Claudette Reichel | 1/28/2019 7:11:20 PM
After a flood, it's now common knowledge that it's necessary to promptly remove floorings (except fully adhered ceramic tile), open walls and discard wet insulation. The next steps in restoration can spawn many questions, and answers unfortunately tend to vary from source to source.
The “best choice” restoration method depends – on the type of construction and materials of the home, the level of damage, location, the budget and resources available, and the goals of the owner. That’s a difficult but important balancing act and decision process.
Although a one size answer can’t fit all situations, following are 23 frequently asked questions, and unbiased information we offer based on building science principles and practices, to help home owners, contractors and workers make informed decisions. If all is now clean and dry, you could skip down to questions 13-23.
1. My home is gutted above the flood level. Now what?
Get it safe, clean and dry ASAP! For a detailed how-to guide, download and refer to Rebuild Healthy Homes: Guide to Post Disaster Restoration for a Safe and Healthy Home – a free mobile app for your smart phone, and a free pdf publication online.
HAZARD ALERT! If your home was built before 1978, it could have lead based paint and asbestos containing materials; the older the home, the more likely the hazard. Disturbing such materials can create a much greater health hazard than existed before.
If the tear-out process didn’t follow lead-safe work practices, it’s not too late to do a lead-safe clean-up. Wear personal protective gear, including a NIOSH certified N-100 respirator. Do not use a typical vacuum cleaner, since they blow fine dust into the air. Use a HEPA filter vacuum and damp wipe methods. Learn more in the Rebuild… guide and at www.epa.gov/lead. Hire only EPA Lead-Safe Certified contractors to help.
2. Does bleach kill mold? Should I clean with bleach?
Since floodwater is contaminated with sewage, and possibly other biohazards, it is recommended to clean first with a detergent solution, then disinfect surfaces before the drying process. Disinfectants also pose hazards, some more than others. Always read the warning label and follow directions carefully.
Household chlorine bleach is a readily available, inexpensive disinfectant. It can kill a wide range of bacteria and mold IF the surface is cleaned first, the solution is the right concentration, and there is enough contact time.
However, bleach is quite corrosive so should never be used on metals or near the air conditioning system and it poses a variety hazards to people (burns, asthma trigger, etc.). It also has no residual effect, so does not prevent new growths of mold or bacteria if conditions remain damp. Bleach should never be mixed with ammonia or an acid (like vinegar) since that can create toxic gas.
3. What should be sprayed in the wall cavities, subfloor, etc.?
The best practice is CLEAN and DRY. Mold and bacteria do not grow on clean and dry materials. That said, it can take time to get everything dry enough. Also, disinfection is recommended after flooding due to potential sewage contamination.
All disinfectants pose some hazard, but some more than others. Investigate the hazards and read warning labels of any disinfectant, fungicide or fungistatic product before use. Some types have ingredients that are known or suspected carcinogens; some can be asthma triggers; some are corrosive; and, they vary in effectiveness. If the materials must be dry before application, then dry materials will not support new mold growth anyway.
Having wood framing and subflooring exposed does offer a valuable opportunity to treat structural woods with a borate solution that penetrates the wood to provide long-term, effective and safe protection from termites and decay fungi. Boron based products tend to also help deter new mold growth, although they may not be formulated or labeled for that.
Do not apply anything that would impede drying to the indoors. If you want to use a fungicide (to kill mold) or fungistatic (to prevent new growth) or even a paint coating, make sure it’s very water vapor permeable (perm rating of at least 5, prefer 20 or higher).
4. Does flooding affect my termite treatment? Is re-treatment needed?
Most chemical soil treatments are not water soluble, so they remain in the soil. However, if any treated soil is washed away or covered by deposits of silt or mud, the chemical barrier is no longer effective. Flooding may also have an adverse effect on termite bait systems; saturated material in the bait stations must be replaced. Note also that soil treatment chemicals currently available last only 5-15 years, and retreatment is needed when they expire.
Gutted walls offer a rare opportunity to see normally hidden termite damage and infestation, and correct moisture intrusion problems that attract termites. As mentioned above, it’s also an opportunity to apply a penetrating borate treatment to structural woods for termite and decay protection, especially if there is evidence of previous infestation.
5. Who should I hire to remediate or apply treatments?
Professionals with specialized equipment and training can provide safer, faster and more effective cleaning, drying and mold clean-up services than doing it yourself. Always check credentials and experience.
