Plywood H Clips

Softwood plywood is used extensively in the construction of homes. Plywood sheathing covers walls and roofs and is used for subflooring. The plywood is expected to span the gaps between supporting structures in all of these applications. While it does this admirably well, it is easy for the plywood to sag over time. When that happens, it tends to occur unevenly, leaving the edges of the plywood not meeting up well and creating opportunities for damage, especially to roofing.

One potential solution to help prevent this is to increase the number of structural members in a home’s construction, reducing the space between adjacent studs and roof trusses. However, this option is unrealistic from a cost point of view, as it can double the cost of framing the home.

Roof sheathing is much more susceptible to this than wall sheathing or flooring. Therefore, architects may specify additional support along the edges of plywood sheets used for roof sheathing. Blocking and tongue-in-groove plywood are the traditional means of accomplishing this, and they were used before the H Clip was invented.

Rather than increasing the cost of framing a home, even by adding blocking, it makes much more sense to attach the edges of the plywood sheets together between the existing frame members. Hence, the invention of the inexpensive H Clip. The H Clip essentially performs the same function as a tongue on the edge of plywood sheets, eliminating the need for blocking and saving the extra milling steps required to make tongue-and-groove sheets of plywood.

The H Clip, more appropriately known as a “panel edge clip,” gets its name from the fact that the cross-section of the clip forms the capital letter H. This allows one piece of plywood to be inserted into what can be considered the letter’s top portion and the other one into what can be viewed as the bottom portion. While small and discreet, these clips are easy to install and provide sufficient support to ensure that one piece of plywood doesn’t sag while its neighbors do not.

When H Clips are used, any weight placed on the panel is partially distributed to the adjacent panels, reducing the chance of deflection and damage caused by that deflection. This increases overall roof stiffness, as no weak points are created at seams between trusses. However, H Clips cannot prevent panels from buckling or warping; they merely help keep them aligned with adjacent sheets, should that happen.

These H Clips are different from the H Strip used for installing siding. That H Strip is a decorative plastic strip used to cover the gaps between pieces of siding when they are butt jointed together. While primarily decorative, they ensure no gap in the siding where water could seep in. However, they have no structural purpose and do not strengthen the siding in any way.

H Clips are not load-rated, so they are not required by building code. They usually are considered at the architect’s discretion. However, a builder or do-it-yourselfer can add H Clips to their project without approval.

While H Clips are mainly used on the roof sheathing, manufacturers make various sizes to accommodate plywood from 7/16 through ¾” thick. Be sure when buying H Clips for your project that they fit snugly enough onto the edge of the plywood that they won’t slide off while not being so tight that it requires more than a light tap with a hammer to get them to sit onto the edge. Tight enough to need that light tap is ideal, as they won’t slide.

The H Clips are installed as the plywood sheathing is being installed. It is recommended to put them every eight inches. So, one should be placed between the roof trusses if the trusses are 16” apart, and two should be installed if the trusses are 24” apart. Attach the clips to the installed sheets before the next piece is implemented. Clips are usually attached with the smaller side up. Then, slip the new sheet of plywood into the clips.

Additional clips can be added where a structural element is unavailable for support, such as where the roof is cut off at an angle. Modern roofs on homes are more complicated and made of more surfaces, so there are many such places where H Clips can provide additional support.

Remember that H Clips will leave a slight gap between the sheets of plywood. This allows for the sheet’s expansion due to moisture without causing buckling. The 1/8” gap will not cause problems for roofing materials because the roofing felt will easily bridge the gap.