Insulating a roof?

[cc-rider]

I don't know if this is called a cathedral ceiling, or a vaulted ceiling, or what.

My rafters are 2X10's. No trusses, bottom chords, or anything. I want to put wood on the bottom of the 2X10's and call that my ceiling. (Because of all the dormers and such up there, I have really cool angles all over the place....I'd hate to cover them all up with a flat ceiling). Was thinking of blowing cellulose as dense as I could into that space, or foaming if I could afford it.

Do I NEED to provide ventilation if there isn't an air space?? I'm thinking a whole house fan type thing vented through the roof to help get rid of the hot air that rises, but I'm concerned about whether I need ventilation for ..... well...there isn't an attic, so I'm not sure what!!!!

How would I insulate under the eaves?? Blow that solid, too?? Block the sidewalls where they join the outside and leave the eaves open (haven't put up soffitt yet. If I leave the eaves open, do I use vented soffitt?)

So many questions......
Thanks!
CC

[GREENCOUNTYPETE]

i think you should leave at least a 1 inch air space between the roof decking and insulation to get the warm air to the top from the eves so it can be vented or i have seen them fill the hole void with that spray in foam but unless you do the foam i would leave space for the convection to remove the hot air

i had a house with a flat roof and it was insulated for the 8 inches between roof and drywall in the summer it would get very hot the heat had no where to go so it heated up the ceiling of the house it would take all night to get that heat out ran the ac a lot
the upstairs would be 90 and it wasn't that hot outside maybe 82

get the heat and moisture out thru good ventilation it will make your roof last a lot and longer and your house a lot more comfortable

[BobDFL]

I would vent unless you are going to use Foam, otherwisse you could have a moisture problem (a big issue here, because you get instant mold).

If you use foam, you want to make sure your soffits aren't vented to keep the roof sealed.

[Witterbound]

CC, timber frame homes put a decking on over the rafters, so the rafters will show in the house. Often that decking is 2x6 tongue and groove, so it looks nice from below. Then, on top of the t&g they add a vapor barrier, 2x6's on edge running the same direction as the rafters, and fill in between the 2x6s with solid foam insulation. Then on top of that they add 2x2's every 2 feet or so, running the opposite direction, onto which metal roofing is attached.

This is simiar to what you want to do . . . ..

[cc-rider]

The problem is that I already have the decking and roofing on. I can't change that now. I have 2X10's for rafters, OSB on top of that, then the felt and shingles. The only place I can add insulation at this point would be in the 2X10's.

The center beam is a tripled 16" LVL that hangs down quite a bit below the 10" rafters. I was going to box that in (LVL looks crappy), but am now thinking to just put a flat "ceiling" just under that. That will give me a space probably 3 or 4 foot wide at the "ceiling" that is flat....can use that to hang ceiling fans, run wires, etc. I will probably have to ventilate that, however, unless I blow it solid with cellulose. Actually, venting it might be good..... I can put the whole house fan into that and run it out the roof. I guess it'd be treated like a mini attic??

If you were to use 8 inch insulation, staple it to the bottom of the roof rafters, there would be a 1.5" air space between the insulation and the bottom of the decking which would be enough for circulation. When putting the insulation in, use a stick to "feel around" between insulation and roof decking to make sure you do get your airspace. Double sided insulation would be easier to install, I'm sure. Here we use styrofoam insulation baffles anywhere theres a tight spot, they give an inch or so air space. If you were to do this, you will need a vent ridge all the way across the top. Then you wont have to have a fan , the air will rise as it heats and escape through the ridge. As long as you have a place where air can get in at the bottom and out at the top, you're good to go.

[cfabe]

I agree with others, you have two choices, use fiberglass and do a continuous ridge and soffit vent, make sure to leave air space between the roof sheathing and the insulation, using the styrofoam forms if necessary. Second choice, use spray foam insulation (you can get DIY kits) and you don't need to ventilate. I would go with the foam if you can afford it, it gets you a higher R-value and 10" of insulation in the ceiling isn't a lot so you want to get the most R-value in there that you can. 9.5" of voam vs 8" of fiberglass. I would also suggest trying to figure out some sort of thermal break using furring strips to hang your interior paneling or hard foam board. Usually this is done on the outside of the structure but should also work on the inside.

