Insulate vaulted ceiling

[sammm]

My new garage has a hip roof. I am going to insulate the ceiling, but would like to leave it open and just fill-in the rafter cavities. I have soffit vents and 2 roof vents, so I can't just fill it up with fiberglass.

I was thinking about using rigid foam board, but I know it's R-value is low.

Any ideas? Thanks in advance.

 

[stingry]

I can't remember what they are called, but there are special "ducts" (can't think of the technical name) that staple to the bottom of the roof decking that allow air to flow from the soffit vents to the attic area. You can then put batt insulation between the rafters. This allows warm air to escape from the attic and be replaced with cooler air from the soffit vents. I am assuming that you will leave the area above the collar ties open with the finished ceiling being on the underside of the collar ties.

Cheers
Steve

 

[dragginbalz]

Baffles
Picture taken from Google

 

[hpw]

I was thinking about using rigid foam board, but I know it's R-value is low.

Any ideas? Thanks in advance.

Foam board has a higher R-value then fiberglass. If you can afford it, look into spray in place foam. $$$

 

[steel 35]

I priced out the Insulation then called a Insulation contractor
for a quote and the price to just have it done was only 150.00 more, then realized I didn't add for caulking, & beading around the windows and the cardboard vent pieces and staples so the cost would have been about the same and they were done in a few hours that is the only thing I didn't do when building my shop. And I didn't have to figure out how, I would recommend trying this and ask about doing it at the same time as the quote. In my area that is the only contractor I can trust. Had them back to work on the house later.

 

[sammm]

Thanks guys. When using baffles, do you put one in every cavity or just the ones that have the soffit vents?

@stingray - I was thinking of using the collar ties for light storage, just insulating the roof line and leaving the rest open.

 

[Qtip]

When insulating the under side of a roof, one will want baffels under the insulation too provide a continuous air gap for ventilation.

http://www.adoproducts.com/provent.html

 

[Qtip]

Every bay should have baffels. Also the baffels make your isolation more effective.

If it were my space. I would put baffels, then unfaced batt, then one Inch foam board spanning the joists. Taping the joints on the foam board makes the board a vapor barrier and thermal brake. Then put a sheathing of your choice.

 

[stingry]

Thanks guys. When using baffles, do you put one in every cavity or just the ones that have the soffit vents?

@stingray - I was thinking of using the collar ties for light storage, just insulating the roof line and leaving the rest open.

To do this correctly, you would need a ridge vent to exhaust the hot air from the baffles and to create an airflow from the soffit vents thru the baffles and out the ridge vents. That being said, When I remodeled our house many years ago, I opened up the attic and just put kraft faced batts between the 2x8's and sheet rocked, making a cathederal ceiling like you want. I didn't know better at the time. The only problem that I have seen was premature shingle failure (still lasted 20 years) on this portion of the roof, due to the heat I suppose.


Cheers
Steve

 

[mobetta]

the problem is that you dont have a continuous ridge vent, only 2 roof deck vents, so you need to either do a hot roof-unvented, or you need to leave the area above collar ties open, like an attic. also your hip design does not really lend itself to a vented roof design- how are the lower corners going to vent up?

I really think spray foam is best for you, forget the venting. asphalt shingles may not last as long.

you already have a radiant barrier, but what i did was rip 3/4" strips and staple up against the deck on each bay(lots of strips) then I stapled up silver bubble wrap insulation. not much true r value,but added a radiant barrier and defined the roof venting, as there is continuous venting up each bay. i have ridge vent and soffit vent.

 

[slickgt1]

Word to the wise. Do not spray foam your roof.
Couple of reasons here. First it will cost a **** ton to do, remember you need the thickness. So every inch is $$$$. Second, is that when your roof leaks, and at some point it will, the foam will block water from coming in, and it will stay trapped against the rafters. By the time you notice the leak, it might be a lot of damage to the rafters.

