Welcome to Ask the Pole Barn Guru – where you can ask questions about building topics, with answers posted on Mondays. With many questions to answer, please be patient to watch for yours to come up on a future Monday segment. If you want a quick answer, please be sure to answer with a “reply-able” email address.
Email all questions to: PoleBarnGuru@HansenPoleBuildings.com
DEAR POLE BARN GURU: i have read some of your advice on insulation and vapor barriers in older barns, most likely not designed for heat. i have a question about your advice. this is a quote from two different replies of yours.
My recommendations are to make sure your attic area is adequately vented (no less than 1/300th of the attic footprint area in venting, provided at least ½ of the vent area is in the top ½ of the attic), make sure the insulation stays dry (no roof leaks), and do not have a vapor barrier between the ceiling and the insulation. Whether you choose fiberglass or cellulose, either should be fine.
Condensation under the roof steel…as the steel is nailed on, it cannot be removed and an insulated vapor barrier (something like A1V reflective insulation available from www.buyreflectiveinsulation.com) added. The best solution is probably going to be to spray foam insulate the underside of the roof steel.
Adding a ceiling – with the trusses verified for the ability to take the load (and correctively upgraded if needed), 2×4 ceiling joists can be placed between the bottom chords every two feet, with LU24 or similar joist hangers at each end.
Screw on 5/8” Type X gypsum board to the underside of the ceiling joists and trusses (it won’t span four feet, so don’t even attempt to). Leave an attic access hole somewhere close to the center, so insulators can blow in the desired thickness of insulation. Do NOT place a vapor barrier between the ceiling drywall and the framing above
here are my questions.
- my planned ceiling is going to be white ribbed steel 1.25 tall ribs. i am also planning on using cellulose blown insulation. if spray foam on the under side of the existing roof panels is not an option, wouldnt there need to be a vapor barrier between the cellulose insulation and the ceiling panels to help the sweating issues?
- by using your calculations, the vent area in the attic would need to be 4 sq. inches. 1200 square foot building /300=4 sq.in.
is this enough? and that needs to be at both ends of the building, correct?
thank you for all the advice you offer for people like me that are fumbling through life. lol.
chris
DEAR CHRIS: Thank you for your kind words and for being a loyal reader. In answer to your questions:
1) You need to somehow create a vapor barrier between the dead attic space and the roof steel. Without it, you will have condensation challenges. Closed cell spray foam insulation does form an effective vapor barrier when properly installed.
2) The venting formula gives four square feet, which can be evenly distributed between the two ends, as long as at least 1/2 of the venting is in the top 1/2 of the attic space.
DEAR POLE BARN GURU: The front poles on my building have been set with the sistered 2 by 8s on the building line, instead of 1-1/2” over it, making the building 1-1/2” shorter from front to back. These are the two 6 by 8 poles on page S-2 of my plans.
Is this going to be a problem or can we just construct the roof per the plans as before and have 18-3/4” overhangs front and back?
I’d appreciate hearing back ASAP as the concrete crew is coming tomorrow morning to put in the forms. We plan to pour the slab on Tuesday.
I’ve Cc’d my contractor, so he can be in the loop on your reply. Thanks. CHUCK IN MOORESVILLE
DEAR CHUCK AND CHAD: Your building has some not so typical features, which the average pole (post frame) building does not. Being a hangar with a full hipped roof, and a bi-fold up door make it interesting.
When I was a teen, working doing framing for my Dad and Uncles, my Father did explain to me the difficulties involved in working with foundations which we either out of square or not level. Being dimensionally undersized is not quite as bad, but on the same short list.
Trying to make up the 1-1/2″ is not as easy as it may appear. In the long run, it would be easiest to add another pressure preservative treated 2×8 to the face of the corner columns. Trust me on this one, it will be cheaper to invest in the two boards, than will be the time which gets burned up trying to work around it.
I could make a list of all of the small things which would be a challenge, and have to be adjusted for – but you don’t even want to spend the time reading the list. Our goal is for you to end up with a completed building which is as close to being right as possible. Avoiding “work arounds” falls in this category.
DEAR POLE BARN GURU: Does Hansen take into account putting a 4” rock base down before installing a 3 ½” – 4” concrete pad when calculating the post height. In reading the instruction manual, it sounds like I will raise my skirt board height 4” above grade to compensate for the rock base since it appears that you want the concrete to be no more than 4” up from the bottom of the skirt board. Is this correct and is there enough post height to measure a 12’ eave height?
It is standard practice to lay a base rock layer before pouring concrete in my area. SCOTT IN AMISSVILLE
DEAR SCOTT: With 16 foot long columns and a 12 foot eave height, there is up to 48 inches of column to “play” with. Bottom of column goes 32 inches below grade, so if you have a clear level site, you could easily add even a foot of rock and still have adequate column length. Most people follow the instructions in Chapter Two of our construction manual and remove all sod, vegetation and topsoil before placing granulated, compactable fill (a.k.a. rock base). Following this process, the target height of the top of the fill is typically at grade – which negates the need to “hold up” the pressure preservative treated skirt boards.
