Insulating without ventilation

[doyle4281]

Hello all, I recently purchased a Daikan mini split for my attached 3 cat garage/workshop, and could use some opinions on the matter of insulation. The walls are not a problem, it the ceiling that is an issue. The garage has a multiple roof angles, which leaves many rafter bays essentially unventable. Short of drilling holes through the ridge beam to get airflow from neighboring rafter bays which have soffits, I don't know how to properly install the installation. I could use closed cell spray foam and create a complete unvented ceiling, however that stuff is very expensive. My intention was to install unfaced insulation between the rafters, and then cover with 1/2 poly iso rather than drywall. Any suggestions?

 

[toyotadriver]

Not sure I understand. Can you post a pic?

 

[doyle4281]

Not sure I understand. Can you post a pic?

Here are some pictures. Being that there are 2 gable ends, it creates some complexity in the rafters/ridge beam arrangement. This leaves many of the rafter bays with no soffit to draw air to bring to the ridge vent (not installed yet). Drilling holes in the rafters to create an airflow from rafter bays that do have soffits would be quite extensive. I know people use closed cell spray foam to insulate unvented ceilings, however it is very expensive, $1.00 per board foot. My only concern is that the moisture from the heating/AC get trapped without venting. Any suggestions?

 

[bczygan]

I would bite bite bullet and foam it. But that only if I wanted an open ceiling.

Otherwise, and the best choice in my opinion, is to add the proper ceiling joists and install the correct amount of insulation of your choice there. Much easier to get the needed depth. Then install eave venting and ridge vents or gable end vents, your choice.

Is there no venting of any kind now?
Bill

 

[doyle4281]

I would bite bite bullet and foam it. But that only if I wanted an open ceiling.

Otherwise, and the best choice in my opinion, is to add the proper ceiling joists and install the correct amount of insulation of your choice there. Much easier to get the needed depth. Then install eave venting and ridge vents or gable end vents, your choice.

Is there no venting of any kind now?
Bill

The issue is not getting the proper amount of insulation, the rafters are quite large, the problem is getting everything vented. I cant add a ceiling as I need the height for the lift.

 

[Jess]

Look up Cathedral Ceilings for some ideas on insulating this type of ceiling. I personally, would frame up the ceiling, sheet and blow in some insulation, leaving an air space above. If no soffit vents are in place, roof vents are an option.

 

[doyle4281]

Look up Cathedral Ceilings for some ideas on insulating this type of ceiling. I personally, would frame up the ceiling, sheet and blow in some insulation, leaving an air space above. If no soffit vents are in place, roof vents are an option.

I actually just insulated a cathedral ceiling in my living, it was quite difficult. The difference here is that the rafter design does not offer soffits for every bay of rafters. If I insulate and sheet, the bays without soffits will essentially be air packets where moisture gets trapped. The ridge vent up top is not an issue as everyone rafter bay eventually joins at the ridge, however a ridge vent with no soffit air flow is counter productive. Aside from spending many thousands of $$$ spraying closed cell foam, or drilling holes in every rafter, im cant think of a conventional solution.

Creative option....
Will a ridge/soffit vent system, still operate if the "intake" (soffit) is on the interior? So, on the rafter bays that dont connect to a soffit, can I leave a few inches at the bottom of each bay open, so interior air move through the bay and out the ridge? My thinking is that if the bay is insulated, enough air can move through the insulation and out the ridge vent in the problem areas. Terrible idea?

Another option...
Installing an electric fan to evacuate moist air from the interior. This would require me to add an intake, similar to a gable vent system, however it would be on the interior. My concern would be that I would be losing to much heat or AC. Terrible?

 

[jav]

Not an expert but my reading suggest that unless you have adequate ventillation under the roof plywood (which would be near impossible in your case), the only generally accepted methods are closed cell directly onto the roof deck or strip the shingles above, rigid insulate above the deck and re-roof.

Closed cell seems cheaper and you only need 2".

 

[doyle4281]

Not an expert but my reading suggest that unless you have adequate ventillation under the roof plywood (which would be near impossible in your case), the only generally accepted methods are closed cell directly onto the roof deck or strip the shingles above, rigid insulate above the deck and re-roof.

