Solving Yet Another Post Frame Condensation and Insulation Challenge
Long time loyal readers will sigh as yet another post frame building has been erected without thoughts to how to properly insulate and control condensation. Had our new friend invested in a Hansen Pole Building, chances are good we would not be having this question and I would have had to write about something else today! Our Building Designers follow with these recommendations: https://www.hansenpolebuildings.com/2019/11/post-frame-building-insulation/.
Our new friend COREY in POST FALLS writes:
“I have a 36×48 pole building with trusses on 12’ with BCDL 5psf, the roof is plywood sheeted with composition roofing with ridge vent and gable vents. The wall Purlins are on the exterior of the poles and there is no vapor barrier. I would like to install a ceiling with insulation and insulate the walls. I am looking for vapor barrier and insulation recommendations. Was thinking of installing 2×4 on 24 centers to bottom of trusses and installing OSB and blown in insulation, and then framing in between poles adding batt insulation and sheeting with OSB, but am unsure of controlling vapor. Thank you.”
Mike the Pole Barn Guru responds:
Small world, many years ago I graduated from Post Falls High School!
A vented ridge relying upon gable vents as an air intake is usually very inefficient. You should make sure your vents in each end are located in the top half of your attic and have at least 415 square inches of net free ventilating area on each end. This means you are probably going to have to add more vents. Effective ventilation of this area is essential to preventing mold and mildew in your attic.
Wall girts flat on column exteriors are inadequate to carry imposed loads and will not meet deflection limitations. I would suggest you reinforce each of them to create either an “L” or a “T”. Assuming you have 6×6 wall columns, you could place a 2×8 bookshelf style girt on top or bottom of each girt, nailing through 2×8 into existing girts with a 10d common nail at say 12 inches on center. This will create an insulation cavity and allow for easy interior finish.
For ceiling joists between your trusses, 2×4 will not be adequate you should use 2×6 #2 with joist hangers on each end.
Unless you have a Weather Resistant Barrier (https://www.hansenpolebuildings.com/2016/01/determining-the-most-effective-building-weather-resistant-barrier-part-1/) between framing and wall steel, my recommendation would be to have two inches of closed cell insulation spray foam to the inside of wall steel. Then fill balance of wall cavity with BIBs insulation: https://www.hansenpolebuildings.com/2011/11/bibs/ with a well sealed vapor barrier towards the inside space.
Common questions we hear from barndominium, shouse (shop/house) and post frame home owners are, “Why are my new windows leaking?” or “Why do I have condensation inside of my windows?” In fact, many new barndominium owners think their windows are defective and need to be replaced in an effort to cure this problem. To answer these questions, let’s review what causes window condensation.
Condensation is visible evidence of excess air moisture. It may appear as water, frost, or ice on window or door surfaces. This occurs more frequently during winter months because of extreme differences between inside and outside air temperatures. Warmer air holds more water meaning air in any given room center will hold more water than air adjacent to window or exterior door walls, since this area is always cooler. When warm, moisture laden air moves toward cooler window or door walls, it becomes cooler and cannot hold as much moisture as it held when it was warmer. This moisture is dropped and appears as water on glass and frames of windows and doors.
Windows do not cause condensation, they just happen to be where moisture is most visible. Condensation is a sign of excess moisture in barndominiums. This can be caused by temporary conditions such as:
Building materials contain a great deal of moisture. As soon as heat is turned on, this moisture will flow out into the air and settle on door and window glass. This will usually disappear following first heating season. During humid summers, houses absorb moisture. This will be apparent during the first few weeks of heating and then should dry out. Sharp, quick, and sudden drops in temperature especially during the heating season will create temporary condensation problems.
Condensation can also be caused by more permanent conditions:
Insufficient attic ventilation and/or soffit ventilation traps moisture in barndominiums. Having sufficient soffit vents to allow adequate air flow in and ridge vents for exhaust will allow moisture and humidity to escape. Excessive humidity may be a result of poor ventilation but can also be a result of an imbalanced heating and air system or a need to add additional ventilation. Inadequate (or missing) vapor barriers under concrete slabs on grade. While Building Codes require a vapor barrier under any concrete slabs in heated buildings, it is all too often overlooked.
Controlled ventilation and elimination of excessive indoor moisture can keep humidity within bounds. Here are some suggestions to help reduce indoor moisture:
Turn off or set back furnace humidifiers until sweating (condensation) stops. Remove pots of water on radiators or kerosene heaters. Use exhaust fans or open windows slightly in kitchen, bathroom and laundry room during periods of high moisture production such as cooking, taking showers, washing and drying clothes. Clothes dryers must be vented outside. Do not hang clothes to dry indoors. Waterproof concrete floors. Make sure attic vents are unobstructed. Place all house plants in one sunny room where the door can be kept shut and avoid over watering. Opening windows slightly for a brief period of time will allow humid air to escape and drier air to enter. Use a properly sized dehumidifier, to reduce humidity.
Excessive indoor humidity and moisture are not a result of your windows. You should view the amount and severity of window condensation as a clue moisture damage may be taking place inside walls or ceiling cavities of your barndominium. This can lead to rotting wood, deteriorating insulation, and blistering paint.