https://www.energyvanguard.com/blog/does-it-make-sense-to-move-the-building-envelope-to-the-roofline/ Building science knowledge, HVAC design, & fun Thu, 10 Jul 2014 02:44:18 +0000 hourly 1 https://wordpress.org/?v=6.6.2 https://www.energyvanguard.com/blog/does-it-make-sense-to-move-the-building-envelope-to-the-roofline/#comment-1675 Thu, 10 Jul 2014 02:44:18 +0000 http://energyvanguard.flywheelsites.com/?blog_post=does-it-make-sense-to-move-the-building-envelope-to-the-roofline#comment-1675 Does anyone ever use foam on
Does anyone ever use foam on the attic side of the ceiling? Eliminates the thermal/ignition barrier issue as it is against the drywall ceiling. Less square footage than the roof deck.

]]> https://www.energyvanguard.com/blog/does-it-make-sense-to-move-the-building-envelope-to-the-roofline/#comment-1674 Wed, 10 Oct 2012 01:33:48 +0000 http://energyvanguard.flywheelsites.com/?blog_post=does-it-make-sense-to-move-the-building-envelope-to-the-roofline#comment-1674 @George, I don’t normally
@George, I don’t normally specify SPF on flat ceilings under a vented attic. There are less expensive ways to seal the ceiling, and then pile on blown-in fiberglass for cellulose. Applying foam to the ceiling provides very little extra benefit.  
 
When encapsulating the attic (e.g., insulating roof deck rather than ceiling), it is necessary to use an air impermeable insulation on the roof to prevent condensation on the cold underside of roof deck (not an issue in a properly vented attic, if ceiling is tight). Code requires a minimum amount of air impermeable insulation when envelope follows the roof line. See Section R806.4.5, and Table R806.4 in particular: http://bit.ly/ORySkx

]]> https://www.energyvanguard.com/blog/does-it-make-sense-to-move-the-building-envelope-to-the-roofline/#comment-1673 Wed, 10 Oct 2012 00:50:25 +0000 http://energyvanguard.flywheelsites.com/?blog_post=does-it-make-sense-to-move-the-building-envelope-to-the-roofline#comment-1673 In all of your experience,
In all of your experience, what is the best way to encapsulate to the ceiling line for new construction?

]]> https://www.energyvanguard.com/blog/does-it-make-sense-to-move-the-building-envelope-to-the-roofline/#comment-1672 Mon, 27 Aug 2012 19:38:36 +0000 http://energyvanguard.flywheelsites.com/?blog_post=does-it-make-sense-to-move-the-building-envelope-to-the-roofline#comment-1672 My husband and I have been
My husband and I have been thinking about the different options that we have for insulation. We are building a new home to live in, and we have been leaning towards the spray foam insulation. We have read and heard that spray foam insulation is much more efficient, and much safer than the fluffy insulation. Another plus to this, is that bugs and other critters cant nest in the spray foam insulation , and so we would never have to worry about any little surprises. Has anyone used the spray foam insulation ? What are the pros and cons to this product? Is it worth the investment to purchase the spray foam insulation ?

]]> https://www.energyvanguard.com/blog/does-it-make-sense-to-move-the-building-envelope-to-the-roofline/#comment-1671 Fri, 08 Jul 2011 17:30:41 +0000 http://energyvanguard.flywheelsites.com/?blog_post=does-it-make-sense-to-move-the-building-envelope-to-the-roofline#comment-1671 Insulation should be removed
Insulation should be removed when spraying foam in an existing attic. Existing insulation can hold in the odors generated when spraying the foam. In the near future, you will not see foam manufacturers standing behind their product when there are odor issues if the insulation is not removed.

]]> https://www.energyvanguard.com/blog/does-it-make-sense-to-move-the-building-envelope-to-the-roofline/#comment-1670 Wed, 08 Jun 2011 05:33:43 +0000 http://energyvanguard.flywheelsites.com/?blog_post=does-it-make-sense-to-move-the-building-envelope-to-the-roofline#comment-1670 Allison, 

Allison, 
 
Long time no see (charleston 2009). I have a small truss roof brick ranch in North Texas. Local foam contractors keep recommending open cell foam, or spray-in radiant barriers. They want to shy away from closed cell foam on the attic roof line.  
 
