insulation questions

[1967rs]

I live in Northern South Dakota and am going to build a 24' x 36' garage. Eight foot side walls, 2x6, for 2 vehicles and a work area. Gas heater for winter

I suppose if I were to put in a ceiling it would be easier to keep warm however what if I didn't put in a ceiling but had the roof insulated with sprayfoam and left the joists open. I guess I think the 8' ceiling might make it seem a bit closed in and this might make it less so.

I had thought about just putting in fiberglass in the walls. Not sure if the guy would want to just do the roof but who knows also maybe he'd give me a better price if it included the side walls too. Any opinions?

Oh second question. So during the winter months there will be snow melting in the garage off the vehicles. I've had garages with floor drains not for winter washing but just for melting snow. Is it worth the cost or effort?

Thanks
vic

 

[gml1998]

Are you sure you will never put a lift in the garage? If so then 8 ft height to ceiling joists should be fine.
If code permits do the floor drain.

 

[[email protected]]

Spray foam is outrageously pricy compared to fiberglass insulation

Sent from my SAMSUNG-SM-G900AZ using Tapatalk

 

[iced98lx]

Greets from Southern SD.

I have no input on the insulation outside of I've never seen the roof deck being spray foamed not end up in rotted ruin in SD with the temp shift so I'd put a ceiling in with proper venting personally. That said, perhaps I've just not seen one properly done!

I would ABSOLUTELY put a floor drain in if you have the opportunity and means. I would also be VERY specific about floor slope so the melting snow doesn't come in contact with any walls if possible.

Good luck, post pictures!

 

[1967rs]

Ha! It's been so long since I posted I forgot my location was actually under my pic so sorry about being redundant.

I once rented a place that had a drain in the garage. The concrete was sloped toward a 12" cube in the floor. There was a metal plate with holes on top and and on the bottom was where the drain was. The landowner told me if it started to smell then I needed to pour some water down the drain. Presumably there was a trap that dried out. This was an attached garage so it was easy to hook up. It was nice in the winter time.

I'll have to see how much the drain will cost I guess.

vic

 

[theoldwizard1]

Spray foam is outrageously pricy compared to fiberglass insulation

Absolutely !

I would blow in cellulose, maybe as much as 30-36" if you are planning on heating the garage more than just a couple f days a month. Just make sure that you have "chute" down to the soffits to keep them open and air flowing above the insulation and below the roof deck. A cold roof deck minimizes snow melt (until spring) and the possibilities of ice dams.


If you plan on working in the garage, seriously consider 2" of rigid foam and a vapor barrier under the concrete. The floor will be a bit warmer and it will be less damp.

 

[theoldwizard1]

Garage floor drains are great, especially if you have heated garage and live in a snowy area.

Local building codes vary widely on garage floor drains. Some place it is complete forbidden. Others require it to "run to daylight" meaning it will likely freeze in winter. Other say it must have a grease/oil trap.

Do your research.

 

[James-W]

Spray foam is outrageously pricey compared to fiberglass insulation

Sent from my SAMSUNG-SM-G900AZ using Tapatalk

That is true initially, but it becomes less true when you consider the long term. Spray foam seals everything up tight and it has a higher "R" value so in the long term you will most likely save enough on heating bills to pay for the extra cost. The initial cost can, and many times does, scare a lot of people way from doing it. But the people who have had it done in their homes invariably feel it is the best thing they ever did to improve their comfort and save on heating/AC bills.

 

[K'ledgeBldr]

Insulated slab, batt walls, and blown ceiling. The economics do not justify the additional expense for "a garage". If this were a dwelling- different story!

The floor drain is something you will have to discuss with your AHJ-
Nobody allows "garage" floor drains to be attached to public sewer, but if they are allowed it's usually to a lined pit. Most AHJ's won't allow them to drain to surface area because of run-off. "Hazardous waste" could end up in natural creeks/streams. Or you have to use a trap.

 

[theoldwizard1]

Insulated slab, batt walls, and blown ceiling. The economics do not justify the additional expense for "a garage".

In YOUR opinion !

The O.P. may spend a lot more time in his garage than you do, so "personal comfort" IS an important consideration !

