Insulation and Air Sealing

[vtjon]

I would like some advice. I have a stick-build 28x40x12 shop that I am working on. I am getting close to my insulation step. I want to insulate without going overboard as it would take a long time to recover my costs (maybe).

I got an estimate on spray foaming my shop including an unvented roof setup. In doing some calculations, I can do R15 batts and blown-in cellulose in the attic for about $3k less (excluding my labor). I will have drywall and I intend to install one of the Mr Cool DIY mini-splits. I am on the line for zone 4 vs zone 5 of the insulation guidance map and this is a hobby shop so just used a few days a week.

I know air sealing is an important part of this equation. I have considered getting a pneumatic/battery operated caulk gun to caulk each stud bay where the sheathing meets the 2x4. After I do that, I would then put R15 (or R13) batts in place. Is this air sealing over kill?

On the ceiling, I have storage trusses that have already been decked for a 10x24 section. I will only be able to get R19 batts in these bays but I can do blown-in everywhere else. Any thoughts on how to do better or if it's wasteful to blown in R38 every where else in the attic and effectively have R19 under the storage decking? I can't take it up to add spacers at this point as it's already been nailed and glued.

 

[tonyciambrone]

What are your details so far, I.E sheathing, WRB, flashing windows, doors, base wall flashing etc? If air sealing was always an important part of this job it should've been mostly taken care of on the exterior.

I am sort of a Matt Risinger shill by now, but I would suggest browsing through these videos and watching what you can. There's a lot of good ideas/ interesting technologies.

 

[Raisedonadeere]

Definitely seal along bottom edge. I was amazed a few years ago at what happened in a bug infested shed with hardboard siding when I sealed up with foam the bottom gaps. no more bugs crawling around in there. On my new 24x38 build I sealed mostly with caulk and bigger gaps with foam along bottom and top plates. I did that mostly for climate control but was well motivated by my bug free experience.

My 24x36 storage trusses had enough space for r30 bats. If yours have 2x6 cord used as floor support that really surprises me.

 

[vtjon]

I have 4 good windows (Andersen, Low-E glass, etc - mainly so they match my house), 2 entry doors and an 18' insulated garage door. The exterior is vinyl siding, Tyvek and 7/16 OSB.

I've watched a lot of Matt's videos as they are interesting. I think a lot of them are overkill for my setup though. My house, built in 2014 as custom-build, only has R15 in the walls and air sealing (I assume). Foam board on the outside isn't too common around here.

The bottom plate has Sill Seal under it.

 

[vtjon]

Definitely seal along bottom edge. I was amazed a few years ago at what happened in a bug infested shed with hardboard siding when I sealed up with foam the bottom gaps. no more bugs crawling around in there. On my new 24x38 build I sealed mostly with caulk and bigger gaps with foam along bottom and top plates. I did that mostly for climate control but was well motivated by my bug free experience.

My 24x36 storage trusses had enough space for r30 bats. If yours have 2x6 cord used as floor support that really surprises me.

It's definitely 2x6 bottom cords. I can understand sealing the bottom and top plates. I wasn't sure if doing the stud bays was worth it. The bug control is a definitely plus.

 

[yeldogt]

Spend the 3k on the foam and never look back ....

You can never seal like foam ... caulk fails ... it's not a sealant.

 

[PWilks]

Better compromise would be buying some Great stuff with the $40 pro gun (the big cans make up the cost difference), and air seal all stud bays as well as electrical boxes, then use blown in in the attic and batts in the walls

 

[vtjon]

Spend the 3k on the foam and never look back ....

You can never seal like foam ... caulk fails ... it's not a sealant.

Well, the whole project was almost $5k. It's just the savings of going with batts and blown-in is $3200. My break even on energy savings might be 10 years or more based on rates around here and expected usage.

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[TractorJeff]

On my shop the Tyvek seams were taped to reduce air infiltration.

 

[vtjon]

Better compromise would be buying some Great stuff with the $40 pro gun (the big cans make up the cost difference), and air seal all stud bays as well as electrical boxes, then use blown in in the attic and batts in the walls

This was a consideration too. It may not be as cost effective as caulk but likely better result for not much more money plus less labor.

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[vtjon]

On my shop the Tyvek seams were taped to reduce air infiltration.

My seams are taped too. It's just hard to tell if I've gone too far or not far enough until after I have my drywall up then it's too late to fix.

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[like2wheel]

Better compromise would be buying some Great stuff with the $40 pro gun (the big cans make up the cost difference), and air seal all stud bays as well as electrical boxes, then use blown in in the attic and batts in the walls

I agree with this. Better yet if you fit the cavities first with sheet foam, foam seal the edges, then fill the rest of the bay with fiberglass or cellulose.

This was a consideration too. It may not be as cost effective as caulk but likely better result for not much more money plus less labor.

I found it more cost effective than caulk. I did all the bays in the walls of my 26 x 54 (10' & 12' walls, bookcase girts 24" oc) with 3 cans of foam & a $20 gun from Amazon. I couldn't guess how many tubes of caulk that would have been. Way faster too.

 

[yeldogt]

Tyvex is not going to air seal .... it may reduce vs some other construction system. Same with foam panels in each bay w/ caned foam --- although the possibility is much better. The overall envelope needs to be looked at as the foam panel needs to be thick enough if the rest is going to be batts

People don't understand what house wrap is and is not doing ... and what it's really for. When you do blower door test on buildings the failings are obvious.

Foam makes for a nice tight building ... smaller HVAC required. Less input ...