Author Topic: retrofit wall insulation  (Read 565 times)

bacchi

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retrofit wall insulation
« on: November 26, 2018, 12:19:41 PM »
I need some thoughts from the hive mind.

I'm insulating an older house and I received some retrofit wall insulation bids recently. The concern is that there is no sheathing behind the siding.

Hardie plank --> moisture barrier --> studs --> drywall.

The cellulose will be blown in from the inside. My fear is that dense packing cellulose into walls without sheathing might blow out or crack the siding. Of course, the contractor (salesperson) assured me that it's never happened and won't happen, etc., etc., but their contract specifically states that "faulty construction" is not covered. While it's not technically faulty construction, it's definitely non-standard and doesn't meet today's code.

Is this a valid concern? Or is there not enough pressure and weight in a 16" stud cavity to crack hardie plank?


GreenEggs

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Re: retrofit wall insulation
« Reply #1 on: November 26, 2018, 12:50:18 PM »
Are you saying that there's no insulation in the walls now?  But there is a vapor barrier in place?


Assuming the siding is properly fastened there shouldn't be any gaps for the insulation to push through.  I'd go ahead and try it.  What other option do you have?





bacchi

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Re: retrofit wall insulation
« Reply #2 on: November 26, 2018, 06:35:34 PM »
Correct, there's no insulation in the walls. There is an air/moisture barrier but it's not strictly a vapor barrier. In any case, it will prevent cellulose from leaking through.

The only other option is to wait until the drywall is replaced probably years from now.

Fishindude

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Re: retrofit wall insulation
« Reply #3 on: November 28, 2018, 12:36:55 PM »
It would be unusual not to have some sheathing behind the Hardie plank siding?
Cut a hole somewhere or take off a piece of siding and see what you really have.

bacchi

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Re: retrofit wall insulation
« Reply #4 on: November 28, 2018, 01:05:42 PM »
Nah, I'm positive that there's no sheathing. There used to be wood siding, which provided the structural stiffness. There is let-in bracing but that won't help individual planks.

I'm going to give James Hardie a call and see if they have an opinion on dense packed insulation. I feel like it'd be ok but, if not, I'll be buying a lot of bondo at best.

J Boogie

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Re: retrofit wall insulation
« Reply #5 on: November 28, 2018, 04:27:01 PM »
Just buy some shrink wrap and make a few trips around the exterior of your house :)

But in all seriousness, I think there is a bit of a risk. I don't know the pressure exerted by blown in densepack, but I do know that siding is typically nailed in and there is no mechanical connection keeping the siding on the house, but rather the friction of the nail in the stud. And the densepack will be exerting force in the direction required to undo this fastener.

It might not be that likely, but it's also possible the nails used were short, or not the best material, or loosened by expansion/contraction due to moisture/temperature (not super likely hardieplank though, but might be worth considering)

Abe

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Re: retrofit wall insulation
« Reply #6 on: November 28, 2018, 05:02:28 PM »
Wouldn't the sheathing also just be nailed in? Any reason the Hardiplank nails would be weaker? Also, if the siding runs overlap as traditionally done, that should somewhat help reduce the risk of ripping out. There is a risk but you can test it on a smaller section of wall and see what happens. Worse case you have to nail the Hardiplank back in.

zolotiyeruki

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Re: retrofit wall insulation
« Reply #7 on: November 28, 2018, 06:24:15 PM »
I've seen demos of dense pack cellulose on a simulated wall, where one side of the studs was 'sheathed' with thin plexiglass.  I personally wouldn't be too concerned with the pressure exerted by the process.

Aha, found the video: https://www.youtube.com/watch?v=ce-mM7R11Lo

HipGnosis

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Re: retrofit wall insulation
« Reply #8 on: November 29, 2018, 09:59:15 AM »
this video shows  dense-packing a 12″ thick wall with landscape fabric on both sides of the studs.   
« Last Edit: November 29, 2018, 10:02:03 AM by HipGnosis »

Kahooli

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Re: retrofit wall insulation
« Reply #9 on: November 29, 2018, 04:02:44 PM »
Does the house have knob and tube wiring? You might just insulate your way to a fire hazard and voiding your homeowners insurance

Fishindude

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Re: retrofit wall insulation
« Reply #10 on: November 30, 2018, 09:03:14 AM »
If there is no sheathing, then every siding end joint would have to occur directly over a stud in order to fasten it, unless they installed a piece of blocking each time this occurred.

DoNorth

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Re: retrofit wall insulation
« Reply #11 on: November 30, 2018, 10:22:19 AM »
I would like to know more about the moisture barrier.  do you mean a precursor to Tyvek or something like poly?  what climate is the house in?  if you're in a cold climate, the problem is that dense pack can give you a pretty good R value and without a vapor barrier on the inner wall (between drywall and studs) you'll have condensation forming in the walls which has no way to escape if you have a moisture barrier on the outer wall (unless that barrier is permeable like Tyvek)  The reason older, drafty houses didn't have this problem is because of the lack of insulation so moisture could escape freely.  In this case, if you're going to use dense pack and don't want to open up the inside, the best bet is to take the siding off, use 2" foamboard and OSB and then reside it.  The 2" foam board negates the need for an interior vapor barrier because warm vapor traveling from inside to out will never come into contact with colder dryer air because of the foam board.




bacchi

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Re: retrofit wall insulation
« Reply #12 on: November 30, 2018, 10:58:43 AM »
Kahooli: The wiring has been upgraded fairly recently; it's romex.

Fishindude: Correct, the ends would be nailed into lumber and probably the studs. Unless, as J Boogie suggested, the installers used a brad nailer or something, the siding won't pop off without a lot of pressure.

DoNorth: The moisture barrier is Tyvek, which, now that I look at it, has more perms than I thought. The climate is mostly cooling. That said, I've love to put rigid foam on the outside but that's a major project and far down the list.

Thanks for the videos, HipGnosis and zolotiyuruki. Those are informative and ease my mind re:cracking and blow outs.


I'm going to delay having this done until after the holidays when I have an entire day to observe. Thanks for everyone's help!

DoNorth

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Re: retrofit wall insulation
« Reply #13 on: November 30, 2018, 11:23:52 AM »
If you move forward with the insulation project, I definitely recommend humidity sensing fan switches on all your bathrooms set specific humidity levels and an air exchanger (ERV or HRV depending on where you live) if you have duct work set up.

Insulation without a proper vapor barrier can wreak havoc on your stud walls and sill plates in a very short amount of time.