Large Scale Central

Real World Wood Water Tank Construction

So it has come up several times that there is a construction issue with putting an octagonal roof on a round water tank. As Dave Taylor has pointed out to me on a couple of occasions, and I think Jon also, that with the design there are gaps at the peaks where the roof panels join and the tank rim. Its a matter of geometry. The tank touches the roof panels only at the center of each flat panel.

My question is how was this dealt with in the real world. I assume I already know the answer, and that answer is that the roof panels sit on rafters where the panels join. So while I get how it is constructed and fastened down, the fact remains that there will still be gaps now between the center of the flat panels and the rafters.

What did they do about the gaps? My assumption is that they left them, or at the very most screened them. Tanks do need ventilation to keep them from imploding. So this would form a natural vent. But I would like to know if anyone knows. As a water guy it is interesting to me. I am only familiar with concrete and steel. I have never had the opportunity to examine a wood tank.

This may be of interest to you Devon. Build Your Own Wooden Water Tank - YouTube

Thanks Dan,

Perfectly answered the question. Never even considered soffit boards. And it also gave me what I needed for the floor construction.

A different style



this is for a round roof i think. but could be octagonal. the thing to remember is that the carpenters framed it all in!

Al P.

David that is a cool tank for many reasons. I love that it has a radial roof instead of an octagonal one. And that it has a lid under the lid and finally that the windmill pump is mounted tot he roof to draw water straight up and in the tank. To bad I have a ceiling in my way or I would model that. Thanks for sharing.

And there is the answer. Along with the video its clear to me now how they solved the real world problem. I knew it lay in the framing and the rafters but then enclosing the soffits solved the problem of the gap.

real tanks don’t have plastic roofpanels.
they have a roof framework with tiles, shingles or corrugated sheets upon it. (or boards as support for roofing felt)
so, lots of ventilating slits.

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Yes and I think that’s is where I was going wrong. In my business of a public water utility, tanks have to be “sealed” from contamination. Things like openings are bad. What vents are in them are screened and built in such a way as the screened opening faces down. I am thinking 21st century drinking water instead of 19th century water for steam locomotives. There would be no practical reason to even attempt to close the gaps that the rafter and the roof panels create between them and the tank rim. It would actually be a good thing as there would be no need to vent the tank by other means.