# foam board, interior ceiling



## spudman17 (Dec 9, 2019)

Dealing with a fairly straight forward problem here. My house was built in 56, and thus has a poorly insulated ceiling. 

Let me expand with more detail.
My house was built in 56, it has a flat roof,with a slight pitch with a cold ventilated space. Its 2x8 construction with a torch on top. Looks to be a single batt of insulation 3.5" thick maybe. My old timer neighbour seems to think it's only R-8 or R-12.
I live in British Columbia and am in climate zone 6
My house is a rancher style duplex, crawlpace below. My ceiling( where I lose alot of heat) are old staple on ceiling tiles. They are stapled to 1x6 furring strips that span my entire ceiling butted up to each other with maybe a 3/16 gap between them. I do not have access to the roof joist bays containing the 3.5" batt exept in one spot.The batt has a paper parchment backing.
When I demo the tiles I want to then screw 3" of foam board to the existing 1 x 6 furring strips. Then strap my ceiling again on 12" centers with new 1 x6 furring strips and install a 5/8 type x drywall ceiling.

I am having trouble finding examples of ppl doing this and info on it. Let me clarify why I want to do this. 
The torch on roof is only 5 years old so I din't want to mess with it. Also as I stated before I have no access to the joist bays in my roof due to my ceiling being completly sheated in 1 x 6 furring strips.

I checked with my local building inspector and they said it would be fine. I also do not need a permit because I am only adding.

The lowes in my town is closing and today I picked up a bunch of silverboard xs exterior wall sheathing. I did some research before I bought and found that silverboard could be used as a vapour barrier. Which was my plan, I would use the silverboard as my vapour barrier then drywall as normal. But now that I am doing more research I am seeing 2 things on silverboards website

1.
The reflective laminated surfaces are micro perforated giving the panel high water vapor permeance greatly reducing the likelihood of trapped moisture through the increased drying potential. 

2.
The reflective lamination can serve as a vapor barrier when taped and sealed.

Basically my question is, 
1.am I doing something stupid insulating like this? Has anyone done a project like this insulating their ceiling from the interior with foam board

2. Should I have a vapour barrier? If so can anyone clarify if silverboard will act as one or I should add a poly vapour barrier? 

Any help or comments would be greatly appreciated. I'm stepping out of my lane a bit here and it's hard to find resources because of how I am trying to do this project.


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## Nealtw (Jun 22, 2017)

You didn't say whether there was venting above the insulation now. What you are after is stopping house air from getting into the structure of the roof. I don't see a problem with taping the foam and sealing the perimeter with caulk 

You can get drywall screws up to 3" long so you may not need to strap it.


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## spudman17 (Dec 9, 2019)

Nealtw said:


> You didn't say whether there was venting above the insulation now. What you are after is stopping house air from getting into the structure of the roof. I don't see a problem with taping the foam and sealing the perimeter with caulk
> 
> You can get drywall screws up to 3" long so you may not need to strap it.


Yes, there is venting above the insulation now.


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## Nealtw (Jun 22, 2017)

spudman17 said:


> Yes, there is venting above the insulation now.


I don't see a problem with your plan.


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## Nealtw (Jun 22, 2017)

spudman17 said:


> Yes, there is venting above the insulation now.


Zone 6 is big, where are you at or close to.


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## spudman17 (Dec 9, 2019)

Nealtw said:


> spudman17 said:
> 
> 
> > Yes, there is venting above the insulation now.
> ...


I'm in Prince George


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## SPS-1 (Oct 21, 2008)

spudman17 said:


> 1.
> The reflective laminated surfaces are micro perforated giving the panel high water vapor permeance.....
> 
> 2.
> The reflective lamination can serve as a vapor barrier when taped and sealed.


These two statements are contradictory. 

If I looked up the correct Silverboard product, it shows it is EPS with R5 per inch and permeability of .075 Perm, which makes it a vapor barrier. So you are putting a vapor barrier on the "warm in winter" side of the existing insulation, which is probably what is recommended for your area, but best to confirm with somebody more familiar with your local conditions.


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## Bud9051 (Nov 11, 2015)

Getting ventilation to work on a flattish ceiling will be difficult.

Sounds like the joist bays are isolated from each other. Venting requires a high exit and a low intake AND some difference in elevation between them, like several feet.

Code in the north may require a vapor barrier but you said no permit was required. The need for a vapor barrier is debatable and they have now applied different levels of vapor retarders to this application. A vapor diffusion retarder would probably be sufficient and the foam board you describe is one.

The real concern from my perspective would be air flow for ventilation. Can you better describe what is there?

Bud


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## 3onthetree (Dec 7, 2018)

If you are ok with losing 4" of ceiling height and adjusting all the ceiling light boxes and whatever else, would it ultimately be better to just remove it all (the 1x6s and R11 batts), address venting, air sealing, and insulation making it closer to the R26.5 required?


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## Nealtw (Jun 22, 2017)

Bud9051 said:


> Getting ventilation to work on a flattish ceiling will be difficult.
> 
> Sounds like the joist bays are isolated from each other. Venting requires a high exit and a low intake AND some difference in elevation between them, like several feet.
> 
> ...


 Quote:
Originally Posted by *Nealtw*  
_ Quote:
Originally Posted by *spudman17*  
 Yes, there is venting above the insulation now.

