Efficient prefab? - Page 6

mk1st · 05-30-11, 11:01 AM

Quote:

Originally Posted by boardom

some people just prefer to spend money on saving energy and comfort, than on something like a granite countertop. Funny how no one ever brings up the ROI on things like that .

After testing hundreds of homes I can safely generalize that homes of a simple shape are tighter and more efficient than those with vaults, angles, cantilevers and floor height changes. Along the lines of boardom's comment above, those features are also never brought up in the ROI discussion, but happen to add much to the cost of construction.

I think once the housing industry gets past this present bump in the road, we'll be seeing folks opting to lop square footage off the typical home design and putting the money saved back into energy efficiency, perhaps paving the way for some of these more exotic building methods to reach the economy of scale they need to be competitive.

S-F · 05-30-11, 12:18 PM

Yes! It doesn't cost much more to go super insulated. If you have a 12" wall full of cellulose the need for meticulous air sealing goes down quite a bit. Building a 12" cavity isn't too much more labor than 2x4 construction and the amount of lumber used isn't too much more than 2x6 framing. Once you start talking about 12" walls you are in a whole world of virtually non existent heating bills, great comfort and better health. Robert Riversong estimates that his methods cost no more than 5% more than regular construction. I personally like to do things a little differently so that figure probably goes up 2%.

silver22553 · 05-30-11, 02:52 PM

Boardom

Sir, my post was general in nature. Being that I have built a few houses that are energy efficient over the years, I get a lot of “I’m thinking of ………what ya think”. Their ideas are a collection of everything on the internet. They get high tech far above our local requirements and actually price themselves out of the house.

Building a stick built house that reduces your HAC costs by 70 percent is fairly easy. Getting that last 30 percent is quite expensive. A house should be a balance between construction methods, internal systems, sex appeal, livability, relationship to the earth and your check book.

Howard

MN Renovator · 05-31-11, 01:25 AM

Insulating an attic ceiling with R60 over R25 is about $400 for 1000 sq ft of attic space, less if you get it directly from a distributer rather than your local megastore. I'm actually looking at getting nearly R75 in my attic after finishing air sealing(top plates, drop soffits, gasketing the access) and its about the only place in my retrofit that I can add additional insulation without tearing out walls. If I had new construction, I'd go with R60 in the attic at the minimum since Energy Star recommends R49-60 where I live and in the mid-80's when my house was built they put in R25. Over time the amount that is recommended will increase and I see no reason why anyone shouldn't be ahead of the curve with air sealing and insulation.

I spoke with a housing builder at the Living Green expo at the Minnesota State Fair earlier this month, they air seal and insulate and I think his numbers were R30 floor, R4x wall, and R60 attic. He said depending on what the owner wants they will add more but he said that they blower door test and the houses get a HERS rating. He said a recent house was less than .5 air changes per hour at 50 pascals. I've read about challenges getting a passive house below .6 and when I told him that he said that it really isn't that difficult with new construction. He showed me a picture of a house and the homeowner wanted a geothermal setup and the homeowner decided to have a different company install it but there was snow on the ground by the time they were going to trench the ground so the homeowner managed to keep the house warm enough using two 1500 watt space heaters to where the occupied rooms were warm and the rest of the house was warm enough to keep the pipes from freezing, we had -22 degrees F this winter. Impressive in my opinion for a house of a little over 3000 sq ft. I think with that kind of insulation that the installation and equipment cost of geothermal would never pay itself off financially with such a low heat load but I don't see that as a reason to not insulate and air seal to lower the heat load. If someone lives in a house for 30 years the additional cost would very easily be covered by the cost of insulation, especially considering inflation, $5/bag of cellulose at a home improvement store will probably seem leagues cheaper than will be in another 20 or 30 years. In 1975 a new house could be bought for $40 grand, the house would be bought used today for around $150 grand. If we had the same insulation and spray foams that we use today available then and that home was owned by the same person today, they would have been stupid not to do what they can with the knowledge and materials available then to take care in building a good envelope as in todays standards the cost would be minuscule by comparison.

If I ever move from my current house to a different one its most likely going to be new construction just so that way I can get the insulation levels I want, air sealing to my satisfaction and tested with a blower door while there are no walls up to fix any issues, HVAC done right, and if I don't buy a new place for some reason, I would be picking one sited properly for solar heat gain, roof pitch and space appropriate for PV solar, have enough space in all rooms to be comfortable with tearing the walls down to insulate the walls, proper access to the attic with no funky knee walls, cathedral ceilings, drop soffits, etc. so the retrofit is easier. In the end it would be cheaper to buy new then to rip walls down. The contractor I spoke too told me that before they started doing retrofits and after they started the pricing increase is so minimal and not much more effort to do that there is no reason why houses shouldn't be built this way and due to the advantages their company provides its helped them tremendously through the housing bust with maintaining business because it was when the whole 'go green' attitude really started to gather momentum.

