In-Ground Passive Solar Home and Formaldehyde Pollution

MOTHER EARTH NEWS staff experts answer questions on building an in-ground, passive solar home and the pollution dangers of formaldehyde.

| November/December 1987


Great care must be taken in using logs in an earth-sheltered dwelling.


MOTHER EARTH NEWS staff experts answer questions from MOTHER readers on building an in-ground passive solar home and the dangers of formaldehyde pollution. 

An In-Ground Passive Solar Home and Formaldehyde Pollution

Underground Oaks

I'm planning to build an in-ground, passive solar home in southwestern Wisconsin. My question: Can I successfully use oak logs for the main structure? Could they be properly water-proofed before backfilling? I know that the usual material is concrete block, but I have 60 acres of white oaks in desperate need of thinning. Right now they're just being cut for firewood. 

It's no doubt possible to use white oak logs in an earth-sheltered house. My question: Do you really want to? Will the effort and cost be acceptable? Assuming you want a house that will still be around half a century from now, here are a few of the things you should worry about.

1. Structure. You must find a way to secure the logs to the footings to resist sliding forces. This could be done by setting threaded rod in the footings, slipping the bottom course over the rods and snugging the log to the footing with nuts. Each subsequent course should be secured to at least the previous two with pins at the joints, and staggered at several locations between joints. Traditional log corners may not offer enough resistance to over-tipping forces unless they are heavily reinforced (by steel rod passing from top to bottom and into the footing, and possibly by a bond beam) and buttressed (by right-angle walls that are secured to the footing and pinned). The sizes and spacing of reinforcing elements will depend on the height of the walls, the soil type and the length of unbuttressed walls. This is a job for an engineer.

2. Waterproofing. An irregular surface with gaps—the typical outside profile of a log building—would place undue demands on a waterproofing membrane. It's unlikely that any manufacturer would recommend use of its product unless the logs are square on three sides to present a smooth, uninterrupted exterior surface. As an alternative, it might be possible to fill the gaps between the logs with chinking, affix insulating panels over this more or less even surface and then apply the waterproofing membrane.

3. Rot resistance. Even if the waterproofing system keeps outside moisture out, there's likely to be some condensation inside. It would be a good idea to apply a preservative to the logs before installing them.

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