Get the baffles, glue them with construction adhesive, PL Premium would be my choice, then insulation. R30 or higher would be ideal. Can't tell from the pics if your rafters would be able to accept all that, height wise. Vent and soffit would be a good idea, but if you can't do it/ afford it, then you should be ok. I've seen them done like that, roof won't last as long as with vents, but it will work.

 

[sammm]

Thanks for all the feedback. I do have 2 low-profile roof vents up near the ridge, but they are both on the same side of the roof. The rafters are 2x6's...if I use insulation made for 2x4 walls (R-13), I'll have a natural air space between the insulation and roof deck. I just need to figure out how to span that across the ridge so the 3 other sides of the roof can breath (See pic for vents)

 

[dlenkewich]

Foam board has a higher R-value then fiberglass. If you can afford it, look into spray in place foam. $$$

Per inch, per the type of foam.

Just direct him where he can pick up some 5.5/6" rigid foam and tell him to bring his checkbook.

 

[Cobra6]

Here's another alternative - same principle - has anyone tried it?
Owens Corning Raft-R-Mate

http://roofing.owenscorning.com/homeowner/accessories/ventilation/raftrmate.aspx

 

[Qtip]

What kind of roofing do you have?

With a hip roof, I don't know if you can use ridge vents. But installing them would give you the best ventilation, and allow you to keep the collar ties open.

Or you could put a second row of collar ties in, above the existing ones but below your roof vents.

 

[sammm]

@dlenkewich - I know spray in foam is $$$ and probably not a good choice for my application.

@cobra6 - As far as I can tell, those are the same as the 'regular' attic baffles mentioned earlier. Did I miss something?

@qtip - I have standard asphalt roofing shingles installed. I could install a rdige vent, but I already have those other 2 in which should provide enough ventilation.

I may just bite the bullet and follow the roofline up to and across the collar ties. That will still give me a 10' ceiling in the center of the garage.

 

[stingry]

@dlenkewich - I know spray in foam is $$$ and probably not a good choice for my application.

@cobra6 - As far as I can tell, those are the same as the 'regular' attic baffles mentioned earlier. Did I miss something?

@qtip - I have standard asphalt roofing shingles installed. I could install a rdige vent, but I already have those other 2 in which should provide enough ventilation.

I may just bite the bullet and follow the roofline up to and across the collar ties. That will still give me a 10' ceiling in the center of the garage.[/QUOTE]

I think that would be the best solution! You could always put an attic door in the ceiling and use the attic for light storage if you used batt insulation.

Cheers
Steve

 

[mobetta]

you still will be wasting money on baffles and the roof will not vent in the corners. the way to properly vent a hip roof is w/ ridge vents up each hip, or to frame it out so the hip board is about an inch lower than the jack rafters.

look at your pic you posted. imagine air flowing up from the soffit vents. where does it go? it doesnt have any place to go, so no need to waste time and money on baffles. the only part that will be properly vented is the center, where the bays run all the way to the ridge, and then only if you make it like a little attic, and allow the air to flow out those 2 vents.

 

[Cobra6]

@cobra6 - As far as I can tell, those are the same as the 'regular' attic baffles mentioned earlier. Did I miss something?

I realize they look to be about the same, but they (the pink) seem to be a lot cheaper everywhere (almost half price of the others) - that is why I asked - I thought maybe I was missing something.

 

[sammm]

I realize they look to be about the same, but they (the pink) seem to be a lot cheaper everywhere (almost half price of the others)

I didn't check the pricing, but that's good to know. Thanks!

 

[ducati]

Baffles
Picture taken from Google

Those baffles will work awesome butted into 2x4's. I'm not sure what air those are going to flow.

