Tag Archives: ridge vent

Gable Fan, Clay Soils, and Condensation Issues

This week the Pole Barn Guru answers reader questions about use of a gable fan to prevent condensation, building with posts in clay soils, and addressing condensation issues in a three-stall garage.

DEAR POLE BARN GURU: I have been reading some post on your site about gable vents. I have a 40×80 building with spray foam on the bottom of the roof, which is sheeted with plywood. The walls have rigid foam and fiberglass. Question is, would an electric gable fan help or hurt condensation in the building, and is it even necessary. Much of the building will become heated and cooled living space. STEVE in SOMERSET

DEAR STEVE: It is very possible a humidity controlled electric fan would assist in reducing condensation, however before moving forward with it, I would recommend you consult with your HVAC provider, as a properly designed heating and cooling system can be set up to provide adequate air exchanges and control humidity.

 

DEAR POLE BARN GURU: I have heavy clay soil that does not drain. If I put posts in ground the bottom 2 feet will be soaked most of the year. Should I use concrete piers or will proper treated post be ok? MATT in MORRISTOWN

DEAR MATT: Having personally built a post frame combination garage/shop/mother-in-law apartment at our son Jake’s then home near Maryville, I feel your pain when it comes to Tennessee clay soil. Properly pressure preservative treated columns are not negatively affected by ground water, however you have other factors to consider before moving ahead with your build. You’ll want to read these articles discussing them: https://www.hansenpolebuildings.com/2019/06/post-frame-construction-on-clay-soils/ and https://www.hansenpolebuildings.com/2020/07/barndominium-on-expansive-soils/.

 

DEAR POLE BARN GURU: Hello, We are building a 3 garage pole barn and would like to know if you suggest the following:
A. Can you spray foam insulation to house wrap and do you leave the paper under mullions if removing the paper?
B. We have sweating on our house wrap and in our bay that will be mostly finished we put insulation boards which had paper on both sides and now will have to remove that side siding to remove it.
C. Our bay 3 floor is just stone, the others are concrete. We didn’t put a vapor barrier plastic under stone, so until spring when we remove stone and do this we were thinking of laying a tarp tight on stone to hold back any moisture into the rooms for humidity and condensation. What do you suggest? LAURIE in NEW YOUR

DEAR LAURIE: While there are some installers who will spray foam to a WRB (Weather Resistant Barrier aka house wrap), we do not recommend it https://www.hansenpolebuildings.com/2020/04/spray-foam-insulation-3/

vented-closure-stripIf you are getting condensation inside of your WRB it is due to excess moisture in your building. You need to eliminate or minimize sources of water vapor (seal any concrete slabs-on-grade if a well-sealed vapor barrier was not installed beneath). Proper ventilation from eave to ridge will also help to alleviate this challenge.

Provided you can well-seal a tarp, it is certainly a better option than just leaving raw stone exposed.

 

Venting an Attic

Saving Money When Venting An Attic?

While some of you may think I have been doing post frame buildings since dinosaurs roamed our planet, I can assure you this is not true. Now my youngest son, when he was pre-school aged, did ask me (in all seriousness) what was it like watching space aliens build Egypt’s pyramids!

When reader DOMINIC in FESTUS wrote his question to me, it got me thinking about when I first had a client ask for a building with insulation at ceiling level. While I truthfully do not remember, in my first 6000 or so post frame buildings (we are talking 1980s here) I doubt there were more than a handful.

Fast forwarding to today’s modern fully engineered post frame buildings and nearly every building – garage, shop, barndominium, etc., is going to be climate controlled to some extent and most of these have enclosed attic spaces with insulation to be placed at ceiling level.

Here is DOMINIC’s question:

“I will be building a 30×40 pole barn soon. I plan on putting a ceiling in with insulation. My question is on attic venting. It seems best practice is to use a ridge vent with vented soffits but are gable vents alone sufficient? It would be cheaper for me to just do gable vents.”

Your best practice is to have even airflow from eave intakes to ridge exhausts. If your building will have sidewall overhangs, you might as well take advantage of this. You COULD (as an alternative) utilize gable vents. Provided at least half of your gable venting is located in the upper half of the attic, you can get by with as little as 576 square inches of NFVA (Net Free Ventilation Area). To achieve this would require (3) three 20″ x 30″ gable vents in each endwall. This could prove unsightly, difficult to install and is unlikely to result in being less of an investment than ridge vents. NOTE: a 20″ x 30″ gable vent provides roughly 106 square inches of NFVA (not 20″ x 30″ for 600″).

Of course, me being me, I had to snoop our records to see if he had requested a quote from us – and indeed he had…..

In looking over your quote from us, you may also want to consider increasing your overhead door width from 14′ to 16 (or even 18′) as you cannot safely get two vehicles side-by-side through a 14 foot wide door. For sake of resale value, with a 14 foot door it will appraise as a single car garage, wider doors will nearly double your appraised value as it is a two-car garage then.

