Attic knee wall insulation

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  #1  
Old 06-26-12, 04:46 PM
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Attic knee wall insulation

I am renovating the top floor (bedroom/attic) of my 1 1/2 story by taking out the knotty pine walls, reinsulating and then re-drywalling.

I am in Ohio, zone 5, which indicates R13 (according to what I read).

1) Since the knee walls will be in the attic and the attic will be getting very hot, in summer, should I make my knee walls out of 2x6 and use R21?

2) Should I or can (I.E. due to code) put rigid foam over the insulation on the attic side? In certain areas of the knee walls there will be electrical outlets and I wasn't sure what I could do wrt the electrical code

Thanks
 
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Old 06-26-12, 05:54 PM
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More important than knee wall insulation how will air move up and over your addition to the ridge vents. Hopefully you have soffit venting and ridge venting. Yes, using 2x6 framing will allow you to install thicker insulation. What is above the ceiling? Remember you must allow air to circulate over whatever you use. That being said if you only have 2x4 framing for the roof, you will be limited, as baffles must be used to allow air flow.
 
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Old 06-26-12, 06:00 PM
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The rafters are 2x6. I am going to build out the rafters (inside the bedroom) a bit and install a combination of mineral wool and rigid foam to increase the R value. I am planning on a 1" gap between the insulation and roof deck.

I will be have to create intake vents (I have another thread about that). That part is going to be tough. There are no intake vents now. Hasn't been in the 80+ year life of the house. It will get to breath for the first time later this summer :-)

What about rigid foam on the knee walls? So from inside out, it will be: drywall, fiberglass insulation, rigid foam, then the cold/hot attic.

Thanks
 
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Old 06-29-12, 01:11 PM
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Sorry to be coming in so late on this.

I am renovating the top floor (bedroom/attic) of my 1 1/2 story by taking out the knotty pine walls, reinsulating and then re-drywalling.

I am in Ohio, zone 5, which indicates R13 (according to what I read).
The insulation that you need, and that will pay you back for the cost of installing it, depends not only on where you live but on the construction method, heating system and cooling system of your house. You can enter that information in the ZIP-Code Insulation Program, developed by the Oak Ridge National Laboratory, to get the answer for your situation. As an example, I entered some typical information for a house in Columbus, OH, and got R-15 for wall insulation.

Since the knee walls will be in the attic and the attic will be getting very hot, in summer, should I make my knee walls out of 2x6 and use R21?
It isn't the heat in the attic that matters. It's the dryness that matters. Insulation that isn't bone dry will perform at less than its rated level. So, no, it is unlikely to be cost effective to install additional insulation, or a higher R-value.

Note: It's the heat in the attic that drives passive ventilation, and it's the ventilation that keeps the insulation dry.

Should I or can (I.E. due to code) put rigid foam over the insulation on the attic side?
That wouldn't affect your electrical work, but why would you want to? The primary effect of rigid foam installed on the attic side of the knee walls - away from the conditioned space - is likely to be to trap moisture in the fiberglass insulation sandwiched in the middle. That's a recipe for reduced effectiveness, mold and rot.

The rafters are 2x6. I am going to build out the rafters (inside the bedroom) a bit and install a combination of mineral wool and rigid foam to increase the R value. I am planning on a 1" gap between the insulation and roof deck.
Why not kraft-faced fiberglass with the built-in vapor barrier? It's easier, cheaper and faster. 1" is minimal clearance, but beats nothing!

I will be have to create intake vents (I have another thread about that). That part is going to be tough. There are no intake vents now.
I will look for that thread.
 
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Old 06-29-12, 02:23 PM
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Thanks for posting.

The 1" gap between the insulation and roof decking is only in the slant part of the room. No more than about 4-5 feet. The rest of the rafters will be open.

I chose mineral wool because it has a higher R factor per inch. In my 2x6 rafters I can only get R19 and that is only after I extend the rafters so I can create a gap under the roof deck.

As far as putting foam on the attic side, I would not put a vapor barrier on the inside. Similar to how they build new constructions today.

Plus I have been reading more and more that fiberglass doesn't seem to be the best choice for effectiveness. It is just lower priced and easier to install.

The gutting of my room has begun so I need to figure all this out soon. :-)

First though, I need to get rid of the last knob and tube out lol

Thanks for posting!!!
 
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Old 06-29-12, 03:09 PM
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The 1" gap between the insulation and roof decking is only in the slant part of the room. No more than about 4-5 feet. The rest of the rafters will be open.
I understand. All I'm saying is that any fluid can only flow as fast as its most constraining bottleneck will allow it to, so I like a little more distance than that - preferably 2". One other thing I just thought of is the Venturi effect. You might be creating quite a wind tunnel along that 4-5 feet. Not sure what that would mean, but I think making that flow gentler is one more reason I would increase the spacing.

I chose mineral wool because it has a higher R factor per inch.
I'm guessing you're talking about mineral wool batts. They are excellent - very effective insulation, and very stable in that slanted space. Just so long as you install an effective vapor barrier on the room side, that should work well.

As far as putting foam on the attic side, I would not put a vapor barrier on the inside. Similar to how they build new constructions today.
I'm saying that the foam itself would act as a vapor barrier. The only vapor barrier you should have is at the interior face - and you should definitely have a good one there. The other side of the insulation needs to be able to breathe as much as possible, to maintain its dryness and effectiveness.

