Tag Archives: rock wool

Housewrap, Roof Insulation, and Ceiling Fasteners

This Wednesday the Pole Barn Guru answers reader questions about a home owner asking builder to install housewrap on the roof, the best solution to insulate underside of roof, and what the best fastener for screwing steel to ceiling or roof trusses would be.

DEAR POLE BARN GURU: Pole Barn Guru, thank you for your knowledge. I have a customer wanting house wrap around the exterior of a 30×40 pole barn. Is house wrap to be installed in between purlins and roof steel or will I need a radiant barrier to prevent condensation? Home owner says house wrap on the roof as well but I’m not sure if that’s the route he really wants to go. House wrap on side walls in between girts and side steel is also the best route correct?

Thank you for your kind words, they are much appreciated. Provided your client will not be doing closed cell spray foam on walls, use house wrap between girts and wall steel. For his roof, housewrap is totally incorrect, as it allows moisture to pass through and become trapped between wrap and roof steel – potentially causing premature degradation. If your client is not closed cell spray foaming directly to roof steel, then order your roof metal with an Integral Condensation Control factory applied (Dripstop, Condenstop or similar) https://www.hansenpolebuildings.com/2020/09/integral-condensation-control-2/. If roof steel has already been ordered (again assuming no closed cell spray foam being applied), then you do need some sort of a thermal break – such as a well-sealed radiant barrier.

 

DEAR POLE BARN GURU: Hi Mike, I built a 32’X40’X12′ pole building, (Shop) I used 1 1/2″ foam board on the inside walls, (on the inside of the girts) I can’t decide how I should insulate the underside of the roof. I have had a couple Spray Foam guy’s quote it , that’s pricy. Of course, the best R Value etc. at the most reasonable price is what I am looking for. In some of your post you have mentioned Rockwool that has gotten my attention. I see they make it up to R30. One thing that sticks in my mind is, my builder suggested not to use an insulation that will give insects a place to live. What would be your suggestion for underside of Roof insulation. Thank you. JIM in SPRING HILL

DEAR JIM: If your building has no current provision for controlling condensation on underside of roof steel, then two inches of closed cell spray foam applied directly to steel is your best insulation option. If you desire a greater R value, you can go thicker, or add open cell.

 

DEAR POLE BARN GURU: What screw is best for installing metal panels on the ceiling to wood trusses. MICHAEL in WENTZVILLE

DEAR MICHAEL: Most people are using #9 or #10 diameter 1″ screws. If you have ceiling framing 24 inches on center and want to utilize strength of ceiling liner panels to help transfer wind shear loads, then 1-1/2″ long diaphragm screws would be a better design solution.

Does My Pole Barn Need a Vapor Barrier?

Does My Pole Barn Need a Vapor Barrier Above the Metal Ceiling?

Reader DAVID in BALDWINSVILLE writes:

“I have a new pole barn with bubble vapor barrier under roof metal. I am installing a metal ceiling with R-38 cellulose in the attic. Do I need a vapor barrier above the metal ceiling? The barn will be heated somewhat in winter.”

From Mike the Pole Barn Guru:

Kudos to you for recognizing bubble wrap products advertised as ‘insulation’ are, at best, a good vapor barrier if properly sealed!

My son Brent is working on his doctorate at UMass Amherst, so I utilized Building and Construction Technology information from their Department of Environmental Conservation in penning this response.

My concern is with blowing in cellulose above a steel ceiling. From UMass:

“Wet insulation of any stripe is bad. But cellulose is hygroscopic. It’s able to soak and hold liquid water. Undetected leaks can wet cellulose causing it to sag within framing cavities. Water leaks can compress the blanket of fiber and in extreme cases, can create a void space, degrading its thermal value. Another concern is that chemicals used to protect cellulose from fire make it potentially corrosive in wet environments. Tests conducted by the Oak Ridge National Laboratory show chemical treatments used to treat cellulose can cause metal fasteners, plumbing pipes and electrical wires to corrode if left in contact with wet, treated cellulose insulation for extended periods of time. “

I’d much prefer to see you blowing in rockwool as it remains unaffected by moisture. Last thing you want is to have damp cellulose insulation chemicals eating holes in your ceiling.

According to building scientist and founding principal of Building Science Corporation Joe Lstiburek, “Plastic vapor barriers should only be installed in vented attics in climates with more than 8,000 heating degree days.”

As your site has under 8000 heating degree days a year, you should not have a ceiling vapor barrier. You do need to ensure your newly created non-conditioned dead attic space is adequately ventilated at eave and ridge (https://www.hansenpolebuildings.com/2018/03/adequate-eave-ridge-ventilation/).

For extended reading on heating degree days, please see: https://www.hansenpolebuildings.com/2022/11/what-is-degree-day/

Replacing Panels, Rebar in Column, and Wholesale Purchases(?)

This Wednesday the Pole Barn Guru answers reader questions about replacing old steel panels and adding an overhead garage door, if rebar is needed in the column to collar connection of the footing, and the ability to buy rock wool insulation wholesale.

DEAR POLE BARN GURU: I’m purchasing a small farm in rural Missouri. It has a 24′ x 60′ pole barn. the framing / structure is in good shape. It has corrugated metal panels. these are sound, but the looks are poor. It also has the sliding barn type door. My hope is to re-face the building with better looking panels and put in an overhead-style door ( garage type door). JOHN in NEWINGTON

DEAR JOHN: New steel cladding would certainly “freshen up” looks of this building. It would also allow for steel siding to be held up from grade (by adding a pressure preservative treated splash plank at base), rather than being run into ground.