Closed cell seems cheaper and you only need 2".

Im beginning to think that is my only option too. Certainly not a bad option, just expensive. In order to get adequate R- value I would need 5-6", a lot of $$$ considering im only heating and air conditioning to a tolerable temperature, not livable temperature.

 

[Voi]

Im beginning to think that is my only option too. Certainly not a bad option, just expensive. In order to get adequate R- value I would need 5-6", a lot of $$$ considering im only heating and air conditioning to a tolerable temperature, not livable temperature.

You don't have to get all of the R value from closed cell to have an unvented, cathedral ceiling.

I'm in climate zone 6 and only need to get about half of my R value from closed cell.

There is some thought that one can cheat the recommended R value ratio in a garage since it typically doesn't have the same moisture producing appliances like a house.

Do you know what climate zone your part of New Jersey is in? Does you slab have a vapor barrier under it? Any sources of humidity besides snow melt from vehicles in the winter?

Rigid above the roof deck is ideal. It reduces thermal bridging much more than spray foam under the deck and is generally cheaper. However, a roof like yours would be more labor intensive and likely produce more waste. I wouldn't even consider it unless the roofing isn't installed yet or is due for replacement.

I'd do spray foam and fiberglass at least in the area(s) you want a lift. Then maybe consider an attic in other areas, if feasible.

 

[doyle4281]

You don't have to get all of the R value from closed cell to have an unvented, cathedral ceiling.

I'm in climate zone 6 and only need to get about half of my R value from closed cell.

There is some thought that one can cheat the recommended R value ratio in a garage since it typically doesn't have the same moisture producing appliances like a house.

Do you know what climate zone your part of New Jersey is in? Does you slab have a vapor barrier under it? Any sources of humidity besides snow melt from vehicles in the winter?

Rigid above the roof deck is ideal. It reduces thermal bridging much more than spray foam under the deck and is generally cheaper. However, a roof like yours would be more labor intensive and likely produce more waste. I wouldn't even consider it unless the roofing isn't installed yet or is due for replacement.

I'd do spray foam and fiberglass at least in the area(s) you want a lift. Then maybe consider an attic in other areas, if feasible.

Okay, I did not know that. Essentially I am using the closed cell to create the air/vapour barrier, and the rest can be regular batt insulation. I believe my area requires R-38. My intention was to cover the ceiling with 1/2 poly iso sheets rather than sheetrock. Reduce some thermal bridging and it will be way easier to install. When combining closed cell with regular fiberglass, do you still apply a vapour barrier on the interior? The garage is a workshop, and will only be heated or cooled a max of a 20 degree difference than ambient. If its 32, ill set it as 50 or so, if it 90-100, ill set it at 80, if its 10, im not going in there.

 

[jav]

That's my understanding as well which is why I posted that you only need 2". I would do 2" of closed cell and fiberglass or rockwool below that, then gyp board. It's my understanding that with 2" of closed cell, no other vapor barrier is needed in the roof system.

 

[doyle4281]

Thanks alot guys, that is a huge bit of information, great to know. HAs anyone has success with the DIY kits or are there little savings there?

 

[Voi]

I believe my area requires R-38. My intention was to cover the ceiling with 1/2 poly iso sheets rather than sheetrock. When combining closed cell with regular fiberglass, do you still apply a vapour barrier on the interior?

The required R value is important, as is the percentage of that R value that should come from foam and fiberglass (or cellulose, rock wool, or whatever).

Here is a picture for rigid foam above the roof deck. I think the percentages shown are the same when doing "flash and batt" below the roof deck.

And that is from the article linked below. Scroll down to section about roofs.

http://www.greenbuildingadvisor.com...mbining-exterior-rigid-foam-fluffy-insulation

So in my area 2" of closed cell might be sufficient to act as vapor barrier but comes nowhere near being 51% of our required R-49.

I only quickly found that article. There might be a better one for using a combination of closed cell and fiberglass below the roof deck (aka "flash and batt").

Hope this helps.

