I am trying to build a home after losing the one I lived in for 30 years to Hurricane Katrina. I really did not know anything! Trusted a fast talking “builder”, bought online plans, had to elevate 19′ in the air on this one. It’s a pretty coastal cottage that I enlarged the porches to 12′ wide on the front, and 14′ on the back. The problems started when the “builder” ordered 2×6 rafters instead of the 2×8 required in my house plans (the building supply salesman also had a copy of the plans). I knocked out a bedroom upstairs to make a two story ceiling in the great room. Since the spans turned out greater than code would allow for the ceiling distance I had to hire an engineer who specified doubling up the rafter’s for strength. I also eliminated the original ceilings to create a cathedral ceiling. I finally passed my rough-in inspection and it’s time for insulation. I am almost completely out of money so am trying to really do the least expensive insulation, but want at least R26 or R30 for my cathedral ceiling since power bills are going up. I only have the doubled up 2×6’s which also makes the spacing more narrow. I have heard about furring 2×4’s and placing fiberglas batts, Bibbs, cellulose, rock wool. Can I fur adequately with screws to hold sheetrock? ( Please scroll down to see the rest of this message below at the end of this page as I cannot bring it up with this text. Thanks for your input)
I am trying to get by with the least expensive but highest R value. I have a shingled roof and am worried about air flow and the shingles “cupping”. I am collecting bids, but so far some are rather expensive. I don’t think I can afford foam, but realize it may be the best. What are your thoughts. I just want a roof over my head, am living in a FEMA camper, have no job. The house has cypress siding, an open floor plan and is really pretty. I’ve just got to get over this insulation hurdle and am confused.
Edited 1/3/2009 2:30 pm ET by CypressTreeHouse
Replies
Go back and edit your post - go down to your last paragraph and start back spacing to take out all those ENTERs you did that make up all that dead space!
Now to your question... Do you have shingles up yet? If not, you could add a layer of foam up there on top to act as a thermal break and as a primary defence layer of insulation.
Is this a cold vented roof, or a hot sealed in roof?
Tu stultus es
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
Interestingly, I can't backspace the text. Don't know why. Yes, the shingles are already up. I appreciate your response. I don't think they are hot sealed. Just felt paper and nailed on.
Not vented. No roof vent.
If there are no vents, it is called a hot roof.
I think your best bet is to cross strap it with 2x4. Then put a layer of mesh up and strap with 1x3 under that. Fill all that space with chopped fiberglass as densly as you can.
It would be great if you could use cellulose, but you would need to take additional precautions against roof leaks before you could do that.
This is basicly a Mooney Roof, as we call these things here. The bulge in the mesh is manageble with the spacing granted by the last 1x3 strapping. You attache the drywall to this strapping.
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
What other measures would be needed to use cellulose?
John
Cellulose is a great, cheap, and green insulator. It's also a sponge that can absorb a great amount of water - likely long before you can even tell you have a problem.
IF the roof was built in a better than standard way - I.E. completely covered w/ I&WS or covered and taped with foam board.
OR
The Tyvec/Typr with the plastic rafter spacers installed creating air chutes that would drain water out the eaves as well as ventelate to a ridge vent, under which you can dense pac insulation.
If none of the above are in play (or maybe another option I haven't heard about yet) then there is a real risk of a minor water leak that would be completely missed until 1000 lbs of water logged insulation suddenly made an appearence in the living space... hopefully not over a crib or a visiting in-laws bed!
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
What other measures would be needed to use cellulose?
Don't let the others scare you away from cellulose. There's no reason you can't use it, though you might want to consider spraying an inch of closed-cell foam under the roof sheathing as a secondary weather barrier since it sounds like your builder did a bare minimum job on the roofing. In your climate, both bulk water and diffused moisture is going to be trying to migrate from outside to in, driven by solar heat on the roof.
And I would recommend against applying foam under the rafters as that would be a wrong-side vapor barrier in a cooling-dominated climate, and would trap any moisture that does leak through the roof in a big blow.
Better to cross-hatch the rafters with 2x3s or 2x4s as was suggested and, if you're going to use insulweb (the mesh) for containing the cellulose (rather than blowing it through the drywall by leaving 4"-6" gaps between courses with mesh or screen to blow through and then filling with strips of 3/8" drywall to create a flat seam), then the 1x3 strapping is a good idea to contain the bulge of the insulweb.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/4/2009 9:28 pm ET by Riversong
That's what I was thinking - he should have just ooooone more thing to back that roof before cells could be used. I was thinking more on top of the deck, but you are right, closed cell foam sprayed under the deck would do just as well.
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
Given that OP is a Katrina victim, then we are talking coastal MS, AL,or LA.
That's a hot-humid maritime environment where the coldest times of the year often have warm spells in them (such as happened yesterday & today).
What can work is to put the thermal break on hte inside, not the outside, as a majority-cooling environment might. So, the inexpensive answer could be to clad the bottoms of the rafters in rigid foam, then blow in cellulose behind that. That'd be 5.5" cells, then I'd go two 1/2" foam layers, laid perpendicularly, with drywall over that.
