Flood resistant housing techniques

Reconstruction of houses in flood prone area
Follow recommended for removal and replacement of existing housing envelope materials.

Siding
• Fiber cement and vinyl sidings better withstand flood conditions than hardboard lap siding and plywood siding.
• Replacing trim and corner boards with plastic or wood/plastic composite is likely more cost-effective than restoring (thorough drying, renailing, crack filling, and repainting) sawn wood trim.

Sheathing
• Plywood sheathing with flood-damage-resistant lap siding is a good combination. Plywood sheathing covered with plywood siding does not dry well and is not recommended.
• Water-resistant, fiber-reinforced gypsum sheathing (e.g., Fiberock WR Sheathing by USG) is a good sheathing material.
• Fiberglass and other moisture-retaining insulation in the exterior cavity is not recommended

Wood Framing
• Wood is a good flood damage-resistant framing material as long as the wall or floor system will allow it to dry. Fiberglass and other moisture-retaining insulation in the exterior cavity or subfloor is not recommended.

Insulation
• Spray polyurethane foam insulation is a much better for flood damage-resistance than fiberglass batt insulation.
Gypsum Wallboard (drywall)
• Water-resistant, fiber-reinforced gypsum exterior sheathing can generally be restored to preflood condition with only cosmetic restoration. Though it supports mold growth on the exposed surface, it can be cleaned, sanitized and restored.
• Gypsum board that is able to dry completely within an appropriate time can generally be restored to preflood condition with only cosmetic restoration. Although it supports mold growth on the exposed surface, it can be cleaned, sanitized and restored.
• Gypsum wallboard is available with a non-paper skin. The paper in wallboard is a source of food for mold and eliminating the food reduces the potential for mold growth
• Gypsum board with fiberglass batt insulation on exterior walls generally dries too slowly to maintain its integrity.
Wall Finishes
• Oil-based flat enamel generally performs better than water-based latex; flaking and blistering very little and much easier to restore than other paints.
• Standard drywall compound and paper joint tape performs very poorly under flood conditions. Quick setting joint compound and fiberglass tape are generally a great improvement. When used with the water-resistant gypsum sheathing and oil-based paint, these materials are expected to require minimal repair.
• Vinyl wall covering will blister, peel, and debond after flooding. It damages the surface of the gypsum board and may inhibit drying of the substrate or wall system.
• Ceramic tile generally performs well under flood conditions with no long-term deterioration.

Exterior Doors
• Exterior wood paneled doors, exterior prehung metal-clad doors in wooden frames; fiberglass and foam-filled metal doors can generally be restored to preflood conditions with minimal effort.
• Do not fill the joints between the outside of the door frame and the rough opening with compressed fiberglass insulation because it may retain excessive moisture. Filling with low expansion foam is the preferred option.

Interior Doors
• Considering the relatively low cost of replacement, it is generally cost effective to replace all types of interior doors.

Windows
• Vinyl and aluminum window frames are generally able to be restored to preflood conditions with a minimal cleaning effort.
• Do not fill the joints between the outside of the window frame and the rough opening with compressed fiberglass insulation because it may retain excessive moisture. Filling with low expansion foam is the preferred option.
Floors
• Sealed concrete floor slab in all slab-on-grade modules generally remain undamaged during and after flooding.
• All carpeting (including water resistant) and padding holds or traps water and should be removed, dried and cleaned as part of the flood recovery process.
• Wood flooring holds or traps water above the slab and slows the overall drying process. If cost-effective, wood flooring should be removed, washed and stacked during the drying process.
• Ceramic and quarry tiles absorb little water and do not significantly slow the drying process.
• Wood and plywood subflooring and framing retains moisture and could be subject to long-term moisture problems when un

faced fiberglass batt insulation is installed underneath the subflooring. With no floor insulation, the subflooring generally dries well.
• Drying of the subfloor is predominantly through its bottom side.
• Both glued-in-place and floating vinyl flooring on padding traps water, so they should be removed during the drying process.


If the flooring can be removed without damaging it, vinyl flooring can be reused if it is cost-effective to do so.

Foundation Vents and Crawl Spaces
• Conventional foundation vents and operable flood vents both perform well.
• Conventional vents may become blocked by debris during flooding, which could cause damage to the structure.
• Block open operable vents throughout the drying period to permit air to circulate through the crawl space.
• Flood-damaged homes undergoing restoration in wet climates may require regrading of the site to promote drying in the crawl space.
• The crawl space area must be effectively sealed at all penetrations in the flooring to cut off potential pathways for the excess moisture and mold to enter the interior of the home. Ductwork, especially return air, within the crawl space should also be sealed after it has been cleaned, sanitized, disinfected, and repaired as necessary.
Install insulation and wall materials to the full height of the walls subjected to flooding. Uncertainty regarding future flood levels and the wicking of floodwater through materials make the combining of conventional materials and flood damage resistant ones imprudent.

When selecting envelope materials and finishes, and caulking/sealing methods it is wise to assume that floodwater will permeate the system and that there will be hidden pockets of moisture that will require a “means of escape”. This escape could be through permeable materials such as gypsum board or through cracks such as through the joints in vinyl siding. Don’t block this means of drying with low permanence paints and wall coverings on walls or with caulking joints.

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