Remember, the real insulation is still, dry air. Every type of insulation we install is a technique to create as much of that as we need in the most cost-effective manner we can come up with. What I'm seeing is that adding any solid material on the back side of the insulation will create a barrier to the air movement and drying - the wicking - of the wall insulation. And I'm thinking that will at least reduce its effectiveness, possibly by as much as the foam would add, plus increase tho opportunity for mold to grow there.

First though, I need to get rid of the last knob and tube out lol
Why? Undisturbed, unextended knob and tube that is still in good condition is acceptable by most jurisdictions.
 
  #7  
Old 06-29-12, 06:25 PM
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Thank you for the advice!

Where I live, you cannot have insulation touching the knob and tube :-(

What do you recommend for a vapor barrier?

I have seen pictures of people using plastic and tape to seal everything nice and tight. However, is all that work worth it once someone hangs a picture or shelf and punctures it?

This room is the top floor of my 1 1/2 story. It was remodeled 10 years ago by adding a bathroom and closet at one end. I wasn't planning on gutting the bathroom. The contractor who did the work, relied on the old insulation that was in the rafters, which had a silver face as a vapor barrier. My concern would be that the part I am renovating will have a vapor barrier but the bathroom won't.

While I have your attention :-)
This old house, before this renovation, had terrible icing issues in winter and was very hot in summer. In my zone, R38 is recommended for attics. With no foam and just mineral wool batts (I.E. Roxul), I can get to R23 or possible R30 (but losing more head room on the slants). Is this going to be enough to make it worth while?

OK. One more. I was planning on going with blown in cellulose above the ceiling of the bedroom (built into the attic) and on the attic floors (ceiling of the lower level). From what I read, this is the way to go. Do you agree?

Thanks again for the help!
 
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Old 06-29-12, 07:54 PM
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Where I live, you cannot have insulation touching the knob and tube :-(
Oh well.

What do you recommend for a vapor barrier?i
I'm a bit of a fiend on vapor barriers. I like to install 10 mil. poly over insulation that is either unfaced or faced with plain kraft paper, starting at the highest point and overlapping each run until I have 4" laying out on the floor. After finishing and trimming out the space, including the baseboard, I trim the poly flush with the face of the base and install the shoe mold.

Either that or I install using the kraft paper with the black vapor barrier on the back and call it good.

I have seen pictures of people using plastic and tape to seal everything nice and tight. However, is all that work worth it once someone hangs a picture or shelf and punctures it?
IMO, yes. A nail for a picture hanger or a screw for a shelf is so small that the barrier can essentially seal itself after it's removed, and it creates no loss while it's on place. In addition, screws for shelf brackets should be run into framing, where there's no opportunity for loss anyway. Spackling any hole left after removing a nail or screw should restore the performance to near original.

It was remodeled 10 years ago by adding a bathroom and closet at one end. I wasn't planning on gutting the bathroom. The contractor who did the work, relied on the old insulation that was in the rafters, which had a silver face as a vapor barrier. My concern would be that the part I am renovating will have a vapor barrier but the bathroom won't.
Isn't that silver facing a vapor barrier? I think it is.

This old house, before this renovation, had terrible icing issues in winter and was very hot in summer.
You and your house are going to love the improvement this project will bring. If, by "terrible icing issues," you mean ice dams on the eaves, those are caused by the combination of a warm roof over the living space and a colder roof over the overhang, or eave. That difference is the result of poor or non-existent ventilation - not insulation. Creating a smooth soffit-to-ridge ventilation flow should resolve that, by itself.

Insulation is installed to reduce the rate of thermal transfer. A vapor barrier is installed on the face of the insulation adjacent to the living space to reduce the rate of transfer of moisture from the living space during the heating season, which then reduces the opportunity for that vapor to condense on the underside of the roof or within the insulation and reduce its effectiveness.

In my zone, R38 is recommended for attics.
Have you used the ZIP-Code Insulation Program yet?

With no foam and just mineral wool batts (I.E. Roxul), I can get to R23 or possible R30 (but losing more head room on the slants). Is this going to be enough to make it worth while?
I make it + 9" of mineral wool batt to get to R-38, if that's what you need. My take on that is that you only need that overhead, over the flat part of the ceiling. Just my take.

I'm thinking that I would treat the slants as being half wall and half ceiling, and install maybe 6" of mineral wool there. which will give you an R-value that's a little more than 25 there. What do you think?

OK. One more.
I was planning on going with blown in cellulose above the ceiling of the bedroom (built into the attic) and on the attic floors (ceiling of the lower level). From what I read, this is the way to go. Do you agree?
Well, no, frankly. I'm not a fan of blown-in insulation because it can migrate. It can wind up not being where you want it and being where you don't want it.

In your project, you would need to install something like a hardware cloth curved fence along each side of the flat part of the ceiling (at the top of the slants) to keep it from blocking the ventilation space above the slants. And you would have to do the same thing along the top of the exterior wall to insure that your new soffit vents remain unblocked. IMX.
 
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Old 06-30-12, 09:37 AM
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We did more demo today. I believe the attic was renovated in the '50s. It made for a very long bedroom. We had a contractor put in a bathroom and walk in closet on one end. Here is a picture of the bathroom end and you can see the old silver faced insulation in the rafters.



I am taken down on the insulation out of the rafters so I can vent. I will also be able to add a lot more insulation, R38 (I did run the calculator :-) ) in the flat part of the ceiling. I am just going to add fiberglass batts. How do I add a vapor barrier to this area with out renovating the bathroom?