Would that be as good as metal roofing on battens over the roof deck to give a reflective barrier seperated from the framing? No, but, those are not options available to the OP. "Flying" a heavily insulated ceiling under the just-enough roof framing might be even better--but still well beyond what OP has for a budget.
Such compromises are a bummer. Going to present a head scratcher for th enext owner, too--but, that's the nature of housing. Even mediocre, highly-compromised houses can stand for a half century or more.Occupational hazard of my occupation not being around (sorry Bubba)
It being such a wet area AND him not having the greatest confidence in the builder, I'd be reticent to recommend cells up above. I had a neighbor who nearly suffered a broken face from a wet drywall bomb dropping on them in the middle of the night (adding on a 2nd story, no roof yet, bad tarp job, rain....= sudden ceiling failure in the bedroom powered by the overhead insulation. And cellulose will hold ALOT more water than the fiberglass).
If you built it, I'mm sure it would be fine... but we don't know anything about this guy who can't even read a plan correctly.
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
but we don't know anything about this guy who can't even read a plan correctly
Well, my impression was that OP has fired the "can't read plans" contractor and is stuck on their own dime.
And, OP could (probably) rent a blower and the cells to make this as cheap as possible. Same reason I said to use 1/2" foam in two layers. First layer is going to be under-pretty after blowing in cells. Running a second layer cross-wise to that gives a better shot at a workmanlike surface to show the BI before the close-up inspection.
Not that I'd wish rocking cathedral ceilings to broke neophytes--or most anyone else.
Now, if mister "2x6, 2x8, ques la difference, cha'?" contractor is to do the work, then all bets are off. Personally, Monseur le Hack and I would have had a boat trip somewhere to work out just how many sou that dimensional "uh oh" was going to get "squa' cha" and tuit suite. (And not just an all-paid weekend in Laq Charles, either . . . )Occupational hazard of my occupation not being around (sorry Bubba)
sounds like a job for clete purcellMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
That about what I would do, and often have done where the need is for good insulation and economical installation.I use 1" foam, taped seams, and then strapping over it to attach the sheetrock, with blown cells or chopped FG filling the 2x6 spaces. That yields about R26-27 Can bump it to 30 using 1-1/2" Thermax
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I bit the bullet on high-density spray foam, but I live in New England with high heating costs and where hot air rising to the underside of the roof causes major problems. The old part of the roof has full 2x6 (rough sawn) rafters in a vaulted ceiling. I went with 2x8's for the new.
With high density foam at R-7 per inch, you don't need to vent the roof (at least my building inspector approved it in advance) and you get a full vapor barrier, and can get almost to R-40 in a 2x6 rafter bay if you fill it. Then I used 1x3 strapping cross-wise to get more of a thermal break before the wall board layer. I now have a 4-season attic instead of a 3-month one (May, mid-Sept. to mid-Nov.). A 1-1/2" vent plus other insulation (R-3.5 per inch for fiberglass, cellulose, or low-density foam) gives (4" * R-3.5 = R-14). The worst part about non-spray-in is air leakage which is eliminated by foam.
(As a note, if you don't have perfectly parallel 14.5" rafter bays, forget batts. The installer won't get a good seal to the edge of the rafters if cutting the batts to fit.)
Material costs are expensive for foam, but labor costs are much lower - no detailed work before or after. And, at least in New England, cost payback in efficiency is quick, and no worries about mold. I know someone else here who had to cost concerns, but decided foam would be one of the few things he's doing that actually starts paying you back in a few years.
sorry to hear about your house; good luck,
---mike...
With high density foam at R-7 per inch, you don't need to vent the roof (at least my building inspector approved it in advance) and you get a full vapor barrier, and can get almost to R-40 in a 2x6 rafter bay if you fill it. Then I used 1x3 strapping cross-wise to get more of a thermal break before the wall board layer.
R-6.25 is a more realistic number for spray urethane, which would give you perhaps R-36 (still quite good). Good that you used a thermal break, otherwise the percent of R-value degradation is greater with higher insulation values, and in your case would have been no more than R-25.
But some building scientists recommend an inch of air cavity above any insulation - including foam - even without vents, to allow drying to the exterior of any moisture that finds its way in, which may likely be from the outside (no roofing is perfect forever).
And remember, it's not a vapor diffusion barrier that's important but an air barrier. In fact, it's often better to allow a roof to dry inwardly by diffusion. And taped drywall makes an excellent air barrier, as long as penetrations are sealed.
A 1-1/2" vent plus other insulation (R-3.5 per inch for fiberglass, cellulose, or low-density foam) gives (4" * R-3.5 = R-14). The worst part about non-spray-in is air leakage which is eliminated by foam.
Dense-pack cellulose can give R-3.8/inch or R-17 for 4.5" with vent. But cellulose functions well in a hot roof and a full 6" would offer R23 (R-18.2 with bridging), or whole ceiling R-24 with cross-hatched 2x4s and 7.5" cellulose.
