shop insulation - Vic?

[rodger.]

Have been looking at using dense packed cellulose in the empty wall cavities of one wall of my attached garage/shop.  I called two reputable insulation companies, and one said "yes, go fo it.  no vapour barrier needed", and the other said "no.  take down the drywall, add batts, use a 6 mil vapour barrier, and then hang new drywall" (even though this means he doesnt get a job blowing cellulose).

 

OF the 4 walls, two are insulated as they are opposite the interior of my home.  The other two are 16" empty stud walls with exterior OSB/Brick veneer, and interior 1/2" mudded and taped drywall.  I really loath the idea of tearing down a finished wall to insulate with batts/barier, but if it must be done I will do it.  I dont want a moisture problem in the future.  The ceiling has been sprayfoamed.

 

Any opinions?  My climate is hot/humid in summer and very cold in the winter.  Space will be heated with an electric heater only when I am in the shop.  No AC, but may want to add in the future (unlikely though).

 

 

[wtnhighlander]

This is not an informed opinion, just a 'common sense' view of the situation.

The wall is already configured as an interior wall would be. You would not add a vapor barrier if you insulated an interior wall ( for noise reduction, etc...) so why would you need a barrier on this wall?

[rodger.]

This is not an informed opinion, just a 'common sense' view of the situation.

The wall is already configured as an interior wall would be. You would not add a vapor barrier if you insulated an interior wall ( for noise reduction, etc...) so why would you need a barrier on this wall?

ii think you misunderstand.  Its an exterior wall, with no insulation.  Exterior walls typically require a 6mm vapour barrier if insulation is in place.

[Dave H]

If this was for living space if the code was a vapor barrier is needed than Okay but, this is non living space so no barrier would be needed.  you can rent the blower insulation rig at most HD stores do this yourself you don't need these guys anyway.

[wtnhighlander]

ii think you misunderstand. Its an exterior wall, with no insulation. Exterior walls typically require a 6mm vapour barrier if insulation is in place.

Sorry, from your description I assumed the uninsulated walls were between the house and garage, rather than true exterior.

[rodger.]

If this was for living space if the code was a vapor barrier is needed than Okay but, this is non living space so no barrier would be needed.  you can rent the blower insulation rig at most HD stores do this yourself you don't need these guys anyway.

Will there be any concerns with moisture?  That is my real worry - I dont want to have to deal with mould or condensation.

[Dave H]

No the vapor barrier on the inside wall is for draft control, you've heard people say that house is really tight, well when a house is too tight you need to introduce fresh air back into the house because there is no natural exchange of air. The exterior wall vapor barrier is to keep moisture from getting into the wall cavity which will cause mold to grow, I assume you have an exterior vapor barrier. Your shop space will only be heated when your out there so super tight envelope isn't essential the interior wall vapor barrier doesn't affect the R value of the insulation. If the inside of your shop is sheet rocked that's where I would drill the fill holes for the blow in insulation that would be the easiest to patch (just my opinion).

[Firehawk]

If you plan to heat the shop a vapor barrier is a must.  Otherwise frost and mold will be an issue.

[estesbubba]

Putting up a new shop I've found if you ask 25 different people about vapor barriers you'll get 25 different answers. Spoke with my insulation supplier today about my ceiling and he said everyone does it differently and installers are using vapor barriers less these days.

[wtnhighlander]

Check you local building codes.

[estesbubba]

Check you local building codes.

Good suggestion. Even counties can differ in codes.

[rodger.]

Check you local building codes.

Building code is not really helpful.  Its technically a non-living space, so no vapour barrier (or insulation) is required.  Thats all the code indicates.

[Jim DaddyO]

yes, check your codes.  You may find that there are acceptable substitutes for vapor barrier.  2 coats of oil based paint will do in some cases.

[wtnhighlander]

At least now you know it isn't a code requirement!

[rodger.]

yes, check your codes.  You may find that there are acceptable substitutes for vapor barrier.  2 coats of oil based paint will do in some cases.

again, not really concerned with the code.  I want it to be appropriate for my purposes.  For example, code says that all i require is one 15A outlet and one bare bulb fixture, but that is obviously not suitable for a woodshop.  I am willing to pay for what needs to be done (or do it myself).  The only concern is what is appropriate?  I cant get a straight answer about the vapour barrier.  Some pros say "no need, or in fact it can be bad" to "yes you must have one or you will get mold".  So frustrating.

[estesbubba]

Unfortunately there isn't an easy answer like use 12-2 wire for 20 amp circuits. Salesman at the insulation warehouse I'm using have different views on vapor barrier, R-value to use, etc. Then if you ask people that install it, they all have different opinions. So the more people you ask, the more confused you are going to be!

 

How about taking the easy way now? That could save you the work of ripping out and putting up new drywall in the future. If you do have problems, then rip out and put back up. Then you might worry about mold problems...

 

Then if you do rip, vapor barrier, and drywall, you'll have the pros that say vapor barriers cause problems. If they are right, you'll rip down and build twice. 

 

I feel your pain of trying to decide what to do. For mine, I'm doing insulation, vapor barrier, and OSB for walls, and insulation, NO vapor barrier, and OSB for ceiling. That's what 2 people recommended. I guess time will tell if it's right.

 

You could always do rock-paper-scissors 101 times with Kiki to decide...