I don't want to drape plastic over the wood joists for fear of rot/mold. I could use craft faced fiber glass and just lay it on top?

In the walls, I plan on using Roxul mineral wool in the walls and slants. The only concern is the formaldehyde. However, if I put in a plastic vapor barrier and it will be vented on the other side, I would think there would be no issue.

The existing frame on the walls are 2x4s. Roxul's mineral wool insulation will give me R15. The calculator said R13. You said R15 so I should be OK?

BTW when I said icing problems, I meant I will get icicles that grow from my extra high gutter, down to the ground! lol

Can't wait to get this project done!

I can only work in the morning as it gets to 115 degrees by afternoon. Plus, I have a day job.

Thanks again for all the great help!
 
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Old 06-30-12, 03:02 PM
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I am taken down on the insulation out of the rafters so I can vent.
I see. First of all, what are we looking at? Is it 2x6 collar ties with 1x3 stringers across them? Maybe 24" oc for the collar ties and the rafters they're tied to? I'll go with that until you tell me different.

(I did run the calculator :-) ) The existing frame on the walls are 2x4s. Roxul's mineral wool insulation will give me R15. The calculator said R13. You said R15 so I should be OK?
I did say R-15, from the guesses I put into the calculator. But you entered the real information and got R-13, so that's the answer. Besides, I ran the calculator a couple more times and never got R-15 again. I kept getting R-13.

I plan on using Roxul mineral wool in the walls and slants. The only concern is the formaldehyde. However, if I put in a plastic vapor barrier and it will be vented on the other side, I would think there would be no issue.
That's correct. I would go with paper-faced fiberglass in the walls, but hey, it's your house. In the slants, screwing a 2x2 to the face of each rafter will give you a nominal 8" deep bay, IIRC. So you can put 6" of rock wool batt in there and get R-25.5, plus 2" or so of space for air flow behind it. That sounds pretty good. Of course you go with the R-38 again on the attic floor (the first floor ceiling) behind the knee walls.

BTW when I said icing problems, I meant I will get icicles that grow from my extra high gutter, down to the ground! lol

I can only work in the morning as it gets to 115 degrees by afternoon.

Can't wait to get this project done!
I'll bet! I'm guessing that you're talking about 115[SUP]o[/SUP] inside this space. The ventilation you're adding should cure both of those problems - the high heat in the summer and the icing in the winter. And yes, I said the ventilation. Not the insulation.

In fact, I would focus on doing the ventilation now. You can do interior work anytime. Getting both the ridge vent and the soffit vent (OK, the fascia vent in this case) done should make this a much more comfortable space to work in. I'm guessing that's your plan.

How do I add a vapor barrier to this area with out renovating the bathroom?
The bathroom is already insulated, and has a vapor barrier, doesn't it? Oh, wait. You said
you can see the old silver faced insulation in the rafters.
That stuff needs to come down. You need to be able to see the underside of the roof deck everywhere.

Since the bathroom doesn't have a vapor barrier in contact with its ceiling, and insulation in contact with that, you need to add it. You can do that with R-38 fiberglass with the paper facing that has the black vapor barrier on the back. You just fold the edges of the paper back to form a U-channel, lay the batt on the ceiling, and push down with your staple gun until you can shoot through the folded-back paper into the framing.

I don't want to drape plastic over the wood joists for fear of rot/mold. I could use craft faced fiber glass and just lay it on top?
I'm confused. The vapor barrier is attached to the inside of the framing. The drywall is screwed through it. The insulation is on the other side. It doesn't matter whether the vapor barrier is poly or coated kraft paper or something else. It goes immediately behind and in contact with the drywall.

Have fun! It sounds like you are.
 

Last edited by Nashkat1; 06-30-12 at 03:19 PM. Reason: to correct misunderstanding about the bathroom insulation.
  #11  
Old 06-30-12, 08:00 PM
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I see. First of all, what are we looking at? Is it 2x6 collar ties with 1x3 stringers across them? Maybe 24" oc for the collar ties and the rafters they're tied to? I'll go with that until you tell me different.
I learned how to quote :-)

The rafters are 2 x 6. Those collar ties are not quite as big. The stringers are maybe 1x2. I was planning on taking the stringers down. The old ceiling was gypsum board screwed into the collar ties and then ceiling tile glued onto the gypsum board. I was going to take down the collar ties and screw gypsum right to the collar ties. Do I need the stringers or wire supports in between the 24" to support the weight of the R38 fiberglass batts?

Since the bathroom doesn't have a vapor barrier in contact with its ceiling, and insulation in contact with that, you need to add it. You can do that with R-38 fiberglass with the paper facing that has the black vapor barrier on the back. You just fold the edges of the paper back to form a U-channel, lay the batt on the ceiling, and push down with your staple gun until you can shoot through the folded-back paper into the framing.
Is this black vapor barrier, R38, stuff you can get at Lowes or HD? In other ceiling projects in my house, I just used paper faced in between the joists and then another, unfaced layer, laid perpendicular, to get to R38.

Thanks!
 
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Old 06-30-12, 08:59 PM
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I learned how to quote :-)
Yay!

The rafters are 2 x 6. Those collar ties are not quite as big. The stringers are maybe 1x2.
Got it. Thanks.

I was planning on taking the stringers down... and screw[ing] gypsum right to the collar ties. Do I need the stringers or wire supports in between the 24" to support the weight of the R38 fiberglass batts?
I've been thinking about this, and imagining you would. But maybe not. There are several ways to skin this cat.