[cc-rider]

I have the ridge vent, so am ok on that part (actually...it will be on this weekend). If there is a vent at the top, as zong says, won't that actually be venting out the hot air in the winter, too, which I want to keep IN? Otherwise, for the summer, it makes sense.

cfabe...how do I find DIY foam kits? I'm not even sure where to start looking! I have a Menards, Home Depot and Lowes nearby, but they are all clueless.

When you mention a thermal break, do you mean between the rafters and my ceiling wood (I'm using pine boards)? Would a very thin styrofoam, like they wrap houses with, work? The tri-fold stuff? Or do I need thicker?

[SolarGary]

Hi,

Here are some of the places that supply foam kits:
http://www.builditsolar.com/Referenc...htm#Insulation

They are listed down the page a little -- Tiger foam etc. ...

Some of these foams are nearly impossible to remove if you get them on things you did not want to. I'm a pretty dyed in the wool DIYer, but I'm not sure I'd try this in my living room. It might be worth getting an estimate from a commercial installer.

If you went with 10 inches of polyurethane foam (eg corbond) this would give you R67!!

Gary

[cc-rider]

Thanks Gary, I'll check those out. I sure know what you mean about getting it someplace it doesn't belong. Even the "window and door" foam in the can sticks to everything. I still have yellow "spots" on my skin. (Ok...I didn't wear gloves...they are too bulky!)

Since the house is still being built, now is the perfect time to foam it, if I were going to do that. What could I hurt? I don't have walls or floors yet....just windows and studs and subflooring. Can I hurt that?

Have you heard anything about a sprayed cellulose that is supposedly sticky, and they scrape it level once they spray it? I guess it was done about 10 years ago or so? The person that had it done can't remember the name of it, or who did it, so I can't find out any info! Sort of like blown in cellulose, but it came out sticky and formed a hard shell. I thought he was talking about foam, but he kept saying, "no....it was cellulose".

[BobDFL]

I would second on the foam if you can afford it.

I just finished a house (1 month ago) and had the Closed Cell Foam sprayed in during construction. It is R20 per inch and I have an average of 2.5" but it is as thisck as 4" in some places. So I've got R50-R80 in the attic and a semi conditioned attic storage at that.

I also second that it gets on everything and is tough to get off (I had to scape all the pocket door frames before the drywall was installed).

[cfabe]

What I meant by thermal break was to install a sheet of hard styrofoam (usually pink or blue 4x8 boards) between the ceiling joists and the interior finish. This technique is usually used on the outside of a house to break the thermal bridge of the framing, but I suppose it should work on the inside as well. If you don't want to use the styrofoam even just hanging the interior finish on firring strips running perpindicular to the framing would help & be cheaper.

The ridge vent will not be venting your hot air from inside the house because you will be installing a vapor barrier between the inside finish and the insulation to prevent air leaks & moisture infiltration into the insulation. The purpose of the ridge vent is two fold - it keeps roof temperatures down in the summer prolonging roofing life and reducing the houses heat load, and it keep the roof cold in the winter which helps prevent ice damming. If you use spray foam it is it's own vapor barrier, otherwise use plastic sheeting sealed with the proper tape.

Once you price the spray foam you will discover why it's not more popular. You can do a combination of both, using say 4" of spray foam and then a 6" fiberglass bat. This will give you the air sealing benefits of the spray foam without as much cost.

I have seen the wet sprayed cellulose on TV I think it is still in use, I don't know much about it though.

Insulation is a tricky part of building. There are many, many ways to go about it wrong. No offense, but since it sounds like you are not very knowledgable on insulation it may be worth getting some professional opinions. I'm not a professional myself though I did do a fair bit of research when considering building my own house. What I would do is either see if you can pay an insulation contractor to write you up a bid (they may do this for free but I think it's of questionable morality to solicit free bids on a job you intend to DIY) or see if your building inspector has any suggestions on best practices. You may also want to contact the insulation manufacturers as they often have good "best practice" information.

[cc-rider]

You are correct, I'm not an expert. That's why I research, research, research before I do anything. And ask my friends here.

