Tag Archives: eave strut

How to Install Roof Reflective Radiant Barriers

How To Install Roof Reflective Radiant Barriers

DAVE in SPRING HILL writes:

“Can you please tell me how the reflective radiant barrier is applied? Does it go directly on top of the fully recessed purlins and then the steel is screwed over top of that? Is it applied vertically or horizontally? All of the videos that I’ve seen say there needs to be an air space between. It should have been stressed to me at the time of purchase that this was a critical material of the construction of my shop and it was not portrayed to me in that manner. I purchased it separate and I am at that step.  I believe the sales person must have been new because a lot of mistakes were made.”

Any steel roofed building should have some sort of provision made to prevent warm moist air from inside contacting cooler roof steel and condensing. There are many possible solutions to this – two inches of closed cell spray foam, an integral condensation control or a reflective radiant barrier being most popular (as well as being aligned from greatest to least in terms of financial investment of materials). Chapter 14 of your Hansen Pole Buildings’ Construction Manual does give detailed instructions for this installation.

Post frame buildings have a myriad of possible options and accessories, as well as being utilized for a plethora of end uses. Considerable discussion is most often involved prior to an order being placed – and on occasion there are cases where important features are lost during discourse.

We do attempt to avoid situations such as yours and you may recall having approved this Dripstop to help control roof condensation.
Here are your requested installation instructions:

Start roof reflective radiant barrier at same building end roof steel installation will begin. galReflective radiant barrier roll end begins flush with eave strut outside edge. Reflective radiant barrier leading “long” edge begins flush with building end truss outside. 

Reflective radiant barrier is installed to run eave to eave over ridge. Splices are best made directly on fully recessed purlin tops.  

Other than to make a roll end square, starting edge will remain untrimmed.  Start flush at eave strut outside edge.  Opposite end is cut flush with opposite eave strut outside edge (or ridge purlin upper edge for translucent or Vented Ridge applications).

Using a minimum 5/16” galvanized staple, staple through reflective radiant barrier to eave strut top.  As an alternative to staples, 1” galvanized roofing nails (with big plastic washers) also work well.  Roll out reflective radiant barrier across fully recessed purlins (up and over ridge) with aluminum side up and white side down (towards building inside). 

Pull reflective radiant barrier past opposite eave strut edge and staple to top. Trim roll off flush with opposite eave strut outside edge.  

Install next roll in same manner, stretching roll tightly, align properly and close butt sides.

For A1V reflective radiant barrier with an “adhesive tab”: These rolls have an approximate 1” tab (without air cells) extending along one reflective radiant barrier roll long side.  At a seam, where two reflective radiant barrier rolls are joined, pull tab across adjacent roll by 1”, remove “pull strip” from adhesive, and firmly press two rolls together. Properly installed, each roll will have a 72” net coverage.

For square edge rolls, use a butt joint and seal seams properly with tape.  

2” white vinyl tape or a silicone bead can be used to make permanent seams between ends and reflective radiant barrier roll sides. 

For maximum air and vapor tightness, keep perforations in reflective radiant barrier to a minimum. Seal all perforations with reflective radiant barrier tape. 

Exaggerated claims are often made for insulating value of reflective radiant barriers and all of them rely upon a dead air space in a completely sealed scenario – great in a laboratory situation, however impossible to achieve in real life building construction. Reflective radiant barriers should be looked upon (when seams are properly sealed) as a condensation deterrent.

Condensation Above Metal Building Roof Insulation

Condensation Above Metal Building Roof Insulation

Only those few long time readers or those who had time on their hands and have read every blog I ever wrote will recall this story about my adventures with metal building roof insulation: https://www.hansenpolebuildings.com/2011/11/metal-building-insulation-in-pole-buildings-part-i/.

Reader JOSH in CORVALLIS is having issues with how metal building insulation is (or in his case is not) performing in his post frame hangar. He writes:

“I am a first time builder and finished a 40×50 Hangar by myself a few years ago. It all came out perfectly with one exception. Every year when the temperatures change rapidly and the moisture is high I get condensation that fills up the roof insulation along the intersection of the roof and the top girt. 

I used fiberglass backed with vinyl laid under the metal roofing. When I installed it I rolled it out from one side of the building up over the peak and down to the other side in a continuous piece. Each piece then was overlapped to the next one, folded over and stapled down to the purlin. I feel that was done well. Where the insulation meets the top girt (purlin) I finished it off there by folding it over on itself and stapled it to the top of the top girt (purlin) so the metal roofing was laid on top of it and screwed down to that top girt (purlin) only touching the vinyl backing. 

