Tag Archives: weather resistant barrier

Pre-Drilling, Housewrap, and Concrete Footings

Today the Pole Barn Guru answers reader questions about pre-drilling steel panels, the proper use of house-wrap and weather resistant barriers, as well as concern for the effectiveness or fresh concretes ability to withstand compression.

DEAR POLE BARN GURU: What size hole should I predrill in panels for the #12 diaphragm screws? Thanks! JOSEPH in KIOWA

DEAR JOSEPH: From Hansen Pole Buildings’ Construction Manual, Chapter 2:

 

“For pre-boring nail holes, 7/64” and 1/8” bits are required. Same size bit can be used for pre-drilling steel roofing and siding.”

 

DEAR POLE BARN GURU: Having read all of the info relating to insulating and am still confused. Main question is my entire 40×48 was wrapped in Tyvek including the roof. Now am trying to figure out if and how I can install a vapor barrier for the roof? Am planning to put in a ceiling with blown insulation above it and would like some options for the vapor barrier. Not sure if the roof Tyvek is a help or a hindrance. KEVIN in MALAD CITY

DEAR KEVIN: I’d like to find builders who are using Weather Resistant Barriers (WRB) under roof steel on post frame buildings, thinking they are installing a vapor barrier, and slap them silly. They have totally wasted their client’s hard earned money and, as in your case, have created a hindrance. Your only real solution is to remove Tyvek from under roof steel and replace it with an actual vapor barrier (one with a thermal break). You might see if a local spray foam installer would be willing to flash spray two inches of closed cell foam on underside of your building’s WRB.

DEAR POLE BARN GURU: My contractor poured concrete in each hole for a 30’ x 32’ pole shed and about 4 hours later started setting poles and put the entire frame up yet that same day. Can the concrete actually cure that fast or should I be concerned? PAUL in MITCHELL

DEAR PAUL: I am guessing you are talking about concrete poured for a footing pad under the columns.

Concrete gains its strength with time after casting. The rate of gain of concrete compression strength in higher during the first 28 days of casting and then it slows down. The compression strength gained by concrete after 24 hours is only 16%!

For practical purposes, a four hour old concrete footing is virtually worthless. Yes, you should be concerned.

 

IBC Requirements for Building Wrap

IBC Requirements for Building Wrap

When using a building wrap as a weather-resistant barrier (WRB), it must meet 2018 International Building Codes (IBC 1402.2) requirements of a WRB for water-resistance and vapor permeability.

A superior building wrap is air- and moisture-resistant, permeable, and has a high UV-resistance and tear strength. It should also be simple and quick to install, to limit damage during application. Using a high-quality building wrap compliant with IBC 1402.2  code creates a structure with a weather-resistant exterior wall envelope. A weather-resistant exterior wall envelope ensures a building is energy-efficient and healthy.

2018 International Building Codes (IBC) mandate buildings meet minimum requirements for exterior walls. IBC Chapter 14  IBC provides these minimum requirements, including wall coverings, exterior doors and windows, exterior wall openings, and architectural trim. Specifically, section 1402.2 states exterior walls must provide a building with a weather-resistant exterior wall envelope. Exterior wall design and construction must include a water-resistant barrier behind exterior veneer preventing accumulation of moisture within wall assemblies. Exterior walls must also include a way for water/condensation entering a wall assembly to drain/evaporate.

IBC specifies a few cases where a weather-resistant exterior wall envelope is not required.

  1. Code does not require a weather resistant wall envelope over concrete or masonry walls designed in accordance with IBC chapters 19 and 21.
  2. Code does not require a weather resistant wall envelope for exterior insulation and finish systems (EIFS) in compliance with IBC 1407.4.1.
    • IBC 1407.4.1 states for EIFS with drainage, water-resistive barrier must comply with IBC Section 1403.2 or ASTM E2570. IBC 1403.2 states attachment of no fewer than one layer of No. 15 asphalt to studs or sheathing, with flashing, must provide a continuous water-resistive barrier behind exterior wall.
  1. Exterior wall envelopes resisting wind-driven rain, including openings, joints, and intersections with a dissimilar material in accordance with ASTM E331 are not required to have a weather-resistant exterior wall envelope.

BENEFITS OF BUILDING WRAP

Applying a high-quality building wrap, like Barricade® Building Wrap, over sheathing, and behind siding, meets or exceeds IBC 1402.2 requirements for weather-resistant barriers. A properly installed building wrap creates a protective envelope against air infiltration and moisture into wall systems. A buildup of moisture within a building’s walls is problematic because moisture can lead to wood rot (caused by fungi) and expensive repairs. High moisture can also cause mold, unhealthy for structure occupants. Uncontrolled air infiltration lowers effective wall system R-value and lessens energy-efficiency and air quality of a building. To reduce air infiltration and stop accumulation of moisture within wall systems, along with meeting requirements of IBC 1402.2, design of a high-performing exterior wall must include a weather-resistive barrier, like building wrap.

Do Vapor Barriers Trap Moisture?

Vapor Barriers Trap Moisture?

Do vapor barriers trap moisture in walls of post frame buildings? They can, but only if they are installed on both sides of a wall insulation cavity.

