Attic insulation

Patchogue Phil_28

Blown loose-fill cellulose has an R-factor of 3.2 to 3.8 depending on manufacturer. Settle of LOOSE cellulose is 20%. As an example, what was installed in my attic (manufactured by Pinnacle Industries in Bohemia, NY) has an R-factor of 3.6 installed, AFTER settling. 16 inches will settle to 12.8 inches. Multiply by 3.6 to get R-factor of 46.

Here's a chart I found online:


Recommended Specifications by Insulation Type</b>

<table border="1" cellspacing="2" cellpadding="0">
<tr>
<td width="240"></td>
<td width="120"><span class="bodysmall"><b>Cellulose</b></span></td>
<td width="120"><span class="bodysmall"><b>Fiberglass</b></span></td>
<td><span class="bodysmall"><b>Rock Wool</b></span></td>
</tr>
<tr>
<td width="240"><span class="bodysmall">R-value/inch</span></td>
<td width="120"><span class="bodysmall">3.2—3.8</span></td>
<td width="120"><span class="bodysmall">2.2—2.7</span></td>
<td><span class="bodysmall">3.0—3.3</span></td>
</tr>
<tr>
<td width="240"><span class="bodysmall">Inches (cm) needed for R-38</span></td>
<td width="120"><span class="bodysmall">10—12 (25—30)</span></td>
<td width="120"><span class="bodysmall">14—17 (35—43)</span></td>
<td><span class="bodysmall">11.5—13 (29—33)</span></td>
</tr>
<tr>
<td width="240"><span class="bodysmall">Density in lb/ft3 (kg/m3)</span></td>
<td width="120"><span class="bodysmall">1.5—2.0 (24—36)</span></td>
<td width="120"><span class="bodysmall">0.5—1.0 (10—14)</span></td>
<td><span class="bodysmall">1.7 (27)</span></td>
</tr>
<tr>
<td width="240"><span class="bodysmall">Weight at R-38 in lb/ft2 (kg/m2)</span></td>
<td width="120"><span class="bodysmall">1.25—2.0 (6—10)</span></td>
<td width="120"><span class="bodysmall">0.5—1.2 (3—6)</span></td>
<td><span class="bodysmall">1.6—1.8 (8—9)</span></td>
</tr>
<tr>
<td width="240"><span class="bodysmall">OK for 1/2" drywall, 24" on center?</span></td>
<td width="120"><span class="bodysmall">No</span></td>
<td width="120"><span class="bodysmall">Yes</span></td>
<td><span class="bodysmall">No</span></td>
</tr>
<tr>
<td width="240"><span class="bodysmall">OK for 1/2" drywall, 16" on center?</span></td>
<td width="120"><span class="bodysmall">Yes</span></td>
<td width="120"><span class="bodysmall">Yes</span></td>
<td><span class="bodysmall">Yes</span></td>
</tr>
<tr>
<td width="240"><span class="bodysmall">OK for 5/8" drywall, 24" on center?</span></td>
<td width="120"><span class="bodysmall">Yes</span></td>
<td width="120"><span class="bodysmall">Yes</span></td>
<td><span class="bodysmall">Yes</span></td>
</tr>
</table>

Matt_21

my attic has r-11

fiberglass. i started laying r-25 on top of the r-11 but have decided to have blown-in installed instead. can i blow it on top of the fiberglass or do i have to remove it? also, how thick should i go?

Big Ed

Oh -No

You will be cleaning that stuff for years to come. Every time some one goes up there . Every time work needs to be done. Being a AC guy (Attic Crawler) I want to talk you out of it....Usethe roll out stuff

Rookie_3

Whatever you put, don't flatten the R-11 or it will loose
some of it's R value.

Ed is right it's messy and usually settles too. Look when it is blown into walls and then settles and drops from the top down. Heat rises and ends up at the top of the wall and ceiling where it has dropped...........ROOKIE

Patchogue Phil_28

cellulose is best

Don't bother with fiberglass insulation in any form. Have cellulose blown ON TOP of whatever you have in the attic.

Fiberglass is not a great insulation product. It was invented as an air filter. Thus it allows heat to flow thru it with drafts.

Cellulose is a better insulator since it blocks air flow and it also blocks radiant heat gain in the summer, thus saves on air conditioning costs too.

Cellulose gains outway any inconvenience to the once in a dozen blue moons when some a/c guy has to go in the attic.

You could construct an elevated catwalk down the middle of the attic for access. Then have 16 inches or more of cells blown in.

Before insulating, air seal all penetrations thru the attic floor i.e. foam seal the holes from wiring; block chimney chases with sheet metal. The drafts thru these holes leaks a lot of your hard earned heating dollars. Cells can block much of this loss but plugging the holes first makes it even better.

Go with cellulose.

Matt_21

phil

thanks for the info. what r value will 16" give me? i was planning on making a catwalk to the air handler since i'm also an a/c guy so i'll be the one walking through it.

Bob Sweet

Conservatively speaking,

R value =3.0 per inch of cellulose.

Patchogue Phil_28

mistaken

Rookie

I respectfully declare that you are mistaken. Cellulose installed in walls will NOT settle. FACT (to borrow a phrase).

Whether dense-packed blown in or wet sprayed, cellulose at proper installation density will completely fill the wall cavity with no gaps.