At the peak of the roof I have a gap of a few inches between the sheet metal from one side to the other, with the ridge cap covering that gap. I used a duckbill plier tool to bend up the sheet metal along the top edge before installing the ridge cap to help keep out a driving rain but let air flow through. 

The roofing tips I had received from other DIY builders influenced the way I did things and I now question if those things are causing this condensation issue I have. The 3 main things are how I tacked the insulation to the top girt (purlin) by folding it over onto itself. The droop of the insulation between each purlin (about 2 inches droop), now I think that maybe should be taut against the metal. And the bending of the metal sheet up under the ridgecap as I see they sell matching foam insulation strips for this area which would obviously block airflow as well as water. So my question is what did I do wrong here and what can I do to correct it?”

Mike the Pole Barn Guru writes:
I lived for a decade roughly 40 miles northeast of you in South Salem so am vaguely familiar with your weather – two seasons, warm rain and cold rain. Now seriously, it was not so bad, until I moved back to Eastern Washington’s high desert and had to have webbing removal surgery from between my fingers.

I have given your scenario some serious thought since you wrote with your challenge.

My general method of problem solving begins with what is causing this situation, beginning with possible sources.

Usually I would point my finger at roof leaks, however you have narrowed this down to only when humidity is high. Most often increased humidity inside of buildings is due to no vapor barrier beneath a slab-on-grade. If this is your particular circumstance, I would recommend applying a sealant to your concrete floor.

Normally when water is collecting just uphill of an eave strut (aka eave purlin or girt) it is due to a raw insulation edge on top of the eave strut. You have eliminated this, however humidity laden air can still enter your system here unless you place inside closures between your fold over and roof steel (my guess is this is your source) https://www.hansenpolebuildings.com/2015/12/the-lowly-inside-closure/

Using Metal Building Insulation as a Condensation Control usually fails due to seams being poorly sealed. A 100% tight seal is essential for adequate performance. Here is how they should be done:

You have no airflow at your ridge, due to having run insulation continuous from eave-to-eave. I would cut away insulation between your ridge purlins and install vented closure strips under your ridge cap. This will give a point for warm moist air to exhaust from inside your building and prevent any blown rain from entering.

I hope this helps….please let me know how it all works once you apply the remedy.

 

Steel Ridge Cap to Roofing Overlap

Hopefully no one wants to create a roof with leaks. Reader MIKE in HARBOR CREEK wants to make sure he is doing things correctly. He writes:

“How much overlap do you have to have with roofing and ridge cap? Is 2.5″ enough and then you use metal to metal screw you do not have to penetrate the purlins?
Ty”

I cannot vouch for how other building providers assemble their buildings, so I will go with how we do it.

To calculate a building’s roof steel length we take one-half of the building’s span (or horizontal measure from peak/ridge to the outside of columns) and multiply this times a factor for roof slope. 

For slope factor – multiply slope by itself and add 144. Take the square root (use a calculator) of this number and divide by 12.

Example to calculate slope factor for 3.67/12:  [3.67 X 3.67] + 144 = 157.47. Square root of 157.47 = 12.549. Divided by 12 = 1.0457.

For a 40 foot width gabled building with a 4/12 slope this length would be 21.082 feet (call it 21’1”).

Outside of columns at eave we have a 2x of some sort as an eave strut, with a width of 1-1/2 inches and roof steel must overhang this by 2-1/4 to 2-1/2 inches. Using 21’1” for our roof steel length, this means the top edge of roof steel will now be four inches from the peak/ridge.

Standard steel ridge caps are generally very close to 14 inches in overall width, giving somewhere around three inches of overlap on each side. Placed in this overlap will be either a form fitted outside closure strip or a vented closure (https://www.hansenpolebuildings.com/2015/11/ridge-cap-foam-closure-strips/). Either of these products properly installed will prevent weather (rain and/or snow) from being driven beneath the ridge cap into your building. You can read a little more on correct placements of closures here: https://www.hansenpolebuildings.com/2015/11/outside-closure-and-vented-closure-installation/.

By using metal-to-metal stitch screws to attach the ridge cap to high ribs of roof steel, there is no need to have to miraculously hit any ridge purlins with screws. Here is a brief tale involving a builder who went off on his own tangent https://www.hansenpolebuildings.com/2011/12/stitch-screws/.

In summary Mike, provided you have a 2-1/2 inch overlap, have used proper ridge closures and stitch screws your life will be good and you will have a happy end result!

Whiskey Tango Foxtrot! Is It Ventilation?

Whiskey Tango Foxtrot! Is it Ventilation?

