insulating shed/workshop 2x4 trusses

[givemethewillys]

Hi everyone, I've been lurking on the site for awhile and learned tons of great things, but I don't usually take the time to post. Well, I recently came upon a bunch of R-13 fiberglass insulation for practically nothing and immediately went to work insulating my 12x16 shed/workshop.

Insulating the walls is going straightforward, but what I'm stuck on is how to insulate the roof trusses. Currently the shed has soffit vents and a full length gable vent.

Should I run my R-13 paperbacked insulation over everything, effectively making it unvented? A search suggests adding vent tunnels from the soffit to ridge but this would take up most of the space of the 2x4 truss. Would this be necessary if the shed will be uncooled in summer, and heated only occasionally by electric or wood in winter?

 

[p_mori7]

the baffle goes perpendicular to the trusses, and should be stapled to allow airflow up thru the soffit and to prevent the insulation from going over the soffit. It goes to the outside of the top-plate, you can angle inwards a bit, and you can leave only about 1 inch gap between the roof sheathing and the baffle. Slide your batts over the top plate just snug against the baffle.

 

[givemethewillys]

So, the way that I'm understanding it, the fiberglass batts fit up into the trusses just as in the walls, but this baffle leaves a small airspace from the soffit into the main space? is there a similar baffle that is needed at the ridge vent? I've never seen these baffles in person, so pardon my ignorance.

 

[Motofixxer]

I have pics indicating one way of insulating trusses. It kinda depends on the size of the trusses. Bottom line is you need free air flow from soffit to ridge with fiberglass. Or you could spray the underside of the roof sheathing with spray foam, and seal it up completely.

 

[givemethewillys]

I definitely want to stick with fiberglass batts, since I have almost 400 sq. ft. for less than $30! I would like to see pictures of what you're talking about if you have a chance, since I've never seen these battens before. If it doesn't end up being cost effective I'll just leave the shed uninsulated and add another layer of clothing when working in the shed in the winter!

 

[Motofixxer]

Sorry I should have been more clear. I have pics in my shop thread Here Scroll down to the ceiling pics and you can see the upper layer insulation running perpendicular to the trusses woven through the chords, then a second layer between them stapled to the bottom chords. I have an R38 up there. Make sure to use the foam Duravents or equivalent above the top of the walls to maintain air flow.
Get some insulation up then some plastic and you will notice a huge difference in temps. Then finish up with some insulation in the walls. 400' won't take much at all. It will make it much more comfortable in there.

 

[Steevo]

johnnyc1999, what kind of roof trusses do you have?

 

[bczygan]

I think he is talking about 2x4 RAFTERS, not trusses, and putting batts in those spaces. I have a solution for him. Pack out those 2x4 rafters by applying a 2x2 on the edge of each one. This will give you the extra space needed to run the baffles needed to create the 1" airspace from eave vents to either ridge vent or a space at the collar ties that connects the gable end vents. Then you can install the insulation batts. Make sure you have adequate number of ceiling joists to resist the added load that the rafters will put on the walls by pushing out at the top plates. Give us photos to confirm your conditions.

 

[givemethewillys]

bczygan, your solution sounds like it might be the most simple. My shed is a betterbarns 12x16, built to the plans on 24" centers. They call the roof structure "trusses" but basically I believe it is very similar if not identical to a roof rafter setup. Basic isosceles triangle shape, with 2x4 rafters and a sill tie to make a loft.

I'm still not 100% sure that I even need a ventilated shed, since it will be unheated/uncooled most of the time. Would insulating it without ventilation in itself cause condensation problems? I've also considered adding a cupola at some point.... would a cupola allegiate the need for soffit/ridge vents? Sorry for so many questions!

 

[Motofixxer]

Yes, you have too options, vented attic or sealed and sprayfoamed. If you just have 2x4 rafters, then using the 2x2 method will work for you. I was under the impression you had regular trusses.
A cupola could probably eliminate the ridge vent. But you also need the whole length of the roof to get ventilation. If you only have 2x4 rafters then you would have to ridge vent. The air has to flow in somewhere and out somewhere. With 2x4 rafters each rafter bay is separate from all the others, you need vents in each one. Like a long soffit vent and a ridge vent

 

[bczygan]

bczygan, your solution sounds like it might be the most simple. My shed is a betterbarns 12x16, built to the plans on 24" centers. They call the roof structure "trusses" but basically I believe it is very similar if not identical to a roof rafter setup. Basic isosceles triangle shape, with 2x4 rafters and a sill tie to make a loft.

I'm still not 100% sure that I even need a ventilated shed, since it will be unheated/uncooled most of the time. Would insulating it without ventilation in itself cause condensation problems? I've also considered adding a cupola at some point.... would a cupola allegiate the need for soffit/ridge vents? Sorry for so many questions!

I took a look at their website and saw how the "Truss" is constructed. Just one big triangle with gussets at the corners. 2x6 bottom chord and 2x4 top chords. The 2x2 will work. But the trusses are on 24" centers. Is your insulation set up for that? If not you will have to cut and tape pieces together. You need a ventilated shed to keep the moisture and temps down to protect the roofing system. I recommend a small plywood chase at the inside of the peak to connect all the rafter air spaces together. Then, whether you install a working cupola or not, the gable end vents and ridge vent will vent the roof and attic space. Frame it like collar ties on each truss. It will allow you to put thicker insulation in this area and still have storage up in the ceiling area. It will also give you a flat horizontal surface for some lights.

 

[givemethewillys]

Ok thanks for your help guys! The insulation that I have is 24" so it fits nicely between the rafters. I'll have to run by lowes today and pick up some 2x2's and vents to get this project wrapped up. Thanks again!