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Question about compressing attic insulation
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posted
I'm in the process of reinsulating the attic of our 1860's Victorian house. We live in MA. Part of the attic had R22 between the floor and 2nd floor ceiling. It was full of dirt and damaged so I pulled it all out.

I have a couple questions about the reinsulating process:

(1) The original insulation had the kraft paper facing the attic NOT the 2nd floor ceiling. Is there any reason to do this? It should go the other way, right?

(2) I only have a 7.5" space between the floor boards and 2nd floor ceiling. Would it be worth compressing R-38C in that space rather than using R22? Owens Corning has a chart of R values for compressed insulation. According to the chart R-38C compressed into a 7.5" space would give me R30.

I would like to keep the floor boards in place for storage. Since we will be tearing down some of the 2nd floor ceiling in the future I would rather not use blown insulation.

Thanks,

Wayne
 
Posts: 3 | Registered: 17 May 2007Reply With QuoteReport This Post
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The ktraft paper should indeed go against the second floor ceiling, in your climate.

I see no reason not to use the R-38 insulation compressed to still give you R-30. It's still a lot better than R-19 or R-21 uncompressed, and also better than R-30 compressed, which would probably end up R-24 or thereabouts.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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Hi Wayne,

Question 1: You are absolutely right the kraft paper as the vapor barrier should have been facing down.

Question 2: I think that it is a real stretch for OC to state that compression of an R-38 will give you an R-30, however it is close enough. I would suggest that you do not make the error that the majority of people make when it comes to R-value. R-value is a measure of conductive heat flow only under perfect laboratory conditions. 4-mechanisms for heat flow exist conduction, convection, radiation and mass transfer and none except for conduction are addressed with R-Value. Fourier's Law of Thermodynamics show that at R-4, 82% of the conductive heat flow is eliminated, R-20, 96% of the conductive heat flow is eliminated and at R-40, 96% of the conductive heat flow is eliminated clearly showing the "value" with R-value and the deminishing returns you can witness. Yes R-value is the industry standard for performance, but that performance is laboratory performance and not field performance. You would be much further ahead in terms of energy efficiency, improved indoor air quality, moisture management and the prevention of conditions conducive for mold and mildew growth to use an insulation and air barrier product in one such as light density flexible polyurethane foam. A product such as this at 5.5-6" (R20) will outperform the air permeable products by a large margin. You will then effectively eliminate the conductive moisture and heat flow which believe it or not can attribute to over 50% of energy loss within the building at the same time eliminating 99% of the moisture loading into and out of the building structure via convection.

It is a more expensive proposition but you will be getting a very high quality product with much superior performance capabilities over traditional insulating methods.

Cheers
 
Posts: 6 | Registered: 17 May 2007Reply With QuoteReport This Post
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Ooops a typo, R-40, should read 98% of the conductive heat flow not 96%
 
Posts: 6 | Registered: 17 May 2007Reply With QuoteReport This Post
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That's all well and good, but when a building code requires R-30 or R-40, you're not going to convince many building officials that R-20 is better. Besides here, a good place to explain and back up statements such as yours would be a conference of building officials which takes commentary from the public toward revising the building code for the next edition.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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Thanks for the replies. We're definitely leaning towards batt insulation. Given that we will be doing more remodeling of the second floor ceilings and running more electrical in the attic I think batts would be the easiest.

Our main question was whether the compressed R-38C would in fact give us close to an R-30 value. Comparing the costs between R-22 and R-38C doesn't show much difference. In fact some places I went to charge more per sq ft for the R-22. Given that, as long as the compressed R-38C doesn't give us less than an R-22 value making the decision should be simple. (unless I'm missing something?)

I've purchased Harley's book on insulating which has been very helpful. I plan on really concentrating on sealing the attic as much as possible before putting in the new insulation. I think that this would give us the best results.

Wayne
 
Posts: 3 | Registered: 17 May 2007Reply With QuoteReport This Post
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To Mr. Hetzels response,

It is not a matter of convincing anyone it is written in the building codes. It is called the performance approach as outlined in the IRC and IECC. Architecural Energy Coorporation designed a software package called REM Design a nationally recognized entity that shows code compliance to IECC and IRC performance aspects to the code.

However, I do realize as a building scientist that jurisdictions at state and moreso county levels are working on codes that have been obsolete for 5+ years. We do get our message out on a daily basis and thus the reasons for the dramatic changes to the building codes recently.
 
Posts: 6 | Registered: 17 May 2007Reply With QuoteReport This Post
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Looking at the AEC web site for REM/Design, I can't find anything in the program that would document in a satisfactory manner a claim that one insulation of R-20 value will outperform another insulation of R-38, for example. It may be true, but as I said, convincing a local building official that R-20 is better than R-30 is not a task that I, as an architect, would look forward to.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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Mr. Hetzel,

You would have to input the building parameters via an architectural drawing/CAD etc. Then you are able to input the air infiltration rate of the building via blower door test data which enables air impermeable insulations credit in terms of energy efficiency. Then you can generate a code compliance report on whatever code cycle the state/county is working on. I have probably generated well in excess of 2000 reports in the last year all of which have been accepted by the BCO.

At any rate this topic is getting way off tangent of that in which Wayne had originated, I was just trying to get the point home that a "tighter" system in the end far outways the misconceptions with R-value.
 
Posts: 6 | Registered: 17 May 2007Reply With QuoteReport This Post
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Hi Wayne,

Insulation Guru is 'right on' with his facts. The 'system' standards have not yet caught up with the performance capabilities of Polyurethane foam. As such, there are many perceptions of its function and measurability.