One is to install unfaced batts held up with support wires, with a poly barrier stapled below that. Another is to install paper-faced R-38 batts and forget the poly, but I'm not sure the paper will hold the weight of the insulation until you can get the gyp board up - especially with 24" bays.

In other ceiling projects in my house, I just used paper faced in between the joists and then another, unfaced layer, laid perpendicular, to get to R38.
That sounds like the way to go. You can staple the thinner paper-faced batts to the framing, and they should stay up while you install the rock. Then you can go up the scuttle hole and lay the unfaced batts across the framing. Don't forget to insulate the back of the scuttle hole cover, BTW.

Is this black vapor barrier, R38, stuff you can get at Lowes or HD?
Yes, except that you'll be installing two layers that add up to R-38, and only the first one will be faced. You don't need (and don't want) to put any poly over that. One vapor barrier - no more and no less.
 
  #13  
Old 07-01-12, 10:01 AM
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I hope I haven't worn you out yet. :-)

The collars are nailed inside the rafters. This means a 24" bat will not fit properly in between the rafters unless I carve the insulation around the collar where it is nailed into the rafter. Is it worth taking down the collars and installing them flush with the rafters? I can't do this in the bathroom area without gutting the bathroom too.

If I don't gut the bathroom, then I can only put in R15 (Roxul) in the rafter bays in the bathroom area. I am talking about the slant part of the ceiling. Do you think this is good enough? It will be R21 or R30 everywhere else.

On one side of the room, there are water pipes and a duct behind the knee wall. Now that I am re-modeling the attic space to be a cold attic, I was going to build a second knee wall to "box" in the plumbing and duct. This also gives me storage space in the attic. I was only going to insulate the outermost knee wall but could I also insulate the inner knee wall without a vapor barrier or is that asking for trouble?

Thanks
 
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Old 07-01-12, 06:54 PM
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Not at all!

The collars are nailed inside the rafters. This means a 24" bat will not fit properly in between the rafters unless I carve the insulation around the collar where it is nailed into the rafter. Is it worth taking down the collars and installing them flush with the rafters?
It's tempting, but, on reflection, I'm not sure what it would serve beyond your sense of aesthetics. IOW, I can't imagine that it will make any measurable difference in the effectiveness of the insulation. Especially for the effort involved - marking, taking down, trimming and re-installing every collar tie just to have it in line with its rafters rather than scabbed onto the sides sounds like a real PITA, especially for one person. So I think I would leave them as they are and shape the insulation around them.

Remember that your goal is to install the insulation without any real gaps, especially on the back. Get out your kitchen shears, your carbon-steel butcher knife, or whatever tools you enjoy, and sculpt the insulation to fit the spaces and to meet without gaps, and I think you'll be fine.

If I don't gut the bathroom, then I can only put in R15 (Roxul) in the rafter bays in the bathroom area. I am talking about the slant part of the ceiling. Do you think this is good enough? It will be R21 or R30 everywhere else.
Yeah, because the bathroom drywall is attached to the rafters at their original 6" depth. Hmmm.

I think I would let it be what it is. I would install the R-15 with a good space for air flow above it and live with it. It seems that the cost, just in time and labor, of gutting the bathroom to add that little bit more could hardly be worth it.

One question here: How are you planning to install an effective vapor barrier for the bathroom insulation in the slants?

On one side of the room, there are water pipes and a duct behind the knee wall. Now that I am re-modeling the attic space to be a cold attic, I was going to build a second knee wall to "box" in the plumbing and duct. This also gives me storage space in the attic. I was only going to insulate the outermost knee wall but could I also insulate the inner knee wall without a vapor barrier or is that asking for trouble?
Yes. If the pipes are noisy, and re-strapping them or adding hammer risers or some other plumbing work won't resolve that, then you might want to place some unfaced Roxul between the "box" and the living space, but I would make sure heat could get past that somehow. You definitely want the actual insulation envelope, with the finished drywall and the vapor barrier, to contain rather than exclude the pipes. The duct may not matter so much - is it a plumbing duct or an HVAC duct?
 
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Old 07-02-12, 07:14 PM
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One question here: How are you planning to install an effective vapor barrier for the bathroom insulation in the slants?
Hmmmm. Wrap a bat in plastic on all sides but the top and slide it in?


Yes. If the pipes are noisy, and re-strapping them or adding hammer risers or some other plumbing work won't resolve that, then you might want to place some unfaced Roxul between the "box" and the living space, but I would make sure heat could get past that somehow. You definitely want the actual insulation envelope, with the finished drywall and the vapor barrier, to contain rather than exclude the pipes. The duct may not matter so much - is it a plumbing duct or an HVAC duct?
It is not a noise issue, just thinking of efficiency. The main stack is in this area, the pressure pipes for the bathroom and an HVAC duct. Maybe I will only insulate on the outer most wall and leave it at that.

Thanks!
 
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Old 07-02-12, 09:38 PM
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Hmmmm. Wrap a bat in plastic on all sides but the top and slide it in?
Hmmm... OK. And then shape a support out of the hardware cloth you bought for the soffit vents and secure that between the rafters at the bottom end to keep it in place?

That could work. A staple or two securing the vapor barrier to the rafters above the slant might help too. Just

... how about securing the barrier w/ the staples and the batt w/ the hardware cloth fence and not worrying about securing them to each other?

It is not a noise issue, just thinking of efficiency. The main stack is in this area, the pressure pipes for the bathroom and an HVAC duct. Maybe I will only insulate on the outer most wall and leave it at that.
Sure. And over the top of it too.
 