 

[dirttracker18]

you still will be wasting money on baffles and the roof will not vent in the corners. the way to properly vent a hip roof is w/ ridge vents up each hip, or to frame it out so the hip board is about an inch lower than the jack rafters.

look at your pic you posted. imagine air flowing up from the soffit vents. where does it go? it doesnt have any place to go, so no need to waste time and money on baffles. the only part that will be properly vented is the center, where the bays run all the way to the ridge, and then only if you make it like a little attic, and allow the air to flow out those 2 vents.

The idea is that the air needs to flow from the soffit up and out the vents. The vents should be as high as possible on the roof.

From what I have read you should not put vents on each hip as they tend to allow flow between them instead of removing all hot moist air from all parts of the attic. The correct number of vents for the attic size can all be placed on one side of the hip. Usually away from view for asthetics.

The issue with putting batts all the way up is that the air can only get out where the upper vents are, thus only venting that space between those trusses.

Spray foam is costly but better to do it right the first time at a little higher cost. With batts and little air flow the condensation will sit on the batss making them virtually useless, like a wet sponge up there.

From my understanding anyway. I am not an expert but have done a lot of research into this for my garage build and to ultimately solve an issue with my cathedral ceiling

 

[sammm]

From my understanding anyway. I am not an expert but have done a lot of research into this for my garage build and to ultimately solve an issue with my cathedral ceiling

That's good info dirttracker. You have any pictures of your insulation install?

 

[dirttracker18]

I should clarify that the issue is with the cathedral ceiling in my house, not the garage. I used blown in insualtion above teh ceiling in my garage as it is cathedralled (is that a word?) but I have enough room to move above the ceiling and between there and the roof. I vapour barriered the entire garage and sealed well with tuc tape, then osb, then blown in in the attic.

As for the house, I bought it that way, messed up. 2 X 8 joists with batts, cheap vapour barrier below and metal roof above. The metal roof condensates and drips onto the batts meaning they are damp at best. I had to remove a section of roof to remove a chimney with rot around it. At that time I changed the batts in the area. they are once again damp 2 years later.

Two issues are at play here that will be fixed this summer.

1 Lack of proper venting. The roof does have a ridge vent but some of the soffits are blocked above the pretty aluminum soffit Some dodo put up the aluminum without removing the old plywood soffit. So no airflow.

2 Batts are not a good idea in a true cathedral ceiling (IMO) Spray foam will avoid the issues with condensation entirely in that the closed cell foam will resist the moisture to give any that does form a chance to dry up. This will also solve the issue of the cheapo vapur barrier that was originally installed, helping to seal up the ceiling very tight.

IMO rigid foam will work OK but does not seal like foam will. Plus with the expense of rigid, you might as well step up to spray and never worry about it again. Spray foam has an R value of about 6 per inch plus it's incredible ability to completely seal air movement.

Long term, I think if you plan to stay for any length of time then spray foam is the way to go. I wish I had used it in my garage, but I didn't.

I hope you find this useful and that I explained myself well. Feel free to ask questions but of course take my advise with a grain of salt as I am learning as I go

 

[sammm]

Thanks again dirttracker. I see you're up in Ontario so you have the cold to deal with. I'm in Texas so I have the heat to deal with.

If I were building a new house, I'd probably go spray foam. Since it's just a garage, I'm looking for the most economical way to go.

 

[dirttracker18]

Hmm
Never thought about that, Texas you say. For certain, insulating becomes an entirely different animal in areas that are concerned with heat instead of cold (although contrary to popular belief we do get heat here

I have even heard it argued that in areas of heat, the VB should be on the outside.

That being said I still contend that a good seal is more important then the insulation it self, insulation being a close second. I think I would still be concerned about moisture getting into the batts in your application but hopefully someone with some expertise from your area can chime in.

 

[Cobra6]

I looked at some of the Durovent baffles (pictured earlier)
http://www.adoproducts.com/duro.html at HD tonight.

There is not much to it - pretty flimsy - I think I am going to try the ProVent plastic ones http://www.adoproducts.com/provent.html

If you shop around - they come in packs of 100, so they don't really cost that much more.