# Attic Roof Insulation - Do I need baffles?



## AttnToDetail

Hey folks,

My home shop is set up in the attic. It's a 20' x 30' footprint and is peaked, altough it is a very decent working/living space. The peak is about 10' from the floor's center and I have 2 small dormers to give you a rough idea of what I'm talking about. Right now, all the roof rafters are exposed and uninsulated.

Mostly because of the cold in winter and heat in summer here near New York City, I have been planning on insulating and finishing the space. My first thought was to use styrofoam baffles and insulation -either fiberglass or foam. I would need to drill soffit vents as they do not exist now. Roof vents near the ridge are already there.

After talking with some buddies, DIY spray foam is all the rage and has really peaked my interest. A few friends have not used any baffles in the attic and simply sprayed foam right to the roof inside. I was very excited to hear this as I would not need to use any baffles or drill any soffit vents.

Anyone out there have any thoughts or concerns on whether or not to use baffles with attic ceiling insulation? Good input would really help me not make the wrong move.

Thanks,
George (cold in NY)


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## BillWhite

Spray foam. Keep the ridge vents. Do ya have adequate flooring, heating/cooling? How are ya gonna handle dust collection? Got plenty of power options?
Tools are gonna get heavy in a hurry. Ya don't wanna have any weight related probs.
Bill


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## devann

No. 
Where I've worked on houses that were goning to use the spray insulation between the rafters they had me close up the attic, seal off the gable vents if there were any. I was told that the attic space was suppose to be sealed off like a top of an ice chest. 
But then what do I know, I'm just the carpenter.


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## a1Jim

Hi George
I've found that DIY foam is very expensive when comparing it to fiberglass insulation. If you are insulating the roof it self you do not need baffles because baffles are used to allow air flow when the ceiling is insulated and not the roof it self.
I'm a contractor of 23 years ,good luck on your project. I'm always a little concerned when folks say their shop is in a attic because most attics are not made to hold the weight of the equipment and materials in a average woodshop and many times attics will not even have joist large enough to be rated for the weight necessary for use as a bedroom.


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## crank49

I think, without baffles, you will collect moisture in the wood/shingle layer in the winter and cook your shingles in the summer. Baffles provide ventilation to remove moisture in the winter and some convection cooling of the roof surface in the summer.

Maybe the moisture is not as much of a problem with foam as it is with fiberglass batt, but I would not think it does the wood structure any good.

I have seen first hand what non ventilated attics do to shingles. Not a pretty sight.


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## AttnToDetail

Bill and Jim (and any other readers)

I understand the weight concern. Let's face it… any attic is not ideal for a wood shop. It is the space I am working with now and I hope to upgrade in a few years when I move. Truth be told, the house is my parents' who have lovingly given me the space and offered to pay for the cost of insulating and finishing. Once I get my own shop, I hope to leave them with a well insulated, lit and heated/cooled storage space or work room.

To give a brief history of the attic space. It was originally built as a living space. There is a radiator, hot and cold water, drain, finished floor (which was blown with insulation 4 years ago) and a proper staircase to the attic. At some point, the walls/ceiling were gutted. The floor joists look like 2×8's space 16" apart. Does this sound substaintial enough, Jim? As far as power, we ran another panel to the attic and will lay out outlets (including 240 V) and switches. I plan on framing out an AC sleeve and dedicated outlet. For the heat, the radiator may be enough with the insulation, but I am still considering an alternative method.

Again, I know attics are not ideal. To me, my biggest challenge will be and has been getting machines, sheet stock and finished projects up to the attic. I am at the drawing board with some hoist and winch ideas. Anyways, thanks for reading and I look forward to more replies!

-George


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## a1Jim

Crank49
There are to ways to insulation attic space one is you insulate the ceiling of the lower floor ,this requires air flow in the attic to prevent moisture build up .This approach requires baffling and gable vents. This approach leaves the attic space cold so there's no heat transfer from the house to the roof preventing things like ice dams.
The other way to insulate a attic is to insulate between the rafters on the roof, this way also stops heat from rising from the interior of the house to the roof and stop ice dams also. Insulating the roof is what is typically done when the attic space is used for living space or in this case a shop and has a heated attic space. Insulating this way you do not use baffles or vents.
George 
It's hard to tell you if the floor joist are strong enough with out knowing what the span is and the weight you have in the attic.


