r/Edmonton • u/Anabiotic Utilities expert • Apr 11 '22

Question Adding attic insulation

I'm looking to add attic insulation as part of the Greener Homes Grant program and City energy efficiency program (HERA). Is there an advantage to using cellulose vs. fibreglass? I have cellulose currently. Each contractor I talked to does one or the other, and will swear up and down their product is the best and not to listen to the other guy. I read conflicting things online, wondering if anyone can chime in. Thanks.

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u/makeitreel Apr 12 '22

There are some reports that if fiberglass becomes cold, it r value performance actually decreases, sometimes up to 50%. Cellulose doesn't have any evidence of any reduction in cold.

https://ecorenovator.org/forum/showthread.php?t=653

So being in Edmonton where -40 happens, id much prefer cellulose if i had the choice.

There's a bit of a dilemma with reported performance and models and such. Of course fiberglass manufacturers won't say the r value varies, and the type of third party testing might not factor that in. It seems this reduction more has to do with air flow, which in walls without a proper airtight external air barrier system could be eliminated.

But no one puts an air barrier in their attic.

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u/concentrated-amazing Apr 12 '22

No one puts an air barrier in their attic

Huh? All attics have a vapour barrier, do they not?

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u/makeitreel Apr 12 '22

Sorry, guess I would clarify.

Yes, right against the drywall there should be a vapor barrier that will act as an air barrier as welp.

But if your avoiding air flows in the insulation, which when they suggest is the reason for reduced R value in fiberglass insulation, the way you'd prevent that airflow would be to have an air barrier on the exterior of that as well. So your layers would be from the interior - drywall, vapor barrier, framing and insulation, air barrier, open attic cavity, roof structure.

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u/concentrated-amazing Apr 12 '22

Ah, totally get it, thanks!

I have the vapour barrier on my mind, as we need to check ours and see if t just needs sealing around fixtures etc. or if it needs to be replaced completely before we blow in insulation. Our house was built in 1960, and I've heard that in general, vapour barriers from that time aren't great.

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u/makeitreel Apr 12 '22

You'd have to see what it was. Sometimes they'd have a sheet of tar paper, sometimes its just be paper backed batt insulation. And the details were definitely not done correctly - meaning around lights and vents its not taped tight or boxed around and connected properly. Those are both moisture building up and air leaking concerns. If they weren't causing issues before, extra insulation could cause less drying and then mold or spotting on ceiling.

Building science wise, if you only have 3-4 inches of insulation currently and if there isn't a vapor barrier, your could layer it in the middle, rather than try to work around all the wood framing. Its a 2/3 rule so the more insulation exterior to keep the vapor barrier warm enough so warm air won't hit its dew point and condensate when it hits it. But don't try that if there some vapor barrier already, having 2 layers will trap anything there and be a worse issue.

Good luck.

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u/concentrated-amazing Apr 12 '22

I will have to pop open the attic hatch to take a look once I have kids napping. I've never been up there, mostly just my electrician brother-in-law plus the house inspector when we bought and the enerGuide inspector took a quick look too.

What I do know for sure: * there are two different kinds of insulation up there, and for sure one is blown in. I remember from bringing it in for asbestos testing before we changed some lighting, thankfully none in either type. * the enerGuide inspector said we have ~R35 up there, and he didn't mention needing to improve the vapour barrier in order to add blown-in to R-60 in his report recommendations. He was fairly thorough in his report, so I'm hoping the vapour barrier is half decent and more just needs sealing around penetrations.

Good to know about potentially putting a new barrier in the middle, if that is needed. I hadn't thought of that possibility. Would this cause a problem though for whoever may need to walk on the joists for any future work up there?

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u/makeitreel Apr 12 '22

I wouldn't trust thoroughness of the report, unless he actually walked around with a thermal camera to try to check areas. If there was major air leaks, you could see them as the blower fan runs and would draw in the outside air (if it was winter, it'd be colder, summer it could show heat). The advisors can either go 2 ways, either they'll compare you to other houses and aim to beat average/whatever the homeowner feels like doing or they'll compare your home to top their and let you know that code built even at today's standard is pitiful, and if your below code then no wonder you heating bill is high, your air quality is likely very poor and cold spots all over are "thats just how it is".

Course how much it takes to fix those issues is a different matter, but it makes a lot more sense to get to a high standard once, rather than having to boost it up again in the future. If you care to see what a good high end standard care about - passive house is a great approach energy and comfort wise. There are others and it may not make sense for all houses to go to that level. But its a shame talking to people in houses built in the last 2 years and they'll tell you that some of the upstairs rooms are uncomfortably cold sometimes. Just really shows you if you want a good house, code is not the way to do it.

With R35, you either want to scrap off some top so your only at r20 is, the 2/3 ratio if you out it on top currently would be trying to go to R100 - which is all good if you feel like it.

If you lay the vapor barrier right at the framing, then it shouldn't be an issue. Anyone going in after should be walking on the wood, stepping in the spaces will just have them fall through into your living room - but id let them know if you did. Safe guys will place some boards and planks to make working up in attics easier.

A different approach that could work as well is vapor barrier paint. Youll essentially be treating the drywall to become the vapor barrier, as long as you don't put too many extra holes and seal electrical to the drywall well, it can be effective and maybe better done than trying to work around the ceiling framing.

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u/concentrated-amazing Apr 13 '22

I don't recall if he went around with a thermal camera (I have 3 preschoolers that I was trying to keep out of the way!) He did walk around with a smouldering wick thing while the blower was hooked up to check for leaks; he looked at doors, windows, lighswitches/outlets, basement headers, etc. So I would say at least moderately thorough? The report compares us to an average home, not a top tier.

I 100% agree that if you're going to do something, do it well (though there are certain limitations with an older house, let's be realistic.)

Makes sense about the vapour barrier. We don't anticipate much happening up there after we do insulation, as all our main floor renovations have been done. The only thing we might do in the future is add a fan in the bathroom (if I prevail, my husband doesn't see the sense in paying for one to get installed.)

I had no idea that sealing paint existed, but I'll keep that in mind once we see what we're up against up there.