Insulation question

Hi there folks, this is my first time posting. Thanks to this forum and others I successfully implemented and completed an attic grow in the later months of the year. It's got some differences from the ones on here, namely because it's not in the attic per se but a right-triangle-shaped crawlspace one floor down. I say this because inevitably there are going to be people who say attic grows are a bad idea, etc -- let's skip that part because this is a good space. The main problem I have right now is that there is no insulation on the underside of the roof (which serves as the slanted ceiling of my grow room). This wasn't a huge problem, as I had good ventilation etc, until it started snowing, and I started melting a perfect square on the roof over my room (lol). So I've temporarily halted all operations (luckily I was just finishing the first set) and am preparing to put in some insulation. My only question is what r-value of insulation I should need to put in there. I have the roof beams on the ceiling, so I plan to fit fiberglass batts in there and cover them with plastic sheeting.

Anyone know if I will need R-13, R-19 or R-30 insulation? The outside surface of the roof needs to remain at around freezing, as long as the rest of the roof also is, to keep the snow from melting. So what we're talking about here is blocking up to 50 degrees (assuming my room temp is 70 or 80) or so from getting from my light/heater to the outside of the roof, which is made of wood. Insulation experts, help me out here. Should I be ok with R-13 or R-19 or am I going to need R-30 for this job?

You may find this link helpfull.


http://www.onlinepot.org/misc/hidefromflair3.htm


J

Sisko197 said:

Hi there folks, this is my first time posting. Thanks to this forum and others I successfully implemented and completed an attic grow in the later months of the year. It's got some differences from the ones on here, but it does have one thing in common with other attic grows, namely the fact that there is no insulation on the underside of the roof (which serves as the slanted ceiling of my grow room). This wasn't a huge problem, as I had good ventilation etc, until it started snowing, and I started melting a perfect square on the roof over my room (lol). So I've temporarily halted all operations (luckily I was just finishing the first set) and am preparing to put in some insulation. My only question is what r-value of insulation I should need to put in there. I have the roof beams on the ceiling, so I plan to fit fiberglass batts in there and cover them with plastic sheeting.

Anyone know if I will need R-13, R-19 or R-30 insulation? The outside surface of the roof needs to remain at around freezing, as long as the rest of the roof also is, so what we're talking about here is blocking up to 50 degrees (assuming my room temp is 70 or 80) or so. Insulation experts, help me out here. Should I be ok with R-13 or R-19 or am I going to need R-30 for this job?

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How thick are your rafters? If they are 2x4 you can only go up to R-13. If they are thicker you could move up to R-30. Understand though, you are still going to have snow melting off your roof. Unless you can divert the heat somewhere else it will still propigate through the insulation and roofing material as it has nowhere else to go. It will create a much more diffused area (not a square) but unless you have other ventilation ideas I am not sure whether it will address your issue.

Use the highest R-value for the space.

If 2x6 use R19, 2x4 use R13, Use a plastic sheeting that is "fire rated" with a flamespread of 25 or less.
You can find white vinyl facer at an insulation supply company, this is fire rated and is a nice white color, and can be washed with a wet rag as needed.

Thanks for the replies! I'll address your comments one by one. The rafters are 2x6 so I guess would need to use R-19, that makes sense. I do have a ventilation system, I'm using a 4" high velocity inline fan for my exhaust, through ducting and eventually to the outside. The problem is not so much the light and too much heat buildup but rather that even at 70 degrees on the inside, the exterior of the roof isn't cold enough to keep the snow frozen. It seems like once it gets down to 50 or 60 in the room generally the snow will start sticking again. My working assumption here was to get this section of the roof insulated so that the heat would not radiate out as quickly if it reaches the roof at all. Assuming I have my ventilation all good, do you think R-19 is going to prevent that snow from melting on the outside of the roof? Or should I consider spray insulation and then the fiberglass? Radiant barrier to deflect the heat from the roof?

Use the highest rated fiberglass for the depth you have.
Then, lay over that lay a sheet of rigid foil backed foam. If you get the right manufacturer, it'll have a nice reflective foil side. I used it to build my growspace

Pullin' weeds said:

Use the highest rated fiberglass for the depth you have.
Then, lay over that lay a sheet of rigid foil backed foam. If you get the right manufacturer, it'll have a nice reflective foil side. I used it to build my growspace

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By rigid foil backed foam you're talking about insulated sheathing, right? Comes in like 1/4, 1/4 and 1 inch foam boards? That does sound like it would definitely get me there, having 2 types of insulation layered. However instead of the foam board, I had considered getting a sheet of radiant barrier foil for the ceiling, that's only $20 or so, but I wasn't sure if it would be safe for the plants to have the extra heat reflected directly onto them, what do you think of that?

Yup. I used the 1/2 in stuff. The radiant barrier would do the same thing but I don't what it's R value is.
I like the foam sheets cause the foil backing is reflective, but diffuse; easy to cut and piece together. I got my sheets for $8 - 4x8.

What Pullin' weeds said.

You are going to get a much higher insulation value from a 1/2" to 1" thick styrofoam barrier with foil rather than just a thin radiant barrier.