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## Sawkerf

Before you get to deeply into insulating etc, you should check the floor load rating for your attic. Putting tools up there might take you well over what the floor can handle.


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## canadianchips

No you will not need baffles. The spray foam is the way to go. Cost is higher but you are going to get more benefits than just R value. You are getting vapor barrier.(No need for extra plastic) The spray foam is waterproof. You are getting sealing benefits (no need for cauking) I am assuming you are going to keep the collar ties if any ? The air space above them can be vented with the exisiting ridge vents. I would avoid BATT type insulation in a situation like this, Unless you give it proper ventilation you are going to deal with mould and moisture caused by condensation. (Any time you have HEAT hitting COLD you end up with moisture, this moisture needs to be dealt with.I can not see any reason why insulating your ceiling with this would cause shingles to deteriorate quickly ?
Your floor joist are minimun size needed, if you leave the supporting walls under them you might be fine. I really hate to judge this without actually seeing them or knowing what is supporting them, by support I mean ALL the way to footings ! This includes load bearing walls , support beams, footings. You will want to consider putting in an AIR exchanger, sealing up the room is great ,but you will need to remove stale air, chemicals smells, fumes, etc, and bring fresh air in ! KEEP us posted with what you are doing.


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## Bill1225

either way you go, you need ice shield for at least 3 feet under your roofing or any ice dam you may get may cause leaks(spray foam may be water proof but your rafters and roof decking are not), you may also want to put your tools on rubber floor mats to avoid intoducing vibrations which will cause drywall pops and seem cracks. worst case you when its comes to weight of the tools you could sisters your joist with lvl's or some kind of engineered lumber that will pick up the load and put it on your exterior


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## AttnToDetail

I know that the load bearing walls on the floors below runs pretty much down the the center of the house, leaving a span of 10'. Soooo, we're looking at 2×8's spaced 16" apart spanning 20' with the load carried at either end (exterior walls) and the center 10' mark (load bearing wall). The house is brick and built in the 1940's if this helps at all. Thanks.


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## a1Jim

Again 
With out knowing your span you can not know if your joist are correct for any particular load if you joist are 2×8" 16" on center but 20' apart then your lucky if you can use the space for light storage near enough a wood shop. take a look at this and decide for your self instead of having us guess if your joist are sufficient or not.

http://www.raisedfloorlivingpro.com/spantables-2.shtml

Just in case it's not clear the span is how far apart the the unsupported part of the joist ends are from each other.


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## AttnToDetail

Thanks for that link. I checked it out and everything looks good. I have been using this space as a work shop for the past few years and am not concerned about current weight issues. Although an attic, it was built as a living space and is actually used as legal apartments in the almost identical neighboring homes. Certainly heavy tools like a jointer/planer combo (440 LBS) and a bandsaw (380 LBS) are on my wish list but I really don't know if that is going to happen in this space considering my current shop budget, getting the machines into (and eventually out of) the attic and plans to have my own shop somewhere else down the road a bit. Yes, I am running 240 V power to the space, but that is mostly ease of doing it now while the space is gutted to have it there if I do ever need it.

My mind is made up to improve the conditions of the current shop space, even though is is not an ideal location. Thank you all for these great replies and eye openers.

George


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## OnlyJustME

You should also look into the differences between a closed cell foam and an open cell foam. Not sure if the open cell foam will give you a vapor barrier. it also will be a different R values per inch so make sure the rafter depth is enough to give you a high enough R value with whatever foam you choose. one might be more expensive than the other but it may be because it's denser and gives you higher R value and better insulation which equals lower heating/cooling bills.


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## AttnToDetail

Yes, closed cell looks like the way to go. A suggestion made was to lay 1 inch of the closed cell foam and then you can add a thicker layer of open cell foam or batt insulation (to save a little dough).

https://www.sprayfoamdirect.com/ <- This website has a lot of info.


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## OnlyJustME

You can do that. It all depends on your target R-value you want to hit and how deep your rafters/joists are. It might be savings in the beginning but a higher R-value over the long run could save you more. Lots to think and research about which i'm sure (with a name like AttnToDetail) you are doing. Also remember it always costs more to do it twice than to do it right the first time. lol Good luck with your endeavor.


