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Construction / Insulation Question

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Old 11-26-2005, 10:58 AM
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Default Construction / Insulation Question

Last night I was presented with a thought that got me to a thinking.............

If someone insulated their actic with say R60 but only had R12 in the walls, would the R60 act as such a good lid that it causes more of the heat to escape through the walls which are only R12? Yes I know heat rises, but after it has rose to the ceiling then what does it do, go outwards through the walls?

Now if this were to be true, what would be the perfect amount of insulation in the actic? Not what is code, but what is the right balance between enough but not to much? Oh, if you don't already know, I do live where winters are cold.
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Old 11-26-2005, 11:13 AM
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I would think that heat loss through the walls would be the same regardless of what insulation you had in the attic. Thermal flow is thermal flow, doesn't matter the relative temperature. BTU is a BTU, doesn't matter if it is 70* or 80* the very same thermal currents will be present.
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Old 11-26-2005, 12:58 PM
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twentynine - 11/26/2005 12:13 PM

I would think that heat loss through the walls would be the same regardless of what insulation you had in the attic. Thermal flow is thermal flow, doesn't matter the relative temperature. BTU is a BTU, doesn't matter if it is 70* or 80* the very same thermal currents will be present.
So therefore you would be inclinded to say that the more I put in the attic the better and just let the walls do as they are going to do anyways?
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Old 11-26-2005, 02:08 PM
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That is my understanding Garret. The limiting factor in your sidewalls is the thickness. 2X4, 2X6, or 2X8. In the ceiling there is rarely a limiting factor. Once your done with the joists you can lay down another layer perpendicular to it.

More importantly is air infiltration. A vapor barrier is good but not everything. All of the openings must be caulked/sealed. The best way is spray foam insulation but the cost is kinda high. 3" in the walls and 7" on the roof and it's a tight dwelling that you can heat with a match. So tight in fact that you now must have an air to air heat exchanger. If you skimp on this detail you end up with a sick house. My last house was a Lindal Cedar Home. 6" walls and at least a 12" roof. 6 mil vapor under the sheet rock/T&G. I don't know what they had in the roof but the walls were full. My new house under construction now will be the same packed walls and 10 in the vented roof I was so happy with the first. I priced the closed cell spray and it was over 16K w/o the extra equipment needed. It was only going to be around 7K more than FG but I just had to cut it. My hope is that the radiant floor heat makes up for it cause that's where the money went.

Get good windows but no need to go over board. They are still holes in the wall but I like them.

Bottom line is heat rises as we all know.
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Old 11-26-2005, 03:03 PM
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Not really an answer to the wall question, but a relevant idea regarding attic insulation. In the very cold northern climes, lay plastic wrapped batts across the blown in insulation. This will help to reduce the amount of really cold air that permeates the "blow in" insulation by adding a barrier. It's apparently not a problem until the thermometer goes to the negative side of zero for extended periods of time.
May God have mercy on each and everyone of you who considers this to be an idea worthy of implementing.
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Old 11-26-2005, 03:04 PM
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Garett, This is something I can actually reply to, instead of asking the question?

Insulation is insulation, regardless of where it is and the thickness of the walls (or the insulation used) is a big factor as to how much insulating you will be capable of. Think about it like this, would your cooler work better with a top of the line lid but only marginal tub insualtion? Nope, you need as uniform as possible to get the most uniform R Value.

That said, did you use 2x4 or 2x6 walls? You can ac tually come out the same price and have a strong wall and higher insulating capability by going with 2x6 walls. If I ever build a house from the ground up, I will be using 2x6 walls and instead of 16 inch centers, you go to 24's. This also allows for better, stronger walls when running electrical and plumbing. Remember, do NOT pack the insulation in, it should still be somewhat loose.

Also, don't bother too much with the insulating boards since you are building from scratch. Go with the fiberglass or as Mist mentioned, the spray in poly - which should be renamed to "spray in money"
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Old 11-26-2005, 03:30 PM
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ReelWork - 11/26/2005 3:04 PM That said, did you use 2x4 or 2x6 walls? You can ac tually come out the same price and have a strong wall and higher insulating capability by going with 2x6 walls. If I ever build a house from the ground up, I will be using 2x6 walls and instead of 16 inch centers, you go to 24's. This also allows for better, stronger walls when running electrical and plumbing.


That's what I did Chris. Framed with 2x6 instead of 2x4, but I still went 16" centers. Walls came out very sturdy, but heavy as heck to raise. Nominal R value of 2x4 wall fiberglass is R-11 to 13 depending on quality. R-value of a 2x6 wall is R-19. Now this is without the R value of sheathing and siding.

Instead of fiberglass batts I used a blown in cellelose product called Cell-bar. It is masticated news paper treated with boric acid and glue, it is sprayed in dampened so it sets up and will not settle. This product fill the wall cavity entirely no gaps around recepticles and stuff like that. It also acts as a sound deadening material. I am not sure of the R value but I think it was higher than fiberglass, plus it filled the cavity better.



