Tag Archives: ridge purlins

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?

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!

Consider Post Frame for New Home!

DEAR POLE BARN GURU: Good morning. My name is Thomas and I am with xxxxxx; we manufacture metal roofing and siding and based out of Tennessee. I wanted to ask you a few questions to gain some information. First, my wife and I are starting to look at metal building for our new home, is this something your company is licensed to do in the state of Tennessee; second, I also would like to know if you manufacture your own metal roofing and siding, or if it is purchased from another company. Hope you had a great Christmas and I look forward to hearing back from you. THOMAS in MURFREESBORO

DEAR THOMAS: Thank you for your inquiry. Hansen Pole Buildings provides engineered post frame buildings in all 50 states, including Tennessee. Post frame (pole) building homes have become quite popular in the past few years and chances are excellent we can provide a customized building shell which will ideally meet with your needs and budget. We outsource our metal roofing and siding and we can provide the building sans roofing and siding in the event you should wish to provide your own.

DEAR POLE BARN GURU: I have submitted a request for a quote on our residence but I’ve needed to make a few modifications. How important is post spacing on a residential post frame building? The residence I’m designing is based on nominal 8′ post spacing but with the interior design I have, a couple of the posts interfere with window/door placement. I’ve been assuming that as long as opposite side posts are aligned so that the trusses are supported, the post position can be varied somewhat. On our design, I’ve assumed nominal 8′ post spacing but actual spacing winds up being as close as 7′ and as wide as 10′ 6″. Can irregular post spacing be accommodated or do I need to modify our interior design? Thanks LONNIE in COLORADO SPRINGS

DEAR LONNIE: Your assumption, “as long as opposite side posts are aligned so that the trusses are supported, the post position can be varied somewhat” is absolutely correct. In most circumstancing having the sidewall columns spaced at 12 foot on center is your most economical, so anything at this spacing or less should not be an issue from an engineering and design standpoint. When you arrive at an ideal spacing, please make sure it is listed on any quotes and invoices, otherwise there is always the possibility of columns being reorganized to the most cost effective combination.

DEAR POLE BARN GURU: Is there a recommended distance from the peak of a roof that the top purlin is installed, and why? WILL in NEWPORT

DEAR WILL: Yes there is a recommended distance. Here is the applicable excerpt from the Hansen Pole Buildings’ Construction Manual:

With standard steel ridge caps, the ridge purlin “uphill” side can be no closer to peak than five inches. This may result in space between ridge purlin and next purlin “downhill” being decreased. Ridge purlins can be further from truss peak than the minimum distances, without negatively affecting building. Roof ridge caps attach to roof steel with metal-to-metal screws, not to ridge purlins, so ridge purlins need not align with future ridge cap fastener locations.

If ridge purlins are “uphill” further than this, roof steel may not have an adequate overhang at eave and challenging situations will result!”

Bridge Bracing

Lauri is one of the newer members to the Building Design team at Hansen Pole Buildings. Pole buildings, while having the appearance of being fairly simple, are actually remarkably complex structures and involve the proper interaction of literally thousands of components.

Due to this, it is not surprising for a question to come up, which there is not an easy answer to. Today, Lauri came up with one for me….from one of her clients….

“Also I would like some bridge bracing between the trusses. I have seen instances where the roof sheeting was used to do this and it seems to me that this is a poor practice. I do want a ridge vent system, so I would like at least 2 lines of bridge bracing using 2X4s on either side of the ridge line between the trusses.”

Having grown up in construction (my paternal grandfather, father and his five brothers were all builders), been involved in the prefabricated roof truss industry as an owner or in a position of authority for over two decades, and been a general contractor myself….I had never heard of “bridge bracing”.

Off I dashed to the wonders of the Internet….Googling and Yahooing as if my life depended upon it.

It took some doing, but I was finally able to find “bridge bracing” as it would apply to wood frame construction. And it wasn’t at all what I (or probably the client) envisioned.

Here is how the term is properly applied…..Say one is framing up an exterior deck. All of the joists, including the rim joist are in place. 4×4 or similar sized posts are fastened to the inside of the rim joists, to support a railing. On the side of the 4×4 opposite the rim joist, are placed two framing members as blocks, equal in size to the joists, and parallel to the rim joist. By use of adequate fasteners, this double block (the bridge bracing), keeps the post from rotating once the final assembly is in place.

My supposition is this client is fairly unfamiliar with post frame construction and has made some assumptions. These could include the prefabricated roof trusses are spaced every two feet, and the roof is sheathed with either plywood or osb (oriented strand board). These assumptions would be true, in the case of typical stick frame construction. Even in stick framing, the stiffness of the roof sheathing is such as to preclude the need for even a single solid block of 2×4, between the top chords of the roof trusses at any point.

Yes, blocking could be added, or in the case of a pole barn, the ridge purlins could be doubled. However, there would be no added structural benefit and it would add to the cost of the building in both materials and labor. As all our buildings are designed to support the weight of the roof, including the framing and whatever roofing materials are chosen, “bridge bracing” becomes a non-issue.