I really enjoy good food. In order to continue doing so and avoid weighing significantly more than I should, I do a treadmill run nearly every morning. To keep from expiring from utter boredom of exercise, I have wall mounted my flat screen LED television within easy viewing distance. With subscriptions to Amazon Prime and Netflix, I have yet to run out of movies and series to view. Most movie selections are either fairly old, or were box office challenged. One of these movies was 2016’s Tina Fay starring in Whiskey Tango Foxtrot, with a budget of $35 million and a box office take of $18.3 million.

Well, this article isn’t about how Tina Fey carried this movie. To be precise, it’s a movie title conveying my expression upon doing some recent reading.

Back in 2016 I had penned an article (https://www.hansenpolebuildings.com/2015/06/overhang/) mentioning a specific pole building company by name. A representative of this company recently contacted Hansen Pole Buildings’ owner Eric to let him know they did not appreciate being named. I was even kind enough to have included a live link to their website in my article, providing them with free press.

While editing, I happened to peruse their website. When a Whiskey Tango Foxtrot moment hit me…..

Under ‘Building Features’ I found this gem, “(Our standard roof to eave or gable design creates a fully ventilated structure making boxed overhangs an option, not a necessity)”.

I had to read it several times to fully get my head around what I thought I had read.

In order for this statement to be true, roof steel high ribs would need to remain unobstructed – allowing a free flow of intake air. This could possibly pose a challenge if one desires to keep small flying critters from entering a dead attic space.

In my humble opinion, this attempted ventilation intake ranges from laughable to totally ridiculous. However, I have found, nearly anything can be spun to sound like a benefit. What should be happening between roof steel and eave strut – placement of an Inside Closure (https://www.hansenpolebuildings.com/2015/12/the-lowly-inside-closure/), to seal these openings.

IBC (International Building Code) 2015 Edition tends to agree with me.

“1203.2.1 Openings into attic.

Exterior openings into the attic space of any building intended for human occupancy shall be protected to prevent the entry of birds, squirrels, rodents, snakes and other similar creatures. Openings for ventilation having a least dimension of not less than 1/16 inch and not more than ¼ inch shall be permitted. Openings for ventilation having a least dimension larger than ¼ inch shall be provided with corrosion-resistant wire cloth screening, hardware cloth, perforated vinyl or similar material width openings having a least dimension of not less than 1/16 inch and not more than ¼ inch.”

Thinking about a post frame building other than from Hansen Pole Buildings? Before possibly throwing away your hard earned cash, give us a call – if we feel someone else’s building has a better value than ours, we will be first ones to tell you to invest in it.

 

Avoid Metal Building Insulation

One More Reason to Avoid Metal Building Insulation

 

Photo isn’t showing the inside of a Hansen Pole Building. This view happens to be inside of an eave sidewall looking up underneath a post frame building roof. White vinyl facing happens to be underside of a product commonly known as Metal Building Insulation, having actual R values so low it should be more appropriately described as Condensation Control Blanket.

For previous words of wisdom in regards to Metal Building Insulation, read more here: https://www.hansenpolebuildings.com/2015/05/metal-building-insulation-3/.

This particular building can be found in Western Washington. 20 years old, construction was done by current building owners. A horse barn, building has a concrete slab floor, other than in horse stalls. Each side of building has open (no soffits) overhangs.
Now our challenge – certain days, with high humidity and fog, building has a problem with water ‘leaking’ along first purlin inside building.

My take regarding the problem’s root cause:
Properly installed in a roof, each roll of Metal Building Insulation should be stretched two inches past eave strut (eave purlin). Fiberglass adhered to vinyl facing should be removed from these two inches, folded back over top of intact fiberglass, then fastened securely to eave strut top until steel roofing installation. This takes a bit more effort than merely cutting rolls off flush with eave strut outside and calling it a day.

My guess, this building’s owners were not given instructions advising how to properly install Condensation Control Blanket, so it was done a quicker and easier way. This leaves a raw edge of fiberglass above the eave strut. When those chilly high humidity days occur, underside of roof steel in eave overhang has condensation collecting. Some of this moisture then contacts raw fiberglass edge and wicks up into building. Please note, in photo the apparent puffiness of insulation between sidewall and first purlin up roof. This would be an indicator water has sat above white vinyl vapor barrier.

A solution exists – remove screws from roofing above fascia and eave strut. Insert form fitted inside closures above eave strut, making certain no fiberglass remains exposed to overhang. More information about inside closures here: https://www.hansenpolebuildings.com/2015/12/the-lowly-inside-closure/)

Replace screws (using larger diameter than original screws). Roofing should be screwed to both sides of high ribs into fascia board. We recommend use of 1-1/2″ Diaphragm screws as a replacement.