# Turning 16'x20' Shed into workshop - Help with Roof Insulation



## clawlan (Nov 29, 2015)

I spent the weekend insulating the walls of my 16'x20' shed/workshop with typical R-15 fiberglass. Now I am trying to figure out what to do with the roof (I'm in GA, zone 3). Like most sheds, it is just a large open space, completely sealed, no ridge vents, no soffit vents, etc. Initial research seems to point towards closed cell spray foam, but given the relatively small size of the area, I am going to end up paying the $1500-$1800 minimum job fee to any of the foam installers out there (I called several already). I know there are DIY kits out there but I'd end up paying about the same amount once I got enough to fill in between the rafters, and I don't think I want to deal with the hassle and mess anyways. Knowing that this is not a house so doesn't need to be perfect, just enough to allow a small mini-split to heat in the winter and cool in the summer, are there any other reasonable alternatives? The easiest thing would be attached 4x8 sheets of rigid foam to the rafters.


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## Knucklez (Oct 21, 2007)

ridged foam is surprisingly expensive, i insulated the slab of 13x26 workshop and i think it was <$1000 for 2" foam. i think if you want to insulate you also have to take care of adding vents and vapour barrier. in my workshop i have soffit vents that go to baffled roof and air exists along the continuous ridge vent. batts + vapour barrier plastic. it was about as cheap as i could DIY it but still get pretty good results. i had a helper and it took about 8 hours.


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## Nealtw (Jun 22, 2017)

can you work in soffet vents, Post a picture of the inside of the roof?


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## Colbyt (Jan 27, 2014)

If you use batts you will need some venting.

I'll throw this out as brain fodder. About 10 years ago I need to insulate what would become attic space before the drywall ceiling was hung. I used thin wire to hold it in place spaced about 16" apart across the joist. If doing that in a workspace with no drywall, I would then staple chicken wire to the bottom of them joists.


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## Randy Bush (Dec 9, 2020)

Actually 2" ridge is not all that bad, about $25 a sheet is what I pay for it . And you would need maybe 12 more or less , which would be $300. If you go that route it needs to be covered with something as it is not be be left exposed. That would give you a R5 per in so might want to double it.


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## Randy Bush (Dec 9, 2020)

Knucklez said:


> ridged foam is surprisingly expensive, i insulated the slab of 13x26 workshop and i think it was >$1000 for 2" foam. i think if you want to insulate you also have to take care of adding vents and vapour barrier. in my workshop i have soffit vents that go to baffled roof and air exists along the continuous ridge vent. batts + vapour barrier plastic. it was about as cheap as i could DIY it but still get pretty good results. i had a helper and it took about 8 hours.


Wow it must be kinda high in Canada.


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## clawlan (Nov 29, 2015)

Randy Bush said:


> Actually 2" ridge is not all that bad, about $25 a sheet is what I pay for it . And you would need maybe 12 more or less , which would be $300. If you go that route it needs to be covered with something as it is not be be left exposed. That would give you a R5 per in so might want to double it.


So you saying in-between rafters or attached on top?


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## clawlan (Nov 29, 2015)

Nealtw said:


> can you work in soffet vents, Post a picture of the inside of the roof?


I'll get some images shortly! 

Basically, I don't have a great understanding of the science of insulation. Vapor barriers, venting, batts, foam, pros, cons, what can happen if you have the wrong combination etc. I'm trying to read as much as possible but I also don't want to redo my entire roof or go overboard for a simple workshop.


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## Randy Bush (Dec 9, 2020)

clawlan said:


> You could depending on rafter size cut and put two in between or one in between and one on bottom of rafters. A few years ago I did a sun room . Sheeted the roof put a layer of 2" ridged the sheeting on top of that with a metal roof. Customer said it make a huge difference . Just went back to finish the inside , he had the whole inside spray foamed .