Zero insulation in my 2 car detached garage. I bought a second LP "tank top" heater. Burning an extra 20-40 lbs per winter season is fine for me, because I only work in the garage when I have a"project" I can't bring in the house (snow blower).

 

[Falcon67]

Insulated slab, batt walls, and blown ceiling. The economics do not justify the additional expense for "a garage". If this were a dwelling- different story!

Agree - hah. I spend a lot of time in my shop and you could live in there if it had a potty LOL. Do it right up if you're going to be doing things other than parking cars and lawn equipment.

Notes -
8' does not seem "tight" to me and makes for a mucho cheaper & easier heating/cooling. Think about the volume of space.

If you wanted to leave the ceiling open for storage, another idea would be removable panels at each long end and each side in the middle. I used that - 4x4 panels - in my old shop and about the only thing I could not get up there was 10' joints of pipe. When we moved it took two days to get everything down.

 

[Rockcam]

Nobody allows "garage" floor drains to be attached to public sewer, but if they are allowed it's usually to a lined pit. Most AHJ's won't allow them to drain to surface area because of run-off. "Hazardous waste" could end up in natural creeks/streams.

Not the case in all areas.

My garage, built in 2013, has drains that run underground directly to the storm sewer catch basin. Approved my city. Storm sewer runs directly into a local lake. Lake does have a system funded by a local benefactor that filters out oil, etc prior to entering lake.

 

[MScott]

Why are you limiting the height to 8 feet? 12 foot walls give you the option of a lift in the future and the cost difference would be negligible. That would also allow a proper ceiling and bat or blown in insulation.
I also agree with the foam under the concrete. It's what I have in mine and with 6 inch walls and R 50 in the ceiling my garage is cool in summer and moderate in winter even before I turn on the in-floor heat. JMHO

 

[iced98lx]

Hey RS- take a read through this before you spray your ceiling:

http://www.energyvanguard.com/blog-...ll-Spray-Foam-Insulation-Really-Rot-Your-Roof

It has some good discussion and then you can weigh if the upside is worth the cost/complexity/risk

 

[ssdave]

If I were going to build a 24x36, I would use trusses on the roof instead of stick framing it, so you'e have a ceiling anyway. Given that, you'd have a ceiling to put insulation in, and blown in would be the most economical.

If you have foamed insulation on the bottom of the roof deck, it is more expensive. It also makes the roof very hot, so if you use shingles, they have a very short life. If you're going with metal, not so much of an issue.

I'm designing a garage to go with my new house and have wrestled with these same issues. What I arrived at is I put in scissor trusses with an "energy heel" design, so I can blow in insulation to a full depth and have good insulation value, but have air flow to the attic area and be able to control the roof temperature. The scissor truss gives me a lot more height at center of the garage, so I can put in a lift if I want. I'm a bit wider and have a center door, so that works well for me. Won't work quite as well in a 2 bay garage.

I'd put the money you would spend on foam insulation into either higher walls or scissor trusses to give more height, and I think overall the product will be better. The cost of insulating a garage might not pay off in energy savings over time, but it sure pays off in better comfort, when the winter stays warmer, and the summer stays cooler. It makes the garage inhabitable for about 10 times as much of the year as one that isn't well insulated.

 

[Randy in Maine]

Suggestion: Investigate using Structural Insulated Panels or SIPS instead. Very cost effective and go up very fast with just 2 or 3 guys. I sent them a rough design of what I wanted and they figured out the rest. I have them set up for 40'x28' walls and the 12' ceiling, precut 2 8'x8' garage doors, 2 man doors & 6 windows, surface mounted conduit electricity. They got delivered by a single semi in 3 weeks. Most of the panels are 48"x 12' x 6 5/8" thick ones. the ceiling ones are 4'x8' by 6 5/8" and mount to the trusses from my local lumberyard. I ended up with the tightest and best insulated garage of anyone I know (every thing is better than R-40) in pretty short order. Precious little waste. I am very pleased. With my radiant floor heat, it is very cost effective to heat all winter and the wind does not infiltrate it.

http://www.murus.com/specs/osb-2100pur

 

[DC73]

. . . I've never seen the roof deck being spray foamed not end up in rotted ruin in SD with the temp shift so I'd put a ceiling in with proper venting personally. That said, perhaps I've just not seen one properly done!