Another option for your attic, if you are inclined to maintain batt insulation: you can have the rafters 'flashed' with foam. YOu will need to consult with your roofing materials supplier to insure (shingles) can withstand the reflected heat from the foams performance.And consult the installer about proper ventilation for your situation. Good Luck!
 
Posts: 3 | Registered: 08 June 2007Reply With QuoteReport This Post
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The construction industry has also not caught up with the fire hazard or outgassing potential of foam insulations either. Architecture by nature must be conservative. If there is any doubt about the ultimate safety or longevity of a material or method, I, for one, will wait until those things are proven beyond a doubt before I inflict them on clients who have trusted me and my judgement.

There is a mandate that professionals perform at the general standard of their profession, and that means not below it, nor above it until the safety of a product is proved beyond a doubt.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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You are correct only in that the CONSTRUCTION industry has not caught-on yet to the multiple benefits: there is NO outgassing of foam--it is inert within 20 minutes of application, it is the GREEN builders choice, and State & government agencies are offering tax rebates based on its effectiveness & environmentally friendly performance.

Typical batt insulation melts very quickly and the now empty space can and does have a chimney affect, feeding air to the source or drawing the fire upward from below.ZERO benefit.

If you are interesed, there are many manufacurers sites that will give detailed spec sheets for educational purposes. Without mentioning names; we acquire ours from the manufacturer that supplies NASA. I think there is sufficient research money and reliability there. Good Luck!
 
Posts: 3 | Registered: 08 June 2007Reply With QuoteReport This Post
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Thanks for all the replies.

Really I just wanted to know whether it was worth taking a high R value batt and compressing it in the attic floor.

We're not looking into installing foam. I have a lot of electrical work to do for the 2nd floor and using batts would be easiest. And since I am doing this myself batts seem like a good choice.

I'm investing LOTS of my time in sealing the attic with expanding foam before laying the batts down. I know foam insulation would do this for me but again I can DIY this. I've already found sizable holes in the attic that I've been able to plug up and I'm only half done.

Wayne
 
Posts: 3 | Registered: 17 May 2007Reply With QuoteReport This Post
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Wayne:

Using a higher than required thickness(and hence a greater R-value) of fiberglass insulation and compressing it is an acceptable alternative.

Up to 50% of a structure's energy loss/gain comes from air infiltration and exfiltration
and one can often do better to make own's structure more energy efficient by addressing air infiltration rather than thickness of insulation issues.
 
Posts: 453 | Registered: 19 July 2005Reply With QuoteReport This Post
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quote:
Originally posted by greenmtnfoam:
Hi Wayne,

Insulation Guru is 'right on' with his facts. The 'system' standards have not yet caught up with the performance capabilities of Polyurethane foam. As such, there are many perceptions of its function and measurability.

Another option for your attic, if you are inclined to maintain batt insulation: you can have the rafters 'flashed' with foam. YOu will need to consult with your roofing materials supplier to insure (shingles) can withstand the reflected heat from the foams performance.And consult the installer about proper ventilation for your situation. Good Luck!


I'm a builder and a nationally certified energy codes inspector...and all I can say to the above statement is that 'insulation guru' is partially 'right on' with his facts as stated.

The reality is, that energy codes like the IRC, IECC and state adopted alternatives allow a wide VARIETY of insulation methods and techniques to meet minimum energy compliance to adopted standards, just a building codes allow a wide variety of materials and methods with which to frame and meet minimum load requirements for a structure.

REMrate, REScheck, UA Alternative and a host of other energy compliance techniques are available for energy compliance just as there are available for framing LVLs, Microlams, sawn lumber, I joists, web trusses and other methods to carry loads for framing.

None is necessarily 'superior' to another.

Just acceptably 'different'.

The marketplace is the ultimate determinant of what becomes "standard practice".

It is complete error and quite false to claim that building/energy codes therefore are 'behind the times' or that builders simply haven't 'caught on'.

Quite the contrary.

The Codes fully allow for alternatives, but most alternatives are neither cost effective nor live up to their claims...and therefore get rejected out in the real world and relegated to the dung heap of history.

Foam insulation has it's benefits, but it STILL remains the most costly way to achieve the same energy benefit compared to say high-density fiberglass...with fiberglass coming in at a cost of 3-5X LESS.

For the average builder and consumer, it makes no sense to pay more for any foam insulation and have to wait 3-5X LONGER to simply pay for the material before he can enjoy the benefit of energy dollars saved, when he can use fiberglass or cellulose and see the savings NOW.

The real 'Gurus' of insulation and energy, like Joe Lstrbek, recognize these facts and it these real 'Gurus' who contribute the most to keeping modern energy Codes not only up-to-date technologically speaking, but also up-to-date with building reality.

I come down moreso on the side of Rich Hetzel on this one.

Somtimes the simpler and most common methods provide the best benefit and are the most economical because they have stood the test of time and the marketplace....the REAL determinate of how energy and other codes should survive.

And the REAL 'intelligence' here is not demonstrated by product researchers or product manufacturers or product intallers...but rather, demonstrated by the builders and owners 'end-users'...who get to see how products work (and fail) in reality and in the field and how that affects their wallets.
 
Posts: 453 | Registered: 19 July 2005Reply With QuoteReport This Post
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Will R-20 worth of foam on top of rigid vent channels be a good choice then to insulate a bonus room ceiling in order to maximize space without sacrificing much energy efficiency?

Thanks,
Brian
 
Posts: 2 | Registered: 08 October 2007Reply With QuoteReport This Post
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