Louisiana law requires that anyone hired to remediate significant mold must be a La. licensed Mold Remediation Contractor who has completed an approved education program and met other requirements. Search licensed Mold Remediation contractors at www.lslbc.louisiana.gov.
Also, anyone hired in La. to apply an anti-microbial product (such as disinfectants, fungicides, mold treatments, etc.) is required to have a Microbial Pest Control certification through the La. Dept. of Agriculture and Forestry. For this 2016 flood emergency, pest control operators with other certifications are temporarily authorized to apply anti-microbial treatments. They can also apply borate treatments and other termite and household pest controls.
6. So how should mold be removed and prevented?
Today, most mold remediation national standards and protocols rely upon cleaning away mold, rather than just killing it, and speed drying. Dead mold spores and remnants have the same health effects as live mold, so it’s better to remove it than just kill it.
Non-phosphate all-purpose cleaners or detergents are recommended for cleaning since phosphate residues can be a food source for new mold. Once cleaned, the safest AND most effective solution to prevent mold is speed drying wet materials.
To clean as safely and effectively you can, read and follow the 10-step Mold Removal Guidelines and Storm Damage Clean-up Highlights on the www.LSUAgCenter.com website or from your parish LSU AgCenter Extension office.
7. What is “speed drying”? I’m using fans, so why is it taking so long?
Well, I made up the term speed dry. It means using every means available to dry wet materials as quickly as possible, ideally within days, to prevent new mold colonies from forming.
Drying is slow to non-existent when the relative humidity (RH) of air around the material is high (70% and higher). The lower the RH, the faster materials dry. Dry air pulls moisture from materials. Fans help evaporate surface moisture, but blowing around humid air doesn’t do the job. Also, warm materials dry faster than cold materials.
Your goal is to create a drier indoor air environment that will cause moisture to transfer from the wood and concrete slab to the indoor air. However you need to find a balance that allows drying, but not so fast to cause cracking and checking of the wood millwork/trim that didn’t get wet.
To speed dry (after cleanup is finished), do all of the following:
8. How do I know when it’s dry enough to restore?
You can’t tell by appearance or time spent drying. A reliable, professional-grade, calibrated moisture meter is recommended to measure the moisture content of flooded materials.
The newer recommended wood moisture content target is 15% or lower, because higher levels could possibly support mold growth. Take readings with a pin type meter at various locations in both the middle and edges of wood studs, bottom plates, wall sheathing and subflooring. Note that treated woods (bottom plates) can produce false readings on some meters.
Previous guidelines cited a 19% target because that’s the national dryness standard for framing lumber. Wood with higher moisture content is vulnerable to decay fungi, a structural risk.
Note that a flooded concrete slab soaks in water like a sponge. A wet slab can lead to flooring failure and rewetting of wood framing. To monitor slab wetness, use a pinless moisture sensor, if possible. Otherwise, as a rough DIY indicator, tape an 18 inch square piece of clear plastic sheeting on the concrete. Monitor for 24 hours, then if visible moisture collects under the plastic, the slab is still wet.
Also inspect for wood decay and termite damage, and repair or replace damaged and soft wood before proceeding.
9. Do I need a “clean home certificate”?
There has been a major buzz about “Clean Home Certification” requirements for flooded homes. This is new, so we asked reps of FEMA, SBA, building officials, lenders, the insurance commission and attorney general’s office in Louisiana, and found NO such requirement. We did, however, learn that scam artists have charged worried homeowners large sums to do an inspection and provide a “clean home certificate” they claim is required.
What we DO recommend is to document (with date stamped photos and written records) the clean-up procedure used and to keep a moisture log of moisture meter readings, showing that wood framing reached the recommended 15% moisture content before restoration. That can provide reassurance for the homeowner and to prospective buyers, renters and lenders in real estate transactions.
Legitimate, licensed or certified mold remediation contractors may provide a “clearance” report of the effectiveness of the remediation and some lenders or insurers may want a copy of it on file.
10. What’s that material between the studs and bricks (or siding)? Is it needed?
Most houses with insulation also have sheathing, typically 4x8 ft. panels, attached to the exterior side of studs. It has several purposes in addition to being a backer for installing insulation. It may have black building paper, housewrap or other weather barrier material on the exterior side to serve as a “drainage plane” to protect wood and insulation from wetting. It may also provide some of the structural capacity needed to withstand wind forces.
Different types of sheathing react differently to flooding:
The next set of FAQ’s addresses wet and damaged sheathing issues.
