Wood Tornado Shelter Provides Safe, Affordable Storm Protection

USDA Forest Service researchers have developed a tornado shelter made of wood that provides powerful protection at an affordable cost.

With safety and security in mind, Forest Products Laboratory (FPL) engineers designed the residential tornado shelter to resist the high wind pressure and debris impacts generated by high-wind events.

Most importantly, the wood shelters can be built into an existing home using readily available materials and tools.

A F3 tornado sets down in a field. Image credit: Clint Spencer via iStock
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Decayed Wood Does Not Hold Paint: Contractor Tips From FPL

The following was adapted from the Forest Products Laboratory’s Wood Handbook, Wood as an Engineering Material.

Decayed wood does not hold paint. Although this may be self-evident to some, it is one of the main tips researchers at the Forest Products Laboratory (FPL) have for contractors across the nation. Even in new construction, where new wood is expected to be free of decay, contractors can do several things to keep it that way.

If possible, paint all end grain surfaces with an oil-alkyd primer, such as the ends of siding and trim, brick molding, railings, balustrade, posts, beams, and edges of panel products.

When repainting, inspect wood for decay. Problematic areas include end grain of balustrade, brick molding, siding that butts against a roof, and the bottoms of posts on porches. Decay often occurs in the center of the wood, so the surface can appear sound; probe several areas with an ice pick to ensure the wood is sound. Replace boards having decay.

Decay and paint failure in a wood railing. Decayed wood does not hold paint.

Siding intersecting a sloping roof should have a gap (50mm) between the end grain of the siding and the roof shingles. Check for a finish on the end grain; if there is no finish, treat the end grain with a water-repellent preservative (WRP), prime, and top-coat. If there is already a coating on the end grain, keep it painted.

End grain of siding that butts directly against roof shingles (not a recommended construction practice) is not accessible for painting, however you can try to wick WRP into the end grain from a wet brush.

Insects seldom cause problems with finishes. However, when repainting a structure, it’s a good idea to inspect it for termite tunnels and carpenter ants. A termite tunnel is a sure sign of infestation.

Presence of carpenter ants may indicate decay in the structure. Carpenter ants do not eat wood, but they often tunnel out decayed areas to build their nests. Note that woodpecker holes often indicate insect infestation, as woodpeckers will destroy the wood to get to the insects beneath.

For more information, please see chapter 16 of FPL’s Wood Handbook, Wood as an Engineering Material.

Homeowners: Sealant is Not a Substitute for Flashing

The final advice from The Ins and Outs of Caulking deals with flashing. Modern sealants are capable of impressive performance in controlled laboratory testing and also in well-executed joints on buildings. As indicated previously, however, sealant joints in residential construction are usually executed by individuals with limited training and cannot be expected to function indefinitely. Sealant joint failure can occur without obvious indication.


Water staining on the back surface of hardboard siding on a test building. Leakage, although modest, occurred in 29 months of service and was determined to be through sealant joints. The sealant used in this installation met industry requirements. None of the joints showed outward indication of failure. Subsequent laboratory testing indicated that the window unit, although not of the highest quality, was not the leak source. Sealant joints were a combination of bedded, butt, and fillet. At fillet joints, sealant adhesion at joint root was a likely contributor to failure. The building was in Florida where conditions at joint installation were hot and humid. These conditions would accelerate cure of the polyurethane sealant used. “Skinning” of the sealant before tooling was therefore also a plausible contributor to joint failure.

Sealant joints should thus not be considered as acceptable substitutes for formed metal flashing. Well-executed formed metal flashing makes use of an exceptionally dependable force of nature: gravity. Water management by drainage is a time-proven strategy in the construction of wood buildings. For example, at horizontal joints in plywood panel siding, metal Z-flashing or shingle-lap joints are effective; sealant joints are not an acceptable substitute. Where there are drainage paths, it is important that caulk, if used, not block them.

Remember, good caulking can protect your doors and windows if applied properly. This report, available free for download on the FPL website, can tell you all you need to know.

Caulking: Application Conditions and Shelf Life

What other things do homeowners need to keep in mind when caulking their doors and windows? The Ins and Outs of Caulking reminds us of two important factors: the conditions when the work is done and the shelf life for the materials.

thermometer2The range of acceptable application temperatures will be indicated by the sealant manufacturer. Emulsion (“latex”) sealants cannot be applied below about 40°F (4.4°C). Silicone sealants typically have the widest acceptable range of application temperatures. Surface frost, however, remains a concern when temperature at application is below freezing. High temperatures will accelerate cure time. In some cases acceleration can be excessive, and adhesion to substrates will be compromised if the sealant “skins” before tooling can be accomplished.

Sealant should not be applied during or immediately after a rain. Freshly installed joints usually can withstand modest rain exposure, provided that the sealant has first “skinned” and provided that raindrops do not forcibly impact the sealant. Latex sealants are more likely to be deformed by rain exposure shortly after installation than are other sealant types. It is good practice to refrain from installing sealant joints if there is a threat of rain within 3 to 6 hours. The acceptable time “window” will depend on ambient temperature and sealant type.

Shelf life is also important with caulk. Do not use caulk that has been stored for excessive periods. The caulk manufacturer may indicate shelf life on the product packaging. If it is difficult to force the caulk from the tube at normal temperatures, the shelf life has probably been exceeded. However, easy dispensing of caulk from the tube does not necessarily indicate product freshness. Some caulks that have exceeded their shelf life may be pumped easily from the tube, but will fail to cure. Latex caulk that has been frozen in storage should be discarded.


More Tips on Caulking: Tooling Helps Adhesion to Substrates

When caulking, what can help sealants adhere to substrates before the sealant cures? Again, The Ins and Outs of Caulking has the answers for homeowners, telling them that tooling assures uniform sealant contact with each of the substrates and works air bubbles from the sealant. Tooling usually results in a more aesthetically pleasing joint as well. What tools?


As the photo shows, homeowners have some sophisticated choices for tools: fingers. Big box stores sell caulking tools, although a plastic spoon is usually satisfactory.

Emulsion acrylic sealants are the easiest to tool. Water is usually used as a tooling liquid (lubricant), and excessive adhesion to the wetted tooling device is rarely a problem. Polyurethane sealants often adhere mightily to tooling devices and thus usually require a lubricant on the tooling device. Some manufacturers of polyurethane sealants allow water or soap solution for tooling; others prescribe proprietary tooling lubricants. Silicone sealant manufacturers usually recommend dry tooling, although some may recommend a tooling lubricant. With some sealants, a tooling lubricant requires that the joint be completely filled prior to tooling.

Lubricant on the surface of just-tooled sealant or on substrate surfaces may interfere with sealant cohesion or adhesion, respectively, if additional sealant is placed in the joint. Because latex acrylic sealants use water as both a suspension agent and a tooling lubricant, they are relatively immune to this problem. Experienced professional tradespersons rarely try to tool underfilled joints.

In contrast, relatively inexperienced homeowners can reasonably be expected to sometimes make (and have to correct for) this error. The purpose of tooling is to improve adhesion between the sealant and the sides of the joint. Tooling will coincidentally push sealant back into the joint. One of the functions of backing material is to prevent excessive depth of sealant in tooled joints.