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Old 07-14-2008, 09:58 AM   #41
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Oh yes, thats another bad idea. A bunch of older homes in a neighborhood near here seem to have all been attacked by the same roofing company who put in some kind of composition/clay tile on homes that formerly had asphalt shingles.

Ripple and bow.

I have to admit having lived in a house with a concrete tile roof that the idea of three or four tons of rock hanging over your head is a mite concerning.
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Old 07-14-2008, 11:50 AM   #42
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I have to admit having lived in a house with a concrete tile roof that the idea of three or four tons of rock hanging over your head is a mite concerning.
On a fault line.

But, hey, at least California outlawed those attractive, lightweight, affordable dangerously flammable cedar shakes...
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Old 07-14-2008, 04:54 PM   #43
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Believe it or not, you can still install them in my county, which has one of the highest fire rates around.

Many of the local cc&r's restrict homes to either shake or concrete tile, no alternatives. Obviously you dont need to replace a concrete roof for at least 50 years, and putting tile on a non sheeted skip lathe roof would be a very bad plan.
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Old 07-18-2008, 09:15 AM   #44
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Update: The radiant barrier is installed. I achieved about 80% coverage, the remaining 20% would require taking down the A/C ducts and due to the layout of the attic and all the insulation I've already crushed, I'm unwilling to do this. The attic still gets quite hot, although with the variations in outside temp and lack of pre-foil baseline data, it's hard to make an accurate comparison.

I purchased the foil from Radiant Barrier Foil Insulation Do-It-Yourself Radiant Barrier Tips. It was the best price I found online (with local pickup in DFW) and the product seems to be high quality. I can't tear the foil with my hands, it's quite sturdy.

In retrospect, I should've started this project with the attic ventiliation. This weekend I'm going to check the soffit vents for obstructions (I suspect they're clogged with insulation). My understanding is that for a ~2000 sq ft attic area, I should have a ventilation ratio of 150:1, or about 13 sq. ft. free vent area (FVA). I have two 9 inch round vents at the peak of the roof which together give me about 1 sq ft FVA, and 10 4x16 inch soffit vents (28 sq in FVA each) which gives me about 2 more sq ft FVA. So I have a total of 3 sq ft of vent area when I should have 13...are my calculations off somewhere or did they build the house with way too little attic ventilation? If anyone has any thoughts on this, please share.

I guess the next quickest/cheapest way to increase ventiliation would be to replace the 4x16 soffits with 8x16 soffits. I probably need to add a few more vents at the top of the roof, but that may be more work than I'm willing to take on.
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Old 07-18-2008, 09:42 AM   #45
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Ideally, the free vent area should be evenly divided between upper and lower vents.
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Old 07-18-2008, 11:22 AM   #46
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I have two 9 inch round vents at the peak of the roof which together give me about 1 sq ft FVA, and 10 4x16 inch soffit vents (28 sq in FVA each) which gives me about 2 more sq ft FVA. So I have a total of 3 sq ft of vent area when I should have 13...are my calculations off somewhere or did they build the house with way too little attic ventilation? If anyone has any thoughts on this, please share.

I guess the next quickest/cheapest way to increase ventiliation would be to replace the 4x16 soffits with 8x16 soffits. I probably need to add a few more vents at the top of the roof, but that may be more work than I'm willing to take on.
The 9-inch vents actually give you about 0.44 sq. ft. FVA. Area = Pi X radius squared = 3.14 x 4.5 X 4.5 = 63.58 sq. in/vent X 2 vents = 127 sq. in.

127/144 sq. in. per sq. ft. = 0.88 sq. ft. This must then be reduced by any obstructions like screening that are in the way. Typically, a 50% reduction is used. So 0.88/2 = 0.44 sq. ft, unless there is no screening or louvers in the way of the air flow. If they are turbine vents, forget all of this because they actually extract air depending on local wind speed.

