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Battle of the Attic Insulation Companies, Which is best?

Battle of the Attic Insulation Companies, Which is best?

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  #1  
Old 07-09-12, 08:03 PM
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Battle of the Attic Insulation Companies, Which is best?

I have a house that the A/C just overworks to keep cool and some rooms are hotter than others. After the A/C people told me that everything was as good as it's going to get and to try more insulation, One of the issues they feel with one room hotter than the others is that it sits over 1/2 of the garage, and the garage roof gets hot and heat soaks the room. The garage didn't even have a vent in it, a vent was put in the garage roof and that has helped some but not enough.

I have had two different insulation people out there.
They both pitch a different method of getting the house cooler.
Company One: Apply a painted radiant barrier to the attic roof in the house only, Put a Solar attic fan in the garage roof and the attic and then blow in 4 more inches (already has 12") in the attic.

Company Two:
They put in a radiant barrier but it is in sheets. They want to lay it down (not affix it to the rafters) on top of the insulation in the attic. I have never heard of this method, I though you always affixed it to the underside of the roof. In the garage they can only suggest to put a access hole in the garage ceiling and affix some of their sheeting to the wall that separates the bedroom from the garage attic space. They say I could use another vent in the attic and one above the garage attic, but say not to use the solar ones as the attic space is too small and I will create a negative pressure, sucking cold air out of the house.

I have got a third company coming out Thursday to look at it, But I did a little research on them and they spray in a radiant barrier also.


So which is better, The spray in? Or the sheets, but laid down on top of the other insulation? Or the sheets but affixed to the rafters? The sheet guy swears that laying down the sheets in the most cost effective way of getting the house under control.

This is how the front of the house looks with 1/2 of the garage covered by the roof and the other half goes under the house,,,,
 
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  #2  
Old 07-09-12, 08:56 PM
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So which is better...?
Neither. Insulation holds heat in, so adding more will only make things worse.

Radiant barriers are seldom effective, no matter how they're installed. And laying one over attic insulation is counter-productive, as you suspected.

I would work on three areas:

Ventilation - Unimpeded soffit-to-ridge flow. NO fans in the attic - that's one solid piece of advice you got.

Solar gain - Windows that face sunlight can be upgraded to Low-e, can have window shades installed (not blinds), can have awnings installed, and/or can be tinted.

Air management - Zoned systems; a 7-day programmable 4-event thermostat for each zone; and the quick and easy fix: cover about 2/3 of the face of the return air grilles on the lower level(s). Open the windows at night; close them early in the morning. Open the windows on the shady side, on the lower level, at the bottom. Open the windows on the sunny side, on the upper level, at the top.
 
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Old 07-09-12, 09:01 PM
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I know very little about it, but from what I understand, radiant barriers only work when there is an airspace above the radiant barrier. So IMO the sheets would be better than the spray. If they only added one roof vent (like the one in the bottom right of picture) I would say they should have used a continuous ridge vent. Putting the radiant barrier on the insulation makes sense, IMO, since it might help prevent some radiation from passing through the insulation, keeping the insulation "cooler". Put it on the rafters and the insulation below the radiant barrier will probably still get almost as hot as before. I'm not a big believer in radiant barriers to begin with.
 
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Old 07-09-12, 09:26 PM
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Neither. Insulation holds heat in, so adding more will only make things worse.
I appreciate your response, but that makes no sense. I am trying to keep the heat from the attic(s) from getting to the house, if adding more insulation makes it worse, then getting rid of the insulation will help?

I cannot afford to zone the house or install another whole system. It's a 3400 sq ft house, The one system should be enough. It already has a 7 day 4 event thermostat, but they like to keep it at 75 and the A/C runs all day and in 100+ degree days the house gets above 80* in some rooms.

We have shades and tint on the windows that face the sun,we are in Houston so opening the windows at night... Well It's 80+ degrees at night

It has five vents in the 1600 sq ft attic, adding a couple of more will probably help. The house does not have ridge vents and honestly the length of the roof line isn't really long enough.

The picture is not of my house, just one with the garage like it.
 
  #5  
Old 07-09-12, 10:00 PM
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t
hat makes no sense. I am trying to keep the heat from the attic(s) from getting to the house
What makes you think it is trying to? Heat rises. So maybe from the garage.

if adding more insulation makes it worse, then getting rid of the insulation will help?
Wouldn't it be nice if we could store the insulation away with the comforters each spring?

To get back to your original question, Company 2 has the far more rational approach.

As for adding insulation, how much do you have in that part of the garage ceiling that is under your second floor? That's where rising heat could really be affecting you. Not from the main attic.

It has five vents in the 1600 sq ft attic, adding a couple of more will probably help. The house does not have ridge vents and honestly the length of the roof line isn't really long enough.

The picture is not of my house, just one with the garage like it.
Is your roof the same shape as the one in the picture?
 
  #6  
Old 07-10-12, 06:30 AM
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No, My roof is actually more like the house on the left. I would have to measure it for sure, but all 4 sides angle to the top ridge and it is probably only 10' long.

They say the can feel the heat on that wall that goes against the garage and on the floor above it, which is probably the main cause on that room being hotter than the rest of the house.


The other day when it was Sunny and 98*, the attic was at 125*, I don't know how hot that garage was.
 