S-F · 05-31-11, 09:58 AM

Getting to .5 ACH @ 50 is pretty hard to do UNLESS you sprayfoam 1" or so over everything. With meticulous air sealing and 12" or more of cellulose in a wall it's still some work to get it under 1 ACH. A friend of mine recently built a house that he's winning all kinds of awards for and he only got it to .9. He only insulated with cellulose though. The only foam was used for air sealing and below grade. It's a 1,200 Sq Ft house and it basically doesn't need heat. It has a 7 BTU/h ASHP but it never really comes on. The owner turned it off when she went on a week vacation this winter (between 0 and 10 degrees F) and the house was 59 degrees when she came home. When there's cooking, lights and human presence nothing is really needed. So you don't really need = < .6 ACH @ 50 to have a passive house. But you need it to have a "passivehaus".

silver22553 · 05-31-11, 03:31 PM

Pardon my ignorance and I am probably ignorant as I’ve been away from this endeavor for a while. I question the phrase “air sealing”. Back in the day it was quite possible to completely seal a house. One could seal it enough that you had to close the front door very slowly. The problem was stale air. The solution at the time was an expensive & intensive air exchange unit or keeping a window cracked open.

Daox · 05-31-11, 03:45 PM

The solution now is an HRV (heat recovery ventilator) or ERV (energy recovery ventilator). Both of these solutions transfer heat or cool from the air exiting the house to the air coming into the house. An ERV also transfers some humidity. These are increasingly used in modern construction as sealing the house has caused problems with stale air, and more so with trapped moisture and mold in houses. However, despite the cost, these units easily pay for themselves in a reasonable amount of time since you are able to recapture 60+% of the heat exiting the house via infiltration versus 0% if it was simply going out a hole in the wall.

silver22553 · 05-31-11, 09:14 PM

That is good to know. 40 years ago, we used 2x6 studs 24 OC stuff with 6” of unfaced insulation. Our vapor barrier was installed on the inside and taped everywhere. The house was so tight, you couldn’t slam the door closed. We ended up burying 100 ft of 12” pipe 6 foot deep to provide fresh air.

AC_Hacker · 05-31-11, 09:46 PM

Quote:

Originally Posted by silver22553

We ended up burying 100 ft of 12” pipe 6 foot deep to provide fresh air.

silver22553,

Passive houses (some, but not all) still utilize that approach, summer & winter, in series with an efficient (85% or better) HRV.

-AC

Quote:

Originally Posted by S-F

...It has a 7 BTU/h ASHP but it never really comes on...

S-F,

I think my gerbil puts out at least 7 BTU/h...

-AC_Hacker

S-F · 05-31-11, 09:48 PM

Quote:

Originally Posted by silver22553

We ended up burying 100 ft of 12” pipe 6 foot deep to provide fresh air.

You rock! Long live the earth tube!

200' of PVC + all your friends + dinner for 20 (home made of course!) + 1/4 keg of beer = earth tube!

Unfortunately for me earth tube = hanging out with 20 friends all day, feeding them and getting them drunk, working FDR labor (digging holes and filling them back in again), wasting money on PVC and then having a radon reading of 30 or so when the windows are closed. The entire part of the continent where I live is situated on a slab of rock it seems.

05-31-11, 03:45 PM	#57
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	The solution now is an HRV (heat recovery ventilator) or ERV (energy recovery ventilator). Both of these solutions transfer heat or cool from the air exiting the house to the air coming into the house. An ERV also transfers some humidity. These are increasingly used in modern construction as sealing the house has caused problems with stale air, and more so with trapped moisture and mold in houses. However, despite the cost, these units easily pay for themselves in a reasonable amount of time since you are able to recapture 60+% of the heat exiting the house via infiltration versus 0% if it was simply going out a hole in the wall. __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

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05-30-11, 12:18 PM	#52
S-F You Ain't Me Join Date: Nov 2009 Location: Northampton MA Posts: 662 Thanks: 6 Thanked 71 Times in 58 Posts	Yes! It doesn't cost much more to go super insulated. If you have a 12" wall full of cellulose the need for meticulous air sealing goes down quite a bit. Building a 12" cavity isn't too much more labor than 2x4 construction and the amount of lumber used isn't too much more than 2x6 framing. Once you start talking about 12" walls you are in a whole world of virtually non existent heating bills, great comfort and better health. Robert Riversong estimates that his methods cost no more than 5% more than regular construction. I personally like to do things a little differently so that figure probably goes up 2%.