A 1:300 ratio may be adequate. See BSD-102: Understanding Attic Ventilation — buildingscience.com

So 6.5 sq. ft. might be adequate, but you are still way below that. Some building codes specify 1:600 - perhaps your house was built under that. And, as HFWR said, it should be equally distributed between soffit and peak.
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Old 07-18-2008, 11:41 AM   #47
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Patrick is right--the "net free area" of the vents isn't just the area of the hole in your roof, because the screening and louvers really cut down on flow of air. Look at the vents in the home stores, the packaging will tell you how many sq inches/sq feet of vent area each one provides.

Yes, you have far too little ventilation. You aren't overlooking anything, like gable vents or ridge venting, are you?

Net Free Vent Area should equal at least 1/300ths of your ceiling area IF you have a very good vapor barrier in your ceiling. If you have a typical vapor barrier, 1/150th is sufficient. These are minimums, and help to assure that homes in cooler climates won't get excess moisture buildup/condensation in the attic. In the DFW area, I'd think the major issue is getting that heat out, and that more is better. I'd want at least 1/150th if I lived in Dallas. Of this total amont, 1/2 should be high, 1/2 should be at the soffits. Be sure the air can flow freely from your soffits into the attic and s not blocked by insulation/etc in the attic.

This ventilation will probably help a lot.

Some folks like the turbines, but I'm not a big fan due to their appearance and that fact that I've experienced more water infiltration from them than with typical "turtle vents (or "hat vents"). Just my opinion.
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Old 07-18-2008, 12:14 PM   #48
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This weekend I'm going to check the soffit vents for obstructions (I suspect they're clogged with insulation)
Ladder and a leaf blower will fix that. Just keep the air flow parallel to the roof line so you dont blow all the insulation away from that area of the attic floor.

In a perfect world they baffle the soffit vents with a piece of plywood a couple of feet up the rafters. Apparently soffit vents arent able to figure out the plywood.

I'm very sorry, the coffee is a little strong today.
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Old 07-19-2008, 07:41 AM   #49
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Ideally, the free vent area should be evenly divided between upper and lower vents.
The house I had in Florida only had soffett vents, but they did add up to the minimum required sq/in for the house size. I cut the shingles at the ridge off and installed ridge vents. I was surprised by the amount of decrease in attic temperatures and electric bills for the summer.
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Old 07-19-2008, 07:46 AM   #50
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Yeah, soffit vents only wont do you any good. Nowhere for the air to go. It might have had some eyebrow vents or gable vents at one time but a prior homeowner might have removed them or covered them up when doing a roof or siding job.
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Old 07-19-2008, 01:03 PM   #51
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Some folks like the turbines, but I'm not a big fan due to their appearance and that fact that I've experienced more water infiltration from them than with typical "turtle vents (or "hat vents"). Just my opinion.
Another alternative, especially in Texas, is solar-powered exhaust fans. We've been through hurricane-force rains with them and had no intrusion problems.
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Old 07-19-2008, 05:07 PM   #52
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I couldnt get mine to turn enough air to make it worthwhile. I even added a second panel.

On medium warm days it was sufficient. On july/august days it just delayed the onset of flamethrowing heat in the attic by an hour or so.
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Old 07-19-2008, 05:30 PM   #53
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I couldnt get mine to turn enough air to make it worthwhile. I even added a second panel.

On medium warm days it was sufficient. On july/august days it just delayed the onset of flamethrowing heat in the attic by an hour or so.
Yep, no substitute for large area venting from the eaves to rooftop. Most solar fans are about as effective as peeing on a volcano. Even in the northeast in August.
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Old 07-19-2008, 06:27 PM   #54
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Yeah, soffit vents only wont do you any good. Nowhere for the air to go. It might have had some eyebrow vents or gable vents at one time but a prior homeowner might have removed them or covered them up when doing a roof or siding job.
I figured a previous owner did away with the ridge vent when a new roof was put on. I couldn't find anyplace else that looked as if it had a vent, except the ridge where the roof boards didn't meet.
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Old 07-19-2008, 06:33 PM   #55
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Yep, no substitute for large area venting from the eaves to rooftop. Most solar fans are about as effective as peeing on a volcano. Even in the northeast in August.
I've installed thermometers in the attic. One of these days, I'll go up there and disconnect the solar gable fan and see what the temperature does, if anything.

