Hi, just wondering your thoughts are regarding blown F.G. specifically the atticcat system with proper air sealing vs. cellulose.


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ok, when you set up a scissor truss, half cathedral, or tray ceiling in the middle of a ranch house, how do you use just cellulose to insulate?  what about the knee walls at each end of a scissor truss bump?  or the wall/ceiling intersection at the top of the knee walls in that system?  with the labor involved in adding some structure to support the blown cellulose, these are acceptable places to integrate foam for best results.  how durable is housewrap stapled to that wall to support cellulose? 

in a scissor truss ceiling, we often install soffit bafles up to a point where they will be above the height where cellulose blown to R-40 at the ridge line of the inner pitch of the scissor will be nearly flat extended out to the roof line.  we want to fill the scissor completely with cellulose as this is much less expensive than spraying the roof.  we also want to avoid crushing those baffles, so we reinforce them with 2 inches of closed cell foam, and we seal at the soffit between the roof and exterior wall top plate with rigid and spray foam.  can you do a similar job with just cellulose? 

how do you insulate a basement wall with cellulose?  band joist?  what if there are ducts suspended below a floor in a crawl space? 

to do it all and do it right, there are times you need more than one material.

unless, as a design build guy you simply refuse to use scissor trusses, tray ceilings, attic duct systems, recessed lights, multi level designs, basements, crawl spaces, or other commonly requested features.   

also, there is convective movement of air through cellulose.  if there were not, we all would stop airsealing attic floors immediately.  loose cellulose applied over a pourous ceiling is of little value.  as a design build guy you may specify airtight ceilings, sheetrock the whole ceiling before any partitions are built design out recessed lighting,  no mechanical penetrations through the ceiling, etc, but that doesn't mean cellulose is the only product used to insulate in common construction processes where you are not the designer.

I agree with you Patrick, you can't use just cellulose unless you have designed everything for it which Robert is fond of doing & as he alluded to - he is pretty much anti-foam (My question is what does he do under the slab & perimeter?) 

With that said for knee walls you can use the cellulose sprayed in with binders or you need to dense pack it using their special mesh/netting material to hold it in place which than can be covered with plywood / osb / foam / drywall or sometimes left alone.

Along those lines, for new construction - why would you design a house now with ducts in the crawl space unless it is a sealed crawl? If they are not going with a sealed crawl than it needs to be run in the conditioned space

Jumping back to the anti-foam - you also got to remember there are a few people out there that are strongly anti-foam. Even if they are honest & remember that the P in GWP stands for potential & it starts off with a 50% error margin before they even begin multiplying the "effects" it won't matter. The "study" that was completed is just icing on the cake in their mind & no there is no changing their minds

No one I know is "anti-foam", but authentically green builders are pro-environment and the greatest crisis humanity ever faced is anthropogenic climate change (you almost sound like a denialist).

GWP (global warming potential) doesn't mean "maybe" - it means that's its scientifically determined contribution to the problem and there is no 50% error margin - the science is very well developed and quite precise (within the complexity and multiple feedback loops that it entails).

Since XPS and closed cell spray foam are very large contributors to global warming, it's wise to use them as little as possible. I still use XPS sub-grade and under slabs since there is not an affordable and effective option at this time (though some are recommending perlite or semi-rigid mineral wool, and Alex Wilson has used cellular glass).

In fact, the 2010 graph that Armando put up is out of date, as Alex Wilson of Environmental Building News has updated his research (with the help of Building Science Inc) and presented new data that shows that XPS and closed-cell spray foam actually increase global warming beyond a modest R-value rather than reduce it over their lifetime.



You're quite right about the problems in retrofitting all the crazy building configurations that are out there today, and many new homes that are simply not designed with the best insulation strategy in mind.

And you're correct that I design to avoid all those common problems - flat ceilings, no ceiling penetrations, stick-built roofs, simple house geometries (a primary cost factor). And, in New England, we don't build crawl spaces and homes are generally hydronically (or woodstove) heated since they don't need AC.

On renovation projects, I've used one-component spray foam, rigid foam board, blue jean batts (fiberglass before I couldn't stand it anymore), and I've even recommended spray closed-cell polyurethane for really problematic situations such as old dry-laid stone foundations that leak like a sieve. 

But, as Sean has already pointed out, the cellulose industry has developed methods for damp spray and netted dense-pack which are becoming the standard today and offer a lot more options. If you use properly rigid vent baffles (not those worthless styrofoam things) then reinforcement is not needed.

As for convection in cellulose, it is close to negligible in loose-fill and virtually non-existent in dense-pack (otherwise code officials wouldn't accept it as a fire-stop). However, it doesn't meet the very strict air barrier requirements of the ABAA - 0.02L/(s•m2) @ 75Pa. or 0.004 cfm/ft2  @ 1.57 psf - the air tightness of ½" drywall. So I rely on air-tight drywall for the air barrier.


Hi all,

I appreciate all the responses, and come to a conclusion.  For projects larger than approx. 500 to 600 sf I'll sub it out for cellulose and anything smaller I'll do it myself with the atticcat and blow fiberglass.

Paul, just make sure your subs understand that any attic should be thoroughly air sealed before they blow the insulation. Also, make sure they understand proper attic ventilation. Finally, with any kind of storage or floored sections of attic, the boards should be pulled and the areas sealed, or the cellulose should be dense-packed under the flooring. Trust me on this stuff, it is typically the difference between just blowing in some additional insulation and a highly effective improvement.

Hey Patrick,

Being that air sealing is a separate improvement, with a cost and profit unto itself, I'll be doing all the air sealing and prep work needed for an attic blow. This way they just need to come in a blow the cellulose.


Patrick is a Saint.  I am a contractor, call me Pat.

have you seen a product called EcoSeal by Knauf Fiberglass?  they recommend a sprayer to use to apply it, and the sprayer has a cost of nearly $5000.  I bought the recommended sprayer and i found in some applications it is just as easy to apply it with a spatula or brush.  the material has a consistency like greased snot, it is odorless and as far as i can tell quite safe.  water cleanup.   we are abandoning the use of the cold applied plural component foam systems and substituting this stuff in attics. i haven't used it enough to find problems yet, but I think it is cheaper and safer than foam for airsealing an attic floor.  the ony reservation I have is it takes several hours to dry, but my theory is if i can do a blower door test, the material has been sucked into the holes and it is held there by gravity.  i think I can assume it will dry fine. 

I would be interested in other folks experience with this stuff. 


please also take command of the roof edge, get the baffles in if you want soffit venting and seal between them and the wall top plates somehow.  we still use foam for that, though I think we will try the EcoSeal spray applied to a fiberglass plug becasue the sprayer I have has a 30" wand applicator. 



Thanks for the info, this looks interesting, But $5000 is a bit pricing, it looks like a fancy paint sprayer.

And yes definitely exterior and interior top plates is a must along with baffles, I agree.


Paul, being that you are a one person show who can use a helper or two, you should still be able to offer different types of insulation and sealing because it really depends on the client, the budget and the specific house. I lean towards blown in cellulose and dense pack cellulose under attic flooring.  I seal off all the bypasses, gaps and the top plates all around and upto the baffles, which 99% of the time I am installing or properly re-installing existing ones.  I don't own my own machine, so when I purchase the Greenfiber cellulose bags from the homecenter, usually Lowe's, I get the machine (blower) for free to use.  You can do the same thing with the Atticat for corning blown in FG.  I find that I get too itchy with the FG and it is really a lot less healthy if it does happen to get into your airway.  Using a combination of materials is usually the best thing for efficiency, budget, durability and comfort.  Don't be afraid to try some new things.


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