I don't have a building inspector....which is both good and bad. There aren't any codes where I am building, so I've been able to do 'most anything I want. I'm OVER engineering it, so I'm not worried about structural problems....but it's the little details that drive me crazy. The things that I didn't know to even WORRY about!

Wish I had a friend that was a homebuilder, or whatever, that could just stop by and say.... "hmmmm....." but I don't. So I read whatever I can. I don't have a TV, so I'm not up on all the new construction stuff out there. My only exposure to "as seen on TV" is the aisle at WalMart.

[cc-rider]

Oops...another question for cfabe.

If I use foam, what purpose does the ridge vent serve? There won't be anything to vent, will there?

Also..... can I use SHEETS of foam somehow glued into the ceiling cavities? Spray the edges of the cavities with "great stuff" and then shove in styrofoam sheets that are cut to fit? The white stuff is cheap.

My walls are 6". If I put dense packed cellulose in those (using the fabric on the interior), can I put firring strips on the inside, put reflectix on top of that, and then install my interior wood or drywall, or do I need ANOTHER gap, so there is a gap on BOTH sides of the reflectix? Or is reflectix not all it is cracked up to be???

[crobar]

25 years ago we blew cellulose between rafters on our house. on the bottom of rafters for a ceiling there was tongue & groove pine, then 4" rough sawn oak rafters, roof sheeting & shingles on top side. Summer heat was totally unbearable. Following a cellulose contractor's direction, we drilled holes & blew cavities full. 25 years, absolutely no problems with anything, roof ceiling, etc. 4" not really enough, it's still warm, but that's just because of R-values; 10" would be plenty. Home Depot online sells a netting to hold cellulose in place until finish wall, ceiling goes on. I've ordered some haven't used it yet. I've heard Doug Rye, a radio host of a show on energy issues, endorse such an approach.

[crafty2002]

It sounds like you got yourself into a position I got stuck in. Started building before the planning was complete. I just took over a job someone else had started tho, LOL.

I had 3 houses side by side that had been started by, well I will leave that alone but I sure had a load of things to redo to pass code.
All three of them had cathedral ceilings like yours with 2x10" rafters.
I had to pass code and that took an air flow to a ridge vent and R-30 insulation.
You can't do it in 9.25". I screwed ecomony 2x4" studs to the bottom of the rafters, put the baffles at the top and bottom of each run, and stapled R-30 pink panther to the bottom of them and then covered with 1/2" drywall. That gave about 3 or so inches of open air flow and the R-30 insulation too.
I bought a cheap drill press because it was worth it for the speed of getting pilot holes and counter sink holes drilled. Worked a lot faster than hand drilling.
I marked one stud off at 16" OC and then used it to mark all the rest. I laid them in the floor on edge and used a framing square to get them all even and then just marked across 10 - 15 at a time where the marked were on the measured one.
Then I took about 5 or 6 of them and a couple of bar clamps and clamped them together. With a helper holding the ends I started drilling 5 or 6 holes with out haveing to move the stack but a little bit and then moved to the next line. It took a couple of hours I guess to drill both sets of holes. .
Oh, I used a long 1/8" drill for the pilot hole and then a 1/4" bit and drilled 2" deep so the screws would counter sink that much.
I used 3 1/2" decking screws to secure them in place. Before going up with them I layed them back out on the floor in rows and ran the screws up to where the heads were just above the wood.
That way when you are on the scaffold, (or ladder which ever may be the case) there is nothing to slow you down.
Get it in the middle and sink the first screw and it is already held in place. I had a screw gun which helps but a battery powered drill will do it, (albiet slower but it will)......
I was screwing them up as fast as Larry could hand them too me and cut the end ones to fit.
I think we put them up faster than we drilled the holes. Heck, I know we did.
That was one job I made some money on. Just set it up like an assembly line. Get them all marked, drill all the 1/8" holes, drill the counter sink holes, start screws, and install them.
I can't think of a better way out of where you are now and not cook your roof or cause sweating, which you want neither.
Use vented soffit no less than 1 for 3 solids and I like it either every other one or all of it vented,,,, and a full ridge vent.
Any run between rafters that doesn't have at least a small section of ridge vent and clear airflow will be where your roof fails first. The air flow is very, very, very, so very important.
Plus the amount of insulation is just as important. R-30 is pretty good but if I were building my on house like this now, with the energy the way it is, I would go with 2x12's plus the 2x4's and put R-13 unfaced and then the R-30 faced under it which would still leave an airflow.
Most of the heat that comes into a house is through the roof if you have any overhang hardly at all. That is where the sun is pointed at when it is kicking the hardest.
Most of the heat loss is also there during the winter.
What you do now will effect your power bill for as long as you own your house. Spend a few extra hundred dollars now and save thousands on top of thousands down the road.
The way energy is going up, a dollar you save today will be 10 dollars before you know it.
JMHO
Dennis