You could try the barrier first and install the styrofoam later if it is not sufficient.

Well you have a point about the foam insulation. I could get enough of it for around the same cost as the radiant barrier material, not risk putting too much reflected heat onto the plants, and have better all around insulation value. You all have been a big help, I very much appreciate it. I'll post an update after I get it all set up (probably just after xmas)!

You cannot insulate directly against the roof deck in that situation, you are stopping the air flow from the lower section to the upper section of the attic "hot air rises" hence why the roof soffits bring in air and expel out the roof vents. Your melting snow cause you have nothing to stop theramal transfer of heat generated in your room to the roof deck. To "properly" insulate the roof deck where your room is located you would batt the 2"x6"'s with R12 fiberglass or R15 Roxul "BUT DO NOT PUSH THE BATT AGAINST THE ROOF" you must leave a minumum of a 2" air gap between the roof deck and your batting. The 2" air gap allows the air to travel from the lower to the upper section and exhaust out your roof vents problem solved. Use foam but theave the same amount of space, spray in place polyurathane is a different ball game all together.

have you consiered gypsum boards with industrial rockwool insulation? keep an airgap between insulation and cieling

pinner73 said:

To "properly" insulate the roof deck where your room is located you would batt the 2"x6"'s with R12 fiberglass or R15 Roxul "BUT DO NOT PUSH THE BATT AGAINST THE ROOF" you must leave a minumum of a 2" air gap between the roof deck and your batting. The 2" air gap allows the air to travel from the lower to the upper section and exhaust out your roof vents problem solved. Use foam but theave the same amount of space, spray in place polyurathane is a different ball game all together.

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I had read about this and considered it, it sounds like a fine idea. You're absolutely correct about the way this space is designed, the soffit vents bring in cool air normally, and I think I could make this work if I could get a good seal on the foam insulation. Cool air could be carried from the vents behind those batts and right up into the ventilation holes to the attic. The only problem is there is only one predesigned ventilation hole up to the attic, there isn't one between each set of beams, but I can fix that. Do you think I would still need both foam and fiberglass then? If so I would probably end up having to use R-13 and 1/2-1" foam to still have that space there.

Gypsum board, is that drywall?

Sisko197 said:

Gypsum board, is that drywall?

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yep

I think I figured out a fairly easy way to do this. Each of the open "sections" between the roof beams I would be insulating does lead up to a rectangular section going up to the attic. Currently there is the end of a piece of insulation on each one, filling the gap (this is the attic floor insulation). What I think I can do is to cut a piece for each section from the foam, allowing for the air gap like you all were talking about, and just find a way to allow that air path to continue through those holes up into the attic space. The only problem to tackle would be finding a relatively painless way to connect those foam boards into those ventilation holes. I suppose I could just cut back the existing insulation a foot or so and push the foam up a bit further in its place. At the bottom (near soffits) I would just leave it open to allow for that fresh cool air to get sucked in. Sound about right?

As a builder for over 30 years I can give you a little advice. First of all you need to purchase a device to form a air channel that will go between the roof joists, that forms a shallow channel to keep an airspace available for air to flow from the roof edge (soffit) up to the ridge cap (peak)Available in most home improvement stores.. I would make sure to use construction adhesive to put it in place ( nailing it to your roof would allow your fasteners to go through the roof and cause leaks) Your idea of fiberglass insulation as thick as the rafters permit without flattening it at all is the next step followed by a layer of plastic. Be sure to tape all seams and staple holes. If your budget permits I would top it with foam insulation board from 1 to 2 inches thick. This board usually has a reflective radiant barrier on one side that is great for reflecting light and will increase your R value

djburns1 said:

As a builder for over 30 years I can give you a little advice. First of all you need to purchase a device to form a air channel that will go between the roof joists, that forms a shallow channel to keep an airspace available for air to flow from the roof edge (soffit) up to the ridge cap (peak)Available in most home improvement stores.. I would make sure to use construction adhesive to put it in place ( nailing it to your roof would allow your fasteners to go through the roof and cause leaks) Your idea of fiberglass insulation as thick as the rafters permit without flattening it at all is the next step followed by a layer of plastic. Be sure to tape all seams and staple holes. If your budget permits I would top it with foam insulation board from 1 to 2 inches thick. This board usually has a reflective radiant barrier on one side that is great for reflecting light and will increase your R value

Click to expand...

Thanks a lot for the suggestions! I think I found the item you're talking about, called an attic chute or rafter vent:

http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053

That significantly reduces the complication of my project. For about $17 I can run those rafter vents from the attic all the way down to where the air comes in from the soffit (about 8ft). Then add my insulation etc as we discussed.

You and everyone else have been a tremendous help, I will keep you updated as I make progress on this, kind of slow right now due to the holidays, but it's looking really good right now.

Got my rafter vents and I'm gonna start setting them up tonight. I got Gorilla wood glue for the adhesive, we'll see how well that works after initial testing. Meanwhile in the makeshift veg chamber my plants are coming along well, hopefully I should have the room done just in time to flower!

sounds like you are on the right path. Best of luck to you