Tag Archives: underlayment

How to Minimize Possible Hail Damage

Welcome back from Friday’s article. As a fan of long suffering professional sports teams (Vikings, Twins, Mariners) I had the opportunity to watch Randy Johnson’s epic relief appearance in game 5 of 1995’s ALDS.

Randy also helped Geico sell some insurance with this snowball (not quite a baseball sized hail chunk): https://video.search.yahoo.com/search/video?fr=crmas&p=randy+Johnson+throwing+snowball+commercial#id=1&vid=2f0c9212ab8080ee8ad0b4b53361f2a3&action=click

Randy was clocked throwing a 5.25 ounce baseball at up to 102 mph (miles per hour).  A 1-1/2 pound hailstone will travel at speeds up to 105 mph – basically impacting whatever is in its way with nearly 3-1/2 times the force of a Randy Johnson fastball!

At this point in time, there is no solution providing a completely hail resistant roofing solution. No traditional roofing materials can come away from these types of hail stones without being dented or damaged. While there are suitable measures able to be taken to prevent damages from most hailstorms, largest hailstones will cause damage to even the most durable of roofing systems.

In order to understand how well a roofing material will hold up against hail, it is first important to understand how these materials are judged. A common test for measuring roofing material effectiveness against hail damage would be UL 2218: Standard for Impact Resistance of Prepared Roof Covering Materials. This test uses a steel ball to impact various locations on a particular assembly including edges, seams or unsupported joints or sections. While this test provides maybe a best gauge of how a roof will hold up against a hail storm, a steel ball is not a hailstone, and even this extensive test does not guarantee a material or product will hold up against a severe hail storm.

Fortunately, baseball-sized hailstones don’t happen every day. In a majority of instances, a Class 4 UL 2218 rating will be sufficient in protecting your barndominium from roof penetration due to a hail storm. A Class 4 test involves a steel ball weighing 1-2 pounds being dropped from a height of 12 to 20 feet on an assembly’s same location. This is considered by most professionals (and insurance companies) as the highest level of protection a roof covering material can provide.

While UL 2218 (and other testing standards) measures abilities of a material to stand up to rips, tears, holes and penetrating issues, it does not consider a material’s visual appearance once testing is complete. In other words, your roof may still be 100% structurally sound after a severe hail storm, but could also look like someone took a baseball bat to every inch of your roof. Beyond a visual nuisance, some insurance companies who provide a discount for metal roofing will not cover cosmetic damage caused by hail as your roof is still intact and structurally sound.

 To minimize cosmetic damage, take into account panel design. Many standing seam metal roofs have large, flat surfaces showing smaller imperfections due to their smooth uniform appearance. Breaking up a standing seam panel with striations or ribs will help minimize visual impact of dents, as well as help with expansion and contraction in areas prone to temperature swings.

A common misconception when it comes to protecting a structure against hail damage is steel roofing thickness. While thicker steel can be better at preventing dents and surface damage, provided it is not softer, it is also often less flexible than a thinner material.  Thinner steel panels may dent easier, but are less likely to tear. While most metal panels ranging from 22 to 29 gauge steel offer a relatively similar level of protection, there is a difference in how each thickness will perform against different aspects of a hail impact.

An important factor in choosing a roofing envelope able to hold up to most hail storms includes selecting the right underlayment material. Like visible roof coverings, underlayment materials are also tested for impacts. Often people spend a significant amount of time carefully choosing their roof system covering, without ever considering this second layer of defense. Underlayments can not only help protect your barndominium from impact, but are also tested for water, air and fire ratings.

Ultimately there are a number of factors to consider when choosing a roof to help hold up against severe hail storms. Choosing the right materials and speaking to your insurance company about actual coverage of your plan are among the most important choices to make.

Tips for designing a hail resistant roofing include maintaining a minimum roof slope of 6:12 and/or using roof decking (well supported plywood sheathing) and a tested underlayment.

Do your research – speak to professionals about your options, and make decisions on those factors most meaningful to you and your new barndominium.

Avoiding Oil Canning of Standing Seam Steel Roofing

BRETT in CUMBERLAND FURNACE writes:

“I was talking to a contractor and he really thinks it is a big mistake to use a 26 gauge thickness vs a 24 gauge. He is stating “I will have less issue with oil canning and it will look a lot better for the extra cost over the life of the roof. I don’t think Fabral even makes a 24 gauge for this roof panel. Any thoughts to his statement?”

Mike the Pole Barn Guru says:

If I would not have recently sold our home near Spokane, Washington I would have re-roofed it with 24 gauge standing seam steel panels. This thickness was not determined by avoiding oil canning, it was a function of being able to get my color choice with Kynar paint.