Installing Steel Liner Panels in an Existing Pole Barn

Installing Steel Liner Panels in an Existing Pole Barn

Reader JASON in WHITEHOUSE STATION writes:

“ Hello! I have a post frame 30X40 Pole Barn that was built prior to me owning the house. Currently, the shop is not insulated. I would really like to insulate it, as it’s quite unbearable in the summer and winter. The building has soffit vents, a ridge vent, and two gable vents. With the way the building is set up with all that ventilation (possibly too much?), is putting in a ceiling with insulation on top my best bet? I know there are many options when it comes to insulation, but I am trying to determine what is best for my application. I am leaning towards 6 mil poly on the bottom side of the truss, ceiling liner panel over that with blown in insulation on top. My truss is 8′ on center. Is there a recommended length of panel I should use? Thank you for your help with this. I’m sorry if I asked too many questions.”

Mike the Pole Barn Guru responds:

Provided your building has roof trusses designed to adequately support a ceiling load, your best bet will be to blow in insulation above a flat level ceiling. If you do not have original truss drawings available to determine if they have a bottom chord dead load (BCDL) of three or more, then you will need to find the manufacturer’s stamp placed on truss bottom chords and contact them with your site address. With this information they should be able to pull up records and give you a yes or no. If you are yet unable to make this determination, a Registered Professional Engineer should be retained to evaluate your trusses and advise as to if they are appropriate to carry a ceiling and if not, what upgrades will be required.

If your building does not have some sort of thermal break between roof framing and roof steel (a radiant reflective barrier, sheathing, etc.) you should have two inches of closed cell spray foam applied to the underside of roof steel, or else you will have condensation issues (even with the ventilation). With trusses every eight feet (again provided trusses can carry ceiling weight), I would add ceiling joists between truss bottom chords every four feet and run 30 foot long (verify from actual field measurements) steel panels from wall to wall.

You do not have too much ventilation – and be careful not to block off airflow at eaves. You can omit poly between liner panels and ceiling framing.

Insulating an Existing Post Frame Building Attic

We are in an era where climate control of brand new post frame buildings is extremely common. It is also much easier to insulate (or plan for it) at time of construction, rather than having to go back and do it afterwards. 

For new post frame buildings, here is my Ultimate Guide to Post Frame Building Insulation: https://www.hansenpolebuildings.com/2019/11/post-frame-building-insulation/.

Loyal reader DAMON in SPOKANE is fortunate to have some parts of his existing post frame shop made easy for retrofit insulation. He writes:

“Hi,

First I want to say I love your web site, the information I’ve been reading is invaluable! I am located in Spokane County. I have a 24x24x10 post frame garage that was here when I purchased the house. The walls have commercial girts R19 insulation. I would like to heat this garage and use it as a woodworking shop. Right now the ceiling is open and there is no insulation. The roof is sheeted with OSB, then felt then steel roofing panels. There is no ventilation or overhangs to install soffit vents. The roof has 4:12 pitch.

I am considering one of two options. The first is to spray foam under the roof decking with closed cell foam, about 2″ which would give me about an R14. This would mean I would have to heat a larger air volume all the way up to the roof. Is this an effective method? Will the closed cell foam seal everything and hold the warm air in efficiently? I supposed I could install a couple of slow turning ceiling fans to push the warm air back down.

The second alternative is to add a ceiling. I was able to confirm that the garage was built with bottom load trusses. I could install joists and an osb ceiling and then go with a blown in insulation, maybe R38. Because there is no ventilation I was thinking of adding large appropriately sized gable vents to provide the ventilation since I do not have soffit vents nor a ridge vent.

Of the two options, is one a better consideration than the other? I know you’re probably pretty busy, I appreciate any time you have to help me with my decision.”

Mike the Pole Barn Guru responds:
Thank you very much for your kind words, hopefully you have been entertained as well as informed!

As your building was built with trusses designed to support a ceiling, I would recommend you pursue this route. You would need to add gable end vents in the upper half of each gable with a net free ventilation area of at least 139 square inches per end. Please keep in mind this is not vent dimension, but net free area only.

Your building’s roof trusses probably do not have raised “energy heels” so it would be most practical to use closed cell spray foam insulation along two feet closest to each eave sidewall (applied to top side of ceiling finish). I would recommend you blow a minimum of R-49 across the balance of the attic area as this will meet minimum recommended attic insulation levels from www.energystar.gov. Your spray foam applicator can make recommendations for the thickness of his or her product.

Also, please consider using 5/8″ Type X sheetrock for your ceiling. It will be less expensive than OSB and provides some degree of fire resistance.

Venting an Attic Without Soffit Air Intake

Venting an Attic Without Soffit Air Intake

Loyal reader KEN has an attic space with only air exhaust points – a vented ridge, and no air intake. His dilemma, how to adequately ventilate his attic without vented soffits.