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## Nealtw (Jun 22, 2017)

clawlan said:


> I'll get some images shortly!
> 
> Basically, I don't have a great understanding of the science of insulation. Vapor barriers, venting, batts, foam, pros, cons, what can happen if you have the wrong combination etc. I'm trying to read as much as possible but I also don't want to redo my entire roof or go overboard for a simple workshop.


Venting cools the roof in the summer giving more life to the roofing 
If you get snow, heat coming off the top of the walls will melt the snow which refreezes a little lower down creating an ice dam and water can back up under the shingles. 
We want to keep moisture out of the area above the insulation so we would like the area closed so no air from below can get into the ceiling. One person beathing in a room can provide moisture with eat it rises so what ever it takes to get real good fit with the insulation, something that will stop the air, low and high venting are all important for a healthy building.


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## Nealtw (Jun 22, 2017)

Nealtw said:


> Venting cools the roof in the summer giving more life to the roofing
> If you get snow, heat coming off the top of the walls will melt the snow which refreezes a little lower down creating an ice dam and water can back up under the shingles.
> We want to keep moisture out of the area above the insulation so we would like the area closed so no air from below can get into the ceiling. One person beathing in a room can provide moisture with eat it rises so what ever it takes to get real good fit with the insulation, something that will stop the air, low and high venting are all important for a healthy building.


I would like to see the roof framing from the inside.


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## clawlan (Nov 29, 2015)

Here are some images of the shed.


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## Knucklez (Oct 21, 2007)

Randy Bush said:


> Wow it must be kinda high in Canada.


Yes.. $61 USD per sheet (4x8x2) + tax + van rental. and i needed 13 sheets to under & sides of slab (i did not do a skirt as prescribed because i'm not in THAT cold a region).


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## Missouri Bound (Apr 9, 2011)

What are you doing after the insulation? Are you putting plywood on the wall and roof?
Either way you need soffit vents and some roof venting.
What I would do is cut in soffit vents. You can get them in a strip where you just rip a long wide path in the soffit and nail the vent in.
You can also install a ridge vent but you will have to cut back the ridge to install it.
Then there are styrofoam baffles you can run from soffit to ridge that goes under your insulation.
That is the approach I would take.
I would be easier if you put in a ceiling and insulated that, but you will still need some ventilation to the "attic area".


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## clawlan (Nov 29, 2015)

Missouri Bound said:


> What are you doing after the insulation? Are you putting plywood on the wall and roof?
> Either way you need soffit vents and some roof venting.
> What I would do is cut in soffit vents. You can get them in a strip where you just rip a long wide path


My plan was OSB or cheap plywood on the walls, no thoughts on the ceiling, though I don't care about having a finished look. It sounds like the "easiest" acceptable solution is closed-cell spray foam the ceiling which doesn't require venting, but that is likely the most expensive. Cheapest, but biggest pain would be soffit vents + ridge vent. I really don't want to install a ridge vent. I suppose I could get away with those foam baffles + batts + soffit vents. 

That being said, no idea how to do soffit vents given how this thing is constructed. Cut holes in those horizontal 2x4's?


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## Missouri Bound (Apr 9, 2011)

A picture would help us understand.
And what is the roofing material?


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## clawlan (Nov 29, 2015)

Missouri Bound said:


> A picture would help us understand.
> And what is the roofing material?


I posted 4 pictures above. Roofing material is 2 y/o architectural shingles. We had a hail claim on the house and the roofers threw the shed in to the claim. I didn't know at that time that I would want/need a ridge vent.


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## Nealtw (Jun 22, 2017)

clawlan said:


> Here are some images of the shed.


They do not open for me??


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## Missouri Bound (Apr 9, 2011)

I cannot open them either.


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## clawlan (Nov 29, 2015)

Nealtw said:


> They do not open for me??





Missouri Bound said:


> I cannot open them either.


Oh sorry! I edited the post. Hopefully you can see them now?


