https://www.energyvanguard.com/blog/how-to-sheathe-an-attic-kneewall-and-how-not-to/ Building science knowledge, HVAC design, & fun Wed, 29 Sep 2021 20:38:47 +0000 hourly 1 https://wordpress.org/?v=6.6.2 https://www.energyvanguard.com/blog/how-to-sheathe-an-attic-kneewall-and-how-not-to/#comment-3810 Wed, 23 Apr 2014 06:27:57 +0000 http://energyvanguard.flywheelsites.com/?blog_post=how-to-sheathe-an-attic-kneewall-and-how-not-to#comment-3810 I live in Peachtree City, GA
I live in Peachtree City, GA and have a house with 9 of these knee wall areas I need to properly insulate. Of 4 companies I called I finally got a quote andwhat they propose is to install vent baffles on underside of roof OSB and then FG Batt insulation. The house was built in 2001 and now only has batt insulation on backside of drywall of knee walls which is slumping and was poorly installed. What is best solution for this situation? Should a perforated radiant barrier be placed over existing batting or should I proceed with attempting to insulate whole space by insulating underside of roof? Thank you for your great website.

]]> https://www.energyvanguard.com/blog/how-to-sheathe-an-attic-kneewall-and-how-not-to/#comment-3809 Tue, 24 Jul 2012 06:21:30 +0000 http://energyvanguard.flywheelsites.com/?blog_post=how-to-sheathe-an-attic-kneewall-and-how-not-to#comment-3809 Allison, I just noticed this
Allison, I just noticed this entry from just before we met.  
 
We deal with knee walls in 1930s-1950s all the time, 2-3/month at least.  
 
I disagree with you (albeit not that strongly, no Fight Club here) that a really solid air seal is necessary over the stud cavities in knee walls. The only air leakage in the stud cavities is typically the outlets, light switches, and access panels. 
 
Most of the air leakage we tackle is below the sole plate above the floor and in the floor joists directly below the knee wall. We are VERY thorough air sealing these areas with excellent results.  
 
A job we finished last week dropped from 4060 to 2150 cfm50 just with knee wall air sealing (we were able to get 8′ of one wall that had no top plate). 1000-2000 cfm50 reductions are fairly common with this method. 
 
Despite all the bad publicity reflective insulation is getting lately, I like to use it quite a bit on knee walls. We use a perforated variety to avoid the double vapor barrier. We like it because the 4′ rolls that fit most older knee walls are easy to drag in and install. It’s even made by your favorite company, Guardian! 
 
Since it encapsulates the fiberglass batts we often find (or install) it allows them to perform at their full R-value, plus it adds 2-4 (admittedly questionable) to the R-value. Also, of pretty big importance in hot days like we have been having, it reflects a big portion of the heat in the attic back into the attic. 
 
In a bit of heresy, we don’t worry too much about taping the seams or caulking/foaming it on, just staples. The customer feedback has been tremendous, and I’ve been shocked at the transformation on the jobs I’ve been on. 
 
So that’s what I think, what is your take?

]]> https://www.energyvanguard.com/blog/how-to-sheathe-an-attic-kneewall-and-how-not-to/#comment-3808 Wed, 18 Apr 2012 17:23:34 +0000 http://energyvanguard.flywheelsites.com/?blog_post=how-to-sheathe-an-attic-kneewall-and-how-not-to#comment-3808 Nathan S:
Nathan S: You make a good point. I think that if you can get your builders to let you be the last one in all the time, that’s great. It would prevent things like what I found recently in Nashville: The Cable Guy Did It! — Attic Insulation Gone Awry.  
 
I think you may have misunderstood my recommendation, though. I said the attic-side sheathing should be done during framing, not the insulation. It would help to get the kneewall completely covered when it’s most accessible. The insulation would still happen later. 
 
Thanks for comment, and I look forward to more comments in the future. We can never have too many educated, conscientious insulation contractors!

]]> https://www.energyvanguard.com/blog/how-to-sheathe-an-attic-kneewall-and-how-not-to/#comment-3807 Wed, 18 Apr 2012 17:10:34 +0000 http://energyvanguard.flywheelsites.com/?blog_post=how-to-sheathe-an-attic-kneewall-and-how-not-to#comment-3807 Hi Allison, 
Hi Allison, 
 
I’m a new guy at a fiberglass insulation contractor just up the road from you in Chattanooga. I’ve found your blog to be a great source of background knowledge to help me understand the weatherization industry and overall building performance – so thanks for creating a great resource. 
 
I need to offer an alternative perspective regarding your closing comments about sheathing the knee walls during framing and ensuring that the other sub-trades seal over the penetrations they create. In our experience the other trades cannot, and perhaps should not, be trusted to have a sufficient understanding of insulation (or the equipment/materials) to “cover their tracks,” so to speak, nor can we always expect the builder to enforce such a guideline. And I’m not faulting anybody for that — in their eyes, we’re the insulation guys, so it’s our job to worry about that stuff. In fact, on the occasions where we insulate a home and then another trade comes back to fix something up they may have missed and happens to disturb our work in the process, we get blamed for it and are called in to fix it. We realize the injustice of that scenario, but it’s the reality we face, and arguing about it loses us customers. 
 
So we typically insist on being the last trade to touch an unconditioned area. That way we can make absolutely sure that our installation is top-notch and is least likely to be disrupted by other trades. While our job would be much easier if we didn’t have to work around pipes and wires (and bears – oh my), our builders and homeowners get the best results from us when we come in last and trim the insulation to fit around all those things, and seal around all those penetrations. 
 
