Cheapest workshop insulation and interior walls?

In reply to thedoc :

I've never heard that.  I would be interested in more info.

Honestly, it sounds questionable to me.  It sounds like a really smart person who is good at researching but doesn't understand how the material is actually used in the real world.

When used on exposed rafters (primary usage), spray foam is sprayed on the entire frame system, encapsulating the entire framing member.  When viewed from the underside, the framing is completely not visible.  Therefore, there is no break in the foam- it is continuous.  Even if it shrunk and pulled away from the framing member it would still be a continuous thermal barrier without breaks. 

When used in enclosed stud walls, the excess is cut off before drywall.  In this case, the shrinkage issue would be relevant, but the worst thing it would do would be to create air gaps at each stud.  The foam would no longer be "glued" to the stud.  This would reduce it's performance regarding air infiltration (when compared to a new foam installation), but it would not be worse than air infiltration for fiberglass.  And it's R value per inch would still outperform fiberglass.

It sounds like a study that shows degradation in the performance of foam, but that it would still outperform fiberglass.

Please forward more info if you have it.  Thanks! 

There seems to be a misunderstanding of insulation vs vapor barrier in this conversation.  Spray foam is both.  Nothing else that comes to mind early on Sunday, is both.

SVreX (Forum Supporter) said:

In reply to mr2s2000elise :

I'm having trouble recognizing the scale in your picture... Are those 2x4 rafters, or 2x6?

Spray foam will seal tighest.  It will cost you quite a bit for a job that small, and I really doubt you will get anyone to do it before Monday.  It requires special equipment.

The cheapest and easiest is fiberglass batts.  Vapor barrier down.

There is a really cost effective way to make the performance rival that of spray foam.  Install the batts first, then install a layer of 1/2" DOW board floam on the bottom of it.  Tape the joints tightly with DOW tape, then sheetrock over it- use long screws to go through it and hit the wood.

The fiberglass will give you your R rating, and the DOW board will seal against air infiltration.  On a job that size, it would perform ALMOST identically to spray foam.

NOTE: this only works if your can light trims can be adjusted for the full 1" thickness of the DOW board combined with the drywall.

This is often referred to as "flash and batt", but it's typically done with the foam to the exterior and fiberglass toward the interior isn't it? That way, you get the air sealing of the foam on the outside, where it prevents air from infiltrating the fiberglass and reducing the effective r value.

You can cut some corners and DIY it yourself with rigid foam panels cut to fit between the rafters and sealing the edges with the cans of spray foam from the big box stores. 

You've got a 5.5 inch deep "bay" between the rafters. Typical fiberglass insulation for a 2x4 wall is 3.5 inches deep and R13. That leaves 2 inches for a foam panel, which might be r10-ish depending on the type of foam. If you have an asphalt roof over the porch that needs some ventilation below, It might be a good idea to leave a half inch gap between the foam and the underside of the roof deck for airflow/cooling. In that case, you'd just use some sort of 1/2" spacer to prevent the panels from contacting the roof deck, and you'd want 1.5" foam rather than 2".

California "title 24" requires a continuous insulation envelope.  The easiest method is to use foam board around the entire exterior walls before the siding goes on.   I achieved approval using a different method which is often called double stud wall.  One exterior set of studs and one interior set of studs, so there is a gap between the inner and outer wall with insulation, and thus no heat loss through the studs.  This seems more popular in colder climates where the wall can be very thick.

In my new shop I moved all my insulation into my office I built, where I put bats between the rafters, and have a layer of foam board as the ceiling.

Oh, and the walls have bats and I used hardboard as the wall covering instead of drywall, because drywall is heavy and I don't care much about appearance to tape and mud seams and make it pretty.

In reply to STM317 :

Yes, that's correct. 

However, the Dowboard when properly sealed also makes an excellent vapor barrier. Therefore, there is no reason it can't be installed on the warm side (interior). 
 

I've done it with great success a few times recently.

Dowboard installed on the exterior is also an excellent air infiltration barrier, but not always a good vapor barrier (because even when the panels are well taped, the top and bottom of the stud bays are not generally sealed).  This is a good thing, because the vapor barrier should not be on the outside.

I don't disagree.  The Dow could also be installed against the roof decking between the rafter bays.  It's a lot more work to get it well sealed.

In spite of years of training regarding building envelope performance and thermal efficiency, I can't find anything wrong with installing it to the interior. (Except possibly the fact that the drywall is not directly against the framing members- this could decrease the structural performance, but should increase the thermal performance).  In this situation, the structural component is a moot point.

You are also correct about airflow.  Every reccomendation would say there should be an air gap under the roof decking.  The thing is in this application, there is no airflow.  It's sealed both top and bottom.  And I've never seen deterioration in roof decking from a lack of airflow, so I am not sure how to offer recommendations (though I know you are right regarding good building practices).

If it was mine, I'd install R19, fill the 2x6, use IC can lights, and install the Dowboard underneath.  It would give an effective R value of R22.5, an excellent air infiltration barrier, and an excellent vapor barrier.

YMMV.

In reply to nimblemotorsports :

That's a good approach for thermal efficiency.

In a shop, I wouldn't leave Dowboard exposed.  It's flammable.  1/2" drywall isn't technically fire rated, but it IS gypsum, and still fire resistant (and draft resistant, which helps contain fire as well)

SVreX (Forum Supporter) said:

In reply to mr2s2000elise :

I'm having trouble recognizing the scale in your picture... Are those 2x4 rafters, or 2x6?

