Expert Advice on Straw Bale Building

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The other way moisture can damage a building is vapor migration through walls. Think about blowing up a balloon. You force warm, moist air from your lungs into the balloon, creating an air-tight container with a higher pressure than what exists outside the balloon. The moist air will do its best to leave the balloon and join the surrounding atmosphere. During the heating season, your house functions similarly to the balloon: When heat is added to your living space, your relatively airtight house is filled with warm, moisture-laden air. Extra moisture is added by breathing, cooking, bathing, etc., and that air will naturally search for a way out of the house and into the cold, dry air outside.

As the warm, moist air tries to travel outdoors, it will begin to cool. As it cools, the water vapor it carries will condense back to liquid. If liquid is deposited in your walls and allowed to remain there without drying, it will reduce the efficiency of your insulation and eventually lead to mold and rot. In hot climates, the process can happen in reverse, especially if you use air conditioning.

The plaster coating on straw bale walls is an effective barrier against moist air leakage. If properly tied in with conventional polyethylene vapor barriers installed in the ceiling and under the floor, a bale house can be made almost airtight. In conventional building practice, moisture is prevented from migrating into the wall cavity through the use of plastic vapor barriers in the walls. This addresses the real concern of air leakage in stud-framed homes, but it is unnecessary in bale walls.

Pests

We share this planet with billions of creatures both large and small. To say that a particular house or style of construction is pest-proof is to ignore the instinct and persistence of our little neighbors.

The ideal homes for pests offer openings, nests and food. Plastered bale walls do not offer any of these three because their coating seals the bales from foundation to roof with a difficult-to-chew barrier. Should a gap be left open in the plaster, the bales themselves are too densely packed to make comfortable housing for mice and other rodents. All those comfy spaces in your neighbors frame walls, lightly packed with batt insulation, make a much more inviting home for pests.

Not much food is available for any living creature in a straw bale wall even termites dislike straw. However, an inordinate amount of seed in the straw could provide a source of food, which is why you should check your bales for excess seed content before purchasing them. But make sure as with any style of construction to keep pests out during the building process.

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