 

[doyle4281]

The required R value is important, as is the percentage of that R value that should come from foam and fiberglass (or cellulose, rock wool, or whatever).

Here is a picture for rigid foam above the roof deck. I think the percentages shown are the same when doing "flash and batt" below the roof deck.

And that is from the article linked below. Scroll down to section about roofs.

http://www.greenbuildingadvisor.com...mbining-exterior-rigid-foam-fluffy-insulation

So in my area 2" of closed cell might be sufficient to act as vapor barrier but comes nowhere near being 51% of our required R-49.

I only quickly found that article. There might be a better one for using a combination of closed cell and fiberglass below the roof deck (aka "flash and batt").

Hope this helps.

Great info, and I will look into the differences for above deck and below deck applications. I am in climate zone 4, however being a garage, I do not intend on applying the full insulation R-value. I have already begun making calls to local installers to get quotes. Ill report back whatever info I get. Thanks again for really helping me out

 

[desmato]

I was told by building inspectors and insulation manufacturers that a dense pack cellulose installation needs no ventilation. Cellulose provides the vapor barrier since nothing can penetrate through it. It's a fire retardant, bug/animal proof, a great sound deadener and recycled. So, use the fabric covering that glues on with wood glue, buy a ton of cellulose from Menards etc., rent the machine and do it yourself for an R-30+ in a 2x10 cavity. no fuss, no mess (alright, it's a horrible mess until done) then you can sheetrock over it once done.

I have a 2x12 conventionally framed roof and dense pack is the bomb ! R-39

P.S. I was also told over the years by numerous of the same people that soffit/ridge systems just don't work. I currently have the only soffit/ridge system that is proven to work and I saw it and felt it in person after years of researching them and firsthand testing (it's on my house, not garage) the soffit doesn't matter, it's the ridge vent that does the work to convect. the one I have is metal and cross section is shaped similar to an arrow. It's designed and made locally by American Metal Roof (Flint MI) who sells, installs and warranties metal and traditional roofing systems. (I have no connection to them) the instant I set the ridge on the open roof, I felt the heat hitting me in the face and my helper's cigarette flared way up. both of us were wide eyed in disbelief.

I will try to post a pic of mine.

 

[DC73]

which leaves many rafter bays essentially unventable.

Do some research on BuildingScience.com and on GreenBuildingAdvisor.com. GBA has a Q&A forum where building science gurus hang out and they can better advise you as to what works and what doesn't for your climate.

It used to be a no-no to put insulation other than spray foam in direct contact with the underside of the roof deck but they are changing their thinking. For climate zones 1, 2, & 3, they now say you can put insulation in direct contact as long as you cut in a ridge vent and then cover the ridge vent with a vapor permeable membrane that blocks air flow. This allows any condensation to escape. They are studying whether this works for other climate zones.

You might be able to get away with insulation in direct contact with the underside of the roof deck since the space will be conditioned by the mini split you've chosen.

Here is one related article that might interest you: https://buildingscience.com/documen...ail&utm_term=0_194890bc8c-c7470a2abe-63891105

Good luck,

DC

 

[DC73]

I was told by building inspectors and insulation manufacturers that a dense pack cellulose installation needs no ventilation.

You were told wrong. It's much more complicated than that and climate is a major consideration. All wall and ceiling assemblies must be able to breathe and to dry out.

Cellulose provides the vapor barrier since nothing can penetrate through it.

This is wrong as well. Cellulose does not block water vapor. It does a better job than fiberglass at blocking air movement but it will allow water vapor to pass. The only insulation that effectively blocks water vapor is closed cell spray foam and even then it has to be thick enough.

. . . the soffit doesn't matter, it's the ridge vent that does the work. . .

This is also wrong. A proper functioning ridge vent must have a source of air intake which is usually soffit vents. The soffit vents should be equal to or greater than the area of the ridge vent.

