I'm reasonably certain the sprayed foam would be more expensive but I'd appreciate any input on about how much more.

Certainly would be faster/easier (assuming I can find an applicator that can fit me into his schedule) and I'm hearing it's more efficient in terms of R Factor. I only have 2x4 walls.

Another question: The building has a 5/12 gable roof with tin over 2x4 wood purlins. I plan to suspend a ceiling at the top of the 8 foot walls both to make it easier to heat and to help with lighting (It'll be painted white). If I do traditional unfaced batts on top of the ceiling I'm worried about condensation from the tin soaking the batts. Would it make more sense to spray-foam the back of the tin and not put batts over the ceiling?

I looked into this for an investment property I was rehabbing several years back. For that use spray foam was prohibitively more expensive. But I don't pay heat for the apartments.

If it were a house I was going to be living in, the increased price might have been worth it.

I can't speak to the difference in cost but foam is quite a bit more expensive but has been worth it to me. It fills voids and does an incredibly good job. Also a small layer on the bottom of your roof would help or eliminate any condensation issue.

PHPaul, the contractor that built my barn used a rolled vinyl back insulation stapled to the purlins to carry the condensation to the outside walls. The insulation is 1 1/2” so not much value but it does prevent drips. You could then use batt insulation over a drop ceiling.

quote:

Originally posted by JWF:
PHPaul, the contractor that built my barn used a rolled vinyl back insulation stapled to the purlins to carry the condensation to the outside walls. The insulation is 1 1/2” so not much value but it does prevent drips. You could then use batt insulation over a drop ceiling.

Interesting. Fully encased, or vinyl side to the metal?

quote:

Originally posted by PHPaul:

quote:

Originally posted by JWF:
PHPaul, the contractor that built my barn used a rolled vinyl back insulation stapled to the purlins to carry the condensation to the outside walls. The insulation is 1 1/2” so not much value but it does prevent drips. You could then use batt insulation over a drop ceiling.

Interesting. Fully encased, or vinyl side to the metal?

Not fully encased, vinyl backed fiberglass, insulation against metal. Actually stapled to the top of purlins (went down and took a look to refresh memory) and the edges sealed to prevent leaks. Might be hard to retro fit under existing metal but you have shown genius before.

Another thought that occurred to me is "Silverboard". Metal foil on both sides over a expanded foam interior. Not a lot of R-value, but would definitely solve the condensation problem. Probably use foil tape on the joints.

I’d spray under the roof 6” thick or more with closed cell foam. After it cured, I’d spray that with white paint.

Would it be possible to properly ventilate the attic space you're creating to eliminate the moisture problem?

Thing is: If you get moisture gathering in there it's not only the R-value of the insulation that will be a problem. Mold will occur and your structural members may start to rot.

7 years ago we had a house built and I had them use closed cell spray insulation in the exterior walls, builder had me pony up $3000 up front. Dude also sprayed the wall between the MBR and the rest of the house and the wall to the MBR bathroom for sound insulation...he didn’t charge me, I was there the day they were spraying...so two more 14’ walls and 8 foot high as well as the exterior of a 2300 square house....

In our Texas house we were not there when it was built, we bought it almost at the end of the construction and it was already dried in and spray insulation was not feasible...I wish we had gotten it as the spray insulation is much quieter- totally worth it

quote:

Originally posted by PHPaul:
Another thought that occurred to me is "Silverboard". Metal foil on both sides over a expanded foam interior. Not a lot of R-value, but would definitely solve the condensation problem. Probably use foil tape on the joints.

The ridged board would be a lot easier to install than the rolled blanket insulation.

Spray foam, spray foam, spray foam... oh, did I mention spray foam?

My spray insulation ran by the sq ft and by thickness and R factor. I went with foam

R-30 open cell 2x10 $2.00 sq/ft open cell
R21 in 2x6 was $1.65 sq/ft open cell
2x10 R38 was $2.78 Open Cell
2x8 R38 closed foam was about $2.98 Sq/ft

Pay back was 3 years in savings over old crappy mix of insulation in the house.

House was built around 1910 and had a mixed of whatever they were using at the time of various repairs.

Batt insulation quote

R38 batt is $1.60 Sq ft
R30 batt is $1.40 sq ft
R21 batt is $1.35 sq ft all installed
Installation was the same per batt.
Price difference was only materiel

Prices are from 8/2019 and prices are going a little nuts at the moment.

We did Spray Foam on roof, batten between rooms for sound and Mylar reflective on furring strips behind Drywall to reflect heat from Cinder blocks. Construction is concrete and cinder blocks.

House is a sealed design - no soffits. Worth it times x1000. Had an 1800 sqft house old school insulation but new AC and heaters…electric costs the same in a 5K sqft house with spray foam, etc. The spray foam and design is well worth it.

Good information so far.

One thing to remember here folks: This is a shed that will be a work shop, not a house. Different goals to some extent, MUCH different goals on costs.

I used closed cell foam on my cabin and it's been great. No drafts, helps with noise, and actually adds strength to the building.

Jim

My brother built a 50'x 30' pole building ten years ago. He purchased enough spray foam kits to spray the whole interior. We sprayed the ceiling and all the walls sealing the interior. That first winter we had very cold weather resulting in many weeks below zero. We were able to work comfortably in the shop. Since then, we've hooked up the radiant floor heat.

As an ENERGY STAR Certified builder I would like to pass along some information that seems lacking here.

First, there are two kinds of foam insulation; open cell and closed cell. Open cell is like your kitchen sponge to an extent and has an R value of about 3.8 per inch. Closed cell insulation has small air pockets that are not pourous and has an R value of about 6.5 to 7 per inch.

The R value of standard fiberglass insulation is the same as open cell insulation but is easily half the cost. That is a fact. This is assuming that the fiberglass installation is a Class 1 install.

Closed cell insulation is 3 to 4 times the cost of fiberglass insulation and is not cost effective as the sole insulation in a structure. However, where closed cell shines is in its ability to effectively seal the surface its applied to creating a fantastic barrier. What most people don’t realize is to effectively insulate a home you have to do an excellent job of creating an effective air barrier first.

In our homes we have found the most effective way to insulate a home it to first spray about 1/2” of closed cell foam onto the interior side of the sheathing followed by properly installing fiberglass insulation. I have achieved an ACH of as low as 0.75 with this method.

As for Pauls project using fiberglass insulation is his best option since it’s just a shed.

PS. If you really want to go down this rabbit hole here is a video produced by the National Association of Insulation Manufacturers Association (NAIMA) where they interview me and my insulation contractor in one of our homes and explains some of the details we address. ( it was in the upper 90’s on the day they shot this so pardon my sweating!).

https://youtu.be/eL63W5nEgAU

Thank you, smlsig. Exactly the sort of concise and specific information I was looking for.

I'd pretty much come to that conclusion myself. Turns out that Owens-Corning isn't producing batts for 2x4 on 24" center walls - not enough demand. I "upgraded" to Roxol batts due to availability.

I'm going to put 1" blue board foam in the rafter bays to cut down on condensation and channel what does accumulate out the eaves. I'll also put 6" of unfaced fiberglass in the ceiling joist bays.

We couldn’t fit it in the plant, but I remember something about ideally we would have the radiant barrier between the rafter and purloins