DEAR TIM: I lived in a mobile home that was destroyed by Hurricane Katrina on August 29, 2005. My mobile home was on concrete blocks set about 32 inches high on a concrete slab. The slab is about 4 inches thick without footers or anything fancy. It does have the wire reinforcement inside the concrete.
Before Hurricane Katrina came along, we had problems with mildew on the bottom of the walls. We primarily noticed the mildew in the closets. Our home was skirted, and probably not ventilated enough.
We are about to purchase a new manufactured home that is larger than our original one. I saw a mobile home with a black plastic liner over it as a vapor barrier. Should we do this? I read on your site that water passes through concrete. Wow! I don't want to have the same problems we had with the previous home.
Our intention is to raise our new home up 5 feet high on concrete blocks. The home dealer says they will go that height, but no more. We can afford to pay big bucks to have the foundation done with reinforced block. It will be tied-down well. I am hoping that in raising the home 5 feet above the surrounding ground, this will save it from possible flooding. Will raising it this high harm the home's structure? Karen T., Slidell, LA
DEAR KAREN: I am sorry to hear about your loss. Hurricane Katrina had a really bad temper, and I have this feeling some of her sisters, brothers and cousins that will come along in the future will be in as bad a mood or possibly worse. For this reason, you must slow down and do a little research before you have this new manufactured home set on its foundation.
The first thing you need to determine is what might the water level be in the event of future flooding. The local weather department or possibly the folks at your local fire department might know how high the water reached above the soil on your land during the height of the storm.
I can see looking at the map you are located very close to water at the northeast corner of Lake Pontchartrain. Since the center of Hurricane Katrina passed east of you, the winds were pushing the water of Lake Pontchartrain away from you. But if the next monster hurricane makes landfall just west of you, the horrific winds could create a storm surge that might flood the land with water 15 - 25 feet above normal levels.
For this reason, you need to get hold of a topographic map that will tell you the height of your lot above sea level. You can also get this information from free software called Google Earth. Find your lot on this software and it has the ability to tell you the height of land above sea level at any given point on the earth.
The mildew in the closets was caused by high humidity in the spaces during the winter months. The exterior wall surfaces of the closets was cooler and the water vapor condensed on the exterior walls. You can solve this by leaving closet doors open in the winter to keep them warmer and encourage air circulation which evaporates the water fog that starts to develop on cooler wall surfaces.
The black liner you saw might have just been a protective covering used to protect the home from roadway dirt and water as the home made its trip from the factory to the dealer. My guess is they have already installed the proper vapor barriers inside the walls of the new manufactured home.
But I would also place a high-quality vapor barrier over the concrete slab after your new manufactured home is in place. This large plastic sheet will stop water vapor from passing from the ground up into your manufactured home.
You must find a way to reinforce the concrete block that will become the foundation of your new manufactured home. I don't care if it means working a second job for a short period of time to pay for this much-needed structural improvement. You will never regret having steel rods inside the cores of the concrete block. Fill the cores with a mixture of small gravel, sand and Portland cement.
A 5-foot high concrete block foundation will not harm the manufactured home structure. But if the concrete block move because they are not reinforced, you could have serious problems.