Perhaps as building performance guidelines become tougher, more GCs and sub trades will pick up some of that knowledge, but until then, our customers’ homes, the quality of our work, and our reputation are best served by our being the last trade to touch knee walls.

]]> https://www.energyvanguard.com/blog/how-to-sheathe-an-attic-kneewall-and-how-not-to/#comment-3806 Fri, 06 Apr 2012 22:46:48 +0000 http://energyvanguard.flywheelsites.com/?blog_post=how-to-sheathe-an-attic-kneewall-and-how-not-to#comment-3806 As a follow-up to my previous
As a follow-up to my previous comment, I verified that EnergyBrace is no longer available. The factory that produced it was purchased by Thermo-Ply maker Berry Plastics. Since the two products were essentially the same, the EnergyBrace name went away. 
 
I just found out that Thermo-Ply maker Berry Plastics recently sold its building products line to Ox Paper Tube. Since this just happened 4 weeks ago, Ox Paper does not yet have a web page up for Thermo-Ply.

]]> https://www.energyvanguard.com/blog/how-to-sheathe-an-attic-kneewall-and-how-not-to/#comment-3805 Mon, 26 Mar 2012 21:29:33 +0000 http://energyvanguard.flywheelsites.com/?blog_post=how-to-sheathe-an-attic-kneewall-and-how-not-to#comment-3805 Glad to see a nuts and bolts
Glad to see a nuts and bolts Building Science article again! Haven’t read the blog in a while, with all the Metric System, Daylight Savings, ACI and RESNET posts lately. Thanks.

]]> https://www.energyvanguard.com/blog/how-to-sheathe-an-attic-kneewall-and-how-not-to/#comment-3804 Mon, 26 Mar 2012 18:54:19 +0000 http://energyvanguard.flywheelsites.com/?blog_post=how-to-sheathe-an-attic-kneewall-and-how-not-to#comment-3804 nightwatch
nightwatch: Storage is good, but move the building envelope to the exterior wall and roofline. You don’t want the contents of those drawers to be your R-value. 
 
John Z.: The space behind the kneewalls shown above is unconditioned attic. One approach would be to move the building envelope to that sloped ceiling and exterior wall so that attic space is conditioned. If you don’t do that, you don’t need to do anything about the roofline back there. 
 
Craig L.: That’s a good approach. 
 
David B.: Well, that may explain why I couldn’t find Energy Brace online. Thanks for the better link for Thermo-Ply. I’ll update as soon as I’m done here. 
 
Franklin M.: Absolutely! I addressed that in the article on Bonus Rooms, listed in the Related Articles section. 
 
Franklin O.: I think this is the first time we’ve had two Franklins commenting in the same article! And yes, kneewalls present all kinds of problems. 
 
Marcus T.: Glad to be of service! 
 
Keith W.: (i) What if the drywall is perfectly sealed but attic air comes in the bottom of a kneewall and exits through the top plate (if there is one)? (ii) Thanks for bringing up the topic of vapor retarders and climate zones. Yes, in a cold climate with a vapor retarder on the inside, you definitely don’t want another one on the outside. (iii) I’ve spent my time working in those small spaces behind kneewalls, so I know how difficult it can be. I still don’t like housewrap for that application, though.  

]]> https://www.energyvanguard.com/blog/how-to-sheathe-an-attic-kneewall-and-how-not-to/#comment-3803 Mon, 26 Mar 2012 17:14:22 +0000 http://energyvanguard.flywheelsites.com/?blog_post=how-to-sheathe-an-attic-kneewall-and-how-not-to#comment-3803 Several things that I do not
Several things that I do not understand in the posted approaches to treating thee knee-walls! 
 
 
 
First, the sealing of the joints of the rigid material or house wrap on the attic side of the knee-wall surface is not NEEDED – if and I strongly state IF, the knee-wall has been throughly air sealed. Air leakage is at the pressure barrier – which is before the thermal barrier. 
 
 
 
Second, it should be noted that in cold climate conditions, a vapor retarder should not be applied on the cold side of the installed instulaton. The use of foil faced (even FSK)materials should never be installed after the cavity insulation has been installed. 
 
 
 
Third, many side attic (knee-wall) areas are very restrictive in accessiblity and working height. This makes is extremely difficult to install a rigid thermal barrier over the stud framing. I suggest installing horizontally stacked R-19 unfaced fiberglass batt insulation across the back side, anchored to the studs and then covered from roof deck to joist top with house wrap material – this material does NOT have to be air thight! It’s purpose is two fold, one to insure stability of the installed batt and second to lower air movement acorss the batt.

]]> https://www.energyvanguard.com/blog/how-to-sheathe-an-attic-kneewall-and-how-not-to/#comment-3802 Mon, 26 Mar 2012 02:05:13 +0000 http://energyvanguard.flywheelsites.com/?blog_post=how-to-sheathe-an-attic-kneewall-and-how-not-to#comment-3802 Alison, we call these short
Alison, we call these short attic walls dormers, but the problem is identical here in Australia. I dont normally cover the back of these batts, so I have learnt something from you today.

]]> https://www.energyvanguard.com/blog/how-to-sheathe-an-attic-kneewall-and-how-not-to/#comment-3801 Sun, 25 Mar 2012 04:48:56 +0000 http://energyvanguard.flywheelsites.com/?blog_post=how-to-sheathe-an-attic-kneewall-and-how-not-to#comment-3801 I seen a good bit of home
I seen a good bit of home with kneewall problems in the bonus rooms and livingroom. Because the wall was not seal correctly.

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