DC

 

[desmato]

I will tell the 5+ professionals who live, breath, sleep all things roofing and insulation in zone 5 that you said they are wrong.
These folks had nothing to gain by telling me the best way to insulate my closed rafters.

the house my father built in '71 was also a 2x12 rafter construction, also dense packed with no venting and after 45 years, still has it's original sheathing and sheetrock with no mold or rot. If all that isn't good enough, how about this ?

http://www.cellulose.org/HomeOwners/AirVaporBarriers.php

Controlling Moisture
A common misconception is that all insulations require vapor barriers. However, CIMA does not recommend the use of vapor barriers with cellulose insulation, except in circumstances of exceptionally high moisture levels, such as an indoor pool facility, or very cold climates. The reason is that cellulose is the only insulation that actually manages moisture.

Moisture moves by two transport mechanism: air movement and diffusion. Of these two, air movement is the more significant, accounting for over 98% of the total, and it is the primary cause for moisture related building failures. As noted above, cellulose impedes the movement of air generated by wind, stack effect, and mechanical imbalances within the building. By blocking the movement of moisture-laden air, cellulose reduces moisture movement to manageable levels within the building assemblies. Any remaining moisture is diffused by the cellulose, and will be further blocked by primers or paints used on the interior surfaces.

A vapor barrier is not only unnecessary but also can be potentially harmful, especially during the summer months in air-conditioned buildings, when warm, moist air passes through wall assemblies and condenses on the outside of the cool poly vapor barrier. The hygroscopic nature of cellulose insulation allows it to manage and wick moisture from areas of greater to lesser concentrations, thus preventing damaging amounts of moisture from accumulating.

Now let me clarify about a soffit. I was not inferring that it is not needed, but that the style, type etc is not important as it is not the working part but merely the intake. the ridge does the work. as for the soffit needing to be equal or greater, I agree. sadly, I bet the vast majority of systems are just thrown together by the rough framers who know nothing other that pounding nails.

Hopefully this clarifies and provides a bit more info on cellulose.

Todd

 

[desmato]

I was given a "formula" of sorts by Regal back in '03 to calculate how much I needed. It allows for vertical, horizontal & slope. I had to copy/paste since the upload was too large.


REGAL INDUSTRIES, INC. 9564 E. 600 S. CROTHERSVILLE, IN 47229
800-848-9687 812-793-2041 FAX www.regalind.com


**DETERMINING NUMBER OF BAGS OF CELLULOSE
REQUIRED FOR A CLOSED CAVITY BLOW AND THE
ACTUAL INSTALLED DENSITY AFTER THE BLOW**
(Vertical or Horizontal )

(Use the following info. when the bag’s own coverage chart is not applicable)

***********************************************************************************************

EXAMPLE: Vertical Sidewalls (other than std. 2x4, 2x6 design dimensions)
NOTE: SEE SPECIAL NOTE BELOW FOR VALUES IF HORIZONTAL CLOSED/OPEN CAVITIES

Select segment of equal sized cavities to be filled…….………. Example: 20 cavities

Determine cavity dimensions.
Example: Each cavity measures 9 ft. Height x 23 in. Width x 6 in. (actual) Depth

(HORIZONTAL = Length x Width x Depth)

Convert all measurements to inches 108” Height x 23” Width x 6” Depth

Determine avg. weight of the bags to be used…………………..….Example: 21 lbs.
NOTE: Wt. is normally listed on bag……Example: Regal Green 40 weighs 21 lbs./bag,
Regal 30 = 15 lbs., 44 = 23 lbs., 50 = 25 lbs.

***********************************************************************************************

CALCULATING SIDEWALL EXAMPLE:

A. VOLUME OF EACH MEASURED CAVITY IN CU. FT.

108” x 23” x 6” = 14904…..divided by 1728 = 8.625 cu. ft. (NOTE: 12x12x12 = 1728)

B. TOTAL CU.FT. VOLUME OF ALL 20 CAVITIES

8.625 cu.ft. x 20 cavities = 172.5 cu. ft.

REMEMBER: MAINTAINING A CONSISTENT BLOW IS IMPORTANT!

C. TOTAL WEIGHT OF CELLULOSE REQUIRED (SAME EXAMPLE)

172.5 x 3.0 lbs. = 517.5 LBS.

Note: 3.0 lbs. is recommended density(wt.) per cu.ft. for sidewalls.



