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Old 05-27-2009, 03:07 PM   #1
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roofing and insulation question


Hi,

It's heating up here in TX and I have doubts that my and my tenant's AC are going to be able to keep up. It's a side by side single story duplex. Since last year I installed new condensers, eave vents, and shot Lomit II radiant barrier over the complete surfaces of the roof sheathing and the upper trusses. I'm still not overly confident though because of the complete sun exposure I get here, and the modest size of the AC systems (2 ton).

So I'm thinking about adding to the insulation which is currently up there. What is there is blown cellulose which has compressed down over 20 years to about 3". I'm considering blown fiberglass which I'm told is very efficient and less itchy to work with than pink.

That all said, here's my problem, or what I think may be a problem. My rafters are 24 on center. I already have noticed that many of my ceiling drywall panels are bowing a bit in the center from lack of support. To get much benefit from this job I'd need to blow an additional 8-12" of this stuff, and I'm worried about how that will affect the ceiling long term.

I've considered nailing in 2x4 studs between the rafters in the center of each panel so that I can drop a few extra drywall screws to give them all added support. Although I'm handy enough to do all of this, I'm a no nothing when it comes to design and construction. I'd like to ask the experts whether this is a bad idea? Are the joints designed such that they simply aren't meant to be connected to each other in this manner?

Also, does what I'm contemplating even make sense from a practical perspective? On my side of the property it wouldn't be terribly hard because I'm in the process of scraping off the old popcorn and it won't add much work to add the necessary screws. However my tentant's side already had the ceiling scraped and textured, so it will result in days of touch up and painting.

Am I being too paranoid about this?

Thanks for the thoughts!

Eric

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Old 05-28-2009, 07:43 AM   #2
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roofing and insulation question


Adding insulation is never a bad idea, if done correctly. Unfaced batts or additional blown is are both good ways to increase insulation. Most codes now require min R 38 in new construction, which is considerably more than 3". Don't block attic ventilation. Do block all holes, openings, etc., that are in the attic floor. One negative about 12"+ of insulation, we often use attic space for storage. That insulation usually makes that unusable space. Reinforcing the ceiling is generally not needed, insulation is very lightweight.

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Old 05-28-2009, 11:08 AM   #3
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roofing and insulation question


As Bill said, you do not need to reinforce the ceiling due to the added insulation. The fastening pattern, if done correctly the first time, should be fine.
The comment about the, " modest size of the A/C's " is a little puzzling. Is that an inference that the units were undersized for the space? If these are old or undersized units, the energy cost would be reduced by updating these.
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Old 05-28-2009, 12:19 PM   #4
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roofing and insulation question


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Originally Posted by Ron6519 View Post
As Bill said, you do not need to reinforce the ceiling due to the added insulation. The fastening pattern, if done correctly the first time, should be fine.
The comment about the, " modest size of the A/C's " is a little puzzling. Is that an inference that the units were undersized for the space? If these are old or undersized units, the energy cost would be reduced by updating these.
Ron
Ron,
The air handlers are 3 years old, and the condensers are only a year old because both of the 3 year old ones failed after a short time due to overwork. Both are fairly efficient and rated for 2 ton. Going by square footage alone it's the perfect size however the cooling challenges are here are immense, brown roof, full sun with all day exposure and no natural shade, and for at least 3-4 months we'll be dealing temps up to 105.

I've done as much as I can to improve the attic by installing vents and turbines, and adding the barrier. Ridge vents won't help because there aren't that many ridges, or maybe I should say there are too many to be feasible. More insulation seems like the only other thing to try.

I'm not sure what you mean by the correct fastening pattern. There only seem to be so many fasteners possible when the rafters are 24 on center. Part of the problem is that they are nailed rather than screwed. I've noticed that I can push up on many of them slightly which seems to indicate that the nails are slipping out. I can replace them all reasonably easily on the un-renovated side since my ceiling is already scraped. The other side, not so much.
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Old 05-28-2009, 12:34 PM   #5
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roofing and insulation question


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Originally Posted by Just Bill View Post
Adding insulation is never a bad idea, if done correctly. Unfaced batts or additional blown is are both good ways to increase insulation. Most codes now require min R 38 in new construction, which is considerably more than 3". Don't block attic ventilation. Do block all holes, openings, etc., that are in the attic floor. One negative about 12"+ of insulation, we often use attic space for storage. That insulation usually makes that unusable space. Reinforcing the ceiling is generally not needed, insulation is very lightweight.
Bill,

I won't be using the main part of the attic for storage at all. It's really a minefield up there. All of the electrics are just laying on top of the rafters, and all strung dead tight so they are pretty much everywhere. There are recessed lighting cans, and a rather chaotic joist system that has one central peak which quickly slopes down in all directions. I am going to refrain from adding a lot of insulation to the area of roof over the garage and am decking that out to use for a bit of storage.