Regular readers of this column will recognize a prevailing trend towards climate controlling both new and existing post frame buildings. An ability to control interior climate extends far beyond merely what one happens to be doing for insulation. It also includes what one does for weather resistant barriers and vapor barriers.

Insulating WallsThe purpose of a vapor barrier is to stop warm, moist, indoor air from infiltrating fiber-type insulation (think fiberglass or cellulose) during cold weather and condensing. Visible moisture or frost on the inside of a vapor barrier is either caused by a leaky vapor barrier or moisture migrating into the wall cavity from the outside. Leaky siding can cause this, and it often happens in basements that are apparently leak free. Vapor barriers are essential for any kind of insulation that air can pass through. Never do the really foolish act of slashing a vapor barrier that you find has moisture behind it or forgetting to install a vapor barrier in the first place. Today’s best vapor barriers prevent moisture from moving into wall cavities while also letting trapped moisture escape.

Recommendations below are for cold-climate construction. As a rule of thumb, if you have to heat your building more than cool it, this probably applies to your circumstance.

A weather resistant barrier (https://www.hansenpolebuildings.com/2016/01/determining-the-most-effective-building-weather-resistant-barrier-part-1/) will prevent moisture from entering a wall from outside of building. It also allows any moisture within a wall to exit. Pretty slick stuff, as it is smart enough to be directional.

Inside of this wall, once unfaced (recommended) insulation batts are installed, should be a vapor barrier (https://www.hansenpolebuildings.com/2017/11/vapor-barriers-post-frame-construction/). It is imperative this vapor barrier not have unsealed tears or holes. It should be sealed to floor and ceiling and any joints, rips or tears should be adequately taped. Where problems most often occur, with vapor barriers, is when penetrations are made for things such as electrical boxes. Properly sealing of these penetrations with closed cell spray foam from a can does more to prevent warm moist air to pass through into your post frame wall insulation cavity, than anything else.

 

 

 

Pole Barn Insulation, Part II

Continued from yesterday’s blog:

(1) Storage – if you ever believe anyone might ever in the future desire to climate control then provision should be made for making it easiest to make future upgrades.

At the very least a reflective radiant barrier (single cell rather than wasting the money for the extra approximately 0.5 R from double bubble), an Integral Condensation Control (https://www.hansenpolebuildings.com/2017/03/integral-condensation-control/) or sheathing with 30# felt should be placed between the roof framing and roof steel to minimize condensation.

If a concrete floor is poured (in ANY use building), it should be over a well sealed vapor barrier.

For now we will assume this building is totally cold storage. If it might ever (even in your wildest dreams) be heated and/or cooled include the following in your initial design: Walls should have a Weather Resistant Barrier (https://www.hansenpolebuildings.com/2016/01/determining-the-most-effective-building-weather-resistant-barrier-part-1/) between the framing and the siding. Taking walls one step further would be ‘commercial’ bookshelf wall girts (https://www.hansenpolebuildings.com/2011/09/commercial-girts-what-are-they/).

In the roof – have the trusses designed to support a ceiling load ideally of 10 pounds per square foot (read about ceiling loaded trusses here: (https://www.hansenpolebuildings.com/2016/03/ceiling-loaded-trusses/). Trusses should also be designed with raised heels to provide full depth of future attic insulation above the walls (https://www.hansenpolebuildings.com/2012/07/raised-heel-trusses/).

Make provision for attic ventilation, by having an air intake along the sidewall using enclosed ventilated soffits and exhaust with a vented ridge.

Any overhead doors should be ordered insulated – just a good choice in general as, besides offering a minimal thermal resistance, they are stiffer against the wind.

(2) Equine only use: Same as #1 with an emphasis upon the ventilation aspect.

(3) Workshop/garage and (4) Garage/mancave/house are going to be the same – other than whatever the client is willing to invest in R value, being the major difference.

Adding onto #1 for the walls the low end would be unfaced batt insulation with a 6ml visqueen vapor barrier on the interior. Other options (in more or less ascending price and R values) would be Mineral wool insulation as it is not affected by moisture (https://www.hansenpolebuildings.com/2013/03/roxul-insulation/),  BIBs (https://www.hansenpolebuildings.com/2011/11/bibs/), closed cell spray foam in combination with batts and just the closed cell spray foam (https://www.hansenpolebuildings.com/2016/07/advantages-spray-foam-over-batt-insulation/).

For added R value and a complete thermal break, add rigid closed cell foam boards to the inside of the wall.

Once a ceiling has been installed, blow in attic insulation.

For (4) a Frost-Protector Shallow Foundation (https://www.hansenpolebuildings.com/2016/11/frost-protected-shallow-foundations/) with sand on the inside rather than a thickened slab is an excellent and affordable design solution.

For insulation solutions which follow the roof line, the best bet is going to be the use of closed cell spray foam, as it solves the potential condensation on the underside of the roofing and does not require ventilation above.

In most cases, the steel trusses fabricated for post frame buildings are either not designed by a registered engineer, are not fabricated by certified welders or both – so it makes it difficult for me to recommend them as part of a design solution.

With scissor trusses, they can be treated the same as a flat ceiling would be, provided the bottom chord slope is not so great as to cause blown in insulation to drift downhill.