REGAL INDUSTRIES, INC.
Page 2


D. TOTAL NUMBER OF BAGS REQUIRED TO COMPLETE JOB

517.5 divided by 21 = 24.64 BAGS (required to fill ALL 20 cavities)

NOTE: Some spillage will occur, so consider purchasing a few extra bags.

*******************************************************************************************
IF HORIZONTAL CAVITIES, SAME FORMULA APPLIES, BUT LESS DENSITY (WT.)

***RECOMMENDED DENSITY (WT.) PER CU.FT. IN EACH CAVITY TYPE***

a.) INSTALL @ 3.0 LBS PER CU.FT. FOR VERTICAL CLOSED CAVITIES.
NOTE: Regal recommends that you not exceed 3.5 lbs. per cu.ft.

b.) INSTALL @ 1.4 LBS. PER CU.FT. FOR HORIZ. CLOSED/OPEN CAVITIES.
*******************************************************************************************

**CALCULATING THE AVERAGE DENSITY (WT.) PER
CU.FT. ACTUALLY DELIVERED TO EACH CAVITY **

RIGHT
If we actually installed 27 bags in the above cavity volume, then:

Total weight installed = number of bags installed x weight of each bag.
27 x 21 = 567 lbs.
Average installed density = pounds divided by total cavity volume.
567 / 172.5 = 3.29 lbs./cu.ft

NOTE: In this example, the installed density (wt.) would result in NO settling.

WRONG
If we only installed 22 bags in the above cavity area, then:

1) 22 x 21 = 462 lbs.
2) 462 / 172.5 = 2.68 lbs./cu.ft.

NOTE: In this example, the installed density (wt.)is too low. Settling will probably occur.


Steve Leighty
Regal Industries, Inc.
Customer Service Mgr. 12-03

These are the notes he sent as well regarding this:

Please review the included attachment. It will give formulas for
determining the # of bags needed for vert. and horiz. cavities. You will
need to know the wt. of the bag you are using (see attachment). Note the
difference in density (wt.) #'s for both horiz. and vert. cavities. Since
you will have a cathedral you will need to determine a compromised density
which,for caluculating purposes, will be in the area of 2/3 to 3/4 the
density used in a vert. sidewall which calculates to 2.0 to 2.5 lbs. based
on a normal 3.0 lb. per cu.ft. sidewall blow. You can blow up to 3.5 lbs
but any more than that is overkill.



Hope it helps, Todd

 

[toyotadriver]

In light of your requirements I would put 2 to 3 inches of closed cell on the under side of roof decking, fill the remainder of the cavity with fiberglass of the right thickness, cover that with rigid foam sheets, then cover all that with whatever finish you want.

 

[DC73]

These folks had nothing to gain by telling me the best way to insulate my closed rafters.

I'm not saying the construction methods recommended to you are necessarily wrong for your climate, just that you can't make a blanket statement that cellulose doesn't require ventilation. The method used in the house your father built seems to work for your climate. It doesn't mean it will work in other climates. Some of what you were told may be correct for your climate but not for others. And that's the rub.

However, you said "Cellulose provides the vapor barrier since nothing can penetrate through it." If anyone told you this, they are most definitely wrong. Cellulose is not and cannot be a vapor barrier. It does not block the movement of moisture but does help control it as the info you provided correctly states. The cellulose info you provided is correct and does not contradict my statements.

I much prefer cellulose insulation over fiberglass but I also prefer mineral wool.

DC

 

[desmato]

While trying to stay on topic and not bicker, I want to point out a few things.

1. the O.P. is in N.J. (possibly same zone as me if in the northern part, not in desert Tx) and has a situation where ventilation of the rafters is near impossible (or should I say improbable) and asked for advice which I provided based on the same/similar zone, same situation, best R value/$, 45 years of usage etc. I did not make a blanket statement based on some state that has a different climate than us. It was made on our area.

2. I stated "I was told by building inspectors and insulation manufacturers that a dense pack cellulose installation needs no ventilation."

3. if the manufacturer says specifically to not use a vapor barrier with a cellulose product except under very specific situations and that it "controls moisture", it should be able to be stated as "provides the vapor barrier" for simplicity sake.

