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Material Selection for Roof Framing in Wastewater Treatment Facilities

Yenni

Structural
Joined
Mar 31, 2025
Messages
2
I’m working on a wastewater treatment facility and trying to figure out the best material for the roof framing.

Is it common to use wood trusses (even if pressure-treated or fire-retardant), or is steel — cold-formed — the standard in these types of buildings?

The structure will be exposed to high humidity and possibly corrosive conditions for its entire life, so I’m leaning toward galvanized cold-formed steel trusses for durability and non-combustibility. Just not sure if that’s typical or overkill.

Many thanks for any advice.
 
Is it common to use wood trusses (even if pressure-treated or fire-retardant), or is steel — cold-formed — the standard in these types of buildings?

It's common here, in Alberta Canada where it is very dry and there is no salty sea air. Wastewater treatment plants here are often in residential areas where we try to make them fit in with the other architecture in the area. So they often look like a big house or a small commercial building from the outside. The tanks are concrete and hoist beams are steel of course. But the super structure often is light frame wood.

If your environmental conditions are more corrosive, wood may well not be a good choice.
 
I'd use aluminum framing or composite/fiberglass if these are directly exposed to more caustic atmospheres.

There are companies that provide roof framing systems in fiberglass (not sure of pitched roofs).

Galvanizing is great until it isn't. Eventually even galvanized metals will begin to rust given enough time and bad air.
 
We supply a lot of precast products for small wastewater facilities. I have never seen a stick of wood used. Wastewater facilities are usually designed for longer lifespans. That is dictated by our codes, so yours may vary. We have used galvanized joists and deck in car wash facilities.
 
Hey guys thanks for all the responses.

Just did quite a bit more research
, it looks like a lot of other engineers in my area like to use precast hollow core planks for the roof system to deal with all the humidity.

I’m also trying to familiarize myself with the Sd factor in ACI 350 now.
 
Cast in place conc, precast conc, hollow core slabs, galvanized steel would be options I would consider. I too have never seen wood in any water or waste water treatment facilities.
 
The only wood I have ever seen in a wastewater treatment plant was in a very old military establishment a couple of decades ago. The hardwood had performed admirably and pre-dated the 1950s but it was impossible to replace like-for-like. Similar old-growth hardwoods were extremely rare and expensive and only available in much smaller sections.

I worked for the water and wastewater treatment organisation of a large municipality for a time and would look towards composites (GRP, etc.) now as hot-dip galvanized steel portal frames and cold-formed members have issues after a couple of decades. Sulphuric acid is pretty aggressive, particularly if this structure is for a large sewerage network with a long catchment transit duration. Most places really stretch a structure's service life before replacement well beyond their nominal design life.
 

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