48x39x14 shop build
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RayfromTX
Silver Member
Insulate the roof, not the ceiling.
EddieWalker
Epic Contributor
There are some studies out there that it's more efficient to heat and cool the entire envelope of a house instead of just the living area. This includes the attic space. This is done with spray foam insulation, and you have to make it really air tight to work. Then it's easier to maintain the temperature inside this envelope then overcoming the extreme heat that comes from the attic space. Another advantage to having the entire house sealed is that there is no access points for fire to get into your attic area, and under your roof since there are not vents. This was discovered during one of the huge fire storms in Southern California.
It's a huge upfront cost, and I don't think it's worth the expense for a barn or workshop.
I personally feel your best return on what you spend is to get R60 in the attic, have excellent air flow from your eaves to your peak, and seal the walls so no air can get through them. Heat goes up and down, so attic insulation is huge. Air flows side to side, so stopping it from defeating your wall insulation is also huge.
Some recent studies that I've read are finding that instead of house wrap, you can improve your efficiency significantly by painting the entire shell of the house, the OSB or Plywood, with a polymer type of waterproofing paint. ZIP System comes with this already applied, and then you use their special tape to seal the seams. By painting it on 100% of the exterior shell, you get an even better seal then ZIP System. In extreme environments, this has proven to be a significant improvement with measurable results.
kevinwak
Platinum Member
In my house we insulated the underside of the roof deck with spray foam. So my attic spaces are warm all winter. I am still torn as to weather I like it. I have one area with a Reoccurring leak and I can’t get resolution on it because everyone takes a look and the first thing they say is “you need to vent your attic” and they don’t look any further. They ignore the fact that the rest of the attic area is drier then a bowl of popcorn at a flour mill and blame my single leak on an “improperly” insulated ceiling.
OP
ovrszd
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In my area it's often discussed that a building can be too airtight. My HVAC guy doesn't recommend spray foam on the entire structure. He likes it on the walls to assist in air transfer. He doesn't recommend it on the roof for fear of being too tight. Says he has installed several dehumidifier systems in houses with spray foam on everything.
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Attic ventilation here is now a big no-no as Eddie stated.
My friend was building a brand new high end home in the Oakland Hills... the approved plans included ample ridge and eve vents... the redwood eve vents were in per plan and he had to remove all of them due to vent being a path for fire...
My home has full ridge vent and ample eve vents... done with permit but before all the big fires.
My friend was building a brand new high end home in the Oakland Hills... the approved plans included ample ridge and eve vents... the redwood eve vents were in per plan and he had to remove all of them due to vent being a path for fire...
My home has full ridge vent and ample eve vents... done with permit but before all the big fires.
JohnBuffaloMN
Silver Member
My first house required running the furnace fan for the first few years when the windows were closed because the windows would sweat profusely filling the sills every few hours! I think it was just wrapped in plastic and couldn't breath. Marvin Windows ended up replacing the whole neighborhood's windows (new development by same builder)... except mine because I stained and finished them myself and I used good sealant.
When we rebuilt our current home, we had them spray foam on the walls. Really nice - super quiet and I've heard stand up well in heavy winds. It basically glues the entire structure together with foam. We did not do the ceilings with foam because of the "too air tight" problems. So far haven't had any problems with it, but some might not like how quiet the interior of the home is.
I'm now considering my options on finishing the ceiling of my shop and still don't quite comprehend what the best approach will be. Fortunately, it's going to be further back on the list for at least the next few months so I'll just stay tuned.
ericm979
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It's not a "no-no". The code requires specific fire safe vents that prevent embers from entering. We just went through this on our house which is in a fire prone area of California. We added ridge vents this summer while we were doing the roof... in fact the roof inspector said we had to have vents (they were planned anyhow).
Since you're in the city you may not be worried, but if I had older non fire safe vents I'd be replacing them with fire safe ones. A lot of recent research has shown that in wildfires many houses burn from the inside out because embers got in.
I'm eagerly following the venting discussion as I'm planning a shop. Humidity is a problem in the winter but as mentioned I also have wild fire safety to worry about.
