Author Topic: DIY Attic Insulation Prep w/pics... (plz help me idiot-proof!)  (Read 834 times)


  • 5 O'Clock Shadow
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DIY Attic Insulation Prep w/pics... (plz help me idiot-proof!)
« on: October 06, 2018, 11:12:52 AM »
Hi Mustachian DIYers! 

I'm hoping to lean on your collective expertise to help me idiot proof the blown-in insulation I'm hoping to install before winter.  This install has been expanded somewhat because our 30-year old AC unit has failed and been replaced with a ductless system.  Ultimately, I'm hoping to cover the ~1000 sqft of the attic with blown-in cellulose to around R60.  Please jump in and correct me if you find errors in my preparation or have points of improvement!

Until I figure out how to link images on this forum with the proper sizing, I'll just link to the imgur directly.  Any help in this regard would be greatly appreciated!

The elephant in the room is the gigantic series of ductwork, air intakes, and evaporator coil in the attic:

You can see it's quite a mess and dominates the attic space.  All of that mess must go.  Any tips or suggestions in removing it would be greatly appreciated!  The electrical connection runs along the ridge line and is easy to access thankfully.  Here's a shot of the backside of the unit that shows the cpvc plumbing connection I'll need to cap, the refridge line (already drained) and electrical connections:

After I wrap my head around the easiest way to clear all that crap, my nitty-gritty questions are as follows:

I'll be cutting off the gable vents with already cut wood pieces.  The soffit vents i've begun installing match the open ridge vent (yes, the previous owners had both ridge and powered gable vent at the same time.)  I've already installed the lowest section of rafter vents to allow the soffit vent to air to pass.  How high should I continue my rafter vents?:

In that picture, the black hashmark on the rafter is high point of the r60 I'll be blowing in.  I'm hoping the 1 and a half sections of rafter vent you see on the right is sufficient to allow air flow.  On the left, I installed two full length sections for contrast.  The right 1.5 sections are just about 6 inches above the blown-in line, so it should be good, but just wanted to check.

I'm also worried about properly filling gaps between the vents and attic floor so blown-in doesn't clog the soffits.

Here you can see my efforts to throw some Roxul into the gaps in the connection points, and the little rake my friend is letting me borrow for that purpose!  I'm thinking some some unfaced r-19 fiberglass insulation (6 inch diameter) will be perfect to cut and shove into those gaps. 

Next up, I'm hoping to fill the cracks and air gaps in the attic floor that occur at room wall junctions:

I'll be using Big Stuff or similar product to fill these very common gaps like so:

This sort of fix prompted questions from my wife that I didn't know how to answer directly (read: with an authority she'd respect and/or without sounding glib).  She's worried about the gap being too tight and the wood not being able to shift and expand naturally.  I don't think that's a problem, but just wanted to check.

Several junction boxes are positioned throughout the attic:

Here's a before and after picture of my covering one such box in Roxul:

Hopefully that is sufficient to prevent blown-in cellulose from creeping inside.  This may be overkill of course, but I just wanted to be super safe regarding electrical fires and also have the outlets be more easily accessible.  I've put notes on the rafters marking each box so it can be found after the blown-in goes on top. 

Next up, our one recessed light:

Here you can see the box of the light just behind the cover I'll be using to protect it.  That cover, once stapled down and gap-filled with Great Stuff, is safe to cover in cellulose I've read, but just wanted to make sure.

On the right hand side of that picture and very dimly lit, you'll see the tube of one of our two bathroom vents.  Both of these vent out to the soffits... ugh.  There are no air intakes within 4-feet of either side of them.  I'm hoping that's sufficient to prevent the moist air from getting sucked back up.

Because they are old and may need to be operated on in the future, I'm planning on covering up the rafters with the bathroom vents with batts of Roxul or pink fiberglass insulation.  That way, if we need to replace them, I can remove the batt and not worry about the cellulose shifting.  I'm also hoping that if (god forbid) there's a leak in one of the vents, the Roxul covering the vents will be less prone to mold than the cellulose.

Any suggestions, criticism, thoughts, tips etc would be greatly appreciated!  I'm a relatively new homeowner and green behind the ears.  Thanks in advance!


  • Walrus Stache
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Re: DIY Attic Insulation Prep w/pics... (plz help me idiot-proof!)
« Reply #1 on: October 06, 2018, 01:37:03 PM »
I'll leave it to true experts to comment on specifics, but from a sometimes DIYer who tackled a similar job it appears you are doing well!  Yes, the expanding foam does expand so you'll probably learn to use less than it appears you need at first.

Adam Zapple

  • Bristles
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Re: DIY Attic Insulation Prep w/pics... (plz help me idiot-proof!)
« Reply #2 on: October 07, 2018, 07:10:07 AM »
I'd say you've thought of everything...almost to a fault.  I am looking at the air gaps you sprayed with Great Stuff, is that just where the wall framing meets the ceiling joists (attic floor joists)?  I would not really consider this an air gap since the wallboard does not allow air to pass through unless I am completely missing something.  I'd be more concerned about any penetration through the sheetrock/plaster like electrical boxes etc.  Where anything penetrates the wood top plate of the walls can be caulked (cheaper) instead of using great stuff if you'd like. 

Great stuff and Roxul are both insanely expensive so use them as sparingly as possible.  If you can use clear plastic for air seepage, that's the route I would take as opposed to Great Stuff, where feasible.  Your goal is to improve efficiency for environmental and FINANCIAL reasons.  If you want to cover junction boxes with roxul, that is fine (though unnecessary unless required by your local building codes) but you only need to encase it with a small piece so use what you already have and don't buy any more.  Junction boxes come in contact with regular insulation everywhere in your house so Roxul is not necessary...but I would never fault someone for being extra fire safe.  I actually like that because the boxes will be easier to find in the future.  To be honest, I don't think I've ever seen Roxul in an attic and I've been in hundreds of them.

Worrying about natural shifts in the wood is unnecessary.

The rafter mates only need to run higher than the cellulose. 

Using fiberglass batts where you will be working in the future is a very good idea.

You are doing a nice, thorough job!  Good luck.  The cellulose is kind of fun to apply.  My home depot lets you borrow the machine for free when you buy enough of the insulation.


  • Stubble
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Re: DIY Attic Insulation Prep w/pics... (plz help me idiot-proof!)
« Reply #3 on: October 28, 2018, 03:44:33 AM »
cool. i have good experience doing this on the place I just built.

follow the EPA guidelines for air sealing.  They really helped--I turned off the light in the attic, but kept the lights on in the room below and went to town using acoustic sealant, caulking and great stuff.

I did run into one problem with the great stuff since my configuration was trusses, 1/2" OsB and then ceder tongue and groove attached to the OSB for my 2nd floor ceiling and that was the great stuff got in between the truss and OSB when I was air sealing and actually expanded the OSB down which made my crown molding really hard to install since I had a little curvature that I couldn't fix even with a floor jack.

My only recommendation would be to use the window and door great stuff since its more flexible, but you may be beyond that point.  I would also tape your rafter vents at the intersections and make sure you have at least 8-12" of vent above above your desired insulation level so you don't accidentally shoot cellulose into your soffit down the vent.

What else...from the picture, I would wrap the gas waste pipe with insulation since it tends to stay warm and can condensate if you don't.  I made sure I put at least 8" of insulation over all my bathroom fan piping up there.  they exhaust out the gable ends.  as a good practice, you should turn them on about 5 min before you shower and leave them on 10-15 after.  Do you have newer LED can lights?  double check, because the new ones don't need those covers.