Tag Archives: roof slope

Things Roof Truss Manufacturers Should Ask

Things Roof Truss Manufacturers SHOULD Ask, But Don’t Always

I didn’t just fall off of a turnip truck yesterday, even though there are a few who may doubt my claim!

Prefabricated metal plate connected wood trusses and I became close friends back in April of 1977. Yes, we had electricity then and no, I did not watch space aliens build Egypt’s pyramids. Eventually I owned and operated two truss plants for 17 years. I know it may sound odd, but I did learn a couple of things.

Most of us do not know to ask (or tell) what we are not asked.  When Hansen Pole Buildings’ Wizardress of Ordering Justine gives information to our trusted truss suppliers, all of these factors below have been incorporated into our order. This insures your trusses will be adequate to handle loads being placed upon them.

Chances are you (as well as most other post frame building kit suppliers and/or contractors) have not taken all of these into account. In failing to do so, your building may not do everything you want it to do not only today, but also years from now (or could even fall down and go boom).

Here we go:

Span from outside of wall to outside of wall. Eave overhangs are not considered as part of a span.

Desired slope(s) – with scissor trusses to achieve a vaulted ceiling or added center headroom, provide an interior or exterior ‘must have’ and other slope will be determined from ‘must have’ slope.

Spacing (ideally you will be using double trusses spaced directly on columns) rather than going into some lengthy dissertation on truss spacing, please read this article: https://www.hansenpolebuildings.com/2011/06/pole-barn-truss-spacing/.

Overhangs on eave sides (measured parallel to ground), as well as beyond endwalls. Why is beyond endwalls important? For sake of discussion assume single trusses placed every two feet, unless specified and designed otherwise and end truss in this scenario can only support a foot of overhang past an end. Single trusses placed every four feet can support a maximum two foot end overhang.


Roofing material and any solar or rooftop arrays. How many psf (pounds per square foot) must your trusses support? Steel roofing is fairly light weight. If using shingles, Code requires incorporation of enough load capacity for a reroofing down the road.

Is roofing over purlins, sheathing? Maybe sheathing AND purlins. Whichever is your case, these weights need to be accounted for as top chord dead loads.

Ceiling? If not now, ever? One of my most asked questions is in regards to adding ceilings in existing post frame buildings. At a bare minimum to support steel liner panels bottom chord dead load should be three psf, for gypsum wallboard (sheetrock) five psf. Last year Hansen Pole Buildings opted to increase bottom chord dead load for all trusses spanning 40 feet or less to five psf. We do not frankly do a very good job of promoting the benefits of this feature.

If attic is insulated, weight of ceiling material, ceiling joists and attic floor insulation.  

Design wind speed and exposure. More buildings fail from roofs blowing off, than from snow. Depending upon Code year and version, wind speed may be expressed as Vult or Vasd. There is a difference and whoever is going to build trusses needs to know. If you do not fully understand differences between B and C wind exposure, learn quick: https://www.hansenpolebuildings.com/2012/03/wind-exposure-confusion/

Heated or Unheated? There is a factor relating to whether your building will be heated and it influences design snow load. Heated buildings help melt snow off.

Overall building dimensions: width, length, height above grade. These factors impact wind design.

Risk Category – How your building will be used impacts design snow and wind loads. Buildings with infrequent human occupancy have less risk and can be designed for a greater probability of failure in event of an extreme weather event.

Energy heels for full depth attic insulation? If ever insulation might be blown into a dead attic space for purposes of climate control, to be effective it should be full depth from outside of wall to outside of wall. For extended reading: https://www.hansenpolebuildings.com/2012/07/raised-heel-trusses/

Siding material (so proper gable truss recommendations can be made). If supporting other than roll formed steel siding, end truss probably will require vertical studs. Without a continuous wall beneath an end truss, it must be ordered as a structural gable.

Is the building fully enclosed, partially enclosed or open? This will again influence wind design.

Are you interested in parallel chords with a heel height to create a vaulted ceiling? You can get the same slope inside and out with this method.

