Building an energy-efficient pole barn
bkeesaman
| Posted in Energy Efficiency and Durability on
We are in the process of planning a metal pole barn used for manufacturing. We need to have metal panels on the inside (or similar) for wash down. We currently have a similar metal pole barn which is not energy efficient. What is a good way to make better use of the insulation / materials to make the building as energy efficient as possible? We also need to maintain a constant temperature of 55-65 degrees if possible.
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Replies
Becky,
From an energy performance viewpoint, a metal pole barn is the worst type of frame imaginable. It has all of the disadvantages of a pole barn, plus all of the disadvantages of a building with steel framing.
If I understand you correctly, and this building has steel framing, then it's going to be challenging to insulate. All of the insulation needs to be on the exterior side of the framing (to avoid the energy penalty of thermal bridging through the structural members). That means that you either need to insulate with a product like SIPs or nailbase, or you need to build a wooden frame on the exterior side of your steel frame to hold your insulation. If you end up needing this wooden frame, you may ask yourself the question, "Why not just skip the steel frame?"
A metal-framed pole barn may be cheap, but it's difficult to insulate. You'll have to choose what you want most: low construction cost or energy efficiency.
Martin,
I should have been more specific. It will be wood poles, wood framing, wood trusses, and with metal 'siding'. We currently have a similar building with batt insulation but it is not efficient.
Becky,
OK, you have half as many challenges as I thought.
It's still tough to insulate a pole barn.
First, there is the question about the floor. Do you have a slab or gravel? If it's a gravel floor, it's hard to air-seal the bottom of the walls. If you have a slab, we'll need to know your climate zone or location, so we can recommend whether you need a horizontal layer of rigid foam under the slab.
Next, you still have issues of how to support the insulation. In most pole barns, you don't have studs. You have posts and horizontal nailers between the posts. This makes air sealing difficult, and using conventional insulation difficult.
The best way to proceed is to work on the exterior side of your structural frame. Again, either SIPs or nailbase is one approach -- and if you use SIPs, you could skip the pole barn structure, and just build a SIP building.
Another approach is to install a stud wall on the outside of your pole barn to hold the insulation -- but again, this raises the question, why not just build an ordinary building with stud-framed walls if you need it for insulation?
I wouldn't build a pole building, either wood or metal, if I needed it insulated. I've done a few jobs converting pole barns into conditioned space, and it basically entails filling in all of the bays with wood framing, then finishing as a conventional wood-frame building. You also need to pour a floor in and around the existing posts, or convert them to piers. It's a lot more work than just starting with stud walls in the first place.
I'm not sure exactly what "wash down" entails, but if you're going to be spraying the interior surfaces of the walls with water, you have additional challenges in terms of waterproofing.
We will have a concrete slab. We are in zone 5 (nw MO). I will look into the SIP's / nailbase. Any other suggestions are helpful. Thanks.
Are you locked into a post frame building for some reason?
We are not locked into a post frame; it is an economical option.
Becky,
If you want an energy-efficient building -- one that stays warm during the winter and cool during the summer -- I doubt that a pole barn is an economical way to go. A conventional frame building will probably be easier to air seal and easier to insulate.
David is right about the waterproofing details. If you will be regularly hosing down the interior walls, there are lots of opportunities for problems. Make sure that the waterproofing details are impeccable.
We plan on having a 16-18' ceiling with the building due to manufacturing equipment. Is a conventional frame building still easiest?
Becky,
The most thoughtful pole structure insulation and air sealing scheme I've seen is this house in upstate New York: prossimo.us/about.php
There's a narrated time-lapse construction video on the page.
The specs I've read are:
Under Floor: 6″ Type II Eps R=23
Slab Edge: 5.5″ Type IV EPS R=21
Walls: 8.5″ Roxul Batts. Clear R= 36.5 Whole R= 30. (1.5″ AFB + 5.5″ ComfortBatt + 1.5″ AFB)
Attic: 16″ Loose Blown Cellulose R=60
.5 ACH
I'm curious to know what the experts think of this construction system. It doesn't address the interior wash-down issue, of course. Fwiw, a friend just built a pole barn workshop with metal paneling on the 16' interior and it is LOUD.
Peter,
You're right -- Ben Freed's home was an exception. He and consultant David Wright managed to build an unusually airtight post-frame building. The credit goes to Wright, who developed unusual air sealing details, and to everyone on the team who was aiming for airtightness from Day One. (You can read more about this building in one of my recent blogs, How Much Insulation is Too Much? Note that homeowner Ben Freed has posted a comment on that page.)
If an owner in another state hires a local contractor to erect a post-frame building, however, they aren't going to get the results obtained by Freed, Wright, and other members of their team.