48x39x14 shop build

[RayfromTX]

As I understand it - a vapor barrier is usually polyethelene or tyvek - something that prevents the passage of moisture.

I'm guessing they are standard trusses - 24" on center? I don't know, but could measure them.

The peak and eves are steel over wood 2x4 construction with enough light coming through the holes I doubt vents would add/improve anything.

A vapor barrier is defined as having a perm rating of 1US perm or less. Polyethylene and metal are vapor barriers. Tyvek is a brand name for spun polyolefin. It is vapor permeable. Spun polyolefin is available in perm ratings ranging from 7-60. Tyvek is not a vapor barrier. It was developed to freely pass water vapor while shedding liquid water which it does unless it is in contact with a surfactant or penetrated with non-gasketed fasteners.

Also the term moisture is confusing in these discussions because it refers to water vapor, liquid water, absorbed water and adsorbed water. The last two terms are different states of water found in and on solid surfaces. These discussions come up routinely and getting this right can be very important for durability.

In the building shown in this thread there exists the potential for water vapor to build up in the attic space to levels to which cold night time and seasonal temperatures can allow condensation to form on the underside of the metal roof. This may or may not occur at a level that causes problems depending on the climate. I think Missouri is not a place I would be comfortable using this construction without attic ventilation. While the metal ceiling will limit water vapor from passing from below, vapor will be drawn into the space due to several factors. The most important of these is probably the fact that as the temperature of the air in that attic changes it will expand and contract which will have the effect of the attic "breathing". Richard has ridge and eve vents to handle this in his building.

There are other ways to handle interior moisture other than attic ventilation but not in the construction to which this project is already committed.

 

[ovrszd]

Good stuff Ray.

I was concerned and asked about the attic space. Before I blew in the insulation I added barriers between the trusses so I didn't cover the soffit vents. The insulation is allowed to "cap" the wall headers to minimize heat loss there. The ridge is vented the full length of the building. All builders I talked to here told me that was sufficient. We'll see.

I am curious enough about it that I will take a look in the attic on susceptible days.

 

[JohnBuffaloMN]

My shop was built in the 70's or early 80's I think. Building codes and practices have changed significantly since then! I'm also pretty sure the 30x40 structure was put up by contractors, then interior finished by the homeowner. The concrete floor was clearly done by amateurs who didn't know how to finish concrete. The whole building obviously lasted 30 years or so without the ceiling coming down, so again I have to go back to the pooling water under the floor. I doubt you'll have any problems with your building ovrszd.

 

[RayfromTX]

Richard, susceptible days will be anytime you have had dew points that are moderate to high and then a cold snap. For instance, right now the dew points in missouri are around 64degrees. If that air is in your attic and a cold snap hits that drops the temps quickly to 50 degrees then condensation may form. If it is windy as the front passes then it may flush the air out more quickly. If however it is still and the temps drop due to clear skies and a condition known as radiant overcooling then you may get condensation then. If the sun comes out and warms the roof then it will evaporate the liquid back into the air. A north facing roof is more susceptible because it doesn't get the solar gain early if at all depending on slope and time of year and latitude of the building. There are lots of variables but what you are looking for is conditions where warm humid air encounters cold surfaces for extended time. You should be fine but you will find intermittent liquid on the underside of the metal because it has no ability to store any within it's structure. Wood structures can collect a bit before becoming wet. (hygric storage capacity) but are susceptible to decay if things go too far for too long.

I feel this is a subject that should be carefully taught in school. It is one of the least understood things there is considering how much it impacts our buildings and our lives. In 5 one hour classes, most students down to the 5th grade level can understand this in a meaningful and lasting way. I try to impart the information to every early teen that I encounter.

 

[ultrarunner]

It sounds like a metal roof over sheathing with felt in between adds a lot to the safety margin regarding condensation?

 

[MoPops]

Sure looks good Richard. It may seem like it’s taking a while,from your perspective, going up fast from my view point! Where is the future house location? Trying to imagine best spot looking at the drone shots.

 

[ovrszd]

Richard, susceptible days will be anytime you have had dew points that are moderate to high and then a cold snap. For instance, right now the dew points in missouri are around 64degrees. If that air is in your attic and a cold snap hits that drops the temps quickly to 50 degrees then condensation may form. If it is windy as the front passes then it may flush the air out more quickly. If however it is still and the temps drop due to clear skies and a condition known as radiant overcooling then you may get condensation then. If the sun comes out and warms the roof then it will evaporate the liquid back into the air. A north facing roof is more susceptible because it doesn't get the solar gain early if at all depending on slope and time of year and latitude of the building. There are lots of variables but what you are looking for is conditions where warm humid air encounters cold surfaces for extended time. You should be fine but you will find intermittent liquid on the underside of the metal because it has no ability to store any within it's structure. Wood structures can collect a bit before becoming wet. (hygric storage capacity) but are susceptible to decay if things go too far for too long.

I feel this is a subject that should be carefully taught in school. It is one of the least understood things there is considering how much it impacts our buildings and our lives. In 5 one hour classes, most students down to the 5th grade level can understand this in a meaningful and lasting way. I try to impart the information to every early teen that I encounter.

Once again, good stuff Ray.

Next to the shop is an all steel machine shed with single slope roof to the North. Next time it "rains" in there I'll check my attic.

If you were building a similar building what would you do differently?

I ask because these threads offer excellent advice for someone considering a build. I take no offense to any suggestions.

 

[ovrszd]

Sure looks good Richard. It may seem like it’s taking a while,from your perspective, going up fast from my view point! Where is the future house location? Trying to imagine best spot looking at the drone shots.

The shop sits North/South. Overhead doors in South end.

House will be East of the shop turned slightly Southwest at 205 degrees. 40ft gap between the two. House, garage, porch overhang will be covered by a 72x40 roof. Front toward Southwest.

 

[RayfromTX]

Once again, good stuff Ray.

Next to the shop is an all steel machine shed with single slope roof to the North. Next time it "rains" in there I'll check my attic.

If you were building a similar building what would you do differently?

I ask because these threads offer excellent advice for someone considering a build. I take no offense to any suggestions.

Richard
What I might do is something similar to what I do on the homes I build with some simplification. I would have to study on it to work out the engineering questions but I would probably sheath the structure with cdx. Cover that with 2" of polyisocyanurate foam insulation and then install the metal over that. I would perhaps use furring strips over the insulation to mount the metal to without having to screw the metal all the way through the insulation. Kind of a yeti cooler approach. For intermittent heating and cooling in a utility structure I would use 1" foam and just screw through it. This approach controls the temperature of the first condensing surface and is the safest way to build in any climate. It has many advantages. In a living space structure I go to great lengths to make the shell air tight. If you are interested, I can talk you through it prior to building your house.

 

[EddieWalker]

The one thing that you have to remember when insulating the roof, and also insulating the ceiling is that you have created an attic area that will also create condensation that needs venting. This is why you only insulate one or the other. It would be very hard to get decent air flow from the eaves to the peak with insulation under the roof.

 

[ovrszd]

Yeah, I was wondering about that?

Also, cost effectiveness?

 

[RayfromTX]

Insulate the roof, not the ceiling.

 

[ovrszd]

Insulate the roof, not the ceiling.

Explain why I would want to heat the attic?

 

[EddieWalker]

Explain why I would want to heat the attic?

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]

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.

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.

 

[ovrszd]

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.

 

[ultrarunner]

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.

 

[JohnBuffaloMN]

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.

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]

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.

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]

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.