Tag Archives: attic space ventilation

Attic Ventilation, Shearwall Stitch Screws, and Adding Sheathing

This week the Pole Barn Guru addresses reader questions about ventilation needed for a new attic with metal ceiling and blown-in insulation, a confirmation for endwall needing stitch screws for shear, and if adding sheathing to an existing pole building would add value.

DEAR POLE BARN GURU: I bought a house with a pole barn that is unfinished inside. The metal walls were not wrapped and the only insulation in the barn whatsoever is double bubble on the underside of the barn roof. I am going to have a metal ceiling put in and then blown fiberglass insulation for an R30 value in what will then be the attic. There is currently no ridge vent nor gable vents either so I am concerned about air flow in the attic once the metal ceiling and blown insulation are complete. The eaves have perforated soffit so I’m hoping even after the blown insulation is done that will provide an air flow into the attic. So am I correct to think that I need to have gable vents put at each end or a ridge vent so that there is positive air flow through the attic? Thanks! BILL in STEVENSVILLE

DEAR BILL: Your thinking is absolutely correct – you need an adequate ventilation exhaust point. Ideally, this would be at your ridge. Gable vents, while meeting code requirements, actually only provide good ventilation immediately closest to vent locations.

This article covers requirements for attic ventilation: https://www.hansenpolebuildings.com/2023/06/274512/

In Queen Anne’s County – you are in Climate Zone 4A. 2021’s IECC (International Energy Conservation Code) specifies R-60 for ceilings in your climate zone. As so much of your cost of blown insulation is having installers show up, you may want to consider going with a greater R value than originally planned. Energy costs are not ever going to go down (nor cost of insulating).

 

DEAR POLE BARN GURU: I have a rear end wall that is labeled shear wall that says I need an inch and a quarter number 12. Stitch screw 9 and 3/8 on center. Is that every 9 and 3/8 on center vertically on each overlap? DAMINA in TONOPAH

DEAR DAMIAN: You are correct. Panels stitched together have roughly twice as much shear capacity as do unstitched panels.

 

DEAR POLE BARN GURU: Question for you Guru! I bought a property with a small pole building/shed. Is there any value in adding sheathing? If so, how do you retroactively figure out if the roof will handle the additional load? JESSE

DEAR JESSE: If the roof steel is properly fastened (1-1/2″ screws in flats along one side of each high rib in field, #12 or #14 x 1-1/2″ screws both sides of each high rib at eave and ridge) chances are it will perform admirably without any sheathing. Think of steel roofing and siding as acting like very strong, very thin OSB or plywood.

 

Builder Placed no Vapor Barrier Between Purlins and Roof Steel

Builder Placed no Vapor Barrier Between Purlins and Roof Steel

Almost client ALEX in CLINTON writes:

I recently had a pole barn home built and after we moved in we discovered our roof does not have any form of vapor barrier, just metal right on top of the purlins. Our contractor stated the entire attic is heavily ventilated so the barrier was not needed, which I did not agree. After going back and forth he offered to fix it only one way. Which would be to take fanfold insulation board between each rafter. I felt this would only hide my condensation problems rather than fix it. My question is, would this be a viable option? As well I’ve looked into adding in ventilation fans in the attic to better control the moisture, thoughts on that as well please!”

Mike the Pole Barn Guru responds:

You have just hit on one of my top peeves when it comes to post frame building contractors and providers – pretending condensation is not going to occur under bare steel roofing installed directly over roof purlins. 

And (even though you did not invest in a Hansen Pole Building) I have to feel we are partially at fault here. 

Why?

Our mission is to assist potential clients so they avoid making crucial errors they will regret forever. In looking back through our records, when you discussed your building needs with us two years ago, we failed – we did not convey to you how important some sort of roof steel condensation control is (at least we neglected to include it in our quotes). 

So now you are left with having spent a great deal of your hard-earned money (or future years of making mortgage payments with hard-earned money) and a home built almost right. 

Let’s start with discussing “heavily ventilated”. To begin with, there is no realistic amount of airflow through an attic capable of eliminating all possibility for condensation. Attic ventilation systems, by Building Code, are very specific as to not only required ventilation, but also correct ratios of intake and exhaust to create proper airflow from eave to ridge. These requirements are based upon building science and studies done on actual full-sized attics. Chances are more than good, your contractor has over done either soffit intakes or ridge exhausts. He or she probably has even used vented soffit in gable end overhangs (sure to mess up proper airflow). 

