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Attic insulation

 
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I had a question about what insulation is recommended for attics. Spray foam or  cellulose or fiberglass? Layer on the attic floor or spray on attic walls and ceiling?

I have read online and various opinions.
 
pollinator
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If it is an attic I would recommend using batting of some sort. You can get recycled blown in cellulose for very cheap and do so yourself. The spray foam is great for doing homes without attic spaces--hot roofs. It is also much more expensive and can have a lot of off gassing from the expanding foam.
 
Chad Pilieri
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Thanks, just to clarify, you feel it is better to insulate the floor of the attic than to cover the ceiling. Does cellulose have any downside?
 
gardener & hugelmaster
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I chose a cellulose insulation. It was made from recycled blue jeans. It does have some sort of fire retardant chemical but I think that is still more environment friendly & less toxic than foam or fiberglass. It also insulates well!!!
 
Chad Pilieri
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Great idea!

On a separate subject, what are your thoughts about heat pumps.
 
pollinator
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Chad Pilieri wrote:Thanks, just to clarify, you feel it is better to insulate the floor of the attic than to cover the ceiling. Does cellulose have any downside?



Generally you do both. It depends how your ceiling is constructed, but most are made up of 2x4 lumber and such. I put bats of insulation between the framing, then run another layer of insulation batts in the opposite direction over what is stapled up to the ceiling. Then I like to toss in some cellulose and spray/rake it across the top so that it helps seal the area up well. I live where it is cold so I make sure to put down 12 inches of batt insulation, and a few inches of cellulose...again as a sort of "seal" over the batts.
 
Travis Johnson
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Chad Pilieri wrote:Great idea!

On a separate subject, what are your thoughts about heat pumps.



I am not a huge fan of them. IF...if...I had a rental unit, I would have a heat pump in a second because renters love to crank traditional heat thermostats since they are not paying for the heat. As an owner, if I let the renters take care of the heat, they let it run out, then more damage is done to the building in costs than if I just pay for the heat. But a heat pump is great because the renters pay for the electricity, they never let that get shut off, and so they learn to live frugally.

A heat pump works by grabbing 2 units of heat for every 3 that a person buys. In this case it takes electricity to pull that 66% of the heat. But it takes electricity. There are better ways I think to heat a home.

If a home had some pretty good alterative power sources then perhaps; a microhydro dam powering a heat pump...heck yeah man. Or a really windy location that could power a heat pump...again yes! But to heat your home with what is essentially 1/3 electric heat coming off the grid? I do not think it is such a great idea.

The power companies get paid by KW usage, and with the world getting more and more efficient, yet the cost of maintaining the lines going up, they are in a death spiral. To make it all work, the power companies have to ask for higher KW rates, and they get that, and so then more people invest in more efficient lights and appliances to get their power bills down, so the spiral starts again. The power companies ask for a rate hike, and on and on it goes. In Maine this has happened 3 times in the last two years.

The Heat Pump was governments answer to this problem. Get people back into what is electric heat, and demand for power goes up, not down. This limits the power companies death spiral. It is not horrific; a person can heat their home with 1/3 the amount of electricity over what a normal electric heated home would be, but there are better ways to do it...solar, compost, go-generation, firewood, wood pellet, etc.. I like doing things myself, not being at the mercy of the power company.
 
steward
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Chad Pilieri wrote:Great idea!

On a separate subject, what are your thoughts about heat pumps.



Heat pumps have their limits, and generally when the temperature outside gets into the teens (fahrenheit) or colder, they no longer extract heat from the air, and when this happens an electric coil inside the air handler turns on and starts glowing, similar to the element in the bottom of an electric oven, to make hot air. The downside to this is the electricity consumption which may result in a higher than normal bill to pay. I live in Tennessee, and this region is about the most northern climate that heat pumps are regularly installed and used, and there's also a good mix of gas fired furnaces in homes in the state as well. Heat pumps generally work great for winter climates in warmer regions, like florida, georgia, alabama, parts of california etc.
 
pollinator
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I wonder why you can't build a solar air collector and blow warm air over the heat pump to improve the COP.
 
Chad Pilieri
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Thanks for the great answers
 
Graham Chiu
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My roof space was only 30 cm high so I had wool blown into it for insulation.
 
pollinator
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> foam insulation

Well done foam insulation seals the area it is applied, renders it air and moisture proof. Sounds good, but when we start making a building air tight we need to consider moisture - where it will go (or not), how it will get there and where we DON'T want it. Search "building science insulation moisture barrier" and read up if you start sealing up a building. Bad moisture can damage a building quickly - w/in 5 years. Way better to let the drafts blow through and wear a sweater than have to deal with a serious moisture problem.


Regards,
Rufus
 
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This site, build it solar, is a great place to find articles on energy savings, including attic insulation.

https://www.builditsolar.com/Projects/Conservation/conservation.htm#Insulating

There are many considerations of course, but the 2 main things being done are insulation and reducing air infiltration.  