Done right you would be offered options to increase load carrying capacities against either wind, snow or both. This is true value added design. Builders most always want bare minimums, while people who are doing DIY homes or barndominiums are most likely to increase capacities. If in doubt – own the last building standing!

When I was building trusses I  had extremely high expectations of my truss staff, we always wanted to offer designs to exceed our client’s expectations.

Too many factors to juggle? You do not have to fret with an engineered Hansen Pole Building. Please call 1(866)200-9657 today.

P.S. Remember, I have no current interest in any truss manufacturing facility so please don’t contact me for truss prices, thanks.

Temporary Client Insanity – Truss Problems?

Temporary Client Insanity – Truss Problems? 

Long ago someone told me during the course of any construction project there comes a time when every client goes absolutely bat-pooh crazy. Personally, even knowing what I know, I am guilty of freaking out and having had a case of temporary client insanity during our own remodel and construction projects for our home.

For hyperventilation they have people breath from a brown paper bag, in my case – perhaps a plastic bag over my head and tied tightly about my neck would have been more appropriate.

Below I will share a client’s concerns. He remained much calmer (totally appreciated) during this process than I might have. He wrote to Justine (Hansen Pole Buildings’ Master of All Things Trusses):

“Justine, one more thing, the top chords of the trusses show 2×8 and the trusses were delivered with a 2×6 top chord, so all the bracing (purlins) will be hanging down. This roof is going to be insulated.

Also, the double trusses are not fastened together and I think I should have more than 1 set of scissored trusses.”

Our Technical Support response:

Building plans are drafted prior to receipt of truss drawings, so trusses as drawn on your plans are merely a depiction of what they may look like. Top and bottom chords as well as internal diagonal webs may be entirely different. The roof slopes will be accurate. Your building’s roof purlins certainly may hang below roof truss top chords, as this has no bearing upon your ability to insulate (please refer to Figure 9-5 of your Hansen Pole Buildings’ Construction Manual). As your roof has a Reflective Radiant Barrier, if you intend to use batt insulation between purlins, make sure to use unfaced insulation without a vapor barrier on underside, otherwise moisture can become trapped between two vapor barriers. This can lead to ineffective damp insulation as well as potential mold and mildew issues.

Per change order #3 your building is to have standard trusses in front 24 feet and a vaulted ceiling in rear 24 feet. With a pair of scissor trusses at 12 feet in front of rear endwall, this allows for the rear 24 feet to be vaulted and front 24 feet to have a level bottom chord.

Truss assembly people are not carpenters – and rarely do truss manufacturing facilities even have nail guns. It also avoids nail wounds from inexperienced or inappropriate use. As an example – back in 1979, I was shopping for a new employer designing and selling trusses. I interviewed with Tilden Truss, near Seattle. They used air guns firing a “T” staple to initially set steel truss plates. Their fabrication shop ceiling was covered with hundreds (if not thousands) of these “T” staples!

You will find it much easier to maneuver single trusses around your building site, than twice as heavy double trusses.

Please feel free to address any building assembly concerns to TechSupport@HansenPoleBuildings.com.

Another crisis averted.

Free Post Frame Foundation Building Calculator

Free Post-Frame Building Foundation Engineering Calculator

No, such a thing as a free post-frame building foundation engineering calculator does not exist. However there always seems to be someone out there who is in search of “engineering for free”.

Reader KELLY writes:


Do you have a link to a pole foundation engineering calculator?

Looking for column depth / diameter for:


10 ft column spacing

35 PFS load

115 wind load.

No floor for constraint.


Mike the Pole Barn Guru responds:

There is no such thing as a “pole foundation engineering calculator” therefore, there is also no link to one. The design of post frame (pole) building foundations is one which is best left in the hands of RDPs (Registered Design Professionals – architects or engineers). When provided with all the pertinent information about your proposed building, they can design not only a structurally sound column embedment, but also your entire structure (which I whole heartedly recommend).