Ken writes:

“I finally was able to make contact with the manufacturer of the open foam like material used under my ridge as a vent. The following is cut and pasted from their technical material: Net Free Area 1”nom.Thickness 8.5 sq.in.per lin.Ft.per side (17 sq.in .per lin.Ft.ridge).  Since I have a 60 foot ridge, that would equal 1020 sq. in. or 7 sq. ft. 

Given the ridge vent, do you still recommend 3 sq. ft.  venting on each end?

You note that an 18×24 would provide 140 sq in (or 0.97 sq. in.), but 18×24 is 432 sq in.  Do the louvers and other components reduce that by a factor of 3, just wanting to confirm.  With a 3 sq. ft. requirement, I would need a vent nearly 3 times an 18×24.  Maybe it just comes down to not the ideal but what can be practically installed. 

In order to prevent rust at the cut line, should I caulk the outside seam where the louver comes through the wall?”

Mike the Pole Barn Guru writes:

Another way of thinking about ventilation – view it like a straw. Obviously with best (and most) straws each end has an opening. What happens when a hole exists somewhere between ends? A reduction occurs in your ability to draw up water or soda. A similar effect happens when different vent types are employed over a shared air space.

Air and water are similar, their flow follows a path of least resistance. In a properly designed and installed attic ventilation system air flow travels from intake vents to exhaust vents, flushing out warm, humid air along roof deck (think underside of roof steel). However, if two or more different types of exhaust vents (gable and ridge) are used above a shared attic air space, one exhaust vent will likely to interrupt air flow to the other. In this arrangement it becomes another intake vent for a primary exhaust vent – leaving large sections of attic space incorrectly vented.

I would be inclined to seal ridge vent off and utilize gable vents. Dimensions of gable vents are overall unit dimension, not net free area (reduced from overall size by both exterior framework and louvers). Each endwall may require multiple vents in order to achieve an adequate airflow.

Caulking cut edges of endwall steel would certainly not hurt. A suggested caulking would be TITEBOND Metal Roof Translucent Sealant.

 

 

 

Dear Guru: Can I Add to My Pole Barn in the Future?

DEAR POLE BARN GURU: I’m very interested in doing business with you, I just have a few questions. I originally asked for a quote of a pole barn of 200×50 I believe it was, my question is, can your buildings be added on to? Would we be able to start with something much smaller and then add on to the barn as we go? NOW IN NEW JERSEY

DEAR NOW: Yes, our buildings can be added on to. I would recommend the initial design be done with the idea of what the ultimate finished goal will be for size. Oftentimes, original structures are not structurally set up for the eventual expansion, which keeps the initial price low, but results in headaches and costs later, which could have been avoided with proper planning. A gabled roof will be the easiest roof style to work with when it comes to future expansion.

We have several customers who have done just as you suggest, adding on to one or both ends as they expand. Get the width you ultimately want, then adding length is much easier You can remove endwall siding, add on additional bays, and put the endwall siding back on. You may have to purchase more trims, but if steel siding, is easily reused for the addition.

And I always recommend – build as much building as you have space for and can afford economically, as whatever size you pick, it will never be large enough.

DEAR POLE BARN GURU: I’ve read ALL of your blogs!  Back to 2010. And love them. I write similar stuff in my business.

The question is do you have, or can you get, closures similar to ridge vent, but as a bottom closure to be used at the eave of a building without overhangs? BREEZY

DEAR BREEZY: Thank you for your dedicated readership and …good question! There is not such a beast, and even if there was, the net ventilation would be tiny – not enough to yield any positive results, as the only area which could have a vent would be just at the high ribs. The correct way to vent would really be with enclosed vented overhangs.

DEAR POLE BARN GURU:I have an existing pole building with badly deteriorating insulation and vapor barrier for the roof.

I plan to pull all of the old insulation and vapor barrier out to replace it.  I’d like to use the reflective radiant barrier / vapor barrier you recommend for new construction.  I’m considering pulling the metal roofing off to do it right so I don’t have to do it again later.

Do you recommend installing the reflective radiant barrier / vapor barrier between the metal roofing and purlins or between the purlins and roof trusses? DETERIORATING IN DELAWARE

DEAR DETERIORATING:
Place the reflective radiant barrier over the purlins and directly under the roof steel. You will need to use larger diameter, longer screws to reattach the roof steel.

DEAR POLE BARN GURU:Where can I buy Owens Corning Foamular Fanfold foam 1/4″ thick? A lot of my fellow RC plane hobbyists are having a hard time finding this stuff. Thanks in advance. FLYING IN FREMONT                          DEAR FLYING: Visit the Contractor Desk of any The Home Depot®. If it is not in stock, it can be ordered in within a matter of just a few days.