Another Insulation Question-Vaulted 2x6 Ceiling

[JRay]

I have a 24x24 that has a 2x6 stick framed vaulted ceiling with some collars about mid way up. See photos for what I'm talking about...

How do I insulate and not completely empty my wallet (speaking spray foam)? Do I just go with r-19 batts with some styrofoam air vents? Is r-19 enough to make a huge difference? Do I screw some 2x2's to the bottom of the 2x6's to get more r-value?

Some info:
I live in Nashville. 2x4 walls will be r-13 faced batts. Summer: I don't plan to use a/c, I have a couple of ceiling fans. Winter: I have a 30k btu gas mr. heater.

 

[p_mori7]

I would do this:

- Styrofoam vent baffles from the eaves to above the collar ties.

- R19 fiberglass batts in between the rafters from over the top plate to level with the tops of the collar ties.

- R19 or R31 in between the collar ties, or blown-in in between the collar ties provided you put up some type of cieling.

By placing an insulated cieling attached to the collar ties, you lower the volume of space that needs to be heated or conditioned. Am presuming you have some type of venting along the ridge or up high on the roof deck.

 

[JRay]

By placing an insulated cieling attached to the collar ties, you lower the volume of space that needs to be heated or conditioned. Am presuming you have some type of venting along the ridge or up high on the roof deck.

It would certainly be more efficient, I just really hate to lose that valuable storage area above the collar ties (see pic for junk, ha). I know they aren't there for that, but as long as I don't get too much weight up there it really helps.

I do have a ridge vent, but I'm thinking a couple more roof vents couldn't hurt. I've thought about a powered attic vent as another option.

Maybe I could build in a loft or something for the storage.

 

[dirttracker18]

Spray foam in the vaulted portion at 5" giving you r30 and blown in for the attic portion. If you want to use the attic, spray up there as well.

Ceiling insulation is of particular importance if you plan to condition the space, which you are.

This is not a good place to cheap out. Do it right the first time and be happy with it.

 

[Yamaguy]

I have the same setup and plan to insulate this year. Do you still have to use the foam baffles if you spray insulate the valted area?

 

[dirttracker18]

I have the same setup and plan to insulate this year. Do you still have to use the foam baffles if you spray insulate the valted area?

There is some debate on the best approach. Some advocate a hot roof with spray foam. If batts, an air space is necessary.

IMHO I would put in the air space pieces and spray foam over it.

 

[Randy in Maine]

High density spray foam 5 1/2" thick. If there is no air let to move around, there is no need for any venting.

 

[dirttracker18]

High density spray foam 5 1/2" thick. If there is no air let to move around, there is no need for any venting.

Part of the idea of the air space is to allow the roof to cool in the summer. Ever been on a roof in the summer

The air space allows hot air to rise up and out the vents or ridge vent from the soffits that pull in cooler air.

The only hot roof evidence I have seen is from the spray foam industry. I love the stuff but if they are the only ones recomending hot roofs, I will take it with a grain of salt.

If someone has seen other evidence (aside from the spray foam industry or paid for by them) of the benefits of a hot roof I would love a link to look.

FWIW I have 6" of spray foam in my catherdral ceiling with an 1 1/2" air space. Easy to do when you spray from the outside though

 

[JRay]

I work for a homebuilder and have some pretty good connections, but even at that, the foam is going to be rather spendy for me (as I originally posted). I'm trying to get this done for more like $500, not $2500+. I'm mainly concerned with managing the summer heat, and I just feel like it MUST be vented properly to keep from baking me. Whoever thought of black shingles, anyway?

So, I'm thinking more along the lines of p_mori7...vent and batt with R-19 and call it a day. My main concern with ceiling, is losing my "storage space" above the collar ties.

Ok, I see your points about the spray foam now...Its only money, I can always make more, right?

 

[dirttracker18]

I work for a homebuilder and have some pretty good connections, but even at that, the foam is going to be rather spendy for me (as I originally posted). I'm trying to get this done for more like $500, not $2500+. I'm mainly concerned with managing the summer heat, and I just feel like it MUST be vented properly to keep from baking me. Whoever thought of black shingles, anyway?

So, I'm thinking more along the lines of p_mori7...vent and batt with R-19 and call it a day. My main concern with ceiling, is losing my "storage space" above the collar ties.

Ok, I see your points about the spray foam now...Its only money, I can always make more, right?

For sure it depends on your needs. The batts will work and provide some reprive from the heat.

Just think long term first. If that will serve your needs then great. if there is a possibility of needing better one day, now is the time to do it.

 

[Randy in Maine]

Suggestion:

Talk to your insulation guy. Usually they will suggest applying about 2" of high density foam directly on bottomside of the roof sheathing to prevent a cold area where moisture from warmer air can condense creating a moisture problem. The foam also provides for a great vapor barrier and an infiltration barrier even if it is only a couple of inches thick. Some people like to put fiberglass or cellulose "below" the foam. Ask your guy.

