Does doubling insulation layer double R value


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Old 08-25-14, 02:19 AM
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Does doubling insulation layer double R value

Ok.. I am trying to build a dwarf wall and build a conservatory. I have access to some metal insulation panel (stuff they use for commercial buildings or fridges.

From the manufacture spec, it have a R value of 15 with a 2 inch profile. I was wondering if I double stack them to 4 inch profile.. will I get a R30 or should I just do a 5.5 inch fibreglass (pink stuff) install on top of the insulation panel?

Also if I do the fibreglass stuff, can the vapor barrier be in between the 2 layers? Because I am thinking that if I do fibreglass I may do it next year instead as an upgrade.

I am hoping to do the dual metal insulation to keep the wall slim.
 
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Old 08-25-14, 03:44 AM
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Installing two panels of equal R-value will double the performance in terms of the R.

The question of of vapor barrier placement is relative to the climate you are in and the amount of water vapor present in the structure or the exterior climate.

If the interior has a metal panel that is the facing of the insulation and the joints are all made air tight the performance as a vapor/air barrier should be outstanding. Perhaps a few more details or a sketch of what you are proposing may help us better understand the situation and how best to proceed.
 
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Old 08-25-14, 01:15 PM
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I am in Toronto.. so avg winter is under -5c

The panel I am using is 200 Inverted Rib - Insulated Metal Wall Panels | Kingspan Panels with 2 inch thickness (shown as R15) water tight.

I am doing this (from outside to inside)
- Brick
- OSB
- insulation panel [maybe double] (silicon to stud?? will that be ok?)
- Water vapor (if needed, I wonder do I needed since the panel is water tight)
- Dry wall
 
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Old 08-25-14, 02:49 PM
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Installing two panels of equal R-value will double the performance in terms of the R.
...provided there is no air space between them, and no air movement between the layers.
 
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Old 08-25-14, 06:15 PM
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Ok, now that we know where you are I would say I am not in total agreement with the proposal.

The placement of the metal skinned insulation up against the osb will undoubtedly leave a space that under certain situations could result in the formation of condensation from exterior temperature/humidity conditions. I would be uncomfortable with that possibility since it would be in a concealed cavity. When I say a space, I mean any space, even as little as an 1/8" would be detrimental to the situation.

I would be more inclined to go to one of either of these two approaches:

1). Install foam sheathing, (not metal skinned panels), over the exterior of the osb to give you 1/2 to 2/3 of the total proposed R value for the wall assembly. This will give you a continuous layer of insulation over the framing/sheathing and better performance than cavity insulation only. You should also be very conscious of detailing the edges of the foam at the perimeter of the construction so as not to allow an air flow between the foam and sheathing. If you want to add the additional insulation in the framing cavity you can use rock wool or fiberglass batts to give you the balance of the total proposed R-value.

2).Frame and sheath as you propose but have closed cell 2lb. density foam spray applied to the back of the sheathing at each stud cavity. Spray to the full proposed R-value and forget the fibrous insulation.
 
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Old 08-25-14, 10:08 PM
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Hey guys.. thanks for your input so far..

I understand that moister could be an issue for the OSB, however I have re-read the spec of those panel.. according to the pdf, these panel are weather proof. and it should be installed as the exterior of the building, hence the galvanized metal for the skin of the panel.

So it should be air tight and water tight. (See attached picture)
Name:  insulation.jpg
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With that say.. I am thing to change the installation a bit and see if any of you thing it is ok..

- Brick
- Insulation Panel (maybe double layer and silicone sealed edges)
- Studs (2x4) with maybe more insulation in the future
- Vapor barrier (maybe)
- Moist resistance drywall or wall pane
(See drawing)
Name:  wall.jpg
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Size:  30.5 KB

The conservatory will mainly be 3 season since I am only doing single pane window.. however I am planning to eventually upgrading the glass to double pane.. therefore I needed to plan out the wall since I am not going to rip it apart to upgrade. I also will be putting copper pipe or pex tubing under the flooring for future radiant heat upgrade.

Do anyone of you think doing double panel of R15 each (and maybe also more fiber insulation) will be enough went I finial changed to double pane?
 
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Old 08-26-14, 03:56 AM
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Probably a better application than your first proposal but there are still a few issues:

1). How can you attach your brick ties to the wall , I don't know if the steel skin on the insulation can be considered structural enough for the purpose of tying in the brick to the wall.

2). How are you attaching the two layers of foam to the wall?

3). You have to be fastidious about sealing the two sheets and the interface of the osb at the perimeter and at all vertical edges to prevent the airflow from negating the value of the outer panels.

4). If you build your proposed wall you have to consider the window unit placement carefully. If you push it to the outer plane, i.e., the brick, you will have glazing that is several inches away from the interior air film which can result in an increased likely hood for condensation. If you bring the glazing to the interior you have to be careful about water management details where any flashing/trim assembly is installed in relation to the panel edges and brick.

I am not saying you can't do a respectable job with this method and maybe someone else will offer points neither of us have considered but planning and execution are vital when you are dealing with materials taken out of their normal context of installation.

I would probably forget the fibrous insulation in the framed wall.
 
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Old 08-26-14, 10:15 PM
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Well the brick wall isn't really for structural so.. maybe I could do faux brick siding..

But isn't it true that most of the brick used on an actual house construction not really attached to the wall? since there usually a 1 inch air gap between brick and the sheathing / paper? If that is the case what do you mean by attaching the bricks to the wall? The brick will just be stand alone isn't it? I mean the top will be capped off with either some stone cap or chance will be wood or some aluminum or vinyl with them grading the water away. The whole structural support will be the framing on the inside.

The foam will be attached to the wall via their own specialized clips so no issue there.

The two sheets will be glued together and all edge will be seal with tape of some sealant before installing.. so it should act as one whole block.. then the whole thing will then be mounted to stud and edges will be sealed with bottle spray foam where it meet the stud for a complete air tight seal

The windows frame will not start on the brick layer, but on the structural wood layer. The whole structural will be build out of wood, wrapped by aluminum and brick.. windows frame will be light weight aluminum extrusion and and roof will be polycarbonate.

Actually I just found this picture of brick siding screw directly to this panel, see here
http://www.steelconstruction.info/im.../K3_Fig_17.png

Also according to the manufacture company picture.. it will support brick slip system.. maybe I should just do that instead of full brick?

Also here is the actual installation video from the manufacture in case anyone wanted to know more https://www.youtube.com/watch?v=HWb-vN5dIUk
 

Last edited by mrfssd; 08-26-14 at 10:53 PM.
 

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