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## Missouri Bound (Apr 9, 2011)

That is not at all what I expected.
Because of your asphalt based roof you only have two options.
Either use the closed cell or ventilate.
The blocks between the rafters complicate the addition or soffit vents.
Ideally those blocks wouldn't be there and the soffit would be closed. Then you could install vents in that soffit (that isn't there) and that would ventilate up to the ridge or roof vent.
Without ventilation your roofing material life will be shortened.
You could move those blocks out about a foot, install a vented soffit material in that area and install a ridge vent. 
I suspect those blocks serve no real structural purpose, just closing off the gap between the rafters.


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## Nealtw (Jun 22, 2017)

clawlan said:


> Oh sorry! I edited the post. Hopefully you can see them now?


You could add collar ties just low enough for insulation under the ridge beam. And add a couple box vents on each side of the beam
You could add anther 2x4 to the bottom of the rafter making them 7 inches deep. 









You can just knock out the blocks between the rafters. 








Then you would run air chutes from the soffet to the common area above the collar ties.


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## Missouri Bound (Apr 9, 2011)

Neal.....what did you use and how in the hell did you draw that so fast???


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## Nealtw (Jun 22, 2017)

Missouri Bound said:


> Neal.....what did you use and how in the hell did you draw that so fast???


Windows paint 2d , it takes a learning curve.


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## Vanner (Oct 11, 2015)

Without high jacking this thread, I’m insulating shop roof as well. Was going to spray foam but holy hell!

Cross section top-down EPDM - 2” polyiso roof insulation - 5/8” plywood deck - 2x6 roxul (in 2x8 rafter cavity - vapour barrier - 1/2” plywood ceiling. 

That’s R39. 

I don’t need to vent any of that assembly, do I?


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## clawlan (Nov 29, 2015)

Nealtw said:


> You could add collar ties just low enough for insulation under the ridge beam. And add a couple box vents on each side of the beam
> You could add anther 2x4 to the bottom of the rafter making them 7 inches deep.
> View attachment 636517
> 
> ...


This is super helpful info, thank you. I like the idea of the collar ties, pretty simple to add. Could I get away with a gable vent on the front and back of the "common area above the collar ties" or really need the box vents (or ridge vent)?


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## Nealtw (Jun 22, 2017)

clawlan said:


> This is super helpful info, thank you. I like the idea of the collar ties, pretty simple to add. Could I get away with a gable vent on the front and back of the "common area above the collar ties" or really need the box vents (or ridge vent)?


I think so, I don't keep up with who is wining that argument this week.


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## clawlan (Nov 29, 2015)

Nealtw said:


> I think so, I don't keep up with who is wining that argument this week.


Perfect, thank you!

Again, this is not a home, this is not new construction, this is just an old shed that I am turning into a workshop that I want to keep moderately warm in the winter and moderately cool in the summer. I really don't care if my shingles only last 20 years instead of 30. I don't care if it's only R15 in the roof instead of R500. I just want to reasonably insulate, not break the bank, and not break my back. It's under pretty heavy shade anyway.


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## Nealtw (Jun 22, 2017)

clawlan said:


> Again, this is not a home, this is not new construction, this is just an old shed that I am turning into a workshop that I want to keep moderately warm in the winter and moderately cool in the summer. I really don't care if my shingles only last 20 years instead of 30. It's under pretty heavy shade anyway.


Understood. keeping a building healthy is keeping people healthy. You can do a closed system with batts, second best but still stopping air from getting to the cold surface is important.


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## Nealtw (Jun 22, 2017)

Cathedral Ceilings & Un-Vented Roof Solutions: how to avoid condensation, leaks, attic mold, insulation mold, & structural damage to roof framing when roof venting is not possible (inspectapedia.com)


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## Knucklez (Oct 21, 2007)

it looks like half your shed is fully open to roof and 1/3 is a loft? very nice! building inspector in my area would not allow that for my workshop. i did the ridge vent method on my workshop and baffles. where i had 2x6 blocking the air movement i used a sawzall to cut it a bit thinner so the air could get past along the roof (like turned the 2x6 into a 2x4.5 .. and ya, it was a crap tonne of work i wish i thought of doing that BEFORE installing the 2x6 blocking).


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