I hear what you are saying about the vents. They took a lot of work to install so I certainly don't want to block them. I'm wondering what I should do about the recessed lighting cans. The ones I bought for my unit are insulation proof so I guess I can just bury them, however I don't think the ones the previous owner put in are. I'm not sure what the concern is; is it a fire hazard to have them buried? Do they need air flow?

My roof has a very shallow pitch, like 1 to 4 or something. If I blow a foot of insulation that will pretty much be right up to the sheathing near the edge. With the exception of the joists that have the vents installed, is it okay to have it that close to the roof?

My fear about weight is that the cellulose that's up there already seems really dense, like it might have been 8" or more at one point and has compressed. I wonder if I should just skip the blown fiberglass and go for batting. It will be more expensive and harder work, but I don't think it compresses like blown stuff would.
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Old 05-28-2009, 01:55 PM   #6
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roofing and insulation question


If you push up on the sheetrock and see nail or screw pops, then the sheetrock was not fastened properly. Any place you see this, you need to put two drywall screws, one on each side of the popped item, at least 1" away from the offending fastener.
By proper pattern, I mean there should be so many screws in the sheet so far apart. Generally 12" apart in the middle of the sheet(the field) and 6" apart at the edges.
If the other side needs this to be done to fix this issue, then do it. Spackle and repaint. It doesn't make sense not to. Who knows, if they had the ceiling worked on and had the same issue with the board movement , it should have been addressed at that time. Roller pressure on the ceiling would have popped nail after nail when the paint went on if they didn't fix the issue.
A/C's are not just sized for the sq ft of a structure. The environmental conditions also need to be taken into account. Sun exposure, # of windows, actual R value in the walls and ceiling, etc... The fact that the first set died tells me that they are too small for the job. You should have a competant HVAC guy come and accurately calculate the correct size you need. I wouldn't even show him what you have until he completes the calculations and tells you what you actually need.
This way when this set goes, you can get the correct size units for the job.
In the attic, all the rafter bays need the baffles that allow air flow, not just some of them.
The blown in cellulose will be a better insulator then the batts and with a correctly fastened ceiling, you should have no issue.
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Old 05-28-2009, 01:57 PM   #7
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roofing and insulation question


Your local home store will carry insulation baffles. These thin plastic channels are stapled to the underside of the decking and preserve the 1" of flowable airspace for soffit to peak ventilation as you place insulation batts against them. They will be no fun at all to retrofit on a 4/12 or lower pitch roof from inside the attic. I installed about 60 of them rafter bay by rafter bay last year during an insulation project. My vertibrea are still resetting.
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Old 06-04-2009, 10:49 AM   #8
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Originally Posted by Ron6519 View Post
If you push up on the sheetrock and see nail or screw pops, then the sheetrock was not fastened properly.
Yep, that's what I'm seeing. I just assumed that nails don't hold that well over time and that they eventually sag. Did they use the wrong nails? In any event, I have been using screws to bolster them which I feel have a more positive connection.


Quote:
A/C's are not just sized for the sq ft of a structure. The environmental conditions also need to be taken into account. Sun exposure, # of windows, actual R value in the walls and ceiling, etc... The fact that the first set died tells me that they are too small for the job. You should have a competant HVAC guy come and accurately calculate the correct size you need. I wouldn't even show him what you have until he completes the calculations and tells you what you actually need.
Oh I definately agree. It's amazing how many "competent" technicians don't seem to know this though. I've dealt with 3 different companies at this point and only at the very end did one guy shake his head and say, "I guess you need a bigger one". I'm not a "competent" technician and I know it, at least I know it now. Finding a competent guy in a place that has such high demand as TX is unfortunately a real challenge. There are a lot of AC Gypsies.

I'm really hoping that adding the insulation will bring the house within range of the systems that are installed. I'm getting close. After shooting the Radiant B the "maintainable temp" dropped by 3-4 degrees. She'll cruise at about 76 now without much strain. Problem is that's not good enough to meet code. If a tenant wants to pay for the juice then you have to bring them down to like 72. My last tenant would set it for 65 which is why it froze and blew up.

