Hi,
I'm having room built in my walk-in attic in Texas. Contractor is using Foamular R-4 insulation. This provides maximum airspace from soffit to ridgevent. However, I'm severely concerned he is not close to R-30 as higher!

Suggetions please!

I'm thinking of ripping this apart, using R-38 or something similar bats and running attic vents on top of them.

Let me know your thoughts.

Attaching a picture...

Relax, I think you are confusing rolled insulation with rigid foam as what yours appears to be.

Insulation R-Value | Today's Homeowner

R-value (insulation) - Wikipedia, the free encyclopedia

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The US Department of Energy has recommended R-values for given areas of the USA based on the general local energy costs for heating and cooling, as well as the climate of an area. There are four types of insulation: rolls and batts, loose-fill, rigid foam, and foam-in-place. Rolls and batts are typically flexible insulators that come in fibers, like fiberglass. Loose-fill insulation comes in loose fibers or pellets and should be blown into a space. Rigid foam is more expensive than fiber, but generally has a higher R-value per unit of thickness. Foam-in-place insulation can be blown into small areas to control air leaks, like those around windows, or can be used to insulate an entire house.^[8]

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Fiberglass Insulation | Builders Websource®

Little hard to tell roof and joist construction. Are these trusses? Stick built roof? If they are straight stick built, there is no way to get R-39 in there, Scissors trusses would have been the ideal, you get the cathedral portion with space for the insulation. Is there insulation on the roof top, it is done that way to get higher R? For R-40 you need 10 or more inches of fiberglass batt.

Aren't those rigid boards labeled R 40 ?

I see R4.0 Foam... something or other 3/4

What is the exact depth of your rafters? With ventilation channels, there is no way you are going to get R 38. Batts require much more thickness for the same R value as foam.
Is there ventilation behind those boards?

Yes, thanks, 4.0. Not enough, is this being built with a permit? Check your building code.

I think the rafters are 6" deep. I'll probably use the Roxul R-23, which is about 5-1/2" thick and run the vent channels. I also have Techshield roofing, so I may be okay even though I'm not quite above 30. Building code recommends 30, but not sure how else I an get there.
Let me know if anyone has experience using Roxul for ceiling insulation.
Thanks for all the suggestions thus far.

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Originally Posted by RowdyTX

I think the rafters are 6" deep. I'll probably use the Roxul R-23, which is about 5-1/2" thick and run the vent channels. I also have Techshield roofing, so I may be okay even though I'm not quite above 30. Building code recommends 30, but not sure how else I an get there.
Let me know if anyone has experience using Roxul for ceiling insulation.
Thanks for all the suggestions thus far.

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Found this at lowes:
Roxul 8-Pack 47-in L x 15-1/4-in W x 5-1/2-in D 23-R Stone Wool Insulation Batts

Item #: 386578 | Model #: RXCB551525

Your rafters look like 24", not 16. Of course all batts come in both widths.
You totally defeat the purpose of any 'wool' if it's packed down. 6" rafters are 5 1/2". It is a waste to throw out the foam. Add the channels, and you do not want 5 1/2" of stone wool. Get 3 1/2" even though you lose some R value.

Are you sure the contractor isn't planning on channels and another layer of foam? (Seems strange and more expensive, but have you asked what the plan is?)

I took out 'rock wool' made in the 30s, and it was absolutely awful - heavy and painful on the skin, tiny sharp fibers. I'm sure it's changed.
Maybe you saw this from a proponent of stone wool (mineral, rock, stone seem interchangeable).
http://blog.lamidesign.com/2012/01/w...eral-wool.html

Maybe it is time to talk to your contractor for a detailed explanation.

Thanks for everyone's response.

My contractor would like to use 3 more of these rigid boards for a combined R value of 16. In a 5-1/2" space, 4 of these rigid boards would take up 3 inches and would leave a good 2+ inches for airflow.

Are re there any negatives when using this plastic sided foam rigid boards? Would they cause any condensation problems in the future?

its for the right half of the roof, which is 7 x 23ft area, so I'm not really concerned about the added expense of using rigid boards as opposed to batts.

If if this is a bad idea and if I should go with r-13 or similar batts with ventilation channels, let me know.

Either way, I will have to compromise around r15 - looks like it. I'm being told that air passage from soffits to ridge vent is pretty important and it's better not to choke it. We are in Texas.

Thanks!

Are you in the drier north, or the very humid south of Texas? Condensate is a bigger consideration in the southern part of Texas around the gulf.

That was reflected in one of the links I provided.

Houston, so close to gulf coast.