You’ve provided some of the information a RDP would require, but I will expand upon it:

Will the building have adequate sheathing (which could be roll formed steel roofing and siding) to transfer wind loads from roof to ground through endwalls? And will the sheathing be adequately fastened to underlying frame to take advantage of sheathing stiffness? If yes, diaphragm design can be utilized in your building design.

The difference in forces carried by sidewall columns with and without an adequate diaphragm is a factor of 4! If diaphragm design cannot be utilized, expect significantly larger columns, deeper holes and more concrete around columns.

What type of soil is at building site? Strength and stiffness of your soil will impact both depth and diameter of holes.

How are you measuring your 14′? It should be from bottom of pressure preservative treated splash plank, to underside of roofing at sidewalls. It does make a difference.

Does your building have overhangs?

What is the roof slope?

What is wind exposure at your site? The difference in force against columns between Exposure B and Exposure C is roughly 20%.

In the event you are not interested in procuring services of a RDP, the NFBA (National Frame Building Association) has available a Post-Frame Design Manual and you could attempt to do calculations yourself. For more information please see: https://www.hansenpolebuildings.com/2015/03/post-frame-building-3/.

Of course you could always invest in a fully engineered post frame building kit package. Besides engineer sealed blueprints and calculations, you would also get materials delivered to your site and a multi-hundred page Construction Manual to guide you through to a successful completion.


Lean To or Not to Lean To?

Lean To, Or Not to Lean To?

Over my post frame building career I have seen a plethora of buildings designed with an enclosed clearspan enclosed space plus a shed roof (or lean to) for one or both sides. Most often just a roof, a lean to provides shade and not much else for whatever it covers.

But, does just a roof provide a best design solution from practicality and economic standpoints?

I suppose I have been awaiting a reader to ask this question, as my radar has seen it coming! Thanks to DAN in OREGONIA who writes:

“I want a barn 40X64 enclosed with 14’ high overhead doors in the ends i also want a 15’ lean to down one 64’ side. I am trying to maintain RV height in the lean to. Would it be more cost effective to use a 55’ span truss designed to enclose 40’ and leave the 15’ open with a ceiling as the lean to, or make the enclosed area taller to continue the pitch to 14’ at the end of the 15’ overhang? I guess that would make the building walls 19’ tall.”

Before we dive into pool’s deep end, a couple of notes in regards to this building Dan ponders. In order to have a 14 foot tall overhead door, an eave height of 16 feet (and more probably 16’6”) will be necessary. More often than not, a roof slope of 4/12 (read about roof slope here: https://www.hansenpolebuildings.com/2018/09/roof-slope/) proves most cost effective. This means across his 15 foot overhang, there will be a five foot difference in slope.

Hansen Pole RV StorageAs an alternative to a five foot elevation drop, a pitch break could be used between main clearspan and lean to roof. I usually try to avoid going steeper-to-flatter as it adds to construction complexity, adds to costs and provides a place for accumulation of debris (tree leaves and needles) as well as snow sliding off the enclosed portion.

Given a five foot difference and wanting to have RV height in the lean to, puts eave height of main portion of structure up to 21 feet or more! Certainly doable, but probably not affording many benefits unless one contemplates a mezzanine area. And while height increases are relatively affordable, they are not free by any means.

Most people view their new post frame buildings as ways to protect their valuables from not only elements, but also theft, vandalism and critters. Just a roof only partially accounts for only one of these.

In most cases, least expensive, easiest to construct and most practical design solution involves a  clearspan of entire area and placing walls around perimeter. This keeps everything securely within a space of adequate headroom – without having to increase heights just to allow for clearance within the lean to.

Considering a barn or shop with an attached lean to? Give some thought to enclosing it all with a clearspan. Affordability might prove surprising and plus you gain practicality benefits.

What Size Posts Should I Use?

What Size Posts Does My Building Need and How Deep Should They Be?

Reader ANONYMOUS in BENTON writes:

“1. If my building has 16 posts and posts are 12 feet apart do I need 4×6’s or 6×6’s?
2. If the plan shows 16 feet above grade how much do I need underground?
3. If the posts are set 12 feet apart will two 2x12s glued together support a truss system with a total length of 36 feet?”

