# Help This DIYer - Insulation Question



## Inner10 (Mar 12, 2009)

Gentlemen,

I'm in the midst of performing a few renovation on my home which is around 90 years old. The house has a very very low pitch roof, no attic space, just around 12-15" of space between the roof and the ceiling. There is no sofiting, or venting to the outside, just an enclosed space (Its not an upside-down roof either). How should I insulate it?

I had a GC take a look at it and he hmmmed and haaaaaed at it...and told me to put batts of insulation but leave a airspace above them, instead of shoving them directly against the roof. I had another handyman tell me if its not vented then cram all the insulation I can in there.

I live in Ottawa, so we get very erratic weather, -40C to +40C.

Thanks!


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## SLSTech (Sep 13, 2008)

No ventilation, no water issues - anything up there now? (knob & tube, romex, junction boxes, pipes, ducts)

If no issues, you could probably treat it like a flat roof / mobile home roof & pack it full of cellulose insulation (dense pack) & air seal from inside the house - but I have a feeling you won't be able to do that & not something I would really recommend (even though DOE & the Weatherization folks do it all the time)

I would really have to see what it looks like, know your budget, and what you hope to accomplish before I could recommend any options


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## Inner10 (Mar 12, 2009)

Thanks! 

I'll throw up some pics, I'm re-enforcing the structure right now...I'm shocked the roof isn't in my kitchen seeing how poorly this place is built.


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## Inner10 (Mar 12, 2009)

There is nothing in the space, no wires, no ducts only the vent stack for the plumbing.


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## Heritage (Mar 20, 2007)

Ideally you would have a ridge vent and soffit vents. This creates continuous airflow. Warm air rises and exits through the ridge as cool air is pulled in through the soffit vents.

Because we live in Canada, you also need a vapour barrier on the warm side.

If the former (ride and soffit venting) is out of the question, look into gable vents accompanied by soffit venting.

If soffit venting is out of the question, go with gable vents and circular aluminum vents. You can just cut out @ the soffit area along the span and install these aluminum vents that come in a variety of sizes.

As for the insulation, either batts or blown in insulation of loose fill in between the ceiling joists. (along with v.b.).

There has to be continuous air movement across the top of the insulation, air has to move. Look into the aforementioned and see if any of those configurations can get the job done for you. But if you did provide pics you would def. get better advice. Best of luck.


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## SDC (Jan 12, 2009)

You could use closed cell foam to fill the space. With the foam you do not need an air space for venting. 
Also you will eliminate the need to cut the soffit or the ridge, no vapor barrier either, but it is very expensive. 
You would have a major R-value too, about 6.9 per inch of foam.

I would spray about 9" of foam (if they are 2x10's) and you get R-62
Most likely be the warmest part of the house


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## Morning Wood (Jan 12, 2008)

Is it 12-15" at the peak, or at the eave? If it is the peak, it will be very tough to put in proper venting for the roof. I would just recommend going with a hot roof at that point. No vent and just use spray foam. If you can put in venting I would and still treat it like a hot roof. For venting I like to screw, staple, nail strips of wood to the side of the rafters 1 1/2" down from the top and then attach rigid foam to the underside of the strips. Creates a 1 1/2" air space. I then foam the the joints everywhere. You are basically making an air tight channel that vents the underside of the roof but does not vent the attic space. You would have to add soffit and ridge vents. I then would dense pack cellulose in the attic space. Filling it completely or as much as possible. When it comes to insulation more is better


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## Inner10 (Mar 12, 2009)

Here's some crappy cellphone pics, as you can see is nailed and glued some 2x8s to the supporting members to level the ceiling.


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## katoman (Apr 26, 2009)

Inner, what's on the roof now?


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## Inner10 (Mar 12, 2009)

Looks like its made from 3/4" pine boards, then sheathed in plywood then coated is some sort of waterproof material? To be honest I've never taken a close look at it, I had a roofer check it out and he said it "looked fine" so I didn't ask questions.

I should add, the entire construction of this part of the house in an addition, I live near the downtown sector and all the houses are around 100 years old and poorly build, it was a blue collar area and they are all scabbed together out of leftover materials. The exterior walls are big pieces of wood about 3" deep and 12" wide stacked ontop of eachother and nailed together with huge nails. Then pine boards are nailed across the exterior.


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## shanekw1 (Mar 20, 2008)

I would use regular batts of r40 and put it between the ceiling joists as normal. 

If you have the area to vent soffit later, use the styrofoam vent things at the eaves(I cant think of the name right now, not enough coffee yet) to keep the insulation from blocking the air moving up and put in a ridge vent.

Otherwise punch a vent in each end at the gables.


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## SLSTech (Sep 13, 2008)

Screw the venting - if it's that open & the roof is in good condition, closed cell foam sprayed against the decking & gable walls

Now it will cost, but you don't have to worry about venting, vapor barriers or any of that other stuff that requires near perfection to prevent air & water issues later


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## Tinstaafl (Jan 6, 2008)

shanekw1 said:


> styrofoam vent things at the eaves(I cant think of the name right now, not enough coffee yet)


Baffles. The crew I started with always called 'em egg cartons. But they had some pretty odd names for other things too.


