Existing Slab in Texas, shall I insulate
Danthecook
| Posted in Energy, Heating & Insulation on
I have a 1966 frame and 20% masonry house in Central Texas, perfect North south exposure, lots of wind and sun. The 12 foundations on our mountain were poured with any expertise and wobble along the edges. Most are not cracking.
Will I get any benifit from insulating the 6 to 10 inches of exposed slab around the edge of the house? I have already redone the siding and am getting ready to do the attics. Windows are new .31 double pane. May even Mooney the south walls. Yes all original doors are being replaced.
Replies
You need to keep that exposed edge exposed to help prevent termite intrusions. That exposed edge is your inspection window to one of the easiest paths of entry for termites.
If your home is like the rest of the 60's home in Central Texas your A/c system is probably in the attic. I would leave the slab alone and foam your attic roof structure to create a conditioned attic space where all your a/c equipment and or duct is located. It will dramatically lower your utility bills.
I do not quite understand what you meant by your slab is wobbly? Could you explain or take pictures.
Thanks
Bruce
imagine a wooden foundation form where the carpenter forgot to thoroughly stake things in to the ground and the wet concrete buldged the form giving a wave where there should have been a straight line. I am just hopeing they thru some metal in with the concrete.
Now I understand, the slab is solid, it is just not straight and flat. My perception of "wobbly" was that the wall was moving, easily.
as far as the attics, they are getting some more insulation down crosswise to the rafters ( after I clear the airways from the new soffet vents to oversize Gable vents). I will use the heat of one attic to preheat the air intake of the HVAC [located in a closet area on the second floor, the return is just a box under it with one side facing the spiral stair and the other the second floor area] using the black-roof techniques used in New Mexico.
Actually heat isn't much of a problem as I have now tripled the airflow thru both attics. My next problem is getting a chunk of the coolness in the night sky wrapped up and bundled into the HVAC. I don't have any old waterbeds to pull a Hays roof system. Guess I will just have to wait for Doubleplay to get out of beta testing.
Listen to john7g. He's right-on about the termites, AND the pest control guarantee, AND the insurance policy, AND the moisture that may enter the house.
Also, when landscaping, keep the dirt well below the foundation line.
Well guys I juxtapose your information to the following from DOE ( just found this morning)
original ref: http://www.builditsolar.com/Projects/Conservation/Insulation/Slab29237.pdfS L A B - O N - G R A D E FLOORS
Slabs lose energy primarily as a result of heatconducted outward and through the perimeter of the slab. In most sections of the country,
insulating the exterior edge of the slab can reduce winter heating bills by 10 to 20 percent. In climates with mild winters, slab insulation in a typical 1,800 square-foot home would save
$50 to $60 annually. R-10 slab insulation for an 1,800 square-foot home would typically cost $300 to $600 to install. Thus, the insulation would pay for itself in 5 to 10 years. The investment in slab insulation is also economical when it is part of the mortgage. An
insulation cost of $450 would add about $38 to the annual mortgage. Since the insulation saves over $50 per year on energy bills,
savings exceed the extra mortgage costs and the investment in slab insulation pays off from the beginning.
Slab insulation is important not only to save on energy bills, but also to improve comfort. Cold concrete slabs are one of the most notorious sources of discomfort in a home.* Installing slab insulation around the perimeter of the slab will reduce heat loss and make the slab easier to heat. An insulated slab also provides
thermal mass to store heat and moderates indoor temperatures.* my excerpt and situation
Did you read the part titled Special Requirements of Slab Insulation for Termite Control? TX is included there. Do what you want but don't be suprised by termite issues & voided termite warranties later.
How much heat are you losing through your perimter there in TX? I'd think you'd be more focused on heat entry via the attic, walls, doors & windows.
Edited 5/1/2009 7:56 am ET by john7g
Those recommendations and figures refer to when done as part of a new construction. Retrofitting always involves higher costs up front, and when not done as part of an overall design, can cause other problems i.e. the termites.You would need treated insulation and copper flashing. Installing the flashing would mean removing some siding....see where this is going? lots of times, the rule, "If it ain't broke, don't fix it" is a good one to live by.
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Installing slab insulation around the perimeter of the slab will reduce heat loss and make the slab easier to heat
Your exposure, if typical of circa '66 Williamson Co, will be 12" or less (hopefully more than 6" vice termites and ants). The slab will be turnd down around 2' deep into the cooler soil. This is useful contact, really. "Ideal" insulation given present costs? Not entirely.
However, you really ought to check the buildingscience web site for recommendations.
You are in climate where attic ventilation is 99% useless. The solar gain from the roof passes through the deck and into the rafters, just pumping unwanted btu into the attic. There's not really enough airchanges, even today where it's only around 81 or so, to cool that attic when the very structure of it ir up in the 100s (mine, probably only about 40-50 north of you is showing 112º; it's 84º/87ºHI in Bryan at 1415 today).
That same attic where your air handler and all its ducts run. That R6 blanket is not much resistance to 20 and 30 degree deltaT in the attic. So, the first 3-4 minutes the a/c runs, you are pushing 90º air into your conditioned spaces. raising the temps. This is under ideal.
The answer to that is to move the conditioned space plane out to the roof deck. In new construction this is easier with rigid foam on top of the deck. In existing work, foam is a better answer until Novmember or so when attics cool back down again. Rigid foam in the bays can be slid down into the tight spots. Then a cross-wise layer over the rafters. Alternately, spraying foam into the bays is a task that can be quickly achieved (may not be cheaply achieved, though).