Spray foam will seal tighest.  It will cost you quite a bit for a job that small, and I really doubt you will get anyone to do it before Monday.  It requires special equipment.

The cheapest and easiest is fiberglass batts.  Vapor barrier down.

There is a really cost effective way to make the performance rival that of spray foam.  Install the batts first, then install a layer of 1/2" DOW board floam on the bottom of it.  Tape the joints tightly with DOW tape, then sheetrock over it- use long screws to go through it and hit the wood.

The fiberglass will give you your R rating, and the DOW board will seal against air infiltration.  On a job that size, it would perform ALMOST identically to spray foam.

NOTE: this only works if your can light trims can be adjusted for the full 1" thickness of the DOW board combined with the drywall.

ALSO IMPORTANT NOTE: If your can lights are not IC rated, you can't insulate tightly against them.  (Insulation Contact).  They will say on the fixture.  If you ignore this, they will cut off frequently, or blow.  On a ceiling that close, you really should be using IC rated cans.  If they are not, I recommend delaying your drywall install a day and swapping them.  If you don't, you will regret it.

My first question was do you want the cheapest to install right now or do you want the cheapest over the long haul.   
So you are right, it will cost more now but save you later. 

Here in Minnesota I can find someone willing to do a spray foam garage ceiling in an afternoon and have them here the next day. 
Maybe because here in the Arctic  Tundra where the snow is still hiding in the shadows in a few places.  Foam is fully appreciated. so it's far more common. 
By the way, one of the big box stores ( Menards ) has a DIY kit for garages and small homes.  
 

Spray foam isn't the only way.  I used SIP's (Structural Insulated Panels )  and ICF's  ( Insulated Concrete Forms )    As a result the house that I more than doubled in size and put 105 windows in  went from $500+ a month for the coldest months  to less than $300 a month for the same periods  and that's after 20 years of inflation and cost savings  ( oh I'm still using the same furnace too) 

As I tore down the old house There wasn't a single flaw in either the vapor barrier or insulation.  Except it was fiberglass. 
 

So foam is that much better

It is not just a "tundra solution".

Here in the Deep South where it is not unusual to have over 100 days per year with a heat index over 100, i insulated the walls and roof of my newer shop with spray foam. Also insulated garage door.  It is amazing how little A/C it takes to keep everything 70 degrees inside.

Yes... it cost more on the front end, but, pay me now, or pay me later.

STM317 said:

SVreX (Forum Supporter) said:

In reply to mr2s2000elise :

I'm having trouble recognizing the scale in your picture... Are those 2x4 rafters, or 2x6?

Spray foam will seal tighest.  It will cost you quite a bit for a job that small, and I really doubt you will get anyone to do it before Monday.  It requires special equipment.

The cheapest and easiest is fiberglass batts.  Vapor barrier down.

There is a really cost effective way to make the performance rival that of spray foam.  Install the batts first, then install a layer of 1/2" DOW board floam on the bottom of it.  Tape the joints tightly with DOW tape, then sheetrock over it- use long screws to go through it and hit the wood.

The fiberglass will give you your R rating, and the DOW board will seal against air infiltration.  On a job that size, it would perform ALMOST identically to spray foam.

NOTE: this only works if your can light trims can be adjusted for the full 1" thickness of the DOW board combined with the drywall.

This is often referred to as "flash and batt", but it's typically done with the foam to the exterior and fiberglass toward the interior isn't it? That way, you get the air sealing of the foam on the outside, where it prevents air from infiltrating the fiberglass and reducing the effective r value.

You can cut some corners and DIY it yourself with rigid foam panels cut to fit between the rafters and sealing the edges with the cans of spray foam from the big box stores. 

You've got a 5.5 inch deep "bay" between the rafters. Typical fiberglass insulation for a 2x4 wall is 3.5 inches deep and R13. That leaves 2 inches for a foam panel, which might be r10-ish depending on the type of foam. If you have an asphalt roof over the porch that needs some ventilation below, It might be a good idea to leave a half inch gap between the foam and the underside of the roof deck for airflow/cooling. In that case, you'd just use some sort of 1/2" spacer to prevent the panels from contacting the roof deck, and you'd want 1.5" foam rather than 2".

 

Here in Minnesota the new house 2 doors north was stick built but insulated between the 2x6's with 2"foam blocks. The wiring was done the normal way and then fiberglass  batts installed before sheetrock placed over.  There was a slight cost savings doing it that way over just building with SIP's  or ICF's  

In reply to SVreX (Forum Supporter) :

Drywall is better for sure, but I'd prefer concrete board, which is what I'm going to use around the work area.

Having pressure washed the floor twice in the new shop to get the prior tenant pizza sauce cooks mess out, they call it drywall because you better not get it wet!   

Planning on some pressure washer blasting it is going to require something to keep the walls from getting wet.

When I was young (right after the last ice sheets had retreated) and we used to put in almost all night garage sessions, we had pretty much insulated one wall with used nested styrofoam coffee cups. I swear is did seem warmer......

In reply to nimblemotorsports :

Concrete board is a pretty good idea. 
 

You said "hardboard". That usually means Masonite.  That wouldn't be a great idea. 
 

I think you meant Hardiboard. That's concrete board. 
 

I still wouldn't leave foam board exposed on the ceiling. 

@SVreX

Thank you. Purchased all the drywall and all the Fiberglass Blatt today. Will start installing tomorrow, as I continue on my thread :

https://grassrootsmotorsports.com/forum/off-topic-discussion/backyard-build-deckconcretepool/163253/page11/#post2990173