Mike the Pole Barn Guru responds:

While I appreciate your questions, we as a company and me as an individual do not provide free engineering services. In answer to your questions:

1) Without knowing the full dimensions of your building, including roof slope and overhangs (if any), if the columns will be adequately tied into a concrete floor, as well as your site’s snow load, design wind speed and exposure, seismic zone as well as the dead loads which will be carried by your building there is no possible way for me or any RDP (Registered Design Professional – engineer or architect) to be able to answer this.

2) The depth of the columns into the ground should be shown on your engineered building plans (you do mention you have plans). At a minimum the holes should be no less than 40″ deep and must extend below the frost line. Ultimately the depth and diameter will need to be determined by the RDP in consideration of the factors listed in (1) above, as well as designing for the ability to adequately prevent uplift.

3) Since I would use double trusses which bear directly upon the columns, there would be no need to use any other type of dimensional lumber to provide headers for a truss system. Again, this is where your RDP can design to adequately provide an engineered system to support the trusses.

My best advice, since I am guessing you are somewhat floundering in this, is to invest in a fully engineered post frame building kit package which includes plans sealed by a RDP and designed specifically for your building, at your site. It just isn’t worth trying to avoid the small expense into a proper design – especially when the lives of the occupants depend upon it.

Here are some other articles which pertain directly to this subject and should be read: https://www.hansenpolebuildings.com/2014/12/free-pole-barn-plans/ and https://www.hansenpolebuildings.com/2017/11/dont-engineering-fool/





Formula for Calculating Wall Girts

An Excel Formula for Calculating Wall Girts, Post Size and Hole Depth
John Minor and I have been friends for nearly 30 years – since his then father-in-law (and my business partner at the time) convinced me John could sell post frame buildings. Well Rod was correct, John could sell buildings – not only for me (twice), but also for some of the better known names in the post frame industry – Morton, Stockade, Cleary and FBi just to name a few.
John is also a cutting edge innovator and has gone from selling post frame buildings, to manufacturing and providing components to the post frame industry. Current he owns and operates Central Perma-column (https://www.heartlandpermacolumn.com/). John is smarter than the average bear and he has the thirst for knowledge which few non-RDPs (Registered Design Professionals – architects or engineers) in the post frame industry do.
December 13, I received this text message on my phone: “I need your help with something”. Although I did not recognize the number it came from, it turned out to be John.
The conversation went on like this – John, “No worries. I’m trying to find an Excel formula for calculating wall girts, post size and hole depth.”
Me, “You would have to write one and they will be very complex due to the tremendous number of variables involved. I’ve thought about having a Wall Girt calculator on our website for Building Officials to use and the reality is, it is a huge undertaking. For it alone, requires all of the building dimensions including roof slope, is building enclosed or partially enclosed? Which means one has to know if doors are wind rated, and where they are placed. Also makes a difference as to where girts are located on building as wind forces are greater at corners. If girts are barn style on outside of columns, do they span a single bay or multiple bays? Then one has to account for lumber species differences as well as visual vs. machine grading.

Best bet would be to layout all of the parameters and put it out for bid on Upwork. Should specify which versions of Code and NDS you want to cover as well as it must conform to the NFBA design manual. For columns, you are now talking 25-35 pages of calcs.
Fun, eh?”
John, “Damn!”
Those “simple” pole barns one drives by every day are in reality highly complex engineered structures (when properly designed). A full set of calculations for a small two car garage can generate nearly 200 pages of single spaced calculations to prove the adequacy of all structural members and connections, from the footings to the last fastener.
Don’t leave your new post frame building to chance – insist upon having only a building which has been designed specifically for you by a Registered Design Professional, on your site, with your dimensions and your doors!

It Is Exactly the Same Building Part I

Well, maybe not exactly the same building.

In April of this year we had a client invest in a brand new 36 foot wide by 60 foot long post frame building kit package with a 16 foot eave height. Three months later, the building has been delivered, and one of the group which ordered the building sends us a quote on “exactly the same building” from a worthy competitor. And, of course, the competitor’s quote is way less expensive!