But, that's my take on it, from being in central Texas for a couple decades; others' differ.Occupational hazard of my occupation not being around (sorry Bubba)
Thanks for the local suggestions, means a lot.
1. The foundations on Mount Chalet are all wavy in edges and I don't really remember how far into the ground the footings went. Your suggestions of adding a porch is a good one. Need to be sure the Termite guys can look under there once and a while. It also guarntees shade. Area is Totally outside of building or homeowner codes, you have no idea how something was done til you check it yourself.
2. My HVAC(Carrier) is in a closet on the second floor west side of the house and the condenser(Janitrol) on the east side ground level with both freon tubes running up the wall and thru the attic. Half the rigid ducts are in the attic for the three rooms and the others go to a false ceiling in the center of the first floor. The rigid tubes are not masticed nor are the connections to vents in each room. Then most of the glasswool blankets around the ducts are open or loose. Will do this as soon as I arrive in June. Thermostat has only one sensor, no Zoneing here. The "return" is an 18"by18"x10" box under the HVAC with two vents one pointed to the stairway and one pointed to the center of the second floor. IF the rule of thumb is equal return to supply I need to add some return.
3. Attics now have soffet vents probably 4 to side. Need to make sure the air can flow easily to the gable vents before I add insulation. Roof will eventually be replaced with a light colored metal one for lower heat gain and better rainwater harvest. Ground water is reallly full of iron, I buy mine from a local vendor (water price is controlled in Texas, only charges are really for the transport.) If I buy water is about 30$/month with no rainwater added in. Misting the roof would be a great idea if I get "long" on water.
4. The attics are filled with light trusses on 18" centers and the rigid foam suggestion is great to fill the areas towards the eaves and then rolls of wool crosswise. Electricians went thru the ceiling once already so I'll be careful.
5. I think I have good cross ventilation thru the house. And I need to check but the prevailing wind seems to be North/South which will work quite well.
6. When the 2 doors are replaced I need to check on air infiltration and then insulating shutters/roladens.
Oh, and what might be the best "insulation" for the esposed slab is what is traditional for the region, a porch. Keep the sun off, and you keep much of the gain off too.Occupational hazard of my occupation not being around (sorry Bubba)
To begin with, there are no mountains in north central Texas. Surely you are just acting like any native Texican and making a mountain out of a molehill under the assumption that everything is bigger in Texas.
;)
I would not insulate that perimeter in your climate, but focus insulation efforts on the attic and preventing infiltration due to wind
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Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
You're right, Piffin. There are no mountains in North Central Texas, but where Danthecook is--near Austin--there ARE mountains. They ain't the Rockies, and you can't snow ski, but they are there.
'em are hills.
For what it's worth, john7g, I agree with you. Them are hills. But I'm telling you for about the MILLIONTH time, Texans don't ever exaggerate.
>Texans don't ever exaggerate<
never ever? LOL
Edited 5/1/2009 4:13 pm ET by john7g
You Ft. Worth types mind your business. They must be mountains. I need to get on top of my roof before I can see the New Mexico border.
Bruce
and I thought all along that all you needed was to stand on a tuna can to see the back of your head.
There are no mountains in North Central Texas, but where Danthecook is--near Austin--there ARE mountains<<<<<<
Usually just referred to as the 'Texas Hill Country'.
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Natural Gas is Clean, Abundant and Domestic. We import almost 70% of our oil from foreign countries yet natural gas is an abundant and domestic natural resource. Natural gas is available on almost every street in America through a network of 1.5 million miles of distribution pipelines across the country. Natural gas as a transportation fuel is a sure way to break our dependence on foreign oil and keep billions of American dollars working here every day.
http://cannibal.mi.org/~chad/pic/tx/bonnell.jpg
I never said it was the Rockies, but here is a pic of some intrepid mountain climbers braving the harsh conditions atop Austin's Mount Bonnell!
This is what the top of a mountain looks like.
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with me standing on the right. There's none of these or glaciers in TX.
Now if you'd kindly refine your definition of what a mountain is, we can get on with the OP.
:)
7g
Edited 5/6/2009 5:08 pm ET by john7g
As others have said, there are places to insulate where you investment would be more efficacious.
However, you may still want to consider the insulation on the slab perimeter. You don't have the same Delta-T as a house in Northern Montana, but a house that is otherwise well insulated will leak from the exposed area you have.View Image
Jon Blakemore
RappahannockINC.com Fredericksburg, VA
Good point and Thanks for the photo! Those cameras are hard to come by. Many of us would not spring for the cost of the photos.
Suggestion from a central Texas resident is be prepared to watch the slab occasionally for termites but add a porch around the house thereby shading the area and the windows. Even a metal porch/awning would shade the slab area and the entire first floor from direct sun. I could complete the floor of the porch later, perhaps with the screens and "insulate" the slab and supplement the original glasswool in the walls especially the south walls. I am hoping to find a nightvision set of goggles to give me the ability to view my house the way your camera does. Looking at the the window in the top floor, suggests it could use some moveable insulation outside or inside. These are all things we need to know. Any of you hunters have infrared sights that could check out your houses. The colors won't be as nice, but if it looks bad you might spring for a real infrared appraisal of your home.