Fabral Stand N Seam

Oil canning in metal roofing is an observed waviness or buckling across sheet metal panels not normally affecting a roof’s structural integrity. While sometimes caused by inferior metal or too-low-gauge thickness, too often, it is caused by under- or over-tightening of roof fasteners causing metal roofing to stretch, pull and dimple in various directions. An over-tightened fastener will pull cladding down locally and can create deformations. Generally speaking, thicker metal means less likelihood there will be oil-canning. Other causes include:
• Uneven substrate
• Width and spacing of seam
Don’t start a panel installation out of square. Leave room for thermal expansion at eaves to lessen oil canning. Most panels accommodate transverse thermal expansion by flexing of webs and by “take-up” at sidelaps. When panels are over-tightened, these relief features are hindered or eliminated, particularly for flat panels without corrugations.

Substrates are often a source of oil canning. Substrate must be made of a material, or set of materials, not adhering to metal underside or restricting metal’s normal thermal movements. Deck deviation, bows, ridges and camber all induce stress in finished panel installation. Substrate needs to be in a level plane. Make sure the substrate has no defections and shim panels when needed. Also, “slip sheets” between metal and underlayment can prevent oil canning. Some underlayments have a surface acting as a slip sheet.

Improper storing, handling, carrying and installing panels can contribute to oil canning. Twisting, buckling and other mishandling of panels can introduce oil canning into a previously flat panel.

Narrower width panels help to alleviate the appearance of oil canning. Darker colors accentuate oil canning, while earth-tone colors hide it best.

Insulating a Steel Truss Building

Insulating a Steel Truss Building

Reader JONATHAN in MISSISSIPPI has been planning a building using steel trusses and has insulating questions. He writes:

“I have recently found your blog and I have to say I am on good information overload.  I’ve read your posts on insulation and air barrier more than twice maybe more.  I live in Mississippi so hot and so humid.

My plan is to build a 32×60 using steel trusses 10′ on center and 2×6 purlins and at the 28′ mark I am wanting to put up a wall to cut the space in two, half wood shop half living area. My biggest question is about insulating the roof for both areas the same, which would be a closed/unvented roof (no attic). I am going to put sheeting over the whole building (walls and roof) and use closed cell spray foam for insulation on the roof, filling the entire cavity of the 2×6’s.  On the underside of the 2×6’s I am going to install some seasoned metal for the ceiling. 

My question is, what if anything do I need to install between the metal roofing and the sheeting? Tyvek? 30# roof felt? or would this work https://www.lowes.com/pd/48-in-x-250-ft-1000-sq-ft-Synthetic-Roof-Underlayment/3151833? Does a unvented/closed roof need to breathe any? Because if it doesn’t I really like the synthetic roof underlayment. Or do you have any suggestions?

On the walls I am going to stud vertically between the posts with 2×6’s with sheeting on the outside, cover it with Tyvek, and metal over that. What suggestions do you have on insulating the walls? Do I need an additional vapor barrier on the inside of the walls? I was thinking maybe a thin layer of closed cell foam on the inside and going with mineral wool insulation batts between the studs.

I had a lot more questions than I thought I did, whew! I just want to make sure I am doing it right, without any problems down the road and I am ok with a little overkill and cost to do it. Just wish I could afford/justify SIP panels for the roof.  

Any and all information and guidance is appreciated.”

Mike the Pole Barn Guru writes:
I will first express my concern for your desire to use steel trusses. Unless your provider can furnish engineer sealed drawings showing adequate load carrying capacity for your particular circumstances (you have added dead loads beyond what they are typically designed for, as well as an appropriate wind load) I’d be running away from them. They also should be designed to minimize deflection. I’d want some written proof of these trusses having been third party inspected for quality as well. You are going to be making a significant investment into your new building – no reason to have it fall down around you.

Moving forward. Between roof sheathing and steel roofing you do need to have something. A minimum of 30# felt should be used, although synthetic underlayment would be just fine. You may want to investigate a system including a ventilated roof mat, as it will reduce thermal heat transmission. A weather resistant barrier such as Tyvek would be an absolute wrong product.

For walls, you should create a thermal break between studs and interior. I’d glue two inch closed cell foam boards to stud inside face and then glue 5/8″ gypsum wallboard to foam board inside face. I’d probably fill wall cavity with BIBs insulation rather than closed cell foam and mineral wool batts. This will more fully fill cavity without creating voids.

I have yet to see SIPs as being economically practical. They appear to be expensive enough so as to preclude ever being able to recoup investment costs.