Now the competitor’s sales person advised the client the quotes were exactly the same, other than he had quoted a 25 psf (pounds per square foot) roof snow load, whereas we provided a 40 psf load, which is 60% more snow carrying capacity!

Turns out there were maybe a couple of other differences as well……

Things we have and they do not:

4/12 roof slope vs. 3/12 The steeper roof slope will look less industrial as well as more readily will shed snow.

C wind exposure vs. B wind exposure (for a detailed explanation of wind exposure please read here: https://www.hansenpolebuildings.com/2012/03/wind-exposure-confusion/).  The benefit of an Exposure C wind load is it makes the building roughly 20% stronger in resisting wind forces, than the B exposure.

12″ enclosed overhangs vs. 18″ open overhangs. Not only are enclosed overhangs far more attractive, they provide ventilation and eliminate the wonderful nesting locations for flying critters which are provided by open overhangs.

12’x14′ residential overhead door vs. 14’x12′ commercial overhead door. If the client wants to get something taller than 12 foot through the other guy’s door, it just isn’t going to fit no matter how big a run one gets at it. Residential overhead doors come with “dog eared” openings and a far more attractive in a residential setting. Here I discuss why 14 foot wide doors are not what they are cracked up to be: https://www.hansenpolebuildings.com/2016/05/14-foot-wide-doors/.

One more entry door. Insulated commercial steel entry doors with steel jambs do not come cheap, especially when they are four foot wide!

Integrated J Channel on windows. So much easier to install than having to cut four pieces of steel trim to fit around a window and have them not leak!

The reflective radiant barrier with pull strip attached adhesive tab on one side vs. Metal Building Insulation (MBI) under the roof steel to minimize condensation challenges. My personal horrors of installing MBI can be visited here: https://www.hansenpolebuildings.com/2011/11/metal-building-insulation-in-pole-buildings-part-i/.

Lifetime paint warranty on steel vs. 40 year pro-rated. Your post frame building is going to be around for a long time, might as well have the best paint warranty available to minimize the effects of fade and chalk.

Base trim – keeps those creepy crawling critters from entering the building through the high ribs of the wall steel.

Top of wall trims – Even though roll formed steel siding lengths are controlled by a computer, they do vary slightly from panel to panel. The bottom of the panels should be kept at the same height as “stair steps” at the base of the walls is quite noticeable. Easiest way to hide any variants is to place the top edge into a piece of trim which covers any fluctuations.

Jamb trim on Overhead Door– exposed wood overhead door jambs are very popular in some parts of the country, however they do turn grey and then eventually black if not kept painted.  The idea of a steel covered post frame building is to minimize future maintenance. Having to paint raw exposed wood does not meet with this criteria.

Heard enough? No? Then come back tomorrow for Part II. You won’t be disappointed!

Single Slope Roof

Single Slope Pole BarnAs a pole building “newbie” the first pole building I constructed back in the Spring of 1981 happened to be a 20 foot by 36 foot three sided loafing shed – with a single slope roof. As a builder, I didn’t make much money on it, as basically my head was still caught up in a stick framer’s mentality (studs and rafters go up and down, girts and purlins go left and right). Dealing with several feet of grade change was also something I was unaccustomed to, it was much different than having the level top of a concrete foundation to work from.

My second building was a 24 foot by 96 foot single slope roof, which was built over existing cattle pens! The pens were a challenge to work over, but at least the site was level.

Neither one of these experiences caused me to see single slope roofs as the less than ideal solution to most pole building needs.

In my humble opinion, in most cases, single slope roofs are neither aesthetically pleasing, nor the most cost effective solution. However, for small (say 12 foot in width by any multiple of 12 feet in length) run in sheds for horses or cattle, they may prove to be economically the best answer.

What are the most common reasons people select a single slope roof?

The top reason – the mistaken belief they will somehow be less expensive.