[DustinK]

Not really sure how a legitimate contractor would ever tell you not to use vapor barrier for an exterior wall in a heated space (especially in Ontario).  Without it, you'll end up with mold in your walls in no time.  The inside of the drywall is paper, and any moisture buildup on there will mold very quickly.  Moisture buildup will be caused by the warm air (which holds more moisture than cold air) meeting the cold air in the wall causing the moisture to condensate.  If that occurs on your vapor barrier no big deal, it's inorganic.  When it condensates on the drywall, hope you plan to wear your respirator at all times in there, otherwise you'll be breathing in more than sawdust.

[Tpt life]

Cellulose comes in mold inhibitive types for remodel contractors to blow into old homes with intact plaster. The cellulose will contain a large amount of moisture and will equalize it throughout dumping it in dry months. It may not be as doom and gloom as portrayed. It worked well in my ancient home with NO mold. I did have modern house wrap under the siding.

[rodger.]

Cellulose comes in mold inhibitive types for remodel contractors to blow into old homes with intact plaster. The cellulose will contain a large amount of moisture and will equalize it throughout dumping it in dry months. It may not be as doom and gloom as portrayed. It worked well in my ancient home with NO mold. I did have modern house wrap under the siding.

I called the contractor, and he confirmed your comment that the dense packed cellulose does contain a mold inhibitive property.

[Jim DaddyO]

Well, if you want to do it right (as Mike Holmes would say), you  need a vapour barrier on the warm (in winter) side of the insulation and under the drywall.  Cellulose batts (like Roxul) also are not liked much by critters such as mice and squirrels, so you can keep that in mind if you are going to DIY.  Another way to go is getting it spray foamed after opening it up.  Make sure it is closed cell foam.  It will act as its own vapour barrier.  Either way, the drywall has to come down in order to do it right.

[Beerboss]

Your climate zone will be a big factor in wether you need a vapor retardor or not, so will the wall construction.

It looks like you are in Ontario I assume Canada, not California since you mentioned cold winters.  Dense packed cellulose would be perfect for a retrofit cavity fill.  Btw Roxul in mineral fiber, not cellulose.  Next we need to look at your internal moisture load.  High?  Cooking, bathing ect or low? electric / wood heat not much added moisture.  A low situation wouldn't require a vapor retarder, a high one would suggest you use one.  The good thing is you can apply one to the interior by using somethng like Sherwin Williams Prep Rite VR primer.  I've specified this paint to builders that had issues with building officials.  To muddy the waters even more the wall construction makes a diffference as well.  Does it have a ventilated cladding such as vinyl  or aluminuim siding?  These assemblies are more forgiving and do not require a vr up into climate zone 5.

[rodger.]

Your climate zone will be a big factor in wether you need a vapor retardor or not, so will the wall construction.

It looks like you are in Ontario I assume Canada, not California since you mentioned cold winters.  Dense packed cellulose would be perfect for a retrofit cavity fill.  Btw Roxul in mineral fiber, not cellulose.  Next we need to look at your internal moisture load.  High?  Cooking, bathing ect or low? electric / wood heat not much added moisture.  A low situation wouldn't require a vapor retarder, a high one would suggest you use one.  The good thing is you can apply one to the interior by using somethng like Sherwin Williams Prep Rite VR primer.  I've specified this paint to builders that had issues with building officials.  To muddy the waters even more the wall construction makes a diffference as well.  Does it have a ventilated cladding such as vinyl  or aluminuim siding?  These assemblies are more forgiving and do not require a vr up into climate zone 5.

Yes, Ontario Canada.  We are in the "COLD" specification according to the building science site.

 

The exterior is stone veneer, builders paper, and then OSB, Studs, drywall.

 

The garage will only be a woodshop, so no cooking, bathing, etc.  The only water is from a hose bib which will occassionally be used to fill a bucket for sharpening plane irons and chisels.  No cars will be in the garage, and no snow.

[Jim DaddyO]

Oops, sorry about that, Roxul is indeed mineral wool.  Critters still don't like it much, plus, it won't burn and stands up to dampness.  A much better solution to fiberglass batts.

 

I would recommend stripping to the studs, putting in Roxul and a vapour barrier.  I too live in Ontario (I even put the "u" in vapour...lol).  It will give you a chance to check everything out while you do it and maybe run some electrical if needed.

[Firehawk]

Here's a thought. Use the cellulose put the vapor barrier on top of the drywall and then cover with OSB.   This will save you ripping out the drywall and you end up with walls that you can mount anything you want on!

[Tpt life]

This has been asked, heat source matters. The temp of the wall will dictate at what point in the depth of the wall the moisture will condense. Moisture barriers under drywall became big with Kraft faced glass which honestly did absorb small amounts of moisture. When transition was made to plastic sheeting, bathrooms and kitchens. as well as dead air corners of bedrooms, saw massive increases in mold and mildew growth in high humidity climates. The vapor barrier forced the moisture inside the conditioned space to condense against the back of the drywall. This led to the development of better papers to use in the manufacturing of drywall, but now you could effectively call it "wetwall." So why do some people get away with this while some contractors say it is not necessary? It comes down to how many months of the year the humidity is controlled. AC controls humidity. Winter air is less humid. Unless you heat with a source that puts humidity into the air, your bigger danger of moisture condensation issues can actually happen in summer mornings. Shops are fantastic in how they tend to be open spaces. One super easy fix for mold and mildew mitigation is cycling the air. Use a fan, don't let it stagnate.

That all challenges the concept "must always use a barrier." It turns it into "most likely should use a barrier." If you decide you need to, for that size shop it is a lot of drywall work, but I find drywall work to be easy if you do not absolutely need glass smooth walls. To the prior comment, OSB as an attachment surface certainly has appeal.