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Old 07-10-12, 01:46 PM
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I agree with the others, the only way to keep the pressure of the heat from going down is give a passive way to go UP. Continuous ridge vents do just that. All the smaller vents, even the electric ones are a total waste of money. They are not at the highest point of the attic, and thus will let less hot air out.
 
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Old 07-10-12, 02:30 PM
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They say the can feel the heat on that wall that goes against the garage and on the floor above it, which is probably the main cause on that room being hotter than the rest of the house.
So the two places you could benefit in hot weather by adding some insulation, it sounds like, are above the back half of the garage and on the front wall under the roof for the front half of the garage. Do you know how much you have there now? I'm not sure you need any insulation above the front half of the garage except on the house wall.

The other day when it was Sunny and 98*, the attic was at 125*, I don't know how hot that garage was.
Those temperatures don't mean much in and of themselves, but they indicate that more ventilation might help your attic. What's your ventilation like now? For the garage, that slope dying into the wall of the house, on the right side, is a challenge, if that's what you have. Does the garage extend in front of the front house wall, so that there's some flat soffit under part of that slope?

My roof is actually more like the house on the left. I would have to measure it for sure, but all 4 sides angle to the top ridge and it is probably only 10' long.
You're right, that's not a lot of ridge. My parents' 50s ranch house had a hip roof, with eyebrow dormers as the exhaust vents. Those, or some turtle vents, are one option, but not the best. Installing as much ridge and soffit venting as you can is best. One company I found online - and that's all I know about them - offers something they call a "Hip Ridge Vent," which they say is installed on the hip ridges - up fairly high, I take it - to add more exhaust venting. Soffit vents - continuous, if possible - provide the intake.

At the risk of seeming to promote a company (I'm not!), here's a link to Air Vent's pdf on attic ventilation. I find it to be a good information piece, not a sales tool so much. The part about the hip ridge vents is on p. 23.
 
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Old 07-10-12, 04:49 PM
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More ventilation will help as will beefing up your insulation. How much insulation do you have now? Over in the boiler forum, we always tell people to do a heat loss calculation when sizing for a new boiler. I think you should do a similar thing and do a heat gain calculation. This will help you determine how much of the issue is an undersized a/c system vs not quite enough insulation. Try this software: HVAC Software, HVAC-Calc for Heat Loss, Heat Load Calculations . I used it for my heat loss and it does a heat gain at the same time. Looks like the homes in your neighborhood are very similar. How are your neighbors fairing?

Keep in mind that a properly designed system will run all day when it is at design temperature. That means if the system was designed to cool the home with 110F outside, it should be running constantly to do it. The trouble with your uneven cooling could be poorly designed and installed ductwork. Is the room where the thermostat is maintaining the set temp?
 
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Old 07-10-12, 09:10 PM
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Old 07-11-12, 06:42 PM
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It's got about 12" of blown in insulation right now.

I got another guy coming tomorrow that does spray foam insulation..... Of course he says his system is the best.
 
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Old 07-11-12, 09:49 PM
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It's got about 12" of blown in insulation right now.
R-38. Where? In the main attic?

How much insulation do you have in the ceiling of the back half of the garage, and against the house wall that's under the garage roof?

I got another guy coming tomorrow that does spray foam insulation..... Of course he says his system is the best.
Of course!
 
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Old 07-12-12, 05:43 PM
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Closed cell spray foam is very good. It completely air seals and will form a vapor retarder at 2" or more in thickness.
 
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Old 07-12-12, 09:36 PM
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Closed cell spray foam... completely air seals and will form a vapor retarder at 2" or more in thickness.
Why does that sound like a recipe for sealing moisture into materials, like wood, where it can cause damage?
 
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Old 07-13-12, 07:12 PM
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Read "Double vapor barrier" and "Perm ratings" here (XPS is similar to 2# SPF); https://docs.google.com/viewer?a=v&q...4EyM707m0gPdXQ

Gary
 
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Old 07-13-12, 08:12 PM
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I read those. They sounded to me like two strong arguments for good, clear ventilation. IOW, it;s not about keeping vapor infiltration below vapor expiration "out the other side." I doubt that can be done. If it was, the conditioned space would start to feel like a sauna, there would be interior mold problems, etc.
 
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Old 07-15-12, 07:48 PM
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Just giving you some current information on vapor barriers/retarders. I'll post this one again for others that missed it also:BSD-102: Understanding Attic Ventilation — Building Science Information
In TX, the OP can use f.g. (IF other concerns are addressed), or spend way more money on SPF, which isn't fully appreciated for his climate. Chart #3 here- eg. Houston: http://www.buildingscience.com/docum...d-roof-systems

D.Rentals, if you go SPF, you only need R-5 to meet minimum current Code, 1" of closed cell, or 1-1/2" of open cell SPF: IRC FAQ: Conditioned Attics — Building Science Information

A big deciding factor is the HVAC unit/ducts- are they in the attic? Will you be air sealing the attic floor, adding ventilation supply in the soffits, new ridge exhaust vents, adding plastic insulation baffles, adding more fiberglass insulation, and air sealing and wrapping the ducting--- or just spraying the roof for a conditioned attic; BSD-149: Unvented Roof Assemblies for All Climates — Building Science Information

Gary
 
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