Insulating my 10x16 Shed

[EastEnder]

I'm getting ready to insulated my 10'x16' shed. My intention is insulated the walls and the ceiling, with the end result being a vaulted and sheet rocked ceiling.

I want to sheet rock over the roof trusses, with a flat section (of sheet rock) in the center.



My question is, can I completely insulate the entire roof with out any vents, much like you would in a cape cod style house or a home with a finished attic? As of now the soffits do not have vents either. The way that my trusses are now, I would have to drill holes through the trusses all the way to the gable ends, and then move the screened vents up.

Thanks for any help.

 

[James-W]

What is this building going to be used for? Will it be heated/cooled?

 

[EastEnder]

Its going to be my workshop. As for heating and cooling, I'm looking into small portable electric heaters, that for the most part will only be on when Im out there using it. Its a hobby building for the most part.

 

[James-W]

Normally a building will have a ridge vent and soffets that allow outside air to come in and the air circulates and then leaves thru the ridge vent. Styrofoam troughs are used to keep insulation away from the roof and allow the air to circulate up to the ridge vent and out of the building. Since you don't have a ridge vent or soffet vents, I am not real sure what to tell you.

 

[The Cobbler]

no venting = less shingle life.

 

[EastEnder]

I'm trying to prevent moisture and mold growing on the inside of the roof sheeting. I had that happen on my former home due to too much insulation...

 

[CNGsaves]

What . . . . Country . . . . or climate . . . are you in ??

East end of China . . . or Russia . . or Florida ???

Update GJ Profile with Location.

 

[EastEnder]

Lower NY- so some snow in the winter, and some heat in the summer

(profile changed)

 

[Voi]

R-20 or R-25 of rigid foam on the underside of the roof deck depending on whether your part of NY is Zone 5 or Zone 6 according to this article:

http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling

If those are 2x4 trusses none of the rigid foams would get you to R-25. Polyiso would get you to R-21 if your part of NY is Zone 5.

In either case an additional layer of foam on the underside of the rafters would greatly reduce thermal bridging and bring you up to recommended or desired R values.

But that's a lot of foam which isn't cheap (although cheaper than spray foam) and seems over kill for an occasionally heated work space.

You could probably just do 2" of foam on the underside of those rafters and upper plywood gussets and be fine. Even at R-10 you'd certainly out perform R-13 fiberglass between the rafters since you'd have a tighter seal with taped seams and would have thermal breaks over the rafters. But it's more expensive -- check Craigslist for rigid foam leftover from building sites, etc.

 

[EastEnder]

Thanks for the link. Good reading! Although I cant make heads or tails of if I should vent it or not. I'd prefer to have it not vented, and I think I can if I can seal it tight enough without an air gap?

Good idea to check craigslist for the leftovers...

Next question- how to I keep the rigid foam in place in between the rafters? Fiberglass faced insulation has tabs to staple it in place, but the rigid foam doesn't, does it? Any ideas besides duct tape spanning the bays?

Also will (1) 1" hole in the soffit in each bay be sufficient to draw air up and through to the two gable vents?

 

[Voi]

How do I keep the rigid foam in place in between the rafters?

Also will (1) 1" hole in the soffit in each bay be sufficient to draw air up and through to the two gable vents?

When I've done it I've cut the rigid slightly undersized and used low expansion spray foam to fill the perimeter gap. It's plenty. In fact just a dab on each side will hold it in place so you can free up a hand while you spray in the rest.

You could also cut them tight and caulk the perimeter with a foam friendly caulk. This will be plenty since you're planning on drywall.

Not sure about the soffit vents. I'd probably put in two per rafter bay.

 

[EastEnder]

When I've done it I've cut the rigid slightly undersized and used low expansion spray foam to fill the perimeter gap. It's plenty. In fact just a dab on each side will hold it in place so you can free up a hand while you spray in the rest.

You could also cut them tight and caulk the perimeter with a foam friendly caulk. This will be plenty since you're planning on drywall.

Not sure about the soffit vents. I'd probably put in two per rafter bay.

Sounds like a good plan- now I need to find some left overs, lol....

 

[EastEnder]

If I wanted to screw the foam panels to the rafters what type of fasteners can I use? Can I attach the sheet rock over it?

 

[VHF]

You need to think about moisture issues in the walls as well as in the roof. Since this is a workshop, you won't be generating as much moisture as in a house (no showers, no cooking), but still some moisture just from breathing in there. What you want to avoid is (a.) having moisture condensing/freezing in the walls and (b.) moisture getting trapped in the walls/roof that could lead to mold growth. Every wall or roof needs to ability to either dry to outside or dry to inside.