In my case (my living room in the house) my only option was to fill the whole cavity with high density foam. My roof rafters are just 2x6s and filling them up with foam also added to the overall strength and stability of the roof. It also gave me about a R value of 36 or a little better. No ventilation up there.

Previously my roof had R-19 batts installed with a plastic film vapor barrier. It was too cold in the winter and too hot in the summer. When it came out it did not not show much evidence of water from condensing or from infiltration.

My roof is also black (or pretty close) asphalt shingles and ice/water shield over the whole thing and the winter cold and the summer heat do not come through the vaulted ceiling. A lot quieter also.

Concerning the "hot roof thinking".....(from http://www.applegateinsulation.com/Product-Info/Technical-Pages/249234.aspx)

"Lastly, myth has it that the ventilation serves to keep shingles cool in summer. This was debunked by a study discussed in the November 1990 issue of Energy Design Update (EDU). In a section entitled "The Non-Effect of Roof Ventilation on Shingle Temperature," they discuss the findings of an experiment conducted by the University of Illinois Small Homes Council which found that:

Contrary to common belief, attic or roof ventilation in cathedral ceilings appears to have little or no effect on shingle or sheathing temperature.

Furthermore, EDU reports, tests at the Florida Solar Energy Center showed no more than three- to five- degree difference in sheathing temperature between vented and unvented roofs…" and "although ventilation appears to have little effect on roof surface temperature, it may have a significant effect on attic air temperature and heat gain into the house."

My insultion guy also told me in person that the "hot roof thinking" was bunk so I never worried about it.

 

[p_mori7]

So, I'm thinking more along the lines of p_mori7...vent and batt with R-19 and call it a day. My main concern with ceiling, is losing my "storage space" above the collar ties.

You don't have to lose your storage space...

R19 will not fluff up higher than your collar ties...so...you can frame in an access hatch...then lay down some perpendicular 2x8's to walk on top of the insulation...

whatever is up there will not be in the conditioned space.

 

[Autorotica]

Look around for used roofing foam panels. They can be bought for about $0.25 per board foot in smaller quantities. This would be an excellent application for this alternative.

Chris

 

[kngelv]

I'm looking at a similar situation. The cost of spray foam is more than I'm willing to spend. I have soffit and ridge vents. I plan on using baffles and polyencapsulated batts.

James

 

[toyotadriver]

I have an idea unique to your shop.

Put in the vent baffles and then use the thickest fiberglass insulation that you can. With the foam baffles, the R19 will compress a little but most likely will be ok. Then, cover the fiberglass as you can afford it with foam sheets attached to the rafters. In my area, 1.5 inch foam is the cheapest for the square footage but I'd recommend trying to get 2 inch. Then, cover that with OSB or drywall.

That way, you'll still vent the roof, have just shy of R30 in your roof, and still be able to use your storage space.

 

[JRay]

I have an idea unique to your shop.



Put in the vent baffles and then use the thickest fiberglass insulation that you can. With the foam baffles, the R19 will compress a little but most likely will be ok. Then, cover the fiberglass as you can afford it with foam sheets attached to the rafters. In my area, 1.5 inch foam is the cheapest for the square footage but I'd recommend trying to get 2 inch. Then, cover that with OSB or drywall.



That way, you'll still vent the roof, have just shy of R30 in your roof, and still be able to use your storage space.

That's a great idea. I was worried about r-19 not being enough...this way I can get that far and then build on top of it, as needed. Thanks for that suggestion.

 

[toyotadriver]

The R10 or so with foam sheets will be better than just the R19 because the R10 is always R10 with foam. Plus, you've seriously slowed the thermal conduction through the roof rafters (heat flowing out in the winter and heat flowing in during the summer).

If you had regular trusses, it would be an issue. But, yours should be easy because of the way it's been done. It'll be a bit of a pain to cut the foam around the collar ties but it'll be worth it.

Another option for the roof vents would be to build your own with at least 1 inch foam sheets. Measure the inside width between the rafters and then cut it 2 inches wider. Then, slice the edges of the foam sheets and fold the 1 inch wide strips over, creating a gap the thickness of the foam sheets you've used. Then, use R13 fiberglass between the rafters and cover that with foam sheets.

 

[volleyball]

That would produce a lot of waste as the extra 1" will mean you only get 2 pieces out of a 4x8 boards. You could use scrap blocks to be a spacer. you don't need an inch gap.
I think putting the fiberglass in first and cover the whole area with foil faced foam, say 1", would give the most bang for the buck. It could even be done in stages. the radiant barrier will go a long way in comfort. Plus easier to seal than just the fiberglass.