0 Helpful?

Dense-packed cellulose OK?

We built a home 11 years ago with 5 inches of Icynene sprayed against the 1/2-inch plywood sheathing, no vent, in our cathedral ceiling.

12 inch I-beam rafters from soffit to ridge, no vapor barrier.

After energy audit it was recommended to fill remaining 7 inches with dense-packed cellulose. Heat is a wood stove and radiant flooring, minisplit for AC and auxiliary heat.

We are in southern Wisconsin Zone5A/6B.

What are your thoughts?

Thank you in advance,

Asked by Scott Doherty
Posted Jan 25, 2013 8:21 PM ET
Edited Jan 28, 2013 8:30 AM ET


4 Answers

Select your preferred way to display the comments and click "Save settings" to activate your changes.

Is the spray-foam open cell or closed?

Answered by Jesse Smith
Posted Jan 25, 2013 8:40 PM ET


Assuming you're talking about open-cell Icynene, your 5 inches of insulation has a value of about R-18 or R-19. That doesn't meet code.

Your insulation is vapor-permeable (that's not good) but air-impermeable (that's good). According to the building code, you need at least R-20 (in climate zone 5) or R-25 (in climate zone 6) of air-impermeable insulation before you can switch to air-permeable insulation (like cellulose). For more information on this topic, see How to Build an Insulated Cathedral Ceiling.

So the Icynene doesn't quite get you to where you want to be, but it's darn close. The bottom line: You will probably be OK if you follow your plan, especially if the relative humidity during the winter on the interior of you house is kept in a reasonable range. If you want to sleep without any worries, though, you might want to install more spray foam instead of cellulose.

Answered by Martin Holladay
Posted Jan 26, 2013 7:24 AM ET


#1. Open Cell
#2 RH is held at 40% or below, without tearing out drywall (dense pack will be done thru 2" holes in each bay) this seems to be the reasonable option, are the concerns moisture forming in the cellulose?

Answered by Scott Doherty
Posted Jan 26, 2013 7:59 AM ET


Q. "Are the concerns moisture forming in the cellulose?"

A. Since your spray foam layer is a little thin, the interior surface of the spray foam may be cold enough to allow moisture to condense or moisture to accumulate. Because the spray foam is vapor-permeable, the most likely location for the moisture to accumulate would be in your roof sheathing (the plywood). Keeping a low level of indoor humidity reduces the risk. You should never use a humidifier.

Answered by Martin Holladay
Posted Jan 28, 2013 8:46 AM ET

Other Questions in Energy efficiency and durability

Building a house in Greenville, SC — insulation and air sealing questions

In Green building techniques | Asked by Farm House | Mar 15, 17

Replacement boiler sizing based on past usage

In Energy efficiency and durability | Asked by Efficiency Fan | Mar 23, 17

Closed-cell spray foam — Basement insulation concerns

In General questions | Asked by user-6803198 | Mar 23, 17

12v dc voltage system to run "micro sized" hydronic heating system

In General questions | Asked by freewillieklr | Mar 23, 17

Hydronic Heating System Hydraulic Buffer Tank vs Hydraulic Seperator

In Mechanicals | Asked by Roger Smith | Feb 26, 17
Register for a free account and join the conversation

Get a free account and join the conversation!
Become a GBA PRO!