Quote:
In the attic, all the rafter bays need the baffles that allow air flow, not just some of them.
Sorry this confuses me. Are you saying that I should have a vent for each rafter bay? If not, and there is no vent in a particular rafter then what is accomplished by allowing air flow in a dead zone that wouldn't be admitting air flow? Just curious...

Thanks for the input!

Last edited by everyman; 06-04-2009 at 10:53 AM.
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Old 06-04-2009, 10:55 AM   #9
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roofing and insulation question


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They will be no fun at all to retrofit on a 4/12 or lower pitch roof from inside the attic. I installed about 60 of them rafter bay by rafter bay last year during an insulation project. My vertibrea are still resetting.
Oh wonderful. It took me weeks to recover from spraying RB down into my eaves. I may just have to break down and pay someone for this job.
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Old 06-04-2009, 01:51 PM   #10
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roofing and insulation question


"Sorry this confuses me. Are you saying that I should have a vent for each rafter bay? If not, and there is no vent in a particular rafter then what is accomplished by allowing air flow in a dead zone that wouldn't be admitting air flow? Just curious..."

The soffit area is generally a common area and not isolated rafter bays. If the soffit material is perpendicular to the house wall, the triangular shape is a common area that shares air space. The air enters the soffit vents and can elevate through any and all rafter bays, as long as there's a clear path to the ridge. The baffles give it that clear path. It's more effective to have continuous soffit vents as it increasese the air flow to the ridge vents. You really want to keep the super heated air under the sheathing from lingering in that closed space.
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Old 06-04-2009, 08:23 PM   #11
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roofing and insulation question


Most of my rafter bays are isolated
The rafter ends were cut perp to the ground & bottoms perp to wall
The soffit material is up against the bottom of the rafters
So I use continous soffit vents
I've seen many houses made this way
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Old 06-08-2009, 05:46 PM   #12
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Most of my rafter bays are isolated
The rafter ends were cut perp to the ground & bottoms perp to wall
The soffit material is up against the bottom of the rafters
So I use continous soffit vents
I've seen many houses made this way
Unfortunately I think that mine are as yours. I'm going to double check but I'm pretty sure it's the case because when I was cutting the holes for the vents I had measure carefully to avoid hitting something. I'm not certain whether it was the rafters (are those the horizontal members?) or the diagonal members (joists?).

I had considered the continuous vents but was dreading the thought of trying to cut a continuous hole. The face of my soffits are masonite and not all that sturdy, and also a pita to cut especially where they pass over a wooden member. I instead put in the wide vents every 4-6 feet. Ultimately I think they are working about as well I could hope for. The spot readings I've taken on sunny days are generally within a few degrees of outdoor ambient. Unfortunately here in Austin that can mean 105 which isn't exactly balmy.

I'm heading over to the depot to see if I can find those guards. Also I'm hoping blown fiber. I was led to believe that they are selling it now but am only seeing blown cell as being in stock for my store. I'd rather go for the fiber. I'm hoping that it will be lighter and compress less over time.

Last edited by everyman; 06-08-2009 at 05:50 PM.
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Old 06-08-2009, 06:40 PM   #13
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roofing and insulation question


The horizontal wood you were hitting was the surfaces the soffit material was nailed into.
I still maintain if you have a fascia board on your rafter tails you have an area that is common to all rafters in that run. And that common area will shoot hot air up the bays. The smaller areas will undoubledly benefit from continuous ventilation to the ridge through a linear vent system in the soffit.
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Old 06-08-2009, 08:16 PM   #14
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roofing and insulation question


When I added insulation to my attic I added 3" of blown in between the joists to bring it up level to the top then rolled batts perpendiculer over top. Just the weight from the 3" of celluose and the little weight of the fiberglass batts on top of the joists caused some areas of my ceiling drywall to sag a little and I had to add drywall screws, my house was built in 1960's with 16 OC joists, Im sure the the fastening pattern isnt up to current code standards like Ron mentioned and thats why it sagged a bit. I also added them pink foam baffels in bewteen the rafters, what a PITA Defibnately noticed a difference with heat in the winter and staying cooler in the summer.
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Old 06-11-2009, 09:11 PM   #15
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Just the weight from the 3" of celluose and the little weight of the fiberglass batts on top of the joists caused some areas of my ceiling drywall to sag a little..
Yep this is what concerns me, and I was planning on adding about 12" to bring me up to R20+. I can only pray that the previous owner actually added some screws before he started retexturing the ceiling else I'm going to have a lot of extra work to do.

Nice shots, what are those big old blue cans? Are they just being used as J-boxes?

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