This is probably because open cell foam was used in a climate not suited for it. In some climates, open cell foam allows interior water vapor to migrate to the roof deck and condense. The OP's plan is sound but he will likely need to only consider closed cell foam. Closed cell foam will block moisture migration from the interior to the roof deck and has been a proven choice when applied properly.

To the OP - Spray foaming the bottom of the roof with closed cell foam is a good way to go for your needs. If you afford it, have them do the whole space. More cost effective options would be to spray foam the roof and use mineral wool in the walls. Mineral wool is a better insulation than fiberglass and is well suited for your climate.

If you go with fiberglass be sure and air seal the insulation cavity to prevent air movement through the fiberglass.

DC

 

[Voi]

I suppose if I were to put in a ceiling it would be easier to keep warm however what if I didn't put in a ceiling but had the roof insulated with sprayfoam and left the joists open. I guess I think the 8' ceiling might make it seem a bit closed in and this might make it less so.

I'm not sure if it's been mentioned yet but another option is rigid foam above your roof deck. If you're doing the work yourself it tends to be cheaper than spray foam and if you pay attention to air sealing it can actually be a more effective way to insulate a roof deck. It's more effective because, unlike spray foam, it greatly reduces thermal bridging through the upper chords of the trusses.

But it can be tedious labor and can also produce a lot of waste depending on roof design. And it takes a lot of foam (whether rigid or sprayed) to get the R value of a deep layer of blown fiberglass or cellulose.

Either way I suspect there are cheaper ways to get a more open look. Scissor trusses, especially with a raised heel, are a cheap way to open things up and get a lot of inexpensive insulation.

Parallel chord trusses are a bit more expensive but really open things up. I've never compared the cost of parallel chord trusses to raised heel scissor trusses but with only a 24' gable I suspect it wouldn't be that bad.

By the way, I live in the Black Hills and know of a number of garages, cabins and chalet styled homes that have un-ventilated roof decks with just fiberglass stuffed between the rafters. I'm sure there have been issues but it's more common than I would have expected. I've heard the argument we can get away with it here due to our drier and more stable climate than the rest of the state but I hesitate to recommend it or do it myself.

 

[theoldwizard1]

Suggestion: Investigate using Structural Insulated Panels or SIPS instead. Very cost effective and go up very fast with just 2 or 3 guys.

SIPS are great, but there are some down sides. Transportation cost and crane cost. If you are not near a big city, these can really add to their cost.

Also make sure you can find a crew to assemble them, but for a garage this should be trivial.

 

[Jlbc212]

i know blown-in insulation is very popular, inexpensive, an excellent insulator and treated to be "fire retardant." However, from my work experience, 37 years as a firefighter in an older urban city where many houses were insulated long after they were built, I must warn that "fire retardant" cellulose does burn. Once it gets burning it can be difficult to extinguish without removing all of it.
I have seen structures in my neck of the woods with structural foam roof decks. Roof shingles on these structures tend to dry out and curl much faster on these roof decks. With no air circulation under the roof the heat from the sun bakes the shingles.

 

[Randy in Maine]

SIPS are great, but there are some down sides. Transportation cost and crane cost. If you are not near a big city, these can really add to their cost.

Also make sure you can find a crew to assemble them, but for a garage this should be trivial.

Actually, delivery to my site was part of the deal. I don't know how much that was but it all fit on one semi. My buddy put loader forks on his Kabota and unloaded it easily in 4 hours. Just bulky, not heavy as my garage is just a big rectangular box. No crane was needed to assemble. The trusses came from my local lumber yard and they just delivered them to the roof. My carpenter guy, his buddy and me did all of the work. Although the carpenter guy had not done a SIPS before, he has since done about 8 of them.

I am pretty sure a house would be a more complicated, but the SIPS guys give you lots of assistance over the phone if you need it.

Might want to think about it if saving energy is a priority.

 

[iced98lx]

This is probably because open cell foam was used in a climate not suited for it. In some climates, open cell foam allows interior water vapor to migrate to the roof deck and condense. The OP's plan is sound but he will likely need to only consider closed cell foam. Closed cell foam will block moisture migration from the interior to the roof deck and has been a proven choice when applied properly.

Cool, good information, obviously open cell is letting moisture into the roof deck to condensate, where as closed cell shouldn't if installed properly, makes sense.