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## shanekw1 (Mar 20, 2008)

Tinstaafl said:


> Baffles. The crew I started with always called 'em egg cartons. But they had some pretty odd names for other things too.


Thats it!:notworthy


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## shanekw1 (Mar 20, 2008)

SLSTech said:


> Screw the venting - if it's that open & the roof is in good condition, closed cell foam sprayed against the decking & gable walls
> 
> Now it will cost, but you don't have to worry about venting, vapor barriers or any of that other stuff that requires near perfection to prevent air & water issues later


Have fun if you ever need to repace some of that roof decking in the future, too.:shutup:

Not a big fan of spray foam, here. Or any foam.


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## SLSTech (Sep 13, 2008)

shanekw1 said:


> Have fun if you ever need to replace some of that roof decking in the future, too.:shutup:
> 
> Not a big fan of spray foam, here. Or any foam.


First, I understand why you might not be a fan & it should be verified that is was installed properly not only visually but with either an IR camera & / or core samples

Now onto the roof deck replacement

First as I said, the roof & roofing needs to be in good shape - if not it needs to be fixed. 

Now why does sheathing fail?

Interior moisture - not an issue with CC as long as it is installed properly & at the proper depth - in his climate, I think it is 6" or 3 to 4 lifts - down here it is 4" (The R Value that you may still need to make up for in codes can then be accomplished with cellulose or spray in FG)

Roofer error - Flippin get the products installed properly, it may take a few extra minutes, but it sure beats having to come back & if you are using staples on that crappy felt, you are not installing the product properly

Expansion & Contraction of the panels - basically eliminated with the foam

Using the code approved minimums for building - seriously 7/16 or 3/8 OSB on 24" OC trusses or rafters, what the he11 does one expect, the product is going to sag leaving openings in the roof covering for water to get in --- well guess what, the CC foam actually adds rigidity to the entire structure and eliminating future sagging

Ice Dams - eliminated as the warm air from inside is not leaking through to the roofing

Oh & Inner10 - can you please space those pictures out so one doesn't have to scroll left to right to read the responses? Thanks


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## katoman (Apr 26, 2009)

Inner, thanks for the pics. I see there is almost no slope, so I think you have a flat roof there. 

It has been cross strapped (the 2x2s ) for ventilation. There may or not be venting to the exterior, but the cross strapping allows air to move unimpedded across the ceiling.

You do not want to loose this cross ventilation, so, there are a couple of options. You should be shooting for R 40 in the ceiling.

One- as morningwood stated, install 2" rigid styrofoam, spray foam any small gaps, then install 5 1/2" fiberglass batts. This will give you R 30. If you use 2" rigid you DO NOT need a vapour barrier.

Two- install two layers of 2" rigid, then 3 1/2" fiberglass batts. This will give you R 32. Not much better.

Three- install cardboard at the top of your 2x8s and have it spray foamed. This will give you your maximum R value, but it is more expensive. The cardboard is to maintain the cross ventilation. Do not spray foam tight to the roof deck. No VB required.

Note- FYI if styrofoam is 2" you do not use a VB. But this is if it is continuous. If styrofoam is less than 2" you do install a VB. This is from the Ontario Building Code. The problem here is that the styrofoam is not continuous, it will not be covering the joists.

That said, if you can afford it go with the spray foam. Second choice would be option 1.

If you simply fill the area up to the top of the joists with fiberglass, you do need a VB.


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## Inner10 (Mar 12, 2009)

> Oh & Inner10 - can you please space those pictures out so one doesn't have to scroll left to right to read the responses? Thanks


I'l see what I can do, are the pics appearing side by side or are they just tooo big for your screen resolution?



> Two- install two layers of 2" rigid, then 3 1/2" fiberglass batts. This will give you R 32. Not much better.


When you say rigid foam do you mean Styrofoam SM?

If the rigid foam path is taken do I still install the rafter-mates to maintain an airflow or do I pack it on tight and seal every crevice with expanding foam?

The spray foam sounds like a wonderful idea but it appears as though it costs as much as sprayfoaming it with cans of great stuff. :laughing: I was quoted about 4 bucks a square foot with a min bill of 1500 bucks...not out of the question but if I went that route I may as well rent a wrecking ball and build a new house....

I can't thank all you guys enough for the great advice, all input is greatly appreciated!


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## Inner10 (Mar 12, 2009)

> It has been cross strapped (the 2x2s ) for ventilation. There may or not be venting to the exterior, but the cross strapping allows air to move unimpedded across the ceiling.


I think those are just to set the pitch of the roof, there is one line of 2x2 and another line of rough cut looking 2x4s turned up on edge at the highest point.


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## katoman (Apr 26, 2009)

Inner - the 2x2 may be there to set roof slope, but use it for your cross ventilation.

So, install styrofoam sm up to the top of your 2x8 joists. This way you are not interfering with the ventilation. Then spray foam any small gaps. Then fill the remaining area with fiberglass.

I don't think the two layers of sm are worth the cost, just go with one layer of the 2".

Make sure there are no voids at the ribbon joist area ( the walls ) fill all gaps with the foam. You can get a foam gun for about $100 bucks, then use foam in the cans. The DIY stuff sucks.

Best of luck. If you get stuck you can pm me, John


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