I'm also looking forward to watching what effect the soon-to-be-added ridge vent has.
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Old 07-19-2008, 07:24 PM   #56
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I've installed thermometers in the attic. One of these days, I'll go up there and disconnect the solar gable fan and see what the temperature does, if anything.

I'm also looking forward to watching what effect the soon-to-be-added ridge vent has.
Yes, definitely interested in results. No substitute for real world numbers.
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Old 07-19-2008, 09:15 PM   #57
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I figured a previous owner did away with the ridge vent when a new roof was put on. I couldn't find anyplace else that looked as if it had a vent, except the ridge where the roof boards didn't meet.
If it was about a 1.75-2" space then yeah, you probably had a ridge vent and the roofer was an idiot. Theres usually a little space between the sheeting at the ridge even when you dont have a ridge vent.

But you had to have had something or the house wouldnt have passed code.

Besides ventilation, that may have created some condensation/moisture issues in the attic.

Thats the one thing I was more or less pleased with as far as the solar gable fan was concerned...at least i was getting some powered ventilation on any sunny day, helpful for moisture removal.
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Old 07-19-2008, 09:34 PM   #58
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The home we're living in now has a "whole house fan" mounted in the ceiling in the central hallway area. We've had temps in the 90s recently and have been able to keep the house quite comfortable by starting the fan and opening the basement windows and basement stairway door. The negative pressure developed by the fan pulls outside air into the cool basement and up the stairway. It flows through the main living areas and is finally blown through the fan and into the attic where it exhausts out the gable and roof vents. It seems to be the next best thing to air conditioning and definitely moves a lot of air through the attic too.
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Old 07-19-2008, 09:47 PM   #59
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With only one panel, our solar fan didn't help a lot. When I added the second panel, it seems that it performed much better...didn't actually measure the temp though. This is in the lower attic that is maybe 600sq ft of ceiling max (only the master bed and master bath). I'm satisfied with it.

When I get around to it, I'm adding more cellulose in the upper attic, and maybe a solar fan or two as well. While it is always warmer upstairs, it seems DD's room is not just warm, it is hot, so I'm thinking there is a thin patch of insulation over her room.

We have a whole house fan as well, but can't use it in the middle of the day or we just bring in the hot air. Rather, we turn it on at night and early morning, cool the house down to about 68F, and it stays under 78 until 4-5pm on most days unless we have 105F++ outside.

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Old 08-04-2008, 11:20 AM   #60
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Update: Over the last month I've made the following improvements.

Install 2000 sq. ft. radiant barrier: $260
Install 8 larger soffit vents: $16 (added 2 sq. ft. of net free vent area)
Replace 4 recessed light fixtures with airtight cans: $24
Tweak A/C thermostat programming: free
Leave attic stairs open to allow more air circulation: free
Add 40 bags of blown-in cellulose insulation to attic: $320

These were done throughout July so it's hard to say what the relative impact of each was, however an initial glance at the electric meter indicates that usage in July was flat compared to June, although July was a few degrees hotter, so there would appear to be some savings there. The insulation wasn't added until the end of July, so I'll have to wait until the end of August to see if that helped any. We blew the cellulose in over about 10 inches of rockwool, but this should take the R-value close to the recommended R-49 for Dallas.

Economics: if I used 12000 kwh/year before the improvements, and can reduce usage by 10%, that's a savings of $180/year at $0.15/kwh for roughly 3.3 year payback period. If usage decreases 15%, payback occurs in 2.2 years. Either way, I'll pick up some more savings since my winter heating bill (gas) will also decrease. I figured these improvments were a fairly low-risk investment because I was able to DIY. If you hired someone to do them all, the total cost could approach $2000, at which point payback is less certain.
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