Blow-in Insulation and Vapor Barrier Paper

[zardthebuilder]

my last house had blow-in insulation. iirc, there was vapor barrier paper underneath, but maybe i'm wrong. my current house also has blow-in insulation, but there is no paper. i can't find any such paper for sale in the home depot website.

i was planning on adding unfaced rolls on top, but do i need to add a vapor barrier under the blow-in insulation first? is vapor barrier paper only needed with rolls but optional with blow-in?

 

[Greenman]

Depends on where you live. Around my area we don't use any vapor barrier at all.
I'd also be inclined to use blow in if you're adding more, bat insulation will have gaps between the pieces.

 

[zardthebuilder]

that makes sense. the good thing about rolls is that i can do it myself and at my own pace.

 

[3chordcharlie]

You can blow in fiberglass or cellulose in a day with a (usually) free rental machine.

 

[Greenman]

Just don't block the vents with insulation when you do it.

 

[DrPizza]

that makes sense. the good thing about rolls is that i can do it myself and at my own pace.

You can do blown in yourself, and more or less at your own pace, provided you finish in a day. Most home improvement stores offer a free rental of the equipment provided you purchase at least (10?) bags of the blown in cellulose or fiberglass.


It's really easy to do, though you'll likely want a helper to dump the bags into the hopper while you're at the business end of the hose. There's some prep work that can be done before hand to make the job go smoother, such as installing some markers to know how high to fill to, and baffles against the roof deck, allowing some air to still be able to pass against the underside of the roof in the area where the insulation would butt up to the roof.

 

[NetWareHead]

Just don't block the vents with insulation when you do it.

This. I have ice dam problems because the previous owner/installer stuffed the soffits FULL of insulation. Lately I've been up in my attic laying face down on the joists with my arm deep in the soffit clearing them manually. Really crappy work so don't do this!

 

[highland145]

This. I have ice dam problems because the previous owner/installer stuffed the soffits FULL of insulation. Lately I've been up in my attic laying face down on the joists with my arm deep in the soffit clearing them manually. Really crappy work so don't do this!

Shop vac. Mine were full too. No ice dams here but I need the attic to breathe.

 

[NetWareHead]

Shop vac. Mine were full too. No ice dams here but I need the attic to breathe.

Yeah the shop vac works. The problem I discovered with the shop vac is once you start sucking up insulation, it expands so much in the bucket and after 5-10 minutes, you have to stop and empty it. As much as it sucks to be face down in the insulation, I have to manually clear the bulk of it from the soffit before bringing in the shop vac. I'm pretty sure its blown in vermiculite.

 

[highland145]

Mine was rockwool (?), 1937 house. Someone put batt insulation over it but it was a tight fit close to the soffit so they just shoved the rockwool forward into it.

 

[Greenman]

Yeah the shop vac works. The problem I discovered with the shop vac is once you start sucking up insulation, it expands so much in the bucket and after 5-10 minutes, you have to stop and empty it. As much as it sucks to be face down in the insulation, I have to manually clear the bulk of it from the soffit before bringing in the shop vac. I'm pretty sure its blown in vermiculite.

You need an insulation vacuum. It's a gas powered vacuum with a couple hundred feet of 6" hose. It hooks to a bag that's about 8' long 3' wide.
Pro tip: Put the bag in the back of your truck before you fill it, they get really heavy. Also, put a piece of plywood behind the bad so that when you suck up an old nail it doesn't rocket through the bag and break your rear window. I learned these lessons the hard way.

 

[Red Squirrel]

Normally you use plastic for vapour barrier, it's applied from the bottom before the drywall goes up. It would be hard to add it after the fact, but if you don't have any I would try to find a way to add some. Drywall is slightly porous so even if you add some stud to stud it will be better than nothing. Wood is porous too though so it wont be as good as if it was installed under. Insulation is NOT air tight, without a vapour barrier it will just act as a filter, and not insulation, as it will still let air movement happen, which will eventually lead to moisture issues, and mold.

Here's a random pic I found of how it normally should be done:

Another option if there is no vapour barrier and you are adding insulation, it may actually be worth to just look into spray foam. Have them spray over the joists too to create a continuous coverage, then add the blown in on top.

 

[pmark]

What do people think, fiberglass or cellulose for blown in?

 

[Red Squirrel]

What do people think, fiberglass or cellulose for blown in?

I think cellulose is the way to go now. Though looking at what's in my attic, it's basically shredded newspaper, possibly mixed in with other stuff. So from a fire rating point of view fibreglass might be better. Fibreglass will be mould city if it ever gets wet though.

 

[zardthebuilder]

my area is prone to termites. i think i should treat my wood before adding insulation.

 

[stormkroe]

Normally you use plastic for vapour barrier, it's applied from the bottom before the drywall goes up. It would be hard to add it after the fact, but if you don't have any I would try to find a way to add some. Drywall is slightly porous so even if you add some stud to stud it will be better than nothing. Wood is porous too though so it wont be as good as if it was installed under. Insulation is NOT air tight, without a vapour barrier it will just act as a filter, and not insulation, as it will still let air movement happen, which will eventually lead to moisture issues, and mold.

Here's a random pic I found of how it normally should be done:

Another option if there is no vapour barrier and you are adding insulation, it may actually be worth to just look into spray foam. Have them spray over the joists too to create a continuous coverage, then add the blown in on top.

Humid zones don't even use vapor barrier. We never used it in missouri, it wasn't until I moved to Alberta that I'd ever even seen it before. By the way, you're no longer allowed to do what your picture shows. The potlight vapor barriers have to be enclosed in rigid construction (basically frame a wooden box around it) so that the weight of the insulation doesn't smash the bag into the light. It makes the job a huge pain in the butt, but it also makes sense.

