Metal T-bracing for wall corners (C) Daniel Friedman Insulating Board Sheathed WalL Bracing
Bracing required for fiberboard covered walls

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Fiberboard insulating board or IB sheathed wall bracing:

Where non-structural exterior wall sheathing is used in construction wind bracing is required.

This article series discusses insulating sheathing board products or IB, fibreboard sheathing, and similar products. We also discuss flood damage and mold damage on fiberboard insulating products and building sheathing products such as Homasote, Celotex, and Masonite insulating board sheathing.

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Add Structural Support Against Racking or Wind Damage?

Gypsum board sheathing with let in diagonal bracing (C) Daniel FriedmanWatch out: during new construction or during repair and renovation work on flood or hurricane damaged buildings, where IB or fiberboard sheathing was used as original sheathing on a building's exterior you should inspect the building wall corners for wood or metal bracing that is intended to protect the structure from leaning or racking during high winds.

Wind bracing may have been installed originally as let-in diagonal wood braces (see our photo), by cut in metal bracing, or by use of solid plywood sheathing at the building corners and at other key locations.

Updating the structure to modern strength and wind resistance by bracing may be necessary if your building lacks wind bracing. This might be accomplished by any of the following means.

Diagonal bracing as we describe below is installed to prevent racking of frame-built structures that are sheathed with non-structural materials such as fiberboard, insulating board, or foam board.

Use of wood or metal diagonal bracing at corners or other walls

Traditional wood let-in braced framing technique notches the wall studs to permit nailing in place of diagnonal braces at the building wall corners.

Braces typically are installed from the top plate to the sill plate on a diagonal, and are nailed to the plates and to the studs they intersect.

The diagonal let-in bracing shown in my photo was installed on the outside of the building stud wall at the time of original construction. This example shows a home that was sheathed using gypsum board on the home's exterior.

But this same techinque can work with let-in bracing as a retrofit installation on the wall interior. Wood diagonal bracing was traditionally installed using a 2x4 along the diagonal but a 1x4 may also be permitted, thus reducing the necessary depth of the cutout notch.

Metal diagonal bracing at corners or other walls

Metal T-bracing for wall corners (C) Daniel Friedman InspectApedia.comMetal diagonal bracing is still easier to install, and is easy to add on an exposed exterior wall frame or on exposed stud wall framing from the interior side of a building exerior wall.

There are several types of metal strapping used for diagonal bracing, of which the traditional T-shape was most familiar to older carpenters.

Two other profiles, flat-strapping and L-shaped strapping are also used for diagonal bracing at wall corners. Flat strapping such as Simpson Strong-Tie's WB product is installed without any requirement for saw cuts or notching, but because it works only in tension, not in compression, it is installed in pairs.

The T-shaped metal strapping is nailed to the top and bottom wall plates and to studs in between along its diagonal, similarly to the wood bracing shown in our photograph.

But instead of having to cut and chisel out a deep and wide notch for the 1x4 or more traditionally 2x4 diagonal brace, the installer simply runs her circular saw along a chalk line snapped along the desired diagonal, making a single cut. The base of the Tee slips into the saw cut.

[Click to enlarge any image]

Use of plywood or OSB sheathing inside at wall corners

With this approach there will remain a decision about furring out other studs or double-layering drywall or as I prefer, coating the plywood with a joint compound veneer before painting, then of course taping all joints to produce a smooth interior wall.

OSB sheathing is commonly-used at the corners and at other strategic locations of the wall exterior in new construction.

If you decide to use structural sheathing on the building interior walls during a flood-damage repair job, plywood, particularly AC plywood with the "A" or smooth side facing the room interior will make subsequent wall finishing and painting easier.

Watch out: Before choosing a metal strapping product for wall bracing check its specifications against what is required by local building codes where you live. Holladay, in an excellent Fine Homebuilding article on shear bracing points out that these products vary in strength, purpose, and acceptability.

You'll want to confirm design alternatives and your choice of wall bracing methods with a structural engineer to obtain a sign-off, but there are alternatives once you've removed moldy drywall, cleaned the wall cavities and sanitized them.

Other suggstions for flood restoration including at brick veneer walls over fiberboard sheathing

Insulation retrofits: Some of our readers have re-insulated wall cavities using a combination of styrofoam cut to fit, foam insulation, and fiberglass.

We presently are working on adding photographs and discussion of that work here in this article. I think sticking fiberglass or any other water-vulnerable insulation back into a wall cavity that is likely to be exposed to future flooding is a bad idea.

Future flood resistance: I'm really glad to see you discussing water-resistant restoration material choices. I am concerned about some Louisiana flood restoration work being done that will be damaged again by the next flood and would prefer that owners, contractors, and insurance companies discuss use of materials and methods that may reduce the cost of damage from the next inundation.

Watch out for hidden mold and moisture damage in walls or ceilings above the actual flood high-water line. Homes that sat for more than 24-48 hours in wet and high humidity are at high risk of hidden mold damage in upper walls and ceiling cavities.

Simply running a dehumidifier or two along with fans will not "extract" water from the cavities of a flooded building and if not started soon enough it may not have prevented extensive but hidden mold contamination higher in the building.

A few strategic test cuts into those areas are worthwhile. Inspect the cavity side of drywall for visible mold. It's much less costly to do this repair now than to have to return to a "restored" flood-damaged home next year to rip out all of that new work to remove a just-discovered harmful mold reservoir in the building.

See HIDDEN MOLD in CEILINGS / WALLS for some examples of strategic test cuts into buildings.

Other hidden mold advice is at HIDDEN MOLD, HOW TO FIND

Watch out for leaving unsafe electrical devices in a flooded building: Be sure that you insist on review and qualification or probably replacement of electrical devices that were flooded in these walls, such as receptacles and splices.

Research on Structural Support & Shear Bracing Where Fiberboard Panels are in Use


Continue reading atSHEATHING FIBERBOARD CONSTRUCTION, for more about these questions and their answers.




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