RayfromTX
Silver Member
Hi y'all.
This is a big issue and there are lots of misunderstood issues involved. I've been helping people to figure it out for 18 years. It was a revelation to me and I would love it if everyone could learn about it but it is time consuming because it requires a bit of physics and physical science along with some construction knowledge and if you understand the second law of thermodynamics that is a big benefit.
Most people have a bit of knowledge about products but it is mostly supplied by marketing from the products and can be incomplete and misleading. I try, as I have here to mostly speak about the physical science of water, heat and air and their interactions with building components. I find that it is better to do that because that understanding empowers good decisions. If I simply give opinions about building methods then people are at a loss as to what to believe and will be guided by faulty opinions that may seem cheaper of easier. A little understanding can be a dangerous thing.
As an example, many times we have been told that a building has to breathe or that a building can be built too tight. That is incorrect. You can't control the air in a leaky building and even defining what tight means is confusing. Air tight, vapor tight and thermally tight are different. While you may or may not want a building to be vapor tight, air tight is always desirable and thermally resistive is always desirable.
On the issue of attic ventilation, there are several reasons why insulating at the roof line rather than the ceiling line might be desirable. This takes a while to explain and I prefer to do it orally rather than in long type written form. There are several books that do a good job of it. One is "building science for building enclosures" by professor John Straube and Professor Eric Burnett. It is currently out of print but may be available although it is widely sought. Another good book about the subject was released last year and is titled "buildings don't lie" by Henry Gifford. It is available on Amazon.
I will briefly say that heat loss is related to wall and roof area and not the volume of the air it encloses. Insulating at the roof line may slightly increase the enclosure area but it will be inconsequential and is likely to be more than compensated by an ability to do a more effective job of insulating and air sealing at the roof line. In buildings that have mechanical equipment or ductwork in the attic, there are substantial benefits to bring those things into the thermal and air enclosure. There are many reasons for that. There are also practical reasons to want to have anything stored in that space to be inside the envelope.
When I consider these metal buildings I have tried to put my mind to solving the building science challenges that are created when they are heated. They have are inexpensive space but are sometimes used in inappropriate ways. I have a friend that has a large cabinet shop with perhaps 20 employees. It is very hot in that metal box on a triple digit day which we have perhaps 50 times a year along with high 90s for another 50. He has approached me many times to try to figure out a cheap way to make his men more comfortable but after the fact it is a difficult challenge. Radiant barriers are only somewhat effective until they get dusty. insulations are expensive when attached from below and then covered with an ignition barrier.
I have a metal building with radiant barrier that helps some but I don't do anything dusty in that building and it is still fairly clean and somewhat effective. If and when I build a personal use metal building that I want to heat and cool, I think I will sheath the entire building with plywood and use 1-2" of polyiso on the walls and 2-4" of polyiso on the roof and then cover that with metal panels either with or without purlins. I would need to think it through a bit and draw up the details but it would be a strong design from a performance angle.
I have recently helped a friend build a 16x32 two story building for his family that is based on this plan but with wood framing. It is however covered with corrugated roofing on the walls and ceilings and is heated and cooled with 3/4 of a ton of ac.
I am currently cooling a 8,000 sq ft building under construction with a 3 ton heat pump that was originally installed in my personal home 27 years ago. It keeps the whole building cold on a 100 degree day with 20 workers present. It has 2,700 sq ft of high performance glass.
I cool my 4,000 sq ft personal home with 2 1/2 tons and it has 50% run times on 100 degree days and this year we had a day of 112 degrees and on that day it ran continuously from 7pm until midnight but held the 73 degree set point. The air quality and purity of these buildings is superior. Pollutants from showering cooking and other activities is exhausted at the source and fresh air is brought in filtered and dehumidified.
Richard, I think your building will work fine depending on how it is used but when you build your home, there are better ways. These methods are not new and were actually first developed by an engineer named Neal Hutcheon in the 50s in Canada.
Again, y'all, this is too complex to do in a post on a tractor forum but we can talk over a cup of coffee if the timing works. Give me a shout. No proof reading so I hope it makes sense.
