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Post-and-Beam Infill for Straw Bale Walls

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Wall Systems
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Post-and-Beam Infill

In post-and-beam infill a structural timber or salvaged steel frame carries the roof and the bales fill the gaps between posts as insulation only, so the building has no bale-imposed height or size limit and can be multi-storey. Erect the frame and roof first, then stack the bales under cover at leisure, sizing bays in multiples of half a bale, 45 cm, to avoid custom bales.

Part of Straw Bale Construction

Infill construction separates structure from insulation: the frame holds the building up and the bales keep it warm.

The Frame Does The Structural Job, So The Bales Can Wait

The parent article lists the advantages: no height or size limitations, multi-storey possible, bales installed after the roof is on so they are protected during construction, easier large window openings, and a frame that goes up quickly while bales are infilled at leisure. The cost is much more timber or salvaged structural material. Because it protects the bales from rain during construction, it is the recommended choice for most post-collapse buildings.

What You Need

Method: Frame, Roof, Fill

Step 1: Lay out the posts so that the clear bays between them fit whole bales or half-bales.

Step 2: Erect the frame and roof. Post spacing is a choice; pick bay widths that are multiples of the half-bale length.

Step 3: Stack the bales between the posts in running bond on the stem wall, tight against the posts.

Step 4: Tie the bales to the frame with stakes, wire or ties so the infill cannot lean out.

Step 5: Frame openings with timber boxes and build the bales against them.

Step 6: Plaster once the bales are in and dry.

Worked Example

  • Inputs: bale length 90 cm, so a half-bale is 45 cm. Clear bay desired: about 4 m.
  • Operation: 4 m = 400 cm; 400 / 90 = 4.4 bales; in half-bales, 400 / 45 = 8.9, so 9 half-bales fill 405 cm.
  • Result: set the clear bay at 405 cm, whole bales and one half-bale per course, instead of 400 cm, which would leave a 400 - 360 = 40 cm gap after four whole bales and need a custom piece cut and retied for it.

Common Mistakes

  • Bays that do not match bale length, forcing many custom bales.
  • Loose infill. Bales not compressed against the posts settle and gap.
  • Frame uprights on the ground. Posts rot; stand them on the stem wall.
  • Bales stacked before the roof is on, losing the main advantage.

Safety

Raising a frame

Posts and beams are heavy and fall in wind. Brace each post as it is raised, use enough people for every lift and keep clear of the frame when working above.

What’s Next