  #17  
Old 07-03-12, 03:43 AM
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... how about securing the barrier w/ the staples and the batt w/ the hardware cloth fence and not worrying about securing them to each other?
Good idea!

Sure. And over the top of it too.
Absolutely. In fact, I can get R23 or R30 (depending on how much height I am willing to lose) in this area.

Thanks again for all the great help!
 
  #18  
Old 07-05-12, 10:30 PM
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Keep in mind when you stack f.g. batts, it compresses them. Usually running the second layer perpendicular to the first works well, only with ceiling joists to support the top layer. You only will have collar ties. I'd blow-in some cellulose without a v.b. and use a v.b. primer on the ceilings.

The sloped ceiling should be as well insulated as possible, at least to minimum code R-30 for your location, as you know. Have you thought much about venting the side attics separate from the peak attic? Then you could use a "closed attic" on the sloped area, filled with foam board and f.g. That way, if you don't store items in the side attics (knee-wall) the foam board on the attic side wouldn't require a thermal/ignition barrier per code. No v.b. required at drywall with foam board on attic side, and you prevent wind-washing of the air permeable f.g. batts. Or--- asphalt faced batts with a housewrap on the attic side to stop the wind. ADA the drywall in either case you choose. Need some links or explained, just ask...

G
 

Last edited by Nashkat1; 07-08-12 at 08:25 PM. Reason: To correct R-value, at poster's request.
  #19  
Old 07-07-12, 05:07 AM
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Keep in mind when you stack f.g. batts, it compresses them. Usually running the second layer perpendicular to the first works well, only with ceiling joists to support the top layer. You only will have collar ties. I'd blow-in some cellulose without a v.b. and use a v.b. primer on the ceilings.
OK. The collars are 2x4 which means the best I could do it R13. But then I can cross that with R30. Would that work? Or is the R30 going to compress the R13 too much in between the collar ties?


The sloped ceiling should be as well insulated as possible, at least to minimum code R-38 for your location, as you know. Have you thought much about venting the side attics separate from the peak attic?
The plan is/was to create a gap between the insulation and the roof deck. If I extend the rafters with 2x4s, I can get R30 by using Roxul's stone wool product. I could cap that with foam to get R36.5 but I will lose more ceiling height on the sloped ceiling.

The other issue is that I did not want to gut the bathroom too. There is a built in shower (cement board and tiles). Without rebuilding the bathroom, I can get more than R15 in the bathroom.

The other problem the bathroom/closet presents is that the door frames are close to the ceiling already and the bathroom door would have to be rebuilt with an angle in the corner. The closet door already is like this.

I am not planning on using the attic for storage, apart from the closet spaces I will be building into both sides. Those will be insulated as well.

Thanks for posting.
 
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Old 07-07-12, 07:51 PM
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The collars are 2x4 which means the best I could do it R13. But then I can cross that with R30. Would that work? Or is the R30 going to compress the R13 too much in between the collar ties?
What if you put mineral wool between the collar ties and fiberglass over that?

The sloped ceiling should be as well insulated as possible, at least to minimum code R-38 for your location,
Not sure why - it isn't a flat ceiling, and heat won't stack up under it.

The other issue is that I did not want to gut the bathroom too. There is a built in shower (cement board and tiles). Without rebuilding the bathroom, I can get more than R15 in the bathroom.

The other problem the bathroom/closet presents is that the door frames are close to the ceiling already and the bathroom door would have to be rebuilt with an angle in the corner. The closet door already is like this.
Hard to realize a return on that much investment.
 
  #21  
Old 07-07-12, 07:54 PM
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The sloped ceiling should be as well insulated as possible, at least to minimum code R-38 for your location,
I'm curious about this. It isn't a flat ceiling, and heat won't stack up under it.
 
  #22  
Old 07-07-12, 08:37 PM
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"What if you put mineral wool between the collar ties and fiberglass over that?"---------------------------- Yes! Good idea. F.g. is the cheapest, easiest to install wrong insulation available, do I sound bias...... The "biggest Loser" In Fiberglass Insulation.... - How To Guides - DIY Chatroom - DIY Home Improvement Forum

R-38 in ceilings; Chapter 11 - Energy Efficiency

OH is under an "I" Code; Ohio Building Codes

2006 IECC -- detached 1 family; http://www.com.ohio.gov/dico/docs/di...eflowchart.pdf

Zone 4, 5; sloped ceiling, not sloped wall......;Chapter 11 - Energy Efficiency

I would go at least minimum code as you said ---" attic will be getting very hot, in summer,".

Gary
 
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Old 07-07-12, 08:48 PM
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sloped ceiling, not sloped wall
Gary, can you please cite the reference for this?

attic will be getting very hot, in summer
Attic will be ventilated.
 
  #24  
Old 07-08-12, 02:44 PM
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Sure, under Roof-ceiling construction, Chapter 8, #3: Chapter 3 - Building Planning

When the ceiling is attached to the rafters the span is reduced; Table R802.5.1(2); Chapter 8 - Roof-Ceiling Construction

Vent enclosed rafter spaces with ceilings applied; Chapter 8 - Roof-Ceiling Construction

Also listed as “Ceilings without attic spaces” under insulation- max. R-30; Chapter 11 - Energy Efficiency I corrected my previous erroneous statement on R-38 sloped ceilings…..