Sadly, everyone wants advice from a huge forum on their situation but seldom contact the experts in their exact area. I posted in my words what I learned from all the research and findings I did on cellulose, from the manufacturers and "experts" in such.

Didn't mean to offend anyone and I hope my "advice" was helpful to someone either in using or staying away from cellulose.

 

[Radix2]

Creative option....
Will a ridge/soffit vent system, still operate if the "intake" (soffit) is on the interior? So, on the rafter bays that dont connect to a soffit, can I leave a few inches at the bottom of each bay open, so interior air move through the bay and out the ridge? My thinking is that if the bay is insulated, enough air can move through the insulation and out the ridge vent in the problem areas. Terrible idea?

yes terrible idea. venting moist inside air directly onto your cold exterior sheathing will keep it wet all winter long...

 

[borisdavenport]

Cellular Expanded Polystyrene Thermal Insulation Board one is a good roofing material with good insulation properties and is also fire retardant . The roofing of above was done using this and is affordable even for us.


1

Rigid Cellular Expanded Polystyrene Thermal Insulation Board
Fire Retardant Grade ** and CFO Free ***

ROOFKING
20

100 cm x 50
cm
125 cm x 62
cm
(as per Table 1)
(as per Table 1)
(as per Table 1)

3 cm, 4 cm, 5
cm, 7 cm, 7.5
cm 8 cm & 10
,
cm

ASTM Type VIII
(as per Table 1)

2

Rigid Cellular Expanded Polystyrene Thermal Insulation Board
Fire Retardant Grade ** and CFC Free ***

ROOFKING
24

ASTM Type II
( as per Table 1)

3

Rigid Cellular Expanded Polystyrene Thermal Insulation Board
Fire Retardant Grade ** and CFC Free ***

ROOFKING
32

ASTM Type IX
(as per Table 1)

4

Rigid Cellular Expanded Polystyrene Thermal Insulation Board
Fire Retardant Grade ** and CFC Free ***

ROOFKING
40

ASTM Type XIV
(as per Table 1)

 

[kbaum187]

What did you ever decide to do here? We are faced with the same problem.

 

[chinboys]

Thermodynamics... Heat travels by conduction (thermal bridging sheet rock, insulation, rafters, studs, plywood, and roofing), convection (drafts leaks, door and window openings, ventilation), and radiation (big surface temperature differences to that of the sky).
In the summer, the heat driving into the space you want to keep cool will be majority be contributed by conduction and convection. The conduction being feed by radiation heating.
Regardless of what type of insulation you use... You need to create buffer or ideally, a vacuum between the hot and the cold area.
Hence, you need to vent or cool with ambient temperature air the space above your ceiling and below roofing deck as a first priority.
If it was up to me.... Install a ceiling and add at least R48 blown in or batted insulation. And make two gable vents with a thermal switched power ventilator.

 

[pcmeiners]

"2. I stated "I was told by building inspectors and insulation manufacturers that a dense pack cellulose installation needs no ventilation."

Agree, densely packed cellulose does not allow air circulation within itself, unlike fiberglass. It also does not lose R value as the temperature drops appreciably, unlike fiberglass. I packed the walls of my parents balloon frame home, a basement fire did not get past 3/4" of the borate infused cellulose in the wall cavities.

Do not allow early morning air exchanges. Early morning air primarily in the spring and fall carries a great deal of moisture, if air exchanges lower the interior garage temps to the dew point you get condensation on everything. Best to insulate so you have slow temperature differences during the entire day

Uncovered foam is a fire hazard. Should you have a garage fire you will have no chance of saving anything. You should have type X covering it. Personally you could wet pack the ceiling/rafters with cellulose, get the R value you need and have fire retardant protection.

"Hence, you need to vent or cool with ambient temperature air the space above your ceiling and below roofing deck as a first priority."

Fully agree about air circulation above ceiling as in attic space, as long as it does not allow the air to infiltrated the living or user space. I have a very large opening via a perforated soffit ceiling, about 125sqft area, it provides a very cool unused attic space (fully insulated), saves my roof also.