 

DEAR POLE BARN GURU: Does rebar need to be installed in the concrete that surrounds the column in a pole barn? I will have holes of 12″, 18″ and 24″. Thanks. LOUIS in STEPHENS CITY

DEAR LOUIS: Unless it is called out for on your engineer sealed plans, there would usually be no requirement for rebar in concrete column encasement.

A 12″ diameter hole would be very unusual as Codes require a 4″ minimum space between corners of columns and edge of holes (a 4×4 perfectly placed in the center of a 13″ hole would meet Code requirements).

 

DEAR POLE BARN GURU: Hi, I was watching a video on Youtube recently and saw a guy hanging 6″ rock wool batt insulation. I was wondering if you might know where I can buy this product wholesale? I built a 30×64 and am at that stage where I’ll be looking to insulate myself soon. MARK in ARAPAHOE

DEAR MARK: Unless you are willing to buy an entire 53′ van box of rock wool, you are not going to be able to purchase it wholesale and even then you would need to provide proof you would be distributing on a regular basis from an established business in construction supply trades.

 

Can No Longer Afford Spray Foam for a PEMB

Can no Longer Afford Spray Foam for a PEMB

Loyal reader CINDY in TYLER writes:

“I had a steel building (20×18)  built with steel frame and metal exterior. This is going to be my house. It will have a loft that is half the size of the building. Originally the builder talked me into spray foam and that’s what Ii planned to do. He said I had to use wood to frame inside the metal walls first, then run electrical and plumbing before the spray foam. That was a couple of years ago. Now that inflation has caused prices to soar, I am simply not able to afford the spray foam. My main concern is the condensation/moisture issue. i am doing the rest of the work by myself. Since I don’t have any help it’s not going to be feasible to remove wall panels to install house wrap or insulation. So I wanted to get your expert advice on how to handle this. Specifically I have a plan to run by you. So the idea is instead of building my framing inside the metal frame, move to the inside of the metal, attach wood frame to the inside edge of the metal frame. Insulate the inside of the wood frame and add a moisture barrier to the inside of the wood frame before drywall. I will lose 3.5″ of space all around the inside but i think that will take care of any moisture issues. Please tell me what you think about this plan and make any appropriate suggestions even if you don’t post this on your blog. Also I wanted to thank you for the wealth of knowledge you have readily available on your site. Can’t tell you how much help you have been.”

Mike the Pole Barn Guru responds:

Thank you for your kind words, they are greatly appreciated.

Normally (in your climate zone of 2A) I would be recommending closed cell spray foam as insulator of choice – due to a combination of heat and humidity. Your builder headed you in a correct direction.

Before we get into how to frame your interior, we need to address what is going to happen with your roof. With steel installed directly over framing (whether wood, or in your case steel), if there is no well-sealed thermal break, you are going to experience condensation issues. You are going to have to find a way to spring for two inches of closed cell spray foam sprayed directly to the underside of your roof steel. Steel frame and steel purlins should also be sprayed. If not, you are going to have condensation on them – steel is a wonderful conductor of heat and cold.

Now – on to your question at hand. For your walls, it appears most folks do exactly as you propose and build a 2×4 wood stud wall inside of their PEMB’s (pre-engineered metal building) steel wall girts. You will want to completely fill your wall cavity with insulation – I would recommend rock wool, as it is not affected by moisture (here is information on one particular product https://www.hansenpolebuildings.com/2013/03/roxul-insulation/). You want to make sure your interior vapor barrier is extremely well sealed, including outlets.

If you do not have a well-sealed vapor barrier under your slab on grade, please seal your concrete now. Your HVAC system should be designed to mechanically dehumidify, else condensation is going to haunt you forever.

Stilt Home Barndominium

Stilt Home Barndominium

For many challenging building sites (those with grade change, in flood zones or close to oceans or seas) stilt homes are a viable and practical design solution for barndominiums.

Reader DAVID in EMINENCE writes:

“We are planning to build in southern Missouri a 30′ x 36′ x10′ post frame home on a rocky slope terrain. We want it on stilts. It would be 3′ on one end and 7′ on the other end approximately. We are planning to put reflective bubble wrap on the floor joists with the subfloor on top then place down rock wool and another subfloor on top. We have 99% humidity most of the year (10 months for sure), lots of rain. We do not want a crawl space; we know the horrors of the crawl space. We may enclose the high end using a simple temporary enclosure to dry it out as needed. We are going to use a mini split heating system and composting toilets. No worries about placement of the utilities and pests. Would this be a sound construction system?

We would like to know your viewpoint on this since you are the wise guru.”

Mike the Pole Barn Guru writes:

Thank you for your kind words. Stilt houses are very easily done using post frame. I have a post frame combination garage/studio apartment/office at our home near Spokane, Washington on 14 feet of grade change and built it as a stilt building. Has been great for going on 30 years and would have been the only practical way to build on this site (for extended reading on stilt houses: https://www.hansenpolebuildings.com/2017/09/stilt-houses/).

Not sure why you are considering two layers of subfloor. I would be inclined to use either steel or an exterior rated sheathing product on the underside of my joists (with a Weather Resistant Barrier between). Rock wool is a good choice for insulation between joists as it is not affected by moisture. Place a vapor barrier on top of joists and then your subflooring. A radiant reflective barrier (bubble wrap) can be used as a vapor barrier, but will not provide any benefits you wouldn’t get from well-sealed visqueen – and would be far more expensive.