Most steel roofing manufacturer warrantees are void on roof slopes of less than 3/12. In order to keep the warranty in effect, this can quickly cause the “high” side of the building to become very tall.

Using the most common roof slope (4/12) a 24 foot wide building will be EIGHT FEET taller on one side than the other! From a structural aspect, building columns act as beams to resist wind loads. The formula for a simple span beam includes the square of the span – think of a 16 foot height having to carry FOUR TIMES the load of eight foot! The resultant is some potentially very large columns.

The resultant is paying to enclose a large area, in cubic feet, which cannot be practically or easily utilized.

The second most common reason for single slope roof, is so the weather (rain or snow) runoff will all travel to one eave side. This becomes more commonplace in snow country, where snow removal in front of sidewall doors can become a constant work in progress.

Rather than single sloping, it would be far less costly to use a pitched gable truss, with snow brakes to actually keep the snow on the roof and from sliding off in piles in front of doors. Having all of the snow slide in one direction could result in a crushing weight of snow piling up against the low side eave wall – buckling the siding, if not causing a catastrophic collapse.

Some single slope roof considerations:

Roof slope should be no less than 3/12 to maintain steel warrantees.

If desiring a clearspan, the overall height of the roof trusses should be no more than 12 feet. Many roof truss fabricators are limited to the ability to build trusses 12 feet in height, and for those who can, shipping becomes an issue as special permits must be acquired as well as pilot vehicles – adding to the expense.

In the event the single roof slope is fairly flat, and the clearspan width is greater than what can be supported by dimensional lumber or LVL (Laminated Veneer Lumber https://www.hansenpolebuildings.com/blog/2013/01/lvl/) rafters, prefabricated trusses are going to require added heel height (truss depth) at the low sidewall. This can result in a decreased ability to utilize all interior aspects of the building, as truss members will be taking up several feet of space below the low eave height.

Interior columns may need to be added to reduce truss costs, or get spans down to dimensional lumber manageable distances. In many cases, interior columns can get in the way, especially if the building is ever re-purposed.

Lofts – while the numerous feet of added height along one eave might prove to be a wonderful space for a second floor, consider the loss of headroom as the tall wall is moved away from. In most cases, those single sloping trusses will not lend themselves well to supporting a usable attic space within the truss. If so, then interior columns will need to be added to support the loft floor.

Doors – be wary of placing doors on the tall sidewall which are equal to or greater than the height of the low sidewall. While tall things might be able to enter the doors, those very same tall things will eventually run into the roof. With prefabricated trussed roofs, the lateral bracing between bottom chords and webs will be in the way.

Considering a single slope roof? Carefully weigh all of the options to insure it is the correct design solution for your circumstances!

What is the Best Solar Panel Roof Slope?

Hansen Pole Buildings’ Designer Rachel asked me today what the best solar panel roof slope?

Solar Panel Pole BarnThere are three main factors which go in to the calculation of how much sun a roof receives. Roof angle or pitch, roof orientation (how south-facing a roof is) and location. Since Rachel asked about roof slope, I will focus on this one aspect.

There is an optimum angle for solar panels on a roof. This is the angle where, over the course of the whole year, the panels get the most amount of direct sunlight which produces the greatest amount of electricity.

The question is: what is the perfect angle, and if the roof is not at exactly this angle how much energy will be missed out on? I’ve arbitrarily picked a location of 49 degrees north (generally the United States – Canadian border in the western U.S.) and a south-facing roof for this example.

So for this roof the optimum angle is 35° (a bit over an 8/12 roof slope) and at this angle the roof generates 1,265kWh/m2/day. The energy reduces as we move away from this optimum angle. At 30° the energy drops to 1,260kWh/m2/year – a reduction of just 0.4%. At 20° (15° away from the optimum angle) the energy drops to 1,229kWh/m2/day – a reduction of 2.6%. It’s only with very steep roofs – say over 60° – when the solar energy really drops off.