[Hooligan]

Originally Posted by cfabe

Second choice, use spray foam insulation (you can get DIY kits) and you don't need to ventilate.

Originally Posted by cfabe

The ridge vent will not be venting your hot air from inside the house because you will be installing a vapor barrier between the inside finish and the insulation to prevent air leaks & moisture infiltration into the insulation. The purpose of the ridge vent is two fold - it keeps roof temperatures down in the summer prolonging roofing life and reducing the houses heat load, and it keep the roof cold in the winter which helps prevent ice damming. If you use spray foam it is it's own vapor barrier, otherwise use plastic sheeting sealed with the proper tape.

This is where I get confused. If venting is not necessary when foam is used because foam is a vapor barrier in itself then why is venting necessary when fiberglass is used with an additional vapor barrier?

I have been following this thread hoping to learn because I am in a similar situation but with a couple key differences. My existing roof system is also a cathedral type that is set up as follows: from the outside in, metal roofing, plywood sheathing, layer of some sort of wrapped foam insulation, t&g pine boards, rafters. It is similar to what witterbound described.

It is also a single pitch roof if that matters.

I want do the same thing as ccrider is doing and add insulation between the rafters and finish by using t&g or shiplap pine nailed to the rafters.

I was thinking I could go with fiberglass batts and a good vapor barrier and be good to go. I also thought of ccrider's idea of using rigid panels cut to fit and foamed in.

Currently I don't have a problem with heat buildup in the summer or with excessive ice ----s in the winter. I was thinking that just adding more insulation would only help but you guys are giving me second thoughts.

Any advice would be appreciated.

[cfabe]

If you use spray foam you do not need a ridge vent. Since you already have it it won't hurt anything but it is not necessary.

You can use sheet insulation to fill the stud cavities, if you did this I am not sure whether you would still need a vapor barrier or not. I would suggest using the blue or pink board insulation over the cheap white - i think it has higher r-value. I think you may find cutting & fitting the foam tedious. I used pink board to insulate a basement and it was a pain cutting holes for outlets & etc, I think trimming every sheet would be a nightmare. With the time it'll take I'd just go spray foam. But if you are cost sensitive, go with fiberglass. Just be aware that you're not going to have as much insulaiton in the ceiling as new code construction would require. May not be a big deal depending on your heating plans.

[Hooligan]

Thanks cfabe.

There is no venting in place right now.

I hear you about trimming the panels. Thankfully there are long straight runs with very few cutouts needed if I decided to go that route.

I guess I am still confused on the necessity of an air space with fiberglass AND a good vapor barrier but not with foam which is it's own vapor barrier?

In other words, isn't a vapor barrier a vapor barrier?

I would love to just go with foam and be done with it and I will look into it but it would have to be applied in an already finished interior and I have some idea of just how expensive it is!

[cfabe]

The venting requirement doesn't have to do with how the vapor barrier is achieved. I think it's more a factor of with foam, you can't have an air space there since it's sprayed directly into the cavity. And I think since it is such a good insulator the need for cooling air agianst the roof decking is reduced. Sorry I can't offer a better explanation than this.

I'm not sure what you mentioend about the foam being installed wiht the finished interior but the foam comes in a fast-set and slow-set formula, one is designed for new construction and is sprayed in before the walls is finished, the other is designed to be sprayed into an existing wall cavity for a retrofit application.

By the way, have you checked out the forum at countryplans.com? It's an owner-builder website with a great forum & some very knowledgable professional tradesmen that post there regularly.