05-30-11, 02:52 PM	#53
silver22553 Lurking Renovator Join Date: Oct 2010 Posts: 6 Thanks: 0 Thanked 0 Times in 0 Posts	Boardom Sir, my post was general in nature. Being that I have built a few houses that are energy efficient over the years, I get a lot of “I’m thinking of ………what ya think”. Their ideas are a collection of everything on the internet. They get high tech far above our local requirements and actually price themselves out of the house. Building a stick built house that reduces your HAC costs by 70 percent is fairly easy. Getting that last 30 percent is quite expensive. A house should be a balance between construction methods, internal systems, sex appeal, livability, relationship to the earth and your check book. Howard

05-31-11, 01:25 AM	#54
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 939 Thanks: 41 Thanked 116 Times in 90 Posts	Insulating an attic ceiling with R60 over R25 is about $400 for 1000 sq ft of attic space, less if you get it directly from a distributer rather than your local megastore. I'm actually looking at getting nearly R75 in my attic after finishing air sealing(top plates, drop soffits, gasketing the access) and its about the only place in my retrofit that I can add additional insulation without tearing out walls. If I had new construction, I'd go with R60 in the attic at the minimum since Energy Star recommends R49-60 where I live and in the mid-80's when my house was built they put in R25. Over time the amount that is recommended will increase and I see no reason why anyone shouldn't be ahead of the curve with air sealing and insulation. I spoke with a housing builder at the Living Green expo at the Minnesota State Fair earlier this month, they air seal and insulate and I think his numbers were R30 floor, R4x wall, and R60 attic. He said depending on what the owner wants they will add more but he said that they blower door test and the houses get a HERS rating. He said a recent house was less than .5 air changes per hour at 50 pascals. I've read about challenges getting a passive house below .6 and when I told him that he said that it really isn't that difficult with new construction. He showed me a picture of a house and the homeowner wanted a geothermal setup and the homeowner decided to have a different company install it but there was snow on the ground by the time they were going to trench the ground so the homeowner managed to keep the house warm enough using two 1500 watt space heaters to where the occupied rooms were warm and the rest of the house was warm enough to keep the pipes from freezing, we had -22 degrees F this winter. Impressive in my opinion for a house of a little over 3000 sq ft. I think with that kind of insulation that the installation and equipment cost of geothermal would never pay itself off financially with such a low heat load but I don't see that as a reason to not insulate and air seal to lower the heat load. If someone lives in a house for 30 years the additional cost would very easily be covered by the cost of insulation, especially considering inflation, $5/bag of cellulose at a home improvement store will probably seem leagues cheaper than will be in another 20 or 30 years. In 1975 a new house could be bought for $40 grand, the house would be bought used today for around $150 grand. If we had the same insulation and spray foams that we use today available then and that home was owned by the same person today, they would have been stupid not to do what they can with the knowledge and materials available then to take care in building a good envelope as in todays standards the cost would be minuscule by comparison. If I ever move from my current house to a different one its most likely going to be new construction just so that way I can get the insulation levels I want, air sealing to my satisfaction and tested with a blower door while there are no walls up to fix any issues, HVAC done right, and if I don't buy a new place for some reason, I would be picking one sited properly for solar heat gain, roof pitch and space appropriate for PV solar, have enough space in all rooms to be comfortable with tearing the walls down to insulate the walls, proper access to the attic with no funky knee walls, cathedral ceilings, drop soffits, etc. so the retrofit is easier. In the end it would be cheaper to buy new then to rip walls down. The contractor I spoke too told me that before they started doing retrofits and after they started the pricing increase is so minimal and not much more effort to do that there is no reason why houses shouldn't be built this way and due to the advantages their company provides its helped them tremendously through the housing bust with maintaining business because it was when the whole 'go green' attitude really started to gather momentum.

05-31-11, 09:58 AM	#55
S-F You Ain't Me Join Date: Nov 2009 Location: Northampton MA Posts: 662 Thanks: 6 Thanked 71 Times in 58 Posts	Getting to .5 ACH @ 50 is pretty hard to do UNLESS you sprayfoam 1" or so over everything. With meticulous air sealing and 12" or more of cellulose in a wall it's still some work to get it under 1 ACH. A friend of mine recently built a house that he's winning all kinds of awards for and he only got it to .9. He only insulated with cellulose though. The only foam was used for air sealing and below grade. It's a 1,200 Sq Ft house and it basically doesn't need heat. It has a 7 BTU/h ASHP but it never really comes on. The owner turned it off when she went on a week vacation this winter (between 0 and 10 degrees F) and the house was 59 degrees when she came home. When there's cooking, lights and human presence nothing is really needed. So you don't really need = < .6 ACH @ 50 to have a passive house. But you need it to have a "passivehaus".

05-31-11, 03:31 PM	#56
silver22553 Lurking Renovator Join Date: Oct 2010 Posts: 6 Thanks: 0 Thanked 0 Times in 0 Posts	Pardon my ignorance and I am probably ignorant as I’ve been away from this endeavor for a while. I question the phrase “air sealing”. Back in the day it was quite possible to completely seal a house. One could seal it enough that you had to close the front door very slowly. The problem was stale air. The solution at the time was an expensive & intensive air exchange unit or keeping a window cracked open.

05-31-11, 09:14 PM	#58
silver22553 Lurking Renovator Join Date: Oct 2010 Posts: 6 Thanks: 0 Thanked 0 Times in 0 Posts	That is good to know. 40 years ago, we used 2x6 studs 24 OC stuff with 6” of unfaced insulation. Our vapor barrier was installed on the inside and taped everywhere. The house was so tight, you couldn’t slam the door closed. We ended up burying 100 ft of 12” pipe 6 foot deep to provide fresh air.