With a small shed already constructed you don't easily have the ability to have a ventilated attic or "rainscreen" walls, and presumably don't have house-wrap (which if properly installed keeps air infiltration out but lets moisture permeate to dry out the wall cavity.)

Foam insulation--either all spray foam or rigid foam board with joints/edges tightly sealed--would give you the snuggest space that you could easily heat. And as discussed above you could leave space for roof ventilation above rigid foam panels.

Lowest cost would be fiberglass batts. If carefully installed this can keep it nice and warm inside also. In this case, make sure to calk any cracks before insulating. Go inside during the day and seal up any cracks where you can see daylight. With no major humidity sources inside I might go with either plain or maybe kraft-paper faced batts, but probably wouldn't worry about a plastic vapor barrier. I don't think I would worry about attic ventilation, either.

Because you aren't living in there, you aren't introducing a huge amount of moisture that is likely to condense in the attic and cause mold. If it seems dry inside then your walls and roof cavities should be fine also.

 

[EastEnder]

You need to think about moisture issues in the walls as well as in the roof. Since this is a workshop, you won't be generating as much moisture as in a house (no showers, no cooking), but still some moisture just from breathing in there. What you want to avoid is (a.) having moisture condensing/freezing in the walls and (b.) moisture getting trapped in the walls/roof that could lead to mold growth. Every wall or roof needs to ability to either dry to outside or dry to inside.

With a small shed already constructed you don't easily have the ability to have a ventilated attic or "rainscreen" walls, and presumably don't have house-wrap (which if properly installed keeps air infiltration out but lets moisture permeate to dry out the wall cavity.)

Foam insulation--either all spray foam or rigid foam board with joints/edges tightly sealed--would give you the snuggest space that you could easily heat. And as discussed above you could leave space for roof ventilation above rigid foam panels.

Lowest cost would be fiberglass batts. If carefully installed this can keep it nice and warm inside also. In this case, make sure to calk any cracks before insulating. Go inside during the day and seal up any cracks where you can see daylight. With no major humidity sources inside I might go with either plain or maybe kraft-paper faced batts, but probably wouldn't worry about a plastic vapor barrier. I don't think I would worry about attic ventilation, either.

Because you aren't living in there, you aren't introducing a huge amount of moisture that is likely to condense in the attic and cause mold. If it seems dry inside then your walls and roof cavities should be fine also.

I like the idea of the fiberglass batts better, and then sealing it up as tight as possible. I only want electric heat, which should be dry, and only on intermittently, not heated or cooled constantly. And like you mentioned, there will be no shower.

Right now, the shed is very dry. All of the wood is in good shape, save for a spot on the floor where a bag of ice melt salt absorbed a bunch of water and made a mess. But otherwise its good.

 

[Wanna Ride]

Just curious; if it's a workshop, why not OSB sheathing instead of dry wall? Faster, easier, less expensive, more durable for the application, less mess, no mud, dust.

 

[EastEnder]

Good question and one my family and friends have asked as well.

The answer is aesthetics really. I like the finished look of drywall over OSB. Without a doubt, I love the simplicity of OSB, plywood, luan, etc, but I wanted a cleaner look. Something akin to this guys: http://garagejournal.com/forum/showthread.php?t=163328&page=3

 

[finn]

You need a "proper vent " which leaves an air gap between the installation and underside of the roof sheathing, along with soffit and ridge venting.

 

[Voi]

If I wanted to screw the foam panels to the rafters what type of fasteners can I use? Can I attach the sheet rock over it?

There are a variety of plastic washer type systems like this.

But I'd just keep in simple and hold it in place just enough until you can screw the drywall through the foam and into the rafter.

I think the other poster makes a good point about not having a lot of moisture in your shed. I wouldn't hesitate to do an unventilated fiberglass roof in a hobby type shed in my area. But it's your peace of mind, not mine.

 

[ROCKNMUD]

Either way foam or batts use strapping (1x3") across the rafters every 16" to fasten the drywall to.

 

[EastEnder]

There are a variety of plastic washer type systems like this.

But I'd just keep in simple and hold it in place just enough until you can screw the drywall through the foam and into the rafter.

I think the other poster makes a good point about not having a lot of moisture in your shed. I wouldn't hesitate to do an unventilated fiberglass roof in a hobby type shed in my area. But it's your peace of mind, not mine.

Considering my barn doors have no weatherstripping on them, I'm with you guys. Im gonna roll the dice with the fiberglass roof.