I used to think that soffit/ridge venting changed the attic air quite often per hour…after doing more research; I was surprised at the results here, using a simulated model (2012). You may appreciate this, as your answers are very informative. Without wind, and only buoyancy-driven attic ventilation, the attic air forms convective loops in the space, moving the air very slowly.
Notice the five points under “Conclusions” pp.9; http://digitalcommons.unl.edu/cgi/vi...ventilation%22

No wonder they use ridge vents with baffles (mainly for the wind), anything less is.....less; Attic Ventilation - Oikos

Ridge Vent Smoke Bomb Demonstration - YouTube

Gary
P.S. strange, no "edit" button here for Post #18 change it in your brain everyone....... sloped ceilings if local AHJ permits = R-30..... LOL.
 
  #25  
Old 07-08-12, 05:29 PM
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I really appreciate all the comments here!

So is ventilation good or bad?

I have seen two smoke bomb ventilation videos. One shows ridge vents don't work and one showing they do work. Of course, the one that shows it working was done by a vendor of ridge vents.

I just opened up one side of the attic for intake vents. There are 4 turtle type vents in that side of the roof. I can't tell that they are doing anything. I called our roofer and he is coming in a week to add ridge vents. Should I still do this?

Thanks
 
  #26  
Old 07-08-12, 08:22 PM
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is ventilation good or bad?
Adequate ventilation is critically essential. I thought we covered this earlier.

I just opened up one side of the attic for intake vents. There are 4 turtle type vents in that side of the roof. I can't tell that they are doing anything. I called our roofer and he is coming in a week to add ridge vents. Should I still do this?
I think so, yes, And get rid of the turtle vents.

But didn't you say something about an unusual roof configuration? Could you post a pic or two of the outside of your house, showing the roof configuration?
 
  #27  
Old 07-08-12, 08:54 PM
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Sure, under Roof-ceiling construction, Chapter 8, #3: Chapter 3 - Building Planning
That link did not tell me that a sloping surface functions as a ceiling for insulation and ventilation purposes. For habitable space, for headroom, for clearances - sure. But those are different matters.

When the ceiling is attached to the rafters the span is reduced; Table R802.5.1(2); Chapter 8 - Roof-Ceiling Construction
I didn't see the text you quoted, and I'm not sure how this applies to this case. I did find this interesting:
f. When rafter ties are substituted for ceiling joists, the heel joint connection requirement shall be taken as the tabulated heel joint connection requirement for two-thirds of the actual rafter-slope.
It brought clarity to something that had been nagging at me: If the collar ties are only nominal 2X4s, and they're spaced 2' o.c., can we expect the bathroom ceiling assembly to support R-38 worth of mineral wool? Should that ceiling be insulated entirely with fiberglass to lessen the dead load on it?

I used to think that soffit/ridge venting changed the attic air quite often per hour
Not sure why you did. It doesn't need to. It just needs to provide a continuous path to reduce moisture and to distribute the roof temperature evenly.

P.S. strange, no "edit" button here for Post #18
Any member can edit their own post for up to 4 hours. After that a mod can still do it. I edited the R-value in post #18, based on what you said here.
 

Last edited by Nashkat1; 07-09-12 at 04:12 PM.
  #28  
Old 07-10-12, 07:28 PM
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It was in the third link; "enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters"---
Chapter 8 - Roof-Ceiling Construction

They are sloped ceilings or cathedral ceilings as we call them.

The span links were for rafters -- both; with ceilings attached and without ceilings attached, showing to reduce spans because of the added ceiling weight.

The ceiling framing would hold if nailed properly, the 1/2" drywall may not, need to read the bag weight per foot as it varies.Residential ENERGYSmart Library
Either leave the strapping to reduce the span to 16"oc or use "light-weight" drywall with an inherent fiberglass band that spans the same as 5/8" regular drywall. If the span is 9'2" or less- good to go- second chart down; 24"oc 10# live load, the cellulose would be 5# plus the drywall (4#) equal 8# total.

Gary
 
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Old 07-10-12, 08:25 PM
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It was in the third link; "enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters"---
Chapter 8 - Roof-Ceiling Construction
I see what you're saying. This reference talks about ceilings being applied directly to the underside of roof rafters.

What if that wasn't true? What if they had, instead, said "enclosed rafter spaces formed where walls are applied directly to the underside of roof rafters?" or if they had said "enclosed rafter spaces formed where interior finishes, such as gypsum board, wood or plaster are applied directly to the underside of roof rafters?"

I agree that sloped finishes work as ceilings when we're constructing them, and when we're walking around and living inside them. But I believe that they function as walls when we're designing the best way to insulate and ventilate them. Maybe as super-walls, but more as walls than as ceilings. Because heat rises.

The span links were for rafters -- both; with ceilings attached and without ceilings attached, showing to reduce spans because of the added ceiling weight.
I know. But the OP is not framing in the rafters. He's adding insulation and an interior surface to them. Are you saying that the areas where he's doing this need to be reinforced to support the added weight?

The ceiling framing would hold if nailed properly, the 1/2" drywall may not.
That was my concern.

Either leave the strapping to reduce the span to 16"oc or use "light-weight" drywall with an inherent fiberglass band that spans the same as 5/8" regular drywall.
Good point. I hadn't thought about the bedroom ceiling, just the existing ceiling over the bathroom.

If the span is 9'2" or less- good to go
I'm pretty sure the flat span is less than 9'2". The OP can tell us that. BTW, I've been assuming 5/8" rock, but we hadn't talked about it.
 
