Tag Archives: straw bale pole buildngs

Insulation and Ventilation, Straw Bales, and Double Bubble

This week the Pole Barn Guru answers reader questions about using cardboard and heavy plastic to vent and insulate a pole building, use of straw bales an insulator, and best way to ventilate and reduce roof noise.

DEAR POLE BARN GURU: On my 42×63 2 story pole building (heated first floor) I have trusses 9’ o.c. standard roof purloins 2’ o.c. I was wondering if I could use cardboard up against steel roofing for venting air flow of the humps in the steel roof panels (standard steel w/ 1” humps not standing seam ) then install heavy plastic on bottom of purlins and fill cavity w/ cellulose blown insulation. Would this work correctly for ventilation of steel and insulate correctly. Combination of being cheap/frugal and I have free heavy cardboard from washers/dryers/refrigerators to fit between purlins. Greatly appreciate your opinions. Thank you. BEN in EDEN

DEAR BEN: Code requires a one inch minimum of airflow across your entire roof surface above batt insulation. Air flowing only at steel ribs would be inadequate to meet requirements. Assuming you have 2×6 roof purlins, 5-1/2 inches of blown cellulose would give you roughly R-19.25. You would be better served by using 2-1/2 to 3 inches (R-17.5 to R-21) of closed cell spray foam applied directly to underside of your roof steel, as it does not have to be vented above.


DEAR POLE BARN GURU: Hi, I read your post on bale infill with a pole building (https://www.hansenpolebuildings.com/2013/04/straw-bale-homes/). When I called to get more info, the rep told me that Hansen strongly advises against it, but he also said he hadn’t heard about that idea. Is there someone there that has worked with a client who has used straw bale walls to infill between the posts? KEVIN in RENO

About Hansen BuildingsDEAR KEVIN: Your call happened to be routed to one of our newer Building Designers. Post frame construction is highly complex, with a literal unlimited number of possibilities, this being one your designer was unfamiliar with.

In general straw bale homes seem to have been a passing fad, however if you strongly feel this is your best option, please call again and ask to speak with Rachel – our most senior Building Designer, and she can assist you better.


DEAR POLE BARN GURU: I am looking for a underlayment for my pole barn. I have metal roofing with horse stables below. There are no side walls to my pole barn. It’s all about ventilation for the animals here in NC. It’s supposed to add a few degrees in R value. It also helps deaden the sound of rain. Everyone talks about double bubble but this is supposed to be different. Thank you, FRANCES in TRYON

DEAR FRANCES: Without having to pull off your building’s roof steel, install some fashion of condensation control then reinstall it – there is only one practical solution – two inches of closed cell spray foam applied directly to underside of your steel roofing. This would provide an R-14 insulation value. It is unlikely to have an effect on reduction of noise from rain, as it is not good at blocking sound waves. “Double bubble” offers little to no R-value and would require being installed between framing and roof steel.


Straw Bale Homes

And he huffed and he puffed and…

straw pole barnOk – couldn’t help myself when I thought about writing about straw houses!

For years I’ve been fielding inquiries from people who are interested in integrating basic pole barn design, with straw bale infills, to use as residential structures.

During a recent visit to a Home Depot in New Mexico, one of the PASAs (Pro Account Sales Associate) recommended I write a blog post about straw bale homes, using post frame construction.

To get started, I whipped out the trusty Google-machine and started searching….and searching…and searching. And found pretty much nothing. At least nothing about using the pole barn as the structural framework, lots of information out there on straw bale homes. Considering the wealth of information available, it was surprising to read how few straw bale homes exist, but that is a different story altogether.

The top advantage of using the post frame technique is it gets a roof over one’s head in a hurry and at a reasonable cost. It also allows the straw bale infill to be non-load bearing, which reduces the costs of the exterior walls (no need for structural headers as long as door and window openings are placed between columns). Most straw bale homes have very small clearspans, as trusses are not usually utilized. The pole barn framework allows for very wide spans, which eliminates the need for interior load bearing walls, and frees up space to allow for a more open design.

The most cost effective column spacing for pole building construction is typically to place them every 12 feet. This increment works out very effectively with either three or four foot bales.

Some design considerations – the one which will be most frequently overlooked is going to be deflection. A roof only “pole barn” will typically have a great deal of deflection at the eave line. Think of the posts (as a roof only building) acting as diving boards.  The IBC (International Building Code) limits the deflection of members supporting exterior walls with brittle finished (like plaster of bales) to L/240.

In layperson’s terms, this would mean a nine foot tall exterior wall (which would be needed to create eight foot high ceilings), could deflect a maximum of 108”/240, or less than ½ of an inch. Do not just assume this type of deflection limitation when ordering – it is essential the company providing the building understands this to be a crucial element. In many cases, it is going to entail columns being larger in size than would otherwise be the case.

Make sure to specify the building is to be used as a residence. Residences will be Occupancy Category II and designated as Use Class R-3. Most roof only “pole barns” are Occupancy Category I and have less stringent requirements for resistance of climactic loads (wind, snow and seismic forces).

Most straw balers are well in tune with energy savings. The pole building roof structure fits well with this. Trusses can easily be designed to allow for a “raised heel”, allowing for the full thickness of insulation to be installed from wall-to-wall. The eaves should have overhangs on the low sides, which are enclosed with vented soffits to allow for an air inlet into the otherwise dead airspace in the attic. Similarly, the ridge should be vented, to allow for an exhaust point.

If using steel roofing over purlins (which will be the most cost effective), condensation needs to be controlled. Easiest is to order steel with an Integral Condensation Control factory applied.

For planning and constructing the bale portion of the project, there are a couple of highly referenced resources. Both “Serious Straw Bale” and “The Natural Building Companion” are available online and offer plenty of information.  Good Luck and let us know if we can help you design your new straw bale home!