You can educate yourself further on ventilation requirements here: https://www.hansenpolebuildings.com/2023/06/274512/

2018 IRC Attic Ventilation Requirements – Hansen Buildings

Hansen Pole Buildings’ reader asks Mike the Pole Barn Guru how much of the ridge of a pole building ridge needs to have vented closures.

www.hansenpolebuildings.com

Attic ventilation fans, short of creating a wind tunnel, are not going to resolve future challenges.

While your contractor’s proposed solution is sort of right, it would only work if an absolute 100% air seal was achieved. Face it, this is just not going to happen.

So, what are your options?

Easiest would be to have two inches of closed cell spray foam applied directly to the underside of your roof steel.

All other options involve removing roof steel and placing a well-sealed thermal break between roof purlins and roof steel, then reapplying roof steel. Roof steel should be either shifted slightly to right or left to not place same sized screws back into same holes in wood (and original screws should not be used), or to use larger diameter, longer screws. This would be a good time to make sure replacement screws are all powder coated with EPDM gaskets.

What would give a capable thermal break?

Fan-fold insulation, reflective radiant barriers and faced metal building insulation are all possible options – provided all seams are tightly sealed. Solid sheathing roof with OSB (Oriented Strand Board) or plywood with either 30# felt or a synthetic ice and water shield between sheathing and roofing would also be a possibility.

Hopefully you have not made your final payment to your builder, so you as yet have some amount of leverage. However unless this was addressed specifically in your contract documents (we do address it in ours) chances are you are looking at some significant out of pocket expense to cure something easily and affordably solved at time of construction.

How to Design a Climate Controlled Pole Building

When I first entered the post frame industry over three decades ago, most pole buildings were barns. Having a climate controlled building  (heating and cooling) was rarely a consideration.

Modern pole buildings, serve a plethora of purposes from homes to offices, retail space to churches and everything in between. HVAC (heating, ventilating and air condition) becomes an important consideration.

This blog is nowhere near an in depth guide to climate control, but intended to give the reader a starting point.

The first stop should be to check the recommended R-value calculator:

https://www.ornl.gov/cgi-bin/cgiwrap?user=roofs&script=ZipTable/ins_fact.pl

If starting with a concrete slab on grade, a layer of A2V insulation should be properly installed below the slab.

Walls should be framed with bookshelf style girts placed at 24 inches on center. Also referred to as commercial girts, they create an insulation cavity, which allows for fiberglass insulation batts to be installed horizontally between the wall girts. If steel siding is used, it could be beneficial to use a quality housewrap between the wall girts and the siding. With commercial girts, to properly size the insulation cavity, create a space equal to the depth of the pole, plus the 1-1/2″ outside of the posts where girts extend. This allows for drywall to be attached to the inside face of the wall girts, creating a smooth wall surface.

Another great option for wall insulation is BIBS – which provide a higher R value than batt insulation, as well as filling all of the voids.  If you are not familiar with BIBS, check out their website: https://www.bibs.com

As a sidebar, I have BIBS in my large three story (84’ x 60’) accessory  climate controlled building (yes, it’s a pole building).  The cost savings on our heating and air conditioning bills is testimony in and of itself for this great product.

Ceilings – use ceiling loaded trusses with ceiling joists 24″ o.c. Sheetrock can be attached to the underside of the ceiling joists and insulation can be blown in above.

Any time a dead attic space is created – the attic space MUST be ventilated. As long as 1/2 of the required ventilation area is in the upper 1/2 of the attic, the area of the attic vents must be 1/300th of the footprint area of the attic. Otherwise, 1/150th is required. The best way to get even attic airflow is to use enclosed vented overhangs in combination with a vented ridge.

As I said, this is a primer for how to ensure a climate controlled pole building.  Ask whoever is designing your new building for more assistance. I have far more concerns for folks wanting to over-design climate controlling their new pole barn, then “under”.  While I want you to be warm (or cool) and comfortable, I also want to be sure you are using the “Three R’s Rule” – selecting the right product, to do the right job, at the right price.