If you want to see how this works for your roof you can create a free report at:  https://www.solstats.com/ – take a look at the bottom of the report and you’ll see a version of the chart above for your location. WARNING: Entering your zip code will NOT take you to United States locations, it takes scrolling across the world map on the website.

It is obviously preferable to have a roof at the perfect angle. While I am not a fan of government subsidies, they are very generous when it comes to solar energy. Including them in the calculation, it absolutely makes sense to install on roofs which are not at the perfect angle. You’ll lose a few percent of solar energy but it should still make financial sense.

Mike’s Roof Rules

Nothing is worse than a roof gone wrong. Leaks frustrate everyone involved, and are usually avoidable. Poor design and poor installation are equal factors in the roofs which just are not happy.

Avoid Valleys

Pole Barn Roof With ValleysDesigning the roof of a pole barn? Then try to design a roof without any valleys. Valleys concentrate water and often clog with ice. It’s far more common to have leaks or ice dam problems near valleys than in the middle of a simple gabled roof. Many valleys exist because of a designer’s conceit rather than necessity. Often, these valleys trace back to the mistaken belief a chopped-up, complicated, multi-plane roof looks better than a simple gable. It doesn’t. And more complicated roofs are more expensive.

Just say no to Dormers and Skylights

Dormer Pole BarnNo good reason exists for a new pole building to have a dormer. When I see a dormer, I conclude the designer or the architect made a mistake. They didn’t include enough interior space, and the building owner was forced to cut a hole in the roof because the ceiling was too low to stand up. Want to build a multi-story pole building – no problem. Want two floors, build two floors. Want three floors, build three floors. Then build a roof over the top floor. This roof should not have any deliberate holes in it. The “no holes” rule covers both dormers and skylights. Skylights are an invitation to leak – no matter how great the flashing kit is, pretty well plan upon them leaking, if they don’t it is a surprise bonus.

In most cases Single Slope Roofs are not less expensive

They also create a very tall wall on one side of the building, which has to be engineered for. Lots of “dead air” space ends up being paid for. There is not a ridge which can be easily vented. Worst of all – most people find them aesthetically unattractive.

An Unconditioned Vented Attic is better than an Insulated Roof

It makes more sense to put insulation on a flat ceiling than to try to insulate a sloped roof, for several reasons. Purlins usually aren’t deep enough to hold a thick layer of insulation; on the other hand, it’s usually easy to add a deep layer of insulation to the attic floor. Insulating the attic floor is also cheaper. Leave the space between purlins uninsulated, it will be easier to locate roof leaks. It is easier to air seal a flat ceiling, rather than a vaulted ceiling. If roof sheathing is used, damp roof sheathing will dry out quicker if it faces an attic than if it is part of a cathedral ceiling.

The Best Roof Shape is a simple Gable Roof

In a cold climate, the ideal design is a simple gable. Since gables don’t have any valleys or hips, they are easy to vent. It’s a straight shot from the soffits to the ridge.  Chopped-up roofs with a variety of intersecting planes are hard to frame, hard to keep watertight, and hard to vent. Every nook and cranny creates somewhere for tree needles and ice to accumulate.

In a hot climate, a hipped roof can make more sense than a gable, because a hipped roof makes it easier to provide shade on all four sides of the pole barn. In a hot climate, shade is good. Fortunately, people in hot climates rarely have to worry about ice dams.

In all climates, make overhangs generous. If  building a gable roof, don’t forget the rake overhangs; most rake overhangs are too stingy. Frame the rake overhang with overhanging purlins.

Don’t reduce the Roof Slope between the Ridge and the Eave

Pole Barn - Shallow Slope RoofA good roof plane has a consistent slope from the ridge to the eave. A roof which changes slope at midpoint is disturbing. Especially disturbing is a steep roof which suddenly switches to a shallow pitch (for example, when a porch with a shallow-pitched roof is affixed to a pole building with a steep roof). Shallow slopes hold snow and are susceptible to leaks. Most steel roofing warranties are void on slopes of less than 3/12.

Make sense so far? Come back Monday when I finish up on my recommendations for making your roof affordable, long lasting, and pleasing to the eye.