Questions: 
 
1. Can the open cell foam provide the same envelope encapsulation on the roofline as closed cell? 
 
Do you know anything about these spray-in radiant barriers (metal paint) ?

]]> https://www.energyvanguard.com/blog/does-it-make-sense-to-move-the-building-envelope-to-the-roofline/#comment-1669 Wed, 25 May 2011 21:42:03 +0000 http://energyvanguard.flywheelsites.com/?blog_post=does-it-make-sense-to-move-the-building-envelope-to-the-roofline#comment-1669 Folks, re: safety with spray
Folks, re: safety with spray foam, please consult the official site established by the Center for the Polyurethanes Industry (CPI), http://www.spraypolyurethane.com; it is intended for SPF contractors, weatherization professionals, do-it-yourselfers (DIYers), and homeowners, and provides guidance on related health and safety issues.

]]> https://www.energyvanguard.com/blog/does-it-make-sense-to-move-the-building-envelope-to-the-roofline/#comment-1668 Tue, 24 May 2011 22:39:51 +0000 http://energyvanguard.flywheelsites.com/?blog_post=does-it-make-sense-to-move-the-building-envelope-to-the-roofline#comment-1668 @M.Johnson said &quot
@M.Johnson said “conditioned volume is increased significantly”, and “roof has significantly more area to be insulated” 
 
Spot on. In fact, I would argue that encapsulating the attic may in some cases actually increase overall loads (even though attic is not directly conditioned). For example, if you assume a nominal 10F delta-t across the uninsulated ceiling plane on a design day, it’s not that hard to calculate conducted heat transfer using the parallel path layers) method, compared to, say, a 50F delta-t in the case of a well insulated ceiling. (You’d also need to account for infiltration in both cases.) What’s difficult to analyze is the annual performance for an encapsulated attic, since I’m not aware of any way to estimate delta-T’s in an hourly sim. This is an area that deserves further research. 
 
I recently worked on a large new home with a 14/12 roof that was specified to be encapsulated. Not surprisingly, the insulation bid was just ridiculous. As usual, there was no possibility of moving HVAC inside. By roughly bracketing potential savings in duct losses, I couldn’t see any way for this turkey to fly. Fortunately, I convinced the builder to vent the roof and spend a small part of the savings on atomic air sealing the ceiling plane. I specified a horizontal AHU (note that upflow in a vented attic is MUCH worse) with maximum verified leakage at 2% of fan flow. 
 
In any case, the real key is to get the ceiling sealed up. To Allison’s original point, the cost of achieving this in retrofit plays heavily in the cost-benefit analysis.

]]> https://www.energyvanguard.com/blog/does-it-make-sense-to-move-the-building-envelope-to-the-roofline/#comment-1667 Tue, 24 May 2011 17:07:47 +0000 http://energyvanguard.flywheelsites.com/?blog_post=does-it-make-sense-to-move-the-building-envelope-to-the-roofline#comment-1667 In cases where its been
In cases where its been impossible (in other words, the builder refused) to install the system in the conditioned space, we have had success in convincing the players to at least install the air handler in the conditioned space. This usually goes in a centrally located closet where the return can stay in the conditioned space. The supply duct goes up into the attic with the outlets located on the inside wall, minimizing exposure. Then we go to the extreme on the duct insulation. Its probable you could spend a fraction of the cost to insulate the roof deck to aggressively insulate the duct instead. We have sprayed closed cell R-19 on trunk ducts in the attics and double insulated with duct wrap. I even saw one contractor wrap the trunk with 2 inch XPS under duct wrap. (no the inspector didn’t see it) But the flex is still the weak link. R-8 is usual and customary but also pitiful. At least they are short runs most of the time.

]]> https://www.energyvanguard.com/blog/does-it-make-sense-to-move-the-building-envelope-to-the-roofline/#comment-1666 Tue, 24 May 2011 16:42:12 +0000 http://energyvanguard.flywheelsites.com/?blog_post=does-it-make-sense-to-move-the-building-envelope-to-the-roofline#comment-1666 Do not forget the simple
Do not forget the simple things about energy efficiency here:  
1) The conditioned volume is increased substantially. 
2) The roof has significantly more area to be insulated, than the ceiling plane. 
 
Remember Lstiburek has gone on record stating a gross efficiency disadvantage (was it 5% or 10%?) which would be surpassed by getting leaky ducts inside conditioned space.

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