11. The studs are dry, but not the sheathing/subfloor. What should I do?
Composite wood materials made with resins, wax, asphalt, glues, pressure, etc. are slower to wet and slower to dry than dimensional lumber (wood cut from a tree). Oriented strand board (OSB) panels may take twice as long as studs to dry. Blackboard may be even slower to dry.
Continue speed drying with dehumidifiers and aim fans to blow low RH air on the wet sheathing. Take moisture meter readings in different spots each time (don’t use the same pin holes) and keep a “moisture log” of readings over time.
Moisture moves from wetter to dryer areas, trying to equalize, so a spot at 15% one day might read higher at a later date if other areas were wetter. Wait for equalization to stabilize before giving up the dehumidifiers.
12. Must siding be removed to help exterior sheathing dry?
When the interior is air conditioned so it's cool and low humidity inside and warm and humid outside, the direction of drying is almost entirely toward the inside. So it would not be helpful enough to justify the cost of removing siding just to help dry sheathing.
Nevertheless, it is recommended to remove any horizontal caulk between lap siding boards since it impedes airflow and drying. Only vertical seams should be caulked.
However, if sheathing is substantially decayed, damaged, missing or infested with penetrated mold or insects, removing siding to replace sheathing and install an effective weather barrier (such as housewrap) may be warranted.
13. What’s that black plastic/tar paper at the bottom of the wall cavity, between the studs and sheathing? What should I do with it?
In brick veneer homes, it’s a flashing that extends to the brick ledge and under the bottom course of bricks. It’s there to protect the framing and insulation from water that drips and collects behind the bricks until it can drain out of the weep holes. However, the visible part of the flashing between studs and sheathing is actually an incorrect placement that was common in years past. That placement tends to result in the bottom of the sheathing getting and staying wet.
If sheathing behind the flashing is soft, crumbly, delaminated or has penetrating mold, the damaged sheathing should be cut out. If only a small section of damaged sheathing is cut away, it should be replaced with a material that can withstand water. One good option is rigid foam board (such as extruded polystyrene or XPS); it can be cut to fit in place of the removed section of sheathing and secured with a foam compatible caulk around its edges. Since XPS is water resistant and can serve as the weather barrier, locate the flashing between the studs and XPS (as it was before).
If the sheathing behind the flashing is undamaged and will be retained, the flashing must be held away from the sheathing to allow air access and drying. One way is to slit the flashing about 2 inches from the studs, fold down the flap until the sheathing is dry, then repair it with asphalt-based, adhesive window flashing tape on both sides of the slits to restore it. Or, you may trim away the top part of the flashing to clean behind it and allow drying, but leave 3-4 inches to protect insulation from water that drains behind the bricks and insert shims or other spacers between the flashing and sheathing to allow air to reach the sheathing during dryout.
If the flashing is cut off, or damaged when removing sheathing, it should be replaced. Flexible, plastic, non-adhesive flashing can be used; do not use metal flashing in contact with cement or pressure treated wood. Alternatively, a Z-flashing could be placed on the bottom plate, tucked under the brick ledge flashing.
It's best for flashing to be installed to continuously cover the brick ledge and fold up on the exterior side of studs. However, mortar protrusions and sheathing remnants on the studs can make this difficult and impractical to achieve. If flashing replacement is limited to sections between studs, it should be sealed in place on the interior side of the WRB.
Another option is to coat the wood bottom plate, bottom of studs and brick ledge with liquid applied flashing, after cleaning away all debris. Make sure that water can drain out from the weep holes in the bottom course of bricks. (See the next question.)
14. What should be done with brick weep holes?
Quite a bit of rain water goes through bricks and drains down the gap between brick veneer and sheathing. That’s why brick veneer should have weep holes in the bottom course that allow water to drain out. It’s best to also have weep holes or an open top behind the top course of bricks to allow air flow, which helps drainage and drying.
It’s common for bottom weep holes to be clogged with mortar droppings behind them and debris in them. Clean out debris. A drill may be helpful to reopen weep holes and improve drainage. It’s best to remove as much of the mortar droppings at the bottom of the gap as you can, since it creates a dam that could lead to pooling of water and wetting of framing or insulation. If there are no weep holes, remove mortar between every third brick on the bottom course.
15. When damaged sheathing is removed (since it’s rotten, soft, crumbly, slow to dry, mold-infested fiberboard, etc.), but there are brick ties on the studs, how can it be replaced?