 

[Red Squirrel]

Humid zones don't even use vapor barrier. We never used it in missouri, it wasn't until I moved to Alberta that I'd ever even seen it before. By the way, you're no longer allowed to do what your picture shows. The potlight vapor barriers have to be enclosed in rigid construction (basically frame a wooden box around it) so that the weight of the insulation doesn't smash the bag into the light. It makes the job a huge pain in the butt, but it also makes sense.

Wow wouldn't not having a vapour barrier be a nightmare to keep heated or cooled? The insulation just acts as an air filter at that point. And yeah the pic was just an example, pot lights have all sorts of special codes now, personally I don't even think I'd want to install pot lights on an "outside" ceiling as it complicates a lot of things and is open to lot of efficiency mistakes.

 

[Greenman]

Wow wouldn't not having a vapour barrier be a nightmare to keep heated or cooled? The insulation just acts as an air filter at that point. And yeah the pic was just an example, pot lights have all sorts of special codes now, personally I don't even think I'd want to install pot lights on an "outside" ceiling as it complicates a lot of things and is open to lot of efficiency mistakes.

We don't use them in California either.

 

[Aikouka]

Wow wouldn't not having a vapour barrier be a nightmare to keep heated or cooled?

Isn't the point of the vapor barrier just to keep the moisture out? I wouldn't expect them to do much to the R-value.

 

[Red Squirrel]

Isn't the point of the vapor barrier just to keep the moisture out? I wouldn't expect them to do much to the R-value.

It stops air movement too and creates an air barrier. Insulation does not do much as far as air sealing, so if there's any kind of air movement it negates the effects. If ever you've been in a house that feels drafty it's possibly because it has not been installed right or there is none at all. My house is old and after opening up some walls I've found that the vapour barrier was not really installed very well and despite there being half decent insulation the house temp drops fairly fast in winter. I redid a section this summer though as part of a project to replace the patio door and front window, and that helped a bit.

Foam is an exception though, a proper spray foam application can also replace the need for a vapour barrier. In fact it does a better job as it really gets into all the nook and crannies.

 

[stormkroe]

It stops air movement too and creates an air barrier. Insulation does not do much as far as air sealing, so if there's any kind of air movement it negates the effects. If ever you've been in a house that feels drafty it's possibly because it has not been installed right or there is none at all. My house is old and after opening up some walls I've found that the vapour barrier was not really installed very well and despite there being half decent insulation the house temp drops fairly fast in winter. I redid a section this summer though as part of a project to replace the patio door and front window, and that helped a bit.

Foam is an exception though, a proper spray foam application can also replace the need for a vapour barrier. In fact it does a better job as it really gets into all the nook and crannies.

It would be better if we could get away with having it in those muggy areas, but it's simply a problem with moisture trying to get in vs out. In canadia, you poly the heated side. In the south, moisture would mostly be collecting on the insulation side of the poly because it's cooler inside most of the year (cold drink condensation) coupled with the much higher outside humidity and BLAMO, petri dish walls. Tyvek on the outside stops virtually all air movement, while allowing moisture to escape, so it's not as bad as you'd imagine.
Fun fact, the heat and high humidity is why most areas in the south don't use stucco; there's nothing like pressure washing mold and moss off your house

 

[Aikouka]

It stops air movement too and creates an air barrier.

I was doing a bit of research into this yesterday, and if I remember correctly, one of the comments that I read was that just because you have a vapor barrier doesn't mean that you have an air barrier. For example, a conditioned crawlspace is an example of where your vapor barrier is also an air barrier.

I'm guessing it has to deal with the thickness of the material and the material itself?

 

[Red Squirrel]

I was doing a bit of research into this yesterday, and if I remember correctly, one of the comments that I read was that just because you have a vapor barrier doesn't mean that you have an air barrier. For example, a conditioned crawlspace is an example of where your vapor barrier is also an air barrier.

I'm guessing it has to deal with the thickness of the material and the material itself?

Yeah some of the older stuff is so thin it does not do it's job very well. I think this is the issue with my house, from the little places I've fixed, I found it was ridiculously thin to begin with. I was told that some of the older stuff is so thin that if you were to paint it, the paint goes right through! So that thin is practically useless. Newer codes now have minimum thicknesses.

It's also important to put it on the hot (living space) side, otherwise you can get condensation issues like stormkroe said.

 

[monkeydelmagico]

Wow wouldn't not having a vapour barrier be a nightmare to keep heated or cooled? The insulation just acts as an air filter at that point.

A well installed moisture barrier (home wrap) will help R value and block some of the draft. The spray foam insulation is a god send for old houses. Those drafty spots just need a bit of the foamy stuff.

Vapor barrier is a different animal. It's for fairly specific builds and can cause alot of problems if done badly. I've been told to avoid it in our location (northeast). Here is a bit of proof but certainly not exhaustive research http://nationalfiber.com/docs/CelluloseInsulationMoistureAndVaporBarriers0909.pdf

 

[Red Squirrel]

Oh yeah spray foam will actually remove the need for vapour barrier. It acts as one on it's own. You also don't want to create a double vapour barrier either as that will cause moisture issues as it will trap moisture in.

Interesting about not having one for cellulose though. I wonder if that document means to not have one on top as that would definitely cause issues. Attic ventilation is also very important, you want some baffles at the eves and perforated soffit so air can go in and then exit the top vents.