Here is a website that describes what it is.

http://www.celbar.com/
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Old 11-26-2005, 03:52 PM
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Best insulation going is Icynene. The stuff seals out drafts, fills all crevases and deadens sounds traveling between rooms. It it unbelievable- gets my vote for best insulation anywhere including the arctic.
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Old 11-26-2005, 04:07 PM
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Another consideration if you were to be considering new construction is "stress skin panels". I built my timber frame home with these and it is the closest thing to a thermos! Stress skin panels typically come as two 10' X 4' sheets with about 8' of foam between them. They can be ordered for your windows and doors to be precut. Stronger than 2X6 constriuction and better insulation.
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Old 11-26-2005, 04:18 PM
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I've read eveything guys but I've got to run - Christmas Dinner tonight
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Old 11-26-2005, 08:28 PM
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The blown in cellulose is great. 3 inches of cellulose is the equivalent to 9 inches of R-19. Big factor would be the windows. Most of your heat loss is going to be through the windows. Also depending on how old the house is, right at the sill plate there is great loss. Nowadays they use the sill sealer as you probably know. Livng in michigan you shouldn't have the house "too tight" due to the air quality issues. In winter your attic should be the same temp as outside, if not than put more up there or get better air flow through your attic. Probably should insulate around the windows with the spray foam (made for windows). Michigan code states that there is suppose to have a gap around the windows and the framing. Let's face it, you can feel that through the mouldings. As far as the furnace goes, the best thing to do IF it's new construction would be geo thermal. Going to build a new house hopefully soon, that's the route I'm going. System should pay for itself in a 10 year time frame if not sooner. I could be wrong but I think you know the right answer.

Jim
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Old 11-26-2005, 09:05 PM
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Well heck Jim - you might as well get a NUKE-YOU-LAR heater!
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Old 11-27-2005, 08:39 AM
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Jim,

You mentioned geothermal in your post above. Six years ago we built a new home in Tennessee (formerly Troy, MI), and used geothermal for our heating/cooling. It cost about double what conventional instulation costs were, but It paid for itself quickly! We built a 5000 sq. ft. timberframe and our monthly average utilities (lighting, heating, cooling, cooking, hot tub, etc.) is about $135 per month. You should also consider stress skin panels instead of traditional "stick built" construction. E-mail me t if you have any questions. Geothermal is the most comfortable heating/cooling system you can get providing it's designed properly, and would work great for Michigan!.

Carl
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Old 11-27-2005, 10:08 AM
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The fast and dirty answer to your question is there is a point of diminishing return when adding insulation. Temperature and humidity difference are what determine the rate of flow. The greater the difference the greater the flow. (more is always flowing toward less) A heat load calculation that is specific to the structure is the only way I know to answer the question with accuracy. The heat load takes into account the house as a system (glass, orientation, walls, roof, etc.) and the local climatic factors that effect the structure. Then it is just a matter of entering different insulation values and/or materials and seeing the changes in heat gain or heat loss.

A good source of information is http://www.buildingscience.com/


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Old 11-28-2005, 05:44 AM
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No this is not new construction, this is just extension work of renovating the bathroom - one has lead to another.

Not to undermind any of the above comments, but between twentynine's first comment and tinmarine's comment of "but I think you know the right answer" seemed to ring the bell for me. A contractor friend of mine keeps telling me that I sell myself short when it comes to this type of work - in my defence I sometimes need that second/ third voice as comfirmation to what I think I know.
Cellulose blow in was always a given, I was just trying to determine how much to use in light of this question.

Later this morning I will take a picture of the attic so I can ask a second question.

Thanks Jibara.
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Old 11-28-2005, 07:35 AM
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Well I just love saving money - I just put together adding R40 cellouse @ $700 which will give me approx. R52 this would be a savings of $600 from regular retail pricing.
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Old 11-28-2005, 10:39 AM
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The additional insulation in the attic will not cause any additional heat loss through the walls – all other things being equal. They way to look at this is that the driving force for the heat loss process is temperature change. Your improvement will reduce heat loss via convection (air movement) in the attic. If as a result you conscientiously increase the temperature of the room below then you will lose some of that additional heat to the outside through the walls since you now have a greater temperature difference between the inside and outside. Go ahead add all you want – but you do eventually get to a point of diminishing returns where the additional costs will not be recouped in energy savings.



This brings to mind another common misconception concerning home heating. Some feel that you should not turn down the heat when you are not home because the additional heat it takes to reheat the house causes a net total increase in energy. This is NOT true. To save energy you should turn down the heat when you are gone. Again, remember that the driving force is temperature change – and the longer you keep the inside temperature closer to the outside temperature, the less energy you will lose – period. Nothing else matters. However, it will take a while to get the home back up to the desired temperature and you will be colder until the temperature gets back up. That is really the only downside. One other consideration is condensation – you don’t want it to get so cold that you will have moisture condense on the cold walls. 50 to 55 is as low as you want to go in most climates.



Finally, you probably already have a vapor barrier at the bottom of the current insulation. Do not add another – not even any plastic sheets – as water will get trapped between the vapor barriers and cause other problems.
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Old 11-28-2005, 04:08 PM
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Just a little addition to LI Sound Grunt; another important factor in comfort in winter is a good humidifer. If you run a humidifier in cold climates in the winter you can keep the temp down in the house a good 4-5 degrees. Set the humidistat around 35. If you go to high with the humidity than the windows sweat and the walls sweat too. (which will cause mold where there is no air movement)

Jim
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Old 11-28-2005, 07:18 PM
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On new construction I was told 40% of energy cost goes to the ceiling/attic

We used Icynene in walls and under roof deck
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Old 11-29-2005, 08:54 AM
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Well it's not quite yesterday morning or anything, but my injuries still don’t allow me to get up into the attic to take pictures, a friend took this one.

My other question is........do I have to remove all of the paper crap that would be found between that glass batting and the drywall?
The stuff laying around on top will be picked up and the piles leveled out before I have the space blown in. Oh, 100% of the house has now been super 6ml polyed.....the bathroom is my last room.



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