(As a note, if you don't have perfectly parallel 14.5" rafter bays, forget batts. The installer won't get a good seal to the edge of the rafters if cutting the batts to fit.)
You're not likely to get a good fit even if the bays are uniform. An R-19 fiberglass batt tests to R=17 perfectly installed and R-13.7 in a typical installation. And fiberglass will do nothing to stop air movement, inhibit insects or rodents or prevent mold.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Hi Cypress Tree House,
I feel for you. I grew up down there and my parents had three feet of water in their house after Katrina... but they were luckier than some.
Riversong may have the right idea with the layer of spray foam on the bottom of the roof deck, followed by blown-in insulation. In addition to the air barrier it provides, it will strengthen your roof structure for the next big blow.
If that approach prices out to be too expensive for you, you can price out another foam option which is buying one or two inch thick foam panels, cutting them to fit loosely in your rafter bays (1/4 to 1/2 inch gap on all sides), taping the seams, and spraying foam around the perimeter of the foam panels, in the gap between the rafters and foam panels, locking them to the structure and sealing the gaps. This will be no fun working overhead and it might not be worth it considering the labor costs and the fact it is not as good as spraying the entire surface, but it is a possible option.
You need to pay particular attention to flashing details and any openings that might allow termites to gain access to the foam. I don't need to tell you about Formosans.
Mike Smith uses borate-treated foam panels called Performguard from R-Control that are not susceptible to termite or carpenter ant infestations.
Billy
Edited 1/5/2009 11:03 pm ET by Billy
To All,
Thanks so much for your ideas and help. Your comments are certainly being weighed seriously by me at this time. I apologize for not replying sooner. Have been out of town.
Now my carpenter (not the one that messed me up) has an idea. Wonder what you think. In Fine Homebuilding Magazine issue January 2008, #192, there is an article "Ceiling Remodel: From Flat to Cathedral" where the builder furs his rafter out and then uses 1" foam board. We wondered what the R factor may potentially be if we install 1" foam board 1" below the roof sheathing (perhaps using vent panels) in the rafter bays, then install 3" fiberglas batting (which would fill the 5-1/2" 2x6 rafter bays, and then cross strip the rafters with 2x4' boards every 24" then place another layer of 1-1/2" foam board between cross stripping. Does anyone know if this would work or what the R-factor may be?
Thanks,
Cypresstreehouse
Add the R's.
Polyurathane foam is about R6 per inch, fiberglass is about 10 for 3 inches, plus another inch of R6
About R22.
But if you are putting in chutes, then you can blow in cellulose and do better in the R value.
Tu stultus esRebuilding my home in Cypress, CAAlso a CRX fanatic!
Look, just send me to my drawer. This whole talking-to-you thing is like double punishment.
Thanks, Paul. I appreciate your help. I am also now looking into Polyisocyanurate board. Seems to have a really high r factor as well.
If you sandwich fiberglass between foam boards, you are putting vapor barriers on both sides of something that likes to hang on to water. I'm thinking major mold with no place for the water to dissipate.Also, won't 24" spacing be kind of wide for hanging sheetrock from the ceiling?The main benefit of spray foam over most other insulation is complete suppression of infiltration, that is, no gaps particularly where the insulation butts up against the rafters. Unless you seal the foam boards to the rafters, perhaps with Great Stuff, you're asking for air (which carries moisture with it) to sneak by and get trapped by the fiberglass.When doing spray foam with supplemental batts, the foam goes down and should be 2/3 of the total R-value, with unfaced batts on the interior side. You want to make sure things are warm enough to prevent condensation on the inside surface of the foam, and then have a place for moisture to vent if necessary. The spray foam would stop air migration, so there isn't new moist air being actively drawn into the rafter bays, so the moisture problems are reduced.If you go with your plan and use Great Stuff, get a Pro gun and use the Pro cans. The guns have a go/no-go trigger, and you dial in the bead size, and can get a perfectly even bead of whatever size you desire (within a range of about 1/4" to maybe an 1" or 1-1/2"). The material costs are cheaper, too. But it seems the Depot no longer stocks the Pro cans around here (Boston). Everyone who's tried my gun has been amazed, particularly compared to the consumer cans.I don't know the details about vapor barrier and condensation in New Orleans. Around here with very cold temps, we need lots of insulation to prevent reaching the condensation point on the inner surface of the insulation within the bays. That's why I filled the section with 2x6 rafters with high density foam, with no vent. Venting doesn't really change the underside of the roof shingles that much, and there would be too little insulation with a vent. Getting high density foam has shown no signs of snow melting on my roof (which could create ice dams) in the past few years.---mike...
Thank you, Mike, so much for your input. I will seriously consider all you and everyone has said. I am still wading through the best possible solution and all of your input has been invaluable in my making some kind of decision. This is a great component of the Fine Homebuilding web site.