Replacement is important, but the brick ties are in the way of attaching new sheathing to the exterior side of the studs. Any method and materials used need to create an effective “drainage plane” (water barrier system) to keep the substantial amount of rainwater that gets through brick from wetting insulation and wood. There also needs to be a drainage gap to allow water to drain down and out the weep holes. If water cannot drain out, the bricks are likely to stay wet enough to grow unsightly algae and cause a maintenance problem.
If the existing sheathing provided a structural function, a means to replace that structural capacity is also needed. A structural engineer, architect or building code tables can help determine needed “shear load” (to resist racking or leaning) and if the sheathing or other methods (such as corner bracing) provided it, or need to be added. The higher the wind zone, the more load capacity needed.
The “best practice” is to remove the brick veneer and brick ties, replace sheathing from the exterior with plywood or other flood-hardy material, install a weather barrier (house wrap, liquid applied, or other type) properly integrated shingle-fashion with new window and brick ledge flashings, then install new brick veneer, siding or other finish. This is costly, but offers the best and lowest risk restoration.
16. I can’t afford to remove and replace the brick veneer to replace damaged sheathing, so now what?
Many homeowners and contractors have grappled with what to do when they just cannot financially manage the best practice approach of removing brick veneer to replace sheathing and weather resistant barriers (WRB). Alternative sheathing replacement methods (whether partial or full height) are being used.
With any method, sections of damaged sheathing should be cut out above the damage or wetness line. If retaining the brick ties, cut sheathing along the inside edge of studs so sheathing strips remain on the exterior side of studs, to retain the full base of support for the brick tie fasteners.
In many cases, the residential brick ties are damaged or the type used doesn't really provide an effective load transfer function (to resist wind forces), so removal of the ties may be a reasonable choice that offers easier and more robust restoration options. If damage is only on the bottom few feet of a wall, it may be structurally unnecessary to replace removed brick ties on some houses (consult a structural professional). If replacement is needed or desired, retrofit brick ties are commercially available. One type is installed from the inside into bricks (held with epoxy) and fastened to the side of studs; another type can be installed from the exterior by screwing a pin-type tie through mortar joints into studs.
Following are alternative restoration approaches (after removal of damaged sheathing, mortar droppings and weep hole blockages) that have some practical advantages along with limitations and risks to consider when making an informed decision. (Note: These methods are not standard building practices. Consult your licensed contractor, building official and insurance inspector for acceptability of any repair method considered.)
Closed cell spray foam with rainscreen method:
Closed cell spray foam with thin, fanfold XPS sheets method:
Considerations with cc spray foam methods:
Rigid XPS foam board sheathing method:
Considerations with XPS rigid foam board method:
17. Where can I get a “rainscreen” or vent baffle product to maintain drainage space behind brick veneer?
We don’t endorse any particular product, but a few rainscreen and attic baffle products we’ve seen which could provide good drainage include (in alphabetical order):
18. What kind of insulation should be used to replace what got wet?
There are many good options to achieve R13 or higher insulating value, but a key recommendation is to use an insulation that does NOT have a “vapor retarder” (such as kraft paper facing) on the interior side. A vapor retarder facing would hamper continued drying to the inside, and is not needed nor recommended in our hot, humid climate.
If using batt insulation (glass fiber, mineral wool or cotton), select unfaced friction-fit batts. Ensure proper installation with no voids or compression for good energy-saving performance.
Any type of spray applied (spray foam, cellulose, mineral wool or fiberglass) or loose fill insulation properly dense-packed within netting (known as BIBS) provides full coverage with no compression, which performs better than flawed batt installations. A product that does not add moisture is preferable.
Spray foam insulations are more expensive but also create an airtight seal, reducing energy losing air leakage. Open cell foam has a similar R value as fibrous insulations, so the wall cavity should be filled. Closed cell spray foam has a higher R-value per inch, so two inches achieve R-13. Closed cell foam (rigid or spray) is a flood resistant material and could be used to create a flood-hardy assembly. (Click here to learn more about “wet floodproofing” and see attached "Flood Hardy Wall" detail below.)
19. Should cellulose and cotton insulation be avoided because they’re absorbent?
No. In fact, the absorbency can be an advantage. It can increase the “buffer capacity” or moisture storage capacity of the wall – allowing moisture to disperse and gradually dry to the inside. In addition, these insulation products may contain a boron based fire retardant, which is a natural compound low in toxicity that may help deter insects and mold (although the insulation may not be labeled for that).
