A potential difficulty is moisture accumulation below the surface of an older foam roofs so make sure it is dry 1st.  

An exception would be extensive storm damage that goes beyond the surface and affects multiple areas.The most common repairs performed on roofs include:90-95 percent occur around flashingBlown- Off or loose shinglesPonding water due to insufficient protective measuresPunctures or penetrations relegated to a single areaShingles that are curling upwards may mean there are leaks underneath the surface or that water is getting into parts of a roof where it shouldn’t be going. roofs with curled shingles often need to be replaced within 1-5 years.Complete replacement is typically recommended when:Damage extends below a roof’s surface layerRepairs are becoming increasingly frequentBald spots are showing up where granules( materials that provide added protection to a roof) are missingA roof is more than 20- 25 years old or has undergone too many re-roofs to make re-roofing a safe option againAn existing roof was poorly installed or not installed according to codeRoof replacement doesn’t necessarily mean completely tearing off an existing roof and starting over from scratch.

Also, consider whether moisture is really an issue though.

(damn you a thousand times moisture!)

Sealing the cracks would be a good place to start (good idea for water penetration, at least!)

Unfortunately, tenants usually do not know how to install them.I've seen cases where they've been poorly installed directing moisture towards the home instead of away from the home.

If I see moisture there I look closer.

The house is in a flood plain, so I can see a benefit to using concrete over a traditional wood supported floor when moisture/rot is an issue. 

If the existing hardwood is not sealed up completely the moisture from the concrete could cause the boards to warp and buckle causing other problems.

Fire damaged lumber must be removed as simply treating it will likely not do the trick down the road when the fire/ash smell starts penetrating into the home.