Tag Archives: condensation roof steel

Electrical Installation, A Frequent “Plans” Question, and Vapor Barriers

This Monday the Pole Barn Guru answers questions about running electrical through posts, a question often received about plans, and vapor barriers.

DEAR POLE BARN GURU: I’m looking for the lvl beam, floor / roof joist and wall purlin penetration layout for plumbing and electrical install.

I will not need many horizontal penetrations. A few for electrical install and the hot and cold water lines

I will need to have vertical penetrations in the wall purlins for the waste and vent lines.

Max hole size

Spacing between holes

Hole location in joist / lvl beams. Upper middle lower?

Thanks, GREG in LEAVENWORTH

DEAR GREG: Here is some information from Hansen Pole Buildings’ Construction Manual:

Q: Can electrical be drilled through framing or columns?

A: Very little drilling, if any, will be needed for holes in order to run electrical wires. Wall framing (girts) extend or are placed so as to leave a 1-1/2 inch space between outside of wall columns and siding.

  Think of a hole being drilled through as being an “open knot”. Lumber grading rules refer to these as being “Unsound or Loose Knots and Holes” due to any cause. Most structural framing – like wall girts and roof purlins or posts and timbers are graded as Number 2.

  For practical purposes, a hole up to just less than ¼ of board face being drilled through will be within grade in #2 lumber. Example: 3-1/2” face of a 2×4 a hole up to 7/8” may be drilled through, as often as every two feet. Allowable hole sizes are reduced and spacing increased for higher grades of lumber.

Here is APA’s guide to drilling holes in LVLs:
http://murphyplywood.com/pdfs/engineered/APA_LVL_Hole_Drilling.pdf

 

Engineer sealed pole barnDEAR POLE BARN GURU: Where do I get plans to take to the state to get a permit? DAVID in EDINBURGH

DEAR DAVID: With your investment in a new Hansen Pole Building, we will provide two sets of third-party structural engineer sealed plans and pertaining calculations for your to submit for your Building permit.

 

DEAR POLE BARN GURU: I have a 40×40 pole barn that is open on one gable end and used for vehicle and trailer parking. I am re-siding and re-roofing with metal over purlins. Do I need a vapor barrier such as roofing felt under the metal? KEVIN

DEAR KEVIN: You should have something to prevent condensation. My first choice for ease of installation would be to order roof steel with dripstop or condenstop attached by roll former. https://www.hansenpolebuildings.com/2014/07/condenstop/

If this is not an option, use a reflective radiant barrier with an adhesive pull strip attached for ease in sealing seams.

 

 

Condensation Under Roof Steel

Condensation Even With Radiant Barrier Installed Under Roof Steel

It seems every winter I get a few messages similar to this, So far, this winter, I have gotten two, both from newly constructed post frame buildings and from the same area of the United States (which is known for high humidity).

Reader SAM in GREENBANK writes:

“Hi there.  I’ve almost completed the building, and It’s been getting cold lately.  I noticed that every time we have a frost I have condensation drips all over inside the barn.  I was under the impression that the foil backed bubble wrap was supposed to prevent this.  Is there something I can do to stop it?   Is this normal?   I’m having to keep all my tools under cover even though they are inside.  Not ideal.”

Mike the Pole Barn Guru Responds:

The radiant reflective barrier does keep warmer moist air from contacting the underside of the colder roof steel and condensing. If it has been below freezing inside your building, and fairly humid, water vapor will freeze to the underside of the barrier as well as the roof framing members. Most often the excess humidity is a product of a relatively freshly poured concrete floor (tremendous amounts of water vapor are expelled from a concrete slab as it cures), a concrete floor which does not have a well sealed vapor barrier beneath it, or (in buildings without a concrete floor) the ground under your building will not freeze and when the ground outside starts to freeze the excess ground moisture rises inside of the building (think of a cork being removed from a bottle).

Possible solutions (may have to be used in combination): heat the building to just above freezing, open the doors to allow excess moisture to escape (especially in cases with a fairly fresh pour or no slab), if no vapor barrier under a slab – seal the surface of the slab to prevent moisture from coming through. Basically it takes a reduction of humidity inside of your building.

In cases where eave and ridge ventilation was not provided for initially, adding gable vents might help to alleviate some of the interior humidity. When I was a builder, we erected a boat storage building over (we found out later) what had been a pit where asphalt waste from old roads had been deposited. Water sat in between the chunks of asphalt – we had basically built over an underground lake!

The only solution was for the owner to install power vents to pull the humidity out of the structure!

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