This is a big issue and there are lots of misunderstood issues involved. I've been helping people to figure it out for 18 years. It was a revelation to me and I would love it if everyone could learn about it but it is time consuming because it requires a bit of physics and physical science along with some construction knowledge and if you understand the second law of thermodynamics that is a big benefit.
Most people have a bit of knowledge about products but it is mostly supplied by marketing from the products and can be incomplete and misleading. I try, as I have here to mostly speak about the physical science of water, heat and air and their interactions with building components. I find that it is better to do that because that understanding empowers good decisions. If I simply give opinions about building methods then people are at a loss as to what to believe and will be guided by faulty opinions that may seem cheaper of easier. A little understanding can be a dangerous thing.
As an example, many times we have been told that a building has to breathe or that a building can be built too tight. That is incorrect. You can't control the air in a leaky building and even defining what tight means is confusing. Air tight, vapor tight and thermally tight are different. While you may or may not want a building to be vapor tight, air tight is always desirable and thermally resistive is always desirable.
On the issue of attic ventilation, there are several reasons why insulating at the roof line rather than the ceiling line might be desirable. This takes a while to explain and I prefer to do it orally rather than in long type written form. There are several books that do a good job of it. One is "building science for building enclosures" by professor John Straube and Professor Eric Burnett. It is currently out of print but may be available although it is widely sought. Another good book about the subject was released last year and is titled "buildings don't lie" by Henry Gifford. It is available on Amazon.
I will briefly say that heat loss is related to wall and roof area and not the volume of the air it encloses. Insulating at the roof line may slightly increase the enclosure area but it will be inconsequential and is likely to be more than compensated by an ability to do a more effective job of insulating and air sealing at the roof line. In buildings that have mechanical equipment or ductwork in the attic, there are substantial benefits to bring those things into the thermal and air enclosure. There are many reasons for that. There are also practical reasons to want to have anything stored in that space to be inside the envelope.
When I consider these metal buildings I have tried to put my mind to solving the building science challenges that are created when they are heated. They have are inexpensive space but are sometimes used in inappropriate ways. I have a friend that has a large cabinet shop with perhaps 20 employees. It is very hot in that metal box on a triple digit day which we have perhaps 50 times a year along with high 90s for another 50. He has approached me many times to try to figure out a cheap way to make his men more comfortable but after the fact it is a difficult challenge. Radiant barriers are only somewhat effective until they get dusty. insulations are expensive when attached from below and then covered with an ignition barrier.
I have a metal building with radiant barrier that helps some but I don't do anything dusty in that building and it is still fairly clean and somewhat effective. If and when I build a personal use metal building that I want to heat and cool, I think I will sheath the entire building with plywood and use 1-2" of polyiso on the walls and 2-4" of polyiso on the roof and then cover that with metal panels either with or without purlins. I would need to think it through a bit and draw up the details but it would be a strong design from a performance angle.
I have recently helped a friend build a 16x32 two story building for his family that is based on this plan but with wood framing. It is however covered with corrugated roofing on the walls and ceilings and is heated and cooled with 3/4 of a ton of ac.
I am currently cooling a 8,000 sq ft building under construction with a 3 ton heat pump that was originally installed in my personal home 27 years ago. It keeps the whole building cold on a 100 degree day with 20 workers present. It has 2,700 sq ft of high performance glass.
I cool my 4,000 sq ft personal home with 2 1/2 tons and it has 50% run times on 100 degree days and this year we had a day of 112 degrees and on that day it ran continuously from 7pm until midnight but held the 73 degree set point. The air quality and purity of these buildings is superior. Pollutants from showering cooking and other activities is exhausted at the source and fresh air is brought in filtered and dehumidified.
Richard, I think your building will work fine depending on how it is used but when you build your home, there are better ways. These methods are not new and were actually first developed by an engineer named Neal Hutcheon in the 50s in Canada.
Again, y'all, this is too complex to do in a post on a tractor forum but we can talk over a cup of coffee if the timing works. Give me a shout. No proof reading so I hope it makes sense.