However, all porous insulations (cellulose, cotton as well a glass fiber, mineral wool and open cell spray foam) must be protected from liquid water leaks. If any of them get wet, they are too slow to dry so should be removed and replaced.
20. Does foam insulation cause moisture problems and mold? Doesn’t the wall need to “breathe”?
“Breathing” is a misleading and misunderstood term for a building. Don’t use it!
A wall or building enclosure that leaks air is not a good thing – it wastes energy (and money), and can cause both comfort and moisture problems. However, it is important for the building assemblies (walls, roof, floors) to drain rain, prevent condensation, manage moisture and allow drying.
In our hot, humid climate and air conditioned homes, the direction of drying is toward the inside (cooler, dryer side) most of the year. The most important feature to prevent hidden condensation, moisture and mold is to have a highly moisture permeable interior finish. Gypsum drywall with latex paint is ideal. Avoid (and remove) vinyl wallpaper and oil based paint.
Closed cell foam insulations (rigid or spray) have a low permeability, yet their insulating quality prevents condensation (just as a foam cup containing a cold drink doesn’t get wet with condensation, but a glass with the same cold drink in it would get very wet). So closed cell foams can provide an all-season solution to prevent condensation inside a wall assembly.
However, closed cell foam and any other material or finish that is not moisture permeable should not fully coat wood wall studs and bottom plates since that could hamper drying after flooding. It can hamper drying of sheathing to the inside during summer, but would not require delaying restoration if it’s air sealed and isolated from the interior; the sheathing would eventually dry to the exterior.
21. What caused my wood flooring to cup before the flood? How should a raised floor be insulated?
In a nutshell, raised floors get wet in summer because air conditioning causes a moisture vapor drive from outside to inside (moisture drive is from warm to cool and high humidity to low humidity). Hot, humid air from outdoors picks up added moisture from soil, condenses on the cool subflooring and moves inward.
If the flooring is impermeable (polyurethane finish on wood, vinyl or laminate flooring), the moisture cannot dry through to the inside, so the subfloor and flooring gets wet, swells and causes cupping or warpage. Typical insulation methods can make things worse because it keeps the subfloor even cooler (from the A/C), but doesn’t stop humid air and moisture diffusion.
If you maintain a high A/C setting (like 78 degrees), have all moisture permeable floorings and good drainage of rain away from the house, you may be OK with standard batt insulation and a ground cover (plastic sheeting) under the house. The batts must be well installed and supported in full contact with the subfloor. It’s also important that rainwater not flow under the house and pool on top of the plastic sheeting. The ground cover can be 6 mil plastic sheeting secured with stakes or gravel on top; no need to tape or seal it.
However, if you like your A/C cool, or want impermeable floor finishes, then the raised floor insulation systems that prevent moisture problems in our climate must be an air-tight, insulating vapor barrier all in one system. Two alternative methods include:
Timing is important! Do not install the insulation while the subflooring is wet. The best time is after heating the home for several weeks, which reverses the vapor drive and dries out the subflooring. Measure subfloor and wood flooring moisture content with a moisture meter, and insulate after it’s stabilized as low as it will go (10-12%). So the best time to insulate is late winter.
22. If I can’t elevate, is there any way to avoid so much damage and hassle after another flood?
Absolutely! I call it flood-hardy, resilient restoration – or the wash-n-wear house. The official term for it is “wet floodproofing”. That refers to doing whatever you can to reduce damage from a future flood. It may include:
These features don’t bring lower flood insurance premiums, but they can greatly reduce the cost, hassle and time it takes to restore your home and life after a flood.
23. What else should I do or consider during my home’s restoration?
The expense, work, time and stress that go into repairing your home CAN have a silver lining. If you restore for MORE than before, you could be rewarded with a more resilient, durable, healthy, energy-efficient and comfortable home. See the Appendix for our comprehensive, updated Building Your High Performance Home CHECKLIST for the Southern Region.
Invest in energy-saving improvements that give you a return on that investment in savings and comfort:
Learn more about how to rebuild a more energy-efficient, durable, healthy and convenient home! Browse the LaHouse Resource Center website (click on My House, My Home), order a copy of the Building Your High Performance Home guidebook, and visit the showcase exhibit house on the LSU campus to explore its many features, displays and information resources. It’s open to the public Monday – Friday from 10:00 - 4:30 – a public service of the LSU AgCenter Extension Service.