  #30  
Old 07-11-12, 08:54 PM
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Maximumpower, leave the strapping and install 1/2" drywall on the ceiling if your local AHJ allows it. Use foamboard if you wish on the attic side of knee walls, no mold will grow, it will stop any fibrous insulation from wind-washing. Can Exterior Foam Insulation Cause Mold & Moisture Problems?
Cover it with an ignition barrier if required locally or show them the ESR report to not cover it (if they accept that from the manufacturer).

The sloped ceiling should be insulated to max to deter solar radiation as at least some/most of it is exposed to the sun. You lose more heat out the walls than the roof, hot air rises-not heat; How heat insulation works: The science of how heat travels

Exterior and interior walls transmit the vertical loads to other framing members, to the earth. The roof deck and roof assembly transmits roof loads to bearing exterior walls - scroll to find the "I" code definitions (I put in bold) here: Chapter 2 - Definitions

If you need further info: Search Results

Just don't use a poly vapor barrier when a vapor retarder will work and meet code; BSD-102: Understanding Attic Ventilation — Building Science Information

Gary
 
  #31  
Old 07-13-12, 05:45 PM
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Sorry for the delayed response. I was on a business trip and when I got back I found that my PC had a nasty virus. I think I am clean now.

I appreciate you guys hanging with me on this.

So, for the sloped walls/ceiling I can go R30?

Where the bathroom is, I can only get R15 in the sloped section.

The bathroom ceiling is made up of 2x4 collar ties, 1x2 strapping, some sort of gypsum board, glued on ceiling tile, then more gypsum board. I think it will support whatever I put up there.

I am planning on going with Roxul stonewool since it has the most R value per inch that I can get in the sloped areas.

The Roxul is unfaced. Earlier in this thread we were talking about putting plastic in between the rafters (on the slopes) and in between the collars (on the flat). Is this still the best method?

In the rest of the bedroom, I am going with R30 Roxul in the slopes and I don't know what in the ceiling. Roxul again perhaps with fiberglass perpendicular? There isn't a lot of room in the flat part of the ceiling. If I go with unfaced stone wool, do I need plastic?

Here are some pictures of the area, inside and out.

First the roof:

Because of how close we all are, this is the best I can do for the roof. This is obviously only one side. You can see the turtle vents put in by the roofer. They are only on this side. The roofer is putting in a ridge vent in another week or so. Let me know if this is still the best way. I create intakes on this side. I need to do the other side but it has been soooo hot lately.

This is the inside of the attic where the perpendicular roof line is. You can see the outside of it in the picture above. BTW the new construction on the left is part of the bathroom. That one piece of insulation is in backwards. The rest isn't. I will fix that when I reinsulate.



This one is of the bathroom door. When I extend the rafters in the bedroom to accommodate the Roxul R30, I will had to do something tricky with the door. You can see the strapping continues into the bathroom. The contractor just put the new bathroom ceiling over the old ceiling. On the flat part of the ceiling, you can see the layers I was describing above.


The other side of the room (the closet side).

You can see the contractor had to do some work to get a door to fit. When I extend the rafters, I will have to change the frame/door even more. You can see a piece of the old paneling still there. I am working on getting it out but that wall was fastened to the paneling. Now that I started getting it out, I need to rebuild that part of the wall. It is loose now.

One last picture. It is a shot looking straight up (I was laying on the floor). That is one of the chimneys (used for venting the furnace). Now that it is exposed, my wife wants me to clean it up and paint it. We'll see.


Thanks
 
  #32  
Old 07-13-12, 09:13 PM
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Nice post! Thank you for the new pictures and the explanation of your absence. I hope you've cured that virus!
The Roxul is unfaced. Earlier in this thread we were talking about putting plastic in between the rafters (on the slopes) and in between the collars (on the flat). Is this still the best method?
Yes, that's the best you can do to maintain its integrity.

I want to respond in some depth, but I may not have time until Sunday - out-of-town trip for us too.
 
  #33  
Old 07-21-12, 06:41 AM
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I am planning on doubling up the rafters with 2x4. This gives me a 9" space. Stonewool R30 is only 7 1/4" so that gives me a 1 3/4" air gap between the insulation and the roof deck on the slopes.

Given what GBR in WA has said about density of fiberglass, I am OK with insulating the walls with R13 fiberglass but the attic floor (outside the storage space) and the bedroom/attic flat ceiling, I can only get R38+ using R21 batts. This might work out since R21 is 5.5", same as my floor joists. I can crisscross in two layers to get R42.

The only problem might be in the ceiling of the bedroom. There isn't much space in there to work. I will have to get creative and lay the fiberglass in as I put the drywall in.

I re-read the post by GBR in WA about venting and it looks like I am doing the right thing by adding generous intake vents. I will have to find the correct ridge vent with the baffle. Do you know who makes this product?

thanks
 
  #34  
Old 07-23-12, 09:30 PM
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I am planning on doubling up the rafters with 2x4. This gives me a 9" space. Stonewool R30 is only 7 1/4" so that gives me a 1 3/4" air gap between the insulation and the roof deck on the slopes.
Are the rafters 2x6s? I thought they were 2x4s.

The only problem might be in the ceiling of the bedroom. There isn't much space in there to work. I will have to get creative and lay the fiberglass in as I put the drywall in.
I was wondering about that. Maybe keeping the stringers might help hold the insulation up while you attach the drywall?