So it is common to seal air leakage spots before insulating.  For example, one place to stop air infiltration in your attic is the top of your walls.  To stop this air infiltration you would use things like caulk or a can of spray foam, depending how big the cracks are.  Stopping the infiltration in those spots makes it so that your wall insulation can do its job. The usual types of wall insulation, such as fiberglass or recycled blue jean batts, are there to stop convection currents in the wall cavity.  But, if you have too much air infiltration into the walls from the top and bottom, you get a chiminey effect and air rises up thru the inside of the walls, and the batt insulation does not stop this.  So, you want to air seal the top of the walls before insulating the attic.  

Where there are other openings in the ceiling, you want to seal those cracks too to keep warm air from escaping, so around light fixtures, woodstove pipe, skylights, etc.... So you do this before you insulate.

So those spots are where you would use cans of spray foam.  And it is not too expensive and makes alot of difference.

After that, you insulate.  Batts or blow in cellulose usually.  Depends what area you live in to how much you do, how deep you want this.

A 3rd thing not mentioned in this thread yet is a radiant barrier.  Radiant heat transfer is not stopped by regular insulation, so many people will do a radiant barrier in the attic.  Around here, I see it done mostly because of summer heat gain that is not wanted in the house, although it would also reduce radiant heat loss in the winter.  So, around here, a radiant barrier is stapled onto the underside of the rafters, so over your head when you are standing in the attic.  They make rolls of perforated metalized kraft paper that is common in this area as it in inexpensive and easy to cut with scissors and put up with a staple gun.  This type is not used for an air barrier, just as a radient barrier.  Other installations might use a combined product that also doesnt alow air thru, I think this can vary by what climate you live in.  

So, I have just mentioned 3 different types of things to address in the attic because there are 3 types of heat transfer, convection, conduction and radiation.  Convection is air currents, conduction is moving thru a material ( like grabbing a metal spoon that is in your saucepan of hot soup, the handle of the spoon is hot even though the bottom of the spoon only is in the hot soup, the metal conducts the heat) and radiation ( radiation is how you can feel hot when the sun is directly shining on you but the surrounding air is cold.  It is how the Earth gets warm from the sun the the space between the sun and earth is very cold.  When your house is warm in the winter heat radiates out from it)

https://www.energy.gov/energysaver/weatherize/insulation/radiant-barriers

The picture in that article shows an attic with a radiant barrier overhead, sealed infiltrations to the house, and dense packed insulation over the ceilings.  


 
pollinator
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Travis, your calculations are off unless you're talking about either a really inefficient heat pump or one running at low ambient outdoor temps. A typical heat pump has a real-world COP of 3. A resistive electric heater has a COP of 1. So a bog-standard heat pump will give you three kWh (not 0.66)  of heat energy for each kWh of electrical energy that it consumes, while the glowing bar can only ever put out 1:1.

However...the COP is not linear and will be poorer if you're trying to put out really hot air or water. This can be solved by running two smaller units in series with each one only responsible for half of the heat increase. Heat pumps also can suck if the outside air temperature is really low. To get around this we can use a ground source for the evaporator side, such as a well where the groundwater temperature stays roughly constant year round.
 
Travis Johnson
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Phil Stevens wrote:Travis, your calculations are off unless you're talking about either a really inefficient heat pump or one running at low ambient outdoor temps. A typical heat pump has a real-world COP of 3. A resistive electric heater has a COP of 1. So a bog-standard heat pump will give you three kWh (not 0.66)  of heat energy for each kWh of electrical energy that it consumes, while the glowing bar can only ever put out 1:1.

However...the COP is not linear and will be poorer if you're trying to put out really hot air or water. This can be solved by running two smaller units in series with each one only responsible for half of the heat increase. Heat pumps also can suck if the outside air temperature is really low. To get around this we can use a ground source for the evaporator side, such as a well where the groundwater temperature stays roughly constant year round.



It is possible. I was basing my thoughts on an old advertisement back when the State of Maine had financial incentives to get people to install them. They had some local professor who made that simplistic statement. Perhaps it was an old style of heat pump that is now outdated, or perhaps it was just simply stated to make a quick point in a 30 second advertisement.

I know here in Maine a lot of people have them that is for sure, but you can never get a straight answer on how much their electrical costs are per month. Everyone says, "Oh it went up some." But I like specifics, just how much?

My house is largely heated by geothermal, so I know the value of it, but if heat pumps were really good, yeah I could conceivably generate my own electricity for domestic use, AND power the heat pumps to heat my home.
 
pollinator
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In Australia Heat pumps are used extensively for heating water with solar electricity.
Since most solar panels produce power when the householder is at work, heating water is an efficient way of gaining a benefit free of cost.
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