Affect of mold on strength of wood joists and sheathing

[mfstructural]

I inspected a house yesterday where we were being asked to issue a report "on the subfloor" of the house. Once I arrived I understood what they were talking about. The floor was spongy underfoot in several areas. From the basement I saw areas with fungal growth and discoloration on the bottom of the floor sheathing and floor joists. The damage was visibly extensive to the sheathing and I would recommend replacing all the sheathing. My question is regarding the 2x10 joists. They spanned 13'-6" which was ok, but many had fungal growth on the sides of the members. I didn't have a moisture meter on me so I don't know what the moisture levels in the wood wood. There was no section loss at the surface so I don't believe the strength of the joists was compromised. There was one area under the bathroom where deteriorated joists were observed and that was probably from a water loss (the house was vacant).
Has anyone come across this, and if so what's your experience been with joists like this? replacing them is a signifcant undertaking. I think I would recommend cleaning the fungal growth from the existing joists and sistering new joists to the existing where required. You'll also see in the pictures I attached that the joists are notched at the bottom, those will have to be replaced as they do not conform to code.

 

[SlideRuleEra]

The photos look like there are more than structural problems. IMHO, the building should be evaluated by a qualified company to see if mold/ fungus remediation is needed.

Concerning your question, mold and fungus being present on wood usually is not a structural problem. See Chapter 14 of the (free) USDA "Wood As An Engineering Material".

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[dik]

In addition, the presence of mold, other than being a health risk, is the same condition that promotes brown rot (aka dry-rot). This can have a significant detriment to wood structures.

You can lose 15% of the material strength without any loss of weight with brown rot. By the time it is visible, you can have significant loss of strength.

Is the basement damp and humid?

Dik

 

[mfstructural]

It was a damp, the humidity levels were not excessive. My first thought was to replace the entire floor framing system to be honest. that's definitely not an easy task though. The subfloor has to come off either way. With respect to replacing the floor joists the exterior walls would need to be temporarily supported as the joists are replaced. The best would probably be to replace the floor joists in sections, maybe 2 to 3 at a time. There is also the issue of the sill plate which was also water damaged. I have no idea how long this house was vacant but the water did some heavy damage.

 

[hokie66]

Looks like the electrical and plumbing are not in good shape either. Are you sure the house is worth saving?

 

[thaidavid40]

If the top plate and/or rim joists are too far gone, you may as well replace the entire framing with new material.
Dave

Thaidavid

 

[mfstructural]

As far as if its worth saving, I'd probably say no. Replacing the sill plates and rim joists is obviously a big issue since they're supporting the walls above. It would be very expensive from a cost perspective to perform this work in my opinion and like you said, would probably be better off rebuilding. it's not like there's anything inside to salvage. I'm not sure if the client is looking to buy or has bought as they haven't indicated that to me. Not that it matters, my opinion doesn't change.