The Roxul is unfaced. Earlier in this thread we were talking about putting plastic in between the rafters (on the slopes) and in between the collars (on the flat). Is this still the best method?
Above the bathroom, that's about all you can do. In the bedroom, the vapor barrier goes across the face of the framing.

If I go with unfaced stone wool, do I need plastic?
Yes, in your zone. One vapor barrier (retarder), and only one, between the conditioned space and the insulation. IOW, if you install fiberglass with the paper that has asphalt on the back, then that's it - no additional vapor barrier on that wall or ceiling. If you install the fiberglass with the plain paper facing, then yes, install the plastic over that. BTW, I like to slash that paper several times in each bay, just to make sure there's no second barrier.

The roofer is putting in a ridge vent in another week or so. Let me know if this is still the best way.
Definitely. Is he going to remove the turtle vents at the same time? I hope so.

That is one of the chimneys (used for venting the furnace). Now that it is exposed, my wife wants me to clean it up and paint it. We'll see.
From the clean look of it, it looks like that chimney has a liner. If so, it might look nice in the room. One point though - some of the framing looks pretty close to the chimney. I think there needs to be a 2" or 3" space. I'll check.
 
  #35  
Old 07-23-12, 10:21 PM
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  #36  
Old 07-24-12, 03:26 AM
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Some jurisdictions require a 2" spacing from a chimney to combustible materials. If it is only being used as a vent for say a dryer or water heater, and cannot be retroverted to a wood burning fireplace then there may be an exception. I would definitely check with AHJ on this.
 
  #37  
Old 07-24-12, 05:24 PM
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Some jurisdictions require a 2" spacing from a chimney to combustible materials. If it is only being used as a vent for say a dryer or water heater, and cannot be retroverted to a wood burning fireplace then there may be an exception. I would definitely check with AHJ on this.
I doubt that it is lined. There is another chimney (once used to burn wood) and it isn't lined. I assume this one is the same. The chimney in the bed room is used to vent the water heater and the gas furnace. There was framing around it that I took out. I will definitely look into the code on it.

As far as vapor barrier, I was planning on going with 2 layers of R21 on the attic floor (outside the bedroom area). I believe all the R21 stuff has no barrier. Should I put plastic down on the floor? If I do that, I had to make sure the floor joists are not covered in plastic.

Nashkat1
Are the rafters 2x6s? I thought they were 2x4s.
They are 2x6. So are the floor joists.

Definitely. Is he going to remove the turtle vents at the same time? I hope so.
I haven't talked to him about that. I am not sure how easy (I.E. inexpensive) that is going to be. The three at the top might not be so bad since he only need to take out a few layers of shingles. There is one down low though. At the very least, I am going to plug them up from the inside. When the roof needs to be redone in the future, I can take them out then.

Thanks!
 
  #38  
Old 07-30-12, 08:50 AM
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I believe all the R21 stuff has no barrier.
What is "the R21 stuff" you're planning to use? If it's fiberglass, then buying fiberglass with the paper facing that has asphalt on the back will provide the vapor retarder.

Should I put plastic down on the floor?
In your area, with more heating degree days than cooling degree days, I would want to provide a vapor barrier next to the conditioned space. The idea is to keep the insulation dry by keeping moisture from getting to it easily and by effectively venting the unconditioned space to remove the moisture that does get there by condensation.

At the very least, I am going to plug them up from the inside. When the roof needs to be redone in the future, I can take them out then.
This will work if the vents don't allow any water to enter them. They shouldn't. Double-check with your roofer.
 
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Old 07-30-12, 03:26 PM
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What is "the R21 stuff" you're planning to use? If it's fiberglass, then buying fiberglass with the paper facing that has asphalt on the back will provide the vapor retarder.
GBR in WA linked to a site that says that R13 and R21 fiberglass were the only two types in that link that were at a density that didn't cause issues. This is what I found wrt R21. It is expensive and I will need a lot of it. Perhaps I will compare it to Roxul Stonewool.

Here is the link: Shop Johns Manville 7-Pack 93"L x 23"W x 5-1/2"D 21-R Fiberglass Insulation Batts at Lowes.com


Regarding the existing turtle vents:
This will work if the vents don't allow any water to enter them. They shouldn't. Double-check with your roofer.
The roofer installed the ridge vent today. It is an AirVent ShingleVent II with baffle. I had asked him to remove the turtle vents but he called me today (I was at work) and suggested I leave them in. However, the holes that were cut for them were not the full size of opening of the vents so he fixed that. The previous vents did not have water issues that I know of. That is, I didn't see any water damage in the areas they were installed.

I now have air intakes in each of the rafter bays on both sides. I also have screen installed. I still need to get the hardware cloth installed and rebuild the siding. The siding (what I was calling facia board) did not come out without a fight. It is totally ruined. I have 1x8x1 to repair it with. It is just going to take a lot of cutting to replace. I have done one so far and it wasn't too bad.

Meanwhile, I am progressing on the demolition on the inside. I am moving the knee walls back a bit to give me more bedroom space.

Thanks
 
  #40  
Old 08-01-12, 06:19 PM
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I answered my own question on the turtle (static vents). I am going to plug them. If the ridge vent does what it is supposed to do (it does have baffles) it will draw air in from the closest air intake which is the static vents. I don't want that. I want them from the air intakes that I just added under the overhangs.

I called the manufacturer of the ridge vent and they agreed with me that the static vents must be plugged (or removed). They also added that the ridge vent could cause weather (ie blowing snow and rain) to be pulled into the static vents.
 
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