree not a great design for blown in.

 

[finn]

Those aren’t “Energy heel” trusses, so they likely aren’t compatible with your R49 insulation code requirement. Energy heel trusses would have additional blocking to increase separation between the upper and lower chords where the truss sits on the wall top plate, giving more room for insulation.

You’re stuck with bats or a hot deck and spray foam.

 

[mike93lx]

You need to meet insulation code in a shed?

 

[billconner]

You need to meet insulation code in a shed?

If your heating or cooling it you do.

 

[Gopherboy6956]

Certainly not at the soffit area, unless maybe if he did a hot deck and filled with foam, even then looks tight.

@Gopherboy6956 is your ridge vented?

Yes! I did vent the ridge last weekend when I finished the roof.

Just a comment on the code required R49. The code anticipates your condition of compressed or reduced insulation at the eaves, and offers this if you actually achieve insulation to the eave.

"Where Section N1102.1.3 requires R-49 insulation in the ceiling or attic, installing R-38 insulation over 100 percent of the ceiling or attic area requiring insulation shall satisfy the requirement for R-49 insulation wherever the full height of uncompressed R-38 insulation extends over the wall top plate at the eaves."

I addressed it by building a soffit so I could get 20" of insulation plus vent space to the wall sheathing.

You might look at using rigid insulation at the eaves for both more insulation and forming the vent baffle.

I agree not a great design for blown in.

I do see they make R-49 batts, although they certainly arent cheap. Maybe what i'll do is use batts for the steep part of the truss, then put in blocking and just do the 3/12 top slopes with blown in to save money.

Can you dumb down the code snippet above? Is that saying I can use R-38, and it would be prefereable to using compressed R-49 in the last two feet where the truss chords meet?

You need to meet insulation code in a shed?

Yes - this is considered a detached accessory building here in Fargo - and if I want to heat it I need R-49 for the ceiling and R-21 in the walls.

 

[billconner]

Can you dumb down the code snippet above? Is that saying I can use R-38, and it would be prefereable to using compressed R-49 in the last two feet where the truss chords meet?

I interpret as if you can get R39 over entire ceiling, all the way to the exterior sheathing, that's acceptable in place of R49 over most of the ceiling and less - because of compression or whatever - at the eaves.

Does that help? I was skeptical you could get R38 over top plate with batts. 8" of rigid foam for first 2 feet and you're close.

 

[Gopherboy6956]

I interpret as if you can get R39 over entire ceiling, all the way to the exterior sheathing, that's acceptable in place of R49 over most of the ceiling and less - because of compression or whatever - at the eaves.

Does that help? I was skeptical you could get R38 over top plate with batts. 8" of rigid foam for first 2 feet and you're close.

Yes!
I also just ran it though ChatGPT, and I have to say I was impressed with it's explanation. (below) and it's recommendation (similar to what everyone is saying) just based on uploading my engineering doc.

I was wondering about rigid foam too - it looks like it would take about 10inches of it to get there - which after doing the math works out to about $1,028 for all 20 truss spaces. Not sure if there's a cheaper way to do that part.

 

[mike93lx]

Yes!
I also just ran it though ChatGPT, and I have to say I was impressed with it's explanation. (below) and it's recommendation (similar to what everyone is saying) just based on uploading my engineering doc.

I was wondering about rigid foam too - it looks like it would take about 10inches of it to get there - which after doing the math works out to about $1,028 for all 20 truss spaces. Not sure if there's a cheaper way to do that part.

There are companies that sell used and salvage building materials, including foam. Might be worth a check on craigslist/marketplace in your area

 

[billconner]

it looks like it would take about 10inches of it to get there

For R39, wouldn't that be 8" of XPS? Maybe just 6 1/2" of polyiso.

And as Mike said, looked for used.

 

[larry4406]

I was reading up on Code changes that will affect my next community. I thought this was interesting.

 

[Jetfixr320]

X2 on looking on Marketplace or Google used Polyiso, or polyisocyanurate foam board. It's used under rubber roofs and Companies resell it after replacing roofs on buildings.
You will save quite a bit over new if you can find it.

 

[Gopherboy6956]

For R39, wouldn't that be 8" of XPS? Maybe just 6 1/2" of polyiso.

And as Mike said, looked for used.

Good catch - yea 8" so likely around $800 then. I guess I never even thought to look at used...

 

[Gopherboy6956]

I was reading up on Code changes that will affect my next community. I thought this was interesting.

Woah - thats kind of a game changer. I'll have to run this by my inspections department and see what they tell me.

 

[Gopherboy6956]

Ok - coming back to this several weeks later -

I had a consultation inspection with the city today as I wanted to be 100% sure my framing was good before I start running wires all over the damn place.

We talked a little about insulation, and I guess because it's a detached structure with NO living qarters, I can actually get away with as little as R13 in the walls and R21 in the ceiling. Crazy!

Of course, I'm still going to do R21 walls and shoot for as high as possible in the ceiling, but this takes a little pressure off of trying to hit R49 where it's extremely challenging.

 

[MikeC55]

Nice to see a reasonable answer to your issue.

 

[FTG-05]

X2 on looking on Marketplace or Google used Polyiso, or polyisocyanurate foam board. It's used under rubber roofs and Companies resell it after replacing roofs on buildings.
You will save quite a bit over new if you can find it.

My local CL:

Reclaimed polyiso insulation for sale – great insulating value!

19" x 96" x 1.5” thick polyiso

$395 per bundle - 60 sheets (760 sf)

Material is located in XXXXXXXX-**. Trucking quotes available upon request.