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## DMIHOMECENTER

It appears by your description that your 2×8 joists have less than 8 feet clear span (that's good) on both sides between the outer walls and the center load bearing wall. At 16" on center, you are in excellent shape. As a matter of fact, 2×6 would be good enough (although deflection would be greater). Go ahead and put the waterbed and the pool table up there, too !


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## lewis62

Contracting for 30 years, and an OCD for insulation too.
You are geting half good and half really bad help so far.
If you spray foam, you will loose your shingles , unless a cold roof is built up for poroper venting under shingles.
Attic ,finished or unfinished, requires venting.
My recommendation.
Fiberglass batts, one size smaller than rafters, 2×6 raf, use r-11 batts, 2×8 rafters use r-19 batts, the space above becomes vent .If you want more insulating power hang 1/2 or 3/4 foam board as if it were drywall keep all joints tight and tape seams, creates a thermal break , than hang drywall use longer screws. If no flat area on top, center peak , roof vent must be continuos ridge vent.
All that should be less cost than foam, and proper cold roof design. Benifit more buget for tools.And no problems down the road.!


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## dwilly

checkout the green building website and they offer some really details on spray foam. Good luck!


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## BlueRidgeDog

I gotta know what your structure is like such that your attic space can support the weight of wood working tools.

There is debate as to what foam does regarding the roof sheathing and shingles. Since you are creating a vapor barrier on the underside of the sheathing, versus on the outside of the sheathing as in the case of walls, some fear that the sheathing caught between the foam and the shingles will suffer over time. However, regardless of the impact, it is the best way to create a livable space in an attic.

The folks that claim it is an issue do so out of theory, whereas the folks that claim it is not an issue have had foam in their attic for a long time, so perhaps experience is the better guide.


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## jonah

The venting is to a) keep the roof shingles cool in the summer due to convection cooling, to b) give moisture that builds up beneath the shingles somewhere to evaporate to, and c) to keep the roof cold in the winter. You need all three, which is why people use those vinyl/plastic soffit-to-ridge vents under the foam. You want as much air circulation between the soffits and ridge as you can get. That will prolong the life of your shingles and keep ice dams from forming.


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## RobS888

> I gotta know what your structure is like such that your attic space can support the weight of wood working tools.
> 
> There is debate as to what foam does regarding the roof sheathing and shingles. Since you are creating a vapor barrier on the underside of the sheathing, versus on the outside of the sheathing as in the case of walls, some fear that the sheathing caught between the foam and the shingles will suffer over time. However, regardless of the impact, it is the best way to create a livable space in an attic.
> 
> The folks that claim it is an issue do so out of theory, whereas the folks that claim it is not an issue have had foam in their attic for a long time, so perhaps experience is the better guide.
> 
> - BlueRidgeDog


We had foam blown into our attic 3 years back and what was funny was we had to have the existing insulation in the attic floor removed and the eave vents blocked. As I understand, you are making the underside of the roof the top of the thermal envelope. Any other insulation will stop air movement and possibly cause condensation. We had 8 inches of open foam blown in and no complaints, warm and quiet now. Someone mentioned ice dams above, doesn't that require the insulation to allow out enough heat to melt the snow? I mean doesn't a properly insulated roof prevent ice dams?


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## RobS888

> The venting is to a) keep the roof shingles cool in the summer due to convection cooling, to b) give moisture that builds up beneath the shingles somewhere to evaporate to, and c) to keep the roof cold in the winter. You need all three, which is why people use those vinyl/plastic soffit-to-ridge vents under the foam. You want as much air circulation between the soffits and ridge as you can get. That will prolong the life of your shingles and keep ice dams from forming.
> 
> - jonah


We had to take the baffles out, no moisture or heat gets up to the deck now, so no need to keep it cold in winter.


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## tvrgeek

Might check the code.
Some suggest spray directly will cook your roof leading to much shorter life span. I do like foam, as it seals, is quiet etc. But expensive. I don't know your local code, but you don't want to pay for enough foam to meet code. SOP is about 2 inches, then bats on the inside to get the R factor up. We need R38 in our ceilings, but R60 is recommended. 
You would have to stud out the ceiling to get that thick.

Is the attic rated by the original engineer for "habitable" space? Many are only rated "light storage" even in houses with unfinished, full stairs, dormers and a floor.


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## PCDub

[[...original post from 9 years ago; most recent reply 2 years ago…]]


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