Zone 6 is big, where are you at or close to._

I'm in Prince George 


Unlike
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## spudman17 (Dec 9, 2019)

Bud9051 said:


> Getting ventilation to work on a flattish ceiling will be difficult.
> 
> Sounds like the joist bays are isolated from each other. Venting requires a high exit and a low intake AND some difference in elevation between them, like several feet.
> 
> ...


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## Bud9051 (Nov 11, 2015)

Pitched roof with a peak in the middle or a single slope with one soffit higher than the other?

Very large soffits is a plus with minimal slope as wind can cause a positive pressure on one side and a negative on the other and it doesn't take a lot of wind to match the natural convection most homes rely on. An outside picture would help.

As in all construction, air sealing is a high priority, even higher than any vapor barrier or retarder. Far more moisture moves through leaks than moves through materials. Note, even a layer or two of paint scores as a vapor retarder, types of paint vary.

Bud


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## spudman17 (Dec 9, 2019)

Update, I took down the old ceiling tiles today. Turns out the 1x6 furring strips are not continuous across the ceiling. It was just double wide in the one place I looked originaly. 
This means if I wanted I have access to the Roof joist bays.
I was considering just going on with my original plan of 3" of foam board, re strap then drywall. Using the silverboard as a vapour barrier or retarder.

I'm open to suggestions on how to get the best insulation value in my situation. I don't mind losing a few inches of ceiling height. There are also not too many lights to have to work around. 

I will post some photos here. Open to any suggestions. Thanks


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## spudman17 (Dec 9, 2019)

The roof has one soffit higher than the other. The front of the house is higher than it is graded back at about 3/8 per foot


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## Nealtw (Jun 22, 2017)

What is or was the hole for and what is your plan for that?


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## Bud9051 (Nov 11, 2015)

Just a note before I go back to sleep, having two vapor barriers is worse than having none.

Bud


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## SPS-1 (Oct 21, 2008)

But his two vapor barriers are separated by just 3/4". You think its worth the effort to reduce that distance to zero ? And I am not sure the paper is even a vapor barrier --- possibly a vapor retarder.


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## Bud9051 (Nov 11, 2015)

Not sure on the paper facing either, basically it's probably 2 vapor retarders and a guess as to how they will perform. As for the 3/4" gap, any gap presents a concern for two vapor layers where moisture could get in.

If the insulation issue were started from new the choices would be obvious. Retrofit that is different becomes a guess.

Bud


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## spudman17 (Dec 9, 2019)

Nealtw said:


> What is or was the hole for and what is your plan for that?


The hole is where the exhaust for my range fan goes through the roof


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## Nealtw (Jun 22, 2017)

Bud9051 said:


> Just a note before I go back to sleep, having two vapor barriers is worse than having none.
> 
> Bud


Perhaps you could explain the problems that arise from this.


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## House Designer (Oct 4, 2019)

The best, but most expensive way to do this job would be to strip out all old insulation, and spray-foam the cavities to get an R-45 insulation value. No vapor barrier needed with spray-foam.
What you plan to do with 3" of styrofoam will add R-15 to the existing R-value (if you use Dow blueboard) which may double your existing R-value and offer a big improvement with less work. If your last layer is foil-faced foam, be sure and seal the joints with tape to maintain the vapor barrier.


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## Wolf_Z (Oct 14, 2019)

That's for some kind of ventilation system, I suppose


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## 3onthetree (Dec 7, 2018)

It seems you have to make it work, the boards and drywall is sitting there. First, is this only for this room (cuts outs spray foam option mentioned), or are you doing the whole house? Is the ceiling sloped to follow the roof rafters, or is there a false ceiling to be level (may mean only 1 layer of batt on one side of house, the 2 existing over this room)?

It looks like your SilveRboard Graphite XS are about 3/4" thick? So you want to layer 2, 3, or 4 thick on the ceiling to get close to 3" of rigid insulation?

The XS means the foil face is perforated. I still would not layer them, having multiple vapor retarders, even perforated. You never want multiple VBs ("retarders") because moisture can get trapped between them. Also, just to mention the main reason to have a foil face is for a radiant barrier, but is nullified when there is no air space next to it.

Take a look at the installation guide, page 16

There's good ways to insulate, and there could be ways to try and make your materials work. Not sure yet without all info.


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## spudman17 (Dec 9, 2019)

3onthetree said:


> It seems you have to make it work, the boards and drywall is sitting there. First, is this only for this room (cuts outs spray foam option mentioned), or are you doing the whole house? Is the ceiling sloped to follow the roof rafters, or is there a false ceiling to be level (may mean only 1 layer of batt on one side of house, the 2 existing over this room)?
> 
> It looks like your SilveRboard Graphite XS are about 3/4" thick? So you want to layer 2, 3, or 4 thick on the ceiling to get close to 3" of rigid insulation?
> 
> ...


I would like to do the whole house, my roof is sloped with the joist,ceiling sloped as well so no false ceiling.

I only have the ceiling out in this room so far

It is silverboard xs, I have 2 differerent sizes, 1.6" and 1.2" (sizes seem odd) anyway I wanted to do a layer of each so 2.8" in total. But if that would cause issues maybe